Glaciers
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Transcript of Glaciers
1. Glacier A thick ice mass that forms over
hundreds or thousands of years Cover nearly 10% of Earth’s land area Form in regions where more snow falls
each winter than melts in the summer Flow downhill Agents of erosion and important part
of the rock cycle
Valley glaciers – ice masses that slowly advance down valleys that were originally occupied by streams
Ice sheets – enormous ice masses that flow in all directions from one or more centers and cover everything
Greenland – 80% is covered with ice Antarctica – the glacier is nearly 4300 m
thick, accounts for 80% of the world’s ice and holds nearly 2/3 of the world’s fresh water.
2. Movement of Glaciers Plastic flow – pressure causes the brittle
ice to distort and change. The ice flows. Basal slip – the entire ice sheet slips and
slides downhill in response to gravity Above the snowline, a glacier forms where
more snow falls in winter than melts in summer. This is called the zone of accumulation.
In the zone of wastage the glacier loses ice to melting.
Glaciers also lose ice in a process called calving. This produces icebergs. Only 10% of the iceberg is visible.
3. Glacial erosion Plucking – blocks of rock are frozen in the
ice and flow with the glacier. Abrasion – the glacier slides on the bedrock
smoothing and polishing the surface The pulverized rock is as fine as flour and
the meltwater leaving the glacier has a milky consistence.
4. Glacial Landforms Glacial trough – U shaped valley
Hanging valleys – some side valleys are left higher when the glacier retreats and this produces spectacular water falls
Cirques – bowl-shaped depressions at the head of the glacier
Aretes – saw-toothed ridges
Horns – sharp pyramid shaped peaks
5. Glacial drift Till – sediments deposited directly by
glaciers, unsorted
Stratified drift – sediment laid down by glacial meltwater, sand and gravel
Glacial erratics – large boulders found lying on the ground (different material than bedrock)
6. Moraines – when glaciers melt layers or ridges of till are left
Lateral moraine – ridges of till that form along the side of glacial valleys
End moraines – deposits of till that forms at the end of the glacier
Ground moraines – the glacier deposits sediment as the ice melts, fills in low spots and clogs old stream channels resulting in poorly drained swamp lands
Terminal and recessional moraines – end moraines formed during stationary periods of glacial advance or retreat
7. Other Glacial Depositional Features
Outwash plains – streams emerging from the glacier slow and drop sediment
Kettles – form when buried blocks of ice melt
Drumlins – streamlined hills of stratified drift, the steep side faces the direction the ice came from
Eskers – snake-like ridges of composed of sand and gravel that were deposited by streams once flowing in tunnels beneath glaciers
8. Glacial Ice Ages In the most recent ice age, glaciers covered
about 30% of the Earth Pleistocene epoch
9. Impact on Drainage Formation of the Great Lakes Basin and Range region of Utah and Nevada
was once filled with a large lake – Lake Bonneville. The Great Salt lake is remnants of that glacial lake.