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- Herausgeber: Icon Books
- Kategorie: Wissenschaft und neue Technologien
- Sprache: Englisch
When the forces that give our planet life exceed our ability to withstand them, they become disasters. Together they have shaped our cities and architecture, elevated leaders and toppled governments, influenced the way we think, feel, fight, unite and pray. The history of natural disasters is a history of ourselves. The Big Ones investigates some of the most impactful natural disasters, and how their reverberations are still felt today. From a volcanic eruption in Pompeii challenging and reinforcing prevailing views of religion, through the California floods of 1862 and the limitations of memory, to what Hurricane Katrina and the 2004 tsunami can tell us about governance and globalisation. With temperatures rising around the world, natural disasters are striking with ever greater frequency. More than just history or science, The Big Ones is a call to action. Natural hazards are inevitable; human catastrophes are not. With this energising and richly-researched book, Jones offers a look at our past, readying us to face down the Big Ones in our future.
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Veröffentlichungsjahr: 2018
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For our unsung heroes: the city planners, building officials, and others who love their communities and work every day to prevent future natural disasters from becoming human catastrophes
CONTENTS
INTRODUCTION
IMAGINE AMERICA WITHOUT LOS ANGELES
Earthquakes are happening constantly around the world. The seismic network that measures earthquakes in Southern California, where I live and spent my career as a seismologist, has an alarm built into it that goes off if no earthquake has been recorded for twelve hours—because that must mean there’s a malfunction in the recording system. Since the network was put into effect in the 1990s, Southern California has never gone more than twelve hours without an earthquake.
The smallest earthquakes are the most common. Magnitude 2s are so small they are felt only if someone is very nearby their epicenter, and one happens somewhere in the world every minute. Magnitude 5s are big enough to throw objects off shelves and damage some buildings; most days a few of these strike somewhere. The magnitude 7s, which can destroy a city, occur more than once a month on average, but luckily for humanity, most take place underwater, and even those on land are often far from people.
But for more than three hundred years, none of these, not even the tiniest, has occurred on the southernmost part of the San Andreas Fault.
Someday that will change. Big earthquakes have happened on the southern San Andreas in the past. Plate tectonics hasn’t suddenly stopped; it is still pushing Los Angeles toward San Francisco at the same rate your fingernails grow—almost two inches each year. Even though the two cities are in the same state and on the same continent, they are on different tectonic plates. Los Angeles is on the Pacific plate, the largest of the world’s tectonic plates, stretching from California to Japan, from the Aleutian Arc of Alaska to New Zealand. San Francisco is on the North American plate, which extends east to the Mid-Atlantic Ridge and Iceland. The boundary between them is the San Andreas Fault. It is there that the two plates get carried slowly past each other; their motion cannot be stopped any more than we could turn off the sun.
In a strange paradox, the San Andreas produces only big earthquakes because it is what seismologists consider a “weak” fault. It has been ground so smooth, across millions of years of earthquakes, that it no longer has rough spots to stop a rupture from continuing to slip.
To understand the mechanics of it, imagine you’ve laid a large rug on the floor of a room that has wall-to-wall carpeting. After placing it, you decide that, on second thought, you want to move it one foot closer to the fireplace. If it had been laid on a hardwood floor, it would be easy enough to move: you could simply grab the side nearer to the fireplace and pull. But it’s on carpeting, so the friction between the carpet and the rug makes that impossible. What could you do? You could go to the far side of the rug, pick it up off the carpeting, and put the edge of the rug where you want it, a foot closer to the fireplace. You now have a big ripple, which you could push across the rug until you’ve reached the end, at which point the entire rug would be one foot closer to the fireplace.
In an earthquake, a seismologist sees not a ripple but a rupture front. The motion of that ripple across the “rug” of the San Andreas Fault creates the seismic energy that we experience as an earthquake. It is a temporary local reduction in friction, allowing a fault to move at lower stress. In the same way that the rug couldn’t move all at once, an earthquake too must begin at one particular spot on its surface, its epicenter, and the ripple must roll across it for some distance.
The distance the rupture front travels is one of the chief determinants of an earthquake’s size. If it moves a yard and stops, it is a magnitude 1.5 earthquake, too small to be felt. If it goes for a mile down the fault and stops, it’s a magnitude 5, causing a little damage nearby. If it goes on for a hundred miles, it is now a magnitude 7.5, causing widespread disruption.
The San Andreas Fault has been smoothed to such a degree that now, when an earthquake begins, there is nothing left to keep it small. The ripple will continue to move down the fault, radiating energy from each spot it crosses, creating an earthquake that lasts for a minute or more and a magnitude that grows to 7 or even 8. Only after such an earthquake has broken the fault and made new jagged edges can it begin to produce smaller, less damaging earthquakes.
So we wait for that big earthquake. And wait.
The southernmost part of the fault had its last earthquake sometime around 1680. We know this because it offset the edges of Lake Cahuilla, a prehistoric lake in much of what is now the Coachella Valley, filling with water the flats where the Coachella music festival meets each year. It left behind geologic markers, as did previous earthquakes, so we know that there were six earthquakes between AD 800 and 1700. That means the 330 years since the last earthquake on this part of the San Andreas is about twice the average time between its previous earthquakes. We don’t know why we are seeing such a long interval. We just know that plate tectonics keeps on its slow, steady grind, accumulating more offset and energy to be released the next time. Since the last earthquake in Southern California, about twenty-six feet of relative motion has been built up, held in place by friction on the fault, waiting to be released in one great jolt.
Someday, maybe tomorrow, maybe in a decade, probably in the lifetimes of many people reading this book, some point on the fault will lose its frictional grip and start to move. Once it does, the weak fault, with all that stored energy, will have no way of holding it back. The rupture will run down the fault at two miles per second, its passage creating seismic waves that will pass through the earth to shake the megalopolis that is Southern California. Maybe we will be lucky and the fault will hit something that can stop it after only a hundred miles or so—a magnitude 7.5. Given how much energy is already stored, however, many seismologists think it will go at least two hundred miles, and thus register 7.8, or even 350 miles and reach 8.2.
If it ruptures as far as central California, all the way to the section of the fault near Paso Robles and San Luis Obispo, it will hit a part of the San Andreas that behaves differently. This part accumulates a fingernail-growth rate of tectonic offset, just like the rest of the fault. But it’s what is known as a “creeping section.” Instead of storing energy to release in one big earthquake, the energy here oozes in small motions, sometimes with little earthquakes, sometimes with no seismic energy at all. We think, we hope, that the creeping section will act as a pressure valve of sorts, keeping the earthquake from growing any bigger than 8.2.
*
In 2007–8, as science advisor for risk reduction at the U.S. Geological Survey, I led a team of more than three hundred experts in a project we called ShakeOut, to anticipate just what such an earthquake will be like. We created a model of an earthquake that moves across the southernmost two hundred miles of the San Andreas, extending from near the Mexican border to the mountains north of Los Angeles—a likely outcome, though still short of the worst-case scenario.
In the earthquake we modeled, we found that Los Angeles would experience intense shaking for fifty seconds (compare this to the seven seconds of the Northridge earthquake in 1994, which caused $40 billion of damage). A hundred other neighboring cities would as well. Thousands of landslides would cascade down the mountains, blocking our roads, burying houses and lifelines.
In our model, fifteen hundred buildings collapsed and three hundred thousand were severely damaged. We know which ones. They are the types of buildings that have collapsed in other earthquakes in other locations, and which we no longer allow to be built. But we have not forced existing buildings to be retrofitted to accommodate what we know. We might see some high-rise buildings collapse. The 1994 earthquake in Los Angeles and the 1995 earthquake in Kobe, Japan, exposed a flaw in how steel buildings had been constructed, causing cracks in their frames. Buildings of that type are still standing in downtown Los Angeles. We are going to see many brand-new buildings “red-tagged,” too dangerous to enter and in need of major repairs or demolition. Our building codes do not require developers to make buildings that can be used after a major earthquake, only buildings that don’t kill you. If the code works as it is supposed to, about 10 percent of the new buildings constructed to the latest code will be red-tagged. Maybe 1 percent will have partial collapse. A 99 percent chance of not collapsing is great for one building, but accepting the collapse of 1 percent of the buildings in a city with a million buildings is a different matter. The earthquake will probably not kill you, but it will likely make it impossible for you to get to work—for a very long time.
Of the results we projected, one of the most frightening was the impact of fires triggered by the earthquake. Earthquakes damage gas lines; break electrical items and throw them onto flammable fabrics; spill dangerous chemicals; and generally have many, many ways of starting fires. Two of the biggest urban earthquakes of the twentieth century were the 1906 San Francisco and 1923 Tokyo (Kanto) earthquakes. Both set off fires that turned into firestorms and burned down much of those cities. Some people think that modern technology has solved much of the fire problem because the two big California earthquakes of the late twentieth century, the 1989 Loma Prieta earthquake in San Francisco and the 1994 Northridge earthquake in Los Angeles, did not lead to devastating fires. This is a mistake. Not because technology hasn’t changed, but because, in the eyes of seismologists, Loma Prieta and Northridge were not big earthquakes. Those who lived through them may disagree, and the damage they inflicted on those cities is undeniable. But these people simply don’t know what a really big earthquake will be like.
What seismologists call “great” earthquakes (magnitude 7.8 and larger) are not just about stronger shaking—they are also about much larger areas. Loma Prieta and Northridge caused their strongest shaking near their epicenters, neither of which was in an urban core. Loma Prieta’s was in the Santa Cruz Mountains; the strongest shaking of Northridge was felt in the Santa Susana Mountains. Even so, more than a hundred significant fires broke out in each of those earthquakes. They were fought through mutual aid. San Francisco and Los Angeles put out calls for help, and firemen from other jurisdictions poured in to help. Citywide fires were averted because of the amazing, courageous work of firemen from across the region.
When an earthquake like the one we modeled happens, every city of Southern California will have fires that need to be fought. Calls for help will be answered with desperate pleas for help in return. Aid will have to come from Northern California, Arizona, and Nevada. Those firemen will have to come to Southern California from the other side of the San Andreas Fault, which will have moved twenty to thirty feet, offsetting all the highways into the region. Those responders will struggle, maybe for days, to bring equipment across broken roads. The firemen who are here will be sent to fight fires in places where the pipes feeding the fire hydrants have broken and gone dry. Our analysis, reviewed by the fire chiefs who had led the firefighting in Northridge and Loma Prieta, concluded that the fires would double the losses of the earthquake, in terms of both economic impact and casualties. Sixteen hundred fires could break out, twelve hundred growing large enough to require more than one fire company. We don’t have that many fire companies in all of Southern California.
As bad as this picture looks, it could be worse. In ShakeOut, I got to specify the weather. I made it a cool, calm day. Unfortunately, I don’t get to do this for the real thing. If the earthquake happens during the infamous Santa Ana winds, which have spread great Southern California wildfires and caused billions of dollars in losses, the fires that get started may be unstoppable.
Most of us will survive. Our estimate was that eighteen hundred people will die and fifty-three thousand will need emergency medical care. A significant number of hospital beds will be out of commission as hospitals suffer their own damage. And it will be very difficult to get to them. Bridges will be impassable, collapsed buildings will leave rubble in the street, and power will be knocked out, darkening traffic lights. Many people will be trapped in buildings; first responders will be overwhelmed. Most victims will be rescued by their neighbors. Losses will exceed $200 billion.
Life will not return to any semblance of normality for quite some time for the residents of Southern California. In the following months, tens of thousands of aftershocks will occur, some of which will be damaging earthquakes in their own right. The systems that maintain urban life—electricity, gas, communication, water, and sewers—will all be broken. The transport systems that bring food, water, and energy into the region all cross the San Andreas and will be cut. In a simpler world, when you lose your sewer system, you build a temporary outhouse in the backyard. In the dense urban environment of a modern city, a lack of sewers is a potentially catastrophic public health crisis. Cities are possible because of the complex engineering systems that support life. Those will be lost in such an earthquake.
Half of the total financial losses in our model were from lost business. A beauty salon cannot reopen without water. Offices cannot function without electricity. Tech workers cannot telecommute without Internet capabilities. Retail stores struggle if their clerks and customers don’t have the means of transportation to get there. Gas stations cannot pump gas without electricity and cannot take your credit card if they’re not online. And how many of us will want to stay in Los Angeles, much less go to work, when none of us have had a shower in a month?
Here we reach the limit of our technical analysis. Our scientists and engineers and public health experts can estimate buildings down, pipes damaged, legs broken, transportation disrupted. But the future of Southern California is the future of communities. We know what will happen to its physical structure, but what will happen to its spirit?
*
Natural disasters have plagued humanity throughout our existence. We plant farms near rivers and near the springs that form along faults, for their access to water; on the slopes created by volcanoes, for their fertile soil; on the coast, for fishing and trade. These locations put us at risk of disruptive natural forces. And indeed we are familiar with the occasional flood, tropical storm, passing tremor. We learn how to construct levees, perhaps a seawall. We add some bracing to our buildings. We are not quite so scared after the tenth minor quake. We begin to feel confident that we can control our natural world.
Natural hazards are an inevitable result of the earth’s physical processes. They become natural disasters only when they occur within or near human construction that fails to withstand the sudden change they wreak. In 2011, a magnitude 6.2 earthquake occurred in Christchurch, New Zealand, killing 185 and causing roughly $20 billion in losses. Yet an earthquake of that size happens every couple of days somewhere in the world. This relatively minor earthquake became a disaster because it occurred right under the city, and the buildings and infrastructure were not built strong enough to withstand it. Natural hazards are inevitable; the disaster is not.
I have spent my professional life studying disasters. For much of my career, I was a researcher in statistical seismology, trying to find patterns and make sense of when and how earthquakes occur. Scientifically, my colleagues and I could prove that compared to human timescales, earthquakes occurred randomly. But we found that “random” was an idea we could not convince the public to accept. So, recognizing that the desire for prediction was really a desire for control, I shifted my science toward predicting the impact of natural disasters. My goal was to empower people to make better choices—to prevent the damage from happening in the first place.
The U.S. Geological Survey, the government agency charged with providing the science about geological hazards, was my lifelong professional home. In a pilot project in Southern California, and later for the nation, we studied floods, landslides, coastal erosion, earthquakes, tsunamis, wildfires, and volcanoes, with the objective of connecting communities to the scientific information that could make them safer, whether it was predicting landslides during rainstorms, recommending wildfire control in ecosystem management, or better judging our priorities when it comes to mitigating the risk of a big earthquake.
I was also one of the scientists who provided information to the public after earthquakes. I found people were desperate for science, but often not for the reason I expected. I saw the ways it could be used to halt the damage. But in times of natural disaster, the public turns to scientists to minimize not just destruction but also fear. When I gave the earthquake a name and a fault and a magnitude, I inadvertently found myself serving the same psychological function as priests and shamans have done for millennia. I was taking the random, awesome power of Mother Earth and making it look as though it could be controlled.
Natural disasters are spatially predictable—where they occur is not random. Floods happen near rivers, big earthquakes (generally) strike along big faults, volcanic eruptions take place at the site of existing volcanoes. But when they happen, especially compared to human timescales, is random. Scientists say an occurrence is “random about a rate.” That means we know, in the very long term, how many of them take place. We know enough about a fault to know that earthquakes occur—have to occur—with a certain frequency. We can study a region’s climate to the extent that its average rainfall becomes predictable. But whether this year brings floods or drought, whether the largest earthquake along the fault this year is a magnitude 4 or 8—that is purely random. And we humans don’t like it. Random means every moment presents a risk, leaving us anxious.
Psychologists describe a “normalization bias,” the human inability to see beyond ourselves, so that what we experience now or in our recent memory becomes our definition of what is possible. We think the common smaller events are all that we have to face, and that, because the biggest one isn’t in anyone’s memory, it isn’t real. But in the earthquake that ruptures through the full length of a fault, the flood described as Noachian, the full eruption of a volcano, we see more than the common disaster. We face catastrophe.
In that catastrophe, we discover ourselves. Heroes are made. We laud the quick thinking, the unquenchable will to survive. We see extraordinary acts of courage committed by ordinary people, and we praise them for it. The firemen who run into a burning building when everyone else is running out hold a special place of honor in our society. Disaster movies always have as their hero the daring responder, from Charlton Heston in 1974’s Earthquake, to Tommy Lee Jones in the 1997 film Volcano, to Dwayne “The Rock” Johnson in 2015’s San Andreas. There is likewise a villain, in the public official who covers up the warning, or a selfish, scared victim who claims the last lifeboat for himself.
We show compassion for the victims, knowing that we could have been the one hit. Indeed, it is the randomness of the victimization that forms much of our emotional response, that encourages generous donations. For many people, helping the victims serves as a sort of unconscious good luck charm, warding off the same fate for themselves. We pray to God to protect us from the danger.
When the prayers fail and the catastrophe is upon us, we seem incapable of accepting that it is inexorably, infuriatingly random. We turn to blame. For most of human history, the great disasters have been seen as a sign of the gods’ displeasure. From the biblical Sodom and Gomorrah to the devastating earthquake of 1755 in Lisbon, those who survived, those who witnessed, declared that the victims were being punished for their sins. It allowed us to pretend that we could protect ourselves by not making the same mistakes—that we had no reason to fear the bolt out of the blue.
Modern science may have changed many of our beliefs, but it hasn’t swayed our subconscious impulses. When that great Southern California earthquake finally strikes, I know two things will happen. First, rumors will spread that the scientists know that another earthquake is coming, but that we aren’t saying anything to avoid scaring the public. This is the all-too-human rejection of the random, an attempt to form patterns, to find reassurance. Second, there will be blame. Some will blame FEMA, accusing them of a poor response. Some will blame the government for allowing bad buildings to have been constructed (maybe even the same people who fought against mandatory improvements of those weak buildings). Some will blame scientists for not listening to that week’s earthquake predictor. Some, in a pattern we have seen for centuries, will blame the sinners of the hedonistic La-La Land.
The last thing any of us will want to do is accept that, sometimes, shift just happens.
Most cities have the potential for a Big One in their future. Those harbors, fertile fields, and rivers that make everyday life viable are there because of natural processes that can produce disasters. And that Big One will be qualitatively different from the smaller-scale disasters in our recent past. It is a disaster when your house is destroyed. It becomes a catastrophe when not just your home but your neighbors’ homes and so much of your community’s infrastructure are destroyed that societal functioning itself collapses. We have choices to make, right now, that could make our cities much more likely to survive and recover from these great natural disasters when they strike. We can make informed choices only if we consider our potential future, and if we take a hard look at our knowable past.
With this book I tell the stories of some of the earth’s greatest catastrophes, and what they reveal about ourselves. Each was the Big One of its region, shifting the nature of that community. Together they show how our fear causes us to respond to random catastrophe—the reasoning we employ, the faith we manifest. We will see the limitations of human memory, which keeps us from believing that the one-in-a-million, or even the one-in-a-thousand, will ever affect us. And we will face the knowledge that our risk is growing. Because of the increasing density and complexity of our cities, more people than ever before are at a greater risk of losing the systems that maintain life.
We will come to a place where all our defenses are stripped bare, forced to consider the kind of suffering without meaning that could crush a human spirit. Because in the end, we face disasters like everything else in our lives—searching for meaning. What is left when we are denied a scapegoat or the specter of divine retribution? Our cries of “Why now?” or “Why us?” may never be satisfactorily answered. But if we can look beyond meaning, we’ll find a question with profound moral implications: How, in the face of catastrophe, do we help ourselves and the people around us survive and make a better life?
CHAPTER ONE
BRIMSTONE AND FIRE FROM OUT OF HEAVEN
Pompeii, Roman Empire, AD 79
The earth rocked and shook, the bases of the mountains trembled and reeled because of God’s anger.
—Psalm 18
We all know the story of Pompeii. An eruption of poisonous gases and heavy ash covered the Roman city some two thousand years ago, burying people in their houses, completely wiping out the city in a matter of days. We look back and see the inevitability of the destruction and pity the inhabitants for not knowing better. Who would build a city on the side of an active volcano? Tourists today visit what might be considered a parable for what happens when you build a community without regard for the threats around you, a place preserved for our edification and amusement. We assure ourselves we wouldn’t make the same mistake.
Mount Vesuvius is a classic conical volcano rising over four thousand feet above the Bay of Naples. Its shape tells geologists much of what is going on inside. The massive cone demonstrates that lava comes out faster than erosion can wash it away, so it is active now, and future eruptions are a certainty on the scale of geologic time. To rise up and form a mountain as it has, and not just flow as a liquid over the landscape, the lava must be fairly sticky (or viscous, to use the technical term). The sticky lava can hold in gases, at least for a while. That means that eruptions can be explosive. Alternating layers of volcanic ash, the result of explosive eruptions, and cooled lava are needed to grow the tallest mountains— a type called stratovolcanoes.
So why build a city here, where the danger is so great? For the same reason that Seattle lies in the shadow of Mount Rainier, Tokyo looks up to Mount Fuji, and Jakarta is encircled by five active volcanoes, including Krakatau: when they aren’t erupting, volcanoes make great homes. Volcanic soils are porous with good drainage and lots of fresh nutrients, producing fertile crops. Deformation of the rocks around a volcano often creates good natural harbors and defensible valleys. Plate tectonics might guarantee that the next event will happen, but which generation will experience the extreme event is determined by chance. And for most human beings, as for the inhabitants of Pompeii in AD 79: if it hasn’t happened to me, it simply hasn’t happened.
*
Vesuvius’s eruption in the sixth century BC led the Osci tribes of that region, and the Roman conquerors who followed, to declare it the home of the god Vulcan. The periodic steam rising from it was a reminder that Vulcan was the smith of the gods, forging their weapons in a celestial furnace. But the volcanic soil was fertile, holding water and supporting some of the richest agriculture of the Roman Empire, and so civilization flourished. Six hundred years without an eruption had made Vesuvius seem the definition of safe.
By the beginning of the first century AD, several towns had been built on the side of the volcano, including Pompeii, Herculaneum, and Misenum. The region had been conquered by Rome in the third century BC, and it had become a flourishing, prosperous community. Excavations have found the remains of a thriving commercial center. Frescoes celebrate the craftsmen who wove and dyed cloth, a major local industry. A sprawling, open-air marketplace has been uncovered, complete with restaurants and snack bars. Tax records show that Pompeii’s vineyards were much more productive than those around Rome and their wine was sold across the empire. (The first known product brand based on a pun is from Pompeii, a jar of wine labeled “Vesuvinum.”)
Wealthy Romans constructed villas there in order to enjoy the seaside. Large public markets, houses of worship, and government buildings reflect a community living well above simple subsistence. Many of the houses excavated in Pompeii are spacious and elegant. Beds were found carved out of marble. Some houses had their own baths, and public baths served the community with water brought in from the Roman aqueduct system. Situated at the end of the Amalfi Coast, Pompeii, even then, hosted the glitterati.
It is from this culture that we get our word disaster—literally, “ill-starred.” Romans believed that disasters happened because their fate had been written in the stars. The random nature of disasters, relative to the scale of one human lifetime, creates such a level of fear that all human cultures have come up with some means for ascribing meaning to them. When Shakespeare, in Julius Caesar, gives Cassius the line “The fault, dear Brutus, is not in our stars, / But in ourselves,” he is speaking against a cultural norm that finds explanation of the unexpected in our fates.
Romans were in the hands not just of destiny but of their capricious gods. Like the Greek before it, Roman mythology portrayed the gods as selfish, careless entities, albeit very powerful ones. Disasters happened to an individual because he got in the way of a spat between these powerful beings. Vulcan, the god of fire, was not physically attractive, but he had been given Venus, the goddess of love, to be his wife. Volcanic eruptions, then, were a sign of his anger when he found out about one of Venus’s infidelities.
This may have provided an explanation for volcanic episodes, but it was not a particularly reassuring one. It left the people powerless in the face of petty gods and their tantrums. So they attempted to soothe Vulcan—to reclaim a sense of control—in their annual feast honoring him. Vulcan represented fire both in its beneficial uses, such as metalsmithing, and in its destructive power, such as in volcanoes and wildfires (the more common threat to grain storage in the heat of the summer). So with the Vulcanalia, held every year on August 23, they placated the god, offering bonfires and sacrifices to keep destruction from being visited upon their harvest.
In AD 79, as the Vulcanalia was being celebrated by unwitting residents of Pompeii, Vesuvius was entering the final phase of what would be one of its largest eruptions. Our knowledge of the eruption comes from two sources. One is, of course, the evidence preserved in the city of Pompeii itself, fifteen miles outside Naples. The ash from the eruption buried the city over the course of a few weeks, completely destroying the community. Ninety percent of the residents escaped alive, but they abandoned the region, and the existence of the city was almost forgotten. The site was rediscovered and excavated in the eighteenth century, including the corpses of the residents who did not escape.
The second source is a young Roman scholar, Pliny, called the Younger, who wrote letters that have come down to us describing the death of his uncle, Pliny the Elder, during the eruption. The younger and elder Plinys were part of Rome’s minor aristocracy, both holding the rank of equestrian, entitled to be a knight in the army, and were originally from the Lake Como region in northern Italy. Pliny the Elder served in the Roman army, primarily in Germany, for the first two decades of his adulthood. He never married, but his widowed sister came to live with him after he left the army, along with her young son. The son was adopted by his uncle and took his name, and thus came to be called Pliny the Younger. Pliny the Elder was famous in Rome both for his writings and for his close relationship with the emperor Vespasian. While in the army, he wrote a history of the German wars, with details like how to use a horse’s movements to fight with a javelin more effectively. In his later diplomatic career as a ruler of various provinces, he collected information about the history of the regions and their natural features.
Two years before the eruption, Pliny the Elder published his thirty-seven-volume Naturalis Historiae, “On Natural History,” often called the first encyclopedia. It represented his observations as he traveled the empire, creating one of the largest literary works to come down to us from Roman times. In the preface, he says that “to be alive is to be watchful,” and we see that passion in the breadth of topics he catalogs. From a modern scientist’s perspective, he may seem a bit credulous (as in, for example, his description of monstrous races of people with the heads of dogs). But he also shows a scientist’s passion for knowledge. He finishes his final volume with the words “Greetings, Nature, mother of all creation, show me your favor in that I alone of Rome’s citizens have praised you in all your aspects.” He seems to have been obsessive about his work, often choosing writing over sleep.
In AD 77, in addition to the release of his On Natural History, Pliny the Elder was appointed by the emperor to be head of the Roman fleet berthed in the Bay of Naples. The Pliny household moved to Misenum, at the mouth of the Bay of Naples. From their villa, they had a commanding view of Mount Vesuvius on the other side of the bay. Pliny the Elder directed fleet operations as he worked on revisions to his Natural History. Pliny the Younger was completing his legal training, studying with his uncle, and becoming a prolific chronicler himself.
After the centuries of quiet, the latter part of the first century had seen an increase in earthquakes, with a particularly severe one in AD 62. That earthquake had damaged quite a few houses in Pompeii (even in AD 79, some of them were still being repaired).
Numerous earthquakes were felt and recorded in the next decade, and people began accepting them as a normal part of life. At the Vulcanalia celebrations on August 23, AD 79, Pliny the Younger’s journal entry noted several earthquakes occurring during the day, but he thought nothing of them, “as earthquakes are common in [the region of] Campagnia.” We now know that magma must move from the magma chamber, often several miles deep in the earth, to the surface for an eruption to occur. That movement can be marked by earthquakes, the bulging of the earth’s surface, and gas emissions. It can take months, years, or even decades before enough pressure has been built to cause an eruption. (This makes volcanic eruptions more likely to be predicted than many other geological phenomena.)
Map of the region of the Bay of Naples, showing Misenum, where the Pliny household lived, and cities all or partially destroyed in the eruption of Mount Vesuvius in AD 79
The next day, August 24, the lives of everyone in Campagnia were turned on end. A little after noon, Vesuvius exploded violently, sending a column of gas and ash high into the sky. Both Plinys observed this from across the Bay of Naples. The Younger wrote, “I cannot give you a more exact description of its appearance than by comparing it to a pine tree; for it shot up to a great height in the form of a tall trunk, which spread out at the top as though into branches.”
True to form, Pliny the Elder wanted to see the eruption more closely. He started arranging for vessels of the fleet to help with evacuations and to take him across the bay to make more detailed observations. Pliny the Younger wisely chose to stay at the villa and continue with his schoolwork. As preparations were under way, the Elder received a message from a noblewoman friend whose villa sat in Stabiae at the foot of Vesuvius, begging him to help them escape. He dispatched the galleys to Herculaneum, but he himself took a “fast-sailing cutter.” As they approached Herculaneum, cinders and ash fell so heavily that the ship’s pilot advised returning to Misenum. Pliny replied that “fortune favors the brave,” ordering the pilot to sail for Stabiae, where his friend lived. Winds whipped up by the eruption brought the cutter into port but then made it impossible to leave.
Pliny’s friend and her household were terrified by the eruption and the inability of the ship to navigate the rough seas roiled by the turmoil of the eruption. In her villa, Pliny tried to reassure his friends by feasting, bathing, and sleeping while waiting for the winds to abate. But as the eruption grew worse, it became clear that the winds were not dying down. (They were in fact being generated by the eruption itself, although Pliny obviously did not know that.) They decided to try again to get the ship to sea. They ventured back to the shore with pillows tied to their heads to protect them from the falling volcanic ash and molten rock. The sea was still too rough to board the ships, and the air was so foul as to make breathing difficult. Pliny the Elder was overcome and fell to the ground, unable to rise. His friends finally abandoned him and boarded the ship. They were able to escape and thus give the tale to Pliny the Younger. The friends returned three days later and found the body of Pliny the Elder under ash but with no obvious injury. Most scholars have decided he died from a heart attack, perhaps triggered by noxious gases.
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The type of explosive eruption that throws lava high into the atmosphere, where it solidifies into a variety of particles called (depending on size) volcanic hairs, ash, and bombs, is characteristic of stratovolcanoes. They are found in places where one tectonic plate is being pushed under another, called subduction zones. In the case of Vesuvius, the African continent is slowly moving toward Europe, pushing up mountains from the Alps to the Pyrenees and the Apennines, and pushing the Mediterranean seafloor under Italy. As the seafloor is pushed under the continent, friction heats the seafloor, melting it and the sediment carried upon it.
This sediment is a key to understanding such volcanoes. First, compared to lava coming from deeper in the earth and found in other types of volcanoes, stratovolcano lava is rich in quartz, which is a light mineral. So as rocks move around (on geologic time, rocks move a lot), it tends to travel upward relative to the heavier minerals around it. It gradually gets concentrated in the continents (rather than deeper in the earth), and in the sediments that erode off continents. This quartz creates magma with a higher viscosity than the kind found in other volcanoes. And second, the sediments have a lot of water incorporated in them, which in turn becomes incorporated in the magma they create.
The stickier quartz means the lava tends to adhere to itself instead of flowing forth, like we see in pictures of Hawaiian volcanoes. The water means there are more gases and vapor in the lava. Those expand when heated, causing explosions. Krakatau, Mount St. Helens, and Vesuvius are all found in subduction zones, and they all have the potential for these explosive eruptions.
Volcanologists have studied the deposits around Pompeii and the record left by Pliny the Younger and have concluded that the eruption had two main phases. The first was the eruptive column on August 24, a type of eruption now called Plinian. It towered into the air with a massive explosive force but then dispersed sideways and down, pulled by gravity—the pine tree shape that Pliny the Younger noted. From across the Bay of Naples, he said that after the first upward explosion, the ash settled back toward the earth and the day took on “a darkness that was not like a moonless or cloudy night, but more like the black of closed and unlighted rooms. You could hear women lamenting, children crying, men shouting. Some were calling for parents, others for children or spouses; they could only recognize them by their voices.”
Most of the approximately eleven thousand inhabitants of the region left on foot through the darkness, escaping with their lives. When the word came to Pliny the Younger about his uncle’s fate, he took his mother (aged and corpulent like her brother) and struggled on foot to get away. Other refugees clogged the roads, floundering through the darkness. Pliny the Younger described a people who believed the end of the world was at hand.
Many besought the aid of the gods, but still more imagined there were no gods left, and that the universe was plunged into eternal darkness for evermore. There were people, too, who added to the real perils by inventing fictitious dangers: some reported that part of Misenum had collapsed or another part was on fire, and though their tales were false they found others to believe them…. I could boast that not a groan or cry of fear escaped me in these perils, but I admit that I derived some poor consolation in my mortal lot from the belief that the whole world was dying with me and I with it.
After several days, Pliny the Younger and his mother escaped to safety, ultimately returning to Rome. Unlike them, some residents decided to stay, at least through the first night. The ash had been falling for a day by that point, and a home protected you from falling rocks. It’s easy to see how the decision to stay in your house could seem like a sensible one. What residents of Pompeii and Herculaneum could not know was that the night would bring the second phase of the eruption.
When stratovolcanoes explode, the ejecta usually travel high into the atmosphere, many tens of thousands of feet. As the eruption proceeds, the material gets heavier, and instead of a mushroom cloud high into the atmosphere, the hot gas and ash start to flow rapidly down the mountain (because they are heavier than air, the gas too can flow down.) These are called pyroclastic flows, from the Greek words pyro meaning “fire” and clastic meaning “broken in pieces.” The gases move quickly, usually at fifty miles per hour, although three hundred miles per hour has been recorded. They are so hot—around 500°F—that they kill instantly.
A pyroclastic flow is one of the deadliest forms of eruption. It is too fast to outrun, and seems to surprise the victims. The contorted positions of the eighteen hundred corpses buried in Pompeii led early observers to assume the victims had undergone extreme suffering. It is more likely that theirs were instant deaths from extreme heat, followed by their cadavers spasming from heat shock. It was only then that deposits of ash came to bury the corpses in their homes, preserving their tragic story for two millennia.
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