HR: 16:45h
AN: C44A-04 [Abstracts]
TI: Evolving Force Balance at Columbia Glacier, Alaska, During its Rapid Retreat
AU: * ONeel, S
EM: shad@colorado.edu
AF: University of Colorado, Boulder
INSTAAR, 1560 30th st., Boulder, CO 80303
United States
AU: Pfeffer, W T
EM: pfeffer@tintin.colorado.edu
AF: University of Colorado, Boulder
INSTAAR, 1560 30th st., Boulder, CO 80303
United States
AU: Krimmel, R
EM: rkrimmel@usgs.gov
AF: U.S.G.S., 1201 Pacific Avenue, Tacoma, WA 98402
United States
AU: Meier, M
EM: Mark.Meier@colorado.edu
AF: University of Colorado, Boulder
INSTAAR, 1560 30th st., Boulder, CO 80303
United States
AB:
Changes in driving and resistive stresses play an essential role in governing the buoyancy forces that are important controls
on the speed and irreversibility of tidewater glacier retreats. We describe changes in geometry, velocity and strain rate,
and present a topdown force balance analysis performed over the lower reach of Columbia Glacier. Our analysis uses new
measurements and estimates of basal topography and photogrammetric surface velocity measurements made between 1977 and 2001,
while assuming depth-independent strain. Sensitivity tests show that the method is robust and insensitive to small changes in
the calculation parameters. Spatial distributions of ice speed show little correspondence with driving stress. Instead,
spatial patterns of ice speed exhibit a nonlinear correspondence with basal drag. Primary resistance to flow comes from basal
drag, but lateral drag becomes increasingly more important throughout the retreat, which may account for observed increases
in speed. Maximum basal drag is always located in a prominent constriction located ~12 km upstream from the pre-retreat
terminus. Once the terminus retreated into deep water off the terminal moraine marking the modern maximum extent, the
upstream location of this maximum basal drag helped to promote thinning and decrease effective pressure in the lower region
by limiting replenishing ice flow from upstream. An increase in both ice velocity and calving resulted, initiating what
appears to be an irreversible retreat.
DE: 0720 Glaciers
DE: 1621 Cryospheric change (0776)
SC: Cryosphere [C]
MN: Fall Meeting 2005