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Usually, no. Antarctic ice cliffs can retreat extremely quickly, but repeated satellite observations show that the fastest failures often stop rather than trigger an unstoppable chain of taller and taller collapses. A 2026 study using NASA’s ICESat-2 followed more than 15,000 cliffs from 2019 through 2023 and found brief bursts of rapid retreat followed by stabilization.
That result weakens the case for runaway, total ice-sheet disintegration in the observed locations, but it does not make sea-level rise harmless. Short-lived failures were faster than many existing models assumed, so partial ice losses could still add to sea-level rise more quickly than conservative projections indicate.
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What the ICESat-2 observations found
The study combined repeat ICESat-2 elevation measurements taken roughly every three months with imagery and analysis of Antarctic glacier fronts. The observed cliffs averaged about 30 meters high. Only a small number approached the approximately 100-meter height commonly used as a critical threshold in earlier marine ice-cliff-instability (MICI) models. One intensively tracked cliff reached 127 meters.
The data show a distinctive pattern: a tall face can fail and retreat faster than models predict, but that acceleration is generally short-lived. After the initial collapse, the ice front often spreads back toward the ocean and settles into a more stable configuration instead of exposing an ever-higher inland wall.
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University of Michigan Engineering’s account of the work also describes a collection of more than 15,000 aerial and satellite images. The imagery and ICESat-2 elevation record provide repeated views of changing cliff faces rather than a single snapshot of their height.
How marine ice-cliff instability was supposed to work
MICI is a proposed feedback loop at the edge of a marine ice sheet:
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- A floating or grounded ice cliff rises above a critical height, often modeled at about 100 meters above the ocean.
- Gravity causes the unsupported face to fracture and collapse.
- The retreat exposes a taller cliff farther inland.
- That new cliff exceeds the critical height and fails in turn, producing a runaway cascade.
In its most extreme form, this mechanism would let a marine ice sheet disintegrate much faster than surface melting or ordinary glacier flow alone. Some sea-level scenarios that include runaway breakdown project rates roughly twice as fast as scenarios in which glaciers remain more stable, according to University of Michigan reporting.
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The observations identify several stabilizing processes that a height-only rule leaves out.
Ice mélange can brace the front
Ice mélange is a dense mixture of sea ice, bergy bits and broken icebergs packed in front of a glacier. It can exert back-force on the cliff and slow the opening of fractures. Peer-reviewed modeling has likewise found that mélange resistance can inhibit runaway retreat.
Water depth changes the forces on the cliff
Deeper water can increase buoyancy and the pressure acting against the submerged part of the ice front. Those forces can reduce the effective load on the face and help a glacier remain grounded or otherwise resist immediate retreat.
Bedrock rises can act as pinning points
Submerged bedrock highs beneath or near a glacier can catch the ice and provide additional resistance. A cliff’s position relative to this topography may therefore matter as much as its visible height.
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A newly exposed, tall face can lose height quickly through fracturing and flow. That thinning removes the geometric condition that made the cliff especially unstable, helping explain why a burst of retreat can end without a second, larger collapse.
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Older MICI scenarios and the new observational interpretation
| Question | Earlier MICI framing | 2026 observational interpretation |
|---|---|---|
| Evidence type | Model experiments built around assumed critical heights | Repeated ICESat-2 measurements and imagery from 2019–2023 |
| Typical collapse behavior | One failure exposes a taller cliff, creating a self-sustaining cascade | Rapid retreat can occur in bursts, then stop as the glacier restabilizes |
| Main control on stability | Cliff height, often near a 100-meter threshold | Height combined with mélange, water depth, bedrock topography and thinning rate |
| Sea-level implication | Potentially extreme rates from total disintegration | Runaway total collapse is not supported by the observed examples, while faster partial losses remain possible |
What this means for Antarctic sea-level projections
The findings narrow, rather than eliminate, uncertainty. The observed cliffs did not behave as if every face above a fixed height must fail repeatedly. That makes projections based on runaway destruction of an entire ice sheet less credible for the cases observed so far.
At the same time, the cliffs that did retreat were moving faster during their active phases than existing models predicted. If similar bursts occur across vulnerable glacier fronts, the cumulative ice loss could be greater than projections that assume uniformly slow retreat. The relevant risk is therefore not only whether a whole ice sheet collapses, but also how often short, high-loss episodes occur and how much ice each episode removes.
West Antarctica remains a key concern because it contains marine-based ice grounded below sea level and complex submarine topography. The study’s authors emphasize that predicting a runaway effect there will require measurements of more than cliff height.
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What the study does—and does not—establish
- Established in the observed cases: collapse and retreat can be rapid; the rapid phase often ends; the ice front can stabilize afterward.
- Established about the sample: most measured cliffs were far below 100 meters, with an average near 30 meters and one closely tracked example at 127 meters.
- Important controls: mélange, water depth, bedrock highs and the rate at which a cliff thins all influence stability.
- Not established: that every Antarctic glacier will stabilize, or that no runaway sequence can ever occur in a different setting.
- Still needed: longer time series and observations from more vulnerable glacier fronts to determine how representative these examples are.
Why the result matters
Caroline Needell, an author of the study, said the faster-than-modeled retreat would imply more ice loss and a larger sea-level contribution, but that the short-lived retreat and eventual stabilization do not show the runaway effect. University of Michigan professor Jeremy Bassis similarly said the observed examples do not support projections relying on total, runaway disintegration.
The practical lesson is to treat cliff height as one measurement among several. Future sea-level models need to represent the mechanical support supplied by mélange and bedrock, the buoyant and pressure effects of the ocean, and the rapid thinning that follows a collapse. That approach can capture both sides of the new evidence: catastrophic, whole-ice-sheet cascades are not appearing in the observed record, yet brief episodes of unusually fast retreat remain a credible source of additional sea-level rise.
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