Understanding of an Iceberg Breaking Off Event Based on Ice-Front Motion Analysis of Amery Ice Shelf, Antarctica

On 26 September 2019, a massive iceberg broke off the west side of the Amery Ice Shelf (AIS) in East Antarctica. Since 1973, the AIS calving front has steadily advanced at a rate of 1.0 km yr(-1). However, the advancement rate of the central portion of the AIS increased dramatically during 2012-2015, which indicates a velocity increase prior to the calving event. Eight calving front locations from 1973 to 2018 were mapped to investigate the advancement rate of AIS over the entire observational period. Additionally, the propagation of rift A was observed unstable from 2012 to 2015. The westward propagation rate of rift A1 increased to 3.7 km yr(-1) from 2015 to 2017, which was considerably faster than the other rifts near the AIS calving front. The increased advancement rate and the increasing propagation magnitude of at least one active rift appear to be precursors of this large calving event.