Crevasses in the Greenland Ice Sheet are expanding faster than previously thought.
Between 2016 and 2021, cracks at the edge of the sheet grew much larger and deeper in response to the ice’s rapid movement from the sheet’s domed center toward the ocean, researchers reported in Nature Geoscience. This growth could drive feedback mechanisms that accelerate ice loss on relatively short timescales.
Covering the majority of Greenland, the ice sheet contains nearly 3 million cubic kilometers of ice, which could raise sea levels by more than 7 meters if it were to melt completely. Ice sheets spread out under their own weight continuously, but they maintain their mass as long as the loss of ice is balanced out by winter snowfall. Rising temperatures, however, can cause the ice to flow faster than normal. Crevasses form where the stress from this acceleration is great enough to fracture the ice sheet’s surface.
“Crevasses are essentially the pathway by which water could make its way into the belly of the ice sheet,” said study coauthor Thomas Chudley, a glaciologist at Durham University. Of the hundreds of gigatons of meltwater that the Greenland Ice Sheet generates every year, the vast majority flows through crevasses to the bed of the ice sheet, where it can buoy the ice on its path to the ocean.
“Being able to inventory individual crevasses with this new analysis brings our observation to a completely different level of detail.”
Because crevasses affect how quickly meltwater and ice enter the sea, they play an important role in predictions of future mass loss from the ice sheet. But crevasses are difficult to observe with satellites: Crevasse surface widths range from less than a meter to a few tens of meters across, whereas the resolution of satellites used to study them is a few tens of meters to hundreds of meters.
“We have been observing the Greenland Ice Sheet with satellites for decades, but crevasses have always been overlooked—literally—because they were smaller than satellite pixels,” William Colgan, a glaciologist at the Geological Survey of Denmark and Greenland, wrote in an email to Eos. Colgan was not involved in the new study. “Actually being able to inventory individual crevasses with this new analysis brings our observation to a completely different level of detail.”
To capture how crevasse volume changed over the study period, the team used digital elevation models of the Arctic surface. These three-dimensional maps, created from overlapping high-resolution satellite images, capture elevation data at 2-meter resolution across the entire Arctic. From the maps, the researchers calculated crevasse volumes over the full Greenland Ice Sheet in 2016 and 2021.
“This is leading edge computer science applied to the ice sheet, stuff that would not have been possible ten years ago,” Colgan wrote.
Near-Ubiquitous Expansion
Crevasse volume increased in regions where ice flow into the ocean was also increasing, the team found. Volume changes varied by region but were particularly pronounced in eastern Greenland and at low elevations where ice meets sea. Central northern Greenland saw the largest relative increase in crevasse volume at 25%.
Averaged across the whole of the ice sheet, the increase wasn’t significant. But that’s mainly because of a temporary decrease in crevassing in just one glacier, Chudley said. A brief influx of cold ocean water from the North Atlantic caused Sermeq Kujalleq, a fast-moving glacier in western Greenland, to slow down between 2016 and 2019.
“What our study captured was almost like squeezing an accordion,” Chudley said. “All the crevasses kind of closed up.”
That slowdown has since ended, and Sermeq Kujalleq is accelerating once again, which means it likely won’t offset increased crevassing and acceleration in the rest of Greenland going forward, Chudley said.
“This is the first study to unequivocally say that the expansion of crevasse zones is ubiquitous across Greenland’s outlet glaciers.”
The team’s findings support anecdotal reports from field researchers. “Those of us working in the field sense that we are seeing more crevasses out there, and indeed we have started assessing crevasse risk at ice-sheet sites where it was traditionally not an issue,” Colgan wrote. “But this is the first study to unequivocally say that the expansion of crevasse zones is ubiquitous across Greenland’s outlet glaciers, which have accelerated in recent years.”
The results also highlight how crevasses affect other processes on the ice sheet. When meltwater flows through crevasses to the bed of the ice sheet, it lubricates the ice, speeds its progress into the ocean, and helps melt the ice that enters the sea. Faster ice flow could open more crevasses in a feedback loop that could further increase ice loss from Greenland and raise sea levels.
Chudley’s team plans to use the findings to better predict future ice sheet behavior and sea level rise, he said. And because digital elevation models of the Arctic will continue to be released each year, the team will be able to add new crevasse data to refine their predictions.
“Hopefully, it’s something we can do again in 5 years,” Chudley said. “We can watch some time pass and see how things have changed.”
—Skyler Ware (@skylerdware), Science Writer