Joe Blow

Around the planet, hundreds of sleeping volcanoes could wake up with a bang at any moment. When the one near you has its day—pay attention, Seattle suburbs—you better hope that scientist Chris Newhall hears it before you do.

Dec 28, 2007
Outside Magazine

ON A HOT APRIL MORNING IN THE PHILIPPINES, Alan Nuñez and five of his friends and relatives and I hiked up a dry creek bed toward Mayon, the country's most active volcano. It's a near-perfect cone, with a steam-plumed crater that towers 8,000 feet above a vast, sloping plain. Mayon has erupted 51 times since the 1600s, killing thousands.

On its lower flanks, we stopped at an area laced with gigantic, sharp-edged boulders. Nuñez, a 31-year-old day laborer, pointed to a nearby slope. Here, at around 1 p.m. on February 2, 1993, 75 people, including Nuñez's uncle and cousin, Apolinaro and Cesar Mirandilla, were cultivating vegetables. Suddenly a cloud exploded from the summit and roiled downward, hugging the ground. Nuñez was watching from a mile off, in his home village of Bonga. The cloud, a grayish, cauliflower-shaped mass, reached the vegetable field in about 60 seconds, with a sound like a low-flying airplane. In his Bicol dialect, Nuñez called it an "uson," or glowing avalanche.

"A pyroclastic flow, though technically we'd call this one a pyroclastic surge," translated Nuñez's godfather, Chris Newhall, a 59-year-old American volcanologist who is perhaps the world's leading expert on the fine art of predicting eruptions and getting people out of the way. Pyroclastic flows are hot, fluid-like mixtures of gases, ash, and boulders that can reach temperatures of up to 1,200 degrees Fahrenheit and travel 100 miles per hour. They usually kill by searing and cementing the lungs or, alternatively, by broiling, dismembering, or vaporizing you.

Nuñez went on, describing what unfolded that day. "Stay with me," Apolinaro said to his son as they saw it approach. "At least they will find us together."

"No, I think I can make it," said Cesar, and he ran.

An hour or so later, Cesar arrived in Bonga straddling a water buffalo. He had been caught by the uson's edge. His skin was charbroiled black, with a consistency like that of "fried chicken," said Nuñez. When Nuñez helped Cesar down, the skin on Cesar's hands came off "like gloves." Cesar lived for three days.

When the ash cooled enough, the villagers went to retrieve the dead. Many were never found. Apolinaro had been hurled some 300 yards downslope and was lying tilted backwards with his upper body sticking above the still-smoking debris. His arms were thrown in front of him, bent at the elbows, hands pushing forward. Apolinaro's face, said Nuñez, was filled with "nasubrahan nín takot."

"An excess of fear," Newhall translated.

Horror stories like these are a big part of what drives Newhall, who has worked around Mayon off and on for more than 40 years. Married to a Filipina, he has a huge extended family nearby—Nuñez is the son of an old friend—and has witnessed many terrifying events here himself. Though he formally retired from his longtime post with the U.S. Geological Survey in 2005, Newhall continues to play a key role on the USGS's Volcano Disaster Assistance Program (VDAP), a geological SWAT team that assesses volcanic crises worldwide. He's also an unpaid consultant to the Philippine Institute of Volcanology and Seismology (PHIVOLCS). In 2005, he moved from Seattle to live year-round at Mayon's foot, thinking he might be of some use here.

Colleagues call Newhall "Saint Christopher" because he seems to care more about people than science. Nearly six feet tall, upright and often somnolent, he looks uncomfortable when anyone talks about his achievements. Off duty, he laughs and jokes easily in English and two Filipino dialects. But when talking volcanoes, he speaks with such slow, unsmiling intensity that some people think he's being unfriendly. Newhall forgets who said it, but he likes the quote that goes something like, "The magnitude of a tragedy may be measured by the degree to which it could have been prevented."

"When it comes to mitigating hazards, Chris is the single most influential volcanologist in the world," says C. Dan Miller, a former head of VDAP. Newhall has an uncanny ability to memorize the unique histories and behaviors of individual volcanoes and has been a pioneer in synthesizing what's known about eruption warning signs. After Washington's Mount St. Helens killed dozens when it blew in 1980, he created a novel risk-calculation system to gauge whether it was safe to reapproach the beast; his principles have since become standard tools for volcano assessment. It was Newhall and colleagues who forecast the 1991 explosion of the Philippines' Mount Pinatubo—the world's largest eruption in almost 100 years—spurring a biblical-scale evacuation and saving up to 20,000 lives.

But Pinatubo was a unique scenario in which almost everything went right. Despite advances in forecasting technology, volcanoes will continue to blow unexpectedly. Even the most sophisticated predictors can fail, and they're so expensive and complex that scientists stationed around the planet keep close tabs on only some 50 obvious suspects. In the United States, a 2005 USGS report identified 13 inadequately monitored "very high threat" volcanoes, including Washington's Mount Rainier, which, when it awakes—not if—could kill tens of thousands with little warning.

"I'd like to say we can always save lives," says Newhall, "but we'd be kidding ourselves if we said we really understood what's going on down there. We cannot yet forecast eruptions as well as we can forecast hurricanes. This is partly because we can't see inside the earth the way we can see in the atmosphere. But I'm optimistic. We're getting better all the time."

DURING THE 20TH CENTURY, volcanoes killed 80,000 people, but not the way you'd probably imagine. Lava is actually a minor threat. It usually moves too slowly to catch anyone—only 100 or so people in the 1900s. Pyroclastic explosions like the one at Mayon are the top danger. Lahars—swift flows of volcanic mud—come in second. Falling ash, ballistic projectiles, poison gas, landslides, and volcanism-generated tsunamis round out the list.

Worldwide, 500 million people live in danger zones, but between eruptions most tend to forget. "Even a decade is a long time in people's memory," says Newhall. "It's just human nature." Earth has 1,500 potentially active volcanoes—ones that have erupted in the last 10,000 years—but during the past 200 years, three-quarters of the biggest eruptions have come at sites with no historically recorded activity. "A sleeping volcano is no cause for reassurance," says Newhall. "It may be building pressure. Bigger booms are typically preceded by longer waits."

Among the United States' 169 active volcanoes are dozens of dozing giants. The Volcanic Explosivity Index (VEI), a kind of Richter scale for eruptions that Newhall helped create, rates blasts on an exponential curve from zero to eight. When Mount St. Helens blew after sitting silent for more than a century, it knocked out a VEI 5—equal to one Hiroshima-size atomic bomb per second for nine hours. Other U.S. volcanoes that could erupt on this scale include the Three Sisters mountains, near Bend, Oregon, which alarmed geophysicists in 2001 when they realized the triplet peaks' flanks had inflated about four inches over four years (they have done little since); Washington's Mount Baker, which briefly melted off some of its glacial coating in 1975; and Oregon's Crater Lake and California's Mount Shasta, which haven't done much of anything lately—which is exactly the problem.

Then there's 14,410-foot Rainier, the dominant feature of the Seattle skyline and probably the greatest potential killer in the U.S. Though it's unlikely to erupt with St. Helens–like ferocity, Rainier's steep, loosely consolidated flanks are coated with some 36 square miles of glacial ice. Even a minor event—an earthquake, hot water bubbling to the surface, a squirt of lava—could produce lahars up to 100 feet tall and traveling downhill at 60 miles per hour. Some 150,000 people now live on lahar deposits, which in the past have reached Puget Sound, 40 miles from the summit.

Like other active U.S. volcanoes, Rainier is monitored with seismometers, which will warn USGS scientists of a possible eruption or rumblings powerful enough to trigger lahars. Last September, the USGS installed GPS units on the mountain to watch for bulges, which could indicate rising magma. If either system indicates trouble, scientists will alert emergency response teams, setting in motion evacuation procedures practiced once or twice a year in the towns lying in Rainier's lahar pathways.

The real nightmare scenario is a lahar unconnected to a quake or other detectable sign. This is of particular concern on the peak's western slope, where sulfuric acid has been eating away at rock layers from the inside. A collapse here could unleash a torrent of ground water and debris. In this case, the first indication of disaster will come from one of ten lahar monitors set in streambeds to pick up ground vibrations. The 5,500 residents of Orting—the closest town to Rainier, resting on deposits left by the last giant flow, 500 years ago—will have roughly 40 minutes to get to high ground.

For any volcano, researchers can calculate the average intervals between eruptions by studying deposits left by previous blasts. But Newhall doesn't labor under the misconception that these are so regular that a volcano is, at some definable moment, due for the Big One. To make a forecast, you have to listen.

"Luckily, magma has to make its way to the surface, and on the way, it makes noise," says Newhall. In a classic sequence, magma cracks through rocks six or 12 miles down, generating modest high-frequency earthquakes. When the magma gets closer to the surface, lower frequencies predominate—probably because of fluids gurgling around or gases coalescing into bubbles. The gathering pressure may deform or crack the surface; gases such as sulfur dioxide, a common eruption indicator, will emerge. Days or hours before an eruption, scientists may observe volcanic tremor—a continuous vibration, often with a steady, musical frequency.

To detect such signals, volcanologists are deploying ever more sophisticated instruments. These include growing seismic networks, satellite imaging systems that note surface bulges as small as an inch, and light sensors that can detect sulfur dioxide from miles away. Unfortunately, data from all these devices rarely provide clear answers. A snoozing volcano can snort, twitch, and turn over for months or years, then go back to sleep. Or explode.

"A volcano can tease you. It'll make you think it's going to blow up, and then at the last moment it'll back off," Newhall says. "This leaves us with an interesting dilemma. For a myriad of reasons, most people resist leaving home without an immediate cause. But if you wait until you're absolutely sure, you'll probably be too late. If you warn too soon, people stop listening to you. Generally you only get one chance."

I ARRIVED IN THE PHILIPPINES ON A MONDAY MORNING TO stay with Newhall and his wife, Glenda, at their newly built house in the hamlet of Salvación. It's near the southern end of Luzon, the archipelago's main island, along a spectacular bay. From the back porch, looking nine miles across the water, we could see Mayon venting a constant bluish cloud. It's been restless lately, spouting eruptions small and large since 2000.

The house sits on ancient volcanic deposits, but Newhall assured me Mayon's modern eruptive pattern does not reach here. "At least as far as I can tell," he said. "There is always a plus or minus with any measurement."

Newhall grew up in Quincy, a logging town in the Northern California Sierra Nevada. Early on, he collected unusual rocks and got some faint sniffs of hydrogen sulfide from volcanic Lassen Peak, where his family visited often. He earned a geology degree from UC Davis in 1970, then joined the Peace Corps. He wanted to do something positive for the world and did not want be drafted into the Vietnam War, which he detested. He ended up teaching Geology 101 at a college in Legazpi, a city near Mayon. He loved it. On weekends he traveled around the volcano's slopes, mapping deposits and clambering into the then-cool, inactive crater. He met Glenda, a local teacher, early on and they married in 1971.

Hoping to combine science with humanitarian aid, in 1980 Newhall completed his Ph.D. at Dartmouth and joined the USGS. For much of his career he was based in Washington State, where he and Glenda raised two kids. He frequently jetted to volcanic trouble spots—Ecuador, Papua New Guinea, Mexico, Indonesia—becoming a major force at VDAP. In the 1980s, he compiled a first-of-its-kind list of the threats posed by the world's so-called supervolcanoes—the mountains geologists believe could blow big enough to affect global climate and kill huge numbers of people. Lately, he's been developing an Internet database that will catalog information from eruptions around the world, telling scientists how particular sequences of indicators played out in the past.

Since Newhall and Glenda resettled in Salvación, much of his pension has gone to help put ten sons and daughters of poor neighbors and Filipino friends through college. Glenda, now a nurse, dispenses free medicine and advice. They also have a family of 11 living in an annex to their house; the parents needed employment, so the Newhalls hired them and put them up.

On my first night in Salvación, I heard Newhall's cell phone chime in the adjoining bedroom at 1:31 a.m. In the morning, he showed me a text message from Ed Laguerta, a PHIVOLCS volcanologist: BULUSAN EXPLOSION ON FLANK. AM HERE AT BULUSAN NOW. Bulusan is a volcano a few hours' drive south from Mayon that explodes moderately about once a decade. A big blast there could reach towns containing some 56,000 people.

After a morning of bouncing along Luzon's potholed roads, we came across a half-dozen PHIVOLCS staffers working from a tiny concrete-block observatory in a goat pasture. Several miles off lay Bulusan, a jungly sawtooth-shaped mass jetting steam from a crack near its bald top. Bella Tubianosa, the resident volcanologist and an old friend of Newhall's, told us seismometers had picked up quakes a few days before. Then explosions shook the area, and a dusting of ash floated down onto nearby towns.

"This is a crisis, but so far it's a minor crisis," said Tubianosa, a slender woman in her forties who projected the calm of a surgeon.

Tubianosa had two cell phones, which kept ringing. A TV news crew came in. In the glare of their lights, she squelched a rumor that PHIVOLCS had called for an evacuation. Afterwards, she took me aside. "Right now I'm feeling a lot of concern, because this volcano is not showing its usual activity," she said. Behind her, the observatory's old-fashioned seismograph drums turned slowly, their narrow ink traces showing that the quakes had abated. As a rule, decreasing seismicity is good. On the other hand, noted Newhall, "When it gets quiet, that can mean magma is right at the surface—there's nothing in its way."

At least four seismometers are needed to precisely locate volcanic quakes, but Tubianosa used only two, which was all PHIVOLCS had here. The Philippines owned one correlation spectrometer, a device that detects sulfur dioxide, but it was at Mayon. For an alternative, Newhall e-mailed a Maryland-based NASA scientist with access to a satellite that can spot the gas from space. He got back an image showing a cluster of red pixels downwind of Bulusan. This, he said, represented about 1,000 tons of sulfur dioxide—proof that magma was indeed somewhere inside the mountain. Tubianosa looked at the image intently. "It doesn't tell us how far down," she said.

We drove to the village of Sangkayon, nestled along the volcano's base, where a fine whitish ash had coated rooftops, trees, and yards and was fueling a dust cloud on the well-traveled road. Many people had pulled shirts or surgical masks over their faces. Newhall interviewed two young men who told him the volcano had roared for ten minutes and a reddish column had lit the sky. We drove upward along a dirt track and found two other men with much the same story. They added that they had smelled something like matches being lit—evidence of magma near the surface.

We parked along a rice paddy with a view of the steaming peak. "So," said Newhall, "the question, as always, is this: Is the volcano clearing its throat and getting ready to say something important? Or has it already said its thing?"

ON MAY 18, 1980, MOUNT ST. Helens exploded, the first major eruption of any volcano in recorded U.S. history. Obvious portents—big quakes, melting snow, a visible bulge—had led to partial evacuation of the area. But the eruption's scale and suddenness caught geologists off guard: 230 square miles were scoured, forests flattened like matchsticks, without any new precursors in the final hours. A young USGS geologist whom Newhall knew, David Johnston, was among the 57 dead.

Months later, with the mountain still firing occasional salvos, Newhall was appointed "hazards coordinator," charged with synthesizing data from seismologists, geochemists, and other specialists into practical advice. It was a breakthrough moment in his career. He invented simple equations based on things like the frequency and force of past eruptions, detection of active fissures, and visitors' proposed locations and length of stay. With these he estimated the risk of visiting St. Helens versus, say, being a wartime soldier or smoking cigarettes. According to his figures—perhaps off by ten times or more, he admitted—loggers salvaging blown-down trees had a one-in-a-thousand chance per year of being killed, provided they complied with evacuation alarms. This was about equal to routine work in a stone quarry, so in 1981 the loggers went in.

"This kind of cold calculation at first met with skepticism, and maybe horror," Newhall says. "But people need some way of making decisions."

Not that they'll always make smart ones. Active craters often exert an almost erotic magnetism for volcanologists. Many like whiffing toxic gases, feeling the ground shake, and generally peering into death's open mouth. Newhall is not like that; he avoids personal risk whenever possible. When he was on St. Helens, he argued with colleagues who he felt made unnecessary visits to the mile-and-a-half-wide crater, where boulders rattled down vertical walls and a dome of congealed lava unpredictably shot out searing gases and basketball-size rocks.

"Right up at the action, it's the little things that will get you—you don't need an eruption," says Newhall.

Of course, some tasks can be done only up close. These include collecting samples of volcanic gases directly from vents in vials, for detailed studies of magma chemistry and evolution. Still, when it comes to immediate hazard assessment, Newhall believes remote sensing now provides most of the essential data.

"Volcanologists take risks in order to reduce the risks to others," he says. "Before you go in, you should ask yourself: If I die, will my family and colleagues be able to say it was worth the data I got?"

Since the 1970s, about 35 volcanologists have been killed on the job. Many were Newhall's buddies or friends of friends. He counted them off to me one day over breakfast. His Dartmouth mentor, Dick Stoiber, had a grad student, Gary Malone, who fell off a cliff on Sicily's Stromboli volcano. There was Russian volcanologist Igor Menyailov, who along with five others was incinerated in 1993 when a lava dome blew at Colombia's Galeras volcano—an event later chronicled in two books. Two Indonesian friends, Asep Wildan and Mukti, were killed in a similar blast in 2000 at Semeru volcano; Newhall helped evacuate four battered survivors.

In the late eighties, Newhall co-wrote the script for a documentary designed to scare the hell out of civilians living near volcanoes so it would be easier to evacuate them. The footage—raging lahars and pyroclastic flows, corpses with burned-off faces, a tiny mud-spattered girl shaking with terror—was supplied by Maurice and Katia Krafft, a French husband-and-wife team famous for jetting to every eruption. On June 3, 1991, the Kraffts were in Japan filming Mount Unzen when a pyroclastic flow carbonized them, along with former USGS geologist Harry Glicken, who had narrowly escaped St. Helens. Some 40 others were also killed.

Most recently, on April 28, 2005, a helicopter carrying five PHIVOLCS staffers clipped a tree and crashed, exploding into flames. Among the dead was former PHIVOLCS director Ray Punongbayan—one of Newhall's closest friends.

"It's been a bad few decades," said Newhall, staring into his coffee cup.

BULUSAN KEPT THROWING OFF GASES AND TREMORS. AFTER a day of watching, we returned to Mayon. While driving the road circling the base, we came upon three boys digging fill from a road cut that exposed about 15 gravelly layers of lapilli, or fallen volcanic stones. Each layer represented a major eruption.

"There's the 1814 one," said Newhall, pointing to an eight-inch swath near the top from a blast that killed 1,200 people. He dug out a thumb-size stone. "If that fell on you from a mile up, it would put a hole in your head. All these places around here are going to be hit again someday."

Outside the city of Legazpi, we visited the ruins of Cagsawa, a village buried by the pyroclastics and lahars of 1814. It's now a tourist site, with souvenir and refreshment stands. About the only thing visible of the old village is the steeple of a Spanish colonial church; the rest of it lies below, along with the people who were praying inside at the time.

Newhall pointed to the six-mile expanse stretching from Cagsawa to Mayon's summit. Fields, roads, and houses have sprung up on top of the eruption deposits. Otherwise-landless subsistence farmers are attracted by the volcanic soils, which need no fertilizer because mineral nutrients get replaced every time the volcano vomits. All told, some 400,000 people are in reach of Mayon. "The root problem is not volcanism—it's overpopulation," he said.

Indeed, no matter how good forecasting technology gets, human factors will continue to cause calamities that could have been avoided. In 2002, the Congo's Nyiragongo volcano blew during a chaotic civil war, leveling much of the city of Goma, uprooting 400,000 people, and mowing down 150 with a rare, fast-moving type of lava flow. Several years before the eruption, Goma's small volcanic observatory had been rocketed and pillaged. When Newhall arrived with colleagues in the aftermath, he learned that Congolese scientists had tried to warn the populace, but without a working government or telephones, they didn't get far.

Others refuse to take heed because it's inconvenient. In 1982, after quakes shook the popular California mountain-resort area of Long Valley, the USGS issued a low-level eruption warning. There was no evacuation, but vacationers were badly spooked; condo sales plummeted, and storefronts went vacant. Furious locals nicknamed the USGS the "U.S. Guessing Society." C. Dan Miller, the volcanologist in charge, considered moving his family after a local suggested that a bomb could wind up in his car.

Around Mayon, people simply accept the danger. In 2000 and 2001, PHIVOLCS successfully called evacuations just before blowouts, and only livestock were killed. However, a typhoon hit on November 30, 2006, dumping 18-plus inches of rain onto the mountain within a few hours. Lahars killed more than 1,000 people, but the ruins were quickly reoccupied.

One hot afternoon in Bonga, I was sitting with Alan Nuñez and his family under the shade of a broad-leafed malabago tree next to his tiny house. "This is where our livelihood is, our memories," said Hercolano Nuñez, Alan's father. "How could we leave?"

Hercolano told a story about a man his grandparents knew, who saw an uson coming during the eruption of 1897. The man tried to escape on his horse, but he was so scared, he forgot to unhitch the animal from the tree where it was tied. When he whipped it, man and horse spun in concentric circles—"One! Two! Three!" Hercolano shouted, running his hands in circles—while the uson burned them alive. Everyone under the malabago guffawed.

WHEN A VOLCANO GIVES CLEAR SIGNS, IT'S POSSIBLE TO avert a massive tragedy. On April 2, 1991, fissures opened on a remote flank of Mount Pinatubo, and steam exploded out. The area, 260 miles northwest of Mayon, was then inhabited by only a few indigenous Aeta people and guerrillas of the communist New People's Army, but the event was reported by Catholic nuns. Three days later, PHIVOLCS brought in a seismometer, and within 24 hours counted hundreds of volcanic quakes. Newhall's old friend Ray Punongbayan was so alarmed that he cleared out 4,000 people living within six miles. On April 23, Newhall arrived from the States with several VDAP specialists and 35 trunks of gear.

Newhall had researched what little was known about Pinatubo and classified it as a "tight" system. These tend to be contained for many years under a plug of cooled magma. Somewhere along the line, pressure rebuilds, and then one day it opens with incredible violence. During its last eruption, in around a.d. 1450, the mountain had totally blown itself up. Hence, it exhibited no pretty Mayon-like cone, just an irregular, hulking mass.

At the foot of Pinatubo lay Clark Air Base, then the United States' main Asian staging facility. Newhall called Clark's weatherman and explained that the 15,000 personnel and the fleets of warplanes could disappear if anything went wrong. Air Force brass were skeptical—they called the scruffy volcanologists "the beards" behind their backs—but gave them air support and a house to live in. When a helicopter ferried them to scout the mountain, a door gunner constantly scanned the ground with his weapon, watching for NPA. Upon landing, the rotor would wash back high elephant grass and the scientists would leap out, instruments at the ready for a quick in-and-out.

One of the first things Newhall spotted was a 230-foot-high cliff of crumbly brownish-gray material cut in cross-sections by a river bordering Clark. It was pyroclastic-flow debris. "Holy moly," he said. "When things go around here, they go big." By mid-May, the team had created a map showing 60 square miles of similar deposits.

Two weeks later, seismometers indicated that quakes were migrating toward Pinatubo's summit. Then a classic pre-eruption volcanic tremor started. During this period, Newhall took repeated helicopter flights to measure sulfur dioxide emissions with a correlation spectrometer lashed to the open gunport. Levels surged from 500 tons a day to 5,000—a sure sign of rising magma. At the start of June, the emissions suddenly dropped to near zero. Either the magma had backed off or the system was totally blocked—and building pressure.

Newhall and Punongbayan met with then–defense minister and future president Fidel Ramos, who listened gravely and then followed their advice for wider evacuations. On June 2, Newhall flew to brief generals at Pacific Command in Hawaii. He figured he would have time to continue on home for a quick visit and be back to catch any fireworks.

He was wrong. While he was in the States, the quakes accelerated. Authorities evacuated more people; eventually 200,000 would flee. On June 10, Clark was cleared. On June 12, a three-day series of pyroclastic blasts started. Orange lightning bolts generated by static electricity in the ash slashed the atmosphere. On June 15, seven great explosions evolved into one continuous, earthshaking roar. Pulverized magma shot 25 miles into the sky, raining darkness. Pyroclastic flows buried surrounding valleys 600 feet deep in hot debris. Then a typhoon swept in. The rain, combined with ash, crushed thousands of roofs far beyond the evacuation area. Lahars took out most bridges, and many villages, for 30 miles around.

When the air cleared, the top of Pinatubo was gone. After blowing out its guts, the summit had collapsed into itself, creating a half-mile-deep, 1.5-mile-wide caldera. Of the 20,000 people who had faced certain death, only about 100 Aeta and maybe a handful of guerrillas were killed in the eruption; no trace of them was ever found. (Two hundred other Filipinos died outside the evacuation zone in roof collapses.) No one was hurt at Clark, but hangars and other buildings collapsed. The U.S. moved out permanently; the remains of the base now comprise a modest business park. "This is the textbook case—a volcano that cooperated," says Newhall.

Three months after the eruption, a hot, acidic lake began collecting in the caldera. With the lake still steaming and occasional small explosions pocking the surface, Newhall had a helicopter fly over it, then had himself lowered down 300 feet on a cable to take important water and rock samples. He did not want the craft to go any lower, for fear that carbon dioxide, another common volcanic gas, might stall the engine. Since it also suffocates humans, he told the pilot to winch him up fast if he stopped waving or moving. He kept moving.

PINATUBO MATERIALIZED FROM A CLEARING MORNING MIST—a row of distant, friendly-looking green hills. "Doesn't look like a volcano at all, right?" said Newhall as we drove around it in a rented jeep. We were on our way to camp out in the crater, which has become a tourist site in the past seven years or so, after the lake grew to a half-mile across and returning trees and plants started drawing hikers.

Closer in, under a blistering sun, we rolled up a vast, barren, and roadless valley still covered with chalky deposits of ash and rock. Here and there, people were gathering golf-ball-size, 1991-vintage volcanic-pumice chunks for sale to manufacturers of stone-washed jeans.

Eventually the valley narrowed to a tortuous canyon, and we started walking. A gushing creek ran through jumbled piles of volcanic boulders and sand. A couple of hours later, we climbed through a fern-shaded defile and emerged onto a one-acre ledge. This overlooked the caldera—a vast bowl hemmed in by cliffs topped by jagged pinnacles. Far below, a deep-turquoise lake shimmered under a breeze.

There were voices. Three dozen people had set up a tent camp and unfurled a banner: PINATUBO 2006—ONLY THE BRAVE AND THE DARING SURVIVE. They were mostly Chinese-Filipino doctors and nurses on a weekend trip. Newhall was dumbfounded. "I knew there were tourists," he said. "But not like this."

A friendly young doctor walked over. "Good afternoon," he said in excellent English. "Your first time at Pinatubo?" Newhall just smiled.

After pitching our tent, we clambered down a few hundred feet to a small beach along the lake. "Sixteen years ago, where we are now, there were 1,000 meters of rock over our heads, and the temperature was about 300 degrees Celsius," he said. "Geology is supposed to move very slowly. But, you see, geology can move very fast."

He suggested a swim. We pushed off, and found the water pleasantly cool. We stuck to the edges, backstroking or crawling slowly along the sheer walls. About half a mile on, we rounded a bend and heard something like a large soup cauldron at work. From small holes in the cliff, boiling water and a faint sulfur smell were spurting—the result, he said, of circulation from some still-cooling rock below.

"It's just the volcano's way of saying, ‘I'm still here!' Now, don't get too close. It will cook you." A few minutes later I stupidly touched a hot rock with my foot, and yelped. Newhall winced. I backed off, and we basked together in the diluted heat plume 50 feet off. "Ah, it's good to be back here," he said with a sigh.

Back at the campsite that night, opaque clouds covered the sky. It was pitch black. The hiking club invited us to their campfire—a Coleman lantern—and one 30-ish doctor produced
a bottle of Fundador brandy. A tin cup was passed around, and we took turns chugging shots in a popular Filipino custom known as tagay.

When the group found out Newhall was a volcanologist, they could not ask enough questions. Sitting cross-legged on the ground, he told them that, these days, PHIVOLCS kept just one seismometer on Pinatubo. Lately it had picked up a few quakes, but small ones. The magma was probably three or five miles below and not going anywhere. The tin cup kept going around.

After a while, one doctor asked what everyone was wondering: "What are the chances of something happening to us tonight?"

Newhall said nothing for a moment, "Well , to make a random calculation the volcano erupts every thousand years, and it just erupted," he said "But we're only here tonight, right? So let's divide that by 365. what's that? About three in a million? Of course, that's for something big. For somthing samll , the chance is greater, but I can't say how much greater. It wouldn't have to very big. Sitting where we are, just a little burp would get us".

The circle fell silent. A bit of wind far above suddenly swept the clouds away. We were now under a great dome of brilliant stars, reflected in the lake.

"Well, in this world, nothing has a zero chance," Newhall finally said. "But whatever the chances are, they are vanishingly small. We should all sleep easy tonight."

Eventually everyone stumbled off to bed, and we did

Imagining the worst at four U.S. volcanoes, where the incredibly unlikely is still very, very scary

Mount Rainier, Washington
THE NIGHTMARE: Lahars—fast-moving flows of volcanic mud—rip down the 14,410-foot peak's western slope into lowland suburbs. The flows might be triggered by earthquakes, lava, steam, or—worst possible case—an undetected slip in surface rock, giving the 5,500 residents of Orting just 40 minutes to evacuate once monitors pick up a slide.
AT RISK: More than 150,000 people who live in potential lahar pathways.

Yellowstone Caldera, Wyoming
THE NIGHTMARE: Though this deep-sleeping supervolcano blows big just once or twice every million years, a massive eruption could conceivably pulverize thousands of square miles with falling rocks and bury what's left with ash, killing everything. Gases and particulates released into the atmosphere would also alter global climate for years.
AT RISK: Much of the western United States.

Long Valley Caldera, California
THE NIGHTMARE: An eruption near the mountain-town getaway of Mammoth Lakes, where historically peaceful magma chambers have the potential to blow ash six miles skyward. Once the debris falls back to earth, it could form into pyroclastic flows speeding toward developments at 100 miles per hour.
AT RISK: Many a nice ski condo and—if the blast is on a peak winter weekend—some 35,000 lives.

Mauna Loa, Hawaii
THE NIGHTMARE: Molten lava rolls down the tropical mountain's northeastern flank and incinerates the city of Hilo, the Big Island's main port and commercial hub.
AT RISK: Hilo's 41,000 residents would have days to evacuate before the slow-moving lava arrived, but the city itself could be burned to nothing and—if lava reached all the way to the water—the port could be permanently shut down.

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