Satellite data reveal how Antarctica’s ice cliffs behave over time
The cliffs don’t always collapse in the runaway process that scientists had expected.
Massachusetts Institute of Technology
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Researchers at MIT and the Woods Hole Oceanographic Institution (WHOI) analyzed over 15,000 ice cliffs in Antarctica to reveal how they behave over time.
view moreCredit: Caroline Needell
With rising temperatures, the buttressing ice shelves at the edges the Antarctic ice sheet are melting and calving off at record rates, leaving behind sheer cliffs of solid ice. The stability of these exposed ice cliffs could influence how Antarctica further breaks apart and contributes to sea level rise around the world.
Scientists have assumed that an ice cliff’s stability depends on its height: Ice cliffs that are taller than 100 meters — about the height of the Statue of Liberty — should collapse under their own weight. And once a cliff sloughs off, it should expose even taller, inland cliffs that collapse in turn. At least, that’s been the idea.
But researchers at MIT and the Woods Hole Oceanographic Institution (WHOI) have found that the stability of an ice cliff depends on more than its height. And even when a cliff topples, it doesn’t necessarily set off a runaway collapse.
In a study appearing in Science, the team presents an analysis of over 15,000 ice cliffs in Antarctica that were monitored by satellites over a four-year period. They observed how the ice cliffs and the larger ice sheet evolved over time, and found that those ice cliffs that collapsed did so at a much faster rate than scientists had predicted. But these collapsing cliffs also quickly stabilized, instead of continuing to erode the larger ice sheet.
“We found that when the cliffs were retreating, they were doing so faster than what has been modeled, which would mean more ice loss and higher contributions of sea level rise,” says study author Caroline Needell, a graduate student in the MIT-WHOI Joint Program. “But because we found that the retreat was short-lived, and all the glaciers eventually stabilized, that would suggest that things won’t be so bad. We don’t see this runaway effect.”
The study’s co-authors are Catherine Walker, assistant scientist at WHOI, and Jeremy Bassis, associate professor at the University of Michigan.
Ice height
In glacial science, ice cliff collapse is described by a process known as marine ice cliff instability (MICI), which assumes that if an ice cliff exceeds a critical height, it will collapse. If then a taller cliff is exposed, it too should collapse, triggering a cascade of instabilities that shrink and erode the ice sheet over time.
In previous studies, scientists have characterized MICI mainly by modeling the physical properties of ice, scaling these relationships up to the size of an ice cliff and combining these predictions with a few observations of actual ice cliffs in Antarctica. Through these efforts, scientists had determined that ice cliffs become unstable and collapse when they are taller about 100 meters.
“Predictive ice-sheet models that have been used so far to represent ice cliff instability just take into account cliff height,” Needell notes. “That’s the only variable that matters. And once the cliff height reaches the critical threshold, usually 100 meters, it should initiate this runaway effect of ice sheet retreat.”
But she and her colleagues wondered: How tall do ice cliffs really get? And when they collapse, do they really set off a runaway retreat?
To answer these questions, they looked to data collected by NASA’s Ice, Cloud, and Land Elevation Satellite-2 (ICESat-2) — a satellite that passes over the Earth’s polar regions and uses a laser altimeter to measure the height of ice sheets, glaciers, sea ice, and the level of the ocean in and around Antarctica.
The team collected the satellite’s data from 2019 to 2023, which included measurements every three months of over 15,000 ice cliffs. From this dataset, they observed that the average ice cliff was about 30 meters tall — much shorter than the proposed critical height. But they did see a few rare ice cliffs that exceeded 100 meters.
They also looked for other features that might influence a cliff’s stability. Interestingly, they found that ice cliffs that more or less stayed in place over time also had thicker mélange — a term for the slushy mix of broken icebergs and sea ice that gathers at the front of an ice cliff.
“We measured mélange height and found taller cliffs have thicker mélange, which could be a built-in stabilizing effect,” Needell explains.
The satellite data also showed that the height of the surrounding water can stabilize a cliff: The deeper the water, the more it can buoy and push back against the cliff, keeping it from collapsing.
Glacial speed bump
“After we did that global analysis, we thought, ok, let’s zoom in on the tallest cliffs and see how they’re behaving,” Needell says.
The team focused in on four regions around the Antarctic ice sheet where the satellite captured the tallest ice cliffs, each about 100 meters tall, with one that was 127 meters tall. They compiled measurements of these four cliffs and how they evolved every three months, over four years.
From these measurements, they saw that indeed, the tallest cliffs collapsed, and the ice sheet in those regions retreated, at a surprisingly faster rate than MICI models had predicted.
“But that retreat was short-lived,” Needell notes.
After that, the ice spread back out toward the ocean.
“It’s this rapid retreat, punctuated by periods of stabilization,” Needell says. “That was puzzling to us. Then, we thought: We need to look at all the things that affect cliff height.”
The first thing they considered was the topography of the land underneath the ice. If that topography is relatively flat, then the slope of the overlying ice sheet reflects that actual height of the ice itself. But if there’s a bump or rise in the land, the ice sitting directly over that bump is in fact shorter than it appears. The topography then could act as a literal speed bump, thinning the overlying ice, and making it less likely to collapse.
When the researchers checked topographic measurements of Antarctic, they found that indeed, ice cliffs stabilized around regions where the land happened to rise up.
They also found that the taller a cliff is, the faster they “thin out” — as they collapse, once tall cliffs settle into shorter, more stable cliffs that prevents further collapse.
“Now we know what to look for,” Needell says. “We really need to know the bed topography, and we need to know the ice thinning rate, in order to get ice cliff instability right, because this value really matters in the context of projecting sea level rise.”
This research was supported, in part, by NASA, the U.S. National Science Foundation, and the DOMINOS project, a component of the International Thwaites Glacier Collaboration.
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Written by Jennifer Chu, MIT News
Journal
Science
Article Title
Empirical constraints on ice cliff calving
Article Publication Date
15-Oct-2026
Global survey sheds light on the forces shaping ice-sheet stability
WHOI researchers use more than 15,000 satellite observations of ice cliffs to reduce uncertainty in future sea level rise projections
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An ice cliff near Brown Bluff on the Antarctic Peninsula. Scientists are usingobservations of ice cliffs like this one to test theories about how tall cliffs may influence glacierretreat and future sea level rise.
view moreCredit: Photo by Caroline Needell, ©WHOI
Woods Hole, Mass. (Oct. 15, 2026) — A new study led by the Woods Hole Oceanographic Institution (WHOI) provides the most comprehensive observational analysis yet of the towering ice cliffs that fringe Earth's ice sheets, giving scientists new evidence to evaluate a long-debated process that could influence future sea level rise. Improving these projections is increasingly important as rising seas threaten coastal communities and infrastructure worldwide.
The Marine Ice-Cliff Instability (MICI) is a theory that proposes extremely tall ice cliffs, taller than about 100 meters above the waterline, can become structurally unstable and trigger a cycle of rapid, self-sustaining ice loss. Because that process has never been directly observed, scientists have debated whether it should be included in projections of future sea level rise. To test the theory against real-world observations, researchers analyzed the characteristics of ice cliffs using 15,330 individual satellite observations collected around the margins of Earth's ice sheets.
The study, published in Science, utilized satellite laser altimetry, a technique that measures surface elevation by timing how long it takes laser pulses to travel from a satellite to Earth's surface and back. Those measurements allowed the researchers to calculate cliff heights and compare them with ice thickness, water depth, crevassing, and calving rates across thousands of locations around the ice sheets.
“Our findings suggest ice-sheet models may underestimate how quickly tall ice cliffs can break apart. At the same time, the observations show that glaciers often thin and retreat into regions where the conditions become less favorable for continued rapid retreat,” said Caroline Needell, an MIT-WHOI Joint Program doctoral student and lead author of the study. “These findings show that some of the processes described by marine ice-cliff instability occur in nature, but they also show that other factors can limit rapid retreat.”
Global sea level has already risen by more than eight inches since 1880, and scientists project it will continue to rise throughout this century as ice sheets lose mass. By identifying the conditions that drive and limit rapid ice-cliff retreat, the study helps scientists improve models of how ice sheets contribute to future sea level rise. More accurate projections are increasingly important for coastal communities, where rising sea levels can worsen flooding, accelerate erosion, damage infrastructure, and intensify storm-surge impacts.
“Understanding how ice sheets lose mass is key to improving projections of future sea level rise,” said Catherine Walker, a glaciologist at WHOI and author of the study. “To make better predictions, we need observations that show how glaciers behave where they meet the ocean and help us improve the models we use to understand future change.”
Unlike previous studies that focused on individual glaciers or computer simulations, this work examines thousands of ice cliffs across Earth's ice sheets using a consistent set of satellite observations. The dataset gives scientists a way to test ice-sheet models against real-world measurements, helping improve predictions of how glaciers may respond as the climate changes.
"When ice sheets start to calve, they can do so very rapidly,” said Jeremy Bassis, a geophysicist at the University of Michigan and author of the study. “Fortunately, all of the examples we have so far suggest that the rapid retreat documented in this study is short-lived and the glaciers eventually re-stabilize. Whether that remains true in the future as climate change continues to push ice sheets out of their comfort zone is something we do not yet know."
“Marine ice-cliff instability has been a source of uncertainty in projections of future sea level rise,” Walker continued. “These observations provide a new global dataset to test the theory against real-world measurements and improve ice-sheet models by identifying the conditions that drive rapid ice loss and those that limit it.”
This research was supported by the National Science Foundation, NASA, the U.S. Department of Energy, the DOMINOS project, a component of the International Thwaites Glacier Collaboration, and the Natural Environment Research Council.
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Woods Hole Oceanographic Institution
Woods Hole Oceanographic Institution (WHOI) is a private, non-profit organization dedicated to marine research, engineering, and higher education. Founded in 1930 and based in Cape Cod, Massachusetts, WHOI’s mission is to understand the ocean and its interaction with the Earth system, and to communicate the ocean’s vital role in the global environment.
Journal
Science
Method of Research
Observational study
Subject of Research
Not applicable
Article Title
Empirical constraints on ice cliff calving
Article Publication Date
15-Oct-2026
