Natural curiosities, natural heritage at Meyras in Ardèche

The Neyrac Mofette is an emanation of carbon dioxide from cooling lava in the subsoil. The site was recently restored by the commune of Meyras. Guided tours are available through the Sources & Volcans tourist office (only in French).

Guided tours of the Neyrac-les-Bains thermal baths and its mofette are available from June to October according to the calendar drawn up by the tourist office. Maximum 20 people per group. Bookings by telephone on 04 75 36 46 26 or directly on our website (only in french).

A little history of the Meyras mofette : The mofette de Meyras, located 1m50 below the road at Neyrac-les-Bains, can be visited on a guided tour with your tourist office (guided visit in French only).This mofette was vaulted when it was built, and for a long time it frightened the locals, who nicknamed it the “path of death”… Why? Because due to the natural presence of carbon dioxide, its air made large animals sick or drove them away, while small ones succumbed to its approach (unfortunately, small birds have even been found dead outside the door). But don’t worry, the redevelopment of the site will allow you to visit the mofette in complete safety, with a completely reworked museography to help you discover all its secrets!

How is a mofette created? The mofette is a place with a high concentration of carbon dioxide directly present on its surface, which rises from the subsoil without encountering groundwater. How do you detect the presence of carbon dioxide? Unlike the oxygen in atmospheric air, carbon dioxide is not an oxidising agent: any lighted object is easily extinguished. However, there is a zone above the carbon dioxide zone that contains a mixture of atmospheric air and CO2. In this zone, the flame of a candle diminishes in intensity. It is a few centimetres thick and becomes richer in CO2 the further down you go.

Did you know? There are only 3 mofettes (covered caves) in Europe: the Grotte du chien in Pozzuoli near Naples, the Mofette in Royat (Puy de Dôme) and the Mofette in Meyras at Neyrac-les-Bains. Two others in Java and Yellowstone National Park in the United States.