Time forecast of a break-off event from a hanging glacier

Abstract

A cold hanging glacier located on the south face of the Grandes Jorasses (Mont Blanc, Italy) broke off on the 23 and 29 September 2014 with a total estimated ice vol- ume of 105 000 m 3 . Thanks to accurate surface displacement measurements taken up to the final break-off, this event was successfully predicted 10 days in advance, enabling local au- thorities to take the necessary safety measures. The break- off event also confirmed that surface displacements expe- rienced a power law acceleration along with superimposed log-periodic oscillations prior to the final rupture. This pa- per describes the methods used to achieve a satisfactory time forecast in real time and demonstrates, using a retrospective analysis, their potential for the development of early-warning systems in real time.