La Chaîne des Puys

Montait une nuée...; elle ressemblait très exactement à un pin. ...laissée seule ou vaincue par son propre poids, s'évanouissait en s'élargissant.

Pline le Jeune

The future

Cathédrale Clermont

La colonne de poussières d'une éruption vue de la Cathédrale de Clermont-Ferrand

Will the "Chaîne" awake ?

Secretly, Auvergnat would wish well a small renewal of activity some where in the Chain to supplement this fantastic landscape. Let us acknowledge that it would be unhoped for local volcanology. The analysis of the eruptions gives many answers to the questions about the volcanic mechanisms. But, reasonably the local and national persons in charge would have to face a situation without precedent.

The risks

From the start one draws aside a sudden eruption. The seismic first steps of a magmatic increase will be well collected by the inspection network in place. The signatures of such a phenomenon are known and one will be able to determine as well as possible, with a complementary instrumentation, the perimeter of the exit point. The problem to be solved by the specialists remains the evaluation of the probable date of the eruption. From there will depend the options retained by the civil authorities which will have to do what is necessary to evacuate without delaying, the zone considered to be dangerous. The nonexplosive character (Plinian) of the volcanos of the Chain makes it possible to circumscribe a sector of only a few tens of kilometers. We can imagine these cases :

- Strombolian " only ": it is the model most present in the Chain. The risks could be very limited. With term, only the lava flows being propagated with dimensions East will be worrying for the Clermont-Ferrand staged habitations.

- Pelean or trachytic: the effects of the last episodes apparently were very limited. But Pelean operation is unforeseeable bus of the volcanic clouds can always develop and devastate the neighbours.

- Phréatomagmatic: it is a very possible scenario because all the sector of the Chain comprises significant water reserves. The explosions of this type are generally of great width with projections of blocks to impressive dimensions.

In addition to the eruptive demonstrations, water the pollution of sources, the always possible gas emissions, the plumes of dust falling down neighbourhoods, are as many effects to consider.

If it were the case, there is no doubt that it would be a whole area which would be upset. The displacement of some five hundred miles people, by its social and economic impacts, would pose surely a serious problem of logistics.

 

Current activity

 

Fiction story

Le journal local

It is interesting to see what it would occur through observations brought back by médias such a significant event. Here in a local newspaper the kind of informationhat we could find, in a context with the limited consequences. It is supposed of course that the daily newspaper is printed elsewhere than in Clermont- Ferrand. (English version of newspaper)

The volcanic activity

The last volcanos died out 6500 years ago (Pavin system). Since there no were recognized demonstrations. This time is too short to conclude that the Chain of Puys is definitively deadened. The probability of a renewal of activity is not negligible. But where? Search does not make it possible to answer this question immediately. It is necessary to have more precise localization of the magmatic tanks and a thorough knowledge of the structure of the base. With the obviousness certain hot sources of the various thermal spas Auvergnates, such as "Chaudes-Aigues", are indication of latent volcanic situation.

The seismic activity current

It is significant and primarily tectonics, in connection with the push of the Alps. Contained in low values, it appears sometimes with the inhabitants of the area. Example the numerous events of August, 2003 (see the usual page), with a shock of magnitude 3.6, and the epicentres of which extended of the sector of Ancizes-Comps until the Gour de Tazenat (RENASS source). This seismic episode, fortunately without consequence, was more intense as usual.

Etna vue par la LC

At left a photograph simulating the western horizon of the Clermont-Ferrand plain. The permanent reddish glow of the craters projecting of incandescent slags is an always extraordinary and attractive night spectacle. The prehistoric men of the area surely observed these phenomena, without being able to give them explanations. Today, an event of this type, by its social and economic repercussions, would have very an other width, in spite of the scientific and tourist interest which it would get.

This picture is Etna in strong Strombolian activity (Christmas 1997) seen live-camplaced on Montagnola (animation 291Ko)

 

Webcam of the site of the General Council pointed at the puy of Dome from Clermont-Ferrand will allow you, for lack of assiter in a possible event directly, to appreciate the remarkable landscape of Clermontois.


© Copyright Jan 2001 Photos et Tableaux: Bernard Dichamp