To build a concrete wall where, two hundred years ago, Ignace Venetz, one of his predecessors, desperately attempted to break the resistance of a deadly ice cone. The people of Bagnes remember these devastating escapades. Flashback: the spring of 1818, in the middle of the Little Ice Age. There had been no sign of summer for nearly five years. It was raining non-stop and it was cold; it was snowing in the mountains. On the steep sides of Mont-Pleureur, the Giétroz Glacier discharged its excess ice into the narrow Mauvoisin Gorge. With seracs falling in avalanches, it ended up obstructing this barrier with hard rocks. Just above the place where, today, a concrete giant reigns, an ice dam was swelling which blocked the waters of the Dranse. When the snow thawed, 30 million cubic metres of water accumulated rapidly behind the unstable dam. If the water had continued to rise, it would have ended up spilling out into all the hamlets located in the valley below. Action had to be taken: Venetz evaluated the rising waters. Relying solely on his intuition, he had a tunnel dug through the ice cone. Around thirty workers had to complete the work in about twenty days, before the lake’s level reached the gallery. His calculations proved precise. On 13 June the tunnel was drilled; two days later the water started to flow into it, but its flow rate quickly increased and started to enlarge the gallery at a worrying speed… The ice cone collapsed on 16 June at 4.30pm, with 20 million cubic metres of water remaining in the lake. The devastating wave destroyed everything in its path and caused around forty deaths up to the town of Martigny. That was two hundred years ago. A book has now been published to describe the disaster, while the Musée de Bagnes is dedicating an exhibition to it, and at the top of the Mauvoisin Dam the photographer Julian Charrière is using an unusual exhibition to remind us that the Little Ice Age was largely caused by the darkening of the sky due to several volcanic eruptions.
As for the glacier responsible for the catastrophe of 1818, the heat has forced it to retreat higher and higher in shame. In around ten years from now it will have lost half of its volume and more than a quarter of its surface area as compared to the time of the disaster. From the top of the dam, take the tunnel on the left side: a 30-minute walk will allow you to observe it from afar, and at the same time visit the beautiful dry-stone vaulted stable at L'Alia.
Giétroz can, however, be proud of having laid the foundations of contemporary glacial theory. The discerning observations of Jean-Pierre Perraudin, a peasant and hunter from Bagnes, are richly illustrated by the Maison des Glaciers, which the municipality of Bagnes has set up in the house in Lourtier where he was born. This summer, Val de Bagnes is offering several activities and cultural visits based on the theme of the catastrophe and risk management.
Article written by François Perraudin
 Giétroz 1818, la véritable histoire, Bureau Clio sàrl, Éditions Faim de siècle and Musée de Bagnes
 Giétroz 2018 - 1818. From 26 June 2018 to 20 January 2019 in Le Châble
 “An invitation to disappear” from 17 June to 30 September 2018 on the Mauvoisin Dam
 Maison des Glaciers in Lourtier: www.museedebagnes.ch