Columbia Glacier, Alaska
The Columbia Glacier descends from an ice field 10,000 feet (3,050 meters) above sea level, down the flanks of the Chugach Mountains, and into a narrow inlet that leads into Prince William Sound in southeastern Alaska. It is one of the most rapidly changing glaciers in the world. Changes to the Columbia Glacier were tracked over more than 30 years using data from Landsat 4, 5, 7, and 8 data.
The Columbia is a large tidewater glacier, flowing directly into the sea. When British explorers first surveyed it in 1794, its nose—or terminus—extended south to the northern edge of Heather Island, a small island near the mouth of Columbia Bay. The glacier held that position until 1980, when it began a rapid retreat that continues today.
False-color images, captured by Landsat satellites, show how the glacier and the surrounding landscape has changed since 1986. The images were collected by similar sensors—the Thematic Mapper (TM), the Enhanced Thematic Mapper Plus (ETM+), and the Operational Land Imager (OLI)—on four different Landsat satellites (4, 5, 7, and 8).
The Landsat images combine shortwave-infrared, near-infrared and green portions of the electromagnetic spectrum. With this combination of wavelengths, snow and ice appears bright cyan, vegetation is green, clouds are white or light orange, and open water is dark blue. Exposed bedrock is brown, while rocky debris on the glacier's surface is gray.
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Credit: NASA/USGS/Landsat/Jesse Allen and Robert Simmon