The electric train to the top of the Puy de Dôme, the sleeping giant of a volcano that overlooks Clermont-Ferrand, was packed with high school students from Brittany. Kornprobst looked around at them, the flower of French youth on a field trip to the mountain observatory that both he and Brunhes had once ruled over. He would be amazed if any of them had a clue who Brunhes was, he confided to me.
We were nearing the end of our first long day retracing Brunhes’s historic steps. We had already made a dispiriting detour to Laschamp, a dot on the map a few kilometers from Clermont-Ferrand. This was where, after sampling more than fifty volcanoes in the area in the 1960s, the PhD student Norbert Bonhommet discovered the Laschamp excursion, or near-reversal, from about 40,000 years ago, the last time the Earth’s magnetic field was in disarray. For a while, it was thought to be evidence of the last full reversal. Kornprobst’s colleague Jean-Pierre Valet has linked the timing of the excursion to the demise of the last Neanderthal. Kornprobst and I had trudged through the snow with a compass, trying to find the spot where Bonhommet had taken his sample. No luck. We finally gave up and went for lunch: a rich local specialty called truffade, made of sliced potatoes and lots of butter and even more melted cheese, served with red wine.
Now Kornprobst was keen to play host at the scientific laboratory up on top of the Dôme. Brunhes had spent vast amounts of time there, arduously riding up the switchbacking old Roman road to its summit by mule, fascinated with the ruins of a monumental, multi-tiered temple to the travelers’ god Mercury built here in the second century CE. It was one of the largest religious sanctuaries of the Roman Empire, visible from the road the Romans built far below.
The temple had been forgotten for centuries, rediscovered in 1872 when workers began excavating the volcano top for construction materials to build the observatory. To Brunhes, who arrived nearly thirty years after that, the discovery represented a potential wealth of information on the magnetism of the large rectangular slabs of pale Dôme lava used to make the temple. His assistant, Pierre David, tested four, finding mainly that they had held their magnetic memory—an important confirmation of their laboratory technique. The two colleagues vowed to do more tests.
But whenever you go up to a volcano’s peak you also go down into its terrifying inner reaches, whether you are there for science or worship or art. Nearly half a million visitors a year flock to the top of the Dôme, at least partly because standing on the lip of a volcano, however long dormant, is like standing at the maw of hell. You’re not sure what terrors could be right below, waiting to pounce. It is catching a glimpse of the unknowable forces deep within the Earth that hold the power to erase the world.
The Romans likely knew that it was an old volcano. That’s probably why they built their sprawling temple to Mercury there, so far above the road. Even today, with the train, you have to want to get there in order to make the trek. To hike back down would take a vigorous hour and a half. But the knowledge that this was once a volcano got lost after the Roman era, along with the memory of the temple. For more than a thousand years, this volcano was thought to be a worn-down mountain like the others in this area. The menace was a faint memory.
Then, in 1751, the French naturalist Jean-Étienne Guettard climbed to the top of the Dôme and saw immediately that it was one of about ninety volcanoes that run across 30 kilometers (nearly 20 miles) of the Auvergne region of central France. He warned that they might wake from slumber and explode again. Modern volcanologists concur. It caused a sensation to find a string of old volcanoes hidden in plain sight in a part of Europe that had been settled for thousands of years. The subsequent intense interest in the volcanoes, known as the Chaîne des Puys, marked the birth of the formal study of volcanoes. Volcanologists made pilgrimages from all over Europe, trying to understand what made the volcanoes spew their lava and when it had last happened, trying to peer down into the bowels of the Earth and back into time.
Like so many elements of geophysics, volcanology represented a challenge to theology. The age of the Earth was of critical, abiding interest to theologians, partly because they believed that if they knew when the world began, they would also know when it would end. Apart from that, to their way of thinking, God had created the world, and his chronicle of that creation was contained within the Bible itself.
This philosophy reached its logical conclusion in the seventeenth century, when James Ussher, the archbishop of Armagh in Ireland, painstakingly went through the Old Testament books to reckon precisely how long before the birth of Christ major events had taken place. He famously put the birth of the planet at early Saturday evening, October 22, 4004 BCE, needing two thousand pages of Latin to explain how he came to that date. Other scholars calculated it to roughly the same period, meaning that they thought the Earth was not quite 6,000 years old. (Modern scientific calculations put it at about 4.6 billion years old.) By the beginning of the eighteenth century, annotated versions of the King James Bible included Ussher’s dates in the margins beside the relevant passages, supporting the idea that the Bible was a reliable chronology. The supposed birth date of the Earth wasn’t academically debunked until the late nineteenth century, and was still debated into the late twentieth century, long after the field of volcanology had begun, after paleontologists had begun digging up ancient human fossils, and after the British naturalist Charles Darwin published On the Origin of Species, outlining the theory that creatures had evolved over time from common ancestors.
On top of that, naturalists of the eighteenth century had dueling theories about what made the material the volcanoes spat out. They were divided between water and fire. The Neptunists, named after the Roman god of the sea, were convinced that basalt, or swiftly cooled lava, was formed at the bottom of the sea as sediment. Volcanoes were formed by underground explosions, perhaps of tar or brimstone. Their rivals, named Plutonists after the Roman god of the fiery underworld, thought lava was molten rock that built up underneath the Earth’s surface and finally let loose. Both Neptunists and Plutonists visited the Auvergne to see the Dôme and the other old volcanoes, each faction trying to use evidence found there to prove its theory. The Plutonists eventually won the day.
But there was still the thorny question of when the eruptions of the Dôme had happened. Modern analysis says the lava began to form about 100,000 years ago 30 kilometers (18.6 miles) below the surface at the top of Kornprobst’s beloved mantle, partly the residue of heat in the core. It was primordial molten basalt, so superheated that it needed an escape valve, migrating inexorably up to a magma chamber underneath the Auvergne until, about 10,800 years ago, the pressure became too great. The magma chamber burst open, loosing the seething lava, which surged to the top of the volcano and exploded into the air. The blast was so powerful that it destroyed the vast east flank of the Dôme, spilling lava into the countryside. And then, 1,600 years later, after the Dôme had partly grown back, came another massive outpouring from a magma chamber fed by primitive mantle basalt. Some scientists believe there could be prehistoric communities buried in the countryside beneath the ancient lava of the Auvergne, just as there were below Mount Vesuvius.
Today, this dome within a dome is grown over, capped by the Temple of Mercury and, at the very tip, the laboratory, itself topped with instruments resembling giant white fluorescent tubes that can be seen for miles. Kornprobst and I were making our way slowly past the temple, onward to the lab, over the treacherous ice. It was late March, a week before Easter, but the cold pierced to the bone. Kornprobst’s cheeks were ruddy, hair windswept. Small piles of snow lay on the ground surrounding the temple’s outer walls. Its pale gray slabs—Brunhes’s assistant, David, must have tested their neighbors—stood out against the whitened sky. We were in an icy cloud, suspended over portending fire.
I could see why a string of religions across time and space have paid homage to the volcano and the underworld it connects to. Vulcan, the Roman god of fire, gave his name to the volcano and its study. He was the disabled god of the forge, son of Jupiter and Juno, who symbolized both life and death, making thunderbolts for his father. Japan’s Mount Fuji, which last erupted in 1708, is a spiritual lodestone, the sacred symbol of Japan itself. Pilgrims climb it at night in order to bear witness from its summit to the sun rising.
That awe has spilled over into the long literary tradition of imagining the inner Earth, a forbidden land of sin and suffering poised for the unleashing. From Dante Alighieri’s fourteenth-century Inferno of punishment to John Milton’s seventeenth-century Paradise Lost to Jules Verne’s nineteenth-century adventure tale Journey to the Center of the Earth. Verne’s heroes descend to the hellish core of the planet through an exhausted two-domed Icelandic volcano, dodging death at every turn, only to ride to the surface again on the boiling plume of a Mediterranean volcano. Or there’s a more recent iteration, the American cult television show Buffy the Vampire Slayer, whose star spent seven fraught seasons trying to keep the Hellmouth, aka Sunnydale, California, closed so the evils wouldn’t come out and destroy civilization.
Kornprobst and I made it to the final stretch of the path around the temple, and then up the slippery outdoor stairs to a single locked door. He rapped on it and a head eventually poked out. Kornprobst introduced himself. He had once been in charge of the whole works and was here to look around.
This scientist was one of the eight or ten who were working in the lab—some temporarily living there—taking samples of the air. It was a far more modern, far-ranging, and technologically intensive process than when Brunhes had run things with his single gas motor. Today, the mountain observatory is part of the World Meteorological Organization’s Global Atmosphere Watch, a network of observatories to monitor humanity’s effect on the global atmosphere. Jean Brunhes, Bernard’s brother, the inventor of human geography, would have approved of the research.
Because the Dôme is the highest of the Auvergne volcanoes and because there is so little heavy industry between the Atlantic Ocean and it, the air quality is unusually pure, Kornprobst told me. The young scientist explained in fluent detail how one of the machines worked, and showed us a raft of that day’s findings. One number stood out: The greenhouse gas carbon dioxide was present at 403.197 parts per million—a shockingly high concentration compared to the preindustrial figure of 280. A marker of climate change, this was one of the figures Bernard Brunhes could never have imagined would be so important just a century later.
Finally, Karine Sellegri, director of research of the National Center for Scientific Research’s Laboratory of Physical Meteorology and an expert in cloud chemistry, among other things, came to meet us. She was the team leader.
“Kornprobst!” my companion declared, bowing slightly. He explained that we were trying to help the world understand the significance of Brunhes’s bold finding that the magnetic field had reversed. Sellegri was apologetic. One small conference room was named after him at the lab, but nobody was told why. His name was not mentioned in courses at the university in Clermont-Ferrand. However, there had been a small lecture on reversals, she recalled, brightening up a little, and she, of course, knew of Brunhes’s experiments.
“They were not experiments!” Kornprobst barked. “They were observations!”
Later, over espresso and a biscuit as we were waiting for the train to take us back down the volcano, Kornprobst was reflective. In retirement, he was scientific adviser to Vulcania, known as the European park of volcanism—an amusement park set up to help the public learn about volcanoes and other inner-Earth mysteries. The park was another sign of just how forcefully volcanoes had shaped the psyche of the region, partly spurred by Kornprobst’s own fiery determination as head of the observatory to make Clermont-Ferrand an international center of excellence in the discipline. Just a few kilometers from the Dôme, Vulcania’s tourist season was launching that evening to great fanfare, and Kornprobst was to be a guest of honor.
As he sipped his espresso, he lovingly tracked the science of the discovery of magnetism back through time, fluidly quoting not only the main figures—Peregrinus and Gilbert, among others—but also landmark papers that had advanced the field. Brunhes was a fulcrum. There was the science of magnetism before him and there was the science of magnetism after, and they were not the same. The next day, we would take the most important journey of all: a trip to try to find the very same seam of rock Brunhes took his fabled samples from, the ones that changed the history of science.