The geology of Lemptégy Volcano - France
Visiting a quarry ? The idea doesn't always inspire enthusiasm. However, the Puy de Lemptégy quarry is an exceptional site, the result of a passionate collaboration between its operator, Jean-Louis Montel (1937-2017), and academic volcanologist Guy Camus (1941-1999), a renowned specialist in the Chaîne des Puys.
This unique site offers exceptional access to the internal structure of a volcano, a true dive into the bowels of the Earth. But Lemptégy is much more than a simple geological cross-section : it reveals a complex history of several successive eruptions, their interactions, and the traces left by climate and vegetation over tens of thousands of years.
Since it opened to the public in 1992, while operations continued, and then finally closed in 2006, the quarry now attracts nearly 200,000 visitors a year, including schoolchildren, academics, and tourists. When exploring the Chaîne des Puys, it has become a must-see, just like the summit of Puy de Dôme or Vulcania. This popularity isn't just due to the fascination with volcanoes, even extinct ones. Geology is an observational science often complicated by vegetation, and the quarry here provides rare insight into a basic cinder cone volcano.
While some see quarries as scars on the landscape, Lemptégy shows that extraction can provide valuable insight into understanding and protecting our geological heritage.
This site is open to everyone, from young children to experienced researchers. It can be visited briefly or spent hours discovering its many facets. Lemptégy is not only a spectacular setting with lunar colors and landscapes ; it is also a classroom, a testing ground, and a permanent laboratory, with unprecedented observations and discoveries within a limited area of 7 hectares. This exceptional and unique setting in Europe constitutes an essential site of national geological heritage and is today, along with the Chaîne des Puys, listed as a UNESCO World Heritage Site !
The geological history of the Lemptégy volcanoes
At the heart of the Chaîne des Puys, the Lemptégy site reveals an exceptional geological sequence, where several distinct volcanic episodes follow one another, separated by phases of stability, erosion, or reworking. Thanks to the opening of the volcano by industrial exploitation, it is now possible to reconstruct with great precision the complete stratigraphic history of the site. Here is this detailed chronology, event by event:
Act I – The birth of the Puy de Lemptégy 1 (~30,000 years)
Around 30,000 years ago, in a landscape still dominated by cold and periglacial steppe, basaltic magma from a deep reservoir rose beneath the future site of Lemptégy. Its composition, bordering on basalt and trachybasalt, and its richness in granulite enclaves (fragments of the basement torn from a depth of more than 20 kilometers) attest to its abyssal origin.
The eruption gave rise to the first volcanic edifice : Lemptégy 1, a classic Strombolian cone composed of red and black scoria. But behind this modest silhouette lies a complex architecture : a base of welded lava pierced by radial veins, large bombs (including one weighing 60 tons), and an elongated vent marked by an eruption on a fissure oriented N160.
However, the edifice failed to fully develop. Since its formation, it has been affected by powerful tectonic movements. Lemptégy 1 partially dislocated under the effect of a syneruptive extension, creating a series of normal faults, horsts and grabens visible in the flanks of the quarry. Flank landslides accentuate this instability, particularly to the south and west. This first volcano was therefore both ephemeral and profoundly transformed from its inception.
Act II – The Puy des Gouttes enters the scene (slightly later event)
As Lemptégy 1 began to decline, a second volcano erupted nearby to the northeast : Puy des Gouttes. It was also fed by basaltic magma, and its activity began in a classic Strombolian style. The projections (black lapilli with a reddish base) fell directly onto the still-hot scoria of Lemptégy 1, where they were welded together by the residual heat. This thermal interaction attests to the near-simultaneity of the two eruptions, or at most, a very short interval between them.
As the eruption progressed, the dynamics changed : a phreatomagmatic phase took over. It generated heterogeneous deposits of ash, lapilli, and boulders, sometimes enriched with granite fragments. These materials were deposited by surging clouds, indicating an interaction between the magma and surface water. This explosive development marks the beginning of the dismantling of the Gouttes cone.
Act III – Lemptégy 2 takes over (shortly after the first two volcanoes)
During or just after the eruption of Puy des Gouttes, the geological history of Lemptégy experienced a major turning point. The differentiated magma, accumulated in a shallow reservoir located beneath the site, became overpressurized. This trachyandesite, lighter and slightly more viscous than the initial basalts, marked a change in magma supply.
A new eruption began : this was the birth of Lemptégy 2. This second Strombolian cone was built partly on the dislocated remains of Lemptégy 1. Its well-preserved vent is surrounded by red scoria and traversed by numerous lava veins, which radiate in a star-shaped pattern before bending southwest. These intrusions destabilized the cone's flanks, causing further landslides. The main flow of Lemptégy 2, about 2 meters thick, then appears and progresses for nearly a kilometer, carrying with it the overlying scoria. The crater takes on a mouthed shape and will culminate at 1019 meters above sea level. The flow presents a typical “block lava” facies (aa type flow) similar to those of Etna. Its summit, fragmented into polyhedral blocks, betrays rapid cooling and subsequent remodeling by frost. This last eruption thus completes the initial volcanic triptych of Lemptégy, the result of two magmas of distinct but nevertheless intimately linked compositions.
Act IV – The eruption of Puy de Côme (~16,000 years ago)
About 14,000 years after the last tremors of the Lemptégy system, a new volcano emerged two kilometers to the south : the Puy de Côme, one of the most massive cones in the Chaîne des Puys. It rises more than 300 meters above the plateau and develops two nested craters, evidence of successive explosions. Its eruption marks the beginning of the region's fourth major volcanic period.
The Puy de Côme emitted a monumental cheyre, a chaotic flow of trachyandesibasaltic blocks that reached the Sioule Valley. But its fallout was not limited to flows : fine gray ash, light lapilli, and scoriaceous rock were carried by the winds to the Lemptégy site, where they were deposited in regular sheets, sometimes several meters thick.
These deposits, visible especially on the northern slope of Lemptégy 2, form characteristic layered strata, with current patterns, aeolian dunes, and internal unconformities. Sometimes, they accumulate in small depressions formed by previous landslides. A very specific reworking is also observed: small red and black scoriaceous blocks, originating from Lemptégy 2's projections, slowly roll downhill, mixing with ochre silts.
These formations are periglacial slope deposits, or "volcanic groise," evidence of a cold and unstable climate, where freeze-thaw cycles led to slow solifluction. This mixture of recent products and older fragments shows that the flanks of Lemptégy continued to reshape well after the end of its eruptive activity.
Act V – Formation of the paleosol (11,000 – 9,500 years ago)
When the Puy de Côme died out, a long silence fell over the Lemptégy region. The climate slowly evolved : the last glaciations ended, and herbaceous vegetation gradually colonized the volcanic slopes. This was a period of climatic transition, between the cold pulses of the Dryas and the arrival of the temperate Holocene.
During this lull, the volcanic deposits stabilized, the slopes stopped sliding, and a brownish paleosol began to develop. Fine, loose, and rich in organic matter, this nascent soil sealed the previous layers of ash and slag. But observations made on the quarry walls revealed the absence of deep roots, even in the loose slag: the vegetation remained sparse, low, and treeless.
This paleosol plays a crucial role in the geological reading of Lemptégy : it marks a real tipping point, a sedimentary boundary between the major ancient volcanic phases (Lemptégy 1, 2, Les Gouttes, Côme) and the cataclysmic event that will follow.
Act VI – The terminal blast : the eruption of Puy Chopine (~9,500 years ago)
After several millennia of respite, the earth awakens one last time in the northern sector of Lemptégy. It is a sudden, violent eruption that will mark the end of the region's eruptive history. Puy Chopine enters the scene.
It all begins with a sudden explosion : a pyroclastic cloud, fueled by gas-rich trachytic magma, sweeps across the slopes of Puy des Gouttes, sweeping away the forest that had had time to establish itself there. In Lemptégy, this cloud deposits a thick layer of ash and white trachytic blocks ; this famous deposit is recognizable by its numerous fragments of charred wood. The branches and twigs, all oriented in the same direction, reveal the direction of the blast and the violence of the phenomenon.
In the newly opened crater, a trachytic needle slowly formed : Puy Chopine as we see it today, the remnant of a viscous lava dome injected into the final conduit of the eruption.
14C dating of the charcoal found in the pyroclastic flow deposit places the event at around 9,500 ± 500 years ago, in the middle of the early Holocene, in a landscape that was already temperate but still fragile. Puy Chopine is thus the last major volcanic event in the Chaîne des Puys before the modern era.
Act VII – Current soil development (Middle Holocene to Present)
Since the eruption of Puy Chopine, the Lemptégy region has entered a phase of lasting geological stability. The ash and lapilli have slowly transformed : under the action of wind, water, roots, and microorganisms, a slow but steady pedogenesis has shaped the modern brown soil, rich and fertile, capable of supporting dense and perennial vegetation.
This current soil seals all previous volcanic deposits. It constitutes the most superficial and most recent layer of the stratigraphic section observable in the quarry. In places, it rests directly on Chopine's ash, elsewhere on older paleosols. Everywhere, it bears witness to the passage of time, the healing of the earth, and the return of a landscape of meadows, forests, and human activity.
Today, this soil shelters vegetation, wildlife, and visitors. It is both the heir to 30,000 years of geological history and the support of contemporary life. The Puy de Lemptégy, thanks to the opening of its rocky belly by mining, has become a living geological museum, a unique site where each stratum tells the story of an era, each fault a jolt in the Earth's crust, each enclave a vestige of the deep mantle.
Puy de Lemptégy : from quarry to tourist site (1946-2025)
In the aftermath of World War II, France was recovering from the massive destruction suffered during the conflict. Rebuilding cities and infrastructure required large quantities of materials. It was in this context that in 1946, a Parisian company, supported by the Marshall Plan, became interested in Puy de Lemptégy. The volcano, rich in light and insulating volcanic scoria, represented a precious resource. For some twenty years, the cinder cone was literally decapitated by open-pit mining carried out by the company "Les Sablières de la Seine."
Technical innovation was at the forefront : the first Caterpillar bulldozers were used in Auvergne to extract this black scoria from the bottom of the cone, renamed "Isovolcan." These materials, known for their lightness and insulating properties, were sorted and then transported by dump truck to the Vauriat train station, from where they were transported by train to Paris and the rest of France. By 1965, production reached 1,500 tons per day, with the finest slag used for sanding roads in winter.
But this intensive exploitation quickly reached its limits. The freeze in the price of Auvergne pozzolan led to a difficult financial situation, and in 1970, the operation was abandoned. The volcano, disfigured by mining, became an abandoned industrial landscape, littered with scrap metal and old machinery, having lost its natural beauty. Between 1968 and 1972, the abandoned quarry was even threatened with becoming a public dump.
This marked the beginning of a new era for Puy de Lemptégy. In 1972, Jean-Louis Montel, a local farmer, seized the opportunity and bought the operation. Taking advantage of the revision of the Mining Code, he obtained an operating permit and set about revitalizing the site. In collaboration with scientists, notably geologist Guy Camus of the University of Clermont-Ferrand, the volcano was cleaned and restored. As early as 1974, the site's exceptional geological significance was highlighted.
At the same time, botanical research was conducted to revegetate the site, with support from the Clermont-Ferrand Botanical Laboratory and INRA. This work, led by Maryse Tort and Michel Frain, laid the foundations for the ecological dynamics of volcanic scoria, initiating a slow return to nature.
During the 1980's, discussions on the future of Puy de Lemptégy intensified. Jean-Louis Montel and Guy Camus considered combining industrial exploitation with educational, tourism, and cultural development. In 1989, a feasibility study and a tourism survey confirmed the merits of a project for an information center on volcanism.
In 1990, a new operating permit was granted, accompanied by strict measures : phased mining, landscape protection, site security, and conservation of mining heritage. Puy de Lemptégy thus became the first full-scale Volcanism Center in Auvergne and Europe.
The opening to the public in 1992 coincided with a national conference of biology and geology professors in Clermont-Ferrand, attracting scientists, students, and visitors from around the world. The site even hosted Apollo astronauts for a filming session, highlighting its scientific and cultural significance. Since 1993, the site has offered exhibitions, guided tours by geologists, and a constant showcase of the local volcanic riches.
In 1994, the Puy de Lemptégy SARL was created, headed by Jean-Louis Montel and his son Philippe. This family-run business ensures the sustainability and protection of the site.
The volcano was gradually enriched with exhibition and screening rooms, followed by several dynamic cinemas. The first tourist train was inaugurated in 2002, followed by a second in 2006. They were electrified in 2020 for greater respect for the environment. Today, in 2025, the Puy de Lemptégy is enjoying a second life, embodying an exemplary success in the conversion of an industrial site into a major tourist and scientific destination. Its dual identity, both as a remnant of intensive mining and a preserved natural gem, attracts tens of thousands of visitors each year, contributing to knowledge of volcanism while ensuring the preservation of Auvergne's heritage.
Photo : The volcano can be visited by miniature train © Volcan de Lemptégy
Conclusion
Puy de Lemptégy is much more than a former mining site or an object of scientific study : it is a place of memory and emotion, a landscape shaped by fire, time, and the hand of man. From its lava flows to its ash strata, from its landslides to its silent paleosols, it recounts 30,000 years of Earth's history with a rare and moving clarity.
Walking through this unique quarry, you're not simply visiting a volcano: you're entering the innermost depths of the Earth, where every fault, every enclave, every vein whispers the secrets of the subsoil. We then understand that geology is not a cold science, but a living adventure, where landscapes, invisible forces, and the passage of time intertwine.
Puy de Lemptégy is an encounter: between scientific rigor and wonder, between the geological past and the perspective of present generations. It's an invitation to slow down, observe, learn... and feel.
Whether you're curious about nature, passionate about volcanoes, a lover of the great outdoors, or simply looking for an extraordinary experience, this unique site awaits you. Come listen to the Earth's heartbeat: in Lemptégy, it resonates in the open air.
References :
MERLE et al. (2023) : "The UNESCO World Heritage Site of the Chaîne des Puys–Limagne Fault Tectonic Arena (Auvergne, France)", Geosciences, 13(198).
PORTAL et al. (2016) : "Cent ans de géophysique éclairent la Chaîne des Puys", Revue d'Auvergne