Izasty

The Fire Below

IN THE SUMMER of 1971, a young geologist named Mike Voorhies was scouting around on

some grassy farmland in eastern Nebraska, not far from the little town of Orchard, where he

had grown up. Passing through a steep-sided gully, he spotted a curious glint in the brush

above and clambered up to have a look. What he had seen was the perfectly preserved skull of

a young rhinoceros, which had been washed out by recent heavy rains. 

A few yards beyond, it turned out, was one of the most extraordinary fossil beds ever

discovered in North America, a dried-up water holethat had served as a mass grave for scores

of animals—rhinoceroses, zebra-like horses, saber-toothed deer, camels, turtles. All had died

from some mysterious cataclysm just under twelve million years ago in the time known to

geology as the Miocene. In those days Nebraska stood on a vast, hot plain very like the

Serengeti of Africa today. The animals had been found buried under volcanic ash up to ten

feet deep. The puzzle of it was that there were not, and never had been, any volcanoes in

Nebraska. 

Today, the site of Voorhies’s discovery iscalled Ashfall Fossil Beds State Park, and it has a

stylish new visitors’ center and museum, with thoughtful displays on the geology of Nebraska

and the history of the fossil beds. The center incorporates a lab with a glass wall through

which visitors can watch paleontologists cleaning bones. Working alone in the lab on the

morning I passed through was a cheerfully grizzled-looking fellow in a blue work shirt whom

I recognized as Mike Voorhies from a BBC television documentary in which he featured. 

They don’t get a huge number of visitors to Ashfall Fossil Beds State Park—it’s slightly in

the middle of nowhere—and Voorhies seemed pleased to show me around. He took me to the

spot atop a twenty-foot ravinewhere he had made his find. 

“It was a dumb place to look for bones,” he said happily. “But I wasn’t looking for bones. I

was thinking of making a geological map of easternNebraska at the time, and really just kind

of poking around. If I hadn’t gone up this ravine or the rains hadn’t just washed out that skull, 

I’d have walked on by and this would never have been found.” Heindicated a roofed

enclosure nearby, which had become the mainexcavation site. Some two hundred animals

had been found lying together in a jumble. 

I asked him in what way it was a dumb place to hunt for bones. “Well, if you’re looking for

bones, you really need exposed rock. That’s why most paleontology is done in hot, dry places. 

It’s not that there are more bones there. It’s just that you have some chance of spotting them. 

In a setting like this”—he made a sweeping gesture across the vast and unvarying prairie—

“you wouldn’t know where to begin. There could be really magnificent stuff out there, but

there’s no surface clues to show you where to start looking.” 

At first they thought the animals were buried alive, and Voorhies stated as much in a

National Geographicarticle in 1981. “The article called the site a ‘Pompeii of prehistoric

animals,’ ” he told me, “which was unfortunate because just afterward we realized that the

animals hadn’t died suddenly at all. Theywere all suffering from something called

hypertrophic pulmonary osteodystrophy, which is what you would get if you were breathing a

lot of abrasive ash—and they must have been breathing a lot of it because the ash was feet

thick for hundreds of miles.” He picked up a chunk of grayish, claylike dirt and crumbled it

into my hand. It was powdery but slightly gritty. “Nasty stuff to have to breathe,” he went on, 

“because it’s very fine but also quite sharp. So anyway they came here to this watering hole, 

presumably seeking relief, and died in some misery. The ash would have ruined everything. It

would have buried all the grass and coated every leaf and turned the water into an undrinkable

gray sludge. It couldn’t have been very agreeable at all.” 

The BBC documentary had suggested that the existence of so much ash in Nebraska was a

surprise. In fact, Nebraska’shuge ash deposits had been known about for a long time. For

almost a century they had been mined to make household cleaning powders like Comet and

Ajax. But curiously no one had ever thought to wonder where all the ash came from. 

“I’m a little embarrassed to tell you,” Voorhies said, smiling briefly, “that the first I thought

about it was when an editor at the National Geographicasked me the source of all the ash and

I had to confess that I didn’t know. Nobody knew.” 

Voorhies sent samples to colleagues all over the western United States asking if there was

anything about it that they recognized. Several months later a geologist named Bill

Bonnichsen from the Idaho Geological Survey got in touch and told him that the ash matched

a volcanic deposit from a place called Bruneau-Jarbidge in southwest Idaho. The event that

killed the plains animals of Nebraska was a volcanic explosion ona scale previously

unimagined—but big enough to leave an ash layer ten feet deep almost a thousand miles away

in eastern Nebraska. It turned out that under the western United States there was a huge

cauldron of magma, a colossal volcanic hotspot, which erupted cataclysmically every

600,000 years or so. The last such eruption was just over 600,000 years ago. The hot spot is

still there. These days we call it Yellowstone National Park. 

We know amazingly little about what happens beneath our feet. It is fairly remarkable to

think that Ford has been building cars and baseball has been playing World Series for longer

than we have known that the Earth has a core. And of course the idea thatthe continents move

about on the surface like lily pads has been common wisdom for much less than a generation. 

“Strange as it may seem,” wrote Richard Feynman, “we understand the distribution of matter

in the interior of the Sun far better thanwe understand the interior of the Earth.” 

The distance from the surfaceof Earth to the center is 3,959 miles, which isn’t so very far. 

It has been calculated that if you sunk a well to the center and dropped a brick into it, it would

take only forty-five minutes for it to hit  the bottom (though at thatpoint it would be

weightless since all the Earth’s gravity would be above and around it rather than beneath it). 

Our own attempts to penetrate toward the middle have been modest indeed. One or two South

African gold mines reach to a depth of two miles, but most mines on Earth go no more than

about a quarter of a mile beneath the surface. Ifthe planet were an apple, we wouldn’t yet

have broken through the skin. Indeed, we haven’t even come close. 

Until slightly under a century ago, what the best-informed scientific minds knew about

Earth’s interior was not much more than whata coal miner knew—namely, that you could dig

down through soil for a distance and then you’d hit rock and that was about it. Then in 1906, 

an Irish geologist named R. D. Oldham, while examining some seismograph readings from an

earthquake in Guatemala, noticed that certain shock waves had penetrated to a point deep

within the Earth and then bounced off at an angle, as if they had encountered some kind of

barrier. From this he deduced that the Earth has a core. Three years later a Croatian

seismologist named Andrija Mohoroviči´c was studying graphs from an earthquake in Zagreb

when he noticed a similar odd deflection, but ata shallower level. He had discovered the

boundary between the crust and the layer immediately below, the mantle; this zone has been

known ever since as the Mohoroviči´c discontinuity, or Moho for short. 

We were beginning to get a vague idea ofthe Earth’s layered interior—though it really was

only vague. Not until 1936 did a Danish scientist named Inge Lehmann, studying

seismographs of earthquakes inNew Zealand, discover that there were two cores—an inner

one that we now believe to be solid and an outer one(the one that Oldham had detected) that

is thought to be liquid and the seat of magnetism. 

At just about the time that Lehmann was refining our basic understanding of the Earth’s

interior by studying the seismic waves of earthquakes, two geologists at Caltech in California

were devising a way to make comparisons between one earthquake and the next. They were

Charles Richter and Beno Gutenberg, though for reasons that have nothing to do with fairness

the scale became known almost at once as Richter’s alone. (It has nothing to do with Richter

either. A modest fellow, he never referred to the scale by his own name, but always called it

“the Magnitude Scale.”) 

The Richter scale has always been widely misunderstood by nonscientists, though perhaps

a little less so now than in its early days when visitors to Richter’s office often asked to see

his celebrated scale, thinking itwas some kind of machine. The scale is of course more an

idea than an object, an arbitrary measure of the Earth’s tremblings based on surface

measurements. It rises exponentially, so that a 7.3 quake is fifty times more powerful than a

6.3 earthquake and 2,500 times more powerful than a 5.3 earthquake. 

At least theoretically, there is no upper limit for an earthquake—nor, come to that, a lower

limit. The scale is a simple measure of force,but says nothing about damage. A magnitude 7

quake happening deep in the mantle—say, four hundred miles down—might cause no surface

damage at all, while a significantly smaller one happening just four miles under the surface

could wreak widespread devastation. Much, too, depends on the nature of the subsoil, the

quake’s duration, the frequency and severity of aftershocks, and the physical setting of the

affected area. All this means that the most fearsome quakes are not necessarily the most

forceful, though force obviously counts for a lot. 

The largest earthquake since the scale’s invention was (depending on which source you

credit) either one centered on Prince William Sound in Alaska in March 1964, which

measured 9.2 on the Richter scale, or one in the Pacific Ocean off the coast of Chile in 1960, 

which was initially logged at 8.6 magnitude but later revised upward by some authorities

(including the United States Geological Survey) to a truly grand-scale 9.5. As you will gather

from this, measuring earthquakes is not always an exact science, particularly when

interpreting readings from remote locations. At all events, both quakes were whopping. The

1960 quake not only caused widespread damage across coastal South America, but also set off

a giant tsunami that rolled six thousand miles across the Pacific and slapped away much of

downtown Hilo, Hawaii, destroying five hundred buildings and killing sixty people. Similar

wave surges claimed yet more victims as far away as Japan and the Philippines. 

For pure, focused, devastation, however, probably the most intense earthquake in recorded

history was one that struck—and essentially shook to pieces—Lisbon, Portugal, on All Saints

Day (November 1), 1755. Just before ten inthe morning, the city was hit by a sudden

sideways lurch now estimated at magnitude 9.0 and shaken ferociously for seven full minutes. 

The convulsive force was so great that the water rushed out of the city’s harbor and returned

in a wave fifty feet high, adding to the destruction. When at last the motion ceased, survivors

enjoyed just three minutes of calm before a second shock came, only slightly less severe than

the first. A third and final shock followed two hours later. At the end of it all, sixty thousand

people were dead and virtually every building for miles reduced to rubble. The San Francisco

earthquake of 1906, for comparison, measured an estimated 7.8 on the Richter scale and

lasted less than thirty seconds. 

Earthquakes are fairly common. Every day on average somewhere inthe world there are

two of magnitude 2.0 or greater—that’s enough to give anyonenearby a pretty good jolt. 

Although they tend to cluster in certain places—notably around the rim of the Pacific—they

can occur almost anywhere. In the United States, only Florida, eastern Texas, and the upper

Midwest seem—so far—to be almost entirely immune. New England has had two quakes of

magnitude 6.0 or greater in the last two hundred years. In April 2002, the region experienced

a 5.1 magnitude shaking in a quake near LakeChamplain on the New York–Vermont border, 

causing extensive local damage and (I can attest) knocking pictures from walls and children

from beds as far away as New Hampshire. 

The most common types of earthquakes are those where two plates meet, as in California

along the San Andreas Fault. As the plates push against each other, pressures build up until

one or the other gives way. In general, the longer the interval between quakes, the greater the

pent-up pressure and thus the greater the scope for a really big jolt. This is a particular worry

for Tokyo, which Bill McGuire, a hazards specialist at University College London, describes

as “the city waiting to die” (not a motto you will find on many tourism leaflets). Tokyo stands

on the boundary of three tectonic plates in a country already well known for its seismic

instability. In 1995, as you will remember, the city of Kobe, three hundred miles to the west, 

was struck by a magnitude 7.2 quake, which killed 6,394 people. The damage was estimated

at $99 billion. But that was asnothing—well, as comparatively little—compared with what

may await Tokyo. 

Tokyo has already suffered one of the mostdevastating earthquakes in modern times. On

September 1, 1923, just before noon, the city was hit by what is known as the Great Kanto

quake—an event more than ten times more powerful than Kobe’s earthquake. Two hundred

thousand people were killed. Since that time,Tokyo has been eerily quiet, so the strain

beneath the surface has been building for eighty years. Eventually it is bound to snap. In 1923, 

Tokyo had a population of about three million. Today it is approaching thirty million. Nobody

cares to guess how many people might die, but the potential economic cost has been put as

high as $7 trillion. 

Even  more  unnerving,  because  they  are less well understood and capable of occurring

anywhere at any time, are the rarer type of shakings known as intraplate quakes. These

happen away from plate boundaries, which makes them wholly unpredictable. And because

they come from a much greater depth, they tend to propagate over much wider areas. The

most notorious such quakes ever to hit the United States were a series of three in New

Madrid, Missouri, in the winter of 1811–12. The adventure started just after midnight on

December 16 when people were awakened first by the noise of panicking farm animals (the 

restiveness of animals before quakes is not an old wives’ tale, but is in fact well established, 

though not at all understood)and then by an almighty rupturing noise from deep within the

Earth. Emerging from their houses, locals found the land rolling in waves up to three feet high

and opening up in fissures several feet deep. A strong smell of sulfur filled the air. The

shaking lasted for four minutes with the usual devastating effects to property. Among the

witnesses was the artist John James Audubon, who happened to be in the area. The quake

radiated outward with such force that it knocked down chimneys in Cincinnati four hundred

miles away and, according to at least one account,“wrecked boats in East Coast harbors and . 

. . even collapsed scaffolding erected around the Capitol Building in Washington, D.C.” On

January 23 and February 4 further quakes of similar magnitude followed. New Madrid has

been silent ever since—but notsurprisingly, since such episodes have never been known to

happen in the same place twice. As far as we know, they are as random as lightning. The next

one could be under Chicago or Paris or Kinshasa. No one can even begin to guess. And what

causes these massive intraplate rupturings? Something deep within the Earth. More than that

we don’t know. 

By the 1960s scientists had grown sufficiently frustrated by how little they understood of

the Earth’s interior that they decided to try to do something aboutit. Specifically, they got the

idea to drill through the ocean floor (the continental crust was too thick) to the Moho

discontinuity and to extract a piece of the Earth’s mantle for examination at leisure. The

thinking was that if they could understand the nature of the rocks inside the Earth, they might

begin to understand how they interacted, and thus possibly be able to predict earthquakes and

other unwelcome events. 

The project became known, all but inevitably, as the Mohole and it was pretty well

disastrous. The hope was to lower a drill through 14,000 feet ofPacific Ocean water off the

coast of Mexico and drill some 17,000 feet through relatively thin crustal rock. Drilling from

a ship in open waters is, in the words of one oceanographer, “like trying to drill a hole in the

sidewalks of New York from atop the Empire State Building using a strand of spaghetti.” 

Every attempt ended in failure. The deepest they penetratedwas only about 600 feet. The

Mohole became known as the No Hole. In 1966, exasperated with ever-rising costs and no

results, Congress killed the project. 

Four years later, Soviet scientists decided to try their luckon dry land. They chose a spot on

Russia’s Kola Peninsula, near the Finnish border,and set to work with the hope of drilling to

a depth of fifteen kilometers. The work proved harder than expected, but the Soviets were

commendably persistent. When at last they gave up, nineteen years later, they had drilled to a

depth of 12,262 meters, or about 7.6 miles. Bearing in mind that the crust of the Earth

represents only about 0.3 percent of the planet’s volume and that the Kola hole had not cut

even one-third of the way through the crust, we can hardly claim to have conquered the

interior. 

Interestingly, even though the hole was modest, nearly everything about it was surprising. 

Seismic wave studies had led the scientists to predict, and pretty confidently, that they would

encounter sedimentary rock to a depth of 4,700 meters, followed by granite for the next 2,300

meters and basalt from there on down. In the event, the sedimentary layer was 50 percent

deeper than expected and the basaltic layer was never found at all. Moreover,the world down

there was far warmer than anyone had expected, with a temperature at 10,000 meters of 180

degrees centigrade, nearly twice the forecasted level. Most surprising of all was that the rock

at that depth was saturated with water—something that had not been thought possible. 

Because we can’t see into the Earth, we have to use other techniques, which mostly involve

reading waves as they travel through the interior. We also know a little bit about the mantle

from what are known as kimberlite pipes, where diamonds are formed. What happens is that

deep in the Earth there is an explosion thatfires, in effect, a cannonball of magma to the

surface at supersonic speeds. It is a totally random event. A kimberlite pipe could explode in

your backyard as you read this. Because theycome up from such depths—up to 120 miles

down—kimberlite pipes bring up all kinds of things not normally found on or near the

surface: a rock called peridotite, crystals of olivine, and—just occasionally, in about one pipe

in a hundred—diamonds. Lots of carbon comes up with kimberlite ejecta, but most is

vaporized or turns to graphite. Only occasionally does a hunk of it shoot up at just the right

speed and cool down with the necessary swiftness to become a diamond. It was such a pipe

that made Johannesburg the most productive diamond mining city in the world, but there may

be others even bigger that we don’t know about. Geologists know that somewhere in the

vicinity of northeastern Indiana there is evidence of a pipe or group of pipes that may be truly

colossal. Diamonds up to twenty carats or morehave been found at scattered sites throughout

the region. But no one has ever found the source. As John McPhee notes, it may be buried

under glacially deposited soil, like the Manson crater in Iowa, or under the Great Lakes. 

So how much do we know about what’s inside the Earth? Very little. Scientists are

generally agreed that the world beneath us is composed of four layers—rocky outer crust, a

mantle of hot, viscous rock, a liquid outer core, and a solid inner core.

1

We know that the

surface is dominated by silicates, which are relatively light and not heavy enough to account

for the planet’s overall density. Therefore there must be heavier stuff inside. We know that to

generate our magnetic field somewhere in the interior there must be a concentrated belt of

metallic elements in a liquid state. That much is universally agreed upon. Almost everything

beyond that—how the layers interact, what causes them to behave in the way they do, what

they will do at any time in the future—is a matter of at least some uncertainty, and generally

quite a lot of uncertainty. 

Even the one part of it we can see, the crust, is a matter of some fairly strident debate. 

Nearly all geology texts tell you that continental crust is three to six miles thick under the

oceans, about twenty-five miles thick under the continents, and forty to sixty miles thick

under big mountain chains, but there are many puzzling variabilities within these

generalizations. The crust beneath the Sierra Nevada Mountains, for instance, is only about

nineteen to twenty-five miles thick, and no one knows why. By all the laws of geophysics the

Sierra Nevadas should be sinking, as if intoquicksand. (Some people think they may be.) 

1

For those who crave a more detailed picture of the Earth's interior, here are the dimensions of the various

layers, using average figures: From 0 to 40 km (25 mi) is the crust. From 40 to 400 km (25 to 250 mi) is the

upper mantle. From 400 to 650 km (250 to 400 mi) isa transition zone between the upper and lower mantle. 

From 650 to 2,700 km (400 to 1,700 mi) is the lower mantle. From 2,700 to 2,890 km (1,700 to 1,900 mi) is the

"D" layer. From 2,890 to 5,150 km (1,900 to 3,200 mi) is the outer core, and from 5,150 to 6,378 km (3,200 to

3,967 mi) is the inner core. 

How and when the Earth got its crust are questions that divide geologists into two broad

camps—those who think it happened abruptly early in the Earth’s history and those who think

it happened gradually and rather later. Strength of feeling runs deep on such matters. Richard

Armstrong of Yale proposed an early-burst theory in the 1960s, then spent the rest of his

career fighting those who did not agree with him. He died of cancer in 1991, but shortly

before his death he “lashed out athis critics in a polemic in an Australian earth science journal

that charged them with perpetuating myths,” according to a report inEarthmagazine in 1998. 

“He died a bitter man,” reported a colleague. 

The crust and part of the outer mantle together are called the lithosphere (from the Greek

lithos, meaning “stone”), which in turn floats on top of a layer of softer rock called the

asthenosphere (from Greek words meaning “without strength”), but such terms are never

entirely satisfactory. To say that the lithospherefloats on top of the asthenosphere suggests a

degree of easy buoyancy that isn’t quite right. Similarly it is misleading to think of the rocks

as flowing in anything like the way we think of materials flowing on the surface. The rocks

are viscous, but only in the same way that glass is. It may not look it, but all the glass on Earth

is flowing downward under the relentless drag of gravity. Removea pane of really old glass

from the window of a European cathedral and it will be noticeably thicker at the bottom than

at the top. That is the sort of “flow” we are talking about. The hour hand on a clock moves

about ten thousand times faster than the “flowing” rocks of the mantle. 

The movements occur not just laterally as the Earth’s plates move across the surface, but up

and down as well, as rocks rise and fall under the churning process known as convection. 

Convection as a process was first deduced by the eccentric Count von Rumford at the end of

the eighteenth century. Sixty years later an English vicar named Osmond Fisher presciently

suggested that the Earth’s interior might well be fluid enough for the contents to move about, 

but that idea took a very long time to gain support. 

In  about  1970,  when  geophysicists  realized just how much turmoil was going on down

there, it came as a considerable shock. As Shawna Vogel put it in the book Naked Earth: The

New Geophysics: “It was as if scientists had spent decades figuring out the layers of the

Earth’s atmosphere—troposphere, stratosphere, and so forth—and then had suddenly found

out about wind.” 

How deep the convection process goes has been a matter of controversy ever since. Some

say it begins four hundred miles down, others two thousand miles below us. The problem, as

Donald Trefil has observed, is that“there are two sets of data, from two different disciplines, 

that cannot be reconciled.” Geochemists say that certain elements on Earth’s surface cannot

have come from the upper mantle, but must have come from deeper within the Earth. 

Therefore the materials in the upper and lower mantle must at least occasionally mix. 

Seismologists insist that there is no evidence to support such a thesis. 

So all that can be said is that at some slightly indeterminate point as we head toward the

center of Earth we leave the asthenosphere and plunge into pure mantle. Considering that it

accounts for 82 percent of the Earth’s volume and 65 percent of its mass, the mantle doesn’t

attract a great deal of attention, largely because the things that interest Earth scientists and

general readers alike happen either deeper down (as with magnetism) ornearer the surface (as 

with earthquakes). We know thatto a depth of about a hundred miles the mantle consists

predominantly of a type of rock known as peridotite, but what fills the space beyond is

uncertain. According to a Naturereport, it seems not to be peridotite. More than this we do

not know. 

Beneath the mantle are the two cores—a solid inner core and a liquid outer one. Needless to

say, our understanding of the nature of these cores is indirect, but scientists can make some

reasonable assumptions. They know that the  pressures at the center of the Earth are

sufficiently high—something over three million times those found at the surface—to turn any

rock there solid. They also know from Earth’s history (among other clues)that the inner core

is very good at retaining its heat. Although it islittle more than a guess,it is thought that in

over four billion years the temperature at the core has fallen by no more than 200°F. No one

knows exactly how hot the Earth’s core is, but estimates range from something over 7,000°F

to 13,000°F—about as hot as the surface of the Sun. 

The outer core is in many ways even less well understood, though everyone is in agreement

that it is fluid and that it is the seat of magnetism. The theory was put forward by E. C. 

Bullard of Cambridge University in 1949 that this fluid part of the Earth’s core revolves in a

way that makes it, in effect, an electrical motor, creating the Earth’s magnetic field. The

assumption is that the convecting fluids in the Earth act somehow like the currents in wires. 

Exactly what happens isn’t known, but it is felt pretty certain that it is connected with the core

spinning and with its being liquid. Bodies that don’t have a liquid core—the Moon and Mars, 

for instance—don’t have magnetism. 

We know that Earth’s magnetic field changes in power from time to time: during the age of

the dinosaurs, it was up to three times as strong as now. We also know that it reverses itself

every 500,000 years or so on average, though that average hides a huge degree of

unpredictability. The last reversal was about 750,000 years ago. Sometimes it stays put for

millions of years—37 million years appears to bethe longest stretch—and at other times it has

reversed after as little as 20,000 years. Altogether in the last 100 million years it has reversed

itself about two hundred times, and we don’t have any real idea why. It has been called “the 

greatest unanswered question inthe geological sciences.” 

We may be going through a reversal now. The Earth’s magnetic field has diminished by

perhaps as much as 6 percent in the last century alone. Any diminution in magnetism is likely

to be bad news, because magnetism, apart from holding notes to refrigerators and keeping our

compasses pointing the right way, plays a vital role in keeping us alive. Space is full of

dangerous cosmic rays that in the absence of magnetic protection would tear through our

bodies, leaving much of our DNA in useless tatters. When the magnetic field is working, 

these rays are safely herded away from the Earth’s surface and into two zones in near space

called the Van Allen belts. They also interact with particles in the upper atmosphere to create

the bewitching veils of light known as the auroras. 

A big part of the reason for our ignorance,interestingly enough, is that traditionally there

has been little effort to coordinate what’s happening on top of the Earth with what’s going on

inside. According to Shawna Vogel: “Geologists and geophysicists rarely go to the same

meetings or collaborate on the same problems.” 

Perhaps nothing better demonstrates our inadequate grasp of the dynamics of the Earth’s

interior than how badly we are caught out whenit acts up, and it would be hard to come up

with a more salutary reminder of the limitations of our understanding than the eruption of

Mount St. Helens in Washington in 1980. 

At that time, the lower forty-eight United States had not seen a volcanic eruption for over

sixty-five years. Therefore the government volcanologists called in to monitor and forecast St. 

Helens’s behavior primarily had seen only Hawaiian volcanoes in action, and they, it turned

out, were not the same thing at all. 

St. Helens started its ominous rumblings on March 20. Within a week it was erupting

magma, albeit in modest amounts, up to a hundredtimes a day, and being constantly shaken

with earthquakes. People were evacuated to whatwas assumed to be a safe distance of eight

miles. As the mountain’s 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 repeatedly

flew in helicopters to the summit, and people were even seen climbing over the mountain. On

one day, more than seventy copters and light aircraft circled the summit. But as the days

passed and the rumblings failed to develop intoanything dramatic, people grew restless, and

the view became general that the volcano wasn’t 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. The

seismologists resolutely based their conclusions on the behavior ofHawaiian volcanoes, 

which don’t blow out sideways. Almost the onlyperson who believed that something really

bad might happen was Jack Hyde, a geology professor at a community college in Tacoma. He

pointed out that St. Helens didn’t have an open vent, as Hawaiian volcanoes have, so any

pressure building up inside was bound to be released dramatically and probably

catastrophically. However, Hyde was not part of the official team and his observations

attracted little notice. 

We all know what happened next. At 8:32 A.M. on a Sunday morning, May 18, the north

side of the volcano collapsed, sending an enormous avalanche of dirt and rock rushing down

the mountain slope at 150 miles an hour. It was the biggest landslide in human history and

carried enough material to bury the whole of Manhattan to a depth of four hundred feet. A

minute later, its flank severelyweakened, St. Helens exploded with the force of five hundred

Hiroshima-sized atomic bombs, shooting out a murderous hot cloud at up to 650 miles an

hour—much too fast, clearly, for anyone nearby to outrace. Many people who were thought to

be in safe areas, often far out of sight of the volcano, were overtaken. Fifty-seven people were

killed. Twenty-three of the bodies were never found. The toll would have been much higher

except that it was a Sunday. Had it been a weekday many lumber workers would have been

working 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 been

manning an observation post 5.7 miles from the mountain, but he had a college placement

interview on May 18 in California, and so had left the site the day before the eruption. His

place 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’s luck, alas, was temporary. 

Eleven years later he was one offorty-three scientists and journalists fatally caught up in a

lethal outpouring of superheated ash, gases, and molten rock—what is known as a pyroclastic

flow—at 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 by

Stanley Williams of the University of Arizona, descended into the rim of an active volcano

called Galeras in Colombia. Despite the deathsof recent years, only two of the sixteen

members of Williams’s party wore safety helmets or other protective gear. The volcano

erupted, killing six of the scientists, along with three tourists who had followed them, and

seriously injuring several others, including Williams himself. 

In an extraordinarily unself-critical book called Surviving Galeras, Williams said he could

“only shake my head in wonder” when he learned afterward that his colleagues in the world

of volcanology had suggested that he had overlooked or disregarded important seismic signals

and behaved recklessly. “How easy it is to snipe after the fact, to apply the knowledge we

have now to the events of 1993,” he wrote. He was guilty of nothing worse, he believed, than

unlucky timing when Galeras “behaved capriciously, as natural forces are wont to do. I was

fooled, and for that I will take responsibility. But I do not feelguilty about the deaths of my

colleagues. There is no guilt. There was only an eruption.” 

But to return to Washington. Mount St. Helens lost thirteen hundred feet of peak, and 230

square miles of forest were devastated. Enough trees to build 150,000 homes (or 300,000 in

some reports) were blown away. The damage was placed at $2.7 billion. A giant column of

smoke and ash rose to a height of sixty thousand feet in less than ten minutes. An airliner

some thirty miles away reported being pelted with rocks. 

Ninety  minutes  after  the  blast,  ash began to rain down on Yakima, Washington, a

community of fifty thousand people about eighty miles away. As you would expect, the ash

turned day to night and got into everything, clogging motors, generators, and electrical

switching equipment, choking pedestrians, blocking filtration systems, and generally bringing

things 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 rumbling

menacingly for two months. Yet Yakima had no volcano emergency procedures. The city’s

emergency broadcast system, which was supposed to swing into action during a crisis, did not

go on the air because “the Sunday-morning staff did not know how to operate the equipment.” 

For three days, Yakima was paralyzed and cut off from the world, its airport closed, its

approach roads impassable. Altogether the city received just five-eighths of an inch of ash

after the eruption of Mount St. Helens. Now bear that in mind, please, as we consider what a

Yellowstone blast would do.