万物简史英文版_比尔·布莱森-第42章

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t　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鈥檚　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鈥檚　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鈥檛　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鈥檛　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鈥檛　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鈥攎uch　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鈥檚　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鈥攚hat　is　known　as　a　pyroclasticflow鈥攁t　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鈥檚　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鈥渙nly　shake　my　head　in　wonder鈥潯�when　he　learned　afterward　that　his　colleagues　in　the　worldof　volcanology　had　suggested　that　he　had　overlooked　or　disregarded　important　seismic　signalsand　behaved　recklessly。　鈥渉ow　easy　it　is　to　snipe　after　the　fact；　to　apply　the　knowledge　wehave　now　to　the　events　of　1993；鈥潯�he　wrote。　he　was　guilty　of　nothing　worse；　he　believed；　thanunlucky　timing　when　galeras　鈥渂ehaved　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。鈥�

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鈥檚emergency　broadcast　system；　which　was　supposed　to　swing　into　action　during　a　crisis；　did　notgo　on　the　air　because　鈥渢he　sunday…morning　staff　did　not　know　how　to　operate　the　equipment。鈥�

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。

锛凤挤w。xi锛�os锛╱otxt。锛ｏ集锛�



15　　　　DANGEROUS　BEAUTY


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鈥檛　find　the　park鈥檚　volcano。　it　had　been　knownfor　a　long　time　that　yellowstone　was　volcanic　in　nature鈥攖hat鈥檚　what　accounted　for　all　itsgeysers　and　other　steamy　features鈥攁nd　the　one　thing　about　volcanoes　is　that　they　aregenerally　pretty　conspicuous。　but　christiansen　couldn鈥檛　find　the　yellowstone　volcanoanywhere。　in　particular　what　he　couldn鈥檛　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　par铆cutin　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鈥檛　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鈥檛　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　on　to　thepark　authorities　on　the　assumption　that　they　might　make　a　nice　blow…up　for　one　of　thevisitors鈥櫋�centers。　as　soon　as　christiansen　saw　the　photos　he　realized　why　he　had　failed　to　spotthe　caldera：　virtually　the　whole　park鈥�2。2　million　acres鈥攚as　caldera。　the　explosion　had　lefta　crater　more　than　forty　miles　across鈥攎uch　too　huge　to　be　perceived　from　anywhere　atground　level。　at　some　time　in　the　past　yellowstone　must　have　blown　up　with　a　violence　farbeyond　the　scale　of　anything　known　to　humans。

yellowstone；　it　turns　out；　is　a　supervolcano。　it　sits　on　top　of　an　enormous　hot　spot；　areservoir　of　molten　rock　that　rises　from　at　least　125　miles　down　in　the　earth。　the　heat　fromthe　hot　spot　is　what　powers　all　of　yellowstone鈥檚　vents；　geysers；　hot　springs；　and　popping　mudpots。　beneath　the　surface　is　a　magma　chamber　that　is　about　forty…five　miles　across鈥攔oughlythe　same　dimensions　as　the　park鈥攁nd　about　eight　miles　thick　at　its　thickest　point。　imagine　apile　of　tnt　about　the　size　of　rhode　island　and　reaching　eight　miles　into　the　sky；　to　about　theheight　of　the　highest　cirrus　clouds；　and　you　have　some　idea　of　what　visitors　to　yellowstoneare　shuffling　around　on　top　of。　the　pressure　that　such　a　pool　of　magma　exerts　on　the　crustabove　has　lifted　yellowstone　and　about　three　hundred　miles　of　surrounding　territory　about1；700　feet　higher　than　they　would　otherwise　be。　if　it　blew；　the　cataclysm　is　pretty　well　beyondimagining。　according　to　professor　bill　mcguire　of　university　college　london；　鈥測ouwouldn鈥檛　be　able　to　get　within　a　thousand　kilometers　of　it鈥潯�while　it　was　erupting。　theconsequences　that　followed　would　be　even　worse。

superplumes　of　the　type　on　which　yellowstone　sits　are　rather　like　martini　glasses鈥攖hin　onthe　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鈥檛always　erupt　explosively　but　sometimes　burst　forth　in　a　vast；　continuous　outpouring鈥攁flood鈥攐f　molten　rock；　such　as　with　the　deccan　traps　in　india　sixty…five　million　years　ago。

（trap　in　this　context　es　from　a　swedish　word　for　a　type　of　lava；　deccan　is　simply　anarea。）　these　covered　an　area　of　200；000　square　miles　and　probably　contributed　to　the　demiseof　the　dinosaurs鈥攖hey　certainly　didn鈥檛　help鈥攚ith　their　noxious　outgassings。　superplumesmay　also　be　responsible　for　the　rifts　that　cause　continents　to　break　up。

such　plumes　are　not　all　that　rare。　there　are　about　thirty　active　ones　on　the　earth　at　themoment；　and　they　are　responsible　for　many　of　the　world鈥檚　best…known　islands　and　islandchains鈥攊celand；　hawaii；　the　azores；　canaries；　and　gal谩pagos　archipelagos；　little　pitcairn　inthe　middle　of　the　south　pacific；　and　many　others鈥攂ut　apart　from　yellowstone　they　are　alloceanic。　no　one　has　the　faintest　idea　how　or　why　yellowstone鈥