Summer is prime iceberg season in Greenland’s glacier-fed fjords, and 2026 was no exception. Especially notable was the iceberg that calved off the Petermann Glacier along the northwest coast of Greenland in August. About the size of St. Thomas in the U.S. Virgin Islands, it was the largest calving of any Arctic glacier since 2020.
Iceberg calving is a routine part of the life cycle of an outlet glacier. However, scientists are closely watching the process, along with many other observations of the ice and its environment, for signs of long-term instability. Petermann is one of the largest marine glaciers in Greenland and acts as a guardian of the ice that flows from the ice sheet into the ocean. Its future stability has implications for sea level rise.
The summer 2026 calving event was detected on August 4 by Adam Garbo, a PhD student in glaciology at the University of Ottawa, in images from the European Space Agency’s Sentinel-1 mission. Garbo and an international team of colleagues have been using remote sensing to study and track the glacier’s ice tongue.
The team reported that the large tabular iceberg, or “ice island,” measured just over 76 square kilometers (29 square miles) at the time of its calving, the largest to calve from the glacier since the 2012 Ice Island (130 square kilometers). The 2012 landslide followed previous major events in 2008 (31 square kilometers) and 2010 (just over 250 square kilometers).
The August 2026 event could have been even bigger. Garbo and his colleagues expected a major calving once one of the large cracks they were monitoring finally broke through Petermann’s ice tongue. “What surprised us was that the calving followed a different fracture, producing a smaller ice island than we had originally anticipated,” Garbo said. As of late August, two large fissures still remained and were expected to eventually produce new ice islands of approximately 94 square kilometers and 84 square kilometers, although the timing remained uncertain.
Glaciologist Mauri Pelto of Nichols College has also been tracking the iceberg, using images from NASA-USGS Landsat satellites, as it descended Petermann Fjord toward Nares Strait. In the week since it broke off, the iceberg has moved an average of 3 kilometers per day. It continued toward the fjord’s junction with Nares Strait, where it struck a small rock outcrop known as Joe Island (Joe Ø). The brief encounter is visible in images captured by the OLI (Operational Land Imager) on Landsat 9 on August 23 (top right) and August 24 (top left). Above is a detailed view of the August 24 image.
Joe Island is located at the mouth of Petermann Fjord, making it one of the first obstacles an ice island encounters on its way out. Collisions with it, like the one that split the ice island in two in 2010, often mark the beginning of an iceberg’s calving. Petermann icebergs tend to be thinner and more fragile than those formed by glaciers like Greenland’s Jakobshavn and Helheim, and thinner even than Antarctica’s giants, Pelto said.
“We were certainly watching closely how he interacted with Joe Island and were impressed that he survived the interaction without further fragmentation,” Garbo said.
The ice island was estimated to be less than 150 meters thick at the time of calving. Wind and surface currents have carried it out of the fjord, and satellite images show it moving away from Joe Island and continuing southwest through Nares Strait. As it moves, it will fracture into smaller pieces as tides, winds, currents and melting continue to weaken the ice.
Thicker icebergs calving from tidewater glaciers without extensions of floating ice shelves can drift and even run aground on the seabed inside the fjord, while ice islands, such as Petermann’s, can run aground later in their drift. Many ice islands have been “stranded” off the coasts of Coburg and Baffin Islands.
Garbo and his colleagues noted that ice islands and their fragments are known to travel considerable distances, posing potential dangers to marine activities and infrastructure, while also distributing fresh water across the ocean as they melt.
NASA Earth Observatory images by Lauren Dauphin, using Landsat data from the US Geological Survey.. Story by Kathryn Hansen.
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