Iceberg Broken From Greenland's Petermann Glacier Survives Collision With Arctic Island

A Manhattan-sized slab of ice that broke away from Greenland's Petermann Glacier last month collided with a small rocky island at the mouth of its home fjord in late August and came through the impact largely intact, according to satellite imagery released by NASA's Earth Observatory. The episode is the latest chapter in what glaciologists are calling the most significant Arctic calving event since 2020, and one that scientists are tracking closely for what it can reveal about the stability of one of the ice sheet's largest remaining floating ice tongues.

The ice island calved from Petermann's ice tongue on Aug. 4 and drifted down Petermann Fjord toward Nares Strait, the narrow channel separating Greenland from Ellesmere Island in Canada. On Aug. 23 and 24, it rammed into Joe Island, a rocky outcrop that sits squarely in the path of ice leaving the fjord. Radar and optical satellites captured the encounter, showing the berg wedged briefly against the island before pivoting free and continuing southwest.

The numbers

The ice island measured just over 76 square kilometers, or about 29 square miles, at the moment it broke free — roughly the footprint of St. Thomas in the U.S. Virgin Islands — and was estimated to be less than 150 meters thick. Since calving, it has drifted an average of three kilometers a day down the fjord. Researchers who have tracked Petermann's ice tongue since 2019 through the European Space Agency's Sentinel-1 mission say it is the largest calving from Petermann since 2012, when a 130-square-kilometer ice island broke away. That event followed a 31-square-kilometer calving in 2008 and a much larger, 250-plus-square-kilometer ice island in 2010 that split in two after striking Joe Island. This year's event is smaller than researchers had expected: two large rifts still cutting across the ice tongue are projected to eventually release additional ice islands of roughly 94 and 84 square kilometers, though the timing remains uncertain.

How researchers spotted it

The calving was first identified on Aug. 4 by Adam Garbo, a doctoral student in glaciology at the University of Ottawa, working with an international team that has monitored Petermann's ice tongue using Sentinel-1 radar imagery, which can see through clouds and darkness. Interferometry from the mission had picked up "pronounced deterioration along the centreline of the ice tongue" as early as April, months before the ice finally gave way. Garbo and colleagues had expected a rift already under close watch to cut all the way across the tongue and produce a larger berg. Instead, the ice broke along a different fracture. "What surprised us was that the calving instead followed a different fracture, producing a smaller ice island than we had originally anticipated," Garbo said, according to the NASA account of the event.

Petermann is one of Greenland's largest marine-terminating glaciers, acting as a gatekeeper for ice flowing off the interior ice sheet into the Arctic Ocean. Unlike many outlet glaciers, it retains a long floating ice tongue that extends far out into its fjord, making it unusually sensitive to ocean warmth reaching its underside as well as to fracturing at the surface. Because that tongue is already floating, its periodic calving does not by itself raise sea levels the way the loss of grounded ice would. But scientists watch Petermann's tongue as an early-warning indicator: continued thinning and retreat could eventually expose more of the glacier's grounded ice to ocean melting, with implications for future sea-level rise that NASA's sea-level science program tracks across the ice sheet.

Who is watching, and why it matters

The Joe Island collision drew particular attention because of the island's history. Its location, right where the fjord opens into Nares Strait, makes it one of the first obstacles a departing ice island meets, and a similar collision in 2010 split that year's berg in two. Glaciologist Mauri Pelto of Nichols College, who has separately tracked the 2026 iceberg using NASA-USGS Landsat 9 imagery in posts on his glacier-monitoring blog, has noted that Petermann's bergs tend to be thinner and more fragile than those calved by glaciers such as Jakobshavn and Helheim in Greenland, and thinner still than Antarctica's largest tabular icebergs — a fragility that made this month's encounter with Joe Island a real test of the berg's structural integrity.

"We were certainly watching closely as it interacted with Joe Island and were impressed that it survived the interaction without further fragmentation," said Adam Garbo, the University of Ottawa doctoral student who first spotted the calving.

The people most directly affected by the drifting ice island are those who operate in or study Nares Strait and the wider Arctic shipping corridors nearby: mariners, fisheries operators and Indigenous communities in the region, for whom large, unpredictable ice islands and their fragments pose navigational hazards as they drift and eventually break apart. Ice islands calved from Petermann have historically traveled long distances before running aground, with many past fragments becoming grounded off Canada's Coburg and Baffin islands years after calving. As they melt, they also release meltwater into ocean currents, a process researchers who study Arctic freshwater budgets are tracking as part of broader efforts to understand how ice-sheet mass loss is reshaping ocean circulation.

The research effort tracking Petermann is a multinational one. Beyond Garbo's team at the University of Ottawa, scientists at the University of Stirling, the University of Lancaster and the University of Leeds have collaborated on the monitoring through the ESA-funded ARCTEX project, which has followed the glacier's ice tongue since 2019. The project benefited this year from a period of near-daily repeat imaging enabled by the tandem commissioning of the newer Sentinel-1C and Sentinel-1D satellites, which let researchers watch the glacier's fractures widen in near-real time rather than waiting weeks between usable images.

What happens next

Satellite images show the ice island has since pivoted away from Joe Island and continued drifting southwest through Nares Strait, propelled by wind and surface currents. Researchers expect it to keep breaking into smaller pieces as tides, winds, currents and summer melt continue to weaken it, a fate common to Petermann's ice islands as they move away from the glacier. Whether the fragments eventually run aground off Ellesmere Island, drift further south toward Baffin Bay, or dissipate at sea will depend on the currents they encounter over the coming weeks.

Attention is also turning back to the ice tongue itself. With two additional large rifts still active, researchers monitoring Petermann via Sentinel-1 and Landsat expect further calving in the coming months or years, though they caution the exact timing is difficult to predict. For now, the scientific interest lies less in any single calving event than in what the pattern shows about the health of a glacier that has held its floating tongue relatively stable since the last major calvings more than a decade ago — and what its next moves might signal about the broader retreat of Greenland's ice sheet into the Arctic Ocean.