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Geological History

In part covered by 1,500 ha of forest, The Comté d’Auvergne constitutes an old sedimentary system marked by a volcanic activity that began around 25 million years ago.
This volcanism is older than the one of the supervolcano of Mont-Dore-Sancy and the range of Puys. The chimneys of these volcanoes eroded and form conical hills that give a specific shape to Limagne.

The Hillock in Buron

At the beginning the hillock was a greater volcanic structure than it is nowadays because of erosion. The peak in Buron stems from a lava lake that filled up a depression called « maar ». It resulted from a phreatomagmatic eruption. While it cooled down, the lava formed volcanic basalt columns that can be seen from the village.


When the magma flows upwards, it can meet with water in the sediments. The water is heated up and vaporised. The resulting increase in pressure triggers a violent explosion that blows off the sedimentary lead that frees the lava. This explosion digs a circular crater in the ground, that is called a maar.
Then should the maar not be filled up by the lava during the eruption (like in Buron), it can fill up with water to form a lake (like the Pavin lake for example).

The basaltic columns

At the end of the eruption the lava filled the maar up.
Then this lake of lava cooled down in the shape of basaltic columns. Subsequently the erosion of the sediments dug out this old lake of lava that can be seen today as the hillock .
These basaltic columns were used to build the castle in Buron as well as other buildings in the village, the reason being that they interlock easily.

Based on Professor Olivier Merle,
Laboratory Magma and Volcanoes,
Observatory of Physics of the Earth – Clermont-Ferrand

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