Gouffre CP21

The pit opens in the Senonian, then develops in the Urgonian, completely crossed at the second P11 (-190 m) where the Hauterivian is reached. The CP21 is formed at the expense of a fault whose privileged axis is 317 degrees (130). This fault, observed at the surface and followed up for about a hundred metres, is perpendicular to the axis of the syncline and thus drains numerous snow holes. Thanks to its position at the centre of the combe, it very quickly collects runoff water.

The main meander widens until it reaches one metre wide by two high. The P11 measures 3 metres in diameter. The bottom of the fault, at -204 m, is occupied by a pool; a squeeze to be blasted allows a glimpse of a 3-metre step still in the same axis (317°), from which the draught emerges. A final squeeze guards access to a muddy step whose base is entirely occupied by a sump, at the lowest point of the cavity, at -235 m.

From the -30 m level, an important active stream roars at the bottom of the meander, giving the pit an anguishing atmosphere. In flood it can reach 40 l/s; it is almost non-existent at low water. The active stream is followed to the bottom of the cavity where it sinks into the Hauterivian layer.

A slight draught seems to come from the bottom at -204 m, but most of it comes from a window in the middle of the P44 towards -170 m. After about 80 metres, the draught is lost in an impenetrable passage to be widened with explosives.

After a crumbling step from which an active stream can already be heard cascading, a P7 is descended followed by a slope inclined at 60° leading to the top of a watered P13. At the bottom, the upstream part of the fault can be seen, but very quickly it becomes impenetrable. A series of steps in the meander allows one to reach the base of a P10 (-58 m), the start of a meander about twenty metres long and fairly narrow. At the end of it, a P18 allows one to return to the axis of the combe. A small meander leads to a P4 where it is necessary to rig a handline to avoid the active stream.

A P15, a P6 and an R3 are then descended; one then enters a new meander that is fairly tiring because it is interspersed with slippery steps. A narrow ledge must be crossed before descending a P5, and after 6 metres of meander one descends into the incised channel (R4 and R3). One is then at the top of an inclined shaft at the end of which starts a P44 fractioned three times to avoid the water, but watered in the last ten metres.

One then finds the privileged axis of the fault (317 degrees) where a meander 5 metres long opens out, after a narrow passage at water level, into a P11 3 metres in diameter. The following shaft, dug in the Hauterivian layer, comes back under the P44. A narrow passage gives onto a 3-metre downclimb.

The window of the P44 leads to a pretty fossil P17. At its base, a 5-metre step leads to a narrow, muddy meander. The main meander continues but it is defended by selective zigzag squeezes.