A long-cooled lava needle volcano, the Gerbier de Jonc, placed like a cone on the Ardèche plateau, is with the Gouléïou located in the Boutières cirque, the archetype of the phonolitic juices of this territory. Its lava, phonolite, is an acidic volcanic rock that emits a particular sound when struck.
From the Gerbier de Jonc and the surrounding phonolitic reliefs, rises the longest river in France: the Loire, whose sources they dominate by 150m.
Resulting from ancient volcanism (10 to 5 million years ago), Mont Gerbier-de-Jonc is a real watering can. From all sides the water escapes from it, southern slope (Sainte Eulalie) towards the Atlantic, northern slope (Saint Martial) towards the Mediterranean. By its relief, its climatic conditions and particular substrates, this site offers an exceptional faunal and floristic richness in addition to a grandiose landscape. Many remarkable and often threatened species have been recorded. (information provided to the triptych).
The 3 km Sources de La Loire trail will allow you to discover the other particularities of the site: from the “authentic” to the “true” source of the Loire, including the “geographical source”. – This classified site is also a stage of the Pradal Valley discovery trail.
The compact shape of the Gerbier is linked to the very pasty nature of the lava emitted at temperatures of 600°C to 800°C. It is a dome built slowly and gradually, about 7 million years ago, from the ascent of magma through faults and breaks in the basement (substratum). As this growth progresses, the surrounding lava cools, becomes brittle, resulting in the appearance of deep and wide cracks as well as the flow of the very massive slab domes around its perimeter. The fragmentation and the fall of these rocks are at the origin of the scree which coats the base of the relief.
The Gerbier de Jonc is also a classified geosite of the Monts d'Ardèche Geopark (UNESCO).

For the ascent, provide hiking shoes. Physical condition required, as some passages are technical.