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The Community Land Model (CLM) is the land component of the Community Earth System Model (CESM) and is used in several global and regional modeling systems. In this paper, we introduce model developments included in CLM version 5 (CLM5), which is the default land component for CESM2. We assess an ensemble of simulations, including prescribed and prognostic vegetation state, multiple forcing data sets, and CLM4, CLM4.5, and CLM5, against a range of metrics including from the International Land Model Benchmarking (ILAMBv2) package. CLM5 includes new and updated processes and parameterizations: (1) dynamic land units, (2) updated parameterizations and structure for hydrology and snow (spatially explicit soil depth, dry surface layer, revised groundwater scheme, revised canopy interception and canopy snow processes, updated fresh snow density, simple firn model, and Model for Scale Adaptive River Transport), (3) plant hydraulics and hydraulic redistribution, (4) revised nitrogen cycling (flexible leaf stoichiometry, leaf N optimization for photosynthesis, and carbon costs for plant nitrogen uptake), (5) global crop model with six crop types and time-evolving irrigated areas and fertilization rates, (6) updated urban building energy, (7) carbon isotopes, and (8) updated stomatal physiology. New optional features include demographically structured dynamic vegetation model (Functionally Assembled Terrestrial Ecosystem Simulator), ozone damage to plants, and fire trace gas emissions coupling to the atmosphere. Conclusive establishment of improvement or degradation of individual variables or metrics is challenged by forcing uncertainty, parametric uncertainty, and model structural complexity, but the multivariate metrics presented here suggest a general broad improvement from CLM4 to CLM5.

The long geological time needed for landform development and evolution poses a challenge for understanding and appreciating the processes involved. The Web-based Interactive Landform Simulation Model--Grand Canyon (WILSIM-GC, http://serc.carleton.edu/landform/) is an educational tool designed to help students better understand such processes, using the Grand Canyon as an example. Although the project is still ongoing, here, we present the initial results of using the WILSIM-GC in an introductory physical geography laboratory course. We used a quasiexperimental design to assess the efficacy of WILSIM-GC as a tool for teaching landform development and evolution. Students were assigned to a control group or a treatment group, alphabetically by last name. Pretests and posttests were administered to measure students' understanding of the concepts and processes related to Grand Canyon formation and evolution. Results show that, although both the interactive simulation and a more-traditional, paper-based exercise were effective in helping students learn landform evolution processes, there were several advantages and affordances to the simulation approach. The improvement effect from pretest to posttest scores was large for the treatment group, but small to moderate for the control group. In addition, for those questions requiring higher-level thinking, the percentage of students answering correctly was higher in the treatment group than it was in the control group. Furthermore, responses to the attitudinal survey indicate that students generally favor the interactive simulation approach. We can leverage these advantages to enhance students' learning by integrating interactive simulation exercises into curricular materials, including materials for online or hybrid courses and flipped classrooms.

This paper presents results from a randomized experimental design replicated over four semesters that compared students' performance in understanding landform evolution processes as measured by the pretest to posttest score growth between two treatment methods: an online interactive simulation tool and a paper-based exercise. While both methods were shown to be effective at enhancing students' learning of the landform concepts and processes, there was no statistically significant difference in score growth between the two instructional methods. However, the attitudinal survey indicated that students consistently favored the simulation approach over the paper-based exercise. With the simulation method, female students showed greater score growth than males, especially for test items requiring higher level thinking. This indicates that the visually rich interactive simulation tool may be integrated to better support female students' learning in geoscience. Science major students generally outperformed non-science major students in terms of score growth, which suggests that background knowledge played an important role in realizing the potential of computer modeling in enhancing students' learning. Sufficient scaffolding is necessary to maximize the effect of interactive earth surface modeling in geoscience education.

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 lithoiogies, 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. doi: 10.1130/B30128.1

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2010.01.007 Byline: Kelly Jean Kolb (a), Alfred S. McEwen (a), Jon D. Pelletier (a)(b) Keywords: Mars, Climate; Mars, Surface; Geological processes Abstract: The origin of the martian gullies has been much debated since their discovery by the Mars Orbiter Camera (MOC, Malin, M.C., Edgett, K.S. [2000]. Science 288, 2330-2335). Several previous studies have looked at slope gradients in and around gullies, but none have used Digital Elevation Models (DEMs) from the High Resolution Imaging Science Experiment (HiRISE, McEwen, A.S., and 14 colleagues [2007]. J. Geophys. Res. 112 (E05), E0505S02), which has a pixel scale down to 25cm/pixel. We use five 1m/post HiRISE DEMs to measure gully apex slopes, the local channel gradient at the upslope extent of the gully debris apron, which marks a shift from erosion to deposition. The apex slope provides information about whether a flow was likely a typical dry granular flow (begins depositing on slopes [approximately equal to]21[degrees]) or fluidized by some extra mechanism (depositing on shallower slopes). We find that 72% of the 75 gully fans studied were likely emplaced by fluidized flows. Relatively old gullies appear more likely to have hosted fluidized flows than relatively fresh gullies. This suggests a time and location dependent fluidizing agent, possibly liquid water produced in a different climate as previously proposed. Our results do not provide evidence for water-rich flows in gullies today. Author Affiliation: (a) Department of Planetary Sciences/Lunar and Planetary Laboratory, University of Arizona, 1629 E. University Blvd., Tucson, AZ 85721, USA (b) Department of Geosciences, University of Arizona, 1040 E. 4th St., Tucson, AZ 85721, USA Article History: Received 27 May 2009; Revised 24 November 2009; Accepted 8 January 2010

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 [km.sup.2] paleo-drainage 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 illustrate that headward erosion of a proto-Grand Canyon could have been sufficient to capture the ancestral Colorado River east of the Shivwitz Plateau. doi: 10.1130/B26403.1

Cordilleran orogenic systems such as the Andes are controlled by shortening rates, climatically-controlled erosion rates, and, in some cases, eclogite production and delamination. All of these processes are coupled, however, making it difficult to uniquely determine the relative importance of each process and the feedbacks among them. In this paper we develop a mass-balanced numerical model that couples an actively-shortening orogen and crustal root with eclogite production, delamination, and climatically controlled erosion. The model provides a first-order quantification of the sources (shortening) and sinks (erosion and eclogite production and delamination) of crustal volume during the Cenozoic in the Andes as a function of latitude and time. Given reasonable estimates for the rates of eclogite production and the threshold size of the eclogitic root required for delamination, the model suggests that, in the central Andes between 5[degrees]S and 32[degrees]S, the orogen has grown to a sufficient height to produce and maintain eclogite, which in turn has promoted delamination in the lower crust and mantle. In this region, climatically controlled erosion rates influence the size of the orogen through two separate mechanisms: by exporting mass via surface processes and by controlling the lithostatic pressure in the lower crust, which modulates the rates of eclogite production and/or delamination. To the north and south of the central Andes, relatively low shortening rates and high precipitation and erosion rates have slowed eclogite production such that delamination likely has not occurred during the Cenozoic. doi: 10.1130/G30755.1

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2009.09.009 Byline: Kelly Jean Kolb (a), Jon D. Pelletier (a)(b), Alfred S. McEwen (a) Keywords: Mars, Surface; Geological processes; Mars Abstract: Our study investigates possible formation mechanisms of the very recent bright gully deposits (BGDs) observed on Mars in order to assess if liquid water was required. We use two models in our assessment: a one-dimensional (1D) kinematic model to model dry granular flows and a two-dimensional (2D) fluid-dynamic model, FLO-2D (, FLO Engineering), to model water-rich and wet sediment-rich flows. Our modeling utilizes a high-resolution topographic model generated from a pair of images acquired by the High Resolution Imaging Science Experiment (HiRISE) aboard the Mars Reconnaissance Orbiter. For the 1D kinematic modeling of dry granular flows, we examine a range of particle sizes, flow thicknesses, initial velocities, flow densities, and upslope initiation points to examine how these parameters affect the flow run-out distances of the center of mass of a flow. Our 1D modeling results show that multiple combinations of realistic parameters could produce dry granular flows that travel to within the observed deposits' boundaries. We run the 2D fluid-dynamic model, FLO-2D, to model both water-rich and wet sediment-rich flows. We vary the inflow volume, inflow location, discharge rate, water-loss rate (water-rich models only), and simulation time and examine the resulting maximum flow depths and velocities. Our 2D modeling results suggest that both wet sediment-rich and water-rich flows could produce the observed bright deposits. Our modeling shows that the BGDs are not definitive evidence of recent liquid water on the surface of Mars. Author Affiliation: (a) Department of Planetary Sciences/Lunar and Planetary Laboratory, University of Arizona, 1629 E. University Blvd., Tucson, AZ 85721, USA (b) Department of Geosciences, University of Arizona, 1040 E. 4th St., Tucson, AZ 85721, USA Article History: Received 31 October 2008; Revised 29 August 2009; Accepted 1 September 2009

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.

Bright gully sediments attributed to liquid water flow have been deposited on Mars within the past several years. To test the liquid water flow hypothesis, we constructed a highresolution (1 m/pixel) photogrammetric digital elevation model of a crater in the Centauri Montes region, where a bright gully deposit formed between 2001 and 2005. We conducted one-dimensional (1-D) and 2-D numerical flow modeling to test whether the deposit morphology is most consistent with liquid water or dry granular flow. Liquid water flow models that incorporate freezing can match the runout distance of the flow for certain freezing rates but fail to reconstruct the distributary lobe morphology of the distal end of the deposit. Dry granular flow models can match both the observed runout distance and the distal morphology. Wet debris flows with high sediment concentrations are also consistent with the observed morphology because their rheologies are often similar to that of dry granular flows. As such, the presence of liquid water in this flow event cannot be ruled out, but the available evidence is consistent with dry landsliding. Keywords: Mars, fluvial, mass wasting, numerical model.

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. Keywords: eolian, dust, alluvial fan, soils, mathematical model.