ANNUAL SEDIMENT TRANSPORT AND LANDFORM DEGRADATION OF MONO BASIN AND TAHOE MORAINES IN THE EASTERN SIERRA NEVADA MOUNTAINS, CA

Mono Basin and Tahoe Moraines - alpine lateral moraines Pleistocene in age in the eastern Sierra Nevada Mountains - are studied as representatives for annual degradation rates and processes occurring on natural landforms in temperate and semi-arid environments. A linear transport law, q = -κ(δz/δx), is used to compare bulk sediment transport and erosion rates on different landforms and slopes. The ratio of sediment flux (q) to slope gradient (δz/δx) is called topographic diffusivity (κ), an expression of landscape smoothing in m²/yr, and it is expected that landforms in similar climates and with similar substrates will have comparable values.

This study combines topographic difference analysis from terrestrial LiDAR data with field methods including sediment trapping, pebble transport markers, and observations of the pebble surface frequency. Preliminary results from annual bulk sediment collected in the traps and LiDAR differences for the 2010-2011 year give values for topographic diffusivity of the moraines within a range cited by literature for similar climates: 10^-4 - 10^-2 m²/yr. However, the LiDAR difference images also show inter-site differences in the amount and distribution of surface removal and deposition. Such differences may reflect different ways sediment is transported on the surface.

While published erosion rates typically report averages derived from time scales on the order of 0.1 - 1 Ma at the km spatial scale, direct measures of landform degradation on a human time scale of years to 100’s of years at the 0.1 - 1 m scale are less frequent. Landform degradation and the environmental factors contributing to the break down and transport of substrate determine the depth to which landform material is exposed to water, ice, wind, solar radiation, cosmic rays and nutrients from vegetation. All such factors relate to the extent of surface processes on daily through annual scales, and so they contribute to landscape evolution at all scales. This study will relate sediment transport and topographic differences found on the moraines to the climate of the eastern Sierra Nevada Mountains.