Grottes de Vallorbe

The Vallorbe caves open where the Orbe comes back out of the limestone, at the head of a blind valley in the Vaud Jura. The river leaves Lake Joux, sinks into the fissured rock and reappears 4.8 kilometres further on, at Vallorbe. Between the two, the underground course measures 2,980 metres as the crow flies, with a drop of 228 metres. The developed entrance stands at 750 metres, the resurgence at 776. Visitors do not follow the water: they take a bored tunnel that opens above an underground lake, some ten metres above the recovered Orbe.

The public route covers about a third of the known development and takes roughly an hour. It crosses the Grande salle, formed by the collapse of blocks fallen from the vault: heavy stalactites hang on one side, while a flow of calcite and moonmilk streams down the other. Elsewhere stalagmites stack up like plates and fine translucent soda straws hang from the ceiling. Near the entrance, four chambers hollowed out of the rock have housed the Trésor des Fées since 1992, a collection of more than 250 minerals.

No one had been able to enter the mountain by a natural way: the first to get in went through the spring itself. In 1893 a diver in a heavy standard suit went down to eleven metres and found that the gallery continued. Not until 1961, with self-contained diving gear, was the sump passed, a small underground lake reached and the dry network opened up. The caves took their first visitors in 1974, and the exploration is not over: in 2015 the furthest point reached was still 800 metres from Lake Brenet, which the cavers are working towards.

Why this place is remarkable

What is visited here is the path of a river: the Orbe enters the Jura limestone and does not emerge for 4.8 kilometres, and the developed route follows part of that underground journey. The cave was in fact reached by water before it was reached on foot — a helmet dive in 1893, scuba in 1961, opening to the public in 1974 — and its map is still unfinished: in 2015 the cavers were 800 metres short of Lake Brenet.

History and origin

The limestones in which the galleries opened were laid down under a shallow sea that once covered the region. That sea withdrew for good about 7 million years ago, as the Alps and the Jura rose; the estimated origin of the caves belongs to that time, at the beginning of the Pliocene. Despite common usage, the spring is not a Vauclusian one: morainic blocks and scree piled at the head of the valley block the lower part of the gallery and force the water upwards.