Send to a friend
Born of a lengthy and complex gestation period, the Cantal mountains form a circle with a diameter of 80 kilometres, making this the largest stratovolcano in Europe.
While the Dore mountains make up three times the area of Vesuvius, those of Cantal form Europe’s widest stratovolcano. Extinct for the past three million years and eaten away by erosion, this titan is hardly recognisable as its mass was completely turned upside down through its active life, which began 13 million years ago.
This is why the sections comprising its valleys reveal only ground-up and displaced volcanic material, which left volcanologists perplexed for a long time. This was until 18th May 1980, when they were able to observe the explosion of another stratovolcano, Mount St Helens in the north eastern United States: in just a few seconds, a massive explosion saw it lose 400 metres in height and one third of its volume! It appears that Cantal experienced at least three similar catastrophes. Indeed this too is made up of viscous magma which causes particularly explosive eruptions, along with materials that make up more than three quarters of the whole massif.
Seen from afar, Cantal has outer slopes called planèzes, suggestive of a lowered cone: this was the shape of the complete volcano, the top of which, it is now estimated, may have been 3,500 metres high. The volcanic history of Cantal therefore continued on top of smoking ruins, with an outpouring of flowing basalt onto the lower slopes. These flows were commensurate with the giant volcano, as they stacked up to a depth of 250 metres at Le Puy Violent.
So Cantal has a magnificent collection of basalt organs, reminders of the way the lava cooled down slowly. A few Strombolian structures were also erected here and there, such as the cinder cone of Tanavelle, near Saint-Flour. The end point of the activity of the massif also corresponds to its current highest point, Le Plomb du Cantal, at 1,855 metres. Looking like a small dome jutting out on one of the ridges of the central area, this peak is a former lava lake which erosion has been unable to finally deal with. The powerful undermining work, which was what caused the large valleys spreading out in a star shape from the heart of the massif, was what brought Le Puy Mary (1,783 metres) to prominence, a Pelean dome broken up by craters, as well as phonolite peaks such as Le Puy Griou and Le Roc d’Hozières.