The Trê-la-Tête rockfall onto the Glacier de la Lex Blanche, Mont Blanc Massif, Italy, in September 2008

In September 2008, a large rockfall (50,000 m3) detached from 3470 m a.s.l. on the east-facing spur of Aiguille de Tré-la-Tête, in the upper part of the Val Veny (Valley of Aosta). It travelled for > 1 km onto the steep Petit Mont Blanc Glacier, the main tributary of the Lex Blanche Glacier. It is the largest rockfall that has occurred in the Mont Blanc massif since the 2005 rock avalanche (260,000 m³) from the pillar of Les Drus, above Chamonix. While debuttressing of the rock wall due to ice downwastage during the last two decades could have reduced rock wall stability, permafrost degradation is probably the main triggering factor for this rockfall, as well as for 55% of the 62 other rockfalls observed in the massif in 2007 and 2008.