During the last ice ages (20 to 000 BC), cold and abundant meltwater from a glacier flowed over the surface of the limestone rocks and infiltrated through draining cracks which they gradually widened. by dissolution of the rock.
Over the course of a few thousand years, an underground network was developed where narrow cracks and vast rooms containing more or less water follow one another.
Today, the Pontoise Cave is no longer the site of significant water circulation.
The water circulating in the underground galleries emerges into the open air through exurgences.
The Grotte de la Pontoise is one of the entrances to a underground network tributary of Biel, of which exploration is possible over the first 315 meters.
With a minimum of equipment and a lot of caution, the Grotte de la Pontoise can be explored by visitors who respect the site.
However, some parts present dangers of falls on slippery and steep terrain.
The path of groundwater:
The Grotte de la Pontoise is an ancient entry point for water into a vast underground circulation system (called "karst"). Coloring with fluorescein, a trickle of water escaping from the large room, shows that the colored water emerges 10 hours later at the sites of the exurgences of Borne à Coupier and the Goudard reach, i.e. a 2km underground route as the crow flies with a height difference of 300m. Known only at this entrance and at the two exits of the exurgences, the karst network of which the Cave is part is certainly very extensive and drains infiltration water from the entire slope of the Bienne Valley.
Any surface pollutant discharge will have harmful consequences on the quality of water from Jura springs.
For an exploration with our guides, contact:
- Noa Guides : by reservation only at 0632802317 or contact@noaguides.com
- The Mountain Box : minimum 5 people. Bring: 1 light long pants, 1 fleece, 1 pair of sneakers or boots and a change of shoes. By reservation at the office/by telephone/by email or via online sales: 03 84 60 39 34 or https://www.la-boite-a-montagne-jura.fr/
- Original Concept: frames on the Pontoise cave, by reservation. And more particularly caving-Fondue evenings! From 12 years old
