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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 of them； and nobody knows when a new vent might open。鈥潯edrove to a place called duck lake； a body of water a couple of hundred yards across。 鈥渋t lookspletely innocuous；鈥潯e said。 鈥渋t鈥檚 just a big pond。 but this big hole didn鈥檛 used to be here。
at some time in the last fifteen thousand years this blew in a really big way。 you鈥檇 have hadseveral tens of millions of tons of earth and rock and superheated water blowing out athypersonic speeds。 you can imagine what it would be like if this happened under； say； theparking lot at old faithful or one of the visitors鈥櫋enters。鈥潯e made an unhappy face。
鈥渨ould there be any warning？鈥�
鈥減robably not。 the last significant explosion in the park was at a place called pork chopgeyser in 1989。 that left a crater about five meters across鈥攏ot huge by any means； but bigenough if you happened to be standing there at the time。 fortunately； nobody was around so nobody was hurt； but that happened without warning。 in the very ancient past there have beenexplosions that have made holes a mile across。 and nobody can tell you where or when thatmight happen again。 you just have to hope that you鈥檙e not standing there when it does。鈥�
big rockfalls are also a danger。 there was a big one at gardiner canyon in 1999； but againfortunately no one was hurt。 late in the afternoon； doss and i stopped at a place where therewas a rock overhang poised above a busy park road。 cracks were clearly visible。 鈥渋t could goat any time；鈥潯oss said thoughtfully。
鈥測ou鈥檙e kidding；鈥潯 said。 there wasn鈥檛 a moment when there weren鈥檛 two cars passingbeneath it； all filled with； in the most literal sense； happy campers。
鈥渙h； it鈥檚 not likely；鈥潯e added。 鈥渋鈥檓 just saying it could。 equally it could stay like that fordecades。 there鈥檚 just no telling。 people have to accept that there is risk in ing here。 that鈥檚all there is to it。鈥�
as we walked back to his vehicle to head back to mammoth hot springs； doss added： 鈥渂utthe thing is； most of the time bad things don鈥檛 happen。 rocks don鈥檛 fall。 earthquakes don鈥檛occur。 new vents don鈥檛 suddenly open up。 for all the instability； it鈥檚 mostly remarkably andamazingly tranquil。鈥�
鈥渓ike earth itself；鈥潯 remarked。
鈥減recisely；鈥潯e agreed。
the risks at yellowstone apply to park employees as much as to visitors。 doss got ahorrific sense of that in his first week on the job five years earlier。 late one night； three youngsummer employees engaged in an illicit activity known as 鈥渉ot…potting鈥濃�攕wimming orbasking in warm pools。 though the park； for obvious reasons； doesn鈥檛 publicize it； not all thepools in yellowstone are dangerously hot。 some are extremely agreeable to lie in； and it wasthe habit of some of the summer employees to have a dip late at night even though it wasagainst the rules to do so。 foolishly the threesome had failed to take a flashlight； which wasextremely dangerous because much of the soil around the war