Date of Award

January 2018

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Geology

First Advisor

Jaakko Putkonen

Abstract

Earth’s landforms constantly change as a result of erosion at the surface. Surface regolith is composed of a variety of different grains sizes, each having a different rate of transport. The varying rates of transport between grain sizes cause the distribution of grain sizes to change along hillslopes over time. The ability to predict grain size distributions as a function of time would be useful for determining slope stability and determining ages of landforms. However, current knowledge is limited for the varying rates of transport of different grain sizes. To better understand grain transport rates, a set of experiments was carried out in Mono Basin, CA, where glacial moraines provide ideal hillslopes to measure grain transport rates and grain size distributions. This data was used within a hillslope diffusion model to simulate transport of grains and generate grain size distributions along the slope over time.

Results from the field experiments showed that transport rate does not necessarily increase with decreasing grain size, and that there may be a certain grain size (1-4 mm) that has the highest velocity on hillslope surfaces. This may be due to cohesiveness of finer grains, a buoyancy of coarser grains in the mobile surface layer, a tendency of finer grains to experience intermittent burial, or a combination of all three factors.

The measured grain size transport rates are consistent with the transport rates predicted by the best fit of the grain size distribution model, which also suggested that grains within the 1-4 mm grain size class have the highest downslope transport rate. The grain size distribution model can somewhat accurately predict grain size distributions at the footslope and crest of the moraines over time.

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