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.
Description
The vaporization of the water in the confined space represented by the supply chimney causes an overpressure and an explosion which pulverizes the rocks of the conduit and the juvenile magma (fresh magma in the process of ascent). The more or less coarse debris is violently projected outwards where they settle to form a ring of tuffs. The maar is probably of very recent formation (a few hundred thousand years at the most), which links it to the volcanism of Bas Vivarais, like the maar of Saint Martial.
The overflow of the lava lake by Echamps fed a flow of which we find some shreds in the Azette valley, in Bois Lantal, Chanéac….
After a calm phase, the activity ended with a brief Strombolian episode (alternation of projections and flows) at the origin of a few small cones installed around the maar. (the Rastillas and the cone supported by the Pialox phonolite, which emitted a small flow towards the Gazeille).
Materials from the explosions: granitic rocks, prodotites, ashes, granules, magma blocks, small cauliflower bombs, slag, pozzolana, etc.
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