The+Glaciation+of+Canada

The Glaciation of Canada

[[file:The Glaciation of Canada.rtf|THE GLACIATION OF CANADA Document]]
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 the glacial features to be worn away.

 To see the effects that the ice sheets had on the landscape, we will examine

 a) features caused by erosion  b) features deposited  i. directly by the ice sheets  ii. by meltwater from the ice sheets

 Glacial Features Caused by Erosion
 The continental ice sheets were often several kilometres thick. As they advanced, they expanded existing river valleys. These deeper and wider troughs are known as U-shaped valleys and are similar to those formed by alpine glaciers. The ice also gouged out the basins of existing lakes making them deeper and wider. The Great Lakes were formed in this fashion.

 As the ice sheets moved, they eroded huge amounts of soil, sand, gravel, and rock. This material was carried by the ice and acted like sandpaper as it scraped and ground away the surface of the land. Grooves called striations were often gouged out in the bedrock under the ice sheet by rocks frozen in the ice. Striations are often visible on the bare rock of the Canadian Shield. They run in the same direction as the movement of the ice sheet, and allow geographers to determine its path.

1. What direction to you think the ice travelled as the ice age was ending? Explain why you think that way.

 Have you ever looked at a wide valley with a tiny stream and asked yourself how such a small river could cut such a big valley? Chances are that glacial meltwater formed the valley. Huge volumes of meltwater carved out deep, wide valleys called spillways. Once the ice sheets melted away, these spillways became the pathways for small present day rivers, called misfit streams.

 ICE DEPOSITS
<span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 150%;"> Till is material such as clay, sand, and gravel that is deposited directly by an ice sheet. It is unsorted; that is, large and small particles are all mixed together. The rock fragments have angular or pointed shapes because they have not been rounded by running water.

<span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 150%;"> Sometimes the till deposited under the ice, formed a gently rolling landscape called a till plain. Till plains are very good for growing crops because deep, well-drained soil developed here. Sometimes an ice sheet deposited ridges of till at its edge. These ridges of till are known as moraines. Moraines are not very good for growing crops because they are thin-soiled, hilly, and swampy. Moraines are better suited for grazing and forestry. A well-known moraine runs between Orangeville and Trenton in southern Ontario.

<span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 150%;"> Ice sheets formed other features which are evident today on Canada's landscape. One that is particularly recognizable is a drumlin, an egg-shaped hill (as seen from above) with a steep side at the wide end, and a gentle slope on the other. The steep side points in the direction that the glacier came from. Drumlins usually occur in clusters called drumlin fields. A large drumlin field is located near Peterborough, Ontario and another smaller one is located near Hamilton, Ontario. Farmers often plant crops on drumlins because the soil is deep and well-drained.

<span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 150%;"> As they moved forward, the ice sheets often picked up large rocks and carried them hundreds of kilometres. These rocks are called erratics. For example, rocks from the Canadian Shield were picked up by the ice, carried along, and deposited many kilometres away in the surrounding lowlands. They can often be identified because they are made of rock which is different from the bedrock of the region in which they were deposited.

<span style="background-color: #e4e2e2; font-family: 'Arial Black',Gadget,sans-serif; font-size: 150%;">2. What effect of glaciation had the most beneficial effect for farming in Canada?

<span style="background-color: #d8b6b6; font-family: 'Arial Black',Gadget,sans-serif; font-size: 150%;"> MELTWATER DEPOSITS
<span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 150%;"> Running water played an important role in the deposition of glacial material. Rivers flowing within or under melting ice carried sand and gravel along with them and laid down this material in the river bed. When the ice sheet melted, the material that had been deposited in the river bed was left as a steep-sided ridge winding across the countryside. This is called an esker. The esker follows the path of the river that created it thousands of years ago. Today, eskers are a source of sand and gravel for the construction industry.

<span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 150%;"> Materials carried off the ice sheet by meltwater were sorted, smoothed, and rounded by the running water. The action of the moving water deposited larger rock particles in one layer and the smaller rock particles <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 20px; line-height: 29px;">in another. Today you might find a deposit of coarse gravel where a fast-moving glacial stream once existed, or silt where a glacial lake once was. About 14 000 years ago, the climate became warmer and the glaciers started to melt. Enormous amounts of meltwater flowed into lakes along the margins of the ice. Some of these lakes, known as glacial ponds, were small. Others, like Lake Agassiz in Manitoba, were larger than any lake in the world today. The Great Lakes were also much larger than their present size. Today, the fertile flat lake plains that were once the bottom of ancient glacial lakes are used for agriculture. You may also find fine clay in an area that was once a glacial lake.

<span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 150%;"> As the glaciers melted, the sea rolled in and covered large areas of depressed land in the St. Lawrence River Valley. Today, these areas are dry, but you can see beaches and sand dunes now located far above current sea levels. By about 6000 years ago, the last Ice Age had come to an end, and the Canadian landscape as we know it was visible.

<span style="background-color: #e4e2e2; font-family: 'Arial Black',Gadget,sans-serif; font-size: 150%;">3. What effect did running water have on the landscape? What industry benefits from this today?