A landscape dissolved by water
The Gorges de l'Ardèche is a 30-kilometer-long canyon carved through a thick plateau of Urgonian limestone. This limestone, formed from marine sediments over 100 million years ago, is particularly susceptible to dissolution by carbonic acid in rainwater. This process, called karstification, is responsible for the region's dramatic landscape of steep cliffs, deep gorges, and extensive underground networks. The canyon itself reaches depths of up to 300 meters.
The entire plateau functions like a sponge. Water infiltrates cracks and fissures in the limestone, enlarging them over millennia into conduits, caves, and underground rivers. Over 2,000 caves have been documented within the gorge system, including the famous Chauvet-Pont-d'Arc Cave, which contains some of the world's oldest known figurative paintings, dating back 36,000 years. These subterranean passages create a complex hydrological system that operates largely unseen. The river's average flow is about 65 cubic meters per second, but during intense autumn and spring floods, known as "coups de l'Ardèche," the discharge can surge dramatically, reaching up to 7,800 cubic meters per second. During one historic flood, the water level in the gorge rose by 21.4 meters.
The Pont d'Arc shortcut
The most famous feature of the gorge is the Pont d'Arc, a natural arch standing 54 meters high and 60 meters wide. This structure shows a river meander being cut off by a karst drainage system. The process began around 500,000 years ago. The Ardèche River originally flowed in a wide loop, or meander, called the Combe d'Arc. Water began seeping into fractures in the narrow limestone neck of the meander, gradually dissolving an underground passage.
This subterranean conduit captured more and more of the river's flow, creating a shortcut. Around 124,000 years ago, the underground passage became large enough to divert the entire river, and the roof of the passage collapsed to form the arch seen today. The river abandoned its old, longer path, which is now the dry, amphitheater-shaped valley of the Combe d'Arc. The Chauvet Cave is located within the cliffs of this abandoned meander. The Pont d'Arc is a bridge and the remnant of a cave system that once channeled the entire Ardèche river.