Jon D Pelletier

Interests

No activities entered.

Courses

Scholarly Contributions

Chapters

• Komatsu, G., Goto, K., Baker, V. R., Oguchi, T., Hayakawa, Y. S., Saito, H., Pelletier, J. D., McGuire, L., & Iijima, Y. (2014). Effects of tsunami wave erosion on natural landscapes: examples from the 2011 Tohoku-oki Tsunami. In Tsunami Events and Lessons Learned(pp 243--253). Springer Netherlands.

Journals/Publications

• Meixner, T., Barron-Gafford, G. A., Durcik, M., Rasmussen, C., Pelletier, J. D., Niu, G., Fang, Y., Knowles, J. F., Dwivedi, R., & Chang, L. (2018). Why Do Large‐Scale Land Surface Models Produce a Low Ratio of Transpiration to Evapotranspiration?. Journal of Geophysical Research: Atmospheres, 123(17), 9109-9130. doi:10.1029/2018JD029159
  More info

  Most land surface models (LSMs) used in Earth System Models produce a lower ratio of transpiration (T) to evapotranspiration (ET) than field observations, degrading the credibility of Earth System Model‐projected ecosystem responses and feedbacks to climate change. To interpret this model deficiency, we conducted a pair of model experiments using a three‐dimensional, process‐based ecohydrological model in a subhumid, mountainous catchment. One experiment (CTRL) describes lateral water flow, topographic shading, leaf dynamics, and water vapor diffusion in the soil, while the other (LSM like) does not explicitly describe these processes to mimic a conventional LSM using artificially flattened terrain. Averaged over the catchment, CTRL produced a higher T/ET ratio (72%) than LSM like (55%) and agreed better with an independent estimate (79.79 ± 27%) based on rainfall and stream water isotopes. To discern the exact causes, we conducted additional model experiments, each reverting only one process described in CTRL to that of LSM like. These experiments revealed that the enhanced T/ET ratio was mostly caused by lateral water flow and water vapor diffusion within the soil. In particular, terrain‐driven lateral water flows spread out soil moisture to a wider range along hillslopes with an optimum subrange from the middle to upper slopes, where evaporation (E) was more suppressed by the drier surface than T due to plant uptake of deep soil water, thereby enhancing T/ET. A more elaborate representation of water vapor diffusion from a dynamically changing evaporating surface to the height of the surface roughness length reduced E and increased the T/ET ratio.
• Campisano, C., Campisano, C., Cohen, A. S., Cohen, A. S., Arrowsmith, J. R., Arrowsmith, J. R., Asrat, A., Asrat, A., Behrensmeyer, A. K., Behrensmeyer, A. K., Brown, E., Brown, E., Deino, A., Deino, A., Deocampo, D., Deocampo, D., Feibel, C., Feibel, C., Kingston, J., , Kingston, J., et al. (2017). The Hominin Sites and Paleolakes Drilling Project: Acquiring High-Resolution Paleoclimate Records from the East African Rift System and Their Implications for Understanding the Environmental Context of Hominin Evolution. Paleoanthropology, 2017, 1-43. doi:10.4207/PA.2017.ART104
• Campisano, C., Cohen, A. S., Arrowsmith, J. R., Asrat, A., Behrensmeyer, A. K., Brown, E., Deino, A., Deocampo, D., Feibel, C., Kingston, J., Lamb, H., Lowenstein, T., Noren, A., Olago, D., Owen, R. B., Pelletier, J. D., Potts, R., Reed, K., Renaut, R., , Russell, J., et al. (2017). The Hominin Sites and Paleolakes Drilling Project: Acquiring High-Resolution Paleoclimate Records from the East African Rift System and Their Implications for Understanding the Environmental Context of Hominin Evolution. Paleoanthropology, 2017, 1-43. doi:doi: 10.4207/PA.2017.ART104
  More info

  The possibility of a causal relationship between Earth history processes and hominin evolution in Africa has been the subject of intensive paleoanthropological research for the last 25 years. One fundamental question is: can any geohistorical processes, in particular, climatic ones, be characterized with sufficient precision to enable temporal correlation with events in hominin evolution and provide support for a possible causal mechanism for evolutionary changes? Previous attempts to link paleoclimate and hominin evolution have centered on evidence from the outcrops where the hominin fossils are found, as understanding whether and how hominin populations responded to habitat change must be examined at the local basinal scale. However, these outcrop records typically provide incomplete, low-resolution climate and environmental histories, and surface weathering often precludes the application of highly sensitive, state-of-the-art paleoenvironmental methods. Continuous and well-preserved deep-sea drill core records have provided an alternative approach to reconstructing the context of hominin evolution, but have been collected at great distances from hominin sites and typically integrate information over vast spatial scales. The goal of the Hominin Sites and Paleolakes Drilling Project (HSPDP) is to analyze climate and other Earth system dynamics using detailed paleoenvironmental data acquired through scientific drilling of lacustrine depocenters at or near six key paleoanthropological sites in Kenya and Ethiopia. This review provides an overview of a unique collaboration of paleoanthropologists and earth scientists who have joined together to explicitly explore key hypotheses linking environmental history and mammalian (including hominin) evolution and potentially develop new testable hypotheses. With a focus on continuous, high-resolution proxies at timescales relevant to both biological and cultural evolution, the HSPDP aims to dramatically expand our understanding of the environmental history of eastern Africa during a significant portion of the Late Neogene and Quaternary, and to generate useful models of long-term environmental dynamics in the region.
• Crouvi, O., Polyakov, V., Pelletier, J., & Rasmussen, C. (2015). Decadal-scale soil redistribution along hillslopes in the Mojave Desert. Earth Surface Dynamics, 3, 251.
• Field, J. P., Breshears, D. D., Law, D. J., Lopez Hoffman, L. -., Brooks, P. D., Chorover, J., Barron-Gafford, G. A., Gallery, R. E., Litvak, M. E., Lybrand, R., Mcintosh, J. C., Meixner, T. -., Niu, Y. -., Papuga, S. A., Pelletier, J. D., Rasmussen, C. -., & Troch, P. A. (2015). Critical zone services: Expanding context, constraints, and curency beyond ecosystem services.. Vadose Zone Journal, 1-7.
• Harpold, A., Marshall, J., Lyon, S., Barnhart, T., Fisher, B., Donovan, M., Brubaker, K., Crosby, C., Glenn, N., Glennie, C., & others, . (2015). Laser vision: lidar as a transformative tool to advance critical zone science. Hydrology and Earth System Sciences Discussions, 12(1), 1017--1058.
• Hayakawa, Y. S., Oguchi, T., Saito, H., Kobayashi, A., Baker, V. R., Pelletier, J. D., McGuire, L. A., Komatsu, G., & Goto, K. (2015). Geomorphic imprints of repeated tsunami waves in a coastal valley in northeastern Japan. Geomorphology, 242, 3--10.
• Hazenberg, P., Fang, Y., Broxton, P., Gochis, D., Niu, G., Pelletier, J., Troch, P., & Zeng, X. (2015). A hybrid-3D hillslope hydrological model for use in Earth system models. Water Resources Research, 51, 8218--8239.
• Kapp, P., Pullen, A., Pelletier, J. D., Russell, J., Goodman, P., & Cai, F. (2015). From dust to dust: Quaternary wind erosion of the Mu Us Desert and Loess Plateau, China. Geology, 43, 835--838.
• McGuire, L. A., & Pelletier, J. D. (2015). Controls on valley spacing in landscapes subject to rapid base-level fall. Earth Surface Processes and Landforms.
• Orem, C. A., & Pelletier, J. D. (2015). Quantifying the time scale of elevated geomorphic response following wildfires using multi-temporal LiDAR data: An example from the Las Conchas fire, Jemez Mountains, New Mexico. Geomorphology, 232, 224--238.
• Orem, C., & Pelletier, J. (2015). Constraining frequency-magnitude-area relationships for precipitation and flood discharges using radar-derived precipitation estimates: example applications in the Upper and Lower Colorado River Basins, USA.. Hydrology \& Earth System Sciences Discussions, 12.
• Pangle, L. A., DeLong, S. B., Abramson, N., Adams, J., Barron-Gafford, G., Breshears, D. D., Brooks, P., Chorover, J., Dietrich, W. E., Dontsova, K., & others, . (2015). The Landscape Evolution Observatory: A large-scale controllable infrastructure to study coupled Earth-surface processes. Geomorphology.
• Pelletier, J. D. (2015). Controls on the large-scale spatial variations of dune-field properties in the barchanoid portion of White Sands dune field, New Mexico. Journal of Geophysical Research: Earth Surface.
• Pelletier, J. D. (2015). Quantifying topographic and vegetation effects on the transfer of energy and mass to the critical zone. Vadose Zone Journal.
• Pelletier, J. D., Brad Murray, A., Pierce, J. L., Bierman, P. R., Breshears, D. D., Crosby, B. T., Ellis, M., Foufoula-Georgiou, E., Heimsath, A. M., Houser, C., & others, . (2015). Forecasting the response of Earth's surface to future climatic and land use changes: A review of methods and research needs. Earth's Future, 3, 220--251.
• Pelletier, J. D., Broxton, P. D., Hazenberg, P., Zeng, X., Troch, P. A., Niu, G., Williams, Z., Brunke, M. A., & Gochis, D. (2015). A gridded global data set of soil, immobile regolith, and sedimentary deposit thicknesses for regional and global land surface modeling. Journal of Advances in Modeling Earth Systems.
• Pelletier, J. D., Sherman, D. J., Ellis, J. T., Farrell, E. J., Jackson, N. L., Li, B., Nordstrom, K. F., Maia, L. P., & Omidyeganeh, M. (2015). Dynamics of sediment storage and release on aeolian dune slip faces: A field study in Jericoacoara, Brazil. Journal of Geophysical Research: Earth Surface, 120, 1911--1934.
• Pelletier, J. D., Sweeney, K. E., Roering, J. J., & Finnegan, N. J. (2015). Controls on the geometry of potholes in bedrock channels. Geophysical Research Letters, 42, 797--803.
• Pelletier, J., & Field, J. (2015). Predicting the roughness length of turbulent flows over landscapes with multi-scale microtopography. Earth Surface Dynamics Discussions, 3, 1107--1142.
• V\'azquez-Ortega, A., Perdrial, J., Harpold, A., Zapata-R\'\ios, X., Rasmussen, C., McIntosh, J., Schaap, M., Pelletier, J. D., Brooks, P. D., Amistadi, M. K., & others, . (2015). Rare earth elements as reactive tracers of biogeochemical weathering in forested rhyolitic terrain. Chemical Geology, 391, 19--32.
• Williams, Z. C., & Pelletier, J. D. (2015). Self-affinity and surface-area-dependent fluctuations of lake-level time series. Water Resources Research, 51, 7258--7269.
• Becerra, P., Byrne, S., Mattson, S., Pelletier, J., Herkenhoff, K., & Team, H. (2014). Polar Stratigraphy from HiRISE Stereo Topography. LPI Contributions, 1791, 1183.
• Becerra, P., Byrne, S., Mattson, S., Pelletier, J., Herkenhoff, K., & others, . (2014). Martian Polar Stratigraphy from Stereo Topography. European Planetary Science Congress 2014, EPSC Abstracts, Vol. 9, id. EPSC2014-647, 9, 647.
• Chorover, J. D., Gavaert, A., Tueling, A. J., Uijlenhoet, R., DeLong, S. B., Huxman, T. E., Pangle, L., Brashears, D. D., Pelletier, J. D., Saleska, S. R., Zeng, X., & Troch, P. A. (2014). Hillslope-scale experiment demonstrates the role of convergence during two-step saturation. Hydrol. Earth Syst. Sci., 18, 1-12.
• Chorover, J. D., Vazquez-Ortega, A., Perdrial, J., Harpold, A., Zapata-Rios, X., McIntosh, J., Rasmussen, C., Schaap, M. G., Pelletier, J. D., Brooks, P. D., & Amistadi, M. K. (2014). Rare earth elements as reactive tracers of biogeochemical weathering in forested rhyolitic terrain. Chem. Geol., 391, 19-32.
• Crouvi, O., Polyakov, V., Pelletier, J., & Rasmussen, C. (2014). Controls on slope-wash erosion rates in the Mojave Desert. Earth Surface Dynamics Discussions, 2(1), 535--574.
• Engelder, T. M., & Pelletier, J. D. (2014). Simulating foreland basin response to mountain belt kinematics and climate change in the Eastern Cordillera and Subandes: An analysis of the Chaco foreland basin in southern Bolivia. Geological Society of America Memoirs, 212, MWR212--17.
• Field, J. P., Breshears, D. D., Law, D. J., Villegas, J. C., L\'opez-Hoffman, L., Brooks, P. D., Chorover, J., Barron-Gafford, G. A., Gallery, R. E., Litvak, M. E., & others, . (2014). Critical Zone Services: Expanding Context, Constraints, and Currency beyond Ecosystem Services. Vadose Zone Journal.
• Hazenberg, P., Broxton, P., Gochis, D., Niu, G., Pelletier, J., Troch, P., & Zeng, X. (2014). An effective hyper-resolution pseudo-3D implementation of small scale hydrological features to improve regional and global climate studies.
• KAPP, P., PULLEN, A., PELLETIER, J. D., RUSSELL, J., & CAI, F. (2014). FROM DUST TO DUST: QUATERNARY WIND EROSION OF THE MU US DESERT AND LOESS PLATEAU, CHINA. 2014 GSA Annual Meeting in Vancouver, British Columbia.
• McGuire, L. A., Pelletier, J. D., & Roering, J. J. (2014). Development of topographic asymmetry: Insights from dated cinder cones in the western United States. Journal of Geophysical Research: Earth Surface, 119(8), 1725--1750.
• Niu, G., Pasetto, D., Scudeler, C., Paniconi, C., Putti, M., Troch, P. A., DeLong, S. B., Dontsova, K., Pangle, L., Breshears, D. D., Chorover, J., Huxman, T. E., Pelletier, J., Saleska, S. R., & Zeng, X. (2014). Incipient subsurface heterogeneity and its effect on overland flow generation – insight from a modeling study of the first experiment at the Biosphere 2 Landscape Evolution Observatory. Hydrology and Earth System Sciences.
• Niu, G., Pasetto, D., Scudeler, C., Paniconi, C., Putti, M., Troch, P., DeLong, S., Dontsova, K., Pangle, L., Breshears, D., & others, . (2014). Incipient subsurface heterogeneity and its effect on overland flow generation--insight from a modeling study of the first experiment at the Biosphere 2 Landscape Evolution Observatory. Hydrology and Earth System Sciences, 18(5), 1873--1883.
• Niu, G., Troch, P. A., Paniconi, C., Scott, R. L., Durcik, M., Zeng, X., Huxman, T., Goodrich, D., & Pelletier, J. (2014). An integrated modelling framework of catchment-scale ecohydrological processes: 2. The role of water subsidy by overland flow on vegetation dynamics in a semi-arid catchment. Ecohydrology, 7(2), 815--827.
• Pelletier, J. (2014). The linkages among hillslope-vegetation changes, elevation, and the timing of late-Quaternary fluvial-system aggradation in the Mojave Desert revisited. Earth Surface Dynamics, 2(2), 455--468.
• Pelletier, J. D., & Jerolmack, D. J. (2014). Multiscale bed form interactions and their implications for the abruptness and stability of the downwind dune field margin at White Sands, New Mexico, USA. Journal of Geophysical Research: Earth Surface, 119(11), 2396--2411.
• Pelletier, J. D., & Orem, C. A. (2014). How do sediment yields from post-wildfire debris-laden flows depend on terrain slope, soil burn severity class, and drainage basin area? Insights from airborne-LiDAR change detection. Earth Surface Processes and Landforms, 39(13), 1822--1832.
• Pelletier, J. D., Brad Murray, A., & Pierce, J. L. (2014). Assessing Ability to Forecast Geomorphic System Responses to Climate and Land-Use Changes. Eos, Transactions American Geophysical Union, 95(1), 3--3.
• Pelletier, J. D., Sweeney, K. E., Roering, J. J., & Finnegan, N. J. (2014). Controls on the geometry of potholes in bedrock channels. Geophysical Research Letters.
• Crouvi, O., Pelletier, J. D., & Rasmussen, C. (2013). Predicting the thickness and aeolian fraction of soils in upland watersheds of the Mojave Desert. Geoderma, 195-196, 94-110.
  More info

  Abstract: Soil thickness and soil texture, and their spatial variability at hillslope scales, are important inputs for hydrologic models. Recent studies have demonstrated that mechanistic models can accurately predict the spatial distribution of soil thickness in areas where soil thickness varies gradually along hillslope profiles. To date, however, these models have not been tested in arid regions, where soils are often thin and highly variable at small scales (i.e., 1-10. m) and where the influence of aeolian accretion on soil thickness and soil texture may be significant. In addition, most of the data available for the fraction of the soil derived from aeolian deposition (which can serve as a proxy for soil texture) originate from soils developed on stable depositional landforms; data for aeolian fractions from upland soils are scarce. In this study, we developed and tested a numerical model for the prediction of thickness and aeolian fraction of soils in arid upland areas. The model assumes a long-term balance between the rates of soil production from bedrock, aeolian accretion, and soil erosion. Rates of soil production are quantified in the model using the exponential and humped soil production functions, and soil erosion rates are quantified using the nonlinear depth- and slope-dependent transport functions, assuming that only the upper soil horizons (A. +. B) are capable of transport. The rate of aeolian deposition is assumed to be spatially uniform. We calibrated the three free parameters of the model at a site in the Mojave Desert with a granite lithology using a combination of 1) field-measured data for soil thickness and 2) estimation of the aeolian fraction in the soil using laboratory analysis of immobile element concentrations. We validated the model results in three nearby sites using a combination of measured soil thickness in soil pits and the presence/absence of soil, and laboratory analysis of the aeolian fraction of soil. The study area is characterized by generally thin soils (
• Engelder, T. M., & Pelletier, J. D. (2013). Autogenic cycles of channelized fluvial and sheet flow and their potential role in driving long-runout gravel progradation in sedimentary basins. Lithosphere, 5(4), 343-354.
  More info

  Abstract: The paleoslope estimation method uses a threshold-shear-stress criterion, together with fi eld-based measurements of median grain size and channel depth in alluvial gravel deposits, to calculate the threshold paleoslopes of alluvial sedimentary basins. Threshold paleoslopes are the minimum slopes that would have been necessary to transport sediment in those basins. In some applications of this method, inferred threshold paleoslopes are suffi ciently steeper than modern slopes that large-magnitude tectonic tilting must have occurred in order for sediments to have been transported to their present locations. In this paper, we argue that autogenic cycles of channelized fluvial and sheet flow in alluvial sedimentary basins result in spatial and temporal variations in the threshold slope of gravel transport that can, under certain conditions, cause gravel to prograde out to distances much longer than previously thought possible based on paleoslope estimation theory (i.e., several hundred kilometers or more from a source region). We test this hypothesis using numerical models for two types of sedimentary basins: (1) an isolated sedimentary basin with a prescribed source of sediment from upstream, and (2) a basin dynamically coupled to a postorogenic mountain belt. In the models, threshold slopes for entrainment are varied stochastically through time with an amplitude equal to that inferred from an analysis of channel geometry data from modern rivers. Our models show that when local threshold slope values vary stochastically and sediment supply is relatively low compared to transport capacity, alluvial gravels can persistently prograde at slopes far below the threshold slopes predicted by paleoslope estimation theory. The result holds whether the stochastic changes in threshold slope are autocorrelated along the entire channel profi le or occur in localized sections of the channel profi le. As such, our model results suggest that long-runout gravels do not require steep regional slopes in order for transport to occur. We conclude that the minimum progradational slopes of fl uvial sedimentary basins adjacent to postorogenic mountain ranges are functions of both the mean and coeffi cient of variation of water-flow depths as well as the density and texture of the bed sediment. © 2013 Geological Society of America.
• Fenton, C. R., & Pelletier, J. D. (2013). Cosmogenic ³He age estimates of Plio-Pleistocene alluvial-fan surfaces in the Lower Colorado River Corridor, Arizona, USA. Quaternary Research (United States), 79(1), 86-99.
  More info

  Abstract: Plio-Pleistocene deposits of the Lower Colorado River (LCR) and tributary alluvial fans emanating from the Black Mountains near Golden Shores, Arizona record six cycles of Late Cenozoic aggradation and incision of the LCR and its adjacent alluvial fans. Cosmogenic 3He (3Hec) ages of basalt boulders on fan terraces yield age ranges of: 3.3-2.2Ma, 2.2-1.1Ma, 1.1Ma to 110ka,
• McGuire, L. A., & Pelletier, J. D. (2013). Relationships between debris fan morphology and flow rheology for wet and dry flows on Earth and Mars: A numerical modeling investigation. Geomorphology, 197, 145-155.
  More info

  Abstract: Liquid water may have flowed on the Martian surface in the recent geologic past. Arguments for and against liquid water flows have been made, in part, using interpretations of the morphology of Martian gullies and their associated debris fans. On Earth, sediment transport on steep, debris-flow-dominated hillslopes is often assumed to be a nonlinear function of hillslope gradient. In detail, however, sediment transport on such slopes must also depend on the rheology of the mass movements that drive the majority of transport, both in magnitude and frequency. In this study, we attempt to provide a firmer basis for (1) interpreting flow constituents and/or rheology from debris-fan morphology on Mars and (2) modeling debris-flow-dominated hillslopes on Earth by developing a mass-conservative numerical model that links the rheology of wet and dry granular flows on steep slopes to the morphology of debris fans deposited at their base. Individual flows are routed from initiation points on a slope to stopping points at the base of the hillslope. Model predictions for the shape and average slope of the fans depend on flow rheology. Model results indicate that debris fans associated with dry granular flows may develop average slopes below the kinetic angle of friction. In both the dry and wet cases, the model results suggest that fan morphology depends on the mean properties of the flows involved in fan formation as well as the amount of variation in flow behavior between individual mass movement events. These results provide an improved basis for interpreting the morphology of debris fans on both Earth and Mars. © 2013 Elsevier B.V.
• McGuire, L. A., Pelletier, J. D., Gómez, J. A., & Nearing, M. A. (2013). Controls on the spacing and geometry of rill networks on hillslopes: Rain splash detachment, initial hillslope roughness, and the competition between fluvial and colluvial transport. Journal of Geophysical Research F: Earth Surface, 118(1), 241-256.
  More info

  Abstract: [1] Rill networks have been a focus of study for many decades, but we still lack a complete understanding of the variables that control the spacing of rills and the geometry of rill networks (e.g., parallel or dendritic) on hillslopes. In this paper, we investigate the controls on the spacing and geometry of rill networks using numerical modeling and comparison of the model results to terrestrial-laser-scanner-derived topographic data from rill networks formed in physical experiments. The landscape evolution model accounts for the transport of sediment due to rain splash and fluvial entrainment as well as the deposition of sediment being advected by the overland flow. In order to develop realistic rill networks in the model, we find that it is necessary to incorporate the effects of raindrop impact within the fluvial sediment transport process. Model results are only consistent with those of experiments when raindrop-aided fluvial sediment transport is accounted for. Dendritic networks are often predicted by the model in cases of high initial topographic roughness and high rates of advective (fluvial) sediment transport relative to diffusive (colluvial) transport. Parallel networks form within numerical experiments in low-roughness cases under a wide range of relative advective and diffusive transport rates as well as in high roughness cases in which diffusive sediment transport is high relative to advective transport. The transition from dendritic to parallel rill networks is shown to occur gradually rather than being associated with a particular threshold. Finally, based on a balance between diffusive and advective sediment transport processes, we predict that the mean spacing between parallel rills scales with the square root of the ratio of diffusivity to channel erodibility. © 2013. American Geophysical Union. All Rights Reserved.
• Pelletier, J. D. (2013). A robust, two-parameter method for the extraction of drainage networks from high-resolution digital elevation models (DEMs): Evaluation using synthetic and real-world DEMs. Water Resources Research, 49(1), 75-89.
  More info

  Abstract: In this article, a method for drainage network extraction from high-resolution digital elevation models (DEMs; e.g., those derived from airborne laser swath mapping) is presented, which requires just two user-defined parameters and is capable of handling discontinuous valley networks. The accuracy and robustness of the method are illustrated using synthetic valley networks that mimic the complexities of real landscapes and for which the true drainage network is known exactly by construction. The method involves six principal steps: optimal Wiener filtering to remove microtopographic noise, mapping of the contour curvature, identification of valley heads using a user-defined contour-curvature threshold criterion, routing of a unit discharge of water from each valley head using a multiple-flow-direction routing algorithm, removal of discontinuous reaches from the drainage network using a user-defined discharge-per-upstream-valley-head threshold criterion, and thinning of the valley network to a single pixel width. The method yields accurate results using the same user-defined parameters for the two field sites considered in this study, suggesting that for DEMs with resolution of approximately 1 m, the method has the ability to produce accurate results for a variety of landscapes by using the same parameter values used in this study. © 2013. American Geophysical Union. All Rights Reserved.
• Pelletier, J. D. (2013). Deviations from self-similarity in barchan form and flux: The case of the Salton Sea dunes, California. Journal of Geophysical Research F: Earth Surface, 118(4), 2406-2420.
  More info

  Abstract: Barchans are the type of aeolian dune associated with a relatively uniform wind direction, incomplete sand coverage of the substrate, and low vegetation cover. Here I present an analysis of the morphology and migration rates of 40 dunes in the Salton Sea dune field using historical aerial orthophotographs, airborne laser swath mapping, terrestrial laser scanning, and measurements of the aerodynamic roughness length derived from wind velocity profiles. The data demonstrate that the Salton Sea dunes deviate from self-similarity such that smaller dunes have a lower ratio of slip face height to crest height and a lower slope, on average, compared with larger dunes and that smaller dunes migrate more slowly than would be predicted based on an inverse relationship between migration rate and dune height. The lack of self-similarity in barchans has been attributed to the dependence of speed-up ratios on dune size and the presence of a finite saturation length in the physics of aeolian transport. Here I argue that deviations from self-similarity at this study site are more likely due to the systematic decrease in aerodynamic roughness length with increasing elevation on stoss slopes. The data set I developed should prove useful to the aeolian geomorphic community for the further testing of models for barchan evolution. Key Points Airborne and terrestrial lidar are used to monitor dune form and migration Barchans deviate from self-similarity as a function of dune size Such deviations may be a result of spatial variations in aerodynamic roughness ©2013. American Geophysical Union. All Rights Reserved.
• Pelletier, J. D., Barron-Gafford, G. A., Breshears, D. D., Brooks, P. D., Chorover, J., Durcik, M., Harman, C. J., Huxman, T. E., Lohse, K. A., Lybrand, R., Meixner, T., Mcintosh, J. C., Papuga, S. A., Rasmussen, C., Schaap, M. G., Swetnam, T. W., & Troch, P. A. (2013). Coevolution of nonlinear trends in vegetation, soils, and topography with elevation and slope aspect: A case study in the sky islands of southern Arizona. J. Geophys. Res. - Earth Surf., 118, 741-758.
• Pelletier, J. D., Pelletier, J. D., Breshears, D. D., Breshears, D. D., Barron-Gafford, G. A., Barron-Gafford, G. A., Brooks, P. D., Brooks, P. D., Chorover, J. D., Chorover, J., Durick, M., Durick, M., Harman, C. J., Harman, C. J., Huxman, T. E., Huxman, T. E., Lohse, K. A., Lohse, K. A., Lybrand, R., , Lybrand, R., et al. (2013). Coevolution of nonlinear trends in vegetation, soils, and topography with elevation and slope aspect: A case study in the sky islands of southern Arizona. Journal of Geophysical Research - Earth Surface, 118(2), 1-18.
• Pelletier, J. D. (2012). A spatially distributed model for the long-term suspended sediment discharge and delivery ratio of drainage basins. Journal of Geophysical Research F: Earth Surface, 117(2).
  More info

  Abstract: Understanding and quantifying the long-term suspended sediment discharge of drainage basins is a key goal of geomorphology, with important implications for the study of water quality, agricultural sustainability, and the evolution of landscapes and sedimentary basins over geologic timescales. Previous studies have highlighted the importance of relief/slope, precipitation, temperature, vegetation, and soil texture in controlling suspended sediment discharge in natural/undisturbed landscapes. However, globally applicable models currently used to predict suspended sediment discharges are limited because they are based on basin-averaged versions of these properties and do not incorporate all of the controlling variables into a single model. In this paper, I propose a spatially distributed, globally applicable model for the long-term suspended sediment discharge of drainage basins that includes all of the principal controls on suspended sediment discharge previously documented in the geomorphic literature. The model explicitly distinguishes the detachment of sediment on hillslopes and in low-order valleys from the transport of sediment in higher-order alluvial channels. The model uses slope, soil texture, mean monthly rainfall, and mean monthly leaf area index as controlling parameters for the detachment component. The transport component is modeled using a Rouse number-dependent transport criterion that explicitly includes the effects of slope and soil texture. The model is capable of reproducing the long-term sediment yield of 128 global rivers with a Pearson correlation coefficient (R value) of 0.79 using just two free parameters. The model also predicts sediment delivery ratios consistent with those measured in natural drainage basins. Copyright 2012 by the American Geophysical Union.
• Pelletier, J. D. (2012). Fluvial and slope-wash erosion of soil-mantled landscapes: Detachment- or transport-limited?. Earth Surface Processes and Landforms, 37(1), 37-51.
  More info

  Abstract: Many numerical landform evolution models assume that soil erosion by flowing water is either purely detachment-limited (i.e. erosion rate is related to the shear stress, power, or velocity of the flow) or purely transport-limited (i.e. erosion/deposition rate is related to the divergence of shear stress, power, or velocity). This paper reviews available data on the relative importance of detachment-limited versus transport-limited erosion by flowing water on soil-mantled hillslopes and low-order valleys. Field measurements indicate that fluvial and slope-wash modification of soil-mantled landscapes is best represented by a combination of transport-limited and detachment-limited conditions with the relative importance of each approximately equal to the ratio of sand and rock fragments to silt and clay in the eroding soil. Available data also indicate that detachment/entrainment thresholds are highly variable in space and time in many landscapes, with local threshold values dependent on vegetation cover, rock-fragment armoring, surface roughness, soil texture and cohesion. This heterogeneity is significant for determining the form of the fluvial/slope-wash erosion or transport law because spatial and/or temporal variations in detachment/entrainment thresholds can effectively increase the nonlinearity of the relationship between sediment transport and stream power. Results from landform evolution modeling also suggest that, aside from the presence of distributary channel networks and autogenic cut-and-fill cycles in non-steady-state transport-limited landscapes, it is difficult to infer the relative importance of transport-limited versus detachment-limited conditions using topography alone. © 2011 John Wiley & Sons, Ltd.
• Pelletier, J. D., & Perron, J. T. (2012). Analytic solution for the morphology of a soil-mantled valley undergoing steady headward growth: Validation using case studies in southeastern Arizona. Journal of Geophysical Research F: Earth Surface, 117(2).
  More info

  Abstract: The geomorphic literature contains many analytic solutions for the topographic evolution of gently sloping soil-mantled hillslopes responding to base level changes. Most of these solutions are limited to vertical base level changes and/or to simplified geometries, however. In this paper we present an analytic solution for the morphology of a valley and its adjacent hillslopes undergoing steady headward growth. The mathematics of this problem were first solved by Ivantsov (1947) in the context of heat flow near a parabolic solidification boundary. Here we test whether the Ivantsov solution provides an accurate first-order prediction of the morphology of valley heads and their adjacent hillslopes by comparing the model predictions to survey data from two study sites in southeastern Arizona. The model predicts that elevation contours of valley heads are parabolas and that topographic transects normal to contour lines are error functions. High-resolution Digital Elevation Models (DEMs) were constructed for the two study sites using Real-Time Kinematic Global Positioning System (RTK-GPS) measurements and a Terrestrial Laser Scanner (TLS). Our analyses show that the model reproduces the first-order morphology of headward-growing valleys and their adjacent hillslopes. We also show that by analyzing hillslope profiles at different distances from the valley head, the model framework can be used to infer likely changes in the valley head migration rate through time. Copyright 2012 by the American Geophysical Union.
• Pelletier, J. D., Delong, S. B., Orem, C. A., Becerra, P., Compton, K., Gressett, K., Lyons-Baral, J., McGuire, L. A., Molaro, J. L., & Spinler, J. C. (2012). How do vegetation bands form in dry lands? Insights from numerical modeling and field studies in southern Nevada, USA. Journal of Geophysical Research F: Earth Surface, 117(4).
  More info

  Abstract: Vegetation bands are periodic bands of vegetation, separated by interband spaces devoid of vegetation, oriented parallel to the topographic contour in some gently sloping arid to semiarid environments. Models of vegetation band formation attribute their formation to positive feedbacks among vegetation density, soil porosity/permeability, and infiltration rates. Here we present an alternative model based on field measurements at our study sites in southern Nevada. In this model, interband spaces between vegetation bands form because topographic mounds beneath vegetation bands detain water upslope from vegetation bands, leading to hydrologic and sedimentologic conditions that inhibit the survival of plants in interband spaces. We used terrestrial laser scanning (TLS) to create high-resolution (∼10 cm2/pixel) raster data sets of bare-earth topography and canopy height for four study sites. Analyses of the TLS data, in addition to measurements of soil shear strength and particle size, document the potential for detention in interband spaces and a near-inverse proportionality between band spacing and regional slope. We describe a cellular automaton model (herein called model 1) for vegetation band formation that includes just two user-defined parameters and that generates vegetation bands similar to those at our field sites, including the inverse proportionality between spacing and regional slope. A second model (model 2) accurately predicts the width of vegetation bands in terms of the number and spacing of plants and the geometry of individual plant mounds. We also present a GIS-based analysis that predicts where bands occur within a region based on topographic and hydroclimatic controls. © 2012. American Geophysical Union. All Rights Reserved.
• Chorover, J., Troch, P. A., Rasmussen, C., Brooks, P. D., Pelletier, J. D., Breshears, D. D., Huxman, T. E., Kurc, S. A., Lohse, K., Mcintosh, J. C., Meixner, T., Schaap, M. G., Litvak, M., Perdrial, J., Harpold, A., Durcik, M., Chorover, J., Troch, P. A., Rasmussen, C., , Brooks, P. D., et al. (2011). How water, carbon, and energy drive critical zone evolution: the Jemez-Santa Catalina Critical Zone Observatory. Vadose Zone Journal, 10, 884-899.
• DeLong, S. B., Pelletier, J. D., & Arnold, L. J. (2011). Late holocene alluvial history of the Cuyama River, California, USA. Bulletin of the Geological Society of America, 123(11-12), 2160-2176.
  More info

  Abstract: Dryland river deposits are archives of past changes in fluvial-system form and process. Chronostratigraphic reconstruction of the late Holocene alluvial history of the Cuyama River in west-central California reveals past spatial and temporal variation in dryland channel form and process. The modern Cuyama River consists of a wide braided reach in the upper drainage basin, a narrower arroyo reach in the middle of the drainage basin, and a bedrock canyon reach in the lower drainage basin that drains to the Santa Maria coastal plain. Along the arroyo reach, late Holocene stratigraphy is well exposed and is the focus of this study. Between ca. 1700 and 350 yr B.P., two widespread deposits of tabular-bedded clay, silt, and fine sand were deposited, separated by a buried soil formed between 950 and 700 yr B.P. Channel incision occurred between 550 and 350 yr B.P. Next, deposition of massive to bedded sands occurred in a pattern alternating between poorly confined deposition on top of older deposits onto the broad valley floor, and channelized deposition along the valley axis inset into older deposits. The superposed deposits now underlie the main valley terrace, and the valley-axis deposits are preserved as inset fill terraces. Historical arroyo cutting then formed a 65-km-long arroyo ca. 150 yr B.P. Based on correlation to regional paleoclimate records, channel aggradation occurred during periods of relative aridity and low peak discharge events, while wet periods, possibly floods after drought, led to fluvial incision. These cycles are superimposed on a transition from a wide, silt- and fine-sand- dominated fluvial system to a modern, narrow, sand- and gravel-dominated arroyo channel. The relationship between times of fluvial process change and climate change in Cuyama Valley bears considerable similarity to other well-studied dryland rivers in the southwestern United States; however, the complex sedimentology and geometry of preserved fluvial deposits suggest that a wider range of fluvial modes occurred along the Cuyama River than has been reported in simpler cut-and-fill-dominated channels elsewhere. These spatial and sedimentological complexities underscore the need to link fluvial deposits and their bounding unconformities along a channel in order to fully understand the spatial and temporal evolution of ancient fluvial systems. © 2011 Geological Society of America.
• Pelletier, J. D., McGuire, L. A., Ash, J. L., Engelder, T. M., Hill, L. E., Leroy, K. W., Orem, C. A., Rosenthal, W. S., Trees, M. A., Rasmussen, C., & Chorover, J. (2011). Calibration and testing of upland hillslope evolution models in a dated landscape: Banco Bonito, New Mexico. Journal of Geophysical Research F: Earth Surface, 116(4).
  More info

  Abstract: In this study we tested upland hillslope evolution models and constrained the rates of regolith production, colluvial transport, and eolian deposition over geologic time scales in a dated volcanic landscape in northern New Mexico using field measurements of regolith thickness; geochemical analyses of regolith, bedrock, and regional dust; numerical modeling of regolith production and transport; and quantitative analyses of airborne light detection and ranging (lidar) digital elevation models (DEMs). Within this volcanic landscape, many topographically closed basins exist as a result of compressional folding and explosion pitting during eruption. The landscape has evolved from an initial state of no regolith cover at 40 5 ka to its modern state, which has highly weathered regolith ranging from 0 to 3+ m, with local thickness values controlled primarily by topographic position. Our models constrain the maximum rate of regolith production in the study area to be in the range of 0.02 to 0.12 m kyr-1 and the rate of colluvial transport per unit slope gradient to be in the range of 0.2 to 2.7 m2 kyr-1, with higher values in areas with more aboveground biomass. We conclude that a depth-dependent colluvial transport model better predicts the observed spatial distribution of regolith thickness compared to a model that has no depth dependence. This study adds to the database of estimates for rates of regolith production and transport in the western United States and shows how dated landscapes can be used to improve our understanding of the coevolution of landscapes and regolith cover. Copyright 2011 by the American Geophysical Union.
• Rasmussen, C., Troch, P. A., Chorover, J., Brooks, P., Pelletier, J., & Huxman, T. E. (2011). An open system framework for integrating critical zone structure and function. Biogeochemistry, 102(1), 15-29.
  More info

  Abstract: The "critical zone" includes the coupled earth surface systems of vegetation, regolith and groundwater that are essential to sustaining life on the planet. The function of this zone is the result of complex interactions among physical, chemical and biological processes and understanding these interactions remains a major challenge to earth system sciences. Here we develop an integrated framework based on thermodynamic theory to characterize the critical zone as a system open to energy and mass fluxes that are forced by radiant, geochemical, and elevational gradients. We derive a statement that demonstrates the relative importance of solar radiation, water, carbon, and physical/chemical denudation mass fluxes to the critical zone energy balance. Within this framework we use rates of effective energy and mass transfer [EEMT; W m-2] to quantify the relevant flux-gradient relations. Synthesis of existing data demonstrates that variation in energetics associated with primary production and effective precipitation explains substantial variance in critical zone structure and function. Furthermore, we observe threshold behavior in systems that transition to primary production predominance of the energy flux term. The proposed framework provides a first order approximation of non-linearity in critical zone processes that may be coupled with physical and numerical models to constrain landscape evolution. © 2010 Springer Science+Business Media B.V.
• Pelletier, J. D. (2010). How do pediments form?: A numerical modeling investigation with comparison to pediments in southern Arizona, USA. Bulletin of the Geological Society of America, 122(11-12), 1815-1829.
  More info

  Abstract: Pediments are gently sloping, low-relief bedrock erosional surfaces at the bases of mountain ranges. Pediments tend to form more readily in arid climates and in weathering-resistant lithologies, but the processes responsible for pediment formation are still not widely understood after more than a century of debate. In this paper, I investigate the behavior of a coupled numerical model for the evolution of mountain ranges and their adjacent piedmonts that includes bedrock erosion in channels, soil production and erosion on hillslopes, and the flexural-isostatic response of the lithosphere to erosional unloading. For relatively small values of the flexural parameter, erosion of the mountain range leads to sufficient flexural-isostatic tilting of the adjacent piedmont that a suballuvial bedrock bench is exhumed to form an erosional surface on the piedmont. In addition, slope retreat at the mountain front and subsequent tilting of the abandoned surface can contribute to pediment formation by lengthening the pediment in the upslope direction. The rate of erosion on the piedmont must also be greater than or equal to the rate of soil production, thereby creating an erosional surface that has, at most, a thin veneer of soil or regolith. The rate of soil production depends primarily on climate and lithology, with lower soil production rates associated with more arid climates and more resistant lithologies. The model predictions are compared to morphometric analyses of pediments in the southwestern United States and to the detailed morphology of two classic pediments in southern Arizona. © 2010 Geological Society of America.
• Pelletier, J. D. (2010). Minimizing the grid-resolution dependence of flow-routing algorithms for geomorphic applications. Geomorphology, 122(1-2), 91-98.
  More info

  Abstract: The results of flow-routing methods currently used in the geomorphic literature depend on grid resolution. This poses a problem for landscape evolution models, which must be independent of grid resolution to the greatest extent possible. Here I illustrate a refinement of currently-used flow-routing algorithms that yields unit contributing areas (i.e. contributing areas per unit width of flow) with minimal grid-resolution effects. I illustrate the application of this method in idealized topography, in high-resolution Digital Elevation Models (DEMs) of real-world topography, and by integration into a landscape evolution model for ridge-and-valley topography. The landscape evolution model produces grid-resolution-independent results in a more straightforward way than previous models for this type of landscape. © 2010 Elsevier B.V.
• Pelletier, J. D. (2010). Numerical modeling of the late Cenozoic geomorphic evolution of Grand Canyon, Arizona. Bulletin of the Geological Society of America, 122(3-4), 595-608.
  More info

  Abstract: The late Cenozoic geomorphic evolution of Grand Canyon has been influenced by three primary tectonic and drainage adjustment events. First, 1 km of relief was produced along the Grand Wash-Wheeler Fault system beginning at 16.5 Ma. Second, the ancestral Colorado River became integrated with the lower Colorado River through Grand Canyon between 5.5 and 6 Ma. Third, the Colorado River was influenced by Plio-Quaternary normal faulting along the Hurricane and Toroweap Faults. Despite the relatively firm constraints available on the timing of these events, the geomorphic evolution of Grand Canyon is still not well constrained. For example, was there a deeply incised gorge in western Grand Canyon before Colorado River integration? How did incision rates vary through time and along the evolving river profile? What is the role of isostatic rebound and Plio-Quaternary faulting on the recent incision history of Grand Canyon? In this paper I describe the results of a process-based numerical modeling study designed to address these questions and to determine the plausibility of different proposed models for the erosional history of Grand Canyon. The numerical model I developed integrates the stream-power model for bedrock channel erosion with cliff retreat and the flexural-isostatic response to erosion. Two end-member paleodrainage and integration scenarios are considered. In the first model, I assume no incision in western Grand Canyon prior to 6 Ma. This model is equivalent to a lake-overtopping scenario for Colorado River integration. In this scenario, the model predicts that Colorado River integration at 6 Ma initiated the formation of a large (700 m) knickpoint that migrated headward at a rate of 100 km/Ma, resulting in rapid incision of western Grand Canyon down to the level of the Redwall Limestone from 6 to 4 Ma and incision of eastern Grand and Marble Canyons from 4 to 2 Ma. Widening of Grand Canyon by cliff retreat triggered flexural-isostatic rebound and renewed river incision of up to 350 m in Plio-Quaternary time according to this model. The model also indicates that Plio-Quaternary normal faulting significantly dampened incision rates in western Grand Canyon relative to eastern Grand Canyon. In the second paleodrainage scenario, I assume that a 13,000 km2 paleodrainage crossed the Grand Wash-Wheeler Fault system at 16.5 Ma. The results of this model scenario indicate that relief production along the Grand Wash-Wheeler Fault system could have initiated the formation of a large (700 m) knickpoint that migrated headward at a rate of 15 km/Ma prior to 6 Ma to form a 150-km-long gorge in western Grand Canyon. Following integration at 6 Ma, the results of this model scenario are broadly similar to those of the first model, i.e., rapid incision through Grand and Marble Canyons from 6 to 2 Ma followed by cliff retreat, isostatic rebound, and fault-controlled incision. The results of the second model scenario illus trate that headward erosion of a proto-Grand Canyon could have been sufficient to capture the ancestral Colorado River east of the Shivwitz Plateau. © 2010 Geological Society of America.
• Pelletier, J. D., Comeau, D., & Kargel, J. (2010). Controls of glacial valley spacing on earth and mars. Geomorphology, 116(1-2), 189-201.
  More info

  Abstract: Low-order alpine glacial valleys on Earth commonly have a characteristic spacing of 1-3 km. Here we develop analytic and numerical solutions of a coupled numerical model for alpine glacial flow and subglacial bedrock erosion to quantitatively determine the controls on glacial valley spacing assuming an initially-undissected landscape, an initially-fluvially-dissected landscape, and an initially-cratered landscape. The characteristic spacing of glacial valleys produced by the model is controlled by a competition between the thickening of ice in incipient glacial valleys, which acts to enhance flow and valley deepening, and viscous/sidewall drag, which acts to limit flow and deepening. The glacial valley spacing that represents the best compromise between these two competing effects is found to be a function of valley slope, the threshold basal shear stress for ice motion, the effective ice viscosity, a bed-friction parameter, and gravity. This model framework provides the preliminary basis for understanding the relative spacing of glacial valleys on Earth and Mars. On Mars, montane glacial valleys have widths and spacings that are approximately 10-20 times larger than those on Earth. Model results suggest that this difference is predominantly a consequence of lower bed slopes and larger temperature-controlled ice viscosities of glacial ice on Mars compared to Earth. © 2009 Elsevier B.V. All rights reserved.
• Pelletier, J. D., Comeau, D., & Kargel, J. (2010). Erratum to "Controls of glacial valley spacing on Earth and Mars" (Geomorphology 116 (2010) 189-201) (DOI:10.1016/j.geomorph.2009.10.018). Geomorphology, 117(1-2), 206-.
• Evans, J. P., Pelletier, J. D., & Russo, R. M. (2009). Welcome to Lithosphere. Lithosphere, 1(1), 3-.
• Murray, A. B., Lazarus, E., Ashton, A., Baas, A., Coco, G., Coulthard, T., Fonstad, M., Haff, P., McNamara, D., Paola, C., Pelletier, J., & Reinhardt, L. (2009). Geomorphology, complexity, and the emerging science of the Earth's surface. Geomorphology, 103(3), 496-505.
  More info

  Abstract: The following is a white paper (adapted here for print) for the U.S. National Research Council's committee on Challenges and Opportunities in Earth Surface Processes, drafted at a National Science Foundation sponsored workshop associated with the 38th Binghamton Geomorphology Symposium, "Complexity in Geomorphology," held at Duke University in October 2007. © 2008 Elsevier B.V. All rights reserved.
• Pelletier, J. D. (2009). Controls on the height and spacing of eolian ripples and transverse dunes: A numerical modeling investigation. Geomorphology, 105(3-4), 322-333.
  More info

  Abstract: Ripples and transverse dunes in areas of abundant sand supply increase in height and spacing as a function of time, grain size, and excess shear velocity. How and why each of these factors influence ripple and transverse dune size, however, is not precisely known. In this paper, the controls on the height and spacing of ripples and transverse dunes in areas of abundant sand supply are investigated using a numerical model for the formation of eolian bedforms from an initially flat surface. This bedform evolution model combines the basic elements of Werner's [Werner, B.T., 1995. Eolian dunes: Computer simulations and attractor interpretation. Geology 23, 1107-1110.] cellular automaton model of dune formation with a model for boundary layer flow over complex topography. Particular attention is paid to the relationship between bed shear stress and slope on the windward (stoss) side of evolving bedforms. Nonlinear boundary layer model results indicate that bed shear stresses on stoss slopes increase with increasing slope angle up to approximately 20°, then decrease with increasing slope angle as backpressure effects become limiting. In the bedform evolution model, the linear boundary layer flow model of Jackson and Hunt [Jackson, P.S., Hunt, J.C.R., 1975. Turbulent wind flow over a low hill. Quarterly Journal of the Royal Meteorological Society 101, 929-955.], generalized to 3D, is modified to include the nonlinear relationship between bed shear stress and slope. Bed shear stresses predicted by the modified Jackson and Hunt flow model are then used to predict rates of erosion and deposition iteratively through time within a mass-conservative framework similar to Werner [Werner, B.T., 1995. Eolian dunes: Computer simulations and attractor interpretation. Geology 23, 1107-1110.]. Beginning with a flat bed, the model forms ripples that grow in height and spacing until a dynamic steady-state condition is achieved in which bedforms migrate downwind without further growth. The steady-state ripple spacing predicted by this model is approximately 3000 times greater than the aerodynamic roughness length of the initially flat surface, which is a function of grain size and excess shear velocity. Once steady-state ripples form, they become the dominant roughness element of the surface. The increase in roughness associated with ripple formation triggers the same bedform instability that created ripples, causing dunes to form at a larger scale. In this way, the numerical model of this paper suggests that ripples and dunes are genetically linked. Transverse dunes in this model have a steady-state height and spacing that is controlled by the effective roughness length of the rippled surface, which is shown to be on the order of 500 times greater than the original roughness length, but varies significantly with the details of ripple morphology. The model predictions for ripple and dune spacing and their controlling variables are consistent with field measurements from the published literature. The model of this paper provides a preliminary process-based understanding of the granulometric control of ripples and dunes in areas of abundant sand supply and unidirectional prevailing winds, and it argues for a genetic linkage between ripples and dunes via a scaling relationship between eolian bedform size and the aerodynamic roughness length. © 2008 Elsevier B.V. All rights reserved.
• Pelletier, J. D. (2009). The impact of snowmelt on the late Cenozoic landscape of the southern Rocky Mountains, USA. GSA Today, 19(7), 4-11.
  More info

  Abstract: The intramontane basins of the southern Rocky Mountains, USA, have undergone up to 1.5 km of erosion from the middle Miocene to the present. Here I explore the hypothesis that this erosion could have been caused primarily by an increase in the intensity of snowmelt flooding. In the middle Miocene, snow-melt runoff was limited to the highest elevations (>3 km) and hence impacted only a small fraction of the regional landscape. As the global climate system cooled during the late Miocene and Plio-Quaternary periods, the fraction of total river discharge derived from snowmelt increased significantly in areas between 1.5 and 3 km elevation, thereby increasing the magnitude of flooding during periods of snowmelt and the resulting bedload sediment flux and erosion of rivers in that elevation range. In this paper, the fraction of modern discharge derived from snowmelt is used, together with an assumed lapse rate, to map the change in snowmelt discharge and sediment flux through time from the middle Miocene to the Quaternary in the southern Rocky Mountain region. These data are then used as input to a landscape evolution model that maps the spatial distribution of late Cenozoic snowmelt-driven erosion in the region. The model predicts a spatial distribution of erosion that broadly matches the actual distribution determined from geographic information system (GIS) analyses and dated basin-fill remnants. In the model, a factor-of-four increase in sediment flux within the 1.5-3 km elevation range, well within reasonable estimates, is capable of producing the observed magnitude of late Cenozoic erosion in the region. The longitudinal profiles of major rivers sourced from the southern Rocky Mountains are also modeled through time in order to better understand the downstream response to intramontane basin erosion. Model results indicate that erosion would have triggered widespread deposition downstream from those basins, which is broadly consistent with the magnitude, timing, and spatial distribution of the Ogallala Formation. The results of this study suggest that snowmelt-driven erosion may be an important component of late Cenozoic landscape evolution in mid- to high-elevation regions worldwide.
• Pelletier, J. D., & Rasmussen, C. (2009). Geomorphically based predictive mapping of soil thickness in upland watersheds. Water Resources Research, 45(9).
  More info

  Abstract: The hydrologic response of upland watersheds is strongly controlled by soil (regolith) thickness. Despite the need to quantify soil thickness for input into hydrologic models, there is currently no widely used, geomorphically based method for doing so. In this paper we describe and illustrate a new method for predictive mapping of soil thicknesses using high-resolution topographic data, numerical modeling, and field-based calibration. The model framework works directly with input digital elevation model data to predict soil thicknesses assuming a long-term balance between soil production and erosion. Erosion rates in the model are quantified using one of three geomorphically based sediment transport models: nonlinear slope-dependent transport, nonlinear area- and slopedependent transport, and nonlinear depth- and slope-dependent transport. The model balances soil production and erosion locally to predict a family of solutions corresponding to a range of values of two unconstrained model parameters. A small number of fieldbased soil thickness measurements can then be used to calibrate the local value of those unconstrained parameters, thereby constraining which solution is applicable at a particular study site. As an illustration, the model is used to predictively map soil thicknesses in two small, ∼0.1 km2, drainage basins in the Marshall Gulch watershed, a semiarid drainage basin in the Santa Catalina Mountains of Pima County, Arizona. Field observations and calibration data indicate that the nonlinear depth- and slope-dependent sediment transport model is the most appropriate transport model for this site. Theresulting framework provides a enerally applicable, geomorphically based tool for predictive mapping of soil thickness using high-resolution topographic data sets. Copyright 2009 by the American Geophysical Union.
• Pelletier, J. D., Engelder, T., Comeau, D., Hudson, A., Leclerc, M., Youberg, A., & Diniega, S. (2009). Tectonic and structural control of fluvial channel morphology in metamorphic core complexes: The example of the Catalina-Rincon core complex, Arizona. Geosphere, 5(4), 363-384.
  More info

  Abstract: Fluvial channels in metamorphic core complexes are preferentially oriented parallel and perpendicular to the direction of tectonic extension. This pattern has been variably attributed to such causes as tectonic tilting during extension, channel elongation by slip along the range-bounding detachment fault, and the exploitation of extension-related joint sets during channel incision. In this paper we use field measurements, digital elevation model analyses, and numerical modeling to test hypotheses for the tectonic and structural control of fluvial channels in metamorphic core complexes, using the Catalina-Rincon core complex in southern Arizona, USA, as a type example. Field measurements and aerial photographic analyses indicate that channels of all sizes exploit steeply dipping joint sets during fluvial incision. As a consequence, channels become preferentially aligned along those joint sets. First and second Strahler-order channels preferentially exploit a joint set oriented perpendicular to the extension direction, while higher-order channels preferentially exploit a joint set oriented parallel to the extension direction. While these observations support the joint-exploitation hypothesis for structural control of drainage architecture, numerical modeling indicates that the spatial distribution of rock uplift during the initial phase of extension plays a crucial role by determining which joint set is preferentially exploited by channels of which Strahler orders. Numerical models indicate that higher-order channels exploit the joint set that is most closely aligned with the direction of initial tectonic tilting, even if that tilting is active for only a short period of time following the initiation of uplift. We conclude that the drainage architecture in the Catalina-Rincon core complex is the result of a combination of joint exploitation and tectonic tilting mechanisms. Structure also plays an important role in controlling the longitudinal profiles of channels in metamorphic core complexes. Channels in the Catalina-Rincon core complex are characterized by structurally controlled knickpoints with a wide distribution of heights and spacings. Field observations indicate that the occurrence of structurally controlled knickpoints and the resulting variability in longitudinal profile form is related to spatial variations in joint density. Numerical models that incorporate spatial variations in joint density using a stochastic bedrock erodibility coefficient are capable of reproducing the statistical properties of longitudinal profiles in the Catalina-Rincon core complex, including the power spectrum of longitudinal profiles and the frequency size distribution of structurally controlled knickpoints. The results of this study illustrate the important roles played by both jointing and the spatial distribution of rock uplift on the geomorphic evolution of metamorphic core complexes. More broadly, the study provides a recipe for how to incorporate joint-related structural controls into landscape evolution models. © 2010 Geological Society of America.
• Pelletier, J. D., Leier, A. L., & Steidtmann, J. R. (2009). Wind-driven reorganization of coarse clasts on the surface of Mars. Geology, 37(1), 55-58.
  More info

  Abstract: Coarse (pebble to cobble sized) clasts on the intercrater plains of the Mars Exploration Rover Spirit landing site exhibit a nonrandom (i.e., uniformly spaced) distribution. This pattern has been attributed to the entrainment and redistribution of coarse clasts during extreme wind events. Here we propose an alternative mechanism readily observable in wind tunnels and numerical models at modest wind speeds. In this process, coarse clasts modify the air flow around them, causing erosion of the underlying substrate on the windward side and deposition on the leeward side until a threshold bed-slope condition is reached, after which the clast rolls into the windward trough. Clasts can migrate across an erodible substrate in repeated cycles of trough formation and clast rolling, "attracting" or "repelling" one another through feedbacks between the local clast density, substrate erosion and/or deposition rate, and substrate elevation. The substrate beneath areas of locally high clast densities aggrades, building up a topographic high that can cause clasts to repel one another to form a more uniform distribution of clasts through time. This self-organized process likely plays a significant role in the evolution of mixed grain size eolian surfaces on Earth and Mars. © 2009 The Geological Society of America.
• Pelletier, J. D., Mitasova, H., Harmon, R. S., & Overton, M. (2009). The effects of interdune vegetation changes on eolian dune field evolution: A numericalmodeling case study at Jockey's Ridge, North Carolina, USA. Earth Surface Processes and Landforms, 34(9), 1245-1254.
  More info

  Abstract: Changes in vegetation cover within dune fields can play a major role in how dune fields evolve. To better understand the linkage between dune field evolution and interdune vegetation changes, we modified Werner's (Geology, 23, 1995: 1107-1110) dune field evolution model to account for the stabilizing effects of vegetation. Model results indicate that changes in the density of interdune vegetation strongly influence subsequent trends in the height and area of eolian dunes. We applied the model to interpreting the recent evolution of Jockey's Ridge, North Carolina, where repeat LiDAR surveys and historical aerial photographs and maps provide an unusually detailed record of recent dune field evolution. In the absence of interdune vegetation, the model predicts that dunes at Jockey's Ridge evolve towards taller, more closely-spaced, barchanoid dunes, with smaller dunes generally migrating faster than larger dunes. Conversely, the establishment of interdune vegetation causes dunes to evolve towards shorter, more widely-spaced, parabolic forms. These results provide a basis for understanding the increase in dune height at Jockey's Ridge during the early part of the twentieth century, when interdune vegetation was sparse, followed by the decrease in dune height and establishment of parabolic forms from 1953-present when interdune vegetation density increased. These results provide a conceptual model that may be applicable at other sites with increasing interdune vegetation cover, and they illustrate the power of using numerical modeling to model decadal variations in eolian dune field evolution. We also describe model results designed to test the relative efficacy of alternative strategies for mitigating dune migration and deflation. Installing sand-trapping fences and/or promoting vegetation growth on the stoss sides of dunes are found to be the most effective strategies for limiting dune advance, but these strategies must be weighed against the desire of many park visitors to maintain the natural state of the dunes. © 2009 John Wiley & Sons, Ltd.
• Pelletier, J. D., Rasmussen, C., Pelletier, J. D., & Rasmussen, C. (2009). Quantifying the climatic and tectonic controls on hillslope steepness and erosion rate. Lithosphere, 1(2), 73-80.
  More info

  Abstract: Hillslopes in humid regions are typically convex to concave in profile and have a relatively thick, continuous regolith cover. Conversely, hillslopes in arid regions are typically cliff-dominated and have a relatively thin, discontinuous regolith cover. The difference between these two end-member slope forms is classically attributed to climate, but climate, tectonics, and lithology all play a role. In this paper, we describe a mathematical model for hillslope gradient and regolith thickness using basic climatic and tectonic input data for a given rock type. The model first solves for the regolith thickness on a planar slope segment in topographic steady state using the soil production function and a prescribed uplift/incision rate. The climatic and lithologic controls on soil production rates are quantified using an empirical energy-based model for the physical weathering of bedrock. The slope gradient is then computed by balancing uplift/incision rates with sediment fluxes calculated using a nonlinear depth- and slope-dependent sediment transport model. The model quantifies the ways in which, as aridity and uplift/incision rates increase, regolith thicknesses decrease and hillslope gradients increase nonlinearly until a threshold condition is reached, beyond which bare, cliff-dominated slopes form. The model can also be used to estimate long-term erosion rates and soil residence times using basic input data for climate and regolith thickness. Model predictions for erosion rates closely match cosmogenically derived erosion rates in granitic landscapes. This approach provides a better quantitative understanding of the climatic and tectonic controls on slope form, and it provides a simple, widely applicable method for estimating long-term erosion rates and the thickness of regolith cover on hillslopes. © 2009 Geological Society of America.
• Banks, M. E., & Pelletier, J. D. (2008). Forward modeling of ice topography on Mars to infer basal shear stress conditions. Journal of Geophysical Research E: Planets, 113(1).
  More info

  Abstract: Understanding the history of ice caps on Mars could reveal important information about Martian geologic and climatic history. To do this, an ice reconstruction model is needed that operates over complex topography and can be constrained with a limited number of free parameters. In this study we developed a threshold-sliding model for ice cap morphology based on the classic model of Nye later incorporated into the models of Reeh and colleagues. We have updated the Nye-Reeh model with a new numerical algorithm. Although the model was originally developed to model perfectly plastic deformation, it is applicable to any ice body that deforms when a threshold basal shear stress is exceeded. The model requires three inputs: a digital elevation model of bed topography, a "mask" grid that defines the position of the ice terminus, and a function defining the threshold basal shear stress. To test the robustness of the model, the morphology of the Greenland ice sheet is reconstructed using an empirical equation between threshold basal shear stress and ice surface slope. The model is then used to reconstruct the morphology of ice draping impact craters on the margins of the south polar layered deposits using an inferred constant basal shear stress of ∼0.6 bar for the majority of the examples. This inferred basal shear stress value is almost 1/3 of the average basal shear stress calculated for the Greenland ice sheet. What causes this lower basal shear stress value on Mars is unclear but could involve the strain-weakening behavior of ice. Copyright 2008 by the American Geophysical Union.
• Blainey, J. B., & Pelletier, J. D. (2008). Infiltration on alluvial fans in arid environments: Influences of fan morphology. Journal of Geophysical Research F: Earth Surface, 113(3).
  More info

  Abstract: Mountain-front recharge through highly permeable alluvial fans can be an important source of groundwater recharge in arid climates. To better understand the geomorphic factors (e.g., fan slope, fan area, active channel proportion of fan area, sediment permeability, and entrenchment of the active channel) that control flow and infiltration on alluvial fans, we developed a coupled numerical model of steady surface water flow and Green-Ampt-type infiltration. The model was applied to synthetic alluvial fans using random walkers to create connected distributary networks. The purpose of this approach is to predict where and how recharge occurs on fans as a function of fan morphology. Using the numerical model, we examined how the fan shape and the sequence of fan surfaces influenced where infiltration occurred on the fan. We also investigated how fan morphology influenced the partitioning of infiltration between the fan and the valley floor. Finally, we examined how infiltration influenced the spatial distribution of flooding. The greatest amount of infiltration occurred on low gradient fans where water spread laterally with shallower ponded water depths, although the large inundation area often included less permeable sediments outside of the active channel. The ratio of the incision depth to the input flow depth was an important predictor of the amount of infiltration. The greatest amount of infiltration occurred on fans with incision depths slightly smaller than the input flow depth. These results have implications for groundwater resource assessment and for development of monitoring networks on fans in arid environments. Copyright 2008 by the American Geophysical Union.
• DeLong, S. B., Pelletier, J. D., & Arnold, L. J. (2008). Climate change triggered sedimentation and progressive tectonic uplift in a coupled piedmont-axial system: Cuyama Valley, California, USA. Earth Surface Processes and Landforms, 33(7), 1033-1046.
  More info

  Abstract: Channels on the north-facing piedmont of the Sierra Madre range in Cuyama Valley, California have alternated between three process regimes during the late Quaternary: (1) vertical incision into piedmont alluvium and older sedimentary deposits; (2) lateral erosion; and (3) sediment accumulation. The state of the piedmont system at a given time has been controlled by upstream sediment flux, regional tectonic uplift and incision of the axial Cuyama River. To better understand the timing and to attempt to interpret causes of past geomorphological processes on the Sierra Madre piedmont, we mapped the surficial geology and dated alluvial deposits using radiocarbon, cosmogenic and optical dating methods. Four primary episodes of sedimentation have occurred since ca. 100 ka, culminating in the most recent period of extensive piedmont sedimentation between 30 and 20 ka. Fill terraces in Cuyama Valley formed by piedmont sediment accumulation followed by vertical incision and lateral erosion are fairly planar and often mantle strath bedrock surfaces. Their vertical spatial arrangement is a record of progressive regional tectonic uplift and concomitant axial Cuyama River channel incision migrating up tributary piedmont channels. Subparallel longitudinal terrace profiles which have a linear age-elevation relationship indicate that multiple episodes of climatically controlled sedimentation overprints ∼1 m kyr-1 of regional uplift affecting the Cuyama River and its tributaries. Sedimentation was probably a result of increased precipitation that caused saturation landsliding in steep catchments. It is possible that increased precipitation during the Last Glacial Maximum was caused by both continental-scale circulation pattern reorganization and increased Pacific storm frequency and intensity caused by 'early warming' of nearby Pacific Ocean surface waters. Older episodes of piedmont sedimentation are difficult to correlate with specific climate regimes, but may correlate with previous periods of increased precipitation. Copyright © 2007 John Wiley & Sons, Ltd.
• Keating, G. N., Pelletier, J. D., Valentine, G. A., & Statham, W. (2008). Evaluating suitability of a tephra dispersal model as part of a risk assessment framework. Journal of Volcanology and Geothermal Research, 177(2), 397-404.
  More info

  Abstract: In volcanic risk assessment it is necessary to determine the appropriate level of sophistication for a given predictive model within the contexts of multiple sources of uncertainty and coupling between models. A component of volcanic risk assessment for the proposed radioactive waste repository at Yucca Mountain (Nevada, USA) involves prediction of dispersal of contaminated tephra during violent Strombolian eruptions and the subsequent transport of that tephra toward a hypothetical individual via surface processes. We test the suitability of a simplified model for volcanic plume transport and fallout tephra deposition (ASHPLUME) coupled to a surface sediment-transport model (FAR) that calculates the redistribution of tephra, and in light of inherent uncertainties in the system. The study focuses on two simplifying assumptions in the ASHPLUME model: 1) constant eruptive column height and 2) constant wind speed and direction during an eruption. Variations in tephra dispersal resulting from unsteady column height and wind conditions produced variations up to a factor of two in the concentration of tephra in sediment transported to the control population. However, the effects of watershed geometry and terrain, which control local remobilization of tephra, overprint sensitivities to eruption parameters. Because the combination of models used here shows limited sensitivity to the actual details of ash fall, a simple fall model suffices to estimate tephra mass delivered to the hypothetical individual.
• Pelletier, J. D. (2008). Glacial erosion and mountain building. Geology, 36(7), 591-592.
• Pelletier, J. D., DeLong, S. B., Cline, M. L., Harrington, C. D., & Keating, G. N. (2008). Dispersion of channel-sediment contaminants in distributary fluvial systems: Application to fluvial tephra and radionuclide redistribution following a potential volcanic eruption at Yucca Mountain. Geomorphology, 94(1-2), 226-246.
  More info

  Abstract: Predicting the fluvial transport and mixing of channel-sediment contaminants is necessary for assessing and mitigating heavy-metal and nuclear-waste contamination in rivers. The dilution-mixing model is widely used for this purpose in tributary channel systems that transport contaminants as bed-material load without significant overbank sedimentation. Here a more general, three-dimensional (3D) contaminant transport numerical model is developed and tested based on bed scour, turbulent mixing of contaminant material with uncontaminated channel-bed sediments, and re-deposition of the mixture by the cumulative effect of many flood events. First, the model is applied to a synthetic alluvial-fan environment downstream from a localized contaminant source in order to illustrate the model behavior. Second, the model is validated against measured tephra concentrations in channels downstream from the Lathrop Wells scoria cone volcano, a localized source of basaltic tephra to downstream channels otherwise comprised of non-basaltic sediments. Third, the model is applied to the problem of predicting the concentration of radionuclide-bound tephra in channels downstream from the proposed nuclear-waste repository at Yucca Mountain, Nevada, in the event of a volcanic eruption through the repository. Contaminated tephra is mobilized from the landscape in this model using threshold criteria for hillslope gradient and channel stream power. Mobilized contaminated tephra is mixed with uncontaminated channel-bed sediments using the contaminant transport model and deposited in channels of the Fortymile Wash alluvial fan where the residents nearest to the proposed repository live. The results of twenty Monte Carlo simulations of eruption fallout and post-eruption redistribution corresponding to a range of wind conditions and eruption magnitudes provide information on the mean and variability of contaminated tephra concentrations to be expected in channels of the Fortymile Wash alluvial fan in the event of an eruption. Mean tephra concentrations are approximately 1% but vary from nearly zero to as high as 26%, reflecting the combined effects of wind direction, eruption magnitude, and dilution of tephra with uncontaminated channel-bed sediments during transport. © 2007 Elsevier B.V. All rights reserved.
• Cook, J. P., & Pelletier, J. D. (2007). Relief threshold for eolian sand transport on alluvial fans. Journal of Geophysical Research F: Earth Surface, 112(2).
  More info

  Abstract: Many arid alluvial-fan terraces downwind from eolian sand sources exhibit an abrupt increase in eolian epipedon thickness and sand content below a critical elevation which varies from fan to fan. Above this elevation, sand accumulates locally and is not transported across the fan. Below this elevation eolian sand from nearby playa and channel sources is readily transported across the distal fan. Here we test the hypothesis that these distal-fan eolian "corridors" are controlled by a threshold fan-surface relief. We propose that when along-strike relief falls below a critical threshold value, an eolian surface of transportation or "corridor" develops. To test this hypothesis, we measured multiple along-strike topographic profiles and eolian epipedon textures on two piedmonts in the Ivanpah Valley and adjacent Hidden Valley in Clark County, Nevada. Both piedmonts are located near sand-dominated playas and exhibit clear evidence of eolian transport across their distal fan regions. The near-surface boundary layer flow above each topographic profile was quantified using the multispectral finite difference (MSFD) numerical model. This model predicts the surface shear stress above complex terrain for any wind condition assuming neutrally stable flow. The minimum shear stress calculated by MSFD for each profile during extreme wind conditions was compared to the shear-velocity threshold necessary to initiate saltation. Model results showed that in proximal fan areas, along-strike relief was large enough to prevent eolian transport of all but fine sand particles. In distal fan profiles within the eolian corridor, model results predict shear stresses everywhere above threshold for both fine and coarse sand. Copyright 2007 by the American Geophysical Union.
• DeLong, S. B., Pelletier, J. D., & Arnold, L. (2007). Bedrock landscape development modeling: Calibration using field study, geochronology, and digital elevation model analysis. Bulletin of the Geological Society of America, 119(1-2), 157-173.
  More info

  Abstract: Stream power-based models of bedrock landscape development are effective at producing synthetic topography with realistic fluvial-network topology and three-dimensional topography, but they are difficult to calibrate. This paper examines ways in which field observations, geochronology, and digital elevation model (DEM) data can be used to calibrate a bedrock landscape development model for a specific study site. We first show how uplift rate, bedrock erodibility, and landslide threshold slope are related to steady-state relief, hypsometry, and drainage density for a wide range of synthetic topographies produced by a stream power-based planform landscape development model. Our results indicate that low uplift rates and high erodibility result in low-relief, high drainage density, fluvially dominated topography, and high uplift rates and low erodibility leads to high-refief, low drainage density, mass wasting-dominated topography. Topography made up of a combination of fluvial channels and threshold slopes occurs for only a relatively narrow range of model parameters. Using measured values for hypsometric integral, drainage density, and relief, quantitative values of bedrock erodibility can be further constrained, particularly if uplift rates are independently known. We applied these techniques to three sedimentary rock units in the western Transverse Ranges in California that have experienced similar climate, uplift, and incision histories. The 10Be surface exposure dating and optically stimulated luminescence (OSL) burial dating data indicated that incision of initially low-relief topography there occurred during the last ∼60 k.y. We estimated the relative dependence of drainage area and channel slope on erosion rate in the stream power law from slope-area data, and inferred values for bedrock erodibility ranging from 0.09 to 0.3 m (0.2-0.4) k.y.-1 for the rock types in this study area. © 2006 Geological Society of America.
• Pelletier, J. D. (2007). Cantor set model of eolian dust deposits on desert alluvial fan terraces. Geology, 35(5), 439-442.
  More info

  Abstract: Available data show that eolian dust accumulation rates on desert alluvial fan terraces are often inversely proportional to the square root of the terrace age for a given area. This temporal scaling is similar to that observed in fluvial and marine stratigraphic sequences in which a fractal distribution of hiatuses occurs (i.e., a Cantor set). Eolian dust accumulation on alluvial fan terraces is controlled by regional climatic influences on dust deposition (e.g., dessication of pluvial lakes in the early Holocene) and local surface characteristics (e.g., vegetation and pavement coverage) that control dust preservation. In order to interpret the observed scaling in terms of these relative influences I consider two end-member models: (1) a deterministic model in which dust deposition is controlled by cyclical climatic changes (i.e., glacial-interglacial cycles) and in which no erosion occurs, and (2) a stochastic model in which erosion and deposition take place with equal probability and magnitude during each time step (i.e., a bounded random walk). The observed temporal scaling is most consistent with the bounded random walk model, suggesting that long-term eolian dust accumulation is predominantly controlled by episodic changes in vegetation and pavement coverage over time and that eolian dust deposits are strongly punctuated by episodes of erosional reworking at a wide range of temporal scales. © 2007 The Geological Society of America.
• Pelletier, J. D. (2007). Erosion-rate determination from foreland basin geometry. Geology, 35(1), 5-8.
  More info

  Abstract: The geometry of foreland basins is controlled by a dynamic balance between thrust-belt migration, flexural subsidence, and fluvial deposition. To improve our ability to quantify the relationships between tectonics, climate, and foreland basin geometry, I developed analytic solutions for basin topography and stratigraphy using a classic two-dimensional mathematical model of foreland basin evolution. Model predictions for basin topography are successfully tested against observed profiles along a humid-to-arid climatic gradient in the central Andes. Using published estimates for the thrust-belt migration rate, flexural parameter, and thrust-front basin depth in this region, I show that basin topographic proffies can be used to estimate the upstream erosion rate at any point along a foreland basin. Basin-averaged erosion rates estimated in this way vary from 0.025 to 0.045 mm/yr in the central Andes, increasing from semiarid to humid climates. © 2007 Geological Society of America.
• Pelletier, J. D. (2007). Fractal behavior in space and time in a simplified model of fluvial landform evolution. Geomorphology, 91(3-4), 291-301.
  More info

  Abstract: Two general approaches have been applied to understanding the fractal structure of fluvial topography: (1) deterministic, process-based models, and (2) stochastic partial differential equations (PDE). Deterministic models reproduce the fractal behavior of fluvial topography but have two limitations: they often underestimate the amount of lateral valley and ridge migration that occurs in nature, and the complexity has made it difficult to identify the precise origin of fractal behavior in fluvial landscapes. The simplicity of stochastic PDE models has made them useful for investigating fractal behavior, but they incorrectly suggest that fractal behavior is only possible with stochastic forcing. In this paper I investigate whether simplified, deterministic PDE models of landform evolution also exhibit fractal behavior and other features of complexity (i.e. deterministic chaos). These models are based on the KPZ equation, well known in the physics literature. This equation combines diffusion (i.e. hillslope processes) and nonlinear advection (i.e. bedrock or alluvial channel incision). Two models are considered: (1) a deterministic model with uniform erodibility and random initial topography, and (2) a deterministic model with random erodibility and uniform initial topography. Results illustrate that both of these deterministic models exhibit fractal behavior and deterministic chaos. In this context, chaotic behavior means that valley and ridge migration and nonlinear amplification of small perturbations in these models prevent an ideal steady state landscape from ever developing in the large-system limit. These results suggest that fractal structure and deterministic chaos are intrinsic features of the evolution of fluvial landforms, and that these features result from an inverse cascade of energy from small to large wavelengths in drainage basins. This inverse cascade differs from the direct cascade of three-dimensional turbulence in which energy flows from large to small wavelengths. © 2007 Elsevier B.V. All rights reserved.
• Pelletier, J. D. (2007). Numerical modeling of the Cenozoic geomorphic evolution of the southern Sierra Nevada, California. Earth and Planetary Science Letters, 259(1-2), 85-96.
  More info

  Abstract: Recent geomorphic studies suggest that significant (∼ 1.5 km) late Cenozoic surface uplift occurred in the southern Sierra Nevada, a conclusion that is difficult to reconcile with recent stable-isotopic paleoaltimetry studies. Numerical modeling can play an important role in resolving this dispute. In this paper I use two models of bedrock channel erosion, the stream-power model and a sediment-flux-driven model, to test hypotheses for the fluvial Cenozoic geomorphic evolution and surface uplift history of the southern Sierra Nevada. Cosmogenic data for upland erosion and river incision rates allow each model parameter to be uniquely constrained. Numerical experiments using the sediment-flux-driven model suggest that the modern southern Sierra Nevada was constructed from a 1.0-km pulse of range-wide surface uplift in the latest Cretaceous (∼ 60 Ma) and a 0.5-km pulse in the late Miocene (∼ 10 Ma). The persistent geomorphic response to latest Cretaceous uplift in this model is the result of limited "cutting tools" supplied from the upland low-relief Boreal Plateau. This uplift history correctly predicts the modern topography of the range, including the approximate elevations and extents of the Chagoopa and Boreal Plateaux and their associated river knickpoints. Numerical experiments using the stream-power model are most consistent with a 1-km pulse of uplift in the late Eocene (∼ 30 Ma) and a 0.5-km pulse in the late Miocene (∼ 7 Ma). Both models suggest that the remaining rock uplift required to produce the 4-km peak elevations of the modern southern Sierra Nevada was produced by flexural-isostatic uplift in response to river incision. The balance of evidence, including the dominance of sediment-flux-driven erosion in granitic rocks, previous paleoaltimetry studies, and the timing of sediment accumulation in the Great Valley, support the conclusions of the sediment-flux-driven model, i.e. that the Sierra Nevada experienced range-wide surface uplift events in the latest Cretaceous and late Miocene. More broadly, these results indicate that nonequilibrium landscapes can persist for long periods of geologic time, and hence low-relief upland landscapes do not necessarily indicate late Cenozoic surface uplift. © 2007 Elsevier B.V. All rights reserved.
• Pelletier, J. D., & Cline, M. L. (2007). Nonlinear slope-dependent sediment transport in cinder cone evolution. Geology, 35(12), 1067-1070.
  More info

  Abstract: Sediment flux on transport-limited hillslopes is well known to vary nonlinearly with slope, diverging as the angle of stability is approached. To date, however, no study has validated the precise form of the nonlinear slope-dependent transport model over geologic time scales in a non-steady-state landform. In this paper, we show how cinder cones can be used to validate the nonlinear transport model using Lathrop Wells cinder cone in Nye County, Nevada, as a type example. Cinder cones are well suited for this purpose because they can be radiometrically dated and their angles of stability can be constrained by measurement of subsurface contacts between primary fallout and overlying colluvial deposits reworked from upslope. Forward model results with a generalized, nonlinear transport model characterized by diffusivity, Κ, and nonlinear exponent, n, show that the evolution of the cone rim and base are most sensitive to Κ, while the cone midpoint is most sensitive to n. Analyses of the full cone shape, therefore, permit the two model parameters to be independently inferred if the cone age and angle of stability are independently known. Results for Lathrop Wells imply that n = 2 in the generalized, nonlinear transport model, which is consistent with Roering et al.'s (1999) widely used form of that model. © 2007 The Geological Society of America.
• Pelletier, J. D., Cline, M., & DeLong, S. B. (2007). Desert pavement dynamics: Numerical modeling and field-based calibration. Earth Surface Processes and Landforms, 32(13), 1913-1927.
  More info

  Abstract: Desert pavements are widely used as a relative surface-dating tool because they are progressively better developed on surfaces ranging from thousands to hundreds of thousands of years in age. Recent work, however, has highlighted the dynamic nature of pavements and undermined their use as surface-age indicators. Quade (2001) proposed that latest Pleistocene vegetation advances destroyed all Mojave Desert pavements above 400 m elevation, making all such pavements Holocene in age. In an effort to reconcile young-pavement evidence with their widespread use as Pleistocene surface-age indicators, we developed a numerical model based on the classic conceptual model in which pavements co-evolve with their underlying eolian epipedons over millennial timescales. In this co-evolutionary process, fine-grained eolian deposition and Av-horizon development within the eolian epipedon promotes surface clast motion and pavement development, enhancing the eolian-sediment-trapping ability of the pavement in a positive feedback. Model results illustrate the multi-scale nature of pavement dynamics: pavements may require tens of thousands of years to fully develop from a newly abandoned alluvial surface, but may heal over timescales of decades to centuries if a mature eolian epipedon is present. As such, there is no inconsistency between rapid pavement healing and a Pleistocene age for the underlying alluvial surface. To calibrate the model, we conducted surficial geologic mapping and pavement-sedimentological analysis on two desert piedmonts. Our study areas include both proximal and distal fan environments, illustrating the role of parent-material texture in controlling the mode of pavement formation. Using available geochronology, our work provides a rigorous calibration of pavement formation rates in our study areas and provides evidence supporting the use of pavements as local relative surface-age indicators over Holocene to late Pleistocene timescales. Copyright © 2007 John Wiley & Sons, Ltd.
• Barnes, J. B., & Pelletier, J. D. (2006). Latitudinal variation of denudation in the evolution of the Bolivian Andes. American Journal of Science, 306(1), 1-31.
  More info

  Abstract: Latitudinal gradients in topography, relief, climate, and deformation have been used to suggest that climate-driven erosion has exerted a first order control on the development of the central Andes. We synthesize the spatial and temporal variations in denudation across the eastern Bolivian Andes (14-22°S) from new and existing estimates to test whether physical evidence exists to support the hypothesis that erosion influences thrust belt evolution. Basin-morphometry, channel network indices, climate, and longitudinal river profiles indicate a northward increase in relative relief, fluvial incision, and denudation. Short-term denudation-rate averages from landslide mapping and sediment-flux data range from 1 to 9 mm/yr in the north compared to 0.3 to 0.4 mm/yr in the south. Long-term denudation-rate estimates from thermochronology, cosmogenic radionuclides, foreland basin sediment volumes, stratigraphy, paleoerosion surface degradation, and balanced cross sections range from 0.04 to 1.6 mm/yr with rates up to more than twice as fast in the north when comparing estimates from the same method. The shorter-term denudation rates exhibit the greatest variance. Our denudation synthesis shows that an along-strike disparity in denudation (greater in the north) has existed throughout the Holocene and perhaps existed since as early as the late Miocene. Our denudation synthesis also suggests that the disparity and denudation rates have increased to the present. Correlations between the thrust belt geology, geometry, geomorphology, climate, and kinematics of the orogenic wedge provides a case study in observing the regional scale interactions between uplift, climate, and erosion. We conclude that the denudation history, uplift history, and tectonic-geomorphic correlations suggest that models of the evolution of the Bolivian Andes should incorporate a latitudinal erosion gradient for the last 10 kyrs to perhaps 10 Myrs.
• Barnes, J. B., Ehlers, T. A., McQuarrie, N., O'Sullivan, P., & Pelletier, J. D. (2006). Eocene to recent variations in erosion across the central Andean fold-thrust belt, northern Bolivia: Implications for plateau evolution. Earth and Planetary Science Letters, 248(1-2), 103-118.
  More info

  Abstract: Quantifying the erosional and kinematic evolution of orogenic plateaus has been limited by insufficient age constraints on their deformation and erosion histories. Palinspastic restorations suggest the central Andean fold-thrust belt and plateau evolved concurrently in Bolivia. We present an analysis that synthesizes 19 new and 32 previous apatite and zircon fission-track and (U-Th)/He mineral cooling ages along a 200 km traverse across the plateau margin and entire thrust belt in northern Bolivia. The new apatite fission-track data are interpreted using a grain-age deconvolution algorithm with inverse thermal modeling of track lengths, grain ages and mineral composition proxy data. Results suggest: (1) Eo-Oligocene (∼ 40-25 Ma) initial rapid erosion of the plateau margin, (2) accelerated, distributed erosion across the entire thrust belt since the early to mid-Miocene (∼ 15 Ma), and (3) the magnitude of erosion decreases eastward from ∼ 10 to 4 km. We compare these results with two end-member models of the central Andes that contrast in duration and magnitude of deformation. The rapid Eo-Oligocene (∼ 40-25 Ma) erosion is only consistent with the end-member that emphasizes the long duration and large magnitude deformation controlled by the sequential stacking of basement thrust sheets. However, the distributed Miocene (∼ 15 Ma) to recent erosion is consistent with both end-members because the recorded cooling could have resulted from active deformation, protracted erosion or both. If the long duration model is correct, the time between the two phases of accelerated cooling brackets the cessation of the first basement thrust sheet and implies the early development of the Andean plateau analogous to its modern width, but unknown elevation by the early Miocene (∼ 20 Ma). © 2006 Elsevier B.V. All rights reserved.
• Pelletier, J. D. (2006). Reply to comment by Kenneth Hinkel on "Formation of oriented thaw lakes by thaw slumping". Journal of Geophysical Research F: Earth Surface, 111(1).
• Pelletier, J. D. (2006). Sensitivity of playa windblown-dust emissions to climatic and anthropogenic change. Journal of Arid Environments, 66(1), 62-75.
  More info

  Abstract: Windblown dust is a significant component of atmospheric PM (particulate matter) in arid regions worldwide, with adverse effects on human health and visibility. In the future, windblown-dust emissions are likely to increase if water tables drop as a result of climatic or anthropogenic changes. To manage this hazard, air-quality managers need quantitative models that predict the impact of climatic and anthropogenic change on dust emissions. To meet this need, we constructed a process-based numerical model that includes Richards' equation for vertical moisture flow in the unsaturated zone, Chepil's model for the effect of surface soil moisture on threshold wind speed, and the saltation equation, which also predicts the rate of dust emission from the surface to within a multiplicative factor. This model is solved analytically for a Weibull distribution of wind speeds under steady-state moisture conditions, providing a single predictive equation for the long-term average saltation flux based on local meteorological and hydrological parameters. The model equations are used to predict the increase in saltation flux and dust emissions resulting from the dessication of a wet playa by climatic change, stream diversion, or groundwater withdrawal. The model is calibrated using CLIM-MET station data collected near Soda (dry) Lake, California. The model results identify a critical range of water-table depths between 3 and 10 m (depending on hydrological parameters) in which small increases in water-table depth cause large, nonlinear increases in windblown-dust emissions. For water tables deeper than 10 m, dust emissions are close to their maximum value and are largely independent of water-table depth. This analysis highlights the importance of preserving the hydrological balance of wet playas in order to minimize windblown-dust emissions. Future climatic changes may also influence dust emissions through changes in the mean or variability of wind speeds. For representative model parameters, 10% increases in the mean and variability of wind speeds, for example, are predicted to increase dust emissions by 80% and 20% within this model framework. © 2005 Elsevier Ltd. All rights reserved.
• Pelletier, J. D., DeLong, S. B., Al-Suwaidi, A., Cline, M., Lewis, Y., Psillas, J. L., & Yanites, B. (2006). Evolution of the Bonneville shoreline scarp in west-central Utah: Comparison of scarp-analysis methods and implications for the diffusions model of hillslope evolution. Geomorphology, 74(1-4), 257-270.
  More info

  Abstract: Wave-cut pluvial shoreline scarps are ideal natural experiments in hillslope evolution because the ages of these scarps are often precisely known and because they form with a range of heights, alluvial textures, and microclimates (i.e., orientation). Previous work using midpoint-slope methods on pluvial scarps in the Basin and Range concluded that scarp evolution is nonlinear and microclimatically controlled. The purpose of this study was to further examine the influence of scarp height, texture and microclimate in an attempt to calibrate a nonlinear model of scarp evolution. To do this, over 150 profiles of the Bonneville shoreline in the adjacent Snake and Tule Valleys, west-central Utah were collected and analyzed by fitting the entire scarp profile to diffusion-equation solutions, taking into account uncertainty in the initial scarp angle. In contrast to previous studies, this analysis revealed no evidence for nonlinearity or microclimatic control. To understand the reason for this discrepancy, we undertook a systematic study of the accuracy of each scarp-analysis method. The midpoint-slope-inverse method was found to yield biased results, with systematically higher diffusion ages for young, tall scarps. The slope-offset method is unbiased but has limited resolution because it requires many scarp profiles to yield a single diffusion age. A method that incorporates the full scarp profile and uncertainty in the initial scarp angle was found to be the most accurate technique. The application of the full-scarp method to the Bonneville shoreline supports the use of a linear diffusion model for scarps up to 20 m in height. Scarp orientation had no discernable effect on diffusivity values. Soil texture was found to have a weak but significant inverse relationship with diffusivity values. © 2005 Elsevier B.V. All rights reserved.
• Kohfeld, K. E., Reynolds, R. L., Pelletier, J. D., & Nickling, B. (2005). Linking the scales of observation, process, and modeling of dust emissions. Eos, 86(11), 113-.
• Pelletier, J. D. (2005). Formation of oriented thaw lakes by thaw slumping. Journal of Geophysical Research F: Earth Surface, 110(2).
  More info

  Abstract: In the classic model for oriented thaw lakes, sublittoral shelves form by wind-driven circulation near shorelines oriented perpendicular to the wind, protecting the adjacent banks from thaw and wave cut erosion. Here I propose an alternative model based on thaw slumping and test the model predictions against observations in northern Alaska. Thermal modeling illustrates that bank height controls the rate of thaw slumping because summertime thaw penetrates only decimeters into a tall bank but as much as tens of meters into a short bank. This effect also leads to oriented lakes because of a nonlinear relationship between bank height and bank retreat rate. Bank material texture also controls the rate of thaw slumping because fine-grained sediments drain slowly and maintain higher pore pressures than coarse-grained sediments, resulting in lower critical angles for slumping. To test the thaw slumping model quantitatively, I constructed a process-based numerical model that includes thaw slumping, lacustrine sediment dispersal, and thawdriven lake floor subsidence. The model predicts that lake orientations and aspect ratios are controlled by topographic aspect and slope, not by wind direction and intensity. The thaw slumping model further predicts inverse correlations between lake area and bank height and between lake area and bank material texture. An analysis of oriented thaw lakes in northern Alaska shows that systematically smaller, deeper lakes form in coarse-grained eolian sediments compared with those formed in fine-grained fluvial marine sediments. This pattern strongly supports the thaw slumping model. Copyright 2005 by the American Geophysical Union.
• Pelletier, J. D., & Cook, J. P. (2005). Deposition of playa windblown dust over geologic time scales. Geology, 33(11), 909-912.
  More info

  Abstract: Thick eolian deposits are commonly observed beneath desert pavements downwind of dust-emitting playas. These deposits play an important role in piedmont-surface evolution, controlling surface hydrologic conductivity and rates of pedogenesis. To better understand the factors controlling the spatial distribution of eolian deposition, we developed a numerical model that treats deposition from spatially distributed playa sources using analytic point-source solutions for deposition from a Gaussian plume. The model also accounts for complex downwind topography. As a test case, model predictions were compared to eolian deposit thicknesses on Eagle Mountain piedmont, southern Amargosa Valley, California, which receives dust from nearby Franklin Lake playa. The close relationship between the model predictions and mapped thicknesses suggests that eolian transport and deposition can be modeled from basin to regional scales within this framework. These results have important implications for hydrologic, pedogenic, and air-quality problems. © 2005 Geological Society of America.
• Pelletier, J. D., Harrington, C. D., Whitney, J. W., Cline, M., DeLong, S. B., Keating, G., & Ebert, T. K. (2005). Geomorphic control of radionuclide diffusion in desert soils. Geophysical Research Letters, 32(23), 1-4.
  More info

  Abstract: Diffusion is a standard model for the vertical migration of radionuclides in soil profiles. Here we show that diffusivity values inferred from fallout 137CS profiles in soils on the Fortymile Wash alluvial fan, Nye County, Nevada, have a strong inverse correlation with the age of the geomorphic surface. This result suggests that radionuclide-bound particles are predominantly transported by infiltration rather than by bulk-mixing processes such as wetting/ drying, freeze/thaw, and bioturbation. Our results provide a preliminary basis for using soil-geomorphic mapping, point-based calibration data, and the diffusion model to predict radionuclide trans desert soils within a pedotransfer-function approach. Copyright 2005 by the American Geophysical Union.
• Pelletier, J. D., Mayer, L., Pearthree, P. A., House, P. K., Demsey, K. A., Klawon, J. E., Vincent, K. R., Pelletier, J. D., Mayer, L., Pearthree, P. A., House, P. K., Demsey, K. A., Klawon, J. K., & Vincent, K. R. (2005). An integrated approach to flood hazard assessment on alluvial fans using numerical modeling, field mapping, and remote sensing. Bulletin of the Geological Society of America, 117(9-10), 1167-1180.
  More info

  Abstract: Millions of people in the western United States live near the dynamic, distributary channel networks of alluvial fans where flood behavior is complex and poorly constrained. Here we test a new comprehensive approach to alluvial-fan flood hazard assessment that uses four complementary methods: twodimensional raster-based hydraulic modeling, satellite-image change detection, fieldbased mapping of recent flood inundation, and surficial geologic mapping. Each of these methods provides spatial detail lacking in the standard method and each provides critical information for a comprehensive assessment. Our numerical model simultaneously solves the continuity equation and Manning's equation (Chow, 1959) using an implicit numerical method. It provides a robust numerical tool for predicting flood flows using the large, high-resolution Digital Elevation Models (DEMs) necessary to resolve the numerous small channels on the typical alluvial fan. Inundation extents and flow depths of historic floods can be reconstructed with the numerical model and validated against field- and satellite-based flood maps. A probabilistic flood hazard map can also be constructed by modeling multiple flood events with a range of specified discharges. This map can be used in conjunction with a surficial geologic map to further refine floodplain delineation on fans. To test the accuracy of the numerical model, we compared model predictions of flood inundation and flow depths against field- and satellite-based flood maps for two recent extreme events on the southern Tortolita and Harquahala piedmonts in Arizona. Model predictions match the field- and satellite-based maps closely. Probabilistic flood hazard maps based on the 10 yr, 100 yr, and maximum floods were also constructed for the study areas using stream gage records and paleoflood deposits. The resulting maps predict spatially complex flood hazards that strongly reflect small-scale topography and are consistent with surficial geology. In contrast, FEMA Flood Insurance Rate Maps (FIRMs) based on the FAN model predict uniformly high flood risk across the study areas without regard for small-scale topography and surficial geology. © 2005 Geological Society of America.
• Hsu, L., & Pelletier, J. D. (2004). Correlation and dating of Quaternary alluvial-fan surfaces using scarp diffusion. Geomorphology, 60(3-4), 319-335.
  More info

  Abstract: Great interest has recently been focused on dating and interpreting alluvial-fan surfaces. As a complement to the radiometric methods often used for surface-exposure dating, this paper illustrates a rapid method for correlating and dating fan surfaces using the cross-sectional shape of gullies incised into fan surfaces. The method applies a linear hillslope-diffusion model to invert for the diffusivity age, κt (m2), using an elevation profile or gradient (slope) profile. Gullies near the distal end of fan surfaces are assumed to form quickly following fan entrenchment. Scarps adjacent to these gullies provide a measure of age. The method is illustrated on fan surfaces with ages of approximately 10 ka to 1.2 Ma in the arid southwestern United States. Two areas of focus are Death Valley, California, and the Ajo Mountains piedmont, Arizona. Gully-profile morphology is measured in two ways: by photometrically derived gradient (slope) profiles and by ground-surveyed elevation profiles. The κt values determined using ground-surveyed profiles are more consistent than those determined using photo-derived κt values. However, the mean κt values of both methods are comparable. The photometric method provides an efficient way to quantitatively and objectively correlate and relatively-date alluvial-fan surfaces. The κt values for each surface are determined to approximately 30-50% accuracy. © 2003 Elsevier B.V. All rights reserved.
• Pelletier, J. D. (2004). Estimate of three-dimensional flexural-isostatic response to unloading: Rock uplift due to late Cenozoic glacial erosion in the western United States. Geology, 32(2), 161-164.
  More info

  Abstract: Alpine glacial erosion may strongly influence mountain building through erosionally driven rock uplift and relief production. In this paper I use a three-dimensional model for the flexural-isostatic response of the lithosphere to estimate the potential for late Cenozoic erusionally driven rock uplift in the western United States. Specifically, I present a map of the ratio of erosionally driven rock uplift to glacial erosion for this region. This ratio depends on the magnitude of the flexural bending stresses that act to limit differential uplift. The map is created by constraining the extent of Pliocene-Quaternary alpine glacial erosion in the western United States and solving the three-dimensional flexure equation for the resulting lithospheric deflection. The map indicates that the magnitude of erosionally driven uplift depends sensitively on the size of the glaciated range and the presence of nearby glaciated ranges. As a result, regional-scale patterns must be considered in order to correctly estimate local amounts of erosionally driven rock uplift. The ranges in the western United States with the greatest ratios of uplift to erosion are the San Juan Mountains and the Yellowstone Plateau-Absaroka Range, because these are extensively glaciated and have glaciated ranges nearby. In contrast, the Wind River Range and Sierra Nevada have ratios of uplift to erosion that are only half as large. These results identify which ranges likely underwent the greatest erosionally driven uplift and relief production and provide a widely applicable technique for modeling the flexural-isostatic response to loading and unloading in three dimensions. © 2004 Geological Society of America.
• Pelletier, J. D. (2004). How do spiral troughs form on Mars?. Geology, 32(4), 365-367.
  More info

  Abstract: A three-dimensional model for the coupled evolution of ice-surface temperature and elevation in the Martian polar ice caps is presented. The model includes (1) enhanced heat absorption on steep, dust-exposed scarps, (2) accumulation and ablation, and (3) lateral conduction of heat within the ice cap. The model equations are similar to classic equations for excitable media, including nerve fibers and chemical oscillators. In two dimensions, a small zone of initial melting in the model develops into a train of poleward-migrating troughs with widths similar to those observed on Mars. Starting from random initial conditions, the three-dimensional model reproduces spiral waves very similar to those in the north polar ice cap, including secondary features such as gull-wing-shaped troughs, bifurcations, and terminations. These results suggest that eolian processes and ice flow may not control trough morphology. © 2004 Geological Society of America.
• Pelletier, J. D. (2004). Persistent drainage migration in a numerical landscape evolution model. Geophysical Research Letters, 31(20), L20501 1-4.
  More info

  Abstract: Numerical landscape evolution models driven by uniform vertical uplift often develop a static drainage network and a precise balance between uplift and erosion. Small-scale physical models of uplifting drainage basins, however, continually reorganize by ridge migration and do not reach an ideal steady state. Here I show that the presence or absence of persistent drainage migration in a bedrock numerical landform evolution model depends on the flow-routing algorithm used to determine upstream contributing area. The model version that uses steepest-descent routing achieves an ideal steady state, while the model version that uses bifurcation routing results in continually-evolving drainage basins, even under conditions of uniform vertical uplift, bedrock erodibility, precipitation, and landsliding threshold. This result suggests that persistent drainage migration can occur by erosional processes alone. This result has important implications for numerical-modeling methodology, our understanding of the natural variability of landform evolution, and the interpretation of thermochronological data. Copyright 2004 by the American Geophysical Union.
• Pelletier, J. D. (2004). The influence of piedmont deposition on the time scale of mountain-belt denudation. Geophysical Research Letters, 31(15), L15502 1-4.
  More info

  Abstract: The linear correlation between modem sediment yields and mean drainage-basin elevation suggests that mountain-belt topography is denuded exponentially with a time scale of approximately 50 Myr following the cessation of active uplift. Some Paleozoic orogens, however, still exist as high-elevation terrain. Here I explore this paradox within the broader question of what variables control the denudational time scales of mountain belts. Using a two-dimensional model that couples the stream-power law for bedrock channel erosion with the diffusion equation for alluvial piedmonts, I determined the time scale of mountain-belt denudation using numerical and analytic techniques. The piedmont plays an important role in mountain-belt denudation because it sets the base level for bedrock erosion, substantially reducing bedrock relief in mountain belts with broad or steep piedmonts. The persistence of the Appalachian and Ural Mountains may be understood within the model framework as largely the result of resistant bedrock and a broad piedmont, respectively. Copyright 2004 by the American Geophysical Union.
• Pelletier, J. D., & DeLong, S. (2004). Oscillations in arid alluvial-channel geometry. Geology, 32(8), 713-716.
  More info

  Abstract: Arid alluvial channels on piedmonts and valley floors often exhibit an oscillating pattern of narrow, deeply incised reaches and wide, shallow reaches with a characteristic wavelength. How do these oscillations develop and what controls their wavelengths? To address these questions we developed a two-dimensional numerical model that couples erosion and deposition in a channel bed with cross-sectional widening and narrowing. This model is inherently unstable over a range of spatial scales dependent on the channel width, depth, and slope. In the initial phase of model evolution, wider-than-average channel reaches become zones of distributary flow that aggrade, lose stream power, and further widen in a positive feedback. Simultaneously, narrower-than-average reaches incise, gain stream power, and further narrow. In the second stage of model evolution, this instability is balanced by the diffusive nature of longitudinal profile evolution, and solitary topographic waves propagate in the upstream direction with a characteristic wavelength and amplitude. The model predicts a specific quantitative relationship between the oscillation wavelength and channel width, depth, and slope that is verified by a database of channel geometries in southern Arizona. © 2004 Geological Society of America.
• Pelletier, J. D. (2003). Drainage basin evolution in the Rainfall Erosion Facility: Dependence on initial conditions. Geomorphology, 53(1-2), 183-196.
  More info

  Abstract: Four experiments in alluvial drainage basin evolution were carried out in the Rainfall Erosion Facility (REF) at Colorado State University to investigate the dependence of basin evolution on initial topography. Basins were initially undissected. Each experiment began with a unique initial condition representing various end-members of relief and hypsometry. Drainage network development, hillslope processes, basin denudation, and basin response to base-level lowering all depended strongly on the initial topography. No classic model of drainage network evolution was found to be generally applicable. Initially, planar slopes first developed subparallel channels that extended headward dendritically during an early phase of extension. Channel incision occurred first in the interior of the basin where saturation overland flow was greatest, not at the basin outlet as assumed in most classic models of network development. Channels widened over time, initiating lateral migration and drainage capture in the downslope portion of the watershed before transferring lateral migration upslope. Planar basins of larger initial gradient grew headward more quickly and become more deeply entrenched, inhibiting late-stage lateral migration. An experiment with initial relief concentrated at a plateau edge evolved in several unique ways. A high ratio of subsurface-to-surface flow gave rise to mass movements at the plateau edge and outlet channels. Deep channels were quickly cut initially but did not extend far upslope because slope instability undermined channel head migration, leaving the plateau undissected and hence very slow to erode. These results suggest that the distribution of relief within a basin exerts an important control on drainage network pattern and basin denudation. In addition, erosional basins may evolve in several distinct modes characterized by particular combinations of hypsometry, hillslope processes, and mean denudation rate. © 2002 Elsevier Science B.V. All rights reserved.
• Pelletier, J. D. (2002). Natural variability of atmospheric temperatures and geomagnetic intensity over a wide range of time scales. Proceedings of the National Academy of Sciences of the United States of America, 99(SUPPL. 1), 2546-2553.
  More info

  PMID: 11875208;PMCID: PMC128574;Abstract: The majority of numerical models in climatology and geomagnetism rely on deterministic finite-difference techniques and attempt to include as many empirical constraints on the many processes and boundary conditions applicable to their very complex systems. Despite their sophistication, many of these models are unable to reproduce basic aspects of climatic or geomagnetic dynamics. We show that a simple stochastic model, which treats the flux of heat energy in the atmosphere by convective instabilities with random advection and diffusive mixing, does a remarkable job at matching the observed power spectrum of historical and proxy records for atmospheric temperatures from time scales of one day to one million years (Myr). With this approach distinct changes in the power-spectral form can be associated with characteristic time scales of ocean mixing and radiative damping. Similarly, a simple model of the diffusion of magnetic intensity in Earth's core coupled with amplification and destruction of the local intensity can reproduce the observed 1/f noise behavior of Earth's geomagnetic intensity from time scales of 1 (Myr) to 100 yr. In addition, the statistics of the fluctuations in the polarity reversal rate from time scales of 1 Myr to 100 Myr are consistent with the hypothesis that reversals are the result of variations in 1/f noise geomagnetic intensity above a certain threshold, suggesting that reversals may be associated with internal fluctuations rather than changes in mantle thermal or magnetic boundary conditions.
• Pelletier, J., & Pelletier, J. D. (2002). Natural variability of atmospheric temperatures and geomagnetic intensity over a wide range of time scales. Proceedings of the National Academy of Sciences of the United States of America, 99 Suppl 1.
  More info

  The majority of numerical models in climatology and geomagnetism rely on deterministic finite-difference techniques and attempt to include as many empirical constraints on the many processes and boundary conditions applicable to their very complex systems. Despite their sophistication, many of these models are unable to reproduce basic aspects of climatic or geomagnetic dynamics. We show that a simple stochastic model, which treats the flux of heat energy in the atmosphere by convective instabilities with random advection and diffusive mixing, does a remarkable job at matching the observed power spectrum of historical and proxy records for atmospheric temperatures from time scales of one day to one million years (Myr). With this approach distinct changes in the power-spectral form can be associated with characteristic time scales of ocean mixing and radiative damping. Similarly, a simple model of the diffusion of magnetic intensity in Earth's core coupled with amplification and destruction of the local intensity can reproduce the observed 1/f noise behavior of Earth's geomagnetic intensity from time scales of 1 (Myr) to 100 yr. In addition, the statistics of the fluctuations in the polarity reversal rate from time scales of 1 Myr to 100 Myr are consistent with the hypothesis that reversals are the result of variations in 1/f noise geomagnetic intensity above a certain threshold, suggesting that reversals may be associated with internal fluctuations rather than changes in mantle thermal or magnetic boundary conditions.
• Pelletier, J. D. (2000). Are large complex ecosystems more unstable? A theoretical reassessment with predator switching. Mathematical Biosciences, 163(1), 91-96.
  More info

  PMID: 10652847;Abstract: Multi-species Lotka-Volterra models exhibit greater instability with an increase in diversity and/or connectance. These model systems, however, lack the likely behavior that a predator will prey more heavily on some species if other prey species decline in relative abundance. We find that stability does not depend on diversity and/or connectance in multi-species Lotka-Volterra models with this 'predator switching'. This conclusion is more consistent with several empirical observations than the classic conclusion, suggesting that large complex ecosystems in nature may be more stable than previously supposed.
• Pelletier, J. D. (2000). Model assessments of the optimal design of nature reserves for maximizing species longevity. Journal of Theoretical Biology, 202(1), 25-32.
  More info

  PMID: 10623496;Abstract: Using a computational model for the population growth and dispersal of a model species in a fluctuating environment, we test three nature reserve geometries (one large, many small, and a self-similar distribution of reserve sizes) to determine which geometry maximizes species longevity. The self-similar distribution is a close approximation to the distribution of managed areas in the conterminous United States. We consider models with and without migration from or between reserve fragments and both short- and long-range dispersal mechanisms. The optimal geometry depends on the type of dispersal and on the relative probability of survival in protected and non-protected areas. When no migration is allowed from or between reserve fragments of the three geometries, many small equally sized reserves are the optimal geometry. When migration is allowed, the optimal geometry is a single large reserve when the survivability in non-protected areas is low and a self-similar distribution when the survivability is high. (C) 2000 Academic Press.
• Pelletier, J. D., & Turcotte, D. L. (2000). Shapes of river networks and leaves: Are they statistically similar?. Philosophical Transactions of the Royal Society B: Biological Sciences, 355(1394), 307-311.
  More info

  PMID: 10724463;PMCID: PMC1692726;Abstract: The structure of river networks is compared with the vein structure of leaves. The two structures are visually similar at the smaller scales. The statistics of branching and side branching are nearly identical. The branching structure of diffusion-limited aggregation clusters is also similar and can provide an explanation for the structure of river networks. The origin of the self-similar branching and side branching of the vein structure in leaves is not clear but it appears to be an optimal network in terms of transporting nutrients to all parts of the leaf with the least total resistance.
• Pelletier, J., & Pelletier, J. D. (2000). Are large complex ecosystems more unstable? A theoretical reassessment with predator switching. Mathematical biosciences, 163(1).
  More info

  Multi-species Lotka-Volterra models exhibit greater instability with an increase in diversity and/or connectance. These model systems, however, lack the likely behavior that a predator will prey more heavily on some species if other prey species decline in relative abundance. We find that stability does not depend on diversity and/or connectance in multi-species Lotka-Volterra models with this 'predator switching'. This conclusion is more consistent with several empirical observations than the classic conclusion, suggesting that large complex ecosystems in nature may be more stable than previously supposed.
• Pelletier, J., & Pelletier, J. D. (2000). Model assessments of the optimal design of nature reserves for maximizing species longevity. Journal of theoretical biology, 202(1).
  More info

  Using a computational model for the population growth and dispersal of a model species in a fluctuating environment, we test three nature reserve geometries (one large, many small, and a self-similar distribution of reserve sizes) to determine which geometry maximizes species longevity. The self-similar distribution is a close approximation to the distribution of managed areas in the conterminous United States. We consider models with and without migration from or between reserve fragments and both short- and long-range dispersal mechanisms. The optimal geometry depends on the type of dispersal and on the relative probability of survival in protected and non-protected areas. When no migration is allowed from or between reserve fragments of the three geometries, many small equally sized reserves are the optimal geometry. When migration is allowed, the optimal geometry is a single large reserve when the survivability in non-protected areas is low and a self-similar distribution when the survivability is high.
• Pelletier, J. D. (1999). Paleointensity variations of Earth's magnetic field and their relationship with polarity reversals. Physics of the Earth and Planetary Interiors, 110(1-2), 115-128.
  More info

  Abstract: Power-spectral analyses of the intensity of Earth's magnetic field inferred from ocean sediment cores and archeomagnetic data from time scales of 100 yr to 10 Myr have been carried out. The power spectrum is proportional to 1/f where f is the frequency. These analyses compliment previous work which has established a 1/f2 spectrum for variations at time scales less than 100 yr. We test the hypothesis that reversals are the result of variations in field intensity with a 1/f spectrum which occasionally are large enough to cross the zero intensity value. Synthetic binormal time series with a 1/f power spectrum representing variations in Earth's dipole moment are constructed. Synthetic reversals from these time series exhibit statistics in good agreement with the reversal record, suggesting that polarity reversals may be the end result of autocyclic intensity variations with a 1/f power spectrum.
• Pelletier, J. D. (1999). Self-organization and scaling relationships of evolving river networks. Journal of Geophysical Research B: Solid Earth, 104(B4), 7359-7375.
  More info

  Abstract: The power spectra S of linear transects of Earth's topography is often observed to be a power law function of wave number k with exponent close to -2: S(k) ∝ k-2. In addition, river networks are fractal trees that satisfy several power law relationships between their morphologic components. A model equation for the evolution of Earth's topography by transport-limited erosional processes which produces fractal topography and fractal river networks is presented, and its solutions are compared in detail to real topography. The model is the diffusion equation for sediment transport on hillslopes and channels with the diffusivity constant on hillslopes and proportional to the three-halves power of discharge in channels. The dependence of diffusivity on discharge is consistent with sediment rating curves. We study the model in two ways. In the first analysis the diffusivity is parameterized as a function of elevation, and a Taylor expansion procedure is carried out to obtain a differential equation for the landform elevation which includes the spatially variable diffusivity to first order in the elevation. The solution to this equation is a self-affine or fractal surface with linear transects that have power spectra S(k) ∝ k-1.8, independent of the age of the topography, consistent with observations of real topography. The hypsometry produced by the model equation is skewed such that lowlands make up a larger fraction of the total area than highlands as observed in real topography. In the second analysis we include river networks explicitly in a numerical simulation by calculating the discharge at every point. We characterize the morphology of real river basins with five independent scaling relations between six morphometric variables. Scaling exponents are calculated for seven river networks from a variety of tectonic environments using high-quality digital elevation models. River networks formed in the model match the observed scaling laws and satisfy Tokunaga side-branching statistics. Copyright 1999 by the American Geophysical Union.
• Pelletier, J. D. (1999). Species-Area Relation and Self-Similarity in a Biogeographical Model of Speciation and Extinction. Physical Review Letters, 82(9), 1983-1986.
  More info

  Abstract: We introduce a generic model for the population growth and dispersal of individuals in species with heterogeneous, fluctuating environments. New species originate with a probability inversely proportional to the abundance of the parent species. The model generates an average number of species which depends on the domain area in agreement with the species-area relation for islands. The model also generates self-similar radiations characterized by a power-law distribution for the number of subtaxa with the same parent taxon and a 1/f power spectrum for the time series of extinctions and originations.
• Pelletier, J. D. (1999). Statistical self-similarity of magmatism and volcanism. Journal of Geophysical Research B: Solid Earth, 104(B7), 15425-15438.
  More info

  Abstract: Magmatism and volcanism exhibit spatial and temporal clustering on a wide range of scales. Using the spatial pair-correlation function, the number of pairs of magmatic or volcanic events whose separation is between r-1/2Δr and r+1/2Δr per unit area, we quantify the spatial clustering of magmatism and volcanism in several data sets. Statistically self-similar clustering characterized by power law spatial pair-correlation functions is observed. The temporal pair-correlation function is used to identify self-similar temporal clustering of magmatism and volcanism in the Radiometric Age Data Bank of 11,986 dated intrusive and extrusive rocks in the North American Cordillera. The clustering of magmatism and volcanism in space and time in this data set is found to be statistically self-similar and identical to those of distributed seismicity. The frequency-size distributions of eruption volume and areal extent of basaltic flows are also found to be self-similar with power laws analogous to the Gutenburg-Richter distribution for earthquakes. In an attempt to understand the origin of statistical self-similarity in magmatism and volcanism we present one end-member model in which the ascent of magma through a disordered crust of variable macroscopic permeability is modeled with a cellular-automaton model to create a distribution of magma supply regions which erupt with equal probability per unit time. The model exhibits statistical self-similarity similar to that observed in the real data sets. Copyright 1999 by the American Geophysical Union.
• Pelletier, J. D., & Turcotte, D. L. (1999). Self-Affine Time Series: II. Applications and Models. Advances in Geophysics, 40(C), 91-166.
• Turcotte, D. L., Pelletier, J. D., & Malamud, B. D. (1999). Preface. Advances in Geophysics, 40(C), ix-xi.
• Pelletier, J. D. (1998). The power spectral density of atmospheric temperature from time scales of 10^-2 to 10⁶ yr. Earth and Planetary Science Letters, 158(3-4), 157-164.
  More info

  Abstract: After removing annual variability, power spectral analyses of local atmospheric temperature from hundreds of stations and ice core records have been carried out from time scales of 10-2 to 106 yr. A clear sequence of power-law behaviors is found as follows: 1) from 40 ka to 1 Ma a flat spectrum is observed; 2) from 2 ka to 40 ka the spectrum is proportional to f-2 where f is the frequency; and 3) below time scales of 2 ka the power spectrum is proportional to f-1/2. At time scales less than 1 month we observe that the power spectra of continental stations become proportional to f-3/2 while maritime stations continue to have power spectra proportional to f-1/2 down to time scales of 1 day. To explain these observations, we model the vertical transport of heat in the atmosphere as a stochastic diffusion process. The power spectrum of temperature fluctuations at the earth's surface expected from this model equation in a two-layer geometry with thermal and eddy diffusion properties appropriate to the atmosphere and the ocean and a radiation condition at the top of the atmosphere agrees with the observed spectrum. The difference in power spectra between continental and marine stations can be understood with this approach as a consequence of the air mass above a maritime station exchanging heat with both the atmosphere above and the ocean below while a continental station exchanges heat mostly with the atmosphere above.
• Turcotte, D. L., Pelletier, J. D., & Newman, W. I. (1998). Networks with side branching in biology. Journal of Theoretical Biology, 193(4), 577-592.
  More info

  PMID: 9745754;Abstract: There are many examples of branching networks in biology. Examples include the structure of plants and trees as well as cardiovascular and bronchial systems. In many cases these networks are self-similar and exhibit fractal scaling. In this paper we introduce the Tokunaga taxonomy for the side branching of networks and his parameterization of self-similar side-branching. We introduce several examples of deterministic branching networks and show that constructions with the same fractal dimension can have different side-branching parameters. As an example of stochastic-branching in biology we consider the vein structure of a leaf. We show that the vein structure of the leaf and river networks have nearly identical side branching statistics. We introduce diffusion limited aggregation (DLA) clusters. These clusters also exhibit Tokunaga side-branching statistics. We consider several alternative explanations for why leaves, river networks, and DLA clusters have similar side-branching statistics. We also consider the allometric scaling relation between metabolic rate and the mass of species in terms of a cardiovascular system with Tokunaga statistics. We find reasonably good agreement between the observed scaling exponent, ≃0.75, and our model for a range of values of the fractal dimension of the network and the blood flow resistance parameter.
• Pelletier, J. D. (1997). Analysis and modeling of the natural variability of climate. Journal of Climate, 10(6), 1331-1342.
  More info

  Abstract: After removing annual variability, power spectral analyses of local atmospheric temperature from hundreds of stations and ice core records have been carried out from timescales of 1 day to 200 kyr. A clear sequence of power-law behaviors is found as follows: 1) from 40 kyr to 200 kyr a flat spectrum is observed, 2) from 2 kyr to 40 kyr the spectrum is proportional to f-2 where f is the frequency, and 3) below timescales of 2 kyr the power spectrum is proportional to f-1/2. At timescales of less than 1 month the authors observe that the power spectra of continental stations become propotional to f-3/2 while maritime stations continue to have power spectra proportional to f-1/2 down to timescales of 1 day. To explain these observations, the authors model the variations in the transport of heat in the turbulent atmosphere by including a noise in the heat flux of a flux-gradient parameterization of convective transport, leading to a stochastic diffusion equation for temperature fluctuations. A correlation analysis of temperature fluctuations vertically in the atmosphere from the TIROS operational vertical sounder is carried out to verify the diffusion model and to estimate the coefficient of vertical eddy diffusivity in the atmosphere. The power spectrum of temperature fluctuations at the earth's surface expected from this model in a two-layer geometry with thermal and eddy diffusion properties appropriate to the atmosphere and ocean and a radiation boundary condition at the top of the atmosphere exhibits the same spectral form as observed in the instrumental and ice core data.
• Pelletier, J. D. (1997). Kardar-parisi-zhang scaling of the height of the convective boundary layer and fractal structure of cumulus cloud fields. Physical Review Letters, 78(13), 2672-2675.
  More info

  Abstract: We present the cumulative frequency-area distribution of tropical cumulus clouds as observed from satellite and space shuttle images from scales of 0.1 to 1000 km. The distribution is a power-law function of area with exponent -0.8. We show that this result and the fractal dimension of cloud perimeters implies that the top of the convective boundary layer (CBL) is a self-affine interface with roughness exponent or Hausdorff measure H ≈ 0.4, the same value as that of the Kardar-Parisi-Zhang equation in 2 + 1 dimensions. In addition, we identify dynamic scaling in a time series of the local altitude of the top of the CBL as measured with FM/CW radar backscatter intensity. A possible growth model is discussed.
• Pelletier, J. D., & Turcotte, D. L. (1997). Long-range persistence in climatological and hydrological time series: Analysis, modeling and application to drought hazard assessment. Journal of Hydrology, 203(1-4), 198-208.
  More info

  Abstract: We present power spectra of time-series data for tree ring width chronologies, atmospheric temperatures, river discharges and precipitation averaged over hundreds of stations worldwide. The average power spectrum S for each of these phenomena is found to have a power-law dependence on frequency with exponent -1/2: s(f) α f(- 1/4 ). An advection-diffusion model of the vertical transport of heat and water vapor in the atmosphere is presented as a first-order model of climatic and hydrological variability. The model generates variability with the observed spectrum. The model is validated with a correlation analysis of temperature and water vapor concentration measurements from the TIROS operational vertical sounder (TOVS). Drought frequency analyses based on synthetic lognormal streamflows with the above power spectrum are presented. We show that the presence of long memory as implied by the power-law power spectrum has a significant effect on the likelihood of extended droughts compared with the drought hazard implied from standard autoregressive models with short memory.
• Pelletier, J. D., & Turcotte, D. L. (1997). Synthetic stratigraphy with a stochastic diffusion model of fluvial sedimentation. Journal of Sedimentary Research, Section B: Stratigraphy and Global Studies, 67(6), 1060-1067.
  More info

  Abstract: Models of stratigraphic completeness and bed formation in fluvial depositional environments have most often assumed that successive depositional and erosional events deposit or erode amounts of sediment independently. This results in a random-walk model for the total amount of deposited sediment locally as a function of time. We consider an extension of the random-walk model of sedimentation in an alluvial plain in which deposition or erosion is concentrated in randomly avulsing channels and sediment transport is modeled by the diffusion equation (Culling's model). In contrast to the random-walk model, this model results in an anticorrelated sequence locally as a function of time, i.e., after an area has aggraded it has a higher elevation and a lower rate of future aggradation. In a previous paper we analyzed the topography generated by the model and argued that porosity variations could be associated with topographic variations. The power spectrum S (the square of the coefficients in a Fourier series) of one-dimensional transects of topography and porosity horizontally and vertically in this model have a power-law dependence on wave number k: S(k) ∝ k-β, with values of β close to those observed. In this paper we show that the model deposits sediment with a rate depending on time interval as a power law with exponent -3/4, more consistent with observations than the random-walk model. The model produces an exponential bed-thickness distribution with a skew dependent on the sedimentation rate of the basin in accordance with observations. We also examine the persistence in the series of bed thicknesses as a function of depth. For the stochastic diffusion model of sedimentation no persistence is observed. If the model fully characterizes the autocyclic dynamics in fluvial sedimentary basins, the lack of persistence in the synthetic bed sequences suggests that observed persistence and cyclicity in real bed-thickness sequences must be the result of allocyclic processes. Copyright © 1997, SEPM (Society for Sedimentary Geology).
• Pelletier, J. D., Malamud, B. D., Blodgett, T., & Turcotte, D. L. (1997). Scale-invariance of soil moisture variability and its implications for the frequency-size distribution of landslides. Engineering Geology, 48(3-4), 255-268.
  More info

  Abstract: Power spectral analyses of soil moisture variability are carried out from scales of 100 m to 10 km on the microwave remotely-sensed data from the Washita experimental watershed during 1992. The power spectrum S(k) has an approximate power-law dependence on wave number k with the exponent -1.8. This behavior is consistent with the behavior of a stochastic differential equation for soil moisture at a point, and it has important consequences for the frequency-size distribution of landslides. We present the cumulative frequency-size distributions of landslides induced by precipitation in Japan and Bolivia as well as landslides triggered by the 1994 Northridge, California earthquake. Large landslides in these regions, despite being triggered by different mechanisms, have a cumulative frequency-size distribution with a power-law dependence on area with an exponent ranging from -1.5 to -2. We use a soil moisture field with the above statistics in conjunction with a slope stability analysis to model the frequency-size distribution of landslides. In our model landslides occur when a threshold shear stress dependent on cohesion, pore pressure, internal friction and slope angle is exceeded. This implies a threshold dependence on soil moisture and slope angle since cohesion, pore pressure and internal friction are primarily dependent on soil moisture. The cumulative frequency-size distribution of domains of shear stress greater than a threshold value with soil moisture modeled as above and topography modeled as a Brownian walk is a power-law function of area with an exponent of -1.8 for large landslide areas. This distribution is similar to that observed for landslides. The effect of strong ground motion from earthquakes lowers the shear stress necessary for failure, but does not change the frequency-size distribution of failed areas. This is consistent with observations. This work suggests that remote sensing of soil moisture can be of great importance in monitoring landslide hazards and proposes a specific quantitative model for landslide hazard assessment. © 1997 Elsevier Science B.V.
• Pelletier, J. D. (1996). Variations in solar luminosity from timescales of minutes to months. Astrophysical Journal Letters, 463(1 PART II), L41-L45.
  More info

  Abstract: We present the power spectrum of solar irradiance during 1985 and 1987, obtained from the active cavity radiometer irradiance monitor project from timescales of minutes to months. At low frequency, the spectra are Lorentzian [proportional to 1/(f2 + f02)]. At higher frequencies, they are proportional to f-1/2. A linear, stochastic model of the turbulent heat transfer between the granulation layer (modeled as a homogeneous thin layer with a radiative boundary condition) and the rest of the convection zone (modeled as a homogeneous thick layer with thermal and diffusion constants appropriate the lower convection zone) explains the observed spectrum. © 1996. The American Astronomical Society. All rights reserved.
• Pelletier, J. D., & Turcotte, D. L. (1996). Scale-invariant topography and porosity variations in fluvial sedimentary basins. Journal of Geophysical Research B: Solid Earth, 101(12), 28165-28175.
  More info

  Abstract: We consider a model of a floodplain evolving with channel avulsion, deposition, and erosion. Avulsion is modeled as a random process in space and time. Sediment transport is modeled by the diffusion equation (Culling's model). The power spectrum of variations in the topographic profiles predicted by the model S(k) is proportional to k-2 (where k is the wavenumber). This is the Brown noise often observed in topography. The power spectrum of variations in fhe local elevation in time is proportional to f-3/2 (where f is the frequency). The model prediction of Brown noise floodplain topography is roughly consistent with spectal analyses of microtopography measured with laser altimetry. We inferred Brown noise paleotopography by comparing the pair correlation function of showing wells in the Denver and Powder River basins with a synthetic oil field based on a caprock with Brown noise topography. Topographic control of variations in the grain size of deposited sediment suggests that porosity variations may exhibit the scale invariance predicted for the topographic profile. To illustrate vertical scale invariance in porosity variations, we computed the power spectrum of vertical porosity well logs in 15 offshore wells in the Gulf of Mexico. At spatial scales above 3 m we find an average power spectral exponent of -1.4, close to our model prediction of -1.5.
• Pelletier, J. D., Shapiro, M. H., & Tombrello, T. A. (1992). Molecular dynamics simulations of low-energy cluster deposition on metallic targets. Nuclear Inst. and Methods in Physics Research, B, 67(1-4), 296-300.
  More info

  Abstract: A modified version of the multiple interaction code SPUT2 was used to simulate impacts of 63-atom Al and Au clusters on 7-layer Au targets. For 1, 5, and 10 eV/atom Al and Au clusters, 50 impacts each were calculated up to a cutoff time of 2 ps. For each case studied, we found that the final shape and penetration depth of the incoming cluster was almost independent of the initial cluster position relative to the target. The 1 and 5 eV/atom Al clusters were flattened to less than 40% of their initial thickness and exhibited registration with the substrate at 2 ps. The 10 eV/atom Al clusters formed a poorly registered monolayer on the Au surface. In these higher-energy collisions a significant number of Al atoms were reflected from the Au surface. The 1 eV/atom Au clusters were flattened to approximately 60% of their initial thickness and also exhibited clear registration with the substrate at 2 ps. Higher-energy Au clusters penetrated deeply into the targets, causing substantial damage and crater formation. © 1992.

Presentations

• Bryan, M., Alyssa, W., Ben, P., Andres, S., Dawson, F., Mcintosh, J. C., Pelletier, J. D., Gallery, R. E., Rasmussen, C., & Chorover, J. D. (2016, Winter). Coring the deep Critical Zone in the Jemez River Basin Critical Zone. 2016 American Geophysical Union Annual Meeting. San Francisco CA: American Geophysical Union.
• Chorover, J. D., Pelletier, J. D., Breshears, D. D., Mcintosh, J. C., Rasmussen, C., Brooks, P. D., Barron-Gafford, G. A., Gallery, R. E., Ferre, P. A., Meixner, T., Niu, Y., Papuga, S. A., Schaap, M. G., Troch, P. A., Chorover, J. D., Pelletier, J. D., Breshears, D. D., Mcintosh, J. C., Rasmussen, C., , Brooks, P. D., et al. (2014, September). The Catalina-Jemez CZO: Transformative Behavior of Energy, Water and Carbon in the Critical Zone II. Interactions between Long and Short Term Processes that Control Delivery of Critical Zone Services.. National Critical Zone Observatory All-Hands Meeting.

Poster Presentations

• Bryan, M., Alyssa, W., Ben, P., Andres, S., Dawson, F., Mcintosh, J. C., Pelletier, J. D., Gallery, R. E., Rasmussen, C., & Chorover, J. D. (2016, Winter). Coring the deep Critical Zone in the Jemez River Basin Critical Zone. 2016 American Geophysical Union Annual Meeting. San Francisco CA: American Geophysical Union.
• Breshears, D. D., Breshears, D. D., Field, J. P., Field, J. P., Law, D. J., Law, D. J., Brooks, P. D., Brooks, P. D., Chorover, J. D., Chorover, J., Pelletier, J. D., Pelletier, J. D., Troch, P. A., Troch, P. A., Lopez Hoffman, L. -., Lopez Hoffman, L., Rasmussen, C. -., Rasmussen, C., Papuga, S. A., , Papuga, S. A., et al. (2013, October 2013). Bridging from soil to ecosystem goods and services provided by the Critical Zone. AGU Chapman Conference: Soil-mediated drivers of coupled biogeochemical and hydrological processes across scales. Tucson.