14 THE FIRE BELOW

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    IN THE SUMMER of 1971, a young geologist named Mike Voorhies was scouting around onsome grassy farmland iern Nebraska, not far from the little town of Orchard, where hehad grown up. Passing through a steep-sided gully, he spotted a curious glint in the brushabove and clambered up to have a look. What he had seen was the perfectly preserved skull ofa young rhinoceros, which had been washed out by ret heavy rains.

    A few yards beyond, it turned out, was one of the most extraordinary fossil beds everdiscovered in North America, a dried-up water hole that had served as a mass grave for scoresof animals—rhinoceroses, zebra-like horses, saber-toothed deer, camels, turtles. All had diedfrom some mysterious cataclysm just uwelve million years ago iime known togeology as the Mioe. In those days Nebraska stood on a vast, hot plain very like theSerei of Africa today. The animals had been found buried under volic ash up to te deep. The puzzle of it was that there were not, and never had been, any voloes inNebraska.

    Today, the site of Voorhies’s discovery is called Ashfall Fossil Beds State Park, and it has astylish new visitors’ ter and museum, with thoughtful displays on the geology of Nebraskaand the history of the fossil beds. The ter incorporates a lab with a glass wall throughwhich visitors  watch paleontologists ing bones. W alone in the lab on them I passed through was a cheerfully grizzled-looking fellow in a blue work shirt whnized as Mike Voorhies from a BBC television dotary in which he featured.

    They don’t get a huge number of visitors to Ashfall Fossil Beds State Park—it’s slightly inthe middle of nowhere—and Voorhies seemed pleased to show me around. He took me to thespot atop a twenty-foot ravine where he had made his find.

    “It was a dumb place to look for bones,” he said happily. “But I wasn’t looking for bones. Iwas thinking of making a geological map of eastern Nebraska at the time, and really just kindof poking around. If I hadn’t gone up this ravine or the rains hadn’t just washed out that skull,I’d have walked on by and this would never have been found.” He indicated a roofedenclosure nearby, which had bee the main excavation site. Some two hundred animalshad been found lying together in a jumble.

    I asked him in what way it was a dumb place to hunt for bones. “Well, if you’re looking forbones, you really need exposed rock. That’s why most paleontology is done in hot, dry places.

    It’s not that there are more bohere. It’s just that you have some ce of spotting them.

    In a setting like this”—he made a sweepiure across the vast and unvarying prairie—“you wouldn’t know where to begin. There could be really magnifit stuff out there, butthere’s no surface clues to show you where to start looking.”

    At first they thought the animals were buried alive, and Voorhies stated as mu aNational Geographic article in 1981. “The article called the site a ‘Pompeii of prehistoriimals,’ ” he told me, “which was unfortunate because just afterward we realized that theanimals hadn’t died suddenly at all. They were all suffering from something calledhypertrophic pulmonary osteodystrophy, which is what you would get if you were breathing alot of abrasive ash—and they must have beehing a lot of it because the ash was feetthick for hundreds of miles.” He picked up a k of grayish, claylike dirt and crumbled itinto my hand. It owdery but slightly gritty. “Nasty stuff to have to breathe,” he went on,“because it’s very fi also quite sharp. So anyway they came here to this watering hole,presumably seeking relief, and died in some misery. The ash would have ruined everything. Itwould have buried all the grass and coated every leaf and turhe water into an undrinkablegray sludge. It couldn’t have been very agreeable at all.”

    The BBentary had suggested that the existence of so much ash in Nebraska rise. In faebraska’s huge ash deposits had been known about for a long time. Foralmost a tury they had been mio make household ing powders like et andAjax. But curiously no one had ever thought to wonder where all the ash came from.

    “I’m a little embarrassed to tell you,” Voorhies said, smiling briefly, “that the first I thoughtabout it was when aor at the National Geographic asked me the source of all the ash andI had to fess that I didn’t know. Nobody knew.”

    Voorhies sent samples to colleagues all over the western Uates asking if there wasanything about it that they reized. Several months later a geologist named BillBonni from the Idaho Geological Survey got in toud told him that the ash matcheda volic deposit from a place called Bruneau-Jarbidge in southwest Idaho. The event thatkilled the plains animals of Nebraska was a volic explosion on a scale previouslyunimagined—but big enough to leave an ash layer te deep almost a thousand miles awayiern Nebraska. It turned out that uhe western Uates there was a hugecauldron of magma, a colossal volic hot spot, which erupted cataclysmically every600,000 years or so. The last such eruption was just over 600,000 years ago. The hot spot isstill there. These days we call it Yellowston?９9lｉｂ?ional Park.

    We know amazingly little about what happeh our feet. It is fairly remarkable tothink that Ford has been building cars and baseball has been playing World Series for lohan we have known that the Earth has a core. And of course the idea that the tis moveabout on the surface like lily pads has been on wisdom for much less than a geion.

    “Strange as it may seem,” wrote Richard Feynman, “we uand the distribution of matterierior of the Sun far better than we uand the interior of the Earth.”

    The distance from the surface of Earth to the ter is 3,959 miles, which isn’t so very far.

    It has been calculated that if you sunk a well to the ter and dropped a brito it, it wouldtake only forty-five minutes for it to hit the bottom (though at that point it would beweightless since all the Earth’s gravity would be above and around it rather thah it).

    Our own attempts to pee toward the middle have been modest indeed. One or two SouthAfri gold mines reach to a depth of two miles, but most mines oh go no more thanabout a quarter of a mile beh the surface. If the pla were an apple, we wouldn’t yethave broken through the skin. Indeed, we haven’t even e close.

    Until slightly under a tury ago, what the best-informed stifids knew aboutEarth’s interior was not much more than what a iner knew—namely, that you could digdown through soil for a distand then you’d hit rod that was about it. Then in 1906,an Irish geologist named R. D. Oldham, while examining some seismograph readings from ahquake in Guatemala, noticed that certain shock waves had peed to a point deepwithin the Earth and then bounced off at an angle, as if they had entered some kind ofbarrier. From this he deduced that the Earth has a core. Three years later a Croatianseismologist named Andrija Mohorovi?i′c was studying graphs from ahquake in Zagrebwheiced a similar odd defle, but at a shallower level. He had discovered theboundary between the crust and the layer immediately below, the mahis zone has beenknown ever since as the Mohorovi?i′c distinuity, or Moho for short.

    We were beginning to get a vague idea of the Earth’s layered interior—though it really wasonly vague. Not until 1936 did a Danish stist named Inge Lehmann, studyingseismographs of earthquakes in New Zealand, discover that there were two cores—an innerohat we now believe to be solid and an outer ohe ohat Oldham had detected) thatis thought to be liquid and the seat of magism.

    At just about the time that Lehmann was refining our basiderstanding of the Earth’sinterior by studying the seismic waves of earthquakes, two geologists at Calte Californiawere devising a way to make parisoween ohquake and the . They wereCharles Richter and Beno Gutenberg, though for reasons that have nothing to do with fairhe scale became known almost at once as Richter’s alone. (It has nothing to do with Richtereither. A modest fellow, he never referred to the scale by his own name, but always called it“the Magnitude Scale.”)The Richter scale has always been widely misuood by noists, though perhapsa little less so now than in its early days when visitors to Richter’s office often asked to seehis celebrated scale, thinking it was some kind of mae. The scale is of course more ahan an object, an arbitrary measure of the Earth’s tremblings based on surfacemeasurements. It rises expoially, so that a 7.3 quake is fifty times more powerful than a6.3 earthquake and 2,500 times more powerful than a 5.3 earthquake.

    At least theoretically, there is no upper limit for ahquake—nor, e to that, a lowerlimit. The scale is a simple measure of force, but says nothing about damage. A magnitude 7quake happening deep in the mantle—say, four hundred miles down—might cause no surfacedamage at all, while a signifitly smaller one happening just four miles uhe surfacecould wreak widespread devastation. Much, too, depends oure of the subsoil, thequake’s duration, the frequend severity of aftershocks, and the physical setting of theaffected area. All this means that the most fearsome quakes are not necessarily the mostforceful, though force obviously ts for a lot.

    The largest earthquake sihe scale’s iion was (depending on which source youcredit) either oered on Prince William Sound in Alaska in March 1964, whichmeasured 9.2 on the Richter scale, or one in the Pacific O off the coast of Chile in 1960,which was initially logged at 8.6 magnitude but later revised upward by some authorities(including the Uates Geological Survey) to a truly grand-scale 9.5. As you will gatherfrom this, measurihquakes is not always a sce, particularly wheninterpreting readings from remote locations. At all events, both quakes were whopping. The1960 quake not only caused widespread damage across coastal South America, but also set offa giant tsunami that rolled six thousand miles across the Pacifid slapped away much ofdowntown Hilo, Hawaii, destroying five hundred buildings and killing sixty people. Similarwave surges claimed yet more victims as far away as Japan and the Philippines.

    For pure, focused, devastation, however, probably the most intehquake in recordedhistory was ohat strud essentially shook to pieces—Lisbon, Pal, on All SaintsDay (November 1), 1755. Just before ten in the m, the city was hit by a suddensideways lurow estimated at magnitude 9.0 and shaken ferociously for seven full minutes.

    The vulsive force was so great that the water rushed out of the city’s harbor aurnedin a wave fifty feet high, adding to the destru. When at last the motion ceased, survivorsenjoyed just three minutes of calm before a sed shock came, only slightly less severe thanthe first. A third and final shock followed two hours later. At the end of it all, sixty thousandpeople were dead and virtually every building for miles reduced to rubble. The San Franciscoearthquake of 1906, for parison, measured aimated 7.8 on the Richter scale andlasted less than thirty seds.

    Earthquakes are fairly on. Every day on average somewhere in the world there aretwo of magnitude 2.reater—that’s enough to give anyone nearby a pretty good jolt.

    Although they tend to cluster iain plaotably around the rim of the Pacific—they occur almost anywhere. In the Uates, only Florida, eastern Texas, and the upperMidwest seem—so far—to be almost entirely immune. New England has had two quakes ofmagnitude 6.reater in the last two hundred years. In April 2002, the region experienceda 5.1 magnitude shaking in a quake near Lake Champlain on the New York–Vermont border,causiensive local damage and (I  attest) knog pictures from walls and childrenfrom beds as far away as Neshire.

    The most on types of earthquakes are those where two plates meet, as in Californiaalong the San Andreas Fault. As the plates push against each other, pressures build up untilone or the ives way. In general, the lohe interval between quakes, the greater thepent-up pressure and thus the greater the scope for a really big jolt. This is a particular worryfor Tokyo, which Bill McGuire, a hazards specialist at Uy College London, describesas “the city waiting to die” (not a motto you will find on many tourism leaflets). Tokyo standson the boundary of three teic plates in a try already well known for its seismistability. In 1995, as you will remember, the city of Kobe, three hundred miles to the west,was struck by a magnitude 7.2 quake, which killed 6,394 people. The damage was estimatedat $99 billion. But that was as nothing—well, as paratively little—pared with whatmay await Tokyo.

    Tokyo has already suffered one of the most devastatihquakes in modern times. Oember 1, 1923, just before noon, the city was hit by what is known as the Great Kantoquake—a more thaimes more powerful than Kobe’s earthquake. Two huhousand people were killed. Sihat time, Tokyo has been eerily quiet, so the straih the surface has been building fhty years. Eventually it is bound to snap. In 1923,Tokyo had a population of about three million. Today it is approag thirty million. Nobodycares to guess hoeople might die, but the potential eic cost has been put ashigh as $7 trillion.

    Even more unnerving, because they are less well uood and capable of anywhere at any time, are the rarer type of shakings known as intraplate quakes. Thesehappen away from plate boundaries, which makes them wholly uable. And becausethey e from a much greater depth, they tend tate over much wider areas. Themost notorious such quakes ever to hit the Uates were a series of three in NewMadrid, Missouri, in the winter of 1811–12. The advearted just after midnight onDecember 16 when people were awakened first by the noise of panig farm animals (therestiveness of animals before quakes is not an old wives’ tale, but is in fact well established,though not at all uood) and then by an almighty rupturing noise from deep withih. Emerging from their houses, locals found the land rolling in waves up to three feet highand opening up in fissures several feet deep. A strong smell of sulfur filled the air. Theshaking lasted for four minutes with the usual devastating effects to property. Among thewitnesses was the artist John James Audubon, who happeo be in the area. The quakeradiated outward with such force that it knocked down eys in ati four hundredmiles away and, acc to at least one at, “wrecked boats i Coast harbors and .

    . . even collapsed scaffoldied around the Capitol Building in Washington, D.C.” OnJanuary 23 and February 4 further quakes of similar magnitude followed. New Madrid hasbeen silent ever si not surprisingly, since such episodes have never been known tohappen in the same place twice. As far as we know, they are as random as lightning. The one could be under Chicago or Paris or Kinshasa. No one  even begin to guess. And whatcauses these massive intraplate rupturings? Something deep within the Earth. More than thatwe don’t know.

    By the 1960s stists had grown suffitly frustrated by how little they uood ofthe Earth’s interior that they decided to try to do something about it. Specifically, they got theidea to drill through the o floor (the tial crust was too thick) to the Mohodistinuity and to extract a<s></s> piece of the Earth’s mantle for examination at leisure. Thethinking was that if they could uand the nature of the rocks ihe Earth, they mightbegin to uand how they ied, and thus possibly be able to predict earthquakes andother unwele events.

    The project became known, all but iably, as the Mohole and it retty welldisastrous. The hope was to lower a drill through 14,000 feet of Pacific O water off thecoast of Mexid drill some 17,000 feet through relatively thin crustal rock. Drilling froma ship in open waters is, in the words of one oographer, “like trying to drill a hole in thesidewalks of New York from atop the Empire State Building using a strand of spaghetti.”

    Every attempt ended in failure. The deepest they peed was only about 600 feet. TheMohole became known as the No Hole. In 1966, exasperated with ever-rising costs and s, gress killed the project.

    Four years later, Soviet stists decided to try their lu dry land. They chose a spot onRussia’s Kola Peninsula, he Finnish border, ao work with the hope of drilling toa depth of fifteen kilometers. The work proved harder than expected, but the Soviets wereendably persistent. When at last they gave up, een years later, they had drilled to adepth of 12,262 meters, or about 7.6 miles. Bearing in mind that the crust of the Earthrepresents only about 0.3 pert of the pla’s volume and that the Kola hole had not cutevehird of the way through the crust, we  hardly claim to have quered theinterior.

    Iingly, even though the hole was modest, nearly everything about it was surprising.

    Seismic wave studies had led the stists to predict, and pretty fidently, that they wouldenter sedimentary rock to a depth of 4,700 meters, followed by granite for the  2,300meters and basalt from there on down. In the event, the sedimentary layer was 50 pertdeeper than expected and the basaltic layer was never found at all. Moreover, the world downthere was far warmer than anyone had expected, with a temperature at 10,000 meters of 180degrees tigrade, nearly twice the forecasted level. Most surprising of all was that the rockat that depth was saturated with water—something that had not been thought possible.

    Because we ’t see into the Earth, we have to use other teiques, which mostly involvereading waves as they travel through the interior. We also know a little bit about the mantlefrom what are known as kimberlite pipes, where diamonds are formed. What happens is thatdeep in the Earth there is an explosion that fires, in effect, a onball of magma to thesurface at supersonic speeds. It is a totally random event. A kimberlite pipe could explode inyour backyard as you read this. Because they e up from such depths—up to 120 milesdown—kimberlite pipes bring up all kinds of things not normally found on or hesurface: a rock called peridotite, crystals of olivine, and—just occasionally, in about one pipein a hundred—diamonds. Lots of carbon es up with kimberlite ejecta, but most isvaporized or turns to graphite. Only occasionally does a hunk of it shoot up at just the rightspeed and cool down with the necessary swifto bee a diamond. It was such a pipethat made Johannesburg the most productive diamond mining city in the world, but there maybe others even bigger that we don’t know about. Geologists know that somewhere in theviity of northeastern Indiana there is evidence of a pipe roup of pipes that may be trulycolossal. Diamonds up to twenty carats or more have been found at scattered sites throughoutthe region. But no one has ever found the source. As John McPhee notes, it may be buriedunder glacially deposited soil, like the Manson crater in Iowa, or uhe Great Lakes.

    So how much do we know about what’s ihe Earth? Very little. Stists aregenerally agreed that the world beh us is posed of four layers—rocky outer crust, amantle of hot, viscous rock, a liquid outer core, and a solid inner core.

    1We know that thesurface is dominated by silicates, which are relatively light and not heavy enough to atfor the pla’s overall density. Therefore there must be heavier stuff inside. We know that togee ic field somewhere ierior there must be a trated belt ofmetallic elements in a liquid state. That much is universally agreed upon. Almost everythingbeyond that—how the layers i, what causes them to behave in the way they do, whatthey will do at any time iure—is a matter of at least some uainty, and generallyquite a lot of uainty.

    Even the one part of it we  see, the crust, is a matter of some fairly stridee.

    Nearly all geology texts tell you that tial crust is three to six miles thider theos, about twenty-five miles thider the tis, and forty to sixty miles thider big mountain s, but there are many puzzling variabilities within thesegeneralizations. The crust beh the Sierra Nevada Mountains, for instance, is only abouteen to twenty-five miles thick, and no one knows why. By all the laws of geophysics theSierra Nevadas should be sinking, as if into quid. (Some people think they may be.)1For those who crave a more detailed picture of the Earths interior, here are the dimensions of the variouslayers, using average figures: From 0 to 40 km (25 mi) is the crust. From 40 to 400 km (25 to 250 mi) is theupper mantle. From 400 to 650 km (250 to 400 mi) is a transition zoween the upper and lower mantle.

    From 650 to 2,700 km (400 to 1,700 mi) is the lower mantle. From 2,700 to 2,890 km (1,700 to 1,900 mi) is the&quot;D&quot; layer. From 2,890 to 5,150 km (1,900 to 3,200 mi) is the outer core, and from 5,150 to 6,378 km (3,200 to3,967 mi) is the inner core.

    How and when the Earth got its crust are questions that divide geologists into two broadcamps—those who think it happened abruptly early in the Earth’s history and those who thinkit happened gradually and rather later. Strength of feeling runs deep on such matters. RichardArmstrong of Yale proposed an early-burst theory in the 1960s, thehe rest of hiscareer fighting those who did not agree with him. He died of cer in 1991, but shortlybefore his death he “lashed out at his criti a polemi an Australiah sce journalthat charged them with perpetuating myths,” acc to a report ih magazine in 1998.

    “He died a bitter man,” reported a colleague.

    The crust and part of the outer maogether are called the lithosphere (from the Greeklithos, meaning “stone”), whi turn floats on top of a layer of softer rock called theasthenosphere (from Greek words meaning “without strength”), but such terms are irely satisfactory. To say that the lithosphere floats on top of the asthenosphere suggests adegree of easy buoyancy that isn’t quite right. Similarly it is misleading to think of the rocksas flowing in anything like the way we think of materials flowing on the surface. The rocksare viscous, but only in the same way that glass is. It may not look it, but all the glass ohis flowing downward uhe relentless drag of gravity. Remove a pane of really old glassfrom the window of a European cathedral and it will be noticeably thicker at the bottom thanat the top. That is the sort of “flow” we are talking about. The hour hand on a ovesabout ten thousand times faster than the “flowing” rocks of the mantle.

    The movements ocot just laterally as the Earth’s plates move across the surface, but upand down as well, as rocks rise and fall uhe ing process known as ve.

    ve as a process was first deduced by the etric t von Rumford at the end ofthe eighteenth tury. Sixty years later an English viamed Osmond Fisher prestlysuggested that the Earth’s interiht well be fluid enough for the tents to move about,but that idea took a very long time to gain support.

    In about 1970, when geophysicists realized just how much turmoil was going on downthere, it came as a siderable shock. As Shawna Vogel put it in the book Naked Earth: TheNew Geophysics: “It was as if stists had spent decades figuring out the layers of theEarth’s atmosphere—troposphere, stratosphere, and so forth—and then had suddenly foundout about wind.”

    How deep the ve process goes has been a matter of troversy ever since. Somesay i<bdi></bdi>t begins four hundred miles down, others two thousand miles below us. The problem, asDonald Trefil has observed, is that “there are two sets of data, from two different disciplihat ot be reciled.” Geochemists say that certais oh’s surface othave e from the upper mantle, but must have e from deeper within the Earth.

    Therefore the materials in the upper and lower mantle must at least occasionally mix.

    Seismologists insist that there is no evideo support such a thesis.

    So all that  be said is that at some slightly ierminate point as we head toward theter of Earth we leave the asthenosphere and pluo pure mantle. sidering that itats for 82 pert of the Earth’s volume and 65 pert of its mass, the mantle doesn’tattract a great deal of attention, largely because the things that i Earth stists andgeneral readers alike happeher deeper down (as with magism) or he surface (aswith earthquakes). We know that to a depth of about a hundred miles the mantle sistspredominantly of a type of rooeridotite, but what fills the space beyond isuain. Acc to a Nature report, it seems not to be peridotite. More than this we donot know.

    Beh the mantle are the two cores—a solid inner core and a liquid outer one. Needless tosay, our uanding of the nature of these cores is i, but stists  make somereasonable assumptions. They know that the pressures at the ter of the Earth aresuffitly high—something over three million times those found at the surface—to turn anyrock there solid. They also know from Earth’s history (among other clues) that the inner coreis very good at retaining its heat. Although it is little more than a guess, it is thought that inover four billion years the temperature at the core has fallen by no more than 200°F. No oneknows exactly how hot the Earth’s core is, but estimates range from something over 7,000°Fto 13,000°F—about as hot as the surface of the Sun.

    The outer core is in many ways even less well uood, though everyone is in agreementthat it is fluid and that it is the seat of magism. The theory ut forward by E. C.

    Bullard of Cambridge Uy in 1949 that this fluid part of the Earth’s core revolves in away that makes it, in effect, arical motor, creating the Earth’s magic field. Theassumption is that the veg fluids in the Earth aehow like the currents in wires.

    Exactly what happens isn’t known, but it is felt pretty certain that it is ected with the corespinning and with its being liquid. Bodies that don’t have a liquid core—the Moon and Mars,for instance—don’t have magism.

    We know that Earth’s magic field ges in power from time to time: during the age ofthe dinosaurs, it  to three times as strong as now. We also know that it reverses itselfevery 500,000 years or so on average, though that average hides a huge degree ofuability. The last reversal was about 750,000 years ago. Sometimes it stays put formillions of years—37 million years appears to be the lo stretd at other times it hasreversed after as little as 20,000 years. Altogether in the last 100 million years it has reverseditself about two huimes, and we don’t have any real idea why. It has been called “thegreatest unanswered question in the geological sces.”

    We may be going through a reversal now. The Earth’s magic field has diminished byperhaps as much as 6 pert in the last tury alone. Any diminution in magism is likelyto be bad news, because magism, apart from holding o refrigerators and keeping ourpasses pointing the right lays a vital role in keeping us alive. Space is full ofdangerous ic rays that in the absenagic prote would tear through ourbodies, leaving much of our DNA in useless tatters. When the magic field is w,these rays are safely herded away from the Earth’s surfad into two zones in near spacecalled the Van Alles. They also i with particles in the upper atmosphere to createthe bewitg veils of light known as the auroras.

    A big part of the reason for norance, iingly enough, is that traditionally therehas been little effort to coordinate what’s happening on top of the Earth with what’s going oninside. Acc to Shawna Vogel: “Geologists and geophysicists rarely go to the samemeetings or collaborate on the same problems.”

    Perhaps nothier demonstrates our ie grasp of the dynamics of the Earth’sinterior than how badly we are caught out when it acts up, and it would be hard to e upwith a more salutary reminder of the limitations of our uanding than the eruption ofMount St. Helens in Washington in 1980.

    At that time, the lower forty-eight Uates had not seen a volic eruption for oversixty-five years. Therefore the gover volologists called in to monitor and forecast St.

    Helens’s behavior primarily had seen only Hawaiian voloes in a, and they, it tur, were not the same thing at all.

    St. Helens started its ominous rumblings on March 20. Within a week it was eruptingmagma, albeit in modest amounts, up to a huimes a day, and being stantly shakenwith earthquakes. People were evacuated to what was assumed to be a safe distance of eightmiles. As the mountain’s rumblings grew St. Helens became a tourist attra for the world.

    Neers gave daily reports on the best places to get a view. Television crews repeatedlyflew in helicopters to the summit, and people were even seen climbing over the mountain. Onone day, more thay copters and light aircraft circled the summit. But as the dayspassed and the rumblings failed to develop into anything dramatic, people grew restless, andthe view became general that the volo wasn’t going to blow after all.

    On April 19 the northern flank of the mountain began to bulge spicuously. Remarkably,no one in a position of responsibility saw that this strongly signaled a lateral blast. Theseismologists resolutely based their clusions on the behavior of Hawaiian voloes,which don’t blow out sideways. Almost the only person who believed that something reallybad might happen was Jack Hyde, a geology professor at a unity college in Taa. Hepointed out that St. Helens didn’t have an ope, as Hawaiian voloes have, so anypressure building up inside was bound to be released dramatically and probablycatastrophically. However, Hyde was not part of the official team and his observationsattracted little notice.

    We all know what happened . At 8:32 A.M. on a Sunday m, May 18, the northside of the volo collapsed, sending an enormous avalanche of dirt and rock rushing downthe mountain slope at 150 miles an hour. It was the biggest landslide in human history andcarried enough material to bury the whole of Manhattan to a depth of four hundred feet. Amier, its flank severely weakened, St. Helens exploded with the force of five hundredHiroshima-sized atomibs, shooting out a murderous hot cloud at up to 650 miles anhour—much too fast, clearly, for anyone nearby to outrace. Many people who were thought tobe in safe areas, often far out of sight of the volo, were overtaken. Fifty-seven people werekilled. Twenty-three of the bodies were never found. The toll would have been much higherexcept that it was a Su></a>nday. Had it been a weekday many lumber workers would have beenw within the death zone. As it eople were killed eighteen miles away.

    The luckiest person on that day was a graduate student named Harry Gli. He had beenmanning an observation post 5.7 miles from the mountain, but he had a college platinterview on May 18 in California, and so had left the site the day before the eruption. Hisplace was taken by David Johnston. Johnston was the first to report the volo exploding;moments later he was dead. His body was never found. Gli’s luck, alas, was temporary.

    Eleven years later he was one of forty-three stists and journalists fatally caught up ihal outp of superheated ash, gases, and molten rock—what is known as a pyroclasticflow—at Mount Unzen in Japan whe another volo was catastrophically misread.

    Volologists may or may not be the worst stists in the world at making predis,but they are without question the worst in the world at realizing how bad their predis are.

    Less than two years after the Unzen catastrophe anroup of volo watchers, led byStanley Williams of the Uy of Arizona, desded into the rim of an active volocalled Galeras in bia. Despite the deaths of ret years, only two of the sixteenmembers of Williams’s party wore safety helmets or other protective gear. The voloerupted, killing six of the stists, along with three tourists who had followed them, andseriously injuring several others, including Williams himself.

    In araordinarily 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 worldof volology had suggested that he had overlooked or disregarded important seismic signalsand behaved recklessly. “How easy it is to ser the fact, to apply the knowledge wehave now to the events of 1993,” he wrote. He was guilty of nothing worse, he believed, thanunlucky timing when Galeras “behaved capriciously, as natural forces are wont to do. I wasfooled, and for that I will take responsibility. But I do not feel guilty about the deaths of mycolleagues. There is no guilt. There was only aion.”

    But to return to Washington. Mount St. Helens lost thirteen hundred feet of peak, and 230square miles of forest were devastated. Enough trees to build 150,000 homes (or 300,000 insome reports) were blown away. The damage laced at $2.7 billion. A giant n ofsmoke and ash rose to a height of sixty thousa ihan ten minutes. An airlinersome thirty miles away reported beied with rocks.

    y  minutes  after  the  blast, ash  began to rain down on Yakima, Washington, aunity of fifty thousand people about eighty miles away. As you would expect, the ashturned day to night and got into everything, clogging meors, aricalswitg equipment, chokirians, blog filtration systems, and generally bringingthings 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 volo that had been rumblingmenagly for two months. Yet Yakima had no volergency procedures. The city’semergency broadcast system, which was supposed to swing into a during a crisis, did notgo on the air because “the Sunday-m staff did not know how to operate the equipment.”

    For three days, Yakima aralyzed and cut off from the world, its airport closed, itsapproach roads impassable. Altogether the city received just five-eighths of an inch of ashafter the eruption of Mount St. Helens. Now bear that in mind, please, as we sider what aYellowstone blast would do.

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