Presentation on theme: "CGC 1D1-03 Canadian Geography Glaciation of Canada: Characteristics of Glaciers."— Presentation transcript:
CGC 1D1-03 Canadian Geography Glaciation of Canada: Characteristics of Glaciers
In the Beginning… Ice Age: period of time when freezing temperatures created ice sheets across continents. Glaciers covered most of Canada and the northern U.S. The last Ice Age ended between 6000 and 10000 years ago. The last Ice age began between one and two million years ago. Ice sheets covered almost all of Canada and parts of the United States, Europe, and South America during each of its glacial advances. Enormous volumes of the world’s water were frozen in these ice sheets. The caused the level of the oceans to fall well below current levels.
A period of glacial activity begins when the earth’s climate cools, and the snow that fall’s in winter does not completely melt in the summer. Over thousands of years, the snow gets deeper and becomes hundreds thousands of meters thick. The tremendous weight of the snow on top causes the bottom layers to turn to ice. The most remarkable fact about a glacier, other than its tremendous size, its that it can move. Solid ice acts like a very thick liquid, and moves along or flows very slowly. During the last Ice Age, glaciers advanced and retreated at least four times. Between each period of glacial activity, the climate was as warm, or warmer than today. Why did such a cycle occur ?
Retreat of the Last Ice Age
Ice sheet: very large thick mass of glacial ice (1000-4000 m thick) flowing outward in all directions from a zone of accumulation. Glacier: slow moving mass of ice. Glacial ice covers 11% of the earth’s surface. Advance of glacier: forward glacial movement. If more snow accumulates than melts, a glacier will advance. Retreat of glacier: shrinking of a glacier, caused when the rate of melting is greater than the rate of snow build-up.
Glaciers move in different ways, depending upon their location and the climate. In mountainous regions, alpine glaciers move down valleys from high elevations to low elevations under the force of gravity. Alpine glaciers sharpen the upper portions of the mountains and give them a rugged appearance. When they move down valleys, they scrape away the valley walls to produce a U-shaped valley. Alpine glaciers exist today in Canada in parts of the Western Cordillera and the Artic islands. The Columbia Icefield is a mass of ice located in Banff/Jasper National Park. It contains 30 glaciers covering about 300km2 to depths of 365 m. Waters from this icefield flow into three different oceans. Tourists from all over the world come to enjoy the beauty created by glacial activity.
Continental glaciers are different from alpine glaciers in that they occupy greater areas of land, and move under their own weight. During the last glacial advance some areas of the ice sheet reached a thickness of 1000m to 4000m! The enormous weight of snow and ice causes the ice to expand outward from its centre or zone of accumulation. The ice of a continental glacier is constantly moving outward, the outer edge or margin of the ice sheet may advance, retreat, or stay in one place. Continental glaciers give the landscape a smoother appearance by eroding higher points on the land and filling in lower areas with the eroded material.
Alpine glacier: glacier occupying one or more valleys in an alpine region (valley glacier). Zone of accumulation: part of the glacier where snow builds up and turns to ice. The glacial ice moves outward from here. Continental glacier: glacier that spreads out to cover a large portion of a continent (Greenland and Antarctica). During the last ice age, huge glaciers formed in northern Canada (Laurentide and Cordilleran) and moved southward.
How can glaciers carve valleys?
The Glaciation of Canada Glaciation is the process most responsible for the topography that we see in Canada today. There are two reasons for this: 1. Glaciation is an extremely powerful force. 2. Glaciation happened very recently in geologic terms, and there has not been enough time for glacial features to be worn away. The massive weight of ice sheets compressed the land downward and gouged the land. When the ice melted, the land rebounded upward, but at a relatively slow rate. In fact, this rebound continues today in much of Canada. To see the effects that the ice sheets had on the landscape, we will examine: 1. Features caused by erosion. 2. Features that were deposited.
Erosional Features Caused by Glaciation Striation: a groove gouged out in the bedrock under the ice sheet by rocks frozen in the ice.
Erosional Features Caused by Glaciation Misfit stream: small stream created by a glacial melt flowing in the much larger U-shaped valley.
Deposited Features Caused by Glaciation Moraine: material deposited by a glacier, often in the form of hills.
Deposited Features Caused by Glaciation Erratic: a rock picked up by the ice, carried along, and deposited many km’s away.
In the End… For thousands of years, glaciers have sculpted the Canadian landscape, and there is no reason why an ice age should not occur again. We know that average yearly temperatures would need only to drop about 4 degrees C! However, it is safe to say that many questions about ice ages and climate change remain unanswered. Food for thought? How does global warming impact the local, regional, and global environment? Where could you locate more information about glaciers?
Bibliography Clark, B.W., and Wallace, J.K. (1999) Making Connections: Canada’s Geography. Prentice Hall Ginn Canada, 118- 126.