Chapter 8, Section 2

What is a glacier?

Large mass of snow and ice that moves on land under its own weight.

Formation of Glaciers

Snow stays on the ground year-round.

Increasing weight of newer layers on top compress the bottom layers into ice.

When the force become large enough, the lower layers become plastic-like and begin to move.

Erosion and Deposition

As glaciers move, they erode the land underneath them and carry the material elsewhere.

Plucking Glacial ice melts and flows into cracks in rocks.

Water in the cracks freezes and expands.

The rock becomes fractured. Pieces of the rock are lifted out

by the moving glacier, resulting in boulders, gravel, and sand being added to the bottom and sides of the glacier.

Transporting

Glaciers can transport large volumes of sediment and rock.

Scouring As glaciers move, the plucked rock fragments carried in the glacier scrape and scour the soil and bedrock over which the glacier travels. Grooves

Deep, long, parallel scars on rocks. Striations

More shallow scars. Grooves and striations indicate

the direction a glacier was traveling.

Melting Glaciers

As glaciers melt, they begin to shrink or retreat.

As the glacier retreats, it cannot carry as much sediment so the sediment is deposited.

Till Unsorted mixture of boulders, sand, clay, and silt left behind by a retreating glacier.

Can cover huge areas of land (enough to fill in whole valleys).

Moraine Deposits

Till that is deposited at the end and sides of a moving glacier. Occurs because rocks and soil

are moved to the ends of the glacier (like groceries piling up at the end of a conveyor belt).

Outwash Deposit

Material that is carried by melting water from the glacier and then deposited in layers beyond the end of the glacier. Heavier sediments are deposited

first and so are closer to the glacier.

Fan-shaped deposits (like at the mouth of a river) can also form.

Eskers Long winding ridge of till. Forms in a melting glacier when

meltwater forms a river within the ice.

The river carries sand and gravel which are deposited within the river channel.

Continental Glaciers

Huge masses of ice and snow. Can be thicker than some

mountain ranges. Cover only 10% of the Earth.

Mostly located near the poles in Antarctica and Greenland.

Climate Changes

Extensive glaciers have covered large portions of the Earth many times over the last 2 to 3 million years.

These periods are known as ice ages. Average air temperature was about 5

degrees Celsius colder than today. Continental glaciers covered as much

as 28% of the surface of the Earth. The last ice age hit its maximum

extent about 18,000 years ago.

Valley Glaciers

Form in high mountains where snow does not melt in the summer.

Evidence of Valley Glaciers

Striations Plucking Cirques

Bowl-shaped basins eroded into the side of the mountain by a valley glacier.

Arête Long ridge eroded between two valley

glaciers. Horn

Sharp peak eroded by many valley glaciers.

U-shaped Valleys (Streams and rivers form V-shaped

valleys.)

Affects of Glaciers

Greatly change the landscape of the Earth.

Leave behind economically important sediments such as sand and gravel deposits