LANDSCAPE EVOLUTION IN THE CLASSROOM WITH THE TOPODOME

Landscape evolution varies with tectonic and climatic forcings. To study the interplay between these two drivers, we created a laboratory-scale physical model coupling a rainfall simulator with a circular erosional basin, inspired by Hasbargen and Paola (2000). Uniform tectonic uplift is simulated through base level fall at an outlet; students vary tectonics by changing the rate of base level fall. Climate is adjusted by varying water discharge through an array of grocery-store vegetable misters embedded in a loop of PVC pipe. Erosional output is measured by scanning the basin surface with a 3D laser scanner producing a digital elevation model (DEM) of the surface at specific points in time. Sand (110 μm) mixed with kaolinite clay was used as an erodible substrate with some cohesion.

Students in an upper-level undergraduate and graduate-student course in tectonic geomorphology used the experimental facility, dubbed the TopoDome, for a three-week final project. Earlier lab exercises introduced students to topographic analyses of DEMs in GIS, including channel delineation, long-profile creation, extraction of hypsometric data, and slope calculations. Students were given freedom to choose scenarios to run in the TopoDome, and data analyses were divided up amongst class members. In 2012, we ran two climate scenarios for the same base-level fall then doubled the rate of base level fall while holding climate constant. Students generated DoDs (DEMs of difference) to calculate volumetric erosion rates, delineated channels and analyzed long profiles, mapped knickpoint locations, and examined erosion rates above and below knickpoints.

Challenges we encountered involved the erodible substrate and base level fall mechanism. Fine sand with kaolinite was not sufficiently cohesive to maintain steep faces, so we are investigating alternative substrates (e.g., silt-sized ceramic spheres) for future runs. The base-level controller leaked, so we are in the process of upgrading it to make the facility research-grade. Finally, we are adding to our apparatus a depositional basin so as to link the sediment flux from the erosional basin directly to the depositional signal. This full source-to-sink facility will be utilized by sedimentology-stratigraphy classes as well as research efforts linking climate, tectonics, and erosion.