Karst

South of France’s Massif Central lie the limestone plateaus that form the Grands Causses region. Bordered by the deep valleys of the Tarn and Jonte rivers, the Causse Méjean is the highest of these plateaus. Its distinctive landscape, known as karst, is marked by the mechanical and chemical erosion of limestone rock. Water seeping through cracks in the surface of the plateau has created a unique topography, characterised by surface phenomena and an extensive network of underground cavities. These cavities, known locally as avens (or sinkholes), are chasms that open up in the ground. Varying in depth and appearance, they are mostly difficult to access, as they take the form of a vertical shaft over all or part of their length. Explored since Neolithic times for the resources they contain (water, calcite, clay), and once considered the entrance to Hell in a land where Catholicism predominated, these abysses and their exploration were brought to light in the 19th century by a young lawyer with a passion for geography. At the end of the century, when photography was invented, Edouard-Alfred Martel and his collaborators carried out numerous explorations in the Causses Majeurs region, thus contributing to its development as a tourist destination and to the foundation of modern speleology.