New satellite imagery shows that the crack in Larsen C has forked.
The fork propagated very quickly – between satellite passes. That’s over the course of approximately 6 days, but the crack may actually have developed considerably faster than that.
Adrian Luckman, lead of the @MIDASonice project, told BBC News:
“This is one of the things I find so fascinating. You look at these rifts and think they’re moving really quite slowly. But when they go, they must go very quickly. People have said they could travel at anything up to the speed of sound. It would be amazing to be on the shelf to hear it.”
The main crack’s development had previously stalled because it had entered a region of suture ice, which is softer and more resistant to fracture. Fittingly, a timely and well-explained paper by Chris Borstad and colleagues has just been published, explaining the importance of different types of ice on the shelf for increasing its stability. That stability largely hinges on the presence of suture zones.
The fork has progressed in a direction more in keeping with what scientists predicted. Glaciologists have been tracking the stress field of the ice shelf, which describes where there is most pressure and force acting on the ice. Cracks usually develop at right angles to the direction of the stress field. However, because a lot of force has to build up before they rip through suture zones, they often overshoot the crack, even if it means the direction isn’t at right angles to the stress field.
The new fork is moving towards the edge of the ice shelf, making it look increasingly likely that the nascent iceberg will calve (break off) imminently.
The existing rift had already made flow velocities downstream increase considerably. The ice shelf near the edge is now moving very fast indeed – exceeding 3.0 m per day nearest the edge, as illustrated by this figure showing ESA Sentinel-1 data from March/April 2017 (courtesy of Adrian Luckman, via MIDAS).
Watch this space!