Modeling moraine degradation in the Sierra Nevada Mountains, California with a 1-D linear diffusion equation
Abstract
In California's Sierra Nevada Mountains, a complex history of glaciations is recorded in an expansive system of glacial moraines. The chronologies of these glaciations have been fairly well studied and ages of many of the moraines have been determined by cosmogenic isotope dating. The ages of these moraines range from approximately 19 to 140 thousand years. Over the expanse of time these formations have been in existence, they have changed significant amounts, however knowing the extent to which these moraines have changed as well as the rates at which these changes occur, is problematic. It is important to understand how much the moraines change because the extent to which we accurately know ages depends on how much the moraines have changed. To address this problem, we constructed a 1-D linear diffusion model that compares model hillslopes to collected topographic profiles to predict diffusion rates. The model is a finite difference model that applies linear diffusion to an initially triangular hillslope with an initial slope of 31°. The cross-sectional area of the triangular hillslope is equal to the area of the measured hillslope profile. The model runs for a period of time equal to the age of the moraine, pulled from existing literature, and with multiple values for diffusivity, k. The model results are compared to the existing topography drawn from NASA's data. From this, we determine the value of diffusivity that best fits the measured profile. From modeling the evolution of many moraines in the same general area and of the same ages, we will determine whether or not moraines of similar ages appear to have evolved at different rates. Diffusivity values for the moraines in the area should be roughly the same due to similar environmental conditions, and if the model shows wide variation in this value, then we may need to reconsider how well we truly know ages or initial conditions. We will also compare model results for erosion and accumulation to cosmogenic isotope depth profiles. From the model and comparisons, we will be able to determine how much change these moraines have undergone and from that, place better constraints on moraine ages.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFMEP23C0765G
- Keywords:
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- 1826 HYDROLOGY / Geomorphology: hillslope