The frontal ice avalanche of Frebouge Glacier (Mont Blanc Massif, Valley of Aosta, NW Italy) on 18 september 2002

Abstract

In September 2002, a part (>0,1 x 10⁶ m³) of the Frébouge Glacier (Val Ferret) front avalanched onto the apex of the polygenic fan. The 0.1 x 10⁶ m² deposit was composed of poorlysorted, subspherical, openwork ice particles and formed a lobate front; the lateral margins are steep metric ridges, along longitudinal shear zones. Some big ice boulders rolled 100-150 m ahead the front. Following Alean’s (1985) ice avalanching typology, the Frébouge event is a type IA event: that is to say, avalanching of a low elevation temperate glacier front on a steep rock bed. Others type IA ice avalanches have probably occured in recent decades, but the rapid fusion of avalanche deposits makes their survey difficult. The ignorance of this process frequency explains its underestimation in alpine hazard analysis.