Massive Iceberg From Greenland's Petermann Glacier Survives Island Collision

A 29-square-mile iceberg that broke from Greenland's Petermann Glacier in August survived a collision with a small rocky island that has previously shattered other large icebergs from the same glacier, according to NASA Earth Observatory. The calving event, roughly comparable in size to the island of St. Thomas in the U.S. Virgin Islands, was the largest from any Arctic glacier since 2020.

Adam Garbo, a doctoral student in glaciology at the University of Ottawa, first identified the calving event on August 4 using images from the European Space Agency's Sentinel-1 satellite mission. The newly formed iceberg, sometimes called an "ice island," covered just over 76 square kilometers when it separated — the largest piece to calve from Petermann since a 130-square-kilometer event in 2012, larger than a 2008 calving of 31 square kilometers but smaller than a 2010 event of just over 250 square kilometers. "What surprised us was that the calving instead followed a different fracture, producing a smaller ice island than we had originally anticipated," Garbo said, noting that scientists had been watching a different rift they expected to produce a larger break.

As of late August, two major rifts remained in the glacier, and researchers expect them to eventually release additional ice islands of roughly 94 and 84 square kilometers, though they could not predict when. Glaciologist Mauri Pelto of Nichols College tracked the new iceberg using NASA and USGS Landsat images as it moved down Petermann Fjord toward Nares Strait, traveling an average of about 3 kilometers a day during its first week.

The iceberg then collided with Joe Island, a small rocky outcrop positioned directly in the path of ice leaving the fjord; a similar collision there split a 2010 ice island into two pieces. Petermann's icebergs are generally thinner and more fragile than those from glaciers such as Jakobshavn and Helheim, and much thinner than the enormous icebergs that break from Antarctica — the researchers estimated this one was less than 150 meters thick when it calved. "We were certainly watching closely as it interacted with Joe Island and were impressed that it survived the interaction without further fragmentation," Garbo said.

Satellite observations show the iceberg pivoting away from Joe Island and continuing southwest through Nares Strait, carried by winds and surface currents. Its survival does not mean it will stay intact indefinitely: tides, winds, currents and continued melting will place additional stress on the ice, eventually fracturing it into progressively smaller pieces that can create hazards for ships and marine infrastructure while releasing freshwater into the ocean as they melt.