Satellite Photos Show New Island Forming From Melting Glacier in Alaska

Sep 23, 2025

Pesala Bandara

Side-by-side satellite images show a glacier and its meltwater lake: on the left, the lake is gray and ice-covered; on the right, the same lake is larger and bright blue, surrounded by green land and snow-capped mountains. — NASA images from 1984 and 2025 show that a mountain once covered by the Alsek Glacier in southeastern Alaska is now surrounded by water, creating a new island called Prow Knob.

Alaska’s newest island can now be seen from space in recently released satellite photographs from NASA.

NASA released a series of images that revealed how a melting glacier created a two-square-mile island in southeastern Alaska over the summer. The island, now known as Prow Knob, was once part of a frozen landscape dominated by the Alsek Glacier.

Over the summer, as the glacier retreated and meltwater filled the area, Prow Knob was left standing on its own, surrounded by water.

Four satellite images show Alsek Lake and glacier retreat from 1984 to 2025. The lake expands and the ice shrinks over time, revealing more water and less glacier in each successive image. — NASA satellite images spanning from July 5, 1984 to August 6, 2025. Since 1984, Alaska’s Alsek Glacier has shrunk by more than 3 miles, leaving the island of Prow Knob surrounded by water

NASA’s Earth Observatory compared current images with those from the early 1980s. In the older photos, the Alsek Glacier almost completely enclosed Prow Knob, with only one side bordered by Alsek Lake. This summer, satellites captured the moment that the glacier finally pulled away, leaving Prow Knob isolated within the lake.

The change is part of a much longer trend. Over the past 40 years, aerial and satellite records have tracked the steady eastward retreat of the Alsek Glacier, along with the shrinking of another ice mass to the south, the Grand Plateau Glacier. As both ice sheets receded, meltwater filled the gap, and Alsek Lake expanded into the space once occupied by glaciers.

Satellite view of a large, grayish lake surrounded by green forests and snow-covered mountains, with glacier ice flows feeding into the lake from the right side of the image. — Alsek Glacier in July 1984.

A large turquoise glacial lake surrounded by dense green forests, rivers, and snow-capped mountains, with several icebergs floating on the water’s surface. — Alsek Glacier has almost completed in August 2025. Instead, Alsek Lake surrounds the island of Prow Knob.

The process ended this summer when NASA’s Landsat 9 satellite captured the last section of ice separating Prow Knob from the lake sometime between July 13 and August 6. With that, the mountain became a true island, entirely enclosed by lake water.

Today, the new island sits in the middle of Alsek Lake, which is almost twice as large as it was four decades ago. The lake continues to grow as it is fed by melting glaciers.

This change is a clear example of climate change, as higher temperatures and melting glaciers alter Alaska’s landscapes. The state is warming two to three times faster than the global average, with its glaciers losing more than 66 billion tons of ice every year.

Image credits: All photos by NASA Earth Observatory. Images by Michala Garrison, using Landsat data from the U.S. Geological Survey.