During the night of 11 July 1892, an underground water pocket burst out of the Tête Rousse Glacier on the slopes of the mountains above the town. It flooded the immediate valley, passing through the hamlet of Bionnay where the local school and other buildings survived, it by passed the town of St Gervais and flooded the Thermal establishment which was a residential establishment at the time in the parc Thermal in Le Fayet, killing 200 people in its path. In 2010, the rediscovery of a large water pocket deep within the glacier caused alarm as it had the potential to threaten another outburst flood. Melt-water pumping, formal evacuation plans and installation of a siren alarm system in 2010 have all been implemented to reduce the threat to life. The risk zone was considerably reduced in 2017 thanks to the measures taken notable that the level of the glacial lake is controlled and pumped out if the water level rises, so reducing the threat to life and to property.
