Hell’s Cauldron
He also had one volcano that was extinct. But, as he said, “One never knows!” So he cleaned out the extinct volcano, too. If they are well cleaned out, volcanoes burn slowly and steadily, without any eruptions. Volcanic eruptions are like fires in a chimney. On our earth we are much too small to clean out our volcanoes. That is why they bring no end of trouble upon us.
—Antoine de Sainte-Exupéry, The Little Prince
The year AD 79 was important in Roman history. A decade earlier, the Roman general Vespasianus had taken over as emperor, ending a year of civil war and anarchy following the death of Nero. Vespasianus had stabilized the empire, gotten the imperial accounts back on the profitable side, and improved the political situation for the middle and lower classes. He began many important construction projects, including great temples and the mighty Colosseum, completed in AD 79, built on the site of one of Nero’s palaces. At his death on June 24, his son Titus succeeded him. Titus proved to be an even more competent emperor, expanding the empire in Wales and Scotland and suppressing revolts in Palestine.
For the residents of towns around the Bay of Naples, AD 79 was also quite eventful. The Naples area was then, as it is now, a sleepy port city popular with vacationers, fishermen, and boaters. Since the reign of second emperor Tiberius, the Roman rulers had had a private villa on the island of Capri, on the southern edge of Naples Bay. Tiberius left Rome altogether in his final years and ruled the empire from his villa. By AD 79, the bay was crowded with towns, and the outlying areas were famous for their agriculture, especially grape and wine growing. Indeed, there were vineyards all around the slopes of Mt. Vesuvius, the great volcano to the northeast.
The Romans probably did not realize that Vesuvius was an active volcano, because its last eruption was more than two centuries before in 217 BC. For the 17 years since the great earthquake of AD 62 that had destroyed much of Pompeii, Herculaneum, and Neapolis (Naples), there had been frequent earthquakes in the region. As early as 30 BC, the Greek historian Diodorus Siculus described the Campanian plain as “fiery” (Phlegrean) because Vesuvius showed signs of the fires that had burned long ago. The Romans thought that the fires of Etna were due to the forges of Vulcan (Hephaistos to the Greeks), the god of the fire. He used the heat of the underworld to hammer out armor, metalwork, and weapons for the gods (including the thunderbolts thrown by Zeus/Jupiter). When eruptions occurred, it was said that Vulcan was angry because his wife Venus had cheated on him. The Romans considered Vesuvius sacred to Hercules (Herakles to the Greeks), and some scholars believe that the name “Vesuvius” is derived from the Greek for “son of Zeus” (as Herakles was Zeus’s son). The Romans named the port city of Herculaneum in honor of Hercules. Despite all these warnings, however, the area around the mountain was heavily populated, with 20,000 people in the town of Pompeii alone, and farming towns all around the base of Vesuvius. Then, as now, the volcanic soil was too rich and the climate too good for people to fear the long-dormant volcano. Even today, the area around Vesuvius has the highest population density of any active volcano in the world.
Fig. 3.1. Eruption of Mt. Vesuvius in 1944. (Photo courtesy USGS Photo Library)
By early August, the earthquakes were more frequent, but most residents ignored them. In addition, springs and wells had dried up, suggesting that the water table was dropping. On August 23, the Romans had celebrated the festival of Vulcanalia, to honor the god Vulcan. Then early in the warm summer’s afternoon of the following day, August 24, Vulcan gave his reply. First was a huge explosion, and the sky darkened as ash and pumice rained down on inhabitants for 18–20 hours (fig. 3.1). Some residents of Pompeii and Herculaneum evacuated immediately, but many remained behind who were unwilling or unable to leave because there were not enough boats in the harbor to carry them, and the roads were blocked by volcanic activity or clogged with traffic. After this phase of eruption, the streets of Pompeii were filled with 2.8 m (9 feet) of ash and pumice, making it harder to evacuate, let alone breathe. Then after almost a day of this rain of hell, the mountain let loose another type of eruption: many nuées ardentes (glowing clouds), or pyroclastic flows, a superheated (up to 850°C, or 1,560°F) mixture of volcanic gases and ash that roared down the mountain slope at 160 km/h (100 mph), incinerating everything in its path, and burying Herculaneum under tens of meters of volcanic deposits, or tuff.
Most eyewitnesses did not record their experiences, or their accounts have been lost in the mists of history. Fortunately, we do have one excellent eyewitness account, written by the historian Pliny the Younger. He was 17 at the time and fleeing with his family in a boat to the town of Misenum, across the bay 35 km (22 miles) from the volcano. In a letter to his friend, the historian Cornelius Tacitus, the younger man described how his 56-year-old uncle, Pliny the Elder, one of Rome’s leading admirals, scholars, and naturalists, decided to take a boat closer to the mountain to rescue his friends. It is one of my favorite accounts of any eruption because I first read it in the original in my high school Latin class:
My dear Tacitus,
You ask me to write you something about the death of my uncle so that the account you transmit to posterity is as reliable as possible. I am grateful to you, for I see that his death will be remembered forever if you treat it [in your Histories]. He perished in a devastation of the loveliest of lands, in a memorable disaster shared by peoples and cities, but this will be a kind of eternal life for him …
He was at Misenum in his capacity as commander of the fleet on the 24th of August [AD 79], when between 2 and 3 in the afternoon my mother drew his attention to a cloud of unusual size and appearance. He had had a sunbath, then a cold bath, and was reclining after dinner with his books. He called for his shoes and climbed up to where he could get the best view of the phenomenon. The cloud was rising from a mountain—at such a distance we couldn’t tell which, but afterwards learned that it was Vesuvius. I can best describe its shape by likening it to a pine tree [today, we would compare it to a “mushroom cloud”]. It rose into the sky on a very long “trunk” from which spread some “branches.” I imagine it had been raised by a sudden blast, which then weakened, leaving the cloud unsupported so that its own weight caused it to spread sideways. Some of the cloud was white, in other parts there were dark patches of dirt and ash. The sight of it made the scientist in my uncle determined to see it from closer at hand. [This style of explosive mushroom cloud of ash and pumice is now called a “Plinian eruption” in his honor.]
He ordered a boat made ready … The expedition that started out as a quest for knowledge now called for courage. He launched the quadriremes and embarked himself … He hurried to a place from which others were fleeing, and held his course directly into danger. Was he afraid? It seems not, as he kept up a continuous observation of the various movements and shapes of that evil cloud, dictating what he saw.
Ash was falling onto the ships now, darker and denser the closer they went. Now it was bits of pumice, and rocks that were blackened and burned and shattered by the fire. Now the sea is shoal; debris from the mountain blocks the shore. He paused for a moment wondering whether to turn back as the helmsman urged him. “Fortune helps the brave,” he said. “Head for Pomponianus.”
At Stabiae, on the other side of the bay formed by the gradually curving shore, Pomponianus had loaded up his ships even before the danger arrived, though it was visible and indeed extremely close, once it intensified. He planned to put out as soon as the contrary wind let up. That very wind carried my uncle right in, and he embraced the frightened man and gave him comfort and courage. In order to lessen the other’s fear by showing his own unconcern he asked to be taken to the baths. He bathed and dined, carefree or at least appearing so (which is equally impressive). Meanwhile, broad sheets of flame were lighting up many parts of Vesuvius; their light and brightness were the more vivid for the darkness of the night. To alleviate people’s fears my uncle claimed that the flames came from the deserted homes of farmers who had left in a panic with the hearth fires still alight. Then he rested, and gave every indication of actually sleeping; people who passed by his door heard his snores, which were rather resonant since he was a heavy man. The ground outside his room rose so high with the mixture of ash and stones that if he had spent any more time there escape would have been impossible. He got up and came out, restoring himself to Pomponianus and the others who had been unable to sleep. They discussed what to do, whether to remain under cover or to try the open air. The buildings were being rocked by a series of strong tremors, and appeared to have come loose from their foundations and to be sliding this way and that. Outside, however, there was danger from the rocks that were coming down, light and fire-consumed as these bits of pumice were. Weighing the relative dangers they chose the outdoors; in my uncle’s case it was a rational decision, others just chose the alternative that frightened them the least.
They tied pillows on top of their heads as protection against the shower of rock. It was daylight now elsewhere in the world, but there the darkness was darker and thicker than any night. But they had torches and other lights. They decided to go down to the shore, to see from close up if anything was possible by sea. But it remained as rough and uncooperative as before. Resting in the shade of a sail he drank once or twice from the cold water he had asked for. Then came a smell of sulfur, announcing the flames, and the flames themselves, sending others into flight but reviving him. Supported by two small slaves he stood up, and immediately collapsed. As I understand it, his breathing was obstructed by the dust-laden air, and his innards, which were never strong and often blocked or upset, simply shut down. When daylight came again 2 days after he died, his body was found untouched, unharmed, in the clothing that he had had on. He looked more asleep than dead. (Pliny the Younger 1963)
In a second letter to Tacitus a few days later, Pliny wrote:
By now it was dawn, but the light was still dim and faint. The buildings round us were already tottering, and the open space we were in was too small for us not to be in real and imminent danger if the house collapsed. This finally decided us to leave the town. We were followed by a panic-stricken mob of people wanting to act on someone else’s decision in preference to their own (a point in which fear looks like prudence), who hurried us on our way by pressing hard behind in a dense crowd. Once beyond the buildings we stopped, and there we had some extraordinary experiences which thoroughly alarmed us. The carriages we had ordered to be brought out began to run in different directions though the ground was quite level, and would not remain stationary even when wedged with stones. We also saw the sea sucked away and apparently forced back by the earthquake: at any rate it receded from the shore so that quantities of sea creatures were left stranded on dry sand. On the landward side a fearful black cloud was rent by forked and quivering bursts of flame, and parted to reveal great tongues of fire, like flashes of lightning magnified in size …
Soon afterwards the cloud sank down to earth and covered the sea; it had already blotted out Capri and hidden the promontory of Misenum from sight. Then my mother implored, entreated and commanded me to escape the best I could—a young man might escape, whereas she was old and slow and could die in peace as long as she had not been the cause of my death too. I refused to save myself without her, and grasping her hand forced her to quicken her pace. She gave in reluctantly, blaming herself for delaying me. Ashes were already falling, not as yet very thickly. I looked round: a dense black cloud was coming up behind us, spreading over the earth like a flood. “Let us leave the road while we can still see,” I said, “or we shall be knocked down and trampled underfoot in the dark by the crowd behind.” We had scarcely sat down to rest when darkness fell, not the dark of a moonless or cloudy night, but as if the lamp had been put out in a closed room. You could hear the shrieks of women, the wailing of infants, and the shouting of men; some were calling their parents, others their children or their wives, trying to recognize them by their voices. People bewailed their own fate or that of their relatives, and there were some who prayed for death in their terror of dying. 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. A gleam of light returned, but we took this to be a warning of the approaching flames rather than daylight. However, the flames remained some distance off; then darkness came on once more and ashes began to fall again, this time in heavy showers. We rose from time to time and shook them off, otherwise we should have been buried and crushed beneath their weight. I could boast that not a groan or cry of fear escaped me in these perils, had I not derived some poor consolation in my mortal lot from the belief that the whole world was dying with me and I with it.
At last the darkness thinned and dispersed into smoke or cloud; then there was genuine daylight, and the sun actually shone out, but yellowish as it is during an eclipse. We were terrified to see everything changed, buried deep in ashes like snowdrifts. We returned to Misenum where we attended to our physical needs as best we could, and then spent an anxious night alternating between hope and fear. Fear predominated, for the earthquakes went on, and several hysterical individuals made their own and other people’s calamities seem ludicrous in comparison with their frightful predictions. But even then, in spite of the dangers we had been through, and were still expecting, my mother and I had still no intention of leaving until we had news of my uncle. (Pliny the Younger 1963)
Pompeii was buried under more than 20 m (66 feet) of ash. It was abandoned and long forgotten as new towns were later built above the buried ruins. Then in 1748, well diggers accidentally rediscovered the ruins of Pompeii (plate 5A). For more than two centuries, it has been gradually and nearly completely excavated, to reveal a picture of everyday life in ancient Rome, complete with frescoes and graffiti on the walls and the tools and implements of daily life. Among the most remarkable discoveries were cavities in the ash that were encountered during digging. When the cavities were filled with plaster, they formed molds of the bodies of Romans who had died in the ash and vaporized, leaving the hollow behind (plate 5B). Hundreds of these bodies were found, usually in poses suggesting agonizing deaths, asphyxiated in a few seconds by volcanic ash and gases, curling up to shelter themselves. Most of the population of 20,000 apparently died instantly. Only a few thousand survivors reached the safety of boats.
Herculaneum was buried under an even thicker blanket of hard tuff. It was rediscovered in 1709. Excavation began in 1738, but digging has been difficult and it is only partly exposed. Unlike Pompeii, Herculaneum was a smaller town (about 5,000) but a rich coastal resort, with a more affluent population, as shown by the clothes and jewelry that have been found. Archaeologists found not only the cavities left by bodies but also 300 skeletons in death poses. They were found near the waterfront attempting to escape and were apparently killed by superheated volcanic gases before they too were vaporized, leaving only bones.
After the great eruption of AD 79, Vesuvius returned to a more active phase, with frequent eruptions nearly every century for another two millennia. The eruption of AD 203 was recorded by the historian Cassius Dio, and in AD 472, its ash reached as far as Constantinople. The most destructive recent eruption was in 1906 when a record number of lava flows appeared and 100 people died. The most recent eruption in 1944 (fig. 3.1) destroyed many villages as well as 88 World War II B-25 bombers that were fighting farther north on the Italian peninsula. For the past 67 years, Vesuvius has been relatively dormant, although plenty of steam still rises from the crater, and there are many small earthquakes. But given its history, it is still considered one of the world’s most active and dangerous volcanoes. Despite these problems more than 3 million people live all around its base, and 1 million live on the actual slope of the volcano.
Although the eruption of Vesuvius is the most famous volcanic disaster in European history, its eruptions are small compared with some of the huge explosive events elsewhere. Perhaps the most famous of these is the eruption of Krakatau (the Indonesian spelling, although it has been anglicized to “Krakatoa”) volcano in the Sunda Straits west of Java and south of Sumatra. (In 1969, Hollywood made a dud of a disaster movie about the volcano, full of scientific inaccuracies, not the least of which was the erroneous title, Krakatoa, East of Java). In 1883, the Indonesian archipelago was part of the hugely profitable colony of the Dutch East Indies. Dutch planters and colonialists occupied many large cities and controlled a huge native population, producing nearly all the world’s supply of pepper and quinine, a third of its rubber, a quarter of its coconuts, and a fifth of its tea, cocoa, sugar, coffee, oil, and other commodities. Heavy ship traffic passed through the Sunda Straits to Batavia (now Djakarta) on the north shore of Java and between the Indian and Pacific oceans.
Fig. 3.2. Changes in the shape of Krakatau before and after the eruption. The three major peaks of the original volcano (Rakata, Danan, and Perboewatan) are shown by triangles; two of them vanished when the mountain exploded. (Map courtesy USGS; redrawn by Pat Linse)
Although the volcanoes of Krakatau had been dormant for more than 200 years, by 1882 and 1883, numerous earthquakes had occurred in the area. On May 20, 1883, ship captains reported seeing plumes of steam rising from Perboewatan, the northernmost of the island’s three cones (fig. 3.2). Soon ash shot out of the vent to an altitude of 6 km (20,000 feet), and the explosions could be heard in Batavia, more than 160 km (100 miles) away. Activity died down for a few weeks, only to resume on June 16 with more explosions and a thick ash cloud that darkened the skies over Indonesia for five days. A wind arose on June 24 revealing two ash plumes, both from vents near the center of the volcano and south of Perboewatan. This eruption increased the tidal range, forcing crews to chain ships to the docks. Many earthquakes followed, and passing ships reported large rafts of pumice floating in the Indian Ocean to the west.
On August 11, H. J. G. Ferzenaar landed on the island and conducted the only study of the early phase of activity before the final cataclysm. All vegetation had been burned down to tree stumps, and there were now three major ash plumes, with the new one coming from the central peak of Danan. Steam plumes rose from 11 other vents, and there was an ash layer 0.5 m (20 inches) deep across the entire island. Ferzenaar reported these discoveries and recommended that no one else visit the island, although life still continued as normal in distant cities like Batavia.
The vents continued to spew ash, pumice, and steam for many more days. The next big eruption occurred on August 25, which spewed a cloud of black ash 27 km (17 miles) high, with explosions occurring about every 10 minutes. Hot ash and pumice up to 10 cm (3 inches) in diameter covered the decks of ships 20 km (11 miles) away. One of the volcanic cones collapsed into the sea, triggering a small tsunami that hit the shores of Java and Sumatra up to 40 km (28 miles) away. The eruption was so loud that people in far off Batavia could not sleep, as the deafening pounding noise kept up hour after hour.
The final paroxysm occurred on August 27, when four large explosions occurred between 5:30 a.m. and 10:41 a.m. (plate 6). They were so loud that they were heard in Perth, Australia, more than 3,500 km (2,200 miles) away, and even on the island of Mauritius north of Madagascar, 4,800 km (3,000 miles) away, where they sounded like nearby cannon fire. These explosions generated a pressure wave that ruptured the eardrums of sailors in the Sunda Strait. The barometric pressure gauges measuring normal air pressure jumped off the scale and were shattered. This aerial shock wave continued around the globe and registered on barographs worldwide up to seven days after the initial explosions. Burning ashes rained down over the region, killing about 1,000 people in the village of Ketimbang more than 40 km (25 miles) north of Krakatau, and incinerating nearly all the forests around the Sunda Strait. Research in the past few decades has shown that pyroclastic flows can move across the water’s surface because of their intense heat and speed, buoyed by a frictionless layer of gases beneath them (like the puck in an air hockey game). This explains why they could spread across the ocean from the volcano to more distant islands and shores. More than 3,000 people on the island of Sebesi were killed with no survivors, even though they were 13 km (8 miles) from Krakatau. The most deadly consequence, however, was the gigantic tsunamis and the collapse of the caldera, which killed at least 36,000 and maybe as many as 126,000 (see chapter 2).
The wife of town controller Janni Beyerinck described her experiences in the village of Ketimbang, where the pyroclastic flows trapped many and killed most of the residents; however, a few were spared:
Suddenly, it became pitch dark. The last thing I saw was the ash being pushed up through the cracks in the floorboards, like a fountain. I turned to my husband and heard him say in despair “Where is the knife? … I will cut all our wrists and then we shall be released from our suffering sooner.” The knife could not be found. I felt a heavy pressure, throwing me to the ground. Then it seemed as if all the air was being sucked away and I could not breathe … I felt people rolling over me … No sound came from my husband or children … I remember thinking, I want to … go outside … but I could not straighten my back … I tottered, doubled up, to the door … I forced myself through the opening … I tripped and fell. I realized the ash was hot and I tried to protect my face with my hands. The hot bite of the pumice pricked like needles … Without thinking, I walked hopefully forward. Had I been in my right mind, I would have understood what a dangerous thing it was to … plunge into the hellish darkness … I ran up against … branches and did not even think of avoiding them. I entangled myself more and more … My hair got caught up … I noticed for the first time that [my] skin was hanging off everywhere, thick and moist from the ash stuck to it. Thinking it must be dirty, I wanted to pull bits of skin off, but that was still more painful … I did not know I had been burnt. (Scarth 1999)
By the next morning on August 28, Krakatau was eerily quiet. Small mud eruptions occurred, but major volcanic activity had ended. Before the volcano, Krakatau had three major cones. Afterward, a huge, drowned caldera 250 m (850 feet) deep with only three small islands remained of the outer base of the volcano (fig. 3.2). About 18–21 km3 (4.3–5.0 cubic miles) of volcanic material (mostly ignimbrites formed by hot flowing ash and gases) had been displaced, deposited over an area of 1.1 million km2 (420,000 square miles). Most of this material filled the basins of the Sunda Strait around Krakatau or covered the shorelines of Java and Sumatra and the adjacent islands. There were rafts of pumice floating on the Indian Ocean, some with human skeletons on top. A few of these rafts washed all the way to the east coast of Africa. The huge amount of ash shot into the stratosphere blocked sunlight and dropped global average temperatures about 1°–2°C for more than a year. Weather patterns were erratic for years, and temperatures did not return to normal until 1888. The skies dimmed, even darkened for months after the eruption, and high amounts of particulate matter in the stratosphere changed the color of the sky, producing spectacular orange red sunsets as depicted in Edvard Munch’s famous 1893 painting The Scream. Munch described the sky over Norway after the eruption as follows: “Suddenly the sky turned blood red … I stood there shaking with fear and felt an endless scream passing through nature” (Prideaux 2005, 17). Rare atmospheric effects, such as a blue moon, a Bishop’s ring around the sun in daytime, and volcanic purple light at twilight were also seen around the world.
Krakatau remained quiet for a few more decades until submarine eruptions were detected in the center of the caldera on December 27, 1927. A few days later, this eruption built a new, much smaller volcano on top of the old vent known as Anak Krakatau (“son of Krakatau”). Most of the initial ash and pumice produced by this eruption were quickly eroded away by the sea until 1930, when a series of lava flows built up the island faster than the sea could erode it. Anak Krakatau has continued to grow about 13 cm (5 inches) per week since the current phase of eruptions began in the 1950s. It goes through phases of activity in which it builds rapidly, then several years of quiescence, followed by renewed eruptions. The most recent eruption was in April 2008, releasing hot gases, rocks, and lava in all directions.
Although the Dutch had ruled the area for centuries, by 1883 the Dutch East Indies colony was in an advanced state of decay, with continual uprisings by the indigenous peoples forcing the Netherlands to suppress revolts in one war after another. Simon Winchester (2003) argued that the eruption of Krakatau helped weaken the Dutch East Indian colony even further by crippling its economy and exposing the incompetence and corruption of the Dutch administrators. It triggered a wave of anti-Western militancy in the native Muslim populations. According to Winchester, these events sped up the eventual demise of the Dutch colonies, which finally ended when the Japanese invaded in January 1942. When Japan surrendered in 1945, the Dutch were unable to regain control of the islands, and by 1949 Indonesia was independent.
Although the Krakatau eruption was spectacular, it wasn’t even the biggest eruption in Indonesia in the past 200 years. (Indonesia has hundreds of active volcanoes, the most of any country in the world.) That distinction goes to the eruption of Mount Tambora, on the island of Sumbawa, east of Java. When it erupted in 1815, it was the largest eruption in recorded history. The explosion was heard on Sumatra, more than 2,000 km (1,200 miles) away, and heavy ash falls covered most of Indonesia. It killed between 70,000 and 90,000 people, 12,000 of whom died from the eruption; the rest starved because crops were destroyed.
After the eruption, the most definitive description of the volcano and its aftermath was given by Sir Thomas Stamford Raffles, a governor-general of the Dutch East Indies, the founder of Singapore, and a respected naturalist. He wrote:
Island of Sumbawa, 1815
In April, 1815, one of the most frightful eruptions recorded in history occurred in the mountain Tambora, in the island of Sumbawa. It began on the 5th day of April, and was most violent on the 11th and 12th, and did not entirely cease till July. The sound of the explosion was heard in Sumatra, at a distance of nine hundred and seventy geographical miles in a direct line, and at Ternate, in an opposite direction, at the distance of seven hundred and twenty miles. Out of a population of twelve thousand, only twenty-six individuals survived on the island. Violent whirlwinds carried up men, horses, cattle, and whatever else came within their influence, into the air, tore up the largest trees by the roots, and covered the whole sea with floating timber. Great tracts of land were covered by lava, several streams of which, issuing from the crater of the Tambora mountain, reached the sea. So heavy was the fall of ashes, that they broke into the Resident’s house in Bima, forty miles east of the volcano, and rendered it, as well as many other dwellings in the town, uninhabitable. On the side of Java, the ashes were carried to the distance of three hundred miles, and two hundred and seventeen towards Celebes, in sufficient quantity to darken the air. The floating cinders to the westward of Sumatra formed, on the 12th of April, a mass two feet thick and several miles in extent, through which ships with difficulty forced their way. The darkness occasioned in the daytime by the ashes in Java was so profound, that nothing equal to it was ever witnessed in the darkest night. Although this volcanic dust, when it fell, was an impalpable powder, it was of considerable weight; when compressed, a pint of it weighing twelve ounces and three quarters. Along the sea-coast of Sumbawa, and the adjacent isles, the sea rose suddenly to the height of from two to twelve feet, a great wave rushing up the estuaries, and then suddenly subsiding. Although the wind at Bima was still during the whole time, the sea rolled in upon the shore, and filled the lower parts of houses with water a foot deep. Every prow and boat was forced from the anchorage and driven on shore. The area over which tremulous noises and other volcanic effects extended was one thousand English miles in circumference, including the whole of the Molucca Islands, Java, a considerable portion of Celebes, Sumatra and Borneo. In the island of Amboyna, in the same month and year, the ground opened, threw out water, and closed again. (Raffles 1830)
Tambora had worldwide effects as well. It injected so much dust into the stratosphere that the earth’s weather patterns changed, and dust blocked sunlight from reaching the surface. The year 1816 came to be known as the “Year without Summer” because it produced cold, dark rainy summer months in North America and in Eurasia. This led to crop failures, livestock starvation, and widespread disease (especially a typhus epidemic) and famine among populations around the world. In June, it snowed in New York, in New England, and in many European cities. In Lord Byron’s villa near Lake Geneva in Switzerland, Percy and Mary Shelley were visiting and told gothic horror stories to pass the time in the cold, dark, wet summer. That gloomy time inspired Mary Shelley to write Frankenstein (1818).
One of the first scientifically documented instances of nuées ardentes, or pyroclastic flows, occurred during the 1902 eruption of Mont Pelée on the Caribbean island of Martinique. At that time, Martinique was a busy, heavily populated island, with a large port city, St. Pierre, home to more than 25,000 people. Mont Pelée had been dormant for centuries when on April 25, 1902, it came to life with geyser-like clouds of ash and steam known as fumaroles, followed a day later by showers of ash and cinders. Each day was marked by more ash falls and other evidence that an eruption was about to happen. About 700 rural folks fled to safety in the city each day. But there was an election scheduled for May 10, and the governor did not want people fleeing the region and changing the results. He commanded the militia to preserve order and turn back people fleeing the city, a fatal decision for him and inhabitants of St. Pierre. On May 2, the mountain produced loud explosions, earthquakes, and a massive pillar of ash, which covered the landscape for miles and darkened the sky for hours. Then the wind changed, the ash was blown northward, and it was thought that the worst was over.
On May 5, a host of bizarre events foretold doom to come. Distressed and agitated livestock tried to jump their fences. At a sugar mill north of the city, yellowish-speckled ants and foot-long black centipedes, driven from the slopes of Mont Pelée by constant tremors and ash, swarmed over the ground. They bit animals and people, but no one died from these attacks. Snakes invaded the streets of St. Pierre, including poisonous pit vipers, 2 m (6 feet) long, known as the fer de lance. They bit pigs, chickens, and people who did not get out of their way, killing more than 200 animals and 50 people. The mayor of St. Pierre ordered soldiers to shoot them, and at least 100 snakes were killed.
On May 8, after several more days of active eruption, the mountain suddenly exploded (fig. 3.3A), and a dense superheated ash cloud rushed down the mountainside at 670 km/h (420 mph), engulfing and burying St. Pierre in less than a minute. Anything flammable was incinerated by the 1,000°F heat. More than 30,000 people died instantly. Sailors who dove into the water as their ships blazed were badly burned and did not survive. A warship approaching from the sea was forced to wait offshore for several days because of the intense heat of the pyroclastic material. When the fires finally burned out, only rubble and ruin were left of this big city (fig. 3.3B). Everything else had been destroyed. Only one man survived in the city. Prisoner Louis-Auguste Cyparis had been confined in a deep dungeon. He was rescued four days later, and for years after, he made a living as the “Lone Survivor of St. Pierre,” a sideshow attraction in the Barnum and Bailey circus. The only other survivor was a young shoemaker, Léon Compere-Léandre, who lived on the outskirts of the city and escaped the worst of the flows. His description of the ordeal follows:
I felt a terrible wind blowing, the earth began to tremble, and the sky suddenly became dark. I turned to go into the house, with great difficulty climbed the three or four steps that separated me from my room, and felt my arms and legs burning, also my body. I dropped upon a table. At this moment four others sought refuge in my room, crying and writhing with pain, although their garments showed no sign of having been touched by flame. At the end of 10 minutes one of these, the young Delavaud girl, aged about 10 years, fell dead; the others left. I got up and went to another room, where I found the father Delavaud, still clothed and lying on the bed, dead. He was purple and inflated, but the clothing was intact. Crazed and almost overcome, I threw myself on a bed, inert and awaiting death. My senses returned to me in perhaps an hour, when I beheld the roof burning. With sufficient strength left, my legs bleeding and covered with burns, I ran to Fonds-Sait-Denis, six kilometers from Saint-Pierre. (Pellegrino 1999, 299)
Fig. 3.3. A, Eruption of Mt. Pelée in 1902, showing the nuées ardentes flowing down to the sea, and ash plumes ejected to the stratosphere. B, Ruins of St. Pierre. (Photos by Angelo Heilprin, 1902. Courtesy Wikimedia Commons.)
Not all volcanoes explode like Vesuvius, Krakatau, Tambora, or Mont Pelée. Hawaiian volcanoes, familiar from nature films, erupt with relatively thin lava flows but do not blow their tops in a catastrophic explosion. Why the difference? The answer lies in the chemistry of the magma. Volcanoes like those on Hawaii or Iceland erupt basaltic lavas, which are composed of material similar to the composition of mantle from which their magma comes. It is rich in magnesium, iron, and calcium, and relatively depleted in silica, aluminum, potassium, and sodium. Basalts are made of olivine (also known as the gemstone peridot), pyroxenes, and calcium-rich plagioclase feldspar. These minerals have very high melting temperatures (typically 1,600°C), so they form fluid, hot magmas. Basaltic lava flows like water. When these volcanoes erupt, they release seemingly endless lava flows. These volcanoes do not explode, except for throwing some small lava blobs into the air from lava fountains.
The lavas from the explosive eruptions of Krakatau or Mont Pelée have different magma chemistry. These lavas are known as andesites, dacites, and rhyolites and are richer in silica, aluminum, potassium, and sodium but were depleted in chemicals found in basalts, such as iron, magnesium, and calcium. This chemistry forms a completely different suite of minerals, especially quartz (silicon dioxide), the black flaky mica biotite, amphiboles like hornblende, and both potassium-rich feldspar and sodium-rich plagioclase feldspar. These magmas form at much lower temperatures (as low as 600°C) than do basalts.
Why are andesite-dacite-rhyolite magmas chemically transformed from their original basaltic mantle sources? The answer is complicated, requiring a detailed understanding of mineralogy and geochemistry. Simply put, magmas change chemistry as they melt their way to the surface from their original source. They can be changed by a number of processes, including contamination by melting silica-rich crustal rocks from the walls of the magma chamber, melting of previously cooled magma chambers that release low-temperature minerals such as potassium feldspar and quartz first (partial melting), and depletion of high-temperature minerals that settled out of the magma chamber early and change the chemistry of the remaining melt (fractional crystallization).
Consequently, andesite-dacite-rhyolite magmas are not only different in chemistry and mineralogy but also in behavior. They are viscous, like sticky peanut butter or molasses. Rather than flow freely like basalts, andesite-rhyolite lavas flow slowly or not at all. If the throat of one of these volcanoes is choked by a sticky, viscous dacite or rhyolite plug, the mountain will build up pressure until it explodes. This produces the full range of pyroclastic materials: ash, pumice, hot, glowing clouds of volcanic material (nuées ardentes, or pyroclastic flows), thick tuff deposits, and so on.
Andesite-dacite-rhyolite magmas are found primarily on the Pacific Ring of Fire (see fig. 1.6), the Mediterranean, and a few other places. As established in chapter 1, these places are subduction zones, where one tectonic plate sinks beneath another (fig. 3.4). As one slab goes down into the mantle, the sinking slab begins to melt, releasing some of its material into magmas that then must melt their way up through the overlying crust (already composed of silica-rich materials) until they erupt to form subduction volcanoes (known as “arc volcanoes” because many are part of island arcs like the Aleutians or Indonesia). Most volcanoes in the world formed in a subduction setting (especially in the Ring of Fire from the Andes to the Cascades to the Aleutians to Japan, the Philippines, and Indonesia) are generated this way.
By contrast, volcanoes that erupt basaltic lavas, with their deep mantle sources, come from different plate tectonic settings (fig. 3.4). Some, like Hawaii, Yellowstone, and Iceland, lie above “hot spots” in the earth’s mantle, where molten plumes of mantle material constantly melt their way to the surface. Others, like the midocean ridges and Iceland, lie above places where the crust is pulling apart in a spreading zone, and fresh basaltic magma wells up to fill the cracks. Most of these ridge volcanoes are small submarine eruptions, although some rise high enough to form islands (or in the case of Iceland, a hot spot lies directly below the midocean ridge).
Fig. 3.4. Plate tectonic settings of volcanic activity. (Image courtesy USGS, redrawn by Pat Linse)
Still others are formed when huge cracks open up in the continental crust, which allow mantle-derived magma to flow up to the surface. These tend to produce long fissures and rifts from which pour immense sheets of lava that cover the landscape in days. Not surprisingly, these are known as “flood basalts.” Such eruptions happened 15–16 million years ago when the Columbia River basalts erupted and flowed across all of eastern Oregon and Washington and parts of Nevada and Idaho. They covered some 130,000 km2 (50,000 square miles), with hundreds of flows totaling more than 1,500 m (5,000 feet) in total thickness, with individual flows up to 100 m (330 feet) thick. These eruptions produced more than 104,000 km3 (25,000 cubic miles) of lava. These lava flows, or the thin soils that developed atop them, can be seen everywhere in eastern Washington and Oregon. Similar gigantic basalt floods occurred in Siberia 250 million years ago, in western India and Pakistan 65 million years ago, and in many submarine eruptions that produced features like the OntongJava Plateau and the Kergeulen Plateau, which are still under the ocean.
Basaltic volcanoes are not nearly as deadly as andesite-dacite-rhyolite volcanoes. Although eruptions on Hawaii or Iceland can produce lava flows that will incinerate everything in their paths, they move slowly, enabling people to escape, unless they behave foolishly or are trapped. Certainly, the landscapes of Washington and Oregon before the flood basalt eruptions were devastated. In the the famous Gingko Petrified Forest near Vantage, Washington, trees that grew on soils atop old lava flows were fossilized when another lava flow covered the forest and entombed them. In another instance near Grand Coulee, Washington, a bloated rhinoceros carcass floating upside down in a lake was surrounded by lava flows that molded its shape as lava cooled. Life was abundant on the Columbia River landscapes 15 million years ago, but it was incinerated each time a new eruption occurred.
Many buildings and forests in Hawaii and Iceland have been wiped out by basaltic lava flows. These eruptions did not explode and produce ash that covered huge areas in hours, circled the globe, or cooled the planet, as andesitedacite-rhyolite volcanoes such as Krakatau, Tambora, or Vesuvius.
Given these simple but critical distinctions, we can now see that basaltic volcanoes are different from andesite-dacite-rhyolite in their magma chemistry and mineralogy, magma behavior, temperature, viscosity, and location on the earth’s surface. Giant fast-moving lava flows come from basaltic eruptions, whereas explosive pyroclastics, ash, and pumice come largely from andesitedacite-rhyolite eruptions, and they are usually not found together. Silly Hollywood movies, such as Volcano and Dante’s Peak, are all that more ridiculous because they throw every possible volcanic event together in a great illogical mixture that would never actually happen in nature (not that Hollywood movies have ever been scientifically accurate).
One geologic term that does come from television is supervolcano, coined by a BBC program in 2000. The Discovery Channel remade the film in 2005 with several other documentary channels. Geologists have still not formally accepted this neologism, but it describes many eruptions in the prehistoric past beyond the scale of anything witnessed in recorded history (although some were within the time that prehistoric humans lived). By definition, supervolcanoes erupt material in excess of 1,000 km3 of ejecta and reach VEI 8 on the scale of volcanoes (“VEI” stands for volcanic explosivity index).
Fig. 3.5. Relative size of some volcanic eruptions, and their ranking on the VEI (volcanic explosivity index) scale. (Courtesy USGS, redrawn by Pat Linse)
Only a handful of eruptions have so far been identified as supervolcanoes (fig. 3.5). Even though Mount St. Helens received tremendous publicity when it erupted in 1980 (mostly because it was in a populated area of the United States and not in the less-developed world), it was a dwarf compared with most other great eruptions. Even Krakatau and Tambora are beneath the threshold for supervolcanoes. About 75,000 years ago, an eruption occurred on Mount Toba in Sumatra, which ejected 2,800 km3 of material. It was believed to be the largest volcanic explosion in the last 25 million years. It released the energy equivalent of 1 gigaton of explosives, forty times larger than the largest nuclear bomb explosion, and about 3,000 times as powerful as the eruption of Mount St. Helens. Toba injected so much ash into the stratosphere that the ash clouds blocked the sun’s radiation and decreased global temperature by 3°–5°C (5°–9°F), further amplifying the cold of the ongoing ice ages. The tree line and snow line dropped 3,000 m (9,000 feet) lower than today, making most high elevations uninhabitable. Global mean temperatures dropped to only 15°C after three years and took a full decade to recover to pre-eruption temperatures. Ice cores from Greenland show evidence of this dramatic cooling in the trapped ash and ancient air bubbles, although so far it has not been detected in Antarctic ice cores.
A number of geneticists and archaeologists have argued that the Toba catastrophe nearly wiped out the human race, leaving a genetic bottleneck of only about 1,000 to 10,000 breeding pairs of humans worldwide. In a genetic bottleneck, there are so few breeding pairs that they do not have the full complement of genes of their ancestors, and their descendants have a different genetic code as well. In addition to the geologic evidence of Toba’s size and atmospheric effects, geneticists have found evidence from the molecular clocks in our genomes that human populations were in a genetic bottleneck at about this time. One other study found a similar genetic bottleneck in the genes of human lice, and in our gut bacterium Helicobacter pylori, which causes human ulcers; both of these date back to the time of Toba, according to their molecular clocks. The Toba catastrophe theory is still debated, but it is reasonable to think that such a global catastrophe would have profound effects on the human population.
Although Indonesia has a lion’s share of the world’s deadliest volcanoes, North America was home to many supervolcano eruptions. The caldera in the heart of Yellowstone National Park, this nation’s first national park, is still a threat. The hot springs, geysers, and fumaroles of Yellowstone indicate that an enormous mantle hot spot lies not far beneath the crust, and Yellowstone’s ring shape is actually due to the collapse of a giant volcano into a caldera. Based on the dates of the volcanic flows all around Yellowstone, it last erupted about 640,000 years ago, ejecting more than 1,000 km3 of material that blanketed the entire western half of the United States. This deposit is known as the Lava Creek tuff. Thin layers of this ash can be detected in ice age deposits as far east as Louisiana and Alabama, more than 3,000 km (1,000 miles) away (fig. 3.6). Another large eruption from the same hot spot occurred on the Idaho side of Yellowstone, when the Island Park caldera exploded about 2.1 million years ago and spewed more than 2,500 km3 of ash and pumice known as the Huckleberry Ridge tuff (fig. 3.6), which blew east as far as Missouri and as far south as Texas.
Fig. 3.6. Map of the distribution of volcanic ash from some of the larger prehistoric eruptions. (Courtesy USGS, redrawn by Pat Linse)
Another active but slightly smaller eruptive source is the Long Valley caldera, near Bishop and Mammoth Mountain, on the east flank of the Sierras in California (fig. 3.6). About 730,000 years ago, it exploded and shot 600 km3 of material into the air, which blanketed the entire western half of the United States as far east as Oklahoma. Its biggest eruption is known as the Bishop tuff, which is found all around the northern Owens Valley and can be traced to ice age outcrops in Kansas and Nebraska.
These eruptions are dwarfed by the eruption of the La Garita caldera in southwestern Colorado. It is a huge hole in the ground, 35 km by 75 km (22 miles by 47 miles), which forms a large irregular oblong valley in the San Juan Mountains. Some of the caldera and its ash deposits can be seen in the Wheeler Geologic Area northwest of South Fork, Colorado (fig. 3.7). In other places, the caldera has been covered up and partially filled by eruptions of the smaller but younger Creede caldera and other younger calderas. When La Garita exploded 27.8 million years ago, it blew more than 5,000 km3 (1,200 cubic miles) of material all over the United States, enough material to fill Lake Michigan. It deposited a widespread ash layer known as the Fish Canyon tuff, which can still be seen in the Arkansas River Canyon, 100 km northeast of the caldera, and beneath the surface of the Alamosa area, 100 km east of the volcano. At one time, it was one of the largest volcanic deposits in the world and probably covered much of the Rockies and the western and central plains of the United States. It is calculated that the energy released by the La Garita explosion was 10,000 times more powerful than the largest nuclear device that humans have ever detonated.
Fig. 3.7. Many layered tuff deposits, eroded into pinnacles, from the Wheeler Geologic area. (Photo courtesy G. LeVelle)
La Garita appears to have been the largest explosive volcanic eruption documented so far, but it pales in comparison to the eruption of the Siberian basalt flows. These occurred about 250 million years ago, in concert with the biggest mass extinction of all time. Although these events did not produce ash clouds that covered the planet, they did release huge amounts of mantle gases that may have triggered a massive “super-greenhouse” global warming event. The thickness and volume of lava flows is truly staggering, estimated to be almost 4 million cubic kilometers of lavas, or about a thousand times as large as any of the eruptions discussed so far. The implications of this eruption will be addressed in chapter 12.
As the case histories have shown, most volcanoes explode with little or no warning, and when they explode, people in the immediate surrounding region have a small chance of survival. As soon as volcanoes become active and show signs of fumaroles and small earthquakes, it is time to evacuate areas closest to the mountain. Unfortunately, many of the historic eruptions before the birth of modern volcanology (such as Vesuvius, Krakatoa, and Mont Pelée) were not taken seriously, and many people died who should have evacuated. In many parts of the world, governments employ volcanologists to monitor volcanic activity and to give them warnings and recommendations. Some countries (especially Indonesia and the United States) that have frequent eruptions have researched their volcanoes and usually can influence the proper authorities to close and evacuate areas. In countries with little investment in geological research, however, government authorities may not understand the seriousness of the volcanic threat or may resent foreign intervention and ignore volcanologists’ recommendations, resulting in unnecessary loss of life when the eruption does come. Chapter 4 looks at the classic example of how Colombia failed to heed the warnings of volcanologists in the 1985 eruption of Nevado del Ruiz, resulting in thousands of deaths.
Volcanologists’ predictions are not easy or always precise. Many volcanoes show signs of life, accompanied by earthquakes, fumaroles, and even small explosive eruptions of ash, and then go dormant. When volcanologists order expensive evacuations and then no catastrophe strikes, ungrateful displaced people are resentful and may sue. As with earthquake prediction, predicting volcanoes can never be perfect because of our limited understanding of volcanoes and because not all volcanoes behave alike.
Still, there have been many successes. Most of the big eruptions in Indonesia in the past few decades were much less deadly because the government has taken volcanology seriously, and people heed warnings to evacuate. In 1980, Mount St. Helens erupted after plenty of warnings, so that most people were evacuated from a large area surrounding the volcano. The only exceptions were geologists who thought they were a safe distance away, and a few hard-headed individuals such as Harry Truman, a crusty old owner of Spirit Lake Lodge. Truman loved the media attention he received for thumbing his nose at authorities and declaring that he would die rather than leave his beloved forest. Unfortunately, he got his wish. Fifty-seven people lost their lives because Mount St. Helens surprised geologists by exploding in a giant sideways blast toward the north, rather than straight up. People closer to the volcano on the south, west, and east sides were not killed, but people up to 37 km (23 miles) to the north, farther than anyone expected, were killed. A well-known victim was Dave Johnston, a 30-year-old U.S. Geological Survey geologist, who had been monitoring the volcano for months. Johnston was the only geologist to predict correctly that Mount St. Helens would erupt with a lateral rather than vertical blast, based on studies of deposits from its past eruptions. His research pioneered the use of volcanic gases to predict an imminent eruption. Even he thought that his observation post 10 km (6 miles) to the north was at a safe distance when on the morning of May 18, 1980, the mountain’s north flank blew outward. His last recorded words were his excited radio message to his base in Vancouver, Washington, “Vancouver! Vancouver! This is it!” His body was never found, although the charred remains of his trailer were discovered in 1993.
Probably the most successful prediction of a serious volcanic event was the eruption of Mount Pinatubo in the Philippines in 1991, the second largest volcanic eruption of the twentieth century. It is one of hundreds of volcanoes in that island nation, due west of Manila on the island of Luzon, near Subic Bay Naval Base and Clark Air Force Base, American military bases that date back to the U.S. colonial era. Mount Pinatubo had been dormant in historic times (see Nova documentary, “In the Path of a Killer Volcano”), but on July 16, 1990, a 7.7 magnitude earthquake struck to the north, devastating the entire region, which may have triggered the upwelling of magma into Pinatubo. On March 15, 1991, Pinatubo awoke, with fumaroles of steam, fissures opening on the summit, and many small earthquakes. Geologists had mapped and dated the ancient deposits around the mountain and realized that it was likely to erupt in a huge explosion, with ash sheets and volcanic mudflows (lahars, which are discussed in chapter 4) on a gigantic scale. The U.S. Geological Survey monitored the activity from Clark Air Force Base and used Air Force planes and helicopters to observe the ash plumes, to take samples on the summit, to measure gases emitted by the vent, and to follow the eruption stages from seismographs placed all around the summit.
On June 3, the first significant magmatic eruption occurred, followed by a large explosion on June 7. The Philippine government heeded the U.S. and Filipino geologists and evacuated the area up to 20 km away from the summit. The mountain went through phases of quiescence and renewed activity, causing stress among geologists who rode the roller coaster of daily change and worried that premature warnings might lead to cynicism and discredit them. By June 14, geologists detected serious signs that the volcano was ready to blow and issued an alert to everyone within 40 km of the volcano, displacing 60,000 residents. Finally, tiltmeters showed that the volcano was becoming inflated, so geologists warned nearly everyone to evacuate, and most of the multi-million-dollar aircraft left Clark Air Force Base. Shortly after noon on June 14, seismographs suddenly stopped sending signals as they were incinerated by the first pyroclastic flows, and the mountain blew its top, turning the day into night and showering the nearby area with a rain of pumice and ash (made worse by a typhoon that struck at the same time). The last brave geologists and military personnel escaped as quickly as they could, and all survived their close call with death. Even though millions of people once lived near the volcano, only about 800 died, mostly killed by houses collapsing under the weight of wet volcanic ash, not by the blast. Economic misery for the Philippines went on for years though thousands survived. Both Subic Bay and Clark bases were too damaged for the United States to fix. With the end of the Cold War and Philippine resentment of their presence, the United States closed the bases and pulled out of the country permanently.
Fig. 3.8. The eruption of Eldfell volcano above the town buried houses to the eaves in ashes and cinders. (Photo courtesy USGS)
All of these andesite-dacite-rhyolite volcanoes are deadly and unpredictable, although geologists are getting better at it. Because of the size of volcanoes and explosive capacity, evacuating—not preventing their effects—is the only option. The less explosive basaltic volcanoes are different. Hawaii regularly experiences lava flows, yet almost no one dies, because lava is easier to outrun; major losses occur to fixed features, such as buildings, roads, and plantations. In one case, humans actually stopped volcanic eruptions from wreaking devastation.
On January 23, 1973, volcanic fissures opened up outside the fishing town of Heimaey, an island off the south coast of Iceland. Lava flows and a huge plume of cinders poured into the hastily evacuated town, but all 5,300 residents escaped, although the town was devastated (fig. 3.8). As the volcano (now named Eldfell) grew larger, it began to issue lava flows that spread around its base. It was soon clear that the flows might block off the harbor and destroy any chance that the town would be able to survive without its harbor and fishing fleet. So the Icelanders took action. They brought in a large number of hoses and pumps and blasted seawater at the front of the advancing lava flows, chilling them down and stopping them. This took several months throughout February and March, but eventually the eruption slowed and the lava flow stopped. The flows partly blocked the mouth of the harbor, creating a natural breakwater that improved the harbor. Normally, humans are at the mercy of volcanoes, but once in a while, it is possible for humans to stop nature actually in its tracks.
Decker, R., and B. Decker. 1981. Volcanoes. W. H. Freeman, New York.
McPhee, J. 1989. Cooling the lava. In The Control of Nature. Farrar, Straus and Giroux, New York.
Scarth, A. 1999. Vulcan’s Fury: Man against the Volcano. Yale University Press, New Haven, CT.
Walker, B. 1982. Volcanoes. Time-Life Books, Chicago.
Winchester, S. 2003. Krakatoa: The Day the World Exploded, 27 August 1883. HarperCollins, New York.
Zeilinga de Boer, J., and D. T. Sanders. 2002. Volcanoes in Human History: The Far-Reaching Effects of Major Eruptions. Princeton University Press, Princeton, NJ.
