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.