What are Glaciers?

Michael Anissimov
Michael Anissimov

A glacier is a large, slow-moving river of ice, formed by many layers of compacted snow. The rate of motion varies greatly, depending on the ambient temperature, depth of the ice, the underlying slope, and other factors. Movement ranges from several meters per hour to several meters per century. Sometimes, when conditions are just right, glaciers experience a surge, accelerating their rate of movement by as much as 100 times. When glaciers surge, they can be a danger to humans, triggering avalanches of rock and snow.

Greenland is almost completely covered by continental glaciers.
Greenland is almost completely covered by continental glaciers.

Glaciers can be found on every continent and in about 47 countries. Most mountains taller than 4,500 meters (14,800 ft) have them, because temperature tends to quickly drop with altitude. There are two main categories of glacier: alpine glaciers, on mountains, and continental glaciers, on flat land where it is very cold. Continental glaciers almost completely cover Greenland, parts of Iceland, northern Siberia and Canada, and most of Antarctica. About 70% of fresh water on the planet can be found in the Antarctic ice sheet alone.

Mountains above 14,800 feet tend to have glaciers.
Mountains above 14,800 feet tend to have glaciers.

Glaciers are present year-round, but vary in their rate of melting. For a pack of ice to qualify as a glacier, it exist continually rather than just seasonally. For reasons that are not completely clear, the planet has experienced several major Ice Ages in its history, when glaciers extended as far south as New York, USA and Paris, France. So many glaciers piled up that the sea level was lowered by 100 m (328 ft), opening up large areas of land such as the North Sea, the Bering strait, and connecting New Guinea to the Southeast Asian mainland.

At one point in the distant past, about 700 million years ago, during the Cryogenian Period, some scientists believe glaciation may have been so severe than the entire planet was covered in an ice sheet. This has been called the Snowball Earth Hypothesis, and it is controversial, especially among scientists who doubt the geophysical feasibility of a completely frozen ocean. What is known is that the glaciers at this time were extremely large in extent, reaching the Equator in at least some areas. Interesting to note is that the first complex multicellular organisms, the Edicaran biota, appear in the fossil record almost immediately after the glaciations of the Cryogenian.

Michael Anissimov
Michael Anissimov

Michael is a longtime wiseGEEK contributor who specializes in topics relating to paleontology, physics, biology, astronomy, chemistry, and futurism. In addition to being an avid blogger, Michael is particularly passionate about stem cell research, regenerative medicine, and life extension therapies. He has also worked for the Methuselah Foundation, the Singularity Institute for Artificial Intelligence, and the Lifeboat Foundation.

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Discussion Comments


I'm doing a report on glaciers and the ice age and this website really helped me out! I can't find anything about the cause of the ice age though.


i was doing a project about melting glaciers. This kind of helped.


glaciers are made of snow that accumulated over thousands of years and contains sediments of rocks, dirt, trees, etc.


i am doing an essay on glaciers, and for the opening paragraph i have to talk about how glaciers are made? Anyone have any ideas?


A glacier is an object, an avalanche is an abrupt event.


What is the difference between glaciers and avalanches?

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