Alaska has a new island – not thanks to new land rising up through the seas, but because of glacial melt so dramatic that it has surrounded a piece of land previously connected to the mainland.

Along the coastal plain of southeastern Alaska, water is rapidly replacing ice. 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.

The Alsek Glacier once encircled a small mountain known as Prow Knob near its terminus. In summer 2025, the glacier lost contact with Prow Knob, leaving the approximately 2-square-mile (5-square-kilometer) landmass surrounded by the water of Alsek Lake.

This pair of images shows the extent of ice retreat and lake growth between 1984 and 2025. They were acquired in the summers of those years with the TM (Thematic Mapper) on Landsat 5 and the OLI-2 (Operational Land Imager-2) on Landsat 9, respectively.

In the early 20th century, the Alsek Glacier terminated at Gateway Knob, about 3 miles (5 kilometers) west of Prow Knob, according to Mauri Pelto, a glaciologist at Nichols College, who first saw this glacier in 1984. By mid-century, the ice had retreated eastward but still encompassed Prow Knob. The late glaciologist Austin Post took aerial photographs of the Alsek’s terminus in August 1960 and would later tell Pelto that he named the feature (considered a nunatak at that point) for its resemblance to a ship’s prow.