Alaska's Prow Knob (the large island to the right of the lake) was once surrounded by ice. (Image credit: NASA Earth Observatory imagery by Michala Garrison using USGS Landsat data.)
NASA satellite images show a 'new' island has emerged in the centre of a southeast Alaska lake after land became disconnected from a melting glacier.
The land mass, called Prow Knob, is a small mountain that was once surrounded by Alsek Glacier in Glacier Bay National Park. However, Alsek Glacier has been retreating for decades, gradually separating from Prow Knob and leaving behind a growing freshwater lake.
According to a statement released by NASA's Earth Observatory, a recent satellite image taken by Landsat 9 in August shows that the glacier has completely lost contact with Prow Knob. Prow Knob is a clear example of how glaciers are thinning and retreating in southeast Alaska.
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Alsek, July 5, 1984 (Image credit: NASA Earth Observatory images by Michala Garrison using U.S. Geological Survey Landsat data.)
Alsek, August 6, 2025. (Image credit: NASA Earth Observatory imagery by Michala Garrison using USGS Landsat data.)
“Along the coastal plain of southeast Alaska, water is rapidly displacing ice,” Lindsay Doermann, a science writer with NASA’s Earth Observatory, wrote in a statement. “Glaciers in the area are thinning and retreating, and meltwater is forming proglacial lakes. A new island has formed on one of these growing bodies of water.”
Alsek Glacier once divided into two channels, skirting Prow Knob, a landmass of about 5 square kilometers. In the early 20th century, the glacier extended across the now-open Alsek Lake and reached Gateway Knob, about 5 kilometers west of Prow Knob.
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The late glaciologist Austin Post, who took aerial photographs of Alsek in 1960, named the glacier Prow Knob for its resemblance to the bow (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 would break away from Prow Knob in 2020 based on its rate of retreat between 1960 and 1990, the statement said. That would leave the glacier hanging on to the mountain somewhat longer than originally thought.
According to the statement, Prow Knob Glacier completely separated from Alsek Glacier between July 13 and August 6.
Many of Earth's glaciers are retreating as the planet warms due to climate change. Last year was the hottest year on record in terms of average global temperature, and 2025 will see a string of record-hot and near-record-hot months.
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Patrick Pester, Social Links Navigator, Popular News Writer
Patrick Pester is a popular news writer for Live Science. His work has appeared on other science sites such as BBC Science Focus and Scientific American. Patrick transitioned to journalism after working for zoos and wildlife conservation organisations earlier in his career. He received a Master's Excellence Scholarship to study at Cardiff University, where he completed an MA in International Journalism. He also completed a second MA in Biodiversity, Evolution and Conservation in Action at Middlesex University in London. When he's not writing news, Patrick is an investigator into the sale of human remains.
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