As the Larsen C ice shelf moves closer to calving one of the largest icebergs on record, there are clear signs of changes in the part of the shelf which is about to calve. In late June 2017, the soon-to-be iceberg tripled in speed, producing the fastest flow speeds ever recorded on Larsen C, and seemed to be on the verge of breaking free.

Map of surface speed in late June 2017 derived using feature tracking between consecutive Sentinel-1 images
Animation of Sentinel-1 interferograms showing significant stages in the propagation of the rift and culminating in the july 2017 multiple branching
Detail of the branching occurring between 24th June and 6th July 2017

The latest data from 6th July reveal that, in a release of built-up stresses, the rift branched several times. Using data from ESA’s Sentinel-1 satellites, we can see that there are multiple rift tips now within 5 km of the ice edge. We expect that these rifts will lead to the formation of several smaller icebergs, as well as the large iceberg which we estimate will have an area of 5,800 sq km. Despite this, the iceberg remains attached to the shelf by a thin band of ice. It is remarkable how the moment of calving is still keeping us waiting.

When it calves, the Larsen C Ice Shelf will lose more than 10% of its area to leave the ice front at its most retreated position ever recorded; this event will fundamentally change the landscape of the Antarctic Peninsula. We have previously shown that the new configuration will be less stable than it was prior to the rift, and that Larsen C may eventually follow the example of its neighbour Larsen B, which disintegrated in 2002 following a similar rift-induced calving event.

The MIDAS Project will continue to monitor the development of the rift and assess its ongoing impact on the ice shelf. Further updates will be available on this blog, and on our Twitter feed.

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