Planet Earth: The work of ice

How does ice shape the land?
In cold mountain areas, snow piles up in hollows. Gradually the snow becomes compacted into ice. Eventually, the ice spills out of the hollows and starts to move downhills to form a glacier. Glaciers are like conveyor belts. On the tops of glaciers are rocks shattered by frost action that have tumbled downhill. Other rocks are frozen into the sides and bottoms of glaciers. They give glaciers the power to wear away rocks and deepen the valleys through which they flow. Ice-worn valleys are U-shaped, with steep sides and flat bottoms. This distinguishes them from V-shaped river valleys.
Which are the world's largest bodies of ice?
The largest bodies of ice are the ice sheets of Antarctic and Greenland. Smaller ice caps occur in the Arctic, while mountain glaciers are found around the world.
What are erratics?
Erratics are boulders made of a rock that is different from the rocks on which they rest. They were carried there by moving ice.
When did the last ice age take place?
The last ice age began about 1.6 million years ago and ended 10,000 years ago. The ice age included warm periods and long periods of bitter cold.
What is an ice age?
During ice ages, average temperatures fall and ice sheets spread over large areas that were once ice-free. Several ice ages have occurred in Earth's history.
How can we tell that an area was once covered by ice?
Certain tell-tale features give this away. Mountain area contain deep, steep-sided valleys that were worn out by glaciers. Armchair-shaped basins where glaciers ice once formed are called cirques. Knife-edged ridges between cirques are called aretes, while peaks called horns were carved when three opr more cirques formed back-to-back. Boulders and other material carried by ice is called moraine. Moraine ridges show that ice sheets once reached that area.
What are fiords?
Fiords are deep, steep-sided valleys that wind inland along coasts. They were once river valleys that were deepened by glaciers during the last Ice Age.
How much of the world is covered by ice?
Ice covers about 10% of the world's land area. But during the last Ice Ages, it spread over much of northern North America and Europe. The same ice sheet reached what is now New York City in America, and covered London.