A significant geological transformation has occurred in southeastern Alaska, with the Alsek Glacier's substantial retreat leading to the emergence of a new island in Alsek Lake. This event, documented by NASA's Earth Observatory using satellite imagery from 1984 and 2025, underscores the profound impact of climate change on glacial landscapes.
The newly formed island, measuring approximately 5 square kilometers, appeared as the 24 km long Alsek Glacier receded over 5 km between 1984 and 2025. This retreat caused Prow Knob, a mountain previously covered by the glacier, to become detached. By the summer of 2025, specifically between July 13 and August 6, the glacier's connection with Prow Knob was severed, leaving it as a distinct island in Alsek Lake. This transformation is part of a wider trend observed across southeastern Alaska, where glaciers are thinning and retreating, leading to the expansion of proglacial lakes.
Glaciologists have been closely observing these changes. Maurie Pelto, a glaciologist at Nichols College, who first encountered the Alsek Glacier in 1984, along with fellow glaciologist Austin Post, had previously predicted that Prow Knob would become an island around 2020. This prediction materialized a few years later. Historically, the Alsek Glacier's terminus was at Gateway Knob in the early 20th century, about 5 km west of Prow Knob. By the mid-20th century, the ice had retreated eastward but still encompassed the mountain.
Lindsey Doermann from NASA's Earth Observatory explained that water is rapidly replacing ice along Alaska's coastal plain, with glaciers in the region thinning and retreating. This process creates new islands within expanding water bodies. The Alsek Glacier's retreat has also contributed to the significant growth of Alsek Lake, which expanded from roughly 17 square miles in 1984 to about 29 square miles by 2025. This expansion, along with neighboring lakes, has more than doubled in size over the same period.
These transformations highlight the significant influence of glacial dynamics on shaping the Earth's surface. The formation of this new island serves as a tangible indicator of accelerating glacial retreat globally. Alaska is experiencing warming at twice the global average rate, leading to a substantial decline in its glaciers. Studies suggest that Alaska could lose up to 69% of its glacier mass under current climate change pledges, a trend that has profound implications for sea levels, freshwater availability, ecosystems, and biodiversity.