The Caves at Vallorbe (Canton de Vaud) in the Swiss Jura were opened to the public a quarter of a century ago. They afford a spectacular display of the beauty of natural rock, enhanced entirely by natural illumination.
For millions of years the limestone layers were eroded by the Orbe, a river which runs underground before bursting from the rocks – seemingly as a natural spring of which the Vallorbe Caves are the faithful guardians.
A BRIEF HISTORY
... 150 million years ago, on the very spot where the famous Vallorbe Caves are today, there was a shallow sea covering the whole region. Little by little the rocks you pass today were formed by deposits of marine sediment. Further north were the slopes of the nascent site of Vallorbe itself and the gorge of the river Dernier where the underground waters of the Orbe break into the open and the land still reverberated at the steps of the great dinosaurs.
The landscape at that time must have been similar to that of the Bahamas today, with many low islands peeping from the blue seas. Millions of years passed and with them the sedimentary layers grew steadily. In the Vallorbe area the strata built up to around 200 metres depth of “Cave Limestone” in less than ten million years.
This complicated geological process continued for 120 million years and a great variety of minerals were deposited in successive layers - limestone, calciferous clays, sandstones, clays, conglomerates and so on.
Finally, some seven million years ago, the sea withdrew from the region following a vast upheaval of continental plates forced from below by unimaginable tectonic activity. This was the moment of collision between the African and European continental plates - giving birth to the mountain chains of the Alps and the Jura. This conflict between the sedimentary rock and the irresistible force of nature created the right conditions for the formation of the extraordinary range of inner spaces which are the Caves of Vallorbe that you see today. Having set the scene in terms of space and time we can now take a look at the principal creator of these miraculous spaces – the underground water.
The Water destroys, the Water builds
Precipitation whether of rain or show persists throughout the year on a “Karst” or calciferous massif
The water becomes “aggressive” when its acidity rises as it reacts with vegetation and above all as it flows over surface layers of soil (humus, micro-organisms &c).
Then as it pervades the calciferous massif through the many fissures and cracks the acid water dissolves the rock and carries away the calcium carbonate in the limestone.
When the water reaches the air in the caves, it precipitates the calcium carbonate with which it is loaded in the form of Calcite (Crystallization). That is how the stalactites and stalagmites and other concretions are formed.
On the floor the concretion process can also happen as the carbon gas in the water is released (rather like when gas bubbles are released as one shakes a bottle of mineral water).
The underground river also excavates large galleries whether by chemical or physical erosion. All this mineral matter, whether dissolved or as particles (sand, clay containing flints &c) eventually reaches the outside world through the “sources”