New Island Forms in Alaska as Alsek Glacier Retreats

A new landform has emerged in Alaska’s icy wilderness, revealing the striking power of nature and climate change. NASA satellite imagery has confirmed that a small mountain, long cloaked by the Alsek Glacier, is now completely surrounded by water, officially creating a new island.

The island, known as Prow Knob, lies within Alsek Lake—a body of water that has steadily expanded as the glacier retreats. Scientists monitoring the glacier for decades say this transformation is both dramatic and unprecedented. Comparing satellite images from July 5, 1984, captured by the Landsat 5 Thematic Mapper (TM), with those from August 6, 2025, taken by the Landsat 9 Operational Land Imager-2 (OLI-2), the evolution of this landscape is vividly clear.

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Over the past 40 years, both arms of Alsek Glacier have retreated more than 5 kilometers, carving out a proglacial lake around Prow Knob. With the glacier now fully separated from the mountain, Prow Knob has officially become an island, encircled by pristine glacial waters.

Glaciologists note that in the early 20th century, Alsek Glacier extended all the way to Gateway Knob, about 5 kilometers west of Prow Knob. Since then, the glacier has continued its slow but steady retreat, a transformation meticulously recorded by decades of satellite imagery.

The glacier’s retreat has fueled a major expansion of Alsek Lake, which has grown from roughly 45 square kilometers in 1984 to about 75 square kilometers today. This growth is driven not only by the glacier’s meltwater but also by nearby proglacial lakes, including Harlequin and Grand Plateau. Until around 1999, Alsek Glacier remained connected with the northern arm of the Grand Plateau Glacier, but as both ice masses receded, a large new branch of Alsek Lake emerged.

According to NASA, the newly formed island covers about 5 square kilometers and is believed to have emerged between July 13 and August 6, 2025. With Prow Knob now separated, the glacier has become less stable and more prone to calving, where large sections of ice break off into the lake.

This discovery is not only a remarkable milestone in glaciology but also a vivid reminder of the impacts of climate change on our planet. As glaciers retreat and reshape landscapes, new islands like Prow Knob are emerging—offering scientists a unique window into these dynamic processes.