Glacier Movement: How Glaciers Move

1. Glacier Movement: How Glaciers Move • The weight of overlying layers of ice and snow push down on the lower layers of the glacier. • This causes melting and refreezing, and thus movement downhill • Some glaciers move only a few cm’s per day, others move as much as 3000 cm per day.

2. Glacial valleys have steep and gentle slopes. • When a valley glacier comes to a steep slope, great fissures called crevasses form across the width of the glacier.

3. Glaciers Move • Glaciers become thinner as they move lower due to melting and evaporation. • The glacier ends at its ice front. • Many glaciers worldwide have receding ice fronts, as the glacier melts faster than it moves forward. • In Alaska and Greenland, many glaciers reach the sea and great blocks break off to become icebergs in a process called calving. • In Antarctica, the ice may extend under water in ice shelves.

4. Glacier Calving in Alaska

5. Glaciers Transport Loose Rock • Glaciers remove loose rock from the valleys through which they move. • Particles range in size from fine powder to giant boulders. Rock flour is a mix of fine sand and silt formed under a glacier. • Large amounts of rock material build up in several areas of a moving glacier. • When these materials are deposited they form moraines. • There are: ground moraines (under glacier), lateral (side) moraines, medial (middle) moraines, and end moraines (at the ice front).

7. Erosion by Glaciers • Glaciers erode mostly because of pieces of rock that are dragged over the bedrock and act as cutting tools. • Long scratches called striations are left on the rock, and show the general direction of ice movement.

8. Bedrock can be shaped into many forms by glaciers. • Bedrock may become smooth and polished, or steep and rough. • Roches moutonnées are rough outcrops. • Potholes may form from meltwater forming whirlpools under a crevasse. Roche moutonnées

9. Frost action and glacial erosion wear away the walls of mountain peaks. • A semicircular basin called a cirque is formed at the head of a glacial valley. • When two cirques are formed next to each other they can create a narrow and sharp divide, called an arête. • When three or more cirques cut into the same peak they can create a pyramid shaped peak, called a horn.

10. Glacial Valleys • A valley glacier touches the entire valley and most of the walls. • The glacier scours away the rock until it flattens the entire valley floor and make the walls nearly vertical, creating a glacial trough.