The waters of Georgian Bay and its many islands are a gift of successive Ice Ages when continental ice sheets, much like those that cover Antarctica and Greenland today, covered Canada in as much as 3 km of ice. As ice flowed outward into the US, deep basins were gouged out to form the modern Great Lakes. Scouring of the knobbly rocks of the Grenville Province left us the 30,000 Islands, while diversion of ice around promontories of the Bruce Peninsula steepened and scalloped the Escarpment. The same ice masses left thick sediments and a wide variety of sedimentary glacial landforms like drumlins and moraines along its southern margin. Postglacial reworking of glacial sediments has produced the world’s longest freshwater beach at Wasaga.
By looking at the landforms and sediment types produced by glacial activity, we get a glimpse into the processes happening below kilometers of ice, which in modern glaciers would be a completely inaccessible environment. By seeing the physical, 'fossilized' results of glacial movement, we can gain key insights into the workings of the glacial system. This information ultimately feeds into models that predict how glaciers will respond in the face of climate change, for example with changes in the rates of melting or fluxes in ice volume.
In particular, the importance of ice streams is becoming central to our understanding of the disintegration of ice sheets. Generally, glaciers grow slowly, taking in the range of 100,000 years in the case of the Laurentide Ice Sheet to build up to their maximum extent, but then melt over a few thousand years. The ice sheet 'pops' like a bubble through the rapid flow of ice along discrete corridors. We can detect and study ancient ice streams by analysing distinct landforms indicative of fast-flowing ice and investigate the factors that contribute to those streams.
Glaciers are sediment factories, ripping up hard rock, grinding it, and transporting the resultant sediments into new areas. These sedimentary deposits, known as till blanket Paleozoic rocks particularly in between Georgian Bay and Lake Ontario. Meltwater both within and in front of active ice sheets sorts this sediment by grain size making different types of deposits. Different glacial sediment types influence the ways in which land can be used and which resources are available for use. Groundwater, for example, flows preferentially through layers of more well-sorted sediment, while layers of till act as aquitards. We quarry gravel for use in construction from glaciofluvial sediment, but not from till. Glacial sediments in general tend to host productive farmland.
Guest lecturer: Shane Sookhan
By the end of this lesson, you will be able to
- Outline factors that cause glaciation and influence glacial flow.
- Use the geomorphological record to characterize the history of glacial activity.
- Compare glacial activity during the Pleistocene with the conditions of the Antarctic Glaciers today.
- Key terms: ice sheet, ice stream, drumlin, till, moraine, streamlined, lidar, drift