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Sierra Nevada

Research Updates (2009-2016): Climate Driven Hillslope Degradation and Time-dependent Topographic Diffusivity

Risa's dissertation (2015):   Climate driven hillslope degradation of Mono Basin moraine, Sierra Nevada, CA, USA, used a space-for-time substitution of present-day topographic diffusivities from climates similar to those over the past 85 ka in the Mono Basin region of Sierra Nevada, CA,  as assessed from paleo-climate records, to test the effects of climate fluctuations on hillslope erosion rates on a glacial/interglacial time scale. Topographic diffusivities that varied in accord with the glacial chronology of the region were used to model  hillslope diffusion of the Mono Basin moraine with the basic hillslope diffusion equation. Using this approach, three scenarios of  the diffusivity parameter were applied to compare the resulting hillslope degradation models: a long term average, a time-dependent parameter, and a diffusivity based on current measures on the moraine. On a glacial/interglacial time scale, the current diffusivity was found to be significantly lower than either the long term average or those of that occurred over the past 85 ka. It was also found that in glacially active environments, diffusivities can vary significantly, depending on the region. Results are published in Geomorphology:

Madoff, R.D. and Putkonen, J., 2016, Climate and hillslope degradation vary in concert; 85 ka to present, eastern Sierra Nevada, CA,  USA, Geomorphology, v. 266, p.33-40.   doi:10.1016/j.geomorph.2016.05.010 

For updates on Risa's research, follow her website here.

Summary of Earlier Group Research: Landscape Evolution, Glacial Geology, and Surface Processes

Glaciers on land leave behind characteristic landforms and bedrock topography. The spatial extent of this signature and dating of the erosional and depositional features has led to good understanding of temporal and spatial shifts in the past glaciers and climate. At best this record contains considerable information on past glacial processes in the forms of moraines, and other depositional landforms. However, evidence suggests that all unconsolidated landforms degrade, manifested in the decreasing slope angles through time. To determine the amount and pattern of degradation on glacial moraines a well documented moraine degradation model was used (Putkonen et al., 2008). The model produced testable predictions of: 1) moraine cross profile, 2) spatial pattern of surface boulders, and 3) relative frequency of surface boulders. Comparable field data was collected by manually counting boulders, running GPS profiles, hand leveling, and low altitude airphoto analysis of alpine, tropical and Antarctic moraines. The correspondence between model and field data was remarkably good and strongly supported our current understanding of the evolution of glacial landscape. These results highlighted the evolving nature of the glacial landforms, complete removal of original moraine surfaces, and postglacial emergence of spatial pattern in boulder frequency.

(Left) Eastern Sierra Nevada Mountains, Bloody Canyon, and  Walker Lake area just south of Mono Lake, California.          

(Right) A lateral moraine near the town of Bishop, CA, eastern Sierra Nevada.