rays that in the absence of magnetic protection would tear through ourbodies； leaving much of our dna in useless tatters。 when the magnetic field is working；these rays are safely herded away from the earth’s surface and into two zones in near spacecalled the van allen belts。 they also interact with particles in the upper atmosphere to createthe bewitching veils of light known as the auroras。
a big part of the reason for our ignorance； interestingly enough； is that traditionally therehas been little effort to coordinate what’s happening on top of the earth with what’s going oninside。 according to shawna vogel： “geologists and geophysicists rarely go to the samemeetings or collaborate on the same problems。”
perhaps nothing better demonstrates our inadequate 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 understanding than the eruption ofmount st。 helens in washington in 1980。
at that time； the lower forty…eight united states had not seen a volcanic eruption for oversixty…five years。 therefore the government volcanologists called in to monitor and forecast st。
helens’s behavior primarily had seen only hawaiian volcanoes in action； and they； it turnedout； 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 hundred times a day； and being constantly 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 attraction for the world。
newspapers 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 than seventy 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 volcano wasn’t going to blow after all。
on april 19 the northern flank of the mountain began to bulge conspicuously。 remarkably；no one in a position of responsibility saw that this strongly signaled a lateral blast。 theseismologists resolutely based their conclusions on the behavior of hawaiian volcanoes；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 munity college in taa。 hepointed out that st。 helens didn’t have an open vent； as hawaiian volcanoes 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 next。 at 8：32 a。m。 on a sunday morning； may 18； the northside of the volcano 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。 aminute later； its flank severely weakened； st。 helens exploded with the force of five hundredhiroshima…sized atomic bombs； 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 volcano； 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 sunday。 had it been a weekday many lumber workers would have beenworking within the death zone。 as it was； people were killed eighteen miles away。
the luckiest person on that day was a graduate student named harry glicken。 he had beenmanning an observation post 5。7 miles from the mountain； but he had a college placementinterview 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 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 alethal outpouring of superheated ash； gases； and molten rock—what is known as a pyroclasticflow—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 bystanley williams of the university of arizona； descended into the rim of an active volcanocalled galeras in colombia。 despite the deaths of recent years； only two of the sixteenmembers 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； andseriously 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 worldof volcanology had suggested that he had overlooked or disregarded important seismic signalsand behaved recklessly。 “how easy it is to snipe after 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 an eruption。”
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 was placed at 2。7 billion。 a giant column ofsmoke and ash rose to a height of sixty thousand feet in less than ten minutes。 an airlinersome thirty miles away reported being pelted with rocks。
ninety minutes after the blast； ash began to rain down on yakima； washington； amunity of fifty thousand people about eighty miles away。 as you would expect； the ashturned day to night and got into everything； clogging motors； generators； and electricalswitching equipment； choking pedestrians； blocking 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 volcano that had been rumblingmenacingly for two months。 yet yakima had no volcano emergency procedures。 the city’semergency broadcast system； which was supposed to swing into action during a crisis； did notgo 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； 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 consider what ayellowstone blast would do。
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15DANGEROUS BEAUTY
生小说＿网
in the 1960s； while studying the volcanic history of yellowstone national park； bobchristiansen 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 knownfor a long time that yellowstone was volcanic in nature—that’s what accounted for all itsgeysers and other steamy features—and the one thing about volcanoes is that they aregenerally pretty conspicuous。 but christiansen couldn’t find the yellowstone volcanoanywhere。 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 orkilimanjaro； 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 tosee smoke rising from a patch on his land。 in one week he was the bemused owner of a conefive hundred feet high。 within two years it had topped out at almost fourteen hundred feet andwas more than half a mile across。 altogether there are some ten thousand of these intrusivelyvisible volcanoes on earth； all but a few hundred of them extinct。 but there is a second； lesscelebrated type of volcano that doesn’t involve mountain building。 these are volcanoes soexplosive 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 bytaking photographs of yellowstone； copies of which some thoughtful official passed