Most areas of the Earth that experience snow in the winter see this snow melt to water with the coming spring. There are certain areas of the world, however, that are so cold, that the snow remains on the ground year-round. These areas are either at:

• high altitude (i.e., in mountainous areas like the Rockies)
• high latitude (i.e., Greenland or Antarctica)

In these cold areas, the snow will build up and compact over time, forming ice. Continued build-up of snow and ice will create enough pressure that the mass of ice will start to slowly flow under the influence of gravity. This mass of moving snow and ice is called a glacier.

Types of Glaciers

There are two main types of glaciers:

• Valley Glaciers: Valley glaciers are formed high in mountainous areas. They are usually seen as long rivers of ice that flow down from, or between, mountains.


The huge ice sheets covering Antarctica are the world’s biggest continental glaciers.
• Continental Glaciers: A continental glacier is a huge mass of snow and ice that covers an extremely large land area. Today, continental glaciers cover 10% of the Earth’s land surface, and can only be found in Greenland and Antarctica.

Ice Ages

Although continental glaciers are currently restricted to Greenland and Antarctica, this was not always the case in the past. Climate change throughout Earth’s history has resulted in large ice sheets covering many parts of the world that are currently ice-free. These periods of widespread ice cover are known as ice ages. Canada, for example, was almost entirely covered by thick ice sheets as little as 16,000 years ago.

• Click here to see the extent of the ice sheet covering North America 16,000 years ago.

(Further information about North America’s last ice age can be found in the unit activity for Unit A, “Investigating the Cryosphere: Analyzing Ice Cover – Past and Present”.)