Volcanic activity in the Monts Dore region started about 10 million years ago, and experienced sleeping phases of hundreds of thousands of years and a gigantic explosive eruption 3 million years ago which led to the collapse of the upper Dordogne’s caldera. The formation of the Sancy stratovolcano between 330,000 and 250,000 years ago marked the end of the area’s volcanic activity. The volcanic morphology of Puy du Sancy is not easily recognizable due in particular to its alpine-like reliefs preserved by its relative youth.