Fosse Dionne
Ever since prehistoric times this natural spring has been prized by humans, and the French town of Tonnerre (between Paris and Dijon) grew around the waters, on the road linking the capital with Burgundy. The construction around the gushing waters (up to 300 litres a second) dates from Roman and Medieval times. Once used as a Roman palace water supply, the village expanded to serve its needs, with the social use made of the spring changing over time. The most recent construction is an 18th century CE village laundry place, a common feature of rural French villages. The process illustrates quite well the connection between history and geography, an intimate relationship that finds expression in the fact that French schools teach them as a single subject. The spring comes from an encounter between water percolating through the nearby limestone plateau meeting an impermeable clay rich layer at the level of the town. The limestone is part of the huge Jurassic platform, a set of mostly marine limestones that draped over much of Europe during the high sea levels of the Mesozoic (256-65 million years ago) which was due to the swelling of the oceanic plates from accumulated mantle heat, resulting in the gradual dismemberment of the supercontinent Pangaea and major marine invasions of what had once been land).
The spring is usually most active in summer, when extra snowmelt has percolated through the feeder system. Dye tracing has also revealed that the spring channels part of a river that vanishes into the limestone on the plateau above. The grotto is deep, and linked to a large hydrological system that stretches as far away as 40km. While divers have tried to find the source, the caves narrow too much for safe exploration, and access has been restricted since several divers died.
Many legends have gathered around the place, including that the virgin created it, while saving an girl from the devil and it was supposedly inhabited by a dragon or giant worm. The name may derive from the Latin water goddess Divona, or the Greek nymph (water spirit) Dione.
Loz.
Image credit: Christophe Finot