A small mountain in southeastern Alaska has formally become a new island after a retreating glacier finally pulled away, a stark landmark captured in satellite images that scientists say underscores how rapidly the region’s icy landscape is changing.
NASA’s Earth Observatory said imagery from the Landsat 9 satellite taken in August shows the Alsek Glacier has lost all contact with Prow Knob, a roughly 2-square-mile (5-square-kilometer) landmass that for decades was ringed by ice. The agency said the glacier’s final separation from the knob took place between July 13 and Aug. 6.
“Along the coastal plain of southeastern Alaska, water is rapidly replacing ice,” Lindsey Doermann, a science writer at the NASA Earth Observatory, said in an agency statement. “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.”
Satellite images show how much the new island has shifted the landscape in Alaska
Photographs and satellite data show how much the landscape has shifted. In the early 20th century, the Alsek Glacier flowed across the basin now occupied by Alsek Lake and reached as far as Gateway Knob, about 3 miles (5 kilometers) west of Prow Knob. By 1984, Landsat images already recorded the glacier splitting to flow around the mountain; the August images reveal that the ice no longer touches the rock.
The change is the latest, highly visible sign of a broader trend. Scientists say many glaciers in Alaska and around the world are retreating as global temperatures rise. NASA noted that last year was the hottest on record for global average temperatures and that 2025 has included a string of record-setting warm months.
Prow Knob’s transition from nunatak, which is a mountaintop protruding through an icefield, to an island may seem a geographic anomaly, but researchers say it has practical consequences. The formation of proglacial lakes alters local hydrology, changes sediment transport, and can create new habitats for plants and animals as barren ground is exposed and colonized. It may also affect downstream ecosystems and, in some places, increase the risk of sudden floods if ice- or moraine-dammed lakes fail.
The mountain’s name dates back to the 1960s
The mountain’s informal name dates to aerial surveys in the 1960s as glaciologist Austin Post, who photographed the area in 1960, named it for its pointed, shiplike profile. Mauri Pelto, a glaciologist at Nichols College in Massachusetts, had warned years earlier that Alsek Glacier would eventually release Prow Knob, predicting a likely separation around 2020 based on retreat rates measured between 1960 and 1990. The glacier held on a bit longer than some forecasts, Pelto has said, but the outcome was expected.
For scientists, the newly exposed island provides another natural lab to track the pace of change. Repeated satellite observations, aerial photography, and field studies allow researchers to document how quickly ice loss converts frozen terrain into open water and exposed land. “Those images become part of a growing record used to track the rapid transformation of glaciated landscapes,” NASA said.
Park officials and researchers say they will continue to monitor the site of the new island in Alaska. As glaciers retreat, such dramatic shifts are likely to become more common across the state. This is a reminder, scientists say, of the scale and speed of climatic changes unfolding in polar and subpolar regions.