When British explorers explored Alaska's Prince William Sound in 1794, the Columbia Glacier reach down from the Chugach Mountains southward until it reached Heather Island. That's how the glacier remained until 1980, when it began rapidly retreating up the valley. Above is a false-color picture NASA's Thematic Mapper on the Landsat 5 satellite captured of the glacier in 2011. Below, for comparison, a picture taken by the same instrument in 1986. In the pictures, snow and ice appear in blue, vegetation is green, the ocean is dark blue, clouds are white or light orange, bedrock is brown, and rocky detritus is gray. The great increase in bedrock between 1986 and 2011 is the clearest indication of the dramatic change that has taken place. The 2011 image was taken in May and thus has more snow than the 1986 image which was captured in July. Over the past decades, the glacier has retreated more than 12 miles and thinned out, losing about half of its total thickness and volume, according to NASA.
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