This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: In August 2026, an iceberg the size of Manhattan broke away from the Petermann Ice Shelf in northern Greenland. It was the glacier's largest calving event since 2020.
Long before the breakup, CIRES scientists were developing a new method to understand the planet's first known ice shelf estuary on the Petermann Ice Shelf. The estuary—where salt water from the ocean and fresh water from a surface meltwater river mix—was discovered in 2021. New CIRES-led research, published in The Cryosphere, explains how and when the estuary formed—something no one had studied until now.
"For the first time, we were able to measure how quickly the river cut into the ice shelf to form the estuary, which revealed more complex estuary behavior than was previously suggested," said Michela Savignano, a CU Boulder geography and CIRES doctoral student and lead author of the study. "We did this using a new method for calculating the elevation of the river channel above sea level during the melt season from satellite imagery." The research may help explain the August calving event. "We think the process of the estuary forming and reforming over multiple melt seasons weakened the ice shelf due to the loading and unloading of ocean water, and potentially contributed to the calving event that happened in August of this year," said Alison Banwell, a research scientist in CIRES' Earth Science and Observation Center and a co-author of the study.
The research builds on a 2021 study led by one of the new study's co-authors, Alexandra Boghosian, that confirmed the first ice shelf estuary using high-resolution satellite images. The images revealed chunks of sea ice floating up the river channel onto the Petermann Ice Shelf. Understanding the estuary requires understanding supraglacial rivers—rivers that flow on the surface of ice shelves and empty into the ocean.
During summer months, when air temperatures are above freezing, glaciers and surface snow melt, and water pools on ice shelves. That can create instability and make the shelves more susceptible to collapse, as in the Larsen B ice shelf breakup in 2002. Yet rivers that flow from these pools can reduce pressure and weight by carrying water from the ice shelf into the ocean.
"We've known for a couple of decades that lakes can be harmful to the overall health of an ice shelf, whereas rivers can actually be beneficial," Banwell said. "Our new research suggests that estuaries can also be harmful." The supraglacial river on Petermann began like any other, but over time it cut deep into the ice, eventually dropping below sea level at its mouth. The authors measured the river's incision rate from the surface of the river all the way down to the bottom of the channel.
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