Icefall
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An icefall is a phenomenon found in some glaciers. When a valley glacier proceeds over a ledge or a cliff, the resulting formation is known as an icefall.
It has been said that an icefall is much like a waterfall, only very much slower. Indeed, it is true that the word icefall is formed by analogy with the word waterfall.
As slow as glaciers generally are, the relative speed of the ice in an icefall is very much faster than other parts of the glacier, although the movement is still imperceptible at most times. However, there are sometimes sudden shifts, in which substantial amounts of ice can fall down in a matter of seconds.
Icefalls generally have a cracked and much less smooth appearance than the rest of the glacier. They also vary greatly in height. There is one at the Lambert Glacier in Antarctica which is about 400 m high (photo at left). A smaller icefall is to be found on the Athabasca Glacier in Banff National Park in Alberta, Canada (photo at right).
Icefalls are often the object of an ice climber's visions of conquest. There are popular icefalls for climbers in many glaciated regions. Perhaps the most popular of all is the Khumbu Icefall on the Nepalese side of Mount Everest, variously described as "treacherous" and "dangerous". It is about 5 500 m above sea level.