Wednesday, March 9, 2011

The nicest columnar joints ever?

The picture this week is from the beautiful village Saint-Flour located about 80 km south of Clermont-Ferrand in the Massif Central (France). You see a lava flow with spectacular columnar joints overlain by a massive flow unit (picture 1). Saint-Flour is built on top of these basaltic flows (picture 2) that once poured out of the volcanoes forming the Massif du Cantal. 

 Picture 1: The columns in Saint-Flour.

Picture 2: Saint-Flour.

The volcanism in the Massif Central is young and rather odd. The most recent eruptions took place some 4000 years ago. Why are there volcanoes in this area at all? Is it linked to the Alpine deformation or to crustal spreading in the Atlantic?  

The volcanoes in Massif Central are numerous, ranging from lava domes to cinder cones, maars, and stratovolcanoes. In the north, the spectacular Chaine des Puys contains a great number of cones and maars, and one of the cones is partly excavated (the Lemptégy volcano; picture 3) as a part of the Vulcania theme park. Is this the best place in the world to see the internal structuring of a volcano, with fumaroles deposits, scoria, feeder dikes and lava flows? 

 Picture 3: Inside the volcano on a veeery gloomy day.

All of the prominent mountains in Massif Central are volcanic in origin, like the tallest one, Puy de Sanchy at 1885 m and Mont-Dore (picture 4). Further to the west, volcanic plugs dominate both the natural and cultural landscape (pictures 5 and 6).

 Picture 4: Mont-Dore in April/May.

Picture 5: One of the plugs in Puy-en-Velay. 

 Picture 6: Puy-en-Velay.

I wonder if the volcanoes will be brought back to life some day. Strictly speaking, they are only dormant.

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