Image credit: NASA Earth Observatory images by Michala Garrison, using Landsat data from the U.S. Geological Survey
Glaciers don’t usually give way overnight, but sometimes their slow retreat reveals something dramatic. That’s what happened recently in Alaska, where a rocky landmass called Prow Knob officially became its own island as the Alsek Glacier pulled back. The change was spotted in satellite images taken this summer, confirming that a stretch of ice that once tethered the rock to the mainland had melted away. According to NASA’s Earth Observatory, the separation happened between mid-July and early August 2025.
Alsek Glacier, like many in Southeast Alaska, has been shrinking for decades. Since 1984, its two main branches have retreated more than three miles, opening up space for Alsek Lake to expand. That growth finally isolated Prow Knob, turning what was once a rocky knob surrounded by ice into a standalone island. Measuring about two square miles, it’s not a small patch either—it’s now a distinct feature in the growing lake.
This is part of a larger story. The rapid expansion of glacial lakes has been striking across the region. Alsek Lake, along with others like Grand Plateau and Harlequin, has more than doubled in area over the past 40 years. These changes aren’t just cartographic curiosities; they reflect the speed at which glaciers are thinning and losing mass. The retreat exposes new land, carves fresh shorelines, and alters the flow of rivers downstream.
Image credit: NASA Earth Observatory images by Michala Garrison, using Landsat data from the U.S. Geological Survey
Scientists say Prow Knob’s detachment will likely accelerate further changes. Once a glacier loses contact with solid ground, the ice that remains can become less stable, making calving events—where chunks of ice break off into the water—more likely. That sets off a cycle where retreat feeds more retreat. For ecologists and geologists, it’s both a rare opportunity to study landscape evolution and a reminder of how climate dynamics play out in real time.
For locals and visitors, the changes are tangible. What was once a feature hidden within a wall of ice is now an island in open water, reshaping how the area looks and functions. It’s a dramatic example of how shifting ice doesn’t just raise sea levels—it rewrites maps.
The new island at Alsek is a clear signal: glaciers that have held steady for centuries are on the move, and the landscapes they leave behind are transforming before our eyes.