La Chaîne des Puys

Je voudrais voir l'intérieur de cette chaudière, dont j'entends déjà le puissant halètement..

Haroun Tazieff

Formation of the Chain

Le Clerziou

The "Clerziou": a dome of an incredible perfection

 

Why volcanos in Auvergne?

The meeting of Africa and Europe

 

Plaque EuropeRemote from ridges of accretion and from big subduction zones the volcanism of the Central Massif is of more complex origin.

It constitutes with the tectonic accidents of Limagnes to which it is associated, a western important geologic constituent European. The first theories are debated by the scientists for the benefit of models supported by the last researches today which connect his origin with the continuous push of the Africa plate on the Eurasian plate.

In fact, the ascents of Italy at the origin of the genesis of the Alps upset the crust and the mantle. This confrontation creates it was 35MY ago an east-west extension of the earth's crust at the origin of the rifts of Limagnes, followed by thermic ascents in the mantle. In this process magmas form by decompression and rise up then in wills of the weaknesses of the crust. This volcanic phase develops there is 25MY ago.

The conjugation of these phenomena so favor the conditions of forming a continental rift valley of the North in the South of the Central Massif, which goes on more in the northeast with the Rhenish ditch and the Eger.

The Auvergne volcanism in place begins it was 25MY ago, with the phase of Limagnes, but the most intense period will be situated later by the construction of Cantal (13 MY in 3 MY), Cézallier (6 MY in 3 MY), the Sancy (3 MY in 200 000 years), more in the southeast group Devés Velay (13 MY in 1 MY.

The first volcanoes of the Chaîne des Puys appear 150 000 years ago (see the chronology). The size, relatively small of the buildings, shows that the activity was not continuous until our days, but rather occasional. Indeed the average life cycle of a volcano has been of some dozens in some hundreds of years at the most.

 

The Chain of Puys: a dominating alignment

The North-South axis of alignment is placed on a crystal stage which dominates by an escarpment about 600m, the sedimentary plain of collapse of "Limagne de Clermont". To the west, the plate goes down soft inclined on the ditch from "Sioule". This topology will have a significant impact on the aspect of lava flow. The magmatic tanks, as well as the intermediate rooms, are probably located in the axis of the Chain, the épanchements being supported by a network of faults fracturing the area.

coupe Limagne/Dôme

The "Chaîne" view of the Thiers city : a large explanation of the formation


© Copyright Jan 2001 Photos et Tableaux: Bernard Dichamp