Culminating at 1754 m, it straddles the municipalities of Borée and La Rochette. It is an immense natural barrier which determines the division of waters between the Atlantic and the Mediterranean.
Description
The Mézenc is a complex phonolithic dome formed by the coalescence of several lava rises. It is located in the heart of one of the most original volcanic provinces of Europe due to its richness in phonolitic reliefs while it dominates landscapes with a contrasting character. Like all the other phonolite reliefs in this area, it was formed after the construction of the eastern Velay volcanic massif, which extends around the Mézenc between 11 and 7 million years (Ma). According to the dates it would be between 7.5 and 8 Ma. It dominates towards the East the country of Boutières, vigorously cut by the rivers of the Rhone slope. From its summit, the view stretches from the Rhône valley over the whole chain of the Alps, from Mont Blanc to Mont Ventoux and towards the west as far as Plomb du Cantal and Puy de Sancy.
The phonolite that makes up this dome is a clear and resonant rock, enriched in silica compared to basalts and therefore more acidic.
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This maar is a superb example of phreatomagmatic volcanic activity. The operation is characterized by an intense explosive activity caused by the meeting of the hot magma during the ascent with the waters infiltrated from the surface.
Sub-lacustrine volcano, the panorama of the cross opens on the needles of viscous lava of the surroundings of Borée. The walk towards the Cirque des Boutières will allow you to find the shape of the ancient volcano which occupied the site.
These are typical examples of viscous lava needles that have moved into place almost in a solid state. Here no craters but massive shapes in the landscape. Interpretation table between the two rocks.
The Rocher des Pradoux corresponds geologically to an isolated phonolite rock bar (phonolite is a volcanic rock).
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