Is there anything as terrifyingly majestic as an erupting volcano? The ground shakes, fountains of incandescent lava spurt skyward, and roiling clouds, alive with lightning, grow with alarming speed. Volcanoes are so much larger than anything human, and they care nothing for us, as revealed by the body casts of Pompeii and Herculaneum, in which the death agonies of some of their victims are frozen forever.

In Mountains of Fire, Clive Oppenheimer, a professor of volcanology at the University of Cambridge, recounts a life spent studying volcanoes up close. He is an extraordinary individual who somehow finds serenity in the chaos at a volcano’s crater and admits to feelings of loss when he must descend back toward civilization. Many of the volcanoes studied by Oppenheimer lie in the remotest reaches of our planet: he is one of the few foreigners ever to be allowed access to North Korea’s sacred Mount Paektu, and he has traversed the war-torn and hostile Danakil Depression, near the border between Ethiopia and Eritrea, with its myriad vents and calderas; Oppenheimer has also ascended Antarctica’s Mount Erebus a dozen times. His book is a tale of gripping adventure, undertaken in the constant shadow of death by volcanic mishap, appalling weather, lawlessness, or warfare.

Oppenheimer’s specialty is the analysis of volcanic gases. When he began his career in the 1990s, the instruments he used were so rudimentary that it was necessary to get very close to volcanic vents to take observations. He recalls having to work within fifty meters of craters on Stromboli, off Sicily’s northern coast, as bombs of molten lava pelted the ground around him and asphyxiating gases shot from nearby crevices. The area is considered so dangerous that today nobody is allowed anywhere near it. Perhaps in an attempt to deter others from the rash ways of his youth, he writes, “It’s an understatement to say that this fieldwork was imprudent.” His measurements, gained at such risk, sadly proved to be of little value.

Mountains of Fire is far more than Oppenheimer’s tale of heroic scientific exploration, for it weaves his personal accounts with a splendid history of volcanology. Before scientific volcanology arose, these fearsome structures were explained by the imagination. In his 1665 book Mundus Subterraneus, the German scholar Athanasius Kircher alleges that the oceans enter the earth’s crust in a giant whirlpool off the coast of Norway, mingle with fire to fuel volcanoes, then exit through a great fundament near the South Pole. In more recent times scientists have established that volcanoes erupt when molten rock (or magma) that has pooled in an underground chamber reaches the surface, releasing lava (as magma is called after it breaches) and gases. Sometimes volcanic vents become blocked; if water enters the magma chamber, the pressure from the resulting buildup of steam leads to explosive eruptions.

Most volcanoes are located at the margins of the earth’s tectonic plates. In Iceland and along the mid-ocean ridges, the plates are moving apart, and magma reaches the surface through the thinning crust. These volcanoes often produce quite fluid flows of lava that can form extensive zones of basalt when they cool. Along the Pacific coast of the Americas, in parts of Asia, in Southern Europe, and elsewhere, two tectonic plates are converging, and one is thrust under the other, causing it to melt. The magma produced when this occurs is rich in silica and can be viscous. In some places, such as Hawaii, volcanoes occur far from the plate margins; they seem to emerge from “hot spots” of magma originating very deep beneath the earth’s crust, at the boundary between the planet’s core and its mantle.

The term “volcano” was coined after the Roman god of fire, Vulcan. Oppenheimer traces the roots of scientific volcanology back at least five hundred years, to the pioneering writings of the Spaniard Gonzalo Fernández de Oviedo y Valdés. In 1529 he climbed Masaya, located in what is today Nicaragua. He found its crater both a marvel and a hellhole, at whose center lay a pit filled with red-hot lava covered in a black scum that repeatedly tore open as gas bubbles burst through it. Lacking scientific instruments, Oviedo studied the phenomenon with his senses, noting the temperature, sounds, and smells, all the while marking time between gaseous eruptions by reciting the credo.

Not surprisingly, given its abundance of easily reached volcanoes, Italy has played an important part in the development of volcanology. In particular Lazzaro Spallanzani, a priest and a professor of natural history at the University of Pavia in the eighteenth century, made crucial advances. Like Oppenheimer, he studied the craters of Stromboli, though wisely he did so from a recess that offered some protection. He was terrified when a fissure broke open nearby, releasing jets of glowing lava, but his guides told him there was no danger. This proved correct, prompting Spallanzani to record much other traditional knowledge concerning volcanoes.


Perhaps the most devastating eruption of recent times was that of Mount Pelée on the Caribbean island of Martinique on May 8, 1902. All but one of the 27,000 inhabitants of Saint-Pierre, the island’s commercial hub, were killed by the ensuing nuées ardentes—glowing clouds of superheated gas and rock fragments. Supposedly the lone survivor was a prisoner in a stone cell who had been locked up the night before for a fight or possibly a murder. His survival was considered so extraordinary that he was hired by Barnum and Bailey’s circus as an exhibit.

Frank Alvord Perret, a thirty-four-year-old Brooklyn-based engineer who suffered incapacitating bouts of depression, was greatly disturbed by news of the catastrophe and decided to change careers. He traveled to Vesuvius, where he met Raffaele Matteucci, the director of the volcanic observatory there. Matteucci, who “lived…‘in mysterious and terrible solitude,’” saw in Perret a kindred spirit and educated him in volcanology. Some of the methods used by volcanologists at the time seem curious by today’s standards. In March 1906 Perret, sensing a subterranean buzzing, bit his metal bedframe to amplify his ability to sense the vibrations, which led him to predict correctly that an eruption would soon follow.

The career change was a good move for Perret, who became the foremost volcanologist of his generation. After Matteucci died in 1909, Perret traveled the world, establishing the first volcano observatory in the US on the Big Island of Hawaii and rushing to Martinique when Mount Pelée reignited in 1929. Determined to prevent another catastrophe, he lived on the mountain day and night, looking for signs that would justify an evacuation. He even walked into a minor nuée ardente. The clouds are typically 400 to 1,300 degrees Fahrenheit, but Perret somehow survived and found the one he walked through to be strangely odorless and absolutely silent.

To this day, deciding when to issue evacuation orders is one of the most fraught questions facing any volcanologist. Evacuations are costly and disruptive, and not everyone obeys them. Sometimes violent disagreements break out among experts as to whether they are necessary. On more than one occasion, an evacuation has been ordered and the volcano has abruptly quietened, bringing volcanology into disrepute with locals who have lived in the area for decades.

As Oppenheimer makes clear, communities near volcanoes are enormous repositories of “knowledge accumulated through experience, wisdom, ancestral culture and spirituality matters.” Yet this knowledge is often expressed in ways that make it difficult for volcanologists and locals to communicate. When he was working on Stromboli, Oppenheimer met a priest who said of the locals, “They believe this is the land of God but also, that the land is God. Even now, when the volcano erupts more violently, the people shudder. It reminds them that another divinity pervades the island.”

In some cultures, people have ventured into the craters of erupting volcanoes to offer sacrifices of appeasement. According to tribal leaders consulted by Oviedo, children and young women were hurled into the magma at a crater’s heart. Archaeological evidence confirms such practices. In 1998 the remains of eight children were found buried just inside the crater rim of Misti volcano in Peru. There is no doubt, as Oppenheimer says, that volcanoes exist at a “thrilling crossroads of nature, spirit, climate, geology, technology, society and culture.”

One of the most fascinating aspects of Oppenheimer’s work involves studying the impact of volcanic eruptions on global climate, and therefore on food production. When Tambora—on the island of Sumbawa, in what is now Indonesia—erupted in April 1815, so much sulfur-rich material was ejected into the stratosphere that temperatures plummeted and less sunlight reached plants, limiting their growth. In North America the effects were so severe that 1816 became famous as “1800 and Froze to Death.” In Vermont farmers who had sheared their sheep were forced to tie the fleeces back on to save their livestock, and thousands of New Englanders simply abandoned their farms. The eruption killed tens of thousands in the area surrounding Sumbawa through nuées ardentes and other effects; the freezing winters of 1816 and 1817 that the blast induced, in contrast, killed millions through starvation and the increased susceptibility to disease that it brought.

Oppenheimer argues that less well-known volcanic eruptions also had very widespread or even global impacts. The last time North Korea’s Paektu volcano erupted was not known with any precision prior to Oppenheimer’s work. He excavated a layer of ash on the flank of the mountain, below which lay an old land surface, replete with partially burned trees. Solar flares are often recorded in astrological chronicles, and because they affect radiocarbon dating they can be detected in wood samples. This allowed Oppenheimer to find evidence of an enormous solar flare that occurred in 774 CE; in the wood samples he took on Paektu he found evidence of it as well in growth rings laid down between 774 and 775 CE.


Through a remarkable concatenation of evidence, which included correlation of dendrochronology, geological data, and historical records, he was then able to show that the eruption occurred in the early winter of 946 CE. But the story does not end there: Oppenheimer found written records of ash falling on a Buddhist temple near Osaka, Japan, on November 3, 946, and discovered that ash from Paektu was preserved in nearby sediments. According to imperial records from the Korean monarch’s palace in Kaesŏng, 280 miles southwest of Paektu, at that time “the sky rumbled, and cried out,” prompting King Chŏngjong to establish twelve granaries in response to a subsequent food crisis.

Oppenheimer has found that eruptions—from areas as diverse as Icelandic volcanoes and Saharan lava fields—coincide with famine. Tying together the varied records to identify the timing of events, from eruption to famine, makes for a gripping detective story. So what are the chances of a damaging eruption in the future? Oppenheimer says that the Yellowstone supervolcano complex (a highly explosive volcano with many eruption points) is so unlikely to erupt that it’s not worth worrying about. But looking globally, he estimates the chances of a large, climate-changing eruption before the end of the century to be around one in two hundred.

Even after the lava starts flowing, actions can be taken to avert tragedy, and Mountains of Fire includes heroic examples of people protecting themselves from volcanism. In 1669 the people of Catania, Sicily, wrapped themselves in water-soaked hides and hacked away at the wall of a lava flow to divert it from their village. Astonishingly, they succeeded, but then a much larger and very angry group of people from the town of Paternò showed up—the lava was now heading toward their houses. The breach dug by the villagers healed itself before conflict broke out, and the lava continued on its prior course, causing only minor damage before the volcano was exhausted. Nevertheless, the authorities were alarmed enough to issue an edict stating that anyone interfering with lava flows would be liable for the subsequent damage.

When Mauna Loa erupted in December 1935, the director of the Hawaiian Volcano Observatory requested that, in an effort to save the town of Hilo from destruction, the US Army bomb the lava flow from the air. Five direct hits with six-hundred-pound bombs were recorded, and one aircraft had its wings pierced with flying molten lava. The next day, the flow stopped. But it had nothing to do with the bombs—the volcano had just run out of puff. Native Hawaiians had been horrified by the bombing, considering it to be an offense against their volcano deity, Pele. They were not surprised when, a few weeks later, two of the aircraft involved in the bombing touched wings over Pearl Harbor and burst into flames. The only survivors of the crash were two men who had not been on the bombing mission.

Volcanoes bring gifts as well as destruction. Obsidian, or volcanic glass, is a noncrystalline form of silica that is produced when certain magmas cool very rapidly. For thousands of years humans have been using obsidian to manufacture cutting tools that are sharper than most modern scalpels. Because each type of magma has its own unique chemical signature, the origin of obsidian tools can be pinpointed. As Oppenheimer has discovered, such tools were traded or carried over long distances. He encountered a thick deposit of obsidian, along with a scattering of tools made from it, on a volcano known as Nabro in the hostile Danakil Depression. The tools were made four to five thousand years ago and lay undisturbed on the surface, just where they had been dropped long ago. Later analysis showed that tools found in Yemen, across the Red Sea from Eritrea, were made from that same Nabro obsidian.

Mount Erebus, Oppenheimer writes, is “the most sublime and imposing sight I ever beheld.” It is just one of three volcanoes on Earth where an observer can stand on the crater rim and peer into the pool of magma at the volcano’s heart. With a latitude of 77 degrees south and thrusting almost 12,500 feet into the sky, Erebus is one of the most inhospitable and difficult-to-reach places on Earth. The renowned Australian geologist Tannatt Edgeworth David led the first party ever to climb it, a feat undertaken in 1908, shortly after the professor’s fiftieth birthday. The ascent involved days of hauling sleighs loaded with scientific equipment and supplies over the most challenging terrain imaginable. During the journey the party of six was beset by a fierce blizzard. After finally reaching the summit and setting up camp, the men awoke to a rolling sea of golden clouds that entirely surrounded the peak. It was a scene of such “transcendent majesty and beauty” that David was lost for words.

Over Oppenheimer’s thirteen visits to Mount Erebus he has spent, cumulatively, a year of his life on the Antarctic volcano. Unlike in David’s time, a well-constructed base camp can be reached by helicopter. During his first visits Oppenheimer was tasked with recording how much sulfur dioxide was being emitted by Erebus. Among other things, that measurement revealed the amount of lava that was coming into the crater. (His estimate is equivalent to about two bathtubs’ worth per second.) He later measured other gases to infer the temperature of the magma and the depth of its source.

Oppenheimer also unexpectedly discovered a repeating pattern in the gaseous emissions, with the volumes going up and down every ten minutes. This, he thinks, results from the volcano’s feeder pipe, in which the flow of magma reverses when the pressure from the lava lake above becomes too great. David, Oppenheimer notes, thought that he could hear a cadence in the sounds emerging from the crater, which probably resulted from the same reversals in the feeder pipe. Furthermore, David and a colleague thought that Erebus, like Stromboli, erupted more frequently when air pressure was low—a valuable example, Oppenheimer says, of recording everything rather than just the things you think are important.

For Oppenheimer, the end of each field season on Erebus was marked by “a wrenching pang of loss.” He is clearly in awe of the pioneers of Antarctic exploration like David, and being on the volcano seems to bring him closer to their spirits. That, and his strange sense of serenity in such a difficult and dangerous place, speaks volumes about this exceptional man. Mountains of Fire is not a perfect book. It meanders, loosely plaiting together many themes amid accounts of Oppenheimer’s investigations in a way that makes it easy to lose track of dates, events, and major threads. On occasion this can be frustrating: for example, a detailed description of the formation and uses of obsidian is divided by ten pages concerning Oppenheimer’s own encounters with the stuff.

And it must be said that much detail is omitted. If you want to learn about the sole survivor of the 1902 eruption of Mount Pelée, you’re better off watching Into the Inferno, Werner Herzog’s extraordinary 2016 documentary made in collaboration with Oppenheimer, as little about him is mentioned in the book. Indeed, both the book and the documentary cover much the same ground, and to my mind the documentary is superior. I have never seen such awe-inspiring images of lava, nor such candid accounts by indigenous people of their beliefs about volcanoes. The film even includes astonishing footage of a nuée ardente storming down the slopes of a volcano in Japan as an emergency vehicle desperately tries to outpace it. Somehow Herzog and Oppenheimer managed to capture visually, without melodrama or exaggeration, the essence of volcanic power and the human response to it.

To its credit, though, Mountains of Fire is filled with brief references that recall a more heroic age. One such reads, “After resolving an encounter with quicksand, we had reached the shore.” In a lesser book that incident might have been expanded into an entire chapter, but Oppenheimer leaves the quicksand behind in favor of far more hazardous features of the natural world.