Thursday, November 13, 2014, 4:30PM - 5:30PM
RL-1 room 269
Use of 10Be to deduce variations in sediment supply from the Front Range to the High Plains
Sediment production on hillslopes affects the supply of sediment to the fluvial systems with which they are coupled. Aggradation or erosion of alluvium occurs when sediment supply is not equally matched with stream transport. In the Colorado Front Range, long-term basin-averaged denudation rates indicate that small basins are producing sediment at a rate of ~2.5 cm/ka (Dethier and Lazarus, 2006). However, fluvial features indicate past sediment production in source basins of the Front Range was higher. Remnants of in-set fill terraces exist within steep mountain canyons, indicating alluvial sediments were deposited and evacuated multiple times as sediment supply fluctuated. 10Be data and OSL data from fill terraces in Boulder Creek and Lefthand Creek suggest that rivers draining both glaciated and nonglaciated basins in the Front Range experienced large and rapid fluctuations in the sediment supply.
Outboard of the Front Range, broad gravel-capped strath terraces also suggest long periods of lateral planation associated ample sediment supply, punctuated by brief periods of vertical incision and strath abandonment. 10Be inheritance in depth-profiles on these surfaces suggests that basin-averaged paleodenudation rates at the time of deposition were higher than modern rates, up to 5.5 cm/ka. We argue that these data support a model in which basin-specific oscillations in sediment supply drive both fluvial aggradation and evacuation in the canyons, and also associated cycles of strath cutting and abandonment on the High Plains.
In addition, I will highlight ongoing work to re-calculate basin-wide denudation rates following the 2013 Boulder Flood.