Prow Knob Becomes Island as Alsek Glacier Retreats

In a striking illustration of climate change's impact, satellite imagery from NASA's Landsat 9 has revealed that Prow Knob, a small mountain in southeastern Alaska, has become a standalone island due to the retreat of the Alsek Glacier.

Between July 13 and August 6, 2025, the Alsek Glacier's continued retreat led to the complete separation of Prow Knob from the mainland, transforming it into an island within Alsek Lake. This event underscores the accelerating pace of glacial melt in Southeast Alaska and its profound effects on the region's geography.

Prow Knob, an approximately 2-square-mile (5-square-kilometer) landmass, was historically encased by the Alsek Glacier. In the early 20th century, the glacier terminated at Gateway Knob, about 3 miles (5 kilometers) west of Prow Knob. By mid-century, the glacier had retreated eastward but still encompassed Prow Knob. The late glaciologist Austin Post took aerial photographs of the Alsek’s terminus in August 1960 and named the feature for its resemblance to a ship’s prow.

The Alsek Glacier has retreated more than 3 miles (5 kilometers) since 1984, leading to the expansion of Alsek Lake from approximately 17 square miles (45 square kilometers) to about 29 square miles (75 square kilometers) over the same period. This rapid transformation highlights the dynamic nature of the landscape and the need for ongoing monitoring and adaptation strategies.

Glaciologist Mauri Pelto of Nichols College has been monitoring the Alsek Glacier's retreat for decades. He noted that both arms of the Alsek Glacier have retreated more than 3 miles (5 kilometers) since 1984, and this trend is likely to continue. Having lost contact with Prow Knob, the ice is less stable and more prone to calving.

The emergence of Prow Knob as an island underscores the accelerating pace of glacial retreat in Southeast Alaska, a phenomenon driven by climate change. This rapid transformation has significant implications for local ecosystems, hydrology, and potentially human activities in the region. The expansion of Alsek Lake and the formation of new landforms like Prow Knob highlight the dynamic nature of the landscape and the need for ongoing monitoring and adaptation strategies.

The transformation of Prow Knob into an island serves as a stark reminder of the tangible effects of climate change on our planet's landscapes. As glaciers continue to retreat, the resulting geographical changes will have far-reaching consequences for ecosystems and human communities alike.