The Columbia Glacier in Alaska descends from an ice field 3,050 metres above sea level down the flanks of the Chugach Mountains and into a narrow inlet that eventually leads into Prince William Sound in the southeast of the state. And it is one of the most rapidly changing glaciers in the world.
The NASA Earth Observatory recently posted two images on its website, the first taken in 1986 and the second in 2011, and I really encourage you to go and look. They show the same location and they’ve provided a function by which you can combine the images to view the changes.
The two false coloure images were captured by the Thematic Mapper instrument aboard the Landsat 5 satellite and show the glacier and surrounding landscape in 1986 and 2011. Snow and ice appear bright cyan, vegetation is green, clouds are white or light orange, and the open ocean is dark blue. Exposed bedrock is brown, while rocky debris on the glacier’s surface is gray. The 2011 image has more snow because it was captured in May, while the 1986 image was captured in July.
The terminus of the Columbia Glacier in 1986 was only a few kilometres north of Heather Island, but by 2011 that terminus had retreated by more than 20 kilometres to the north. Over the time that the glacier has retreated, it has also thinned considerably, as shown by the increased amount of brown bedrock in the images.
The retreat has also changed the way the glacier flows. The medial moraine, a line of debris deposited when separate channels of ice merge (seen here as a line in the center of the 1986 image) served as a dividing line between the Main Branch and West Branch of the glacier. By 2011, the retreating terminus had essentially split the Columbia into two glaciers, causing calving to occur on two fronts.