GLACIERS A glacier is: • Any large mass of ice that moves slowly over land
Two Kinds of Glaciers • Valley glacier – a long narrow glacier that forms when snow and ice build up high in a mountain valley • Continental glacier – a glacier that covers much of a continent or large island
Valley Glaciers • Found in high mountain ranges such as the Rockies, Alps, and Himalayas • These glaciers move down valleys that have already been cut by rivers
Continental Glaciers • Much larger than valley glaciers • Cover about 10 percent of Earth’s land • Examples: Antarctica and most of Greenland are covered by continental glaciers
How Glaciers Form… • A glacier can only form in an area where more snow falls than melts. This is because the temperatures seldom rise above freezing and layers and layers of snow compact into ice. • Once the depth of snow and ice reaches more than 30 to 40 meters, gravity begins to pull the glacier down.
How Glaciers Move… • Valley glaciers flow at a rate of a few centimeters to a few meters per day. Sometimes, a valley glacier slides down more quickly in what is called a surge. • Continental glaciers can flow in all directions and spread out much as pancake batter spreads out in a frying pan.
Two Processes of Glacial Erosion… • Plucking – as a glacier flows over the land, it picks up rocks; the weight of the ice breaks the rocks apart and they freeze to the bottom of the glacier • Abrasion – the many rocks that remain on the bottom of the glacier get dragged across the land, causing gouges and scratches in the bedrock
Glacial Deposition • When a glacier melts, it deposits the sediment it eroded from the land, creating various landforms. • The mixture of sediments that a glacier deposits directly on the surface is called till. • Clay, silt, sand, gravel, and boulders can all be found in till.
Glacial Deposition • A moraine forms when the till is deposited at the edges of a glacier and forms a ridge • It is made up of a mixture of particles of different sizes: from sand and gravel to boulders.
History of the Great Lakes • The continental glacier of the last ice age formed the Great Lakes. • Before the ice age, there were large river valleys in the area now occupied by the lakes. • As the ice advanced over these valleys, it scooped out loose sediment and soft rock, forming broad, deep basins. • The Great Lakes formed over thousands of years as the glaciers melted and the basins filled with water.
Videos about Glaciers • Watch the following video segments. Click on the hyperlink below to go to the videos. • Glacial Erosion • Tumble Glacier Video
Exploring Glacial Landforms • Go to pages 92-93 in your textbook. Study the glacial landforms pictures and answer the questions on your sheet.