1. On a natural landscape, what would be the primary causes or processes for variation in erosion rates (Erodibility) of the land surface? 2. The natural progression of drainage development through time can most easily be observed by setting the WILSIM parameters to a uniform SLOPE with uniform ERODIBILITY (the default settings). Describe how the drainage network develops over the land surface - pay particular attention to whether it develops over the entire surface simultaneously or from headward erosion. Look carefully at all parts of the landscape and observe how the small tributaries (lower order streams) develop in relationship to the larger channels (higher order streams) as time passes. 3. Why do you think headward erosion is the natural process for drainage development? 4. Natural variation in rates of erosion of a landscape (or the resistance of rock to erosion) can be simulated by varying the “Erodibility” of the surface in WILSIM. One of the best ways to discover this variation is to set the “Break” in Erodibility at X=30 (i.e., left = 0.01 and right = 0.05 or vice versa). In addition, turn on a row profile at row 20 under Profiles tab. Run the model and observe the progression of drainage development on either side of the break in the animation window and the row profile. After running the animation, answer the following; a: How does the drainage develop geographically across the entire surface? b: How does the rate of headward extension vary? c: Is the drainage pattern more complex in the easily eroded landscape compared to the more resistant surface? d: which side of the break has more sediment deposits as shown in the lower panel of the row profile? 5. Now set the ERODIBILITY for a break in the Y direction at Y = 20 and run 2 animations. The first should be with an easily eroded surface at lower elevations (bottom = 0.05 and top = 0.01) and the second with an easily eroded surface at the higher elevations (bottom = 0.01 and top = 0.05). In addition, turn on the average profile under Profiles tab. Compare the results by describing the rates and patterns of erosion for each setting. Is the drainage complexity (degree of stream branching) different for differing geographic locations on the surface? Is there a significant difference in average profile on either side of the break line? 6. When tectonic uplift is added to the animation a pronounced break in slope (an escarpment) develops. Describe the differences in the form of the Hypsometric curves for a uniform slope eroded by rainfall and a complex slope with an escarpment caused by tectonic uplift. 7. As canyons are eroded into a tectonic escarpment, and alluvial fans form at the canyon mouths, how does the hypsometric curve change through time? Why does deposition occur at the locations where you see the alluvial fans developing? You can see a more dramatic effect of alluvial fans in the average profile by noticing the sediment thickness in the bottom panel. 8. Run two differing animations for rate of uplift with a break at Y = 40. Observe and describe the degree of incision (canyon development) just upstream from the tectonic escarpment in both cases (the first with a slow rate of uplift, the second with a high rate of uplift). Does the rate of incision match the rate of uplift in both cases? 9. Now compare escarpment erosion rates under dry and wet climate conditions. Run two differing simulations, both with a fixed rate of uplift but the first with a wet climate and the second under a dry climate. Compare the drainage form and complexity as well as the rate of escarpment erosion under differing climates. 10. Define the difference between Diffusion and Erosion within WILSIM. 11. Climate change over extended periods of geologic time is incorporated as an integral part of WILSIM by varying the rate of precipitation through time (from drier to wetter condition, or from wetter to drier). Complete two simulations with varying climate. a: Climate varying from drier to wetter through time b: Climate varying from wetter to drier through time Describe the differences in drainage development from start to finish for each animation. For the climate regime that becomes progressively drier, how do the tributary slopes change in the upper portion of the drainage? 12. In #11, diffusion lessens the upper tributary slopes as climates become drier. Diffusion and Erosion in WILSIM relate to natural processes operating to create landforms. What slope processes do you think Diffusion simulates? 13. Can the hypsometric curve be used to calculate volumes of sediment in the alluvial fans and relate that to the volume of sediment eroded from the landscape upstream from the fan? Describe why or why not the curves can be used to calculate these volumes. 14. What limitations of WILSIM have you discovered so far by running the above simulation scenarios? How might the WILSIM program be modified and improved to account for these limitations?
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