Located in the municipality of Besse-et-Saint-Anastaise in the Puy-de-Dôme department, Lake Pavin is the youngest crater lake in mainland France and was formed 6,900 years ago by phréatomagmatism, as evidenced by its maar crater. This type of volcanic eruption is the result of the encounter between magma and groundwater. The contact between water and lava causes a thermal shock and an explosive vaporisation of water, leading to the formation of circular explosion craters a few hundred metres wide and a few dozen metres deep.