A Short History of Nearly Everything-第48章
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a day as he goesabout doing whatever it is a park geologist does。 the first assignment today is to give anintroductory talk to a new crop of tour guides。
yellowstone； i hardly need point out； is sensationally beautiful； with plump； statelymountains； bison…specked meadows； tumbling streams； a sky…blue lake； wildlife beyondcounting。 “it really doesn’t get any better than this if you’re a geologist；” doss says。 “you’vegot rocks up at beartooth gap that are nearly three billion years old—three…quarters of theway back to earth’s beginning—and then you’ve got mineral springs here”—he points at thesulfurous hot springs from which mammoth takes its title—“where you can see rocks as theyare being born。 and in between there’s everything you could possibly imagine。 i’ve neverbeen any place where geology is more evident—or prettier。”
“so you like it？” i say。
“oh； no； i love it；” he answers with profound sincerity。 “i mean i really love it here。 thewinters are tough and the pay’s not too hot； but when it’s good； it’s just—”
he interrupted himself to point out a distant gap in a range of mountains to the west； whichhad just e into view over a rise。 the mountains； he told me； were known as the gallatins。
“that gap is sixty or maybe seventy miles across。 for a long time nobody could understandwhy that gap was there； and then bob christiansen realized that it had to be because themountains were just blown away。 when you’ve got sixty miles of mountains just obliterated；you know you’re dealing with something pretty potent。 it took christiansen six years to figureit all out。”
i asked him what caused yellowstone to blow when it did。
“don’t know。 nobody knows。 volcanoes are strange things。 we really don’t understandthem at all。 vesuvius； in italy； was active for three hundred years until an eruption in 1944and then it just stopped。 it’s been silent ever since。 some volcanologists think that it isrecharging in a big way； which is a little worrying because two million people live on oraround it。 but nobody knows。”
“and how much warning would you get if yellowstone was going to go？”
he shrugged。 “nobody was around the last time it blew； so nobody knows what thewarning signs are。 probably you would have swarms of earthquakes and some surface upliftand possibly some changes in the patterns of behavior of the geysers and steam vents； butnobody really knows。”
“so it could just blow without warning？”
he nodded thoughtfully。 the trouble； he explained； is that nearly all the things that wouldconstitute warning signs already exist in some measure at yellowstone。 “earthquakes aregenerally a precursor of volcanic eruptions； but the park already has lots of earthquakes—1；260 of them last year。 most of them are too small to be felt； but they are earthquakesnonetheless。”
a change in the pattern of geyser eruptions might also be taken as a clue； he said； but thesetoo vary unpredictably。 once the most famous geyser in the park was excelsior geyser。 itused to erupt regularly and spectacularly to heights of three hundred feet； but in 1888 it juststopped。 then in 1985 it erupted again； though only to a height of eighty feet。 steamboatgeyser is the biggest geyser in the world when it blows； shooting water four hundred feet intothe air； but the intervals between its eruptions have ranged from as little as four days to almost fifty years。 “if it blew today and again next week； that wouldn’t tell us anything at all aboutwhat it might do the following week or the week after or twenty years from now；” doss says。
“the whole park is so volatile that it’s essentially impossible to draw conclusions from almostanything that happens。”
evacuating yellowstone would never be easy。 the park gets some three million visitors ayear； mostly in the three peak months of summer。 the park’s roads are paratively few andthey are kept intentionally narrow； partly to slow traffic； partly to preserve an air ofpicturesqueness； and partly because of topographical constraints。 at the height of summer； itcan easily take half a day to cross the park and hours to get anywhere within it。 “wheneverpeople see animals； they just stop； wherever they are；” doss says。 “we get bear jams。 we getbison jams。 we get wolf jams。”
in the autumn of 2000； representatives from the u。s。 geological survey and national parkservice； along with some academics； met and formed something called the yellowstonevolcanic observatory。 four such bodies were in existence already—in hawaii； california；alaska； and washington—but oddly none in the largest volcanic zone in the world。 the yvois not actually a thing； but more an idea—an agreement to coordinate efforts at studying andanalyzing the park’s diverse geology。 one of their first tasks； doss told me； was to draw up an“earthquake and volcano hazards plan”—a plan of action in the event of a crisis。
“there isn’t one already？” i said。
“no。 afraid not。 but there will be soon。”
“isn’t that just a little tardy？”
he smiled。 “well； let’s just say that it’s not any too soon。”
once it is in place； the idea is that three people—christiansen in menlo park； california；professor robert b。 smith at the university of utah； and doss in the park—would assess thedegree of danger of any potential cataclysm and advise the park superintendent。 thesuperintendent would take the decision whether to evacuate the park。 as for surroundingareas； there are no plans。 if yellowstone were going to blow in a really big way； you would beon your own once you left the park gates。
of course it may be tens of thousands of years before that day es。 doss thinks such aday may not e at all。 “just because there was a pattern in the past doesn’t mean that it stillholds true；” he says。 “there is some evidence to suggest that the pattern may be a series ofcatastrophic explosions； then a long period of quiet。 we may be in that now。 the evidencenow is that most of the magma chamber is cooling and crystallizing。 it is releasing itsvolatiles； you need to trap volatiles for an explosive eruption。”
in the meantime there are plenty of other dangers in and around yellowstone； as was madedevastatingly evident on the night of august 17； 1959； at a place called hebgen lake justoutside the park。 at twenty minutes to midnight on that date； hebgen lake suffered acatastrophic quake。 it was magnitude 7。5； not vast as earthquakes go； but so abrupt andwrenching that it collapsed an entire mountainside。 it was the height of the summer season；though fortunately not so many people went to yellowstone in those days as now。 eighty million tons of rock； moving at more than one hundred miles an hour； just fell off themountain； traveling with such force and momentum that the leading edge of the landslide ranfour hundred feet up a mountain on the other side of the valley。 along its path lay part of therock creek campground。 twenty…eight campers were killed； nineteen of them buried toodeep ever to be found again。 the devastation was swift but heartbreakingly fickle。 threebrothers； sleeping in one tent； were spared。 their parents； sleeping in another tent besidethem； were swept away and never seen again。
“a big earthquake—and i mean big—will happen sometime；” doss told me。 “you cancount on that。 this is a big fault zone for earthquakes。”
despite the hebgen lake quake and the other known risks； yellowstone didn’t getpermanent seismometers until the 1970s。
if you needed a way to appreciate the grandeur and inexorable nature of geologic processes；you could do worse than to consider the tetons； the sumptuously jagged range that stands justto the south of yellowstone national park。 nine million years ago； the tetons didn’t exist。
the land around jackson hole was just a high grassy plain。 but then a forty…mile…long faultopened within the earth； and since then； about once every nine hundred years； the tetonsexperience a really big earthquake； enough to jerk them another six feet higher。 it is theserepeated jerks over eons that have raised them to their present majestic heights of seventhousand feet。
that nine hundred years is an average—and a somewhat misleading one。 according torobert b。 smith and lee j。 siegel in windows into the earth ； a geological history of theregion； the last major teton quake was somewhere between about five and seven thousandyears ago。 the tetons； in short； are about the most overdue earthquake zone on the planet。
hydrothermal explosions are also a significant risk。 they can happen anytime； pretty muchanywhere； and without any predictability。 “you know； by design we funnel visitors intothermal basins；” doss told me after we had watched old faithful blow。 “it’s what they eto see。 did you know there are more geysers and hot springs at yellowstone than in all therest of the world bined？”
“i didn’t know that。”
he nodded。 “ten thousand of them； and nobody knows when a new vent might open。” wedrove to a place called duck lake； a body of water a couple of hundred yards across。 “it lookspletely innocuous；” he said。 “it’s just a big pond。 but this big hole didn’t used to be here。
at some time in the last fifteen thousand years this blew in a really big way。 you�
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