Virtual tour of the Chourum Clot underground glacier

In the Dévoluy massif, chourum is the name given to the natural cavities that open in the limestone. The Chourum Clot opens at an altitude of around 1,730 metres, in the former municipality of Agnières-en-Dévoluy, merged since 2013 into that of Dévoluy. It holds a glacier underground: the snow that falls into the chasm builds up there and is preserved from one year to the next. A cave of this type, containing a large volume of ice, is called an ice cave.

The first known descents date back to the 1890s, with Édouard-Alfred Martel and the Martin brothers. On 15 September 1936, a team reached a depth of 100 metres. In 1982 and 1983, the Spéléo-Club du Var redid the survey and recorded 460 metres of galleries with a vertical range of 102 metres; the current inventory gives 805 metres in length and 114 metres in depth.

The bottom of the glacier

The tour goes down to the bottom of the glacier, at a depth of around 80 metres. It is probably possible to go further down, but the ice blocks the rest of the system. As early as 1982, explorers reported huge, very unstable ice stalactites in one of the shafts.

A melting glacier

Since October 2025, the Edytem laboratory, a joint unit of the Université Savoie Mont-Blanc and the CNRS, has been monitoring changes in the ice. Four temperature sensors have been placed at different levels, along with eight ablation stakes: one-metre rods driven into the ice, whose exposed part is measured from one reading to the next. In October 2026, a year later, the ice had lost about 50 centimetres in thickness, and the team surveyed the cavity in three dimensions with a laser scanner.

In forty years, the level of the ice has dropped by around ten metres. The ice is also becoming dirtier and dirtier, as it concentrates debris on its surface.

The Chourum Clot in pictures