Columbia Glacier (Alaska)

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Columbia Glacier
Columbia Glacier from Prince William Sound.
Type	Tidewater Glacier
Location	Descending from the Chugach Mountains to Prince William Sound, Alaska.
Coordinates	60°59′42″N 147°04′07″W / 60.995, -147.06861
Area	1,000 km² (400 sq mi)
Length	51 kilometres (32 mi)
Thickness	550 m (1,800 ft)
Terminus	Sealevel (Prince William Sound)
Status	Retreating

The Columbia Glacier is a glacier in Prince William Sound on the south coast of the U.S. state of Alaska. It is one of several glaciers in the area named for elite U.S. colleges, in this case Columbia University, and was named by the Harriman Alaska Expedition in 1899. It is one of the fastest moving glaciers in the world, and has been retreating since the early 1980s. The glacier at the present terminus is approximately two kilometers wide, and 550 meters thick, of which approximately 70 meters stands above sea level. The glacier is approximately 1,000 square kilometers in area and as of September 2006 approximately 51 kilometers in length, of which the last 15 kilometers rests on bedrock below sea level. Like all Alaskan tidewater glaciers, the ice is not floating but is resting on bedrock below sea level, with a significant fraction of its weight supported by buouyancy. Speed at the terminus reached a maximum of nearly 30 meters per day in 2001, when the glacier was discharging icebergs at approximately seven cubic kilometers per year; the glacier has subsequently slowed down, resulting in an increase in retreat rate. The terminus has retreated a total of 16 kilometers at an average rate of approximately .6 kilometers per year since 1982. Retreat has been accompanied by nearly 500 meters of thinning at the present position of the terminus. In the next few decades it is expected to retreat another 15 kilometers, to a point where the bed of the glacier rises above sea level. Tidewater glacier advance and retreat is not directly forced by climate (adjacent tidewater glaciers may be simultaneously advancing and retreating), but rapid retreat appears to be triggered by climate-forced long-term thinning ^[1].

The Alaska Marine Highway vessel M/V Columbia is named after the Columbia Glacier.