The Puy de Dôme

To each lord, all honor It's the star of this overview. An iconic mountain of Auvergne, it gave its name to the department (the officials at the time had considered 'Monts Dore,' but, in true Auvergnat fashion, that sounded too fancy). The Giant of the Dômes, from the Romans to Pascal, and even the cycling duo Anquetil-Poulidor, is truly a star. Besides, it can be seen from far away: its high altitude compared to the surrounding plateaus makes it a legendary mountain. On foot, on horseback, by steam, by bike, by car, and now thanks to the Panoramique des Dômes, the rack railway, it makes you want to climb it. And it's tempting, because at its summit, it offers an exceptional view. Seen from above, the Puy de Dôme shows a western dome that must have been perfect > And when "la burle" blowes on the top   A 10,000-year-old youngster Ci dessus : le Puy de Dôme aujourd'hui Ci dessous : le Puy de Dôme il y a 10 000 ans Cliquez sur la photo pour les explications It's its age. It's little compared to the first buildings of the Chain (100,000 years). Before its formation, the few inhabitants of the Limagne plain near Clermont observed in its place a modest Strombolian scoria cone. Not enough to put up a television antenna. The western profile of the Clermont horizon was, of course, very different. Its construction and the history of events can be summarized as follows. It is in the initial Strombolian cone that a first trachyte dome is born and likely built. Trachyte is a very viscous lava that does not flow but remains directly over the vent. The development experienced no major incidents, and the altitude approached exceptional values for this type of volcanic activity. During this phase, pyroclastic flows of limited extent covered the surrounding areas, scorching the nearby forests. The dome is almost perfect, comparable to the dome of La Soufrière in Guadeloupe (also worth seeing). The building could have remained as it was, but a collapse, possibly resulting from an explosion, opened up the eastern part. The growth of the dome continues in the collapsed section. A progression similar to the first, but sharper, which will give it the characteristic shape we see today. It is referred to as a Pelean dome, with the point of comparison being Mount Pelée in Martinique, which apparently underwent the same growth scenario (resulting in the destruction of the town of Saint Pierre). But the comparison ends there, as the dome of Mount Pelée is a summit dome of a stratovolcano with very different lavas from a subduction context. The surrounding area is covered, on one hand, by deposits from pyroclastic flows emitted during the formation phase, and, on the other hand, by fragments from the eastern part. Vegetation then gradually colonizes the region, until the later occurrence of side events, such as the eruption of Puy Kilian about 8,500 years ago, which covered Puy de Dôme with pyroclastic materials. Does this episode mark the end of volcanic activity in the central area of the Chaîne des Puys? Relief The Puy de Dôme remains the highest volcano in the Chaîne des Puys at 1,465 meters. Its ascent has been made since Roman times via the Muleteers' Path on its southwest face. In 1907, a steam cogwheel tram allowed the people of Clermont to effortlessly climb the giant of the domes from the city. The development of the automobile led to the disappearance of this means of access, and the route was converted into a road for cars in the mid-20th century. This path makes a one and a quarter tour around the volcano with a steady 12% incline. Ironically or as a sign of changing times, the road has been abandoned since 2012 in favor of a new electric cogwheel train. This original solution, initiated by the General Council, allows the widest audience to discover this emblematic summit while preserving the environment. The hike up the Muleteers' Path is still an enjoyable experience. Starting from the Col de Ceyssat, the path climbs 400 meters in elevation, offering a wide panorama of the southern volcanoes and the Sancy Massif. The round-trip can take between 2 to 4 hours, depending on the pace you set for yourself. By looking at the 3D map with a pair of 3D glasses (right-eye filter: blue; left-eye filter: red), you will get a unique view of the Puy de Dôme. If you don't have any, you can make a pair using transparent paper in the indicated colors, or order your glasses. Equipped in this way, look directly at the screen from about 0.5 meters away (or print the map). But today's Lidar image (Source Géoportail) is even more striking. Lavas types The Puy de Dôme did not produce lava flows, except for pyroclastic flows and fallout, ash, and boulders ejected during the growth of the dome and its collapses. The lava is a trachyte which, when cooling, produces a white and friable rock. The lava of Puy de Dôme was long called Dômite. The rock's matrix contains phenocrysts (large crystals) of black biotite (mica) and quartz. Its silica content (SiO2), one of the highest at 65%, is a testament to the final evolution of the magmas of the Chaîne des Puys.   Science and the Puy de Dôme On September 19, 1648, the summit was the scene of Blaise Pascal's experiment, who, using Torricelli's barometer, demonstrated the variation of atmospheric pressure with altitude. It was his brother-in-law, Mr. Perrier, who carried out the operation. The story goes that Pascal never climbed the Puy de Dôme for fear of being suffocated. In fact, he was ill, and because of this, he had entrusted the work to his brother-in-law. Atmospheric pressure as a function of altitude

© Copyright Feb 2026 Photos, Cartes et Tableaux: Bernard Dichamp