Description
The volcanic juice of Gouléïou takes its name from the particular site it occupies. “Gouléïou” actually comes from “goulet”, that is to say “col”. It is a relief formed of phonolite, a clear volcanic rock enriched in silica.
The lava emitted at a temperature of 700 to 800°C was too pasty to be able to spread and accumulated above its emission point. This one far from responding to the usual image that we forge of a volcano; with its cone and its crater, corresponds to a simple fracture open towards the surface.
The particular conditions which presided over the establishment of this relief (temperature of the lava at the time of emission, degree of viscosity, speed of ascent towards the surface, shape of the supply conduit) explains its so educational form. , unparalleled around.
Like all the phonolite reliefs of this sector, the Gouléïou must have appeared between 8.5 and 6.5 million years ago after the construction of the eastern Velay.
It is thus later than the large basaltic plateaus of the Saint-Clément type that the phonolite had to cross through cracks to reach the surface.
The emission of phonolites gave rise to a type of very dangerous eruptive dynamism, called Péléen (from Montagne Pelée in Martinique). The violent explosions which characterize this type of volcanism are linked to the accumulation of gases contained in the magma during the ascent. They are at the origin of the famous “fiery clouds”, a sort of avalanche of rocky debris mixed with hot and toxic gases, with devastating effects.
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