Bufo Fret

The cavity develops along a subvertical fault, allowing the network to cross 3/4 of the Pic de Bugarach massif. Fossil tube galleries are arranged in tiers along this fault, drained by a stream. The fault is the major axis of the Bufo Fret network, which develops in dolomite. Numerous "boxworks" are visible on the walls, highlighting the micro-veins of calcite. Well-visible fractures on the walls and ceiling show that the tubes preferentially established themselves on them.

Tube galleries are rather specific to mountain karsts, which generally show significant phreatic-lift heights. Indeed, these lifts temporarily drown the entire phreatic zone in which the tubes develop. Roughly, the phreatic-lift height corresponds to the thickness of limestone in which the tubes develop. If the tubes are arranged in tiers over 300 metres of elevation difference, one must envisage something larger, and a somewhat longer history of the network. One must therefore imagine a more mountainous environment, a more extensive limestone massif and, above all, a base level located higher up.

At the foot of a new ascending shaft (elevation difference 20 m), a gallery branches off to the left (galerie du Sable); it leads to a graveyard of speleothems broken by the reactivation of a fault inclined at 45°. This fault, which originated the gallery, was reactivated after the formation of the speleothems and columns. The upper "downthrown" block clamped the stalagmites and columns resting on the lower "upthrown" block. The offset observed in a small descending conduit is only about 2 cm. This 45° fracture does not correspond to that of the major axis, which is clearly closer to vertical. Further on, there are even more interesting examples of displacement of the order of 20 to 25 cm. The phenomenon is very demonstrative and clearly illustrates the displacement or sliding of the upper block over the lower block (or vice versa) in the manner of a normal fault. But it is possible that this fault is a reverse fault that was reactivated in the other direction (perhaps by gravity), giving the illusion of a normal fault. Given that the Pic de Bugarach is a thrust-sheet klippe, one may suppose that it is a reverse fault, but in the absence of a survey of the network and a geological cross-section of the massif, it is difficult to decide.

The stream follows the same discontinuity as the fault and incises the tubes. Towards the lower parts of the network, that is, towards the entrance or the fossil outlet, a few patches of red clay are found in the hollows of the ceiling. Sands and yellow silts derived from the dolomitic limestone partially cover the floor of the galleries. In the upstream parts of the network, a grey superficial fill is occasionally found in the galleries developed along the axial fracture. The present stream therefore appears as a curiosity that has practically left no mark in the tube network, which is now completely fossil. The Bufo Fret network is a set of galleries followed by a stream that has no real connection with the much older tube system.

The cave is entered through an artificial entrance opened a little above the natural entrance. One then reaches a small conduit that must have functioned as an overflow, since tubes of larger diameter still develop somewhat below. After a few hundred metres, one arrives at the foot of a chimney that is none other than a vertical tube allowing access to the upper zone of the network. We enter through a fossil outlet (alt. approx. 700 m) and progress from downstream to upstream of the network.

a survey of the cavity was made during the national "équipier scientifique" course: http://hotwaker.free.fr/images%20speleo/bugarach%20bufo%20fret/bufo%20fret%20%281%29.JPG.