British Antarctic Survey (BAS) recently captured this video footage of a huge crack in the Larsen C Ice Shelf, on the Antarctic Peninsula.

Currently a huge iceberg, roughly the size of Norfolk, looks set to break off Larsen C Ice Shelf, which is more than twice the size of Wales. Satellite observations from February 2017 show the growing crack in the ice shelf which suggests that an iceberg with an area of more than 5,000 km² is likely to calve soon.

Researchers from the UK-based MIDAS project, led by Swansea University, have reported several rapid elongations of the crack in recent years. BAS scientists are involved in a long-running research programme to monitor ice shelves to understand the causes and implications of the rapid changes observed in the region. They shot this footage as they flew over the ice shelf on their way to collect science equipment.

During the current Antarctic field season, a glaciology research team has been on Larsen C using seismic techniques to survey the seafloor beneath the ice shelf. Because a break up looks likely the team did not set up camp on the ice as usual. Instead they made one-off trips by twin otter aircraft supported from the UK’s Rothera Research Station.

Ice shelves in normal situations produce an iceberg every few decades. There is not enough information to know whether the expected calving event on Larsen C is an effect of climate change or not, although there is good scientific evidence that climate change has caused thinning of the ice shelf. Once the iceberg has calved, the big question is whether Larsen C will start to retreat.

Dr Paul Holland, ice and ocean modeller at British Antarctic Survey, says: “Iceberg calving is a normal part of the glacier life cycle, and there is every chance that Larsen C will remain stable and this ice will regrow. However, it is also possible that this iceberg calving will leave Larsen C in an unstable configuration. If that happens, further iceberg calving could cause a retreat of Larsen C. We won’t be able to tell whether Larsen C is unstable until the iceberg has calved and we are able to understand the behaviour of the remaining ice. “The stability of ice shelves is important because they resist the flow of the grounded ice inland. After the collapse of Larsen B, its tributary glaciers accelerated, contributing to sea-level rise.”

About ice shelves

An ice shelf is a floating extension of land-based glaciers which flow into the ocean. Because they already float in the ocean, their melting does not directly contribute to sea-level rise. However, ice shelves act as buttresses holding back glaciers flowing down to the coast. Larsen A and B ice shelves, which were situated further north on the Antarctic Peninsula, collapsed in 1995 and 2002, respectively. This resulted in the dramatic acceleration of glaciers behind them, with larger volumes of ice entering the ocean and contributing to sea-level rise.

The largest icebergs known have all calved from ice shelves. In 1956, a huge iceberg of roughly 32,000 km² – bigger than Belgium – was spotted in the Ross Sea by a US Navy icebreaker. However, since there were no satellites in orbit at this point, its exact size was not verified. In 1986, a section of the Filchner ice shelf roughly the size of Wales calved – but this iceberg broke into three pieces almost immediately. The largest iceberg recorded by satellites calved from the Ross ice shelf in 2001, and was roughly the size of Jamaica at 11,000 km².

The MIDAS Project is funded by the NERC (Natural Environment Research Council).