In a matter of weeks this summer, a small mountain once embedded in a vast glacier in southeastern Alaska became the region’s newest island—visible from space and confirmed by NASA satellite imagery. The landform, called Prow Knob, is now entirely surrounded by water following the sudden retreat of the Alsek Glacier, which had encased it for centuries.
Captured between July 13 and August 6, 2025, the separation was observed using data from NASA’s Landsat 9 satellite. The area had been under close observation for decades, with researchers like Mauri Pelto, a glaciologist at Nichols College, anticipating this development as part of a long-term melt trend. “The ice was holding on longer than we expected,” Pelto noted in an interview with the NASA Earth Observatory. “But this was coming.”
While the change might appear sudden, it’s the outcome of over a century of glacial retreat in the region—a pattern that has intensified in recent decades, reshaping entire watersheds and redrawing Alaska’s coastline.
Satellite Evidence Shows Decades of Silent Retreat
Comparative imagery published by NASA Earth Observatory shows just how drastically the landscape has changed since 1984, when Prow Knob was still tightly gripped by ice on its eastern and southern flanks. Today, it sits as a fully detached island in Alsek Lake, which itself has expanded from 45 to 75 square kilometers in four decades.
The Alsek Glacier, located in Glacier Bay National Park, has been thinning steadily. Once connected to the Grand Plateau Glacier via northern and southern ice tongues, the Alsek has now lost both feeds, making it more vulnerable to calving—when large ice chunks break off and fall into surrounding water.
According to historical aerial photographs archived by the US Geological Survey (USGS), the glacier had already retreated about 5 kilometers between 1894 and 1960. Since then, the pace has only accelerated.
By 1999, satellite data showed the glacier pulling away from nearby ridges, fragmenting into separate tongues. By 2018, the once-unified terminus had splintered completely. Then, during summer 2025, the final link between ice and land snapped.
A “New Lake District” Is Forming Across the Region
This isn’t an isolated event. According to a 2024 USGS climate report, the southeastern Alaskan coast is undergoing what scientists describe as one of the fastest glacial retreats in the Northern Hemisphere. Alongside Alsek, the Yakutat and Grand Plateau glaciers are also contributing to what Pelto calls a “new lake district” emerging along the fjord-laced landscape.
“These are not small ponds forming in remote valleys,” he told NASA. “These are massive, fast-growing proglacial lakes.” Combined, Alsek, Harlequin, and Grand Plateau lakes have more than doubled in size since the early 1980s, turning once-frozen land into liquid basins that now stretch toward the coast.
As glaciers thin and pull back from high ground, nunataks like Prow Knob—which once peeked through the ice—are becoming standalone islands. That transformation doesn’t just alter the geography. It also affects hydrology, vegetation, sediment transport, and ecosystem dynamics. New shorelines form. Sediment-rich meltwater reshapes river flow. And pioneer species begin colonizing the freshly exposed terrain.
Implications for Climate, Ecology, and Flood Risk
The creation of new islands might seem like a cartographer’s curiosity, but the underlying mechanisms carry serious environmental implications. As glaciers collapse, they often leave behind unstable moraine-dammed lakes. These water bodies can burst unexpectedly, triggering what experts call glacial lake outburst floods (GLOFs)—a known threat to communities downstream.
The shift also disrupts regional climate regulation, as ice—which reflects solar radiation—gives way to darker water surfaces that absorb more heat. This process, called albedo reduction, fuels a feedback loop of further melting.
Local ecology is changing too. Wildlife adapted to high-altitude glacial environments—such as ptarmigans or cold-water fish—face habitat shrinkage. Meanwhile, new species are moving in, potentially shifting food webs in unpredictable ways.
The National Park Service, which oversees Glacier Bay, has confirmed ongoing monitoring of the area. According to statements released in late August, the transformation of Prow Knob into an island is now considered irreversible—and emblematic of wider changes sweeping across the Arctic.
