How a sudden retreat at Hektoria Glacier threatens sea levels

How a sudden retreat at Hektoria Glacier threatens sea levels (File image)

Antarctica’s Hektoria Glacier has just set an alarming benchmark for how quickly land-tethered ice can unravel. Researchers report that the glacier’s front retreated roughly five miles in only two months—about ten times faster than the previous record for a grounded glacier. Between January 2022 and March 2023, Hektoria shrank by around 16 miles in total, transforming from a coherent river of ice into a churned field of jagged, overturned bergs. For scientists who had tracked it for years, the speed and violence of the collapse were jarring, according to an article in the Washington Post.

How a protective shield failed

The trigger began offshore. Hektoria is a tidewater glacier that flows to the sea, where seasonal sea ice and shorefast ice can act as a rim of armour, damping waves and stabilizing the floating tongue. As the Antarctic Peninsula—one of the planet’s fastest-warming regions—saw diminished sea ice, waves were able to pummel and fracture that protective fringe. Once this buffer failed, the glacier’s floating front started calving rapidly, shedding icebergs and exposing more surface to ocean forcing, setting off a chain reaction.

The bed that invited the ocean in

After the floating section disintegrated, thinning propagated upstream. Crucially, Hektoria sits over a gently sloping, shallow bed. That geometry allowed seawater to intrude beneath the ice, “unpinning” it from the seafloor and encouraging further flotation and breakup. Scientists liken it to toppling dominos: remove the restraining force at the edge and the rest of the system, primed by warm water and a slick bed, can unravel far faster than expected. Seismic sensors even recorded clusters of small earthquakes during the retreat, consistent with grounded ice grinding and failing as the ocean intruded.

A scientific debate over what, exactly, failed

Not all glaciologists agree on how much of Hektoria was truly grounded during the fastest retreat. Some argue the grounding zone—the point where ice lifts off bedrock to float—may lie farther inland than the new study suggests. If so, the event would resemble a dramatic, but less unusual, ice-shelf calving episode. The study’s authors counter that the seismic “icequake” signature is hard to reconcile with a purely floating shelf, implying at least parts of the fracturing front were still anchored to the bed as the collapse began.

Why this small glacier matters

Hektoria is modest by Antarctic standards, but its behaviour is a warning shot. If larger outlet glaciers elsewhere on the continent share similarly shallow, slippery beds, their margins could retreat in the same runaway fashion once protective sea ice or buttressing shelves fail. That would quicken the pace of global sea-level rise, raising risks for low-lying islands and coastal cities. The research team’s next step is to identify other Antarctic sectors with the same vulnerable geometry—places where, given the right ocean and sea-ice conditions, the dominos could fall just as fast.