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The Columbia Glacier descends from an icefield 3,050 meters (10,000 feet) 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.
As the glacier terminus has retreated, the Columbia has thinned substantially, as shown by the expansion of brown bedrock areas in the Landsat images. Since the 1980s, the glacier has lost more than half of its total thickness and volume. Rings of freshly exposed rock, known as trimlines, become especially prominent around the inlet throughout the 2000s.
Between 2007 and 2010, part of the terminus began to float as it passed through deep water between the Great Nunatak Peak and Kadin Peak. This changed the way icebergs calved significantly. When the Columbia was grounded, calving occurred at a fairly steady rate, and the bergs that broke off were small. When the glacier began to float, larger chunks of ice tended to break off, as seen in the image from 2009.
The retreat has also changed the way the glacier flows. In the 1980s, there were three main branches. 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 two of the main branches. In 1986, there was a branch to the west of the medial moraine (West Branch), a large branch that flowed to the east of it (Main Branch), and a smaller branch that flowed around the eastern side of Great Nunatak Peak.
As the Columbia lost mass and thinned, the flow in the smallest branch stalled, reversed, and eventually began flowing to the west of Great Nunatak Peak. By 2011, the retreating terminus essentially split the Columbia into two separate glaciers, with calving now occurring on two distinct fronts.
The West Branch was thought to have stabilized by 2011, but it surprised scientists with an unexpected retreat that shows up in the 2013 image. By 2019, scientists again thought the branch could be at the limit of its retreat. But until the glacier can be visited in person, they cannot say for sure.
In 2014, researchers found that the Main Branch had thinned so much that it no longer had traction against the bed. With less traction, the glacier can be affected by tidal motion as far as 12 kilometers (7.5 miles) upstream, leaving the Main Branch unstable again. The branch resumed retreat, and in 2019 shed ample icebergs during an anomalously warm summer.
The retreat of the Columbia Glacier contributes to global sea-level rise, mostly through iceberg calving. This one glacier accounts for nearly half of the ice loss in the Chugach Mountains. However, the ice losses are not exclusively tied to increasing air and water temperatures. Climate change may have given the Columbia an initial nudge off of the moraine, but mechanical processes help drive its disintegration. When the Columbia reaches the shoreline, its retreat will likely slow down. The more stable surface will cause the rate of calving to decline, making it possible for the glacier to start rebuilding a moraine and advancing once again. 041b061a72