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What are glaciers?

Glaciers are large masses of ice that form over hundreds, or thousands of years from layers of compressed snow. They move very slowly and are sometimes referred to as ‘rivers of ice’.

Glaciers

There are two main types of glaciers, Valley glaciers and Continental glaciers.

Valley Glaciers

Valley Glaciers mainly form in cold mountain ranges where snow still accumulates, for example in the Alps. The glaciers then flow slowly down the valley.

Continental Glaciers

Continental Glaciers are extremely slow moving thick ice sheets that cover part of a continent, for example in Antarctica. In Antarctica ice forms a dome in the centre of the continent and extremely slowly moves down towards the edges of the ice sheet.

Valley glacier
Valley glacier
Continental glacier
Continental glacier

How do glaciers form?

There are two key requirements for glaciers to form:

Low temperature: for a glacier to form temperatures need to be low enough for snow to remain all year round, this is why glaciers tend to be found only at high latitudes (polar regions) and at high altitudes (in mountain ranges).

Snow: glaciers are formed from compressed layers of snow so an adequate supply of snow over a long period of time is required. As layers of snow accumulate they get squashed (compacted) and over time this turns into ice. Once the snow and ice become big enough the glacier starts to move very slowly under its own weight and the force of gravity.

Pine Island Glacier satellite view
Location of Pine Island Glacier
Pine Island Glacier satellite view
Pine Island Glacier satellite view
Skidoos and scientists on Pine Island Glacier
Skidoos and scientists on Pine Island Glacier

Glacier science: what is happening to Pine Island Glacier?

Pine Island Glacier in Antarctica is one of the largest glaciers in the world, and one of the most important because it is changing rapidly.

Pine Island is located on the West Antarctic Ice Sheet and is currently the most rapidly shrinking glacier on the planet.

ISTAR traverse image

It is around 2km thick but it has been thinning by more than 1 metre each year for the past 15 years. This means it has the potential to make a large contribution to sea level rise, particularly as the glacier is accelerating. In July 2013 a large iceberg broke away (calved) from the ice sheet. Scientists are investigating why the glacier is accelerating.

Some think that it may be due to warmer water melting the underside of the ice shelf.

Scientists are now trying to measure the rate of movement of the glacier but also the conditions around it in the sea, to try and find out why these changes are taking place.

The edge of the Pine Island ice shelf
Warmer water may be melting the underside of the ice shelf.
A crack in the Pine Island ice shelf
Cracks in the Pine Island ice shelf are evidence of movement.

To find out more have a look at the Exploring ice section.