HR: 0800h
AN: C51A-0265    [Abstracts]
TI: Application of a 1-Dimensional Viscoelastic Bending Beam Model to the Buoyant Terminus of Lake-Calving Mendenhall Glacier, Southeast Alaska
AU: * Boyce, E
EM: esb@gi.alaska.edu
AF: Geophysical Institute, U. of Alaska, Fairbanks, 903 Koyukuk Drive, Fairbanks, AK 99775-7320 United States
AU: Motyka, R J
EM: jfrjm@uas.alaska.edu
AF: Geophysical Institute, U. of Alaska, Fairbanks, 903 Koyukuk Drive, Fairbanks, AK 99775-7320 United States
AU: Bueler, E
EM: ffelb@uaf.edu
AF: Dept. of Mathematics and Statistics, U. of Alaska, Fairbanks, PO Box 756660, Fairbanks, AK 99775-6660 United States
AB: Mendenhall Glacier is a lake-calving glacier in southeastern Alaska that is experiencing substantial thinning and increasingly rapid recession. The recent retreat of the terminus has been controlled mainly by calving dynamics, and therefore may not be directly driven by climatic trends. Lake-terminating glaciers form a population distinct from both tidewater glaciers and polar ice tongues, with some similarities to both groups. Unlike polar ice tongues, it is generally thought that temperate tidewater glaciers are unable to maintain a floating front. Studies of Mendenhall Glacier and other temperate lake-calving glaciers suggest that partial terminus floatation may not be uncommon, and may play a role in calving. At Mendenhall, we observed upward displacement of the calving front during a two-year period, which culminated in large-scale calving and terminus collapse during summer 2004. Rapid thinning and simultaneous retreat into a deeper basin led to floatation conditions along approximately 50 % of the calving front. This unstable terminus geometry lasted for ~ 2 years. We used a simple 1-dimensional model to investigate the transient response of a floating glacier tongue to buoyant forcing. The basic equations we used to model a viscoelastic bending beam of ice were developed by Reeh et al. (2003) We solve the model numerically using a Chebyshev spectral method. Rather than look at deflections along a transverse profile, we apply the appropriate boundary conditions for a grounding line and floating front. The model results may be compared to the measured glacier upwarping. Temperatures in Mendenhall Lake adjacent to the calving face show a cooling trend (4 to 2 °C) over the summer melt season and a stable thermal stratification, suggesting little or no convection along the calving front. Although melting of a submerged ice cliff may be an important mechanism for ice loss at tidewater glaciers, lack of convection and low water temperatures indicate it is much less so for lake-calving glaciers. Reeh, N., E. L. Christensen, C. Mayer, O. B. Olesen, 2003. Tidal bending of glaciers: a linear viscoelastic approach. Annals of Glaciology 37(1), 83-89.
DE: 0720 Glaciers
DE: 0732 Icebergs
DE: 0746 Lakes (9345)
DE: 0774 Dynamics
DE: 0776 Glaciology (1621, 1827, 1863)
SC: Cryosphere [C]
MN: Fall Meeting 2005