HR: 15:25h
AN: H53I-07    [Abstracts]
TI: Above the glacier: non-glacial erosion rates and processes feeding the Matanuska Glacier, Alaska
AU: OFarrell, C R
EM: Colin.R.O'Farrell.03@Alum.Dartmouth.ORG
AF: Dartmouth College, Dept. of Earth Sciences, Hanover, NH 03755 United States
AU: * Heimsath, A M
EM: arjun.heimsath@dartmouth.edu
AF: Dartmouth College, Dept. of Earth Sciences, Hanover, NH 03755 United States
AU: Lawson, D E
EM: Daniel.E.Lawson@erdc.usace.army.mil
AF: CRREL, Lyme Rd., Hanover, NH 03755 United States
AU: Jorgensen, L M
EM: Laura.H.Jorgensen.05@Alum.Dartmouth.ORG
AF: Dartmouth College, Dept. of Earth Sciences, Hanover, NH 03755 United States
AU: Evenson, E B
EM: ebe0@lehigh.edu
AF: Lehigh Univ., Dept. of Earth and Environmental Sciences, Bethlehem, PA 18015 United States
AU: Larson, G A
EM: larsong@msu.edu
AF: Michigan State Univ., Dept. of Geological Sciences, East Lansing, MI 48824 United States
AB: Glacial erosion rates are estimated as some of the highest in world, with glacial landscapes representing an upper bound on physical erosion processes. Few studies have attempted, however, to quantify the contribution of sediment from the unglaciated, periglacial landscape above a glacier to glacial sediment loads. Here, we present erosion rates from the unglaciated landscape above the Matanuska Glacier, Alaska, and compare them with a seven-year record of proglacial suspended sediment yield. We calculated non-glacier lowering rates ranging from 0.36 to 2.5 mm/yr based on estimates of rock fall and debris-flow fan volumes and their source catchment areas. To quantify the background attrition rates from the unglaciated landscape, we measured in situ produced 10-Be from ridge crests. Erosion rates from cosmogenic nuclide analyses yield lowering rates roughly an order of magnitude lower, ranging from 0.16 to 0.045 mm/yr, and are strongly correlated (R-squared of 0.98) with topographic curvature. Using morphometry to extrapolate each calculated rate to the entire Matanuska basin implies an annual sediment flux of 0.8 million tonnes due to non-glacial processes. The seven-year average sediment flux from the terminus is 1.3 million tonnes. Assuming steady state, these results suggest that 62 % of the sediment flux is non-glacial. A similar mass balance for a retreating cirque glacier in a tributary valley to the Matanuska Glacier, implies non-glacial contribution of 36 % to the sediment budget. Our results suggest that erosion of the unglaciated upland landscape may contribute as much sediment as erosion of the glacier bed, thus implying a potentially rapid response of the unglaciated landscape to changes in climate, base-level or regional tectonism.
DE: 0720 Glaciers
DE: 1625 Geomorphology and weathering (0790, 1824, 1825, 1826, 1886)
DE: 1815 Erosion
DE: 1886 Weathering (0790, 1625)
SC: Hydrology [H]
MN: Fall Meeting 2005