Grotte de Bordes de Crues

The progression begins with a series of easy climbs on a very handsome marmorised limestone. You cross the hinge of the fold: a passage of great beauty. The gallery then becomes more chaotic and you arrive at the foot of a small 3-metre climb. A few tens of metres further on, you come out of the boulder choke into a more spacious ascending gallery whose floor is littered with recrystallised blocks. You can then slip between the boulder choke beneath the chamber to reach the river easily, but this passage may be flooded. If, on the other hand, you climb right to the top of the chamber to a squeeze widened in the 1970s and where a noticeable draught blows, you can descend a shaft of about twenty metres in the ceiling of the river a little further downstream than the previous route.

The river begins with easy progression. You pass a few small cascades, some of which require equipment; then a pool whose crossing is a little acrobatic allows you to set foot in front of a fine 10-metre cascade which is bypassed on the right bank along a long handline. At the end of it, back in the bed of the river, you pass as quickly as possible beneath a fine tributary that falls from the right bank, spraying the left bank. This was climbed about thirty years ago, over about a hundred metres of height gain, up to an aquatic narrowing.

You continue for a while along the watercourse until you come up against a large boulder choke which can only be passed at the bottom in very low water, and even then not easily. But by climbing and weaving through the boulder choke, you can gain a few tens of metres and descend on the other side at the foot of a splendid 30-metre cascade. At the top of it you step into the Delors chamber, at the foot of the cascade of the same name. This cataract is certainly the most grandiose in the cavity and one cannot fail to think admiringly of the first explorers who passed it. You continue along the river, avoiding deep pools by small easy climbs, up to the first sump.

Shortly before the sump, a fossil gallery starts on the right bank. It gives access to a vast, very chaotic and sometimes decorated fossil passage, but also, at the lower level, to a boulder choke in which a complex route allows the sump to be bypassed. Beyond the boulder choke, the gallery widens to a well-quadrangular crossroads. To the left and below is a view down onto the river: upstream and downstream sumps. Opposite, shortly after the crossroads, there opens in the calcited floor of a depression a most unpleasant squeeze (cold water, violent draught, a really narrow conduit length) which leads beyond the second sump. The cave then continues following the river, with the fossil passage just above, to a boulder choke, the present unhappy terminus of explorations.

The Hercynian metamorphism produced original minerals, not studied at Bordes de Crues, of which an original example, located near the end, is a red stalagmite whose richness in haematite is supposed to be responsible for its texture and its intense pigmentation, comparable to those of lipstick.

At low water the flow of the rivière souterraine (underground river) emerges through the spring below and can be estimated in the large perennial cascades that can be seen from the borde, 300 m above, to the west. The spring of Bordes de Crues rises near the synclinal gutter of the small S1 syncline, at a vertical WNW-ESE fault (Pyrenean direction) which appears to direct its almost rectilinear underground course. The catchment area extends west of the spring, including the sinkholes of the immense doline des Clots (1671 m), the dolines des Clots de Gariès with their ice pits, the ridges culminating above 2300 m and probably water captured behind the ridges, to the west, in the sector of the grotte des Espugues (2120 m). Karstic potential: 1200 m.

The Estours marble, blocks of which, abandoned by the marble works, can also be seen on the path, is a handsome dark rock, formed of 3 cm bottle-green nodules surrounded by black veins, generally more prominent. It is the main karstic rock of Mont Valier (2838 m), if one sets aside the very numerous outcrops of grey crinoidal limestone of Devonian, Pragian stage, which are of karstic interest a few kilometres to the south. The Estours marble, a Devonian, Fammenian stage griotte marble (the “cherries” would be green here), is seen in the cave and in various outcrops where it was quarried. The bed overlying the Estours marble is another marble, white with dark veins: the Carboniferous limestone of Dinantian stage. It is well karstified. It contrasts with the dark marble in several places such as the pale cliffs above the entrance porch and the entrance slides. These two karstic rocks are shown in brown on the interpretation diagram of the geological map (after the Aulus 1/50 000 map). It can be seen that these rocks are of slight thickness, very folded and metamorphosed by burial beneath overthrusts during the Hercynian compression (-300 Ma). This accounts for the complexity of their outcrop, all cut through by numerous faults (photo and interpretation diagram). The two karstic rocks form two successive synclines of different size, with a west-east axis (WNW-ESE) which I shall call S1 for the small southern syncline and S2 for the large northern syncline, each framed by anticlines (named A1, A2 and A3: see the south-north geological section).

The rivière souterraine (underground river) is one of the subterranean splendours of Ariège, including in its present upstream zone. The marbles there are handsome, even if they are not polished. Indeed, the black veins of the griotte marble generally stand proud, forming a non-slip surface under the boot. These veins being weakly carbonated, dissolution spares them more than the nodules. As they break under pressure or abrasive impacts, they leave in other places the bottle-green nodules more prominent when sand impacts outstrip dissolution. The balance of differential erosion varies along the river according to how erosion acts on these two minerals arising from metamorphic recrystallisations.