Cordilleran ice sheet

Context

During the last glacial cycle, much of North America has been covered by ice. During the Last Glacial Maximum (LGM), peak of glaciation, three major ice sheets had collided to form a continuous blanket of ice that spanned from southern Alaska to Newfoundland, connecting with the Greenland ice sheet in the Canadian Arctic, and extending as far south as Chicago. The Laurentide ice sheet, largest of the three, was centred on the Hudson Bay, and fully covered the Canadian Prairies, Eastern Canada, and the Great Lakes Basin. The Innuitian ice sheet, much smaller, covered the northernmost Canadian archipelago. Finally, the Cordilleran ice sheet, intermediate in size, capped the mountain ranges of the Western Cordillera.

../_images/julien-z650-120722-085925-120722-090032-5x8.jpg

The Tuya Lake moraine complex in northern British Columbia.

Animations

Numerical modelling can help to our understanding of the Cordilleran ice sheet’s glacial history. However, the ubiquitously mountainous topography of the region renders this task particularly challenging. Because of the irregular arrangement of valleys and ridges that forms the ice sheet’s floor, ice moved along tortuous and intertwined pathways, sometimes following the major topographical troughs, and sometimes flowing across them. The complexity of regional climate adds to the complexity of topography. Strong differences in seasonality and timing of precipitation exist, for instance, between the rain-drenched coastal areas, and the dry interior.

Simulations of the Cordilleran ice sheet.

Finally, the Cordilleran ice sheet rested directly on a complex patchwork of crustal blocks progressively accreted by geologically old yet still active subduction zones, which are responsible for significant geothermal variability in the region. This geothermal variability may have affected basal melt, water routes beneath the ice sheet, and the distribution of subglacial meltwater landforms in the Western Cordillera, including vast esker systems, deep canyons and subglacial lake sediments.