Retreating Alsek Glacier Turns Alaska’s Prow Knob Into a New Island

In southeastern Alaska, a small mountain known as Prow Knob has officially become an island following the retreat of the Alsek Glacier, according to satellite images captured by NASA's Earth Observatory. The transition was observed between July 13 and August 6, 2025, when the glacier finally separated from the 2-square-mile (5-square-kilometer) landmass.

NASA's Lindsey Doermann explained that water is rapidly replacing ice in the region, with glaciers thinning and retreating, forming proglacial lakes off their fronts. The newly formed island has altered the local landscape, with Alsek Lake now occupying the area where the glacier once flowed. The change underscores the broader trend of many glaciers worldwide retreating due to rising global temperatures.

The phenomenon also has practical consequences, as it alters local hydrology, sediment transport, and can create new habitats for plants and animals. The mountain's informal name, Prow Knob, was given in the 1960s due to its pointed, shiplike profile. Glaciologist Austin Post had previously predicted a likely separation around 2020 based on retreat rates from 1960 to 1990, although the glacier held on longer than expected.

The newly exposed island serves as a natural laboratory for scientists to track the pace of climate change through repeated satellite observations and field studies. Park officials and researchers plan to continue monitoring the site, as such dramatic shifts are expected to become more common across Alaska as glaciers continue to retreat.