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sure knows and loves geology。 鈥渁nd i鈥檝e got the best place inthe world to do it；鈥潯e says as we set off in a bouncy； battered four…wheel…drive vehicle in thegeneral direction of old faithful。 he has agreed to let me acpany him for 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。 鈥渋t really doesn鈥檛 get any better than this if you鈥檙e a geologist；鈥潯oss says。 鈥測ou鈥檝egot rocks up at beartooth gap that are nearly three billion years old鈥攖hree…quarters of theway back to earth鈥檚 beginning鈥攁nd then you鈥檝e got mineral springs here鈥濃�攈e points at thesulfurous hot springs from which mammoth takes its title鈥斺�渨here you can see rocks as theyare being born。 and in between there鈥檚 everything you could possibly imagine。 i鈥檝e neverbeen any place where geology is more evident鈥攐r prettier。鈥�
鈥渟o you like it？鈥潯 say。
鈥渙h； no； i love it；鈥潯e answers with profound sincerity。 鈥渋 mean i really love it here。 thewinters are tough and the pay鈥檚 not too hot； but when it鈥檚 good； it鈥檚 just鈥斺��
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。
鈥渢hat 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鈥檝e got sixty miles of mountains just obliterated；you know you鈥檙e dealing with something pretty potent。 it took christiansen six years to figureit all out。鈥�
i asked him what caused yellowstone to blow when it did。
鈥渄on鈥檛 know。 nobody knows。 volcanoes are strange things。 we really don鈥檛 understandthem at all。 vesuvius； in italy； was active for three hundred years until an eruption in 1944and then it just stopped。 it鈥檚 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。鈥�
鈥渁nd how much warning would you get if yellowstone was going to go？鈥�
he shrugged。 鈥渘obody 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。鈥�
鈥渟o it could just blow without warning？鈥�
he nodded thoughtfully。 the trouble； he explained； is that nearly all the things that wouldconstitute warning signs already exist in some measure at yellowstone。 鈥渆arthquakes aregenerally a precursor of volcanic eruptions； but the park already has lots of earthquakes鈥�1；260 of them last year。 most of them are too small to be felt； but they are earthquakesnonetheless。鈥�
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。 鈥渋f it blew today and again next week； that wouldn鈥檛 tell us anything at all aboutwhat it might do the following week or the week after or twenty years from now；鈥潯oss says。
鈥渢he whole park is so volatile that it鈥檚 essentially impossible to draw conclusions from almostanything that happens。鈥�
evacuating yellowstone would never be easy。 the park gets some three million visitors ayear； mostly in the three peak months of summer。 the park鈥檚 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。 鈥渨heneverpeople see animals； they just stop； wherever they are；鈥潯oss says。 鈥渨e get bear jams。 we getbison jams。 we get wolf jams。鈥�
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鈥攊n hawaii； california；alaska； and washington鈥攂ut oddly none in the largest volcanic zone in the world。 the yvois not actually a thing； but more an idea鈥攁n agreement to coordinate efforts at studying andanalyzing the park鈥檚 diverse geology。 one of their first tasks； doss told me； was to draw up an鈥渆arthquake and volcano hazards plan鈥濃�攁 plan of action in the event of a crisis。
鈥渢here isn鈥檛 one already？鈥潯 said。
鈥渘o。 afraid not。 but there will be soon。鈥�
鈥渋sn鈥檛 that just a little tardy？鈥�
he smiled。 鈥渨ell； let鈥檚 just say that it鈥檚 not any too soon。鈥�
once it is in place； the idea is that three people鈥攃hristiansen in menlo park； california；professor robert b。 smith at the university of utah； and doss in the park鈥攚ould 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。 鈥渏ust because there was a pattern in the past doesn鈥檛 mean that it stillholds true；鈥潯e says。 鈥渢here 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。鈥�
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。
鈥渁 big earthquake鈥攁nd i mean big鈥攚ill happen sometime；鈥潯oss told me。 鈥測ou cancount on that。 this is a big fault zone for earthquakes。鈥�
despite the hebgen lake quake and the other known risks； yellowstone didn鈥檛 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鈥檛 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鈥攁nd 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。 鈥測ou know； by design we funnel visitors intothermal basins；鈥潯oss told me after we had watched old faithful blow。 鈥渋t鈥檚 what they eto see。 did you know there are more geysers and hot springs at yellowstone than in all therest of the world bined？鈥�
鈥渋 didn鈥檛 know that。鈥�
he nodded。 鈥渢en thousand