Glacial Landscapes - What is a Glacier?

A glacier consists of fallen snow that over many years has been compressed into a large, dense ice mass.

How glaciers form

Air between snowflakes is compressed and pushed out in order to turn it into ice. Each year, new layers of snow form on the glacier’s upper surface and compress the lower layers. This compression forces the snow to re-crystallize, forming grains similar in size and shape to grains of sand.

Gradually the grains merge and the air pockets between the grains get smaller, causing the snow to slowly compact and increase in density. After two winters, the snow turns into firn—a state between snow and glacier ice. At this point, it is about two-thirds as dense as water.

Over time, larger ice crystals become so compressed that any air pockets between them are very tiny; this eventually turns into the characteristic clear, hard, blue glacier ice. For most glaciers, this process takes more than a hundred years.

Glaciers - key features

Glaciers move due, largely, to the effect of gravity; they flow downhill like very slow rivers. The size of glaciers can vary too, with some being smaller than a football field and others being as long as several hundred kilometres.

Glaciers cover 10% of the world’s land area. Most glaciers are located in Greenland, Antarctica and Canada due to their high latitude and reduced insolation from the sun. They are also found in high altitude mountain ranges, such as the Himalayas.

There are different types of glacier, including:

Valley glaciers - glaciers which follow river valleys in high altitude areas

Piedmont glaciers - glaciers which emerge from a valley and spread out onto an open plain

Ice caps and sheets - glaciers covering much larger areas of land mass