Évent de Coumescure

A cliff porch is followed by a straight gallery, slightly sloping, 4x2 m and 70 m long. The first sump begins with a fine gallery 6x2 m that descends gently to less than -10 to end at a vertical scree slope 100 m from the entrance. Opposite, a 3 m clayey step drops into a large chamber 25 m wide and 50 m long, strewn with large clayey blocks. The exit pool of the S2 is 2 m wide and 8 m long. The S3 begins with a fine 2x3 m shaft down to -18 m; a fine gallery 4x3 m and 90 m long follows, then ends at a narrower ascending passage 1 m in diameter down to -12. Further on, a large chamber with a ceiling that is a bedding plane at -6 m, and another large chamber measures 20 x 50 by 30 m high. The active stream issues from a small conduit 80 x 50 cm, 8 m above the scree slope.

The cave is the former outlet of the spring captured below. It becomes flooded rarely, following heavy continuous rain. It is the downstream branch of the sump that brings water to the captured springs.

The entrance gallery ends at the S1 (110 m; -10). Right at the start of the sump on the left bank, the downstream of the sump begins, which can be followed for 40 m at -10 m, stopping at a constriction. The passage of the first sump is found by following the right wall of the gallery; the exit is between the blocks. At the end of the large chamber and on the left side plunges the S2 (45 m; -10). The entry into the water is of the same kind as the exit of the S1, and one must slip between the blocks down to -6. There, the gallery becomes wider down to -8. At the low point, one must turn 90° to a new ascending scree slope between -8 and -5. The sump exits a few metres further on. At the end of the exit pool an active stream discharges; one must ascend it for about fifty metres to the gaping mouth of the S3 (135 m; -21 m). From the 1 m diameter passage, one must squeeze between the blocks to come out into a large chamber. The continuation is between large blocks on the right bank at -5 m. The exit is 20 m further on, in the middle of a scree slope of enormous blocks 4x3x3; once this is passed, one reaches a large chamber with no obvious continuation. The active stream, after a few metres, ends in an emissive pool.

Geology: marly terrain of the Cuisien (Eocene).