Numerical Modelling Investigations of the Conditions under the Southern Laurentide Ice Sheet

 

The southern margin of the Laurentide ice sheet (LIS) is dominated by the presence of relatively thin and sensitive reacting ice lobes. Extent and dynamics is highly influenced among other factors by subglacial conditions, permafrost interaction, and the existence of the Great Lakes. The three-dimensional thermomechanical UBC ice sheet model was used to investigate the spatial distribution of subglacial conditions and interacting lobe dynamics. The model contains thickness evolution, ice flow, temperature evolution, isostasy, and basal processes including the thermal regime of the bed. The time dependent evolution of the whole LIS was calculated for the last glaciation cycle with primary attention on correct reconstruction of the southern margin.

The sensitivity of subglacial process assumptions was examined. The transient physical conditions are being analysed with the aim of better understanding the reasons for the distribution of landforms produced by the southern LIS. The existence of permanently frozen ground has a major influence on the dynamics of an advancing ice sheet and the formation of landforms. Subglacial permafrost affects directly the evolution of basal temperature and subglacial hydrology, both critical conditions for formation of landforms and fast flow instabilities. Surge-type flow instabilities may account for the relatively thin ice lobes, the dominant features around the southern margin of the Laurentide Ice Sheet (LIS).