Underground for the Past 30 Million Years

A fantastic landscape created by dripping water

Some 200 million years ago, the limestone rock of the Causse Méjean was formed at the bottom of a warm, shallow sea from the deposits of corals, crustaceans and other marine organisms.

100 million years later, the rock gradually emerged under the same terrific thrust that created the Alps and the Pyrenees

The cavity’s creation began 30 million years ago, as the limestone rock was dissolved by acidic rainwater. Rainwater isn’t normally acidic, but it gained acidity as it fell through the atmosphere and even more so when it penetrated the soil and became enriched in carbon dioxide. As it seeped into cracks in the limestone, the rainwater hollowed out cavities of various shapes and sizes. The dissolved substances were carried away as the water flowed towards the Jonte gorges. Once this process was underway, the initial cavity increased in volume with the progressive collapse of its ceiling, to reach its current size 1 million years ago.

Stalagmites began to form 700,000 years ago. The encounter between the hard water and the cavity air caused carbon dioxide to escape, releasing the limestone which remained on the cavity ceiling to form stalactites. Particularly rich in limestone, the water at the Aven Armand formed drops that were too heavy to remain on the ceiling long enough to create stalactites of any significant size.

The cavity’s exceptional height of 45 metres meant the drops fell at an accelerated speed. As they hit the ground, they burst into a countless number of droplets, releasing their substantial mineral load around the point of impact, which resulted in the formation of stalagmites. The dispersal of the water drops and the diversion of their trajectory caused by the movement of air in the cavity, explain the stalagmites’ unusual shape.