La Grotte de la Glacière

The Glacière cave is at Chaux-lès-Passavant, in the Doubs, in the middle of the forest. At 525 m altitude, it is the lowest known natural ice cave in France. It is a cavity where cold air, trapped in winter, stays denser than the warm outside air in summer, which limits heat exchange and lets ice be preserved.

Ice forms there by direct accumulation, from water falling from stalactites or forming ice stalagmites. In the eighteenth century, between 1743 and 1745, the engineer Jean-François Charpentier de Cossigny studied the cave and corresponded about it with the scholar Réaumur.

The phenomenon has greatly diminished: from tall columns of ice, only about 500 m³ of ice remained, and no ice has been seen since winter 2004-2005. Nearby, a mineral exhibition presents more than 5,000 crystals from around the world.

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