The geology of the Gorges du Verdon

The great walls of the Verdon are carved from an Upper Jurassic limestone, formed around 150 million years ago. At the time, the region was covered by a warm, shallow sea where corals thrived: the limestone of the gorges is a reef limestone, a former tropical barrier reef. A vast lagoon then stretched over what is now the Canjuers plateau.

In the Plans du Verdon area, this limestone slab reaches nearly 1,000 metres thick; it thins towards the north, around Castellane. Above it, a more marly — softer — Cretaceous layer has survived only in the folded troughs (the synclines). Below, at the base, a Triassic layer of clays and gypsum acted as a sliding surface during the alpine uplift. It is this stacking — soft Triassic, thick Jurassic limestone, marly Cretaceous — that explains the silhouette of the canyon: high vertical walls in the hard limestone, gentler slopes where the rest outcrops.

Limestone has a weakness: slightly acidic rainwater dissolves it. This is karstic erosion — the process that has patiently opened up the canyon and continues to sculpt it. It marks the landscape everywhere: lapiaz (grooved limestone pavement), dolines, caves such as the Baume Bonne (carved into the Jurassic limestone above the Verdon), avens (vertical shafts), and clues — those narrow transverse gorges, such as the Clue de Taulanne or de Chasteuil, near Castellane.

Water that seeps in re-emerges further down as springs; where it redeposits the dissolved limestone, it builds up travertine — these are the tufières of Saint-Maurin, at the north-western entrance to the gorges, where the stone rebuilds itself before your eyes. The river itself behaves partly like a karstic watercourse, with losses and resurgences. It was in 1905 that Édouard-Alfred Martel, helped by Isidore Blanc, a schoolteacher in Rougon, led the first complete exploration of the canyon.

The Verdon belongs to what the European Geoparks Network presents as the largest open-air geology museum in Europe. Created by decree in 1984, the Réserve naturelle géologique de Haute-Provence is commonly described as the largest geological reserve in Europe: eighteen classified sites (269 hectares under strict protection) within a vast protection perimeter of around 2,300 km² covering 59 communes. This territory is also the birthplace of geoparks: the Géoparc de Haute-Provence was the first in the world (in 2000) and has held UNESCO Global Geopark status since 2015; it covers 67 communes, including Moustiers-Sainte-Marie, at the gateway to the gorges.

Among its treasures: the Mur des Siréniens, at the Col des Lèques near Castellane, where the rock preserves the bones of sirenians — marine mammals ancestral to manatees — 35 to 40 million years old; the famous ammonite slab of Digne; and several ichthyosaurs, marine reptiles fossilised in the limestone.