Monday, January 24, 2011, 12:00PM - 1:00PM
Advances and retreats of alpine glaciers over glacial-interglacial cycles have strongly influenced the evolution of alpine landscapes and have led to variations in the patterns and rates of sediment erosion and transport. I will present case studies from Yosemite National Park and the Colorado Front Range to show how glaciers erode the landscape and to demonstrate the variability of sediment transport outside of the glacial footprint through time.
In Yosemite National Park, differences in the degree of fracture spacing control the efficiency of glacial erosion processes during glacial times. The broader the fracture spacing, the lower are the rates at which a glacier can erode blocks from its bed. We suggest that the lack of cracking in some of the plutons of Yosemite National Park makes subglacial less efficient than elsewhere, leading to Yosemite’s characteristic landscape with its smoothly polished bedrock surfaces and granitic domes.
The amount of glacial erosion dictates how much sediment is fed into the fluvial system at the glacier terminus. In the Boulder Creek watershed the timing of glacier retreat appears to influence the pattern of sediment transport and deposition. Absolute dates from terraces in Boulder Canyon and from terraces along the Colorado Front Range suggest that sediment aggradation and lateral planation of surfaces were dominating during glacial times and during the transition from glacial to interglacial climate conditions when sediment supply is high. During deep interglacial conditions, however, the lack of sediment supply from the mountain watersheds led to the incision of Boulder Canyon and the High Plains. The presence of multiple levels of gravel-capped terraces in Boulder Canyon and immediately adjacent to the Colorado Front Range most likely represents a direct evidence for the influence of glacial-interglacial climate variations on the incision history in this area.