Laser survey finds Antarctic ice cliffs calve fast, but rarely sustain runaway retreat
A survey of 15,330 ice cliffs in Antarctica and Greenland found that very tall cliffs are rare and that those observed calve faster than some models assume. In Science, Caroline Needell and colleagues report that dynamic thinning and gradual changes in inland ice thickness can limit the height build-up needed for marine ice-cliff instability; they say Thwaites Glacier is unlikely to retreat immediately through this process if its ice shelf fails.
Bottom line — At Thwaites, gradual inland thickening appears to limit cliff growth, but the study does not rule out future instability.
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The Science study found that 95% of Antarctic cliffs were below 52.2 metres and 95% of Greenland cliffs below 76.6 metres.
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Cliff height was strongly associated with water depth, ice mélange thickness and crevassing, according to the researchers.
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Only 16 glaciers in the survey had cliffs taller than 90 metres; four had repeat observations and measurable retreat.
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Earth.com reports that the team tracked retreat at those four glaciers over periods of roughly three months, so the measured rates do not establish long-term behaviour.
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Earth.com says a roughly 100-metre cliff calved at more than three times the rate predicted by the formula behind some high-end projections.
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The researchers say dynamic thinning and low inland ice-thickness gradients can stop successive failures from exposing ever-taller cliffs.