HR: 09:30h
AN: C41C-07    [Abstracts]
TI: Evidence for an Extensive Tributary-Type Ice Flow System in the Interior of the Laurentide Ice Sheet: Implications for Ice Sheet Stability
AU: * Ross, M
EM: maross@uwaterloo.ca
AF: University of Waterloo, 200 University Avenue West, Waterloo, ON N2L 3G1, Canada
AU: Parent, M
EM: miparent@nrcan.gc.ca
AF: Geological Survey of Canada, 490 de la Couronne, Quebec, QC G1K 9A9, Canada
AB: It has been demonstrated that many modern ice streams are fed by complex systems of tributaries extending far into the interior of ice sheets, thus raising questions about their potential implications in past and modern ice sheet response to climate forcing. However, little is known about the timing of initiation of these systems and the mechanisms involved in their development. Here we present evidence for a major glacial dynamics shifts in the southwestern sector of the Laurentide Ice Sheet (LIS) that lead to the development of a tributary-type flow system prior to the final retreat of the LIS in that sector. The system apparently extended more than 1500 km into the interior of the ice sheet, a distance similar to what has been modeled for east and west Antarctica (~ 1000 km). This interpretation is based on the analysis of SRTM-derived digital elevation models over the North American Interior Plains, satellite imagery, available digital geologic maps, ¹⁴C databases and associated published ice margin retreat sequences as well as limited new field observations. The development of this tributary-type flow system may be coeval with readvance of the James Lobe (~ 14.6 cal ka BP) in South Dakota. This system also clearly crosscuts a large but less complex set of paleo-ice stream tracks. This older (~ 16.0 cal ka BP) ice flow configuration is associated with prominent ice marginal glaciotectonic features in southern Alberta and southwestern Saskatchewan. As the ice sheet thinned and the ice margin retreated, the tributary system evolved into a set of smaller outlet lobes just prior to the retreat of the ice margin onto the Canadian Shield (~ 12.5 cal ka BP). These smaller lobes left several belts of ice-thrust features. Based on the proposed reconstruction, we suggest that the development of the tributary-type ice flow system in the interior of the LIS marked the onset of its collapse. If such internal reorganization of ice-flow systems was indeed characteristic of the collapsing LIS, concerns over the stability of modern ice sheets become even more justified as flow systems of this type are known to exist in Antarctica and Greenland.
DE: 0726 Ice sheets
DE: 0730 Ice streams
DE: 9350 North America
SC: Cryosphere [C]
MN: 2007 Fall Meeting