Chapter 7.3 Glaciers

Glacier Any large mass of ice that moves slowly over land. Two kinds: – Continental Glaciers – Valley Glaciers

Continental Glacier Any glacier that covers much of a continent or large island. Right now continental glaciers cover Antarctica and most of Greenland. Continental glaciers can flow in all directions, spreading out like pancake batter in the pan.

Ice Ages A time when continental glaciers covered larger parts of Earth’s surface, There have been many ice ages over the past 2 million years…the most recent ending only about 10,500 years ago.

Valley Glaciers This is a long, narrow glacier that forms when snow and ice build up high in a mountain valley. The sides of the mountains sides keep these from spreading out like the continental glaciers.

Continued… Valley glaciers tend to move down valleys that have already been cut by rivers. Although they are much smaller than continental glaciers, valley glaciers can still be tens of kilometers long.

Continued… High in mountain valleys, snow builds up year after year. The weight of the snow compacts the snow at the bottom into ice. Once the depth of snow and ice reach meters, gravity begins to pull the glacier downhill.

How Glaciers Shape the Land There are two process in which a glacier can erode the land: – Plucking – Abrasion

Plucking As a glacier flows over the land, it picks up rocks in a process called plucking. The weight of the ice beneath a glacier can break and pick up rocks. The rocks the freeze to the bottom of the glacier. The glacier then carries the rocks along with it.

Abrasion Many rocks remain on the bottom of the glacier. The glacier drags these rocks along. This process is called abrasion. Abrasion scratches and gouges the bedrock.

Glacial Deposition A glacier gathers a huge amount of rock and soil as it moves along the land in its path. When a glacier melts, it deposits the sediment it eroded from the land, creating various landforms. The mixture of sediments that deposits directly on the surface is called “TILL.”

Moraine The till that is deposited at the edges of a glacier forms a ridge called a moraine.

Kettle A kettle is a small depression that forms when a chunk of ice is left in glacial till. When the ice melts, the kettle remains Kettles often fill with water to create small ponds or lakes. These are called kettle lakes.