Tête Rousse Glacier

The glacier is located on the northwestern slopes of the Aiguille du Goûter, on the northern side of Mont Blanc and 11 km upstream of the town of Saint-Gervais.

[5][6] Everything in the path of the rushing water, mud and boulders was swept away, leaving behind some 800,000 cubic metres (1,000,000 cu yd) of sediment.

Joseph Vallot, the glaciologist and Director of the Mont Blanc Observatory at the time of the incident, published detailed accounts of his investigations into the Catastrophy of Saint Gervais.

Together with the soil and rock broken away by the force of the rushing water, Vallot estimated that a weight of 500,000,000 kilograms (500,000 t; 550,000 short tons) of material had borne down on the villages.

It was believed that meltwater had drained through the glacier and become trapped as an intraglacial cavity, i.e. as an underground lake within a crevasse which itself had then become enlarged and widened by the water.

[8] However, recent re-analysis of historic photographs, accounts and contemporary meteorological precipitation data and field measurements, including radar analysis and magnetic resonance imaging, has presented an alternative and more plausible mechanism in which meltwater collected much closer to the surface (as a supraglacial lake) in a period when the glacier had a negative mass balance (i.e. was experiencing year-on-year melting and retreat).

[7][14] At 1:47am on 29 July 2013 during a heavy storm, the alarm system on the glacier triggered, alerting the authorities to a serious flood risk.

95 firefighters and 70 soldiers of the gendarmerie were mobilised, and an evacuation plan put into effect, involving the townspeople of St Gervais, Sallanches and Passy Domancy gathering at pre-arranged assembly points.