The geology of a ghost city
The Chaos de Montpellier-le-Vieux is a 120-hectare geological park of ruin-like rock formations on the Causse Noir, a limestone plateau in southern France. The story of this "City of Stones" begins 170 million years ago, during the Jurassic period. A shallow, tropical sea covered the region, and the skeletons of marine organisms accumulated on the seafloor, eventually forming a thick layer of dolomitic limestone.
The landscape's transformation from a flat seabed to a chaotic labyrinth started around 100 million years ago with the tectonic uplift that formed the Alps and Pyrenees. This process raised the Grands Causses plateaus and fractured the dolomite bedrock, creating a network of cracks and fissures. For millennia, rainwater, made slightly acidic by absorbing atmospheric carbon dioxide, seeped into these fractures. This weak carbonic acid preferentially dissolved the rock, a process known as karstification. Water and freeze-thaw cycles widened the cracks, carving the stone into the strange pinnacles and towers seen today. This specific type of landscape is known as a blockfield or a "stone forest." The shapes are so evocative that many have been given names, such as the Gate of Mycenae, the Queen's Face, and the Elephant.