Bauder, A., Mickelson, D.M., and Marshall, S.J., 2004, Effects of water on glacier and ice-sheet flow: EGU Geophysical Research Abstracts,v. 6, CD version. (04-16)

-- Abstract --

The influence of water on basal processes is a critical issue in understanding

the dynamics of glaciers and ice sheets. Subglacial conditions not only

infuence the flow regime of ice masses, but also the formation of glacial

landforms. A detailed knowledge of the physical processes involved is rather

limited. In particular, existence and interaction of water and permanently

frozen ground overridden by a glacial advance is of major importance for

further understanding these processes.

The southern margin of the Laurentide Ice Sheet (LIS) was dominated by the

presence of relatively thin ice lobes that seem to have been very sensitive to

external and internal conditions. Their extent and dynamics were highly

influenced among other factors by the interaction of subglacial and proglacial

conditions, and by the existence of the Great Lakes. Cooling early in the

last glacial cycle produced extensive permafrost along parts of the ice

margin. The insulating effect of the ice sheet after advancing over areas of

permafrost led to a slow degradation of permafrost under the ice. Finally,

warming after the glacial maximum caused the disappearance of subglacial

permafrost. Subglacial permafrost affects directly the evolution of basal

temperature and subglacial hydrology, both critical conditions for the

formation of landforms and fast flow instabilities.

The three-dimensional thermomechanical UBC ice sheet model was used to

investigate the spatial distribution of subglacial conditions and interacting

lobe dynamics. The ice sheet model, which contains thickness evolution, ice

flow, temperature evolution, and isostasy was extended with a model for the

thermal regime in the upper earth crust. The evolution of the whole LIS was

modeled for the last glaciation cycle, with primary attention on correct

reconstruction of the southern margin.

The sensitivity of the model to subglacial process assumptions was examined.

Time-transient physical conditions are analyzed with the aim of better

understanding the reasons for the distribution of landforms produced by the

southern LIS. Surge-type flow instabilities may account for the relatively

thin ice lobes, that were the dominant features around the southernmost margin

of the Laurentide Ice Sheet.