Erosion and Deposition by Ice

Objectives • Explain the difference between alpine

glaciers and continental glaciers. • Describe two ways in which glaciers

move. • Identify five landscape features

formed by alpine glaciers. • Identify four types of moraines.

Glacier National Park

I. Glaciers: Rivers of Ice A. A glacier is a large mass of moving ice. They are capable of eroding, moving, and depositing large amounts of rock materials.

B. Glaciers form in areas so cold that snow stays on the ground year-round. Because glaciers are so massive, the pull of gravity causes them to flow slowly, like “rivers of ice.”

Glaciers

Elephant Foot Glacier in Greenland

I. Glaciers: Rivers of Ice continued C. Alpine Glaciers form in mountainous areas. One common type of alpine glacier is a valley glacier.

D. Valley glaciers form in valleys originally created by stream erosion. As these glaciers slowly flow downhill, they widen and straighten the valleys into broad U shapes.

I. Glaciers: Rivers of Ice continued E. Continental Glaciers are huge, continuous masses of ice that can spread across entire continents.

F. The largest continental glacier in the world covers almost all of Antarctica. This ice sheet is approximately one and a half times the size of the United States, and is more than 4,000 m thick in some places.

Pine Island Glacier (Antarctica)

I. Glaciers: Rivers of Ice continued

F. Glaciers on the Move When enough ice builds up on a slope, the ice begins to move downhill. Thick glaciers move faster than thin glaciers, and the steeper the slope, the faster the glaciers will move.

G. Glaciers move in two ways: sliding and flowing. A glacier slides when its weight causes the ice at the bottom to melt. A glacier flows as ice crystals within the glacier slip over each other.

I. Glaciers: Rivers of Ice continued

H. Glacier movement is affected by climate. As the Earth cools, glaciers grow. About 10,000 years ago, a continental glacier covered most of North America.

II. Landforms Carved by Glaciers A. Continental glaciers and alpine glaciers produce landscapes that are very different from one another.

B. Continental glaciers smooth the landscape by scraping and eroding features that existed before the ice appeared.

C. Alpine glaciers carve out large amounts of rock material and create spectacular landforms.

III. Types of Glacial Deposits

A. As a glacier melts, it drops all the material it is carrying. Glacial drift is the general term used to describe all material carried and deposited by glaciers.

B. Glacial drift is divided into two main types, till and stratified drift.

III. Types of Glacial Deposits continued

C. Till Deposits Unsorted rock material that is deposited directly by the ice when it melts is called till. Unsorted means that the till is made up of rock material of different sizes.

D. The most common till deposits are moraines. Moraines generally form ridges along the edges of glaciers.

III. Types of Glacial Deposits continued E. Stratified drift is a glacial deposit that has been sorted and layered by the action of streams or meltwater.

F. Streams carry sorted material and deposit it in front of the glacier in a broad area called an outwash plain.

G. Sometimes, a block of ice is left in an outwash plain when a glacier retreats. As the ice melts, sediment builds up around the block of ice, forming a depression called a kettle.