Examination of Landsat imagery of the bed of the last North American (Laurentide) Ice Sheet has revealed a previously undetected pattern of glacial streamlining. Superimposed, cross-cutting, sub-parallel sets of glacial lineations of the order of 2-50 km in length are found to be widespread. They are assumed to reflect successive phases of sustained ice flow, revealing major changes in the geometry of ice sheet flow. Using six scales of remotely sensed imagery to map the lineations, and establish their cross-cutting relationships, permits relative ages of continent-wide ice flow phases to be determined. Comparison of the principal ice flow sets with established stratigraphies suggests that the inferred shifts in ice flow occurred during the last (Wis-consinan) glacial cycle. The configuration of ice flow indicates that ice divides migrated by the order of a thousand kilometres. The evolution of the Laurentide Ice Sheet through the Wisconsinan is reconstructed. There is evidence that during the Early Wisconsinan, ice sheet formation in Keewatin may have been independent of that in Labrador-Quebec, and that these two ice masses coalesced to form a major Early Wisconsinan ice sheet. The palaeo-ice flow evidence indicates that this ice sheet configuration consisted of a trans-Laurentide divide aligned NW-SE across Hudson Bay. Subsequently, the western sector decayed whilst the eastern dome remained stable (Middle Wisconsinan). An ice dispersal centre in the west reformed and fused with the eastern ice mass to form the Late Wisconsinan Ice Sheet. Decay of this ice sheet is well known from existing analyses. The probability of strong coupling between ice sheet topography and atmospheric circulation suggests that the major changes in Laurenlidc Ice Sheet geometry must have been associated with large-scale atmospheric circulation changes. The corollary is that the high mobility of mid-latitude ice sheets may help explain the non-linear response of glacial climates to the insolation changes produced by external forcing.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:643209 |
| Date | January 1990 |
| Creators | Clark, Christopher D. |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/13406 |
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