Gouffre des Mentalo

The pit is essentially one large single shaft 85 metres deep, with two intermediate ledges, one at -30 m and the other at -45 m, which can be used as belay points. The bottom is littered with numerous medium-sized rock fragments.

Further south, at -85 m, a 15-metre step follows the large shaft, bringing the depth to -100: there the floor is strewn with collapsed blocks. Finally, 3 metres from the bottom, a steep upward-sloping gallery is soon interrupted by a suspended debris cone.

In the large shaft itself, the beginnings of two galleries are visible at -30 m: one, located on the first ledge, is very quickly choked with clay; the other, more delicate of access and located opposite the said ledge, has not been explored. In addition, a small opening, distinctly less obvious than the first two, also remains out of reach.

At the top of the large shaft, opposite the entrance skylight, receding perspectives suggest that a continuation is possible.

The pit develops in a highly fractured zone, and among the number of fractures visible at the surface, the most important ones, including that of the Mentalo, could show a slight local collapse. This is doubtless due to the collapse of the westernmost block of the Rochers de Leschaux. The subsidence fault that results from this is in fact subdivided into multiple fractures with slight throw or without notable offset. On the other hand, it is not improbable that the tilting of this same block facing the Petit Bornand is the cause of the slight throws of the few fractures running along, to the north, the cliff of the Rochers de Leschaux.