Rising temperatures are causing the buttressing ice shelves at the edge of the Antarctic ice sheet to melt and calve at record rates, leaving behind sheer cliffs of solid ice. The stability of these exposed cliffs directly influences how the ice sheet may further fragment and how much sea level will rise globally.
The conventional marine ice cliff instability (MICI) framework assumes that once a cliff exceeds a critical height of about 100 m—roughly the height of the Statue of Liberty—it collapses under its own weight, exposing taller inland cliffs and triggering a cascade of failures.
Researchers from MIT and WHOI used NASA’s ICESat‑2 laser altimeter to gather three‑monthly height measurements of more than 15 000 Antarctic ice cliffs between 2019 and 2023, then analyzed their four‑year evolution.
They found the average cliff height to be only ~30 m, far below the proposed threshold, with only a handful exceeding 100 m. Importantly, thicker mélange (the slushy mix of broken icebergs and sea ice) and deeper surrounding water were observed to provide additional buoyant support, enhancing cliff stability.
Focusing on the four tallest cliffs (the highest reaching 127 m), the team saw that these cliffs did indeed collapse faster than MICI models predict, but the retreat was brief; the ice subsequently readvected toward the ocean, stabilizing quickly.
Further analysis revealed that bedrock topography acts as a “speed bump”: where the seabed rises, the overlying ice thins, reducing collapse risk. Moreover, tall cliffs thin rapidly after collapse, transitioning into shorter, more stable configurations.
Consequently, accurate sea‑level projections must incorporate bed topography, ice‑thinning rates, water depth, and mélange thickness rather than relying solely on a height threshold.
The work was supported by NASA, the U.S. National Science Foundation, and the DOMINOS component of the International Thwaites Glacier Collaboration.
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