This is not a page about a place, but it is one about the funniest accident we know of, which is based on karst geology.
At the end of the 19th and the beginning of the 20th century a drink called Absinth was very famous in France. It was a liquour with many ingredients, including anis. Like all those anis liquours (e.g. Ouzo, Raki,...) it is a clear liquid until it is mixed with water, then it becomes milky.
As a matter of fact the original Absinth contained some slightly poisonous ingredients. It would have been hard to get a lethal dose without being killed by the alcohol much earlier, but this poisonous touch was part of the Absinth myth. And there was a rumour of it being an aphrodisiac. Unfortunately those peculiarities where the reason why it was forbidden some years later.
On 11th August 1901 a lightning hit the plant of the Pernod company in Pontarlier. It was set on fire, and the high temperature made the huge tanks with alcohol explode. Some one million litres of Absinth poured across the plant, down the sewer system and straight into the river Doubs. The river turned white and smelled of anis.
Two days later, André Berthelot visited the Source de la Loue more than 15km from Pontarlier, on the other side of a high mountain ridge. While enjoying the romantic atmosphere at the clear spring, he suddenly noticed a change. The water turned milky, and a smell of anis filled the air.
He knew this smell from the pub, but he had to take a mouthfull, to believe it: The water of the big spring turned into a free apéritiv! It is not handed down, if he filled his water-bottle...
This story was heard by the founder of modern speleology, E. A. Martel, and nine years later he made a dye tracing experiment. He found a swallow hole in the bed of river Doubs and added a strong, non-toxic, green colour. 64 hours later, the Source de la Loue turned green. The connection of the Loue and the Doubs across the mountain ridge was proofen and the dye tracing of ground water invented.
But now the next act in this play started: the owners of some small mills along the Doubs had problems with a strange lack of water for many years now. As they heard of the swallow holes, the started to look for them and filled theme with concrete when they found them. So the water stayed in the Doubs.
But now the residents along the Loue had problems with missing water. And so the case came before court. The decision: the already sealed sinks may stay as they are, but new changes of the course of the water will be punished.
This kind of story happened in many karst areas all over the world. Another famous one is the Donauversickerung (Danube Sink), where the water of the young Danube sinks to reappear in the Aachtopf (Aach spring). But Pernod was never used for dye tracing experiments again!