Like all the other volcanoes in the Puys chain, the Puy de Dôme (in the background of the photo) rests on a granite plateau. Its truncated cone-shaped lava dome, 550 metres high and two kilometres wide at its base, rises from the crystalline basement, which is located at an average altitude of 3,280 feet (1,000 metres). The high viscosity of the magma prevented lava from flowing down the sides of the volcano during successive eruptions and blocked the eruption chimney. The Puy de Dôme summit is currently 4,806 feet (1,465 metres) high, making it the highest volcano in the Puys chain.