The immense amount of energy required to cool and freeze a lake the size of Lake Servières in the Puy-de-Dôme department is delivered to the outside atmosphere in contact with the water surface and gradually transferred to the lake. The rate of energy exchanged is proportional to the surface of the lake, here 37 acres (15 ha), and the temperature difference between the two environments. The larger the difference is, the faster the lake cools and freezes.