AR ZONE
GROWING GLACIERS
How these vast ice flows form, grow and why they vanish
WORDS SCOTT DUTFIELD
Glaciers are made up of compacted snow, rocks and sediment that over millennia has formed sheets of dense ice on land. Every one of the 98,000 glaciers that remain on Earth are the frozen leftovers of the last ice age, which occurred during the Pleistocene epoch between 2.6 million and 11,700 years ago. There are many different types of glaciers on Earth, such as continental ice sheets and alpine glaciers that descend from mountaintops and shape the rocks they pass through.
Over the course of the last ice age, new layers of ice formed and compressed the previous layers, creating ever-growing glaciers. During the formation of a glacier, the compressed snow will transform into firn, a compressed and crystalline form of ice that is around two-thirds as dense as water. At this point, firn is held under so much pressure that it reaches a density of 917 kilograms per cubic metre and becomes pure glacier ice – for comparison, fresh snow has a density of 50 to 70 kilograms per cubic metre. Firn’s transformation takes up to 300 years.