Gouffre Mirolda

Gouffre Mirolda is a karstic cave located in the Haut-Giffre mountain range, in the commune of Samoëns, Haute-Savoie, France. It is connected to the Lucien Bouclier cave system, and has a depth of -1661 m. It is the fifth deepest cave in the world and the deepest one in Europe.

Exploration
The cave was discovered in 1971 by Marc Degrinis, a shepherd. In 1972, the AVEN group in Lyon widened the entrance, and explored to a depth of -127 m to an impenetrable meander. In 1976, an upper entrance, the VF3, at 2324 m, was discovered by the Villefranche Caving Club (EESV) and explored as far as the base of the first 30 m shaft on a narrow slope. The Gouffre Mirolda (CD11) was reinvestigated in 1980 by SC Lyon. With the help of the GS Cavernicole and the SC du Chablais, a depth of -850 m was reached. In 1981, the river was explored down to -1100 m. Reinforced by the SS Genève and the Thonon Tauping Club, fossil galleries and upstream tunnels enabled the network to reach a height difference of 1143 m in 1988. The unblocking of the Gouffre VF3 gave access to the system named after Lucien Bouclier, a speleologist who died in 1987 on the massif. The junction was made by the Ursus group between the Gouffre Mirolda and the Réseau Lucien Bouclier in 1992 for a depth of -1436 m, and also with the Gouffre de la Rondelle Jaune (2220 m). At the bottom of CD11 the depth was increased in 1993 to -1520 m, and -1610 m in 1998. The Gouffre du Joker (2332 m) was connected to the network in 1999, increasing its depth to -1616 m. The terminal sump was dived in 2003, increasing the depth to its current -1733 m, making it the deepest natural cave in the world from January 2003 until July 2004, when it was passed by the cave Krubera-Voronja in Georgia. In September 2022 and 2023 the Collectif Mirolda, took over the topography, updated the in-situ equipment and examined the possibilities of further discovery. The cave is the deepest in France. Its name is derived from the forenames of the Rhodanien cavers Michel Schmidt, Roland Chenevier, and Daniel Trouilleux, who were lost in a flood in Gournier Cave in November 1976.

Description
The highest entrance of the system is at 2332 m. The lowest point of the cave is at -1733 m at the grand siphon in the gallery. The bottom of the gallery (after the second siphon) has only been explored once, with potential for further exploration. Behind the second siphon (approximately -1620 m) the gallery continues for 22 m horizontally and down 8 m, leading to an ancient drainage system. Downstream, the gallery descends over a length of 251 m and a vertical drop of  110 m before coming up against the first siphon at -1733 m. Past the siphon the gallery divides in two, the left leading up towards the roof and the right leading  50 m to a fossil gallery.

Karst Development
The Gouffre Mirolda is developed in Urgonian Limestone at its contact of the Hauterivian marl following the dip first (E-W), and then (S-W) towards the Giffre valley. The water flows into the alluvial aquifer, and no resurgence is known. As at the Gouffre Jean-Bernard, the upstream section of the Réseau Lucien Bouclier appears to be the oldest part of the system, with the base of the CD 11 developed following the incision of the Giffre valley.