WASHINGTON: NASA satellite imagery has revealed a new island off the coast of Alaska that emerged after long-standing glacial ice melted, isolating a small mountain that was once part of the mainland.
The island lies within Alsek Lake, where the Alsek Glacier has been steadily thinning and flooding the region with meltwater. Two Landsat images — captured on 5th July, 1984 by the Thematic Mapper (TM) on Landsat 5, and on 6th August, 2025 by the Operational Land Imager-2 (OLI-2) on Landsat 9 — illustrate the transformation in striking detail, according to a NASA statement.
Alsek Glacier once enveloped a small mountain known as Prow Knob. Over the past four decades, both arms of the glacier have retreated more than 5 kilometres, carving out a proglacial lake in the process. The latest imagery confirms that the glacier has now completely separated from Prow Knob, which is surrounded by water and officially classified as an island, NASA added.
Glaciologists have monitored Alsek Glacier for decades. In the early 20th century, the glacier is believed to have terminated at Gateway Knob, around 5 kilometres west of Prow Knob on the opposite side of what is now Alsek Lake. Since then, the glacier has continued its steady retreat, with satellite data documenting the transformation.
The retreat has fuelled a major expansion of Alsek Lake, which has grown from roughly 45 square kilometres in 1984 to about 75 square kilometres today. Its growth is driven not only by Alsek Glacier’s meltwater but also by nearby proglacial lakes such as Harlequin and Grand Plateau. Until around 1999, Alsek Glacier remained connected with the northern arm of the Grand Plateau Glacier. As both ice masses receded further, they created a major branch of Alsek Lake visible in later satellite images.
The newly formed island measures about 5 square kilometres. Based on satellite data, scientists believe it emerged between 13th July and 6th August 2025. With the separation of Prow Knob, the glacier is now less stable and more prone to calving, when large sections of ice break away into the lake, according to NASA. –Agencies
