HR: 11:05h
AN: C42A-04    [Abstracts]
TI: Exploring similarities between tidewater and ice sheet outlet glaciers
AU: * Truffer, M
EM: truffer@gi.alaska.edu
AF: Geophysical Institute, 903 Koyukuk Dr, Fairbanks, AK 99775-7320 United States
AU: Motyka, R
EM: roman.motyka@uas.alaska.edu
AF: Geophysical Institute, 903 Koyukuk Dr, Fairbanks, AK 99775-7320 United States
AU: Echelmeyer, K
EM: kechel@gi.alaska.edu
AF: Geophysical Institute, 903 Koyukuk Dr, Fairbanks, AK 99775-7320 United States
AB: Tidewater and outlet glaciers pose a serious challenge to glaciologists because of their complicated behavior. Yet, they exhibit some of the largest changes observed in glacial systems, often defying regional trends of nearby land-terminating ice masses. For example the Chugach Range of Alaska, while generally losing ice mass, contains one growing tidewater glacier. Also, about 50% of the current mass loss there is due to the rapidly retreating Columbia Glacier. In Glacier Bay, several tidewater glaciers are advancing while land terminating and lake calving glaciers are rapidly wasting away. We will explore some of the common features found between temperate tidewater glaciers and the cold or polythermal outlet glaciers of the big ice sheets. These commonalities include patterns of ice draw-down, particularly far upstream, and acceleration of ice flow during the retreat phase that propagates much farther upstream than suggested by effects of longitudinal coupling. Rapid retreats are initiated at the glacier terminus and we suggest that they are linked to warming ocean temperatures and glacial freshwater runoff. We will also outline the modeling challenges for the upstream propagation of a drawdown event. These require a full treatment of the three dimensional Stokes equations. However, it is not clear how to treat the basal boundary condition and the possibility of temporal changes at the ice base. A particular challenge for outlet glacier systems is posed by free surfaces, such as the grounding line or the cold-temperate-surface (CTS). One striking feature of tidewater glaciers is their evolution through a tidewater glacier cycle of rapid retreat and slow advance as proposed by Austin Post. This cycle is well documented for Alaska's tidewater systems, and we suggest that the possibility of such a cycle should be explored for ice sheet outlet glaciers. The often asynchronous behavior of these systems poses a challenge for the assessment of regional or global ice volume changes. Similarly, ice sheet mass balance can be dominated by a few rapidly changing outlet systems. Such systems must be carefully examined for their disproportionate effects on volume change and sea level studies.
DE: 0720 Glaciers
DE: 0730 Ice streams
DE: 0762 Mass balance (1218, 1223)
DE: 0774 Dynamics
SC: Cryosphere [C]
MN: Fall Meeting 2005