15 DANGEROUS BEAUTY
《万物简史英文版》章节: 15 DANGEROUS BEAUTY,宠文网网友提供全文无弹窗免费在线阅读。!
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 on to thepark authorities on the assumption that they might make a nice blow-up for one of thevisitors’ centers. As soon as Christiansen saw the photos he realized why he had failed to spotthe caldera: virtually the whole park—2.2 million acres—was caldera. The explosion had lefta crater more than forty miles across—much 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’s vents, geysers, hot springs, and popping mudpots. Beneath the surface is a magma chamber that is about forty-five miles across—roughlythe same dimensions as the park—and 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, “youwouldn’t be able to get within a thousand kilometers of it” while it was erupting. Theconsequences that followed would be even worse.
Superplumes of the type on which Yellowstone sits are rather like martini glasses—thin 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’talways erupt explosively but sometimes burst forth in a vast, continuous outpouring—aflood—of molten rock, such as with the Deccan Traps in India sixty-five million years ago.
(Trap in this context comes 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—they certainly didn’t help—with 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’s best-known islands and islandchains—Iceland, Hawaii, the Azores, Canaries, and Galápagos archipelagos, little Pitcairn inthe middle of the South Pacific, and many others—but apart from Yellowstone they are alloceanic. No one has the faintest idea how or why Yellowstone’s ended up beneath acontinental plate. Only two things are certain: that the crust at Yellowstone is thin and that theworld beneath it is hot. But whether the crust is thin because of the hot spot or whether the hotspot is there because the crust is thin is a matter of heated (as it were) debate. The continentalnature of the crust makes a huge difference to its eruptions. Where the other supervolcanoestend to bubble away steadily and in a comparatively benign fashion, Yellowstone blowsexplosively. It doesn’t happen often, but when it does you want to stand well back.
Since its first known eruption 16.5 million years ago, it has blown up about a hundredtimes, but the most recent three eruptions are the ones that get written about. The last eruptionwas a thousand times greater than that of Mount St. Helens; the one before that was 280 timesbigger, and the one before was so big that nobody knows exactly how big it was. It was atleast twenty-five hundred times greater than St. Helens, but perhaps eight thousand timesmore monstrous.
We have absolutely nothing to compare it to. The biggest blast in recent times was that ofKrakatau in Indonesia in August 1883, which made a bang that reverberated around the worldfor nine days, and made water slosh as far away as the English Channel. But if you imaginethe volume of ejected material from Krakatau as being about the size of a golf ball, then thebiggest of the Yellowstone blasts would be the size of a sphere you could just about hidebehind. On this scale, Mount St. Helens’s would be no more than a pea.
The Yellowstone eruption of two million years ago put out enough ash to bury New YorkState to a depth of sixty-seven feet or California to a depth of twenty. This was the ash thatmade Mike Voorhies’s fossil beds in eastern Nebraska. That blast occurred in what is nowIdaho, but over millions of years, at a rate of about one inch a year, the Earth’s crust hastraveled over it, so that today it is directly under northwest Wyoming. (The hot spot itselfstays in one place, like an acetylene torch aimed at a ceiling.) In its wake it leaves the sort ofrich volcanic plains that are ideal for growing potatoes, as Idaho’s farmers long agodiscovered. In another two million years, geologists like to joke, Yellowstone will beproducing French fries for McDonald’s, and the people of Billings, Montana, will be steppingaround geysers.
The ash fall from the last Yellowstone eruption covered all or parts of nineteen westernstates (plus parts of Canada and Mexico)—nearly the whole of the United States west of theMississippi. This, bear in mind, is the breadbasket of America, an area that produces roughlyhalf the world’s cereals. And ash, it is worth remembering, is not like a big snowfall that will melt in the spring. If you wanted to grow crops again, you would have to find some place toput all the ash. It took thousands of workers eight months to clear 1.8 billion tons of debrisfrom the sixteen acres of the World Trade Center site in New York. Imagine what it wouldtake to clear Kansas.
And that’s not even to consider the climatic consequences. The last supervolcano eruptionon Earth was at Toba, in northern Sumatra, seventy-four thousand years ago. No one knowsquite how big it was other than that it was a whopper. Greenland ice cores show that the Tobablast was followed by at least six years of “volcanic winter” and goodness knows how manypoor growing seasons after that. The event, it is thought, may have carried humans right to thebrink of extinction, reducing the global population to no more than a few thousandindividuals. That means that all modern humans arose from a very small population base,which would explain our lack of genetic diversity. At all events, there is some evidence tosuggest that for the next twenty thousand years the total number of people on Earth was nevermore than a few thousand at any time. That is, needless to say, a long time to recover from asingle volcanic blast.
All this was hypothetically interesting until 1973, when an odd occurrence made itsuddenly momentous: water in Yellowstone Lake, in the heart of the park, began to run overthe banks at the lake’s southern end, flooding a meadow, while at the opposite end of the lakethe water mysteriously flowed away. Geologists did a hasty survey and discovered that a largearea of the park had developed an ominous bulge. This was lifting up one end of the lake andcausing the water to run out at the other, as would happen if you lifted one side of a child’swading pool. By 1984, the whole central region of the park—several dozen square miles—was more than three feet higher than it had been in 1924, when the park was last formallysurveyed. Then in 1985, the whole of the central part of the park subsided by eight inches. Itnow seems to be swelling again.
The geologists realized that only one thing could cause this—a restless magma chamber.
Yellowstone wasn’t the site of an ancient supervolcano; it was the site of an active one. It wasalso at about this time that they were able to work out that the cycle of Yellowstone’seruptions averaged one massive blow every 600,000 years. The last one, interestingly enough,was 630,000 years ago. Yellowstone, it appears, is due.
“It may not feel like it, but you’re standing on the largest active volcano in the world,” PaulDoss, Yellowstone National Park geologist, told me soon after climbing off an enormousHarley-Davidson motorcycle and shaking hands when we met at the park headquarters atMammoth Hot Springs early on a lovely morning in June. A native of Indiana, Doss is anamiable, soft-spoken, extremely thoughtful man who looks nothing like a National ParkService employee. He has a graying beard and hair tied back in a long ponytail. A smallsapphire stud graces one ear. A slight paunch strains against his crisp Park Service uniform.
He looks more like a blues musician than a government employee. In fact, he is a bluesmusician (harmonica). But he sure knows and loves geology. “And I’ve got the best place inthe world to do it,” he 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 accompany 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. “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 come 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 comparatively 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 comes. Doss thinks such aday may not come 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 cometo see. Did you know there are more geysers and hot springs at Yellowstone than in all therest of the world combined?”
“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 lookscompletely 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’d 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’ centers.” He made an unhappy face.
“Would there be any warning?”
“Probably 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—not 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’re not standing there when it does.”
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. “It could goat any time,” Doss said thoughtfully.
“You’re kidding,” I said. There wasn’t a moment when there weren’t two cars passingbeneath it, all filled with, in the most literal sense, happy campers.
“Oh, it’s not likely,” he added. “I’m just saying it could. Equally it could stay like that fordecades. There’s just no telling. People have to accept that there is risk in coming here. That’sall there is to it.”
As we walked back to his vehicle to head back to Mammoth Hot Springs, Doss added: “Butthe thing is, most of the time bad things don’t happen. Rocks don’t fall. Earthquakes don’toccur. New vents don’t suddenly open up. For all the instability, it’s mostly remarkably andamazingly tranquil.”
“Like Earth itself,” I remarked.
“Precisely,” he 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 “hot-potting”—swimming orbasking in warm pools. Though the park, for obvious reasons, doesn’t 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 warm pools is crusty and thin andone can easily fall through into a scalding vent below. In any case, as they made their wayback to their dorm, they came across a stream that they had had to leap over earlier. Theybacked up a few paces, linked arms and, on the count of three, took a running jump. In fact, itwasn’t the stream at all. It was a boiling pool. In the dark they had lost their bearings. None ofthe three survived.
I thought about this the next morning as I made a brief call, on my way out of the park, at aplace called Emerald Pool, in the Upper Geyser Basin. Doss hadn’t had time to take me therethe day before, but I thought I ought at least to have a look at it, for Emerald Pool is a historicsite.
In 1965, a husband-and-wife team of biologists named Thomas and Louise Brock, while ona summer study trip, had done a crazy thing. They had scooped up some of the yellowy-brown scum that rimmed the pool and examined it for life. To their, and eventually the widerworld’s, deep surprise, it was full of living microbes. They had found the world’s firstextremophiles—organisms that could live in water that had previously been assumed to be much too hot or acid or choked with sulfur to bear life. Emerald Pool, remarkably, was allthese things, yet at least two types of living things, Sulpholobus acidocaldarius andThermophilus aquaticus as they became known, found it congenial. It had always beensupposed that nothing could survive above temperatures of 50°C (122°F), but here wereorganisms basking in rank, acidic waters nearly twice that hot.
For almost twenty years, one of the Brocks’ two new bacteria, Thermophilus aquaticus,remained a laboratory curiosity until a scientist in California named Kary B. Mullis realizedthat heat-resistant enzymes within it could be used to create a bit of chemical wizardry knownas a polymerase chain reaction, which allows scientists to generate lots of DNA from verysmall amounts—as little as a single molecule in ideal conditions. It’s a kind of geneticphotocopying, and it became the basis for all subsequent genetic science, from academicstudies to police forensic work. It won Mullis the Nobel Prize in chemistry in 1993.
Meanwhile, scientists were finding even hardier microbes, now known ashyperthermophiles, which demand temperatures of 80°C (176°F) or more. The warmestorganism found so far, according to Frances Ashcroft in Life at the Extremes, is Pyrolobusfumarii, which dwells in the walls of ocean vents where the temperature can reach 113°C(235.4°F). The upper limit for life is thought to be about 120°C (248°F), though no oneactually knows. At all events, the Brocks’ findings completely changed our perception of theliving world. As NASA scientist Jay Bergstralh has put it: “Wherever we go on Earth—eveninto what’s seemed like the most hostile possible environments for life—as long as there isliquid water and some source of chemical energy we find life.”
Life, it turns out, is infinitely more clever and adaptable than anyone had ever supposed.
This is a very good thing, for as we are about to see, we live in a world that doesn’t altogetherseem to want us here.
PART V LIFE ITSELFThe more I examine the universeand study the details of its architecture,the more evidence I find that theunivers