'New' island emerges from melting ice in Alaska

A satellite photograph of Alsek Lake and the new island of Prow Knob as Alsek Glacier retreats.

A 'new' island has appeared in the middle of a lake in southeastern Alaska after the landmass lost contact with a melting glacier, NASA satellite images reveal.

The landmass, named Prow Knob, is a small mountain that was formerly surrounded by the Alsek Glacier in Glacier Bay National Park. However, Alsek Glacier has been retreating for decades, slowly separating itself from Prow Knob and leaving a growing freshwater lake in its wake.

A recent satellite image, taken by Landsat 9 in August, reveals that the glacier has now lost all connection to Prow Knob, according to a statement released by NASA's Earth Observatory. Prow Knob provides a clear visual example of how glaciers are thinning and retreating in southeastern Alaska.

Alsek on July 5, 1984. (Image credit: NASA Earth Observatory images by Michala Garrison, using Landsat data from the U.S. Geological Survey.)

Alsek on August 6, 2025. (Image credit: NASA Earth Observatory images by Michala Garrison, using Landsat data from the U.S. Geological Survey.)

"Along the coastal plain of southeastern Alaska, water is rapidly replacing ice," Lindsey Doermann, a science writer at the NASA Earth Observatory, wrote in the statement. "Glaciers in this area are thinning and retreating, with meltwater forming proglacial lakes off their fronts. In one of these growing watery expanses, a new island has emerged."

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Alsek Glacier used to split into two channels to wind its way around Prow Knob, which has a landmass of about 2 square miles (5 square kilometers). In the early 20th century, the glacier extended across the now-exposed Alsek Lake and as far as Gateway Knob, about 3 miles (5 kilometers) west of Prow Knob.

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The late glaciologist Austin Post, who captured aerial photographs of Alsek in 1960, named Prow Knob after its resemblance to the prow (pointed front end) of a ship. Post and fellow glaciologist Mauri Pelto, a professor of environmental science at Nichols College in Massachusetts, previously predicted that Alsek Glacier would release Prow Knob in 2020, based on the rate it was retreating between 1960 and 1990, according to the statement. The glacier has therefore clung on to its mountain for slightly longer than initially predicted.

Prow Knob completely separated from Alsek Glacier between July 13 and Aug. 6, according to the statement.

Many of Earth's glaciers are retreating as the planet gets warmer due to climate change. Last year was the hottest year for global average temperatures since records began, while 2025 has been marked by a string of record-breaking and near-record-breaking hot months.