Iceberg A-81 slows beside South Georgia’s underwater shelf
A satellite image and new analysis track iceberg A-81 near South Georgia after its journey from Antarctica. The berg slowed beside the island’s shallow underwater shelf, which has grounded other large icebergs. Its separation from the Brunt Ice Shelf dates to January 2023; the current development concerns its position and movement in October. The image was acquired on 20 October.
Science··Midday
A-81 slows near South Georgia
A new satellite assessment follows Antarctic iceberg A-81 near South Georgia, an island in the South Atlantic.[1], [2]
The iceberg’s progress slowed as it approached the edge of the island’s shallow underwater shelf. NASA’s Earth Observatory released the analysis on 27 October, using an image taken a week earlier. The new observation concerns this stage of its journey from Antarctica.[1]
The Moderate Resolution Imaging Spectroradiometer, or MODIS, on NASA’s Terra Earth-observing satellite acquired the image on 20 October. Jan Lieser of Australia’s Bureau of Meteorology and retired University of Maryland scientist Christopher Shuman interpreted the earlier slowdown as the berg apparently bumping along the shelf edge. South Georgia has previously slowed or stopped large icebergs. The image fixes A-81’s position on its acquisition date.[1]
The journey began with a 2023 break
A-81 separated from Antarctica’s Brunt Ice Shelf in January 2023, when it covered about 1,550 square km. The Weddell Sea’s clockwise circulation carried it along the Antarctic coast for more than three years. By May it had reached the tip of the Antarctic Peninsula, then moved north into the Scotia Sea. Its late-October position near South Georgia lies roughly 2,300 km north-northwest of the Brunt Ice Shelf. The 2023 calving is the starting point for this trajectory.[1]
Brunt’s long fracture history precedes the drift
Chasm 1, the Brunt fracture that eventually released A-81, remained relatively stable for about 35 years before growing again around 2012. By 2019 its advance suggested a break was approaching, but the ice held on until January 2023. Calving is part of an ice shelf’s normal cycle. Brunt also shed A-74 in 2021 and A-83 in 2024; these earlier breaks form the regional background to A-81’s route.[1]
Another iceberg, A-23A, grounded on South Georgia’s shelf in 2025 and subsequently broke apart. That earlier encounter illustrates the shelf’s physical influence on large drifting ice masses. A-81’s subsequent movement will require later observations; its October image records the current encounter rather than a completed grounding or breakup.[1]
Brunt also hosts the British Antarctic Survey’s Halley Research Station, a base for Earth, atmospheric and space science since the 1950s. Scientists continue monitoring the ice shelf as its fractures develop and large pieces detach.[1]
