Bill Bryson - A short history of nearly everything

The luckiest person on that day was a graduate student named Harry Glicken. He had been manning an observation post 5.7 miles from the mountain, but he had a college placement interview on May 18 in California, and so had left the site the day before the eruption. His place was taken by David Johnston. Johnston was the first to report the volcano exploding; moments later he was dead. His body was never found. Glicken’s luck, alas, was temporary. Eleven years later he was one of forty-three scientists and journalists fatally caught up in a lethal outpouring of superheated ash, gases, and molten rock-what is known as a pyroclastic flow-at Mount Unzen in Japan when yet another volcano was catastrophically misread.

Volcanologists may or may not be the worst scientists in the world at making predictions, but they are without question the worst in the world at realizing how bad their predictions are. Less than two years after the Unzen catastrophe another group of volcano watchers, led by Stanley Williams of the University of Arizona, descended into the rim of an active volcano called Galeras in Colombia. Despite the deaths of recent years, only two of the sixteen members of Williams’s party wore safety helmets or other protective gear. The volcano erupted, killing six of the scientists, along with three tourists who had followed them, and seriously injuring several others, including Williams himself.

In an extraordinarily unself-critical book called Surviving Galeras , Williams said he could “only shake my head in wonder” when he learned afterward that his colleagues in the world of volcanology had suggested that he had overlooked or disregarded important seismic signals and behaved recklessly. “How easy it is to snipe after the fact, to apply the knowledge we have now to the events of 1993,” he wrote. He was guilty of nothing worse, he believed, than unlucky timing when Galeras “behaved capriciously, as natural forces are wont to do. I was fooled, and for that I will take responsibility. But I do not feel guilty about the deaths of my colleagues. There is no guilt. There was only an eruption.”

But to return to Washington. Mount St. Helens lost thirteen hundred feet of peak, and 230 square miles of forest were devastated. Enough trees to build 150,000 homes (or 300,000 in some reports) were blown away. The damage was placed at $2.7 billion. A giant column of smoke and ash rose to a height of sixty thousand feet in less than ten minutes. An airliner some thirty miles away reported being pelted with rocks.

Ninety minutes after the blast, ash began to rain down on Yakima, Washington, a community of fifty thousand people about eighty miles away. As you would expect, the ash turned day to night and got into everything, clogging motors, generators, and electrical switching equipment, choking pedestrians, blocking filtration systems, and generally bringing things to a halt. The airport shut down and highways in and out of the city were closed.

All this was happening, you will note, just downwind of a volcano that had been rumbling menacingly for two months. Yet Yakima had no volcano emergency procedures. The city’s emergency broadcast system, which was supposed to swing into action during a crisis, did not go on the air because “the Sunday-morning staff did not know how to operate the equipment.” For three days, Yakima was paralyzed and cut off from the world, its airport closed, its approach roads impassable. Altogether the city received just five-eighths of an inch of ash after the eruption of Mount St. Helens. Now bear that in mind, please, as we consider what a Yellowstone blast would do.

IN THE 1960s, while studying the volcanic history of Yellowstone National Park, Bob Christiansen of the United States Geological Survey became puzzled about something that, oddly, had not troubled anyone before: he couldn’t find the park’s volcano. It had been known for a long time that Yellowstone was volcanic in nature-that’s what accounted for all its geysers and other steamy features-and the one thing about volcanoes is that they are generally pretty conspicuous. But Christiansen couldn’t find the Yellowstone volcano anywhere. In particular what he couldn’t find was a structure known as a caldera.

Most of us, when we think of volcanoes, think of the classic cone shapes of a Fuji or Kilimanjaro, which are created when erupting magma accumulates in a symmetrical mound. These can form remarkably quickly. In 1943, at Parícutin in Mexico, a farmer was startled to see smoke rising from a patch on his land. In one week he was the bemused owner of a cone five hundred feet high. Within two years it had topped out at almost fourteen hundred feet and was more than half a mile across. Altogether there are some ten thousand of these intrusively visible volcanoes on Earth, all but a few hundred of them extinct. But there is a second, less celebrated type of volcano that doesn’t involve mountain building. These are volcanoes so explosive that they burst open in a single mighty rupture, leaving behind a vast subsided pit, the caldera (from a Latin word for cauldron). Yellowstone obviously was of this second type, but Christiansen couldn’t find the caldera anywhere.

By coincidence just at this time NASA decided to test some new high-altitude cameras by taking photographs of Yellowstone, copies of which some thoughtful official passed on to the park authorities on the assumption that they might make a nice blow-up for one of the visitors’ centers. As soon as Christiansen saw the photos he realized why he had failed to spot the caldera: virtually the whole park-2.2 million acres-was caldera. The explosion had left a crater more than forty miles across-much too huge to be perceived from anywhere at ground level. At some time in the past Yellowstone must have blown up with a violence far beyond the scale of anything known to humans.

Yellowstone, it turns out, is a supervolcano. It sits on top of an enormous hot spot, a reservoir of molten rock that rises from at least 125 miles down in the Earth. The heat from the hot spot is what powers all of Yellowstone’s vents, geysers, hot springs, and popping mud pots. Beneath the surface is a magma chamber that is about forty-five miles across-roughly the same dimensions as the park-and about eight miles thick at its thickest point. Imagine a pile of TNT about the size of Rhode Island and reaching eight miles into the sky, to about the height of the highest cirrus clouds, and you have some idea of what visitors to Yellowstone are shuffling around on top of. The pressure that such a pool of magma exerts on the crust above has lifted Yellowstone and about three hundred miles of surrounding territory about 1,700 feet higher than they would otherwise be. If it blew, the cataclysm is pretty well beyond imagining. According to Professor Bill McGuire of University College London, “you wouldn’t be able to get within a thousand kilometers of it” while it was erupting. The consequences that followed would be even worse.

Superplumes of the type on which Yellowstone sits are rather like martini glasses-thin on the way up, but spreading out as they near the surface to create vast bowls of unstable magma. Some of these bowls can be up to 1,200 miles across. According to theories, they don’t always erupt explosively but sometimes burst forth in a vast, continuous outpouring-a flood-of molten rock, such as with the Deccan Traps in India sixty-five million years ago. ( Trap in this context comes from a Swedish word for a type of lava; Deccan is simply an area.) These covered an area of 200,000 square miles and probably contributed to the demise of the dinosaurs-they certainly didn’t help-with their noxious outgassings. Superplumes may also be responsible for the rifts that cause continents to break up.