Manhattan-sized ice island breaks from Greenland's Petermann Glacier

A slab of floating ice roughly the size of Manhattan has broken away from Petermann Glacier in northwest Greenland, in what researchers monitoring the site call the glacier's largest loss of ice since 2012 and the most significant calving event recorded anywhere in the Arctic since 2020. The separation was confirmed on August 4, capping years of visible fracturing that scientists had tracked by satellite since 2019.

The break was detected using radar imagery from the European Space Agency's Copernicus Sentinel-1 mission, which showed pronounced deterioration along the centerline of the glacier's floating ice tongue on August 3. By 20:00 UTC the following day, the ice island had fully detached from the tongue's eastern side and begun drifting into Nares Strait, the waterway separating Greenland from Canada's Ellesmere Island.

The numbers

The newly formed tabular iceberg covers an area of 76.4 square kilometers and is estimated to be as much as 150 meters thick, according to researchers at the University of Ottawa, whose glaciology team was among the first to flag the detachment. The event is not expected to be an isolated one. Two additional sections of Petermann's floating tongue, estimated at roughly 94 and 84 square kilometers, show signs of imminent separation. If both break away as projected, the three combined calving events would strip approximately 254 square kilometers from the ice tongue — close to a quarter of what remains of it.

Petermann's ice tongue, which historically extended some 70 kilometers out into its fjord, functions as a floating buttress that slows the seaward flow of grounded ice behind it. Its retreat does not by itself raise sea levels, since the floating portion already displaces its own weight in seawater. But glaciologists say its thinning and fragmentation removes resistance on the ice sheet upstream, an effect that can accelerate the discharge of land-based ice — which does contribute to sea-level rise — across the glacier's grounding line.

Watching the fracture for years

The detection is the product of an ongoing collaboration between the University of Ottawa, the Universities of Stirling, Lancaster and Leeds in the United Kingdom, and the Canadian Ice Service of Environment and Climate Change Canada, working under ESA's FutureEO-funded ARCTEX project. The team has used Sentinel-1's radar imagery, which penetrates cloud cover and works in polar darkness, to track crack propagation across the ice tongue since 2019, building a record of exactly how the structure weakened before it gave way.

An interferogram released alongside the satellite imagery of the calving event shows deformation patterns that had already developed across the ice tongue by April, roughly four months before the final break. Because Arctic tabular icebergs of this scale are uncommon compared with their much more frequent Antarctic counterparts, researchers say the event offers a rare, closely documented case study in how these ice masses form, drift and eventually disintegrate.

ARCTEX itself is broader than Petermann alone. Funded through an ESA Polar Science Cluster call and led by Norway's Science and Technology research institute alongside the Technical University of Denmark and the Universities of Lancaster, Leeds and Tromsø, the project is designed to use satellite observation to understand extreme events across the Arctic system — the interplay between atmosphere, ocean, sea ice and land ice — through dedicated case studies at the Austfonna and Flade Isblink ice caps and the Nioghalvfjerdsfjorden Glacier, also known as the 79N Glacier, in northeast Greenland. The Petermann monitoring effort draws on the same funding stream and satellite methods, applied to a glacier whose instability researchers have followed independently since well before the project began.

Who is watching it now

Environment and Climate Change Canada is tracking the iceberg's trajectory through Nares Strait, where large ice islands can pose hazards to shipping and to research and resupply operations in the region. Historically, fragments from Petermann's earlier calvings have carried satellite tracking beacons that transmit their position several times a day as they drift, feeding into the Canadian Ice Island Drift, Deterioration and Detection Database that the country's ice service uses to warn vessels operating in the strait and in Baffin Bay.

The glacier's last major calving, in July 2012, offers a template for what may follow. That event, along with earlier calvings in 2008 and 2010, was analyzed in detail by a research team that included Anna Crawford — the same University of Stirling scientist now involved in tracking the 2026 break. Writing in the Journal of Geophysical Research: Oceans, Crawford and colleagues found the 2008 event released about 30 square kilometers of ice, the 2010 event roughly 293 square kilometers containing about 20 gigatons of ice, and the 2012 event about 137 square kilometers containing roughly 22 gigatons. Tracked fragments drifted south through Nares Strait and along the western edge of Baffin Bay into the Labrador Sea, breaking apart along the way in a pattern the researchers found followed a consistent power-law size distribution — meaning fracture, rather than gradual melting, was the dominant process by which the ice islands broke down. The same 2018 study calculated that meltwater from those three events reaching the Baffin Island and Labrador currents was too small to meaningfully disrupt the Atlantic Meridional Overturning Circulation, though it added measurably to regional freshwater in the fjord and near the glacier's grounding line.

"Petermann Glacier has long been one of Greenland's largest remaining ice tongues. We've anticipated this break for years, and seeing it finally happen is remarkable," said Adam Garbo, a PhD student in glaciology at the University of Ottawa's Department of Geography, Environment and Geomatics, who has monitored the site.

Anna Crawford noted that Arctic ice islands "are far rarer" than the tabular icebergs common around Antarctica, making their formation and breakup especially useful for scientists studying "calving and deterioration of ice islands" and their downstream effects on glacier dynamics, sea-level contributions and the surrounding ocean environment. Molly Hammond, a PhD student at the University of Leeds who worked on the interferometric analysis, said the changes at Petermann were "occurring very rapidly," which made tracking the crack's progression with radar interferometry especially useful for anticipating the break before it happened.

What happens next

Researchers say the two remaining large sections of the ice tongue identified in current satellite data are likely to separate in the coming months to years, continuing a pattern of retreat that has left Petermann's floating tongue significantly shorter than it was before the 2012 calving. The ARCTEX collaboration plans to keep using Sentinel-1's near-daily radar coverage to track both the drifting ice island and the ongoing fracturing of what remains of the tongue, data that feeds into broader assessments of how quickly Greenland's marine-terminating glaciers are responding to a warming Arctic.

Scientists have also pointed to shifting precipitation patterns on the Greenland ice sheet as part of the broader backdrop. In August 2021, rain fell for several hours at the ice sheet's 3,216-meter summit, the first rainfall ever recorded there, according to the National Snow and Ice Data Center. Surface mass loss the following day ran roughly seven times above the mid-August average, and melting spread across an estimated 337,000 square miles of the ice sheet over two days. Researchers say episodes like that one illustrate how the balance between snow accumulation and ice loss governing glaciers such as Petermann has become less predictable, even as the fate of the newly detached ice island itself will likely play out over years, not months, as it drifts south.