The sudden propagation of a major pre-existing rift (full-thickness crack) in late 2016 on the Larsen C Ice Shelf, Antarctica lead to the calving of tabular iceberg A68 in July 2017, one of the largest icebergs on record, posing a threat for the stability of the remainder of the ice shelf. As for other ice shelves, the physical processes that led to the activation of the A68 rift and controlled its propagation have not been elucidated.  Here, we model the response of the ice shelf stress balance to ice shelf thinning and to thinning of the ice mélange encased in pre-existing rifts. We find that  ice shelf thinning does not re-activate the rifts; it heals them. In contrast, thinning of the mélange directly controls the opening rate of the rift, with an above-linear dependence on thinning. The simulations indicate that a thinning of the ice mélange by 10-20 m is a sufficient condition to re-activate the rifts and trigger a large calving event, thereby establishing a direct link between climate forcing and ice shelf retreat that has not been used in ice sheet models. Rift activation may explain the early initiation of ice shelf retreat many years prior to hydro-fracture caused by the ponding of melt water at the ice shelf surface, hence for a smaller amount of climate warming.   

The dataset used to run the JPL/UCI Ice Sheet and Sea Level Model (ISSM) (Version of the development trunk, 22904, available at issm.jpl.nasa.gov upon request) includes: 

1) runme.m: Matlab script use for the modeling: all routines and steps (pre and post processing as well as simulation runs) to carry out all the model runs.

2) firn.mat: a firn layer from the SeaRISE Antarctica5km_shelves_v1.0 experiment development data set at http://websrv.cs.umt.edu/isis/index.php/Present_Day_Antarctica

3) vel_final_2014-07-01_2015-06-31_LC.nc: A velocity map from Sentinel 1-a interferometry SAR data  from Mouginot et al, 2017 in netcdf format. The netcdf contains several variables: CNT (number of points averaged to get result), errx (error in velocity along x-axis), erry (same for y-axis, stdx (standard deviation of velocity along x-axis), stdy (same for y-axis), vx (velocity along x-axis in meters per year), vy (same for y-axis), lat (latitude of each point in the grid), lon (same for longitude). The projection is EPSG:3031 - WGS 84 / Antarctic Polar Stereographic. 

4) TDX_ANTPEN450m_msl_v18july2017.tif: A TanDEMx 50-m resolution Digital Elevation Model (surface elevation above mean sea level) from Rizzoli et al, 2017 in geotif format. The projection is EPSG:3031 - WGS 84 / Antarctic Polar Stereographic. Elevation in meters. 

5) Rift2014_Passive.* and Rift2014_Active.*: ESRI Shapefiles for active and passive rits on Larsen C. Projection is EPSG:3031 - WGS 84 / Antarctic Polar Stereographic. 

6) s1a-ew-grd-hh-20170727t002304-20170727t002404-017649-01d8bc-001.tiff: A Sentinel S1a Extended Width image in ground range from 2017-7-27 in geotiff format. Projection is EPSG:4326 - WGS 84 - Geographic.