Glaciers

Glacial Ice

• A glacier begins when snow doesn't completely melt away during the summer. Each winter new snow falls on top of the old snow. Thick layers of snow are gradually compressed into glacial ice.

Glacial Sediment

• Glaciers are made up of more than just ice and snow. They contain water, rocks and sediments. This can make the ice look very dirty.

Glacial Movement

• A glacier might look like a solid block of ice, but it is actually moving very slowly. The glacier moves because pressure from the weight of the overlying ice causes it to deform and flow. Meltwater at the bottom of the glacier helps it to glide over the landscape.

Glaciers move very slowly. Most of the time they only advance a few centimetres to a few meters each day. Occasionally a glacier speeds up. This is called surging. A surging glacier can advance tens or even hundreds of meters a day.

Glacial Meltwater

• Meltwater streams begin in tunnels under the ice. Meltwater carries rock, gravel, sand and mud away from the glacier. The debris is transported and deposited by rivers and in lakes.

Ice Shelves• Ice shelves form when

glaciers reach the sea and begin to float. The Ross Ice Shelf in Antarctica is a famous ice shelf.

• Chunks of ice can break off an ice shelf or a glacier that reaches the sea. This is called calving. The ice chunks form icebergs up to 250 km long and 100 km wide.

Moraines

• Piles and ridges of sediment deposited at the edges and front of glaciers are called moraines.

• Lateral moraines form along the sides of alpine glaciers.

• A medial moraine forms where two glaciers join together.

There are different types of glaciers:

• Alpine glaciers begin high up in the mountains in bowl-shaped hollows called cirques. As the glacier grows, the ice slowly flows out of the cirque and into a valley. Several cirque glaciers can join together to form a single valley glacier. When valley glaciers flow out of the mountains, they spread out and join to form a piedmont glacier.

• Continental glaciers are continuous masses of ice that are much larger than alpine glaciers. Small continental glaciers are called ice fields. Big continental glaciers are called ice sheets. Greenland and Antarctica are almost entirely covered with ice sheets that are up to 3500 m (11 500 ft) thick.