Alaska's Excelsior Glacier Is Being Replaced by a Lake 5 Times the Size of Central Park

excelsior glacier
Three Landsat satellite images show how Alaska's Big Johnstone Lake doubled in size from 1994 to 2018. According to glaciologist Mauri Pelto, the lake is growing as the nearby Excelsior Glacier retreats by more than 650 feet (200 meters) per year. (Image credit: Mauri Pelto/ Landsat)

Seventy years ago, Alaska's Excelsior Glacier stretched its cold fingers from a vast plain in the state's southern edge nearly all the way to the North Pacific Ocean. Now, the glacier is separated from the sea by a meltwater lake more than five times the size of New York City's Central Park.

In a recent blog post on the American Geophysical Union (AGU) website, glaciologist Mauri Pelto of Nichols College in Massachusetts shows how that relatively new lake — now called Big Johnstone Lake — has more than doubled in size over the last 24 years as rising global temperatures force Excelsior Glacier into a hasty retreat. [The Coldest Places on Earth]

Meanwhile, Big Johnstone Lake has doubled in size, from 3.5 to 7 square miles (9 square km to 18 square km), and it has been gradually filled by slabs of ice calved from the edge of the melting glacier.

As long as researchers have been photographing the lake, large flotillas of these ice chunks have been plainly visible bobbing through the cold waters like oversized bath toys. But not anymore, Pelto wrote. For the first time, 2018 Landsat images show the lake without any slabs of glacial ice — likely because the lake is close to reaching its maximum size. Near the lake's new northern edge, Excelsior Glacier steepens suddenly, probably lifted by elevated terrain underneath, Pelto wrote.

Even if no more calving ice makes its way into Big Johnston Lake, the glacier will continue to retreat, but probably at a slower pace than the rapid melting observed over the last 25 years. A similar fate has already befallen many neighboring glaciers in Alaska and British Columbia, Pelto wrote, providing yet more examples of how climate change is rapidly redrawing the map of our world.

Originally published on Live Science.

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Brandon Specktor
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Brandon is the space/physics editor at Live Science. His writing has appeared in The Washington Post, Reader's Digest, CBS.com, the Richard Dawkins Foundation website and other outlets. He holds a bachelor's degree in creative writing from the University of Arizona, with minors in journalism and media arts. He enjoys writing most about space, geoscience and the mysteries of the universe.