Sedimentation and Denudation Rates of a Tidewater Glacier Eroding Batholithic Bedrock: Leconte Glacier, Alaska
Abstract
LeConte Glacier erodes a basin approximately 500 km2 that consists primarily of resilient tonalite of the Coast Mountains batholith. In 1994, the glacier began a rapid calving retreat after 32 years of stability. The terminus retreated 2 km by 1998 when it entered a phase of temporary stability at a constriction in the fjord. Surface ice speeds indicate that sliding dominates ice flow in the glacier's lower reaches and is probably a significant component of total flow at higher elevations. In this paper we will describe the results of oceanographic monitoring in the ice-proximal basin made between 1998 and 2000, and relate these to recent glacier dynamics. Oceanographic monitoring included repeat bathymetric surveys, CTD casts and near-surface velocity measurements. Suspended sediment concentrations near the ice margin were up to 55 mg/l, but drop off to 20 mg/l by 10.5 km away from the terminus. Near surface velocity measurements range from 12 to 52 cm/s within 0.25 to 0.5 km of the ice margin where flow was generally away from the ice margin in a radial pattern; however, large gyres created significant shear flows along the margin of the upwelling plume. Total discharge is estimated at 6,088 m3/s with a unit discharge normal to the ice face of 4.4 m3/s. Fjord bathymetry in the upper 4 km of LeConte Bay recorded grounding-line water depth locally exceeded 260 m along the 1.4 km wide terminus. Sediment accumulation is restricted to a small basin near the ice margin where approximately 7 x 106 m3 of sediment has been trapped since December 1998. If extrapolated across the entire glacier, this equates to approximately 5 mm/yr of denudation, which is the lowest so far proposed for southeast Alaska.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2001
- Bibcode:
- 2001AGUFMIP52A0747H
- Keywords:
-
- 1625 Geomorphology and weathering (1824;
- 1886);
- 1815 Erosion and sedimentation;
- 1827 Glaciology (1863);
- 3000 MARINE GEOLOGY AND GEOPHYSICS