When Science Goes Wrong: Twelve Tales From the Dark Side of Discovery - Simon LeVay (2008)

VOLCANOLOGY: The Crater of Doom

VOLCANOES DEMAND RESPECT, but they don’t always get it.

In 1993, when geologist Stanley Williams led a party of scientists to their deaths in the crater of an active volcano, he triggered an eruption of controversy and blame.

The volcano in question was Galeras (“the galleons”), a 14,000ft-high peak in the cordilleras of south-western Colombia. On its eastern flank, just four miles from the summit but 5,000 feet below it, lies the city of San Juan de Pasto. Although it has a population of more than 300,000 and is the capital of the Colombian department of Nariño, Pasto is a fairly sleepy provincial town that is largely cut off from the bustling metropolitan centres to the north. If anything keeps the citizens of Pasto on their toes, it is the rumblings and occasional eruptions of their local volcano.

Galeras presents a real danger, in the sense that it has erupted frequently over recorded history. Significant eruptions occurred in or around 1580, 1616, 1797, 1830, 1865-1869, 1891, and 1936. With a record like this, one always has to keep the possibility of an eruption in mind, especially with a fair-size city so close by.

Galeras is also dangerous on account of the type of magma (molten volcanic rock) that it produces. Known as ‘andesite’, Galeras’s magma is rich in silica and consequently is thick and pasty, especially after it is exuded onto the surface and has a chance to cool. Unlike the more liquid magmas found in Hawaiian volcanoes, which run smoothly down the volcanoes’ outer slopes as incandescent lava flows, the magma at Galeras tends to pile up where it erupts, forming solid domes of lava that eventually seal off the vents through which the magma reached the surface. Thus, if pressure continues to build as more magma is forced upward from below, the result may be a sudden and difficult-to-predict explosion.

Frequent, explosive eruptions are dangerous, but there are also factors that tend to lessen the hazards posed by Galeras. For one thing, the historical eruptions have been fairly small - most of them have been confined to the volcano’s caldera, the mile-wide sunken amphitheatre that was created when the volcano’s summit collapsed during some prehistoric eruption. Also, the occasional lava flows and pyroclastic flows - lethal surges of ash and pumice buoyed by hot gases - have generally exited the caldera toward the west, because the caldera’s walls have been breached on that side. The city of Pasto, on the eastern side of the volcano, is partially protected by the caldera’s 500ft rampart.

One more feature of Galeras limits the hazard it poses to the local population. Because of its moderate altitude, combined with its location barely 80 miles north of the equator, its summit is free of snow or ice. Snow banks or glaciers may enhance a volcano’s beauty, but they also spell danger because an eruption can rapidly melt the ice. The resulting meltwater, mixed with soil, rock, and ash, is likely to rush downhill in the form of all-consuming mudflows. In 1985, an eruption of the 17,400ft Nevado del Ruiz volcano, 300 miles northeast of Galeras, melted its glacial cap: the resulting mudflow travelled more than 20 miles to the town of Armero, which was nearly totally destroyed at a cost of more than 23,000 lives. Such an event could not happen at Galeras.

Whatever its danger level, Galeras was largely ignored by the world’s volcanologists until 1988. In that year, after half a century of inactivity, the volcano showed renewed signs of life. A series of small earthquakes struck the area. In addition, steam began to vent from the volcano. The Colombian government, hypersensitive to volcanic hazards after the Nevado del Ruiz tragedy, sent several volcanologists to investigate and monitor the situation.

Climbing Galeras is a simple matter: one gets into a jeep and drives up. The access road zigzags its way up to the south-eastern rim of the caldera. There, in 1988, was located a small police post and several communications towers. A few policemen were always stationed at the post to guard the towers against sabotage by the leftist guerrillas who were active in Nariño province. From the rim, one could look down on the interior of the caldera: its main feature was a central volcanic cone. About half a mile wide at its base, the cone rose 450ft from the floor of the caldera but did not rise as high as the caldera rim. At the top of the cone was the actual crater of the volcano - a 100ft-deep cavity. Getting from the caldera rim to the edge of the crater was an arduous journey: it involved edging down the very steep eastern rampart of the caldera with the aid of a fixed rope, crossing the floor of the caldera (the ‘moat’), and then climbing the cone. From there, it was another tricky descent into the crater itself.

When the Colombian volcanologists visited the caldera in 1988, they did not descend into the central crater, because it would have meant death to do so: the crater floor was incandescent with heat. Obviously, something very serious was going on inside Galeras. They returned to Pasto and reported their findings to the director of the Colombian National Institute of Geology and Mines, or INGEOMINAS. He called in turn for help from the United States. A few weeks later, David Harlow, of the US Geological Survey (USGS) in Menlo Park, California, brought a small team of scientists to Galeras. They installed several more seismographs around the volcano.

In the spring of 1989, a larger group of Colombian and foreign volcanologists met in Pasto. Two eruptions took place that spring, and though they had both been very small, they got the attention of the people of Pasto. The local government began issuing colour-coded warnings, and as so often happens, these induced more confusion than comprehension. Furthermore, the city experienced serious economic problems, as banks stopped issuing loans to local businesses and tourism dried up.

Soon after the 1989 meeting, Galeras quieted down. Then, in the autumn of 1991, eruptions began again. A lava dome rose slowly from the floor of the crater, eventually reaching a height of 150ft. In response to this alarming development, the governor of Nariño called for yet another meeting of scientists, which took place later that month. Among the attendees was Marta Calvache, a young Colombian volcanologist who grew up in the shadow of Galeras and who had been at Nevado del Ruiz during the deadly 1985 eruption. In the aftermath of that event she had met Stanley Williams, an expert in volcanic gases at Louisiana State University. Calvache later went to LSU and did a master’s thesis with Williams. (Williams moved to Arizona State University in 1991.) The relationship between Calvache and Williams was an obvious and immediate benefit to Calvache, furthering her expertise and her career. But, as it turned out much later, it was an even greater benefit to Williams, for it was Calvache who saved his life while his colleagues died.

Another attendee at the 1991 meeting was Bernard Chouet, a Swiss-born geophysicist with the USGS in Menlo Park. Chouet’s speciality was the interpretation of the seismic signals emitted by active volcanoes. Over the course of a few years before the meeting, Chouet had come to believe that he had discovered a hitherto unknown method for using these signals to predict eruptions.

The seismic signals generated by volcanoes are of two basic kinds. The more common kind are basically little earthquakes: they are produced by the fracturing of rock as magma creates passageways for its ascent to the surface. On seismograms, these events look quite like the common, nonvolcanic earthquakes that are generated by the motion of geological faults: brief, jittery signals that, if sped up and played through a loudspeaker, sound like bangs, pops, rips, crunches, roars or other unattractive noises. They are assigned magnitudes just like regular earthquakes and, though most are tiny, a few range up to magnitude 5 or so, and are thus easily felt by people living in the vicinity of the volcano. They are called volcano-tectonic earthquakes.

The other, less common seismic signals are quite different. They are low-pitched (infrasonic) vibrations that may continue for half a minute or longer. When sped up and converted into sound, they have an eerily musical quality - they may be reminiscent of whale song, a dirge played on trombones, or Tuvan throat-singing.* Unlike volcano-tectonic earthquakes, these events confine most of their energy to a single, very low frequency - a deep-pitched tone - along with some higher-pitched harmonics that add to the musical quality of the sound. They are called long-period events - ‘long-period’ in this context means the same thing as ‘low-pitched’.

Prior to Chouet’s work, much more attention had been paid to the volcano-tectonic earthquakes than to the long-period events as predictors of volcanic eruptions. It is certainly true that most volcanic eruptions are preceded by volcano-tectonic earthquakes. They may start months or years before an eruption, as magma begins to rise from deep magma chambers and collect nearer the surface. These earthquakes are commonly the long-term warning signs that tell volcanologists - and the local populations - that they need to pay attention to the volcano.

Sometimes an intense swarm of volcano-tectonic earthquakes may immediately precede an actual eruption. This happened at the Rabaul caldera in Papua New Guinea in 1994, for example. The port city of Rabaul was evacuated within hours. Next day, the twin volcanoes that guard the harbour entrance both erupted, destroying much of the city. Thanks to the warning provided by the earthquake swarm, only five people died - one of them from a lightning strike.

Yet, just as often, volcano-tectonic earthquakes don’t give timely warning of an eruption. An earthquake swarm may occur without a subsequent eruption, or an eruption may occur without a preceding swarm. The fallibility of volcano-tectonic earthquakes as short-term predictors of eruptions is the main reason why local populations are sometimes kept in a prolonged state of needless anxiety or, conversely, given false reassurance in the face of a looming catastrophe.

During the 1980s, Bernard Chouet turned his attention to the long-period events as possible predictors of eruptions. Chouet had an insight about the nature of these events. He realised that their musicality - the pure tones with their added harmonics - must result from a resonance, that is to say, the reverberation of acoustic waves within a limited space. When Chouet analysed long-period events mathematically with this idea in mind, he was able to define the characteristics of the system that created them. Long-period events, he concluded, occur when a slug of magma jerks forward within a sheet-like crack in the rock. The motion of the magma is quickly arrested by the confining rock, triggering an acoustic wave. This is analogous to the ‘water-hammer’ that may be generated by household water pipes when a tap is turned off too quickly. ‘It’s as if you’re pinging it with a hammer blow,’ Chouet told me during a 2006 interview. ‘The acoustic pulse will travel through the fluid and hit a boundary and reflect, and keep going back and forth.’ Nevertheless, some of the acoustic energy escapes into the solid rock and radiates to the surface, where it can be detected by seismic instruments as a long-period event.

According to this model, long-period events will occur when the path of the advancing magma is at least partially obstructed, rather than being open to the surface, just as water-hammer occurs in closed pipes. Obstructed magma is put under increasing pressure as more magma is forced up from the deep. Thus a series of long-period events may signal an increase in pressure that will end only when the pressure within the magma exceeds the weight of the overlying rock. At this point, an explosive eruption will occur.

During the mid-1980s, Chouet looked through the seismographic records of past eruptions at a number of volcanoes. He found long-period events in the run-up to several eruptions, including the disastrous 1985 eruption of Nevado del Ruiz. Then, on January 2, 1991, he successfully predicted an eruption of the Redoubt volcano, which lies 100 miles southwest of Anchorage, Alaska, and 25 miles upriver from an oil-storage terminal. He made the prediction when there was a sudden increase in the frequency of long-period events - they began occurring every minute or so. In response to his prediction, the terminal was closed down and evacuated by 5pm that same day. Just two hours later the volcano erupted, and the resulting mudflow left parts of the terminal standing in three feet of muddy water.

Thus, when he came down to Pasto for the meeting later that year, Chouet was highly focused on looking for long-period events in the seismographic signals from Galeras. At the time, the volcano was venting excess gases through a long fissure in the lava dome which opened up every few minutes to release a cloud of gas. Because of the action of this ‘safety valve’ the dome’s internal pressure was not building in any dangerous way. Chouet predicted, however, that the crack would eventually seal off, and he advised Calvache and the other Colombian volcanologists to keep a lookout for long-period events once that happened. ‘When it seals,’ says Chouet, ‘the source itself doesn’t know it’s sealed; it’s going to keep on pumping, but now it’s pumping into fractures that are embedded in a solid, so instead of pumping into the atmosphere you are pressurising the whole system.’

During the early part of 1992 the lava dome did in fact seal itself off, as minerals deposited by the venting gases clogged the fissure through which they had been emerging. To all external appearances, the volcano was going back into dormancy. But one day in early July, the local volcanologists noticed an odd-looking signal on their seismographs. It was a long-period event, but a particular kind of long-period event in which the vibration quickly built to a peak amplitude and then gradually faded to silence over a period of minutes.

On the seismographic recording, the event looked like a screw viewed from the side, and the scientists later named it a tornillo - the Spanish for ‘screw’. Eight more tornillos occurred over the following five days, and then, on July 16, the lava dome exploded, sending a shower of rocks across the caldera that destroyed some of the communications towers on the caldera rim. It was a small eruption - the city of Pasto was never threatened - but it added strength to Chouet’s hypothesis that long-period events could be used to predict eruptions.

Because of Galeras’s continued activity, yet another scientific meeting was planned for January of 1993. This time the organiser was Marta Calvache’s graduate advisor, Stanley Williams. Williams was a very different kind of volcanologist from Bernard Chouet. For one thing, his specialty was not studying volcanoes’ seismic signals, but collecting and analysing the gases they emit - gases such as water vapour, carbon dioxide, sulphur dioxide, and the ‘rotten egg’ gas, hydrogen sulphide. These gases are dissolved in the magma, but as the magma approaches the surface they come out of solution and, if there are open conduits to the surface, they enter the atmosphere at vents called fumaroles. Williams believed that changes in the amount or kinds of gases discharged at fumaroles were potential indicators of impending eruptions. The track record for prediction on this basis was spotty, however.

Williams and Chouet also differed in their styles. Chouet was primarily a theoretical geophysicist, whose work consisted of creating mathematical models on computers at the USGS headquarters in Menlo Park. He did sometimes visit volcanoes, as for example when he went to the 1991 Galeras meeting, but such visits were not really essential to his work. Williams, on the other hand, was very much a field volcanologist. His work required him to enter active volcanoes and approach as close as possible to fumaroles while they were discharging literally tons of superheated, toxic, corrosive, or asphyxiating gases. Thus, even putting aside the chance of an explosive eruption while he was on the volcano, there were significant risks in his work, and he seemed to revel in them. As he acknowledged in his own published accounts, Williams sometimes dispensed with the protective gear that the USGS mandated for their scientists - hard hats, gas masks, fire-resistant coveralls, and the like - and worked in nothing more than street clothes and a stout pair of boots. He spoke of ‘sucking volcanic gases’ as if that were a required initiation rite for would-be volcanologists.

Williams obtained funding for the 1993 meeting from the United Nations, and he was able to invite a stellar cast of experts from around the world. From Russia came Igor Menyailov, like Williams an expert on volcanic gases. From Britain came Geoff Brown, who studied changes in gravity caused by magma movement within a volcano. From Switzerland came Bruno Martinelli, a seismologist and Marta Calvache’s long-distance boyfriend. Others came from as far away as Iceland and Japan. The main contingents, however, were from Colombia and the United States. Among the Colombians were three seismologists, Fernando Gil (a collaborator with Chouet in his research on the long-period events), Diego Gomez, and Roberto Torres, as well as two gas experts, José Arles and Nestor Garcia. Marta Calvache also attended; in fact, as a local geologist and Williams’s ex-student she did much of the advance planning for the meeting.

The American group, besides Williams, included Fraser Goff, a chemist from the Los Alamos National Laboratory, Andrew Macfarlane of Florida International University, and Charles Wood, a planetary scientist from the University of North Dakota who was working on technologies for predicting volcanic eruptions with satellites. Williams also invited Bernard Chouet as well as other USGS scientists. In what may have been a fateful decision, however, the USGS prohibited its scientists from attending the meeting, citing the unstable security situation in Colombia. Thus Williams and the other meeting participants were deprived of the expertise of the one person who, in retrospect, was best qualified to save them from tragedy. ‘If I had been down there at the time and I had seen the long-period events,’ says Chouet, ‘I would certainly have voiced my opinion that it was not an appropriate time to go into the crater. But I couldn’t have just jumped in front of them and said, “Over my dead body!” so I don’t know what the outcome would have been.’

The meeting began with three days of scientific talks. Most of the talks were not specifically about Galeras, but two of the Colombian seismologists, Gomez and Torres, did talk (in Spanish) about the seismic history of the volcano, including mention of the tornillos that had preceded the eruption of the previous summer. This issue was particularly relevant because, after several months of relative calm, the volcano had begun to show signs of renewed activity toward the end of the year. Two days before Christmas a new tornillo had been recorded, and further tornillos had been occurring at a rate of about one a day, right up through the beginning of the meeting. If Chouet was right, the new series of tornillos signalled that the magma was knocking insistently at the roof of the mountain and would soon blow its lava cap to pieces - a scenario that would make a trip to the caldera a risky, even foolhardy, enterprise.

In view of the tragedy that followed, the question of what was discussed about the current status of Galeras has great significance, yet there are very divergent accounts of the matter. One account was presented by geologist-turned-science-writer Victoria Bruce in her 2001 book No Apparent Danger. According to Bruce, there was explicit discussion of the tornillos, Chouet’s theory, and the imminent likelihood of an eruption. The linkage between long-period events and eruptions was, in her eyes, pretty much established scientific fact at the time of the meeting, and Williams decided to go ahead with the field trip in the face of explicit warnings from seismologists that an eruption might be looming. His decision, in Bruce’s view, could be explained only by a reckless ‘cowboy’ attitude, perhaps combined with blind belief in the superiority of his own favourite technique - gas analysis.

In his own 2001 book, Surviving Galeras (written with Fen Montaigne), Williams painted a very different picture. ‘As our conference got under way,’ he wrote:

INGEOMINAS and foreign seismologists were not alarmed by this desultory pattern of tornillos; at the time, such small numbers were considered benign… Only after further eruptions in 1993 did we finally come to understand that small numbers of tornillos at Galeras - even as few as one or two a day - might presage an eruption. But there was no such understanding then. In the days before our trip into the crater, no one brought the tornillos to my attention or warned that the volcano might be poised to blow… Based on all available evidence, the consensus at the observatory was that Galeras was safe.

I asked Charles Wood (who is now at Wheeling Jesuit University in West Virginia) for his view of the matter, and he generally sided with Williams. ‘My perception is that there was no serious question about whether we should take this field trip,’ he said. If the Colombian scientists discussed the ominous significance of the tornillos, their message was lost on Wood and perhaps the other foreigners too. ‘My Spanish is rudimentary, and I mostly talked with the English-speakers,’ he said. ‘I would say that the work Bernard [Chouet] had done was not well enough known, and probably not well enough documented - I’m speculating - to say that if you see any of these screw-type features, you know there’s going to be an eruption in the next 24 hours or whatever. It’s not clear to me that there was that level of awareness of their predictive value.’ Wood also complained that Virginia Bruce, who interviewed him twice for her book, never disclosed her critical views of Williams, and thus gave Wood no motivation or opportunity to defend him.

Another scientist who took issue with Bruce’s book was Chouet’s colleague, Fernando Gil. In Bruce’s account, Gil had a conversation with Williams on the night before the field trip, in which he warned Williams about the tornillos and emphasised the danger of an impending eruption. Williams, Bruce says, refused to cancel the trip, though he did agree to cut down the number of scientists who would be allowed to enter the crater. But when Bruce’s book was published in 2001, Gil told the Chronicle of Higher Education that this purported conversation between him and Williams didn’t happen.

The field trip was originally scheduled for the third day of the meeting, January 13. In what would turn out to be a fateful change of plan, however, the organisers rescheduled the trip for the following day - the reason being a planned power outage on January 14 that would make indoor lectures impossible on that day. According to Wood, heavy rain on the 13th was another factor in the decision to postpone the trip. In any event, the scientists set out early on the morning of the 14th in a fleet of vehicles, and they reached the rim of the caldera at about 9am.

It had stopped raining, but thick clouds and fog enveloped the volcano’s summit, reducing visibility to a few feet. The interior of the caldera was completely hidden. ‘It was a disappointing touristic experience,’ said Wood. ‘It was cold; we were all in our down jackets, milling around, getting some talks from different people.’

By 10am, the fog had lifted slightly - enough, in Williams’s judgment, to permit the descent into the caldera. Only 12 scientists were to accompany Williams on that leg of the field trip, however. As had been previously arranged, the remaining scientists were to make a variety of other trips around the flanks of the volcano. Wood, for example, joined a group led by Marta Calvache and Patty Mothes, a young American volcanologist living in Ecuador. Their group would explore some deposits left by earlier eruptions, about a half-mile below the caldera rim. Wood was quite happy not to join Williams’s party. ‘Just going down into the caldera with that poor visibility would be dangerous,’ he said.

One by one, the members of Williams’s group backed down the steep wall of the caldera while clinging to the fixed rope. Because of the fog, they were quickly lost to view from the rim. Within the caldera, however, visibility was better. By the time the scientists reached the ‘moat’ - the lowest part of the caldera between the outer ramparts and the central volcanic cone - they could see one another and the cone ahead of them. After crossing the moat they began trudging up the side of the cone toward the crater rim. It was slow going; the terrain was steep and exceedingly rough on account of the rocks and cinders that had been scattered across the slope during previous eruptions. The altitude of more than 13,000ft didn’t help, either: some of the party were decidedly out of shape and needed to pause for breath after every few steps.

Among the 13 men, only one was wearing full protective gear. This was Andy Adams of Los Alamos: as a US government employee, he had to follow safety guidelines that mandated a hard hat, steel-toed boots, and fire-resistant coveralls. One other scientist, the Guatamalan Alfredo Roldan, wore a hard hat. Most of the others were bare-headed and wore down parkas. Williams poked fun at Adams for his seemingly excessive safety-consciousness, something that Adams didn’t find amusing.

Three hikers followed the scientists into the caldera. These were a local professor, his teenage son and his son’s friend, who were visiting the caldera out of pure curiosity. They were dressed even less suitably than Williams: rather than boots, they were wearing trainers - a poor choice for navigating the clinker-strewn slopes of the volcanic cone.

Once the scientists reached the top of the cone they could look down into the crater - a depression about 400ft wide, surrounded by almost sheer 100ft-high walls. Clouds of gas and steam were emerging from various spots on the crater floor, as well as from a group of fumaroles named Deformes on the southwest part of the crater rim. Aside from the gas venting, which had been going on for months, there was no sign of volcanic activity in the crater.

About this time, the seismologist who was watching the seismographs back at the Observatory in Pasto noted the occurrence of a tornillo. She radioed the information up to Roberto Torres, who was on the caldera rim, and he relayed it to José Arles on the cone. José noted the information but didn’t consider it particularly worrisome - 15 tornillos had occurred over the previous three weeks, after all, without the volcano having shown the slightest sign of erupting.

The scientists in the caldera now split up into small groups to carry out a variety of tasks and observations. Geoff Brown, the British gravity expert, led a group around the rim of the crater. They took measurements of gravity as they went, using a bulky but highly sensitive piece of equipment that they had lugged up the cone. Several other members of the group, including the chemist Andrew Macfarlane, gathered at the Deformes fumaroles to measure the temperature of the emitted gases and to collect samples for later analysis in the laboratory. The various tasks kept the scientists busy for a couple of hours.

Around noon, two members of the party climbed down into the crater itself. These were two chemists, the Russian Igor Menyailov and the Colombian Nestor Garcia. They had finished sampling at the Deformes fumaroles and wanted to take more samples at the vents within the crater. The other scientists, including Williams, were content to watch from the crater rim. Williams took the opportunity to chat with the three hikers. About an hour later, most of the scientists began their return trip to the rim of the caldera - a trip that involved the descent of the central cone, the crossing of the moat, and the strenuous ascent of the 400ft-high caldera wall.

At 1.41pm, the members of the party were positioned thus: one Colombian, Alfredo Roldan, had just completed the journey and was standing on the caldera rim giving an interview to reporters from a local television station. Two other Colombians, Fabio Garcia and Carlos Estrada, were in the process of climbing the caldera wall with the aid of the fixed rope. Andy Adams, the safety-conscious Los Alamos employee, was at the base of the caldera wall, preparing to start the climb. Eight other men - Williams, Macfarlane, Arles, an Ecuadorian geochemist named Luis LeMarie, an American geochemist named Mike Conway, and the three local hikers - were at various points between the top and the base of the central cone. Geoff Brown and the Colombians Carlos Trujillo and Fernando Cuenca were standing on the opposite, western, side of the crater rim, far from the trail that led out of the caldera. Igor Menyailov and Nestor Garcia were still on the floor of the crater.

Precisely at 1.41pm was the moment when the upward force exerted by the magma within the volcano’s cone finally exceeded the downward force exerted by the weight of the overlying rock, and a devastating explosion ensued. The blast was followed by an unending roar as rocks and magma flew skyward. The blast ripped the floor of the crater to shreds, instantly killing Igor Menyailov and Nestor Garcia and vaporising their bodies. The three men who had been standing on the western rim of the crater were also killed instantly. Carlos Trujillo’s body was cut cleanly in half by a flying boulder; as for Geoff Brown and Fernando Cuenca, nothing was ever found of them beyond small fragments of flesh stuck to rocks.

The eight men who were descending the cone broke into an instinctive mad downward rush. A barrage of incandescent rocks - some as small as bullets, some as big as television sets - began falling among them. As the rocks struck the ground they exploded like shells, firing off secondary showers of red-hot shrapnel in all directions.

Four of the men - José Arles and all three of the local hikers - were killed within seconds as flying rocks stove in their skulls and smashed their bodies. Andrew Macfarlane was knocked down several times, once by a rock that struck his forehead, creating a hairline fracture in his skull and sending blood pouring into one eye. For a brief time he took refuge behind a rock, then he continued on his stumbling downward run. Every time he fell, his hands or body were seared by the rocks they touched, and he was forced to get up and struggle on. Then he came across Mike Conway and Luis LeMarie, who had found partial protection in a small hollow. The three men hid there for about five minutes, while the rain of rocks gradually abated and changed to harmless ash.

Stanley Williams also took off running at the first explosion, but he was quickly knocked down by falling rocks. One rock smashed his right lower leg with such force as to almost completely sever it: his foot was left dangling at an unnatural angle from the leg, connected to it by a few strips of flesh. His other leg was also broken, and a third rock struck his head above his left ear: It dislocated his jaw, partially detached the retinas of both eyes, and drove fragments of skull into his brain. Smaller rocks burned holes in the skin of his back. He lay helpless, just a few feet from the lifeless body of José Arles. In spite of his terrible injuries, Williams remained alive and conscious, and he cried out for help. For a long time he received none.

Roldan’s television interview on the rim of the caldera was rudely interrupted by the blast, as both he and the newsmen dived for cover. Roldan was struck on the head by a flying rock, but his hard hat saved his life. He crouched down behind the rim of the caldera and watched a cloud of ash and hot gas rise from the crater and reach more than a mile into the sky. At about the same time one of the policemen who was stationed at the guardhouse was also struck: the rock hit his lower arm and completely amputated one of his hands.

Fabio Garcia and Carlos Estrada, who had been climbing the caldera wall at the time of the blast, were able to complete their climb safely, though they had to dodge a hail of rocks during the first five minutes. Andy Adams, who had not yet begun the climb at the time of the blast, was also able to climb out unaided. He was struck by innumerable small rocks, but his fireproof clothing and hard hat saved him from serious injury - he sustained only some burns on his unprotected neck.

After the initial barrage of rocks subsided, Mike Conway, Luis LeMarie and Andy Macfarlane left their foxhole and began to make their way down the cone and out of the caldera. It was slow going. All three men had numerous cuts and burns. LeMarie had fractures in both legs. Macfarlane had several severe lacerations in addition to his head wound. It wasn’t until an hour after the eruption that the three men made it down to the moat, and then they faced the arduous ascent of the caldera wall. Conway, the least injured, was able to clamber to the caldera rim unaided. LeMarie was assisted up the rope by Carlos Estrada, who had climbed back down into the caldera to help him. Macfarlane could only make it as far as the bottom of the rope before he collapsed in pain and exhaustion.

The initial explosion had alerted the groups of scientists who were on the outer flanks of the volcano. From where Marta Calvache and Patty Mothes’s group was positioned, about halfway down the volcano, the sound was not especially loud. ‘We were having lunch,’ said Wood. ‘We looked up, thinking, “What was that?” and we saw the [ash] cloud. Marta and Patty said, “OK, we’re going up; we have the most experience with this volcano - the rest of you evacuate down to Pasto.” So they got into a jeep and went up to the summit.’

It took Calvache and Mothes about 30 minutes to reach the summit, because they first had to hike from their location to the access road where their vehicle was parked. Then, on the way up the road they met a military truck that contained most of the policemen who had been stationed at the guardhouse, including the man who had lost a hand. Calvache told a couple of the men to accompany them back to the summit in order to help with the rescue.

When they got to the summit, they were met by a chaotic scene: a battered guardhouse, vehicles with windows smashed out, blood and rocks on the ground, and a large number of people, including a civilian rescue squad, who were milling about ineffectually. No one had dared to descend into the caldera, but at that same moment two Colombians from the Observatory in Pasto, Ricardo Villota and Milton Ordoñez, arrived on the scene. They had been alerted by the violent signals that were appearing on their seismographs and, fearing the worst, they had rushed up the mountain in a truck. Villota and Ordoñez immediately began descending the steep rampart, and Calvache and Mothes followed them. They could see Andrew Macfarlane lying half-conscious at the bottom of the fixed rope, and although they couldn’t see Stanley Williams they could hear his calls for help. Thus they were spurred on to attempt a rescue, in spite of the danger of a renewed eruption.

When they reached Macfarlane, Ordoñez and Mothes started to attend to his wounds. Soon, other helpers arrived, and eventually they were able to get Macfarlane onto a stretcher, haul him up to the caldera rim, and place him in an ambulance that rushed him off to a hospital in Pasto.

Meanwhile Calvache and Villota had gone off in search of other survivors. They soon saw that the three local hikers were dead. José Arles was dead, too, with a huge gash in his skull that exposed most of his brain. Villota, a close friend of Arles, made a futile attempt to revive him by raising him into a sitting position, whereupon his brain fell out onto the rocks. Villota was too shocked to continue with the rescue efforts.

Stanley Williams was the only person still alive on the volcanic cone, but he was horribly wounded, with a nearly-severed right foot, a broken left leg, a depressed fracture of his skull, a broken jaw and burns and lacerations over much of his body. Calvache, Mothes, Ordoñez and another rescuer placed Williams in a blanket and, painfully slowly, hauled him down the cone and across the moat. The journey of a few hundred yards took nearly two hours, and throughout that time the volcano continued its ominous rumblings. By the time they arrived at the base of the caldera wall, professional rescuers had reached the scene. Williams was placed on a stretcher, hauled up to the rim of the caldera, and airlifted by helicopter to a hospital in Pasto. Calvache and Mothes continued their search for more survivors, but by 6pm they realised there were none, and they in turn were airlifted off the mountain.

Williams had been rescued, but his ordeal had barely begun. At a hospital in Pasto, he had surgery to remove a blood clot and bone fragments from his brain. His legs were put in plaster casts, and he was flown by air ambulance to Bogotá and from Bogotá back to the United States. There he underwent further surgery to his head and legs: after some unsuccessful operations to repair his shattered right leg, the entire lower leg was stabilised with a ‘birdcage’ of embedded metal rods, which Williams wore for 11 months. He also had operations - only partially successful - to restore the hearing in his left ear. Later, Williams developed pneumonia, and he also had a grand mal epileptic seizure.

Besides the physical problems, Williams was plagued by other kinds of difficulties. Whether on account of the horrifying experience he had lived through or because of the brain damage he had suffered, he recalled events incorrectly. In media interviews - of which he gave many - he allowed himself to be presented as the sole survivor of the scientists who had been on the volcanic cone, or even of the entire party who entered the caldera. This naturally irked the other survivors, who came to see Williams as a publicity hound.

Allegations that he had ignored the signs of an impending eruption culminated in Victoria Bruce’s scathing book. Some of Williams’s colleagues echoed Bruce’s point of view. In a 2001 review in Science, volcanologist Haraldur Sigurdsson of the University of Rhode Island took issue with Williams’s claim that ‘the best work… comes from those of us who walk into the crater.’ Dismissing this as more bravado than science, Sigurdsson asserted that the most modern techniques in volcanology don’t require risky excursions into danger zones. Still, there have been other volcanologists, such as Charles Wood, who have steadfastly defended Williams.

In response to the Galeras tragedy, as well as a string of other events that had taken the lives of volcanologists, a group of scientists put together a set of safety guidelines that was published in 1994 by the International Association of Volcanology and Chemistry of the Earth’s Interior. The guidelines recommend that scientists should not visit active volcanoes unless it is absolutely necessary for data gathering: field trips to active volcanoes should not be offered as add-ons to scientific meetings. The guidelines also describe the kinds of protective gear that should be worn, as well as other precautions that should be taken, such as radio communications, emergency preparedness, and so on.

But the guidelines haven’t put a stop to the deaths and injuries, because volcanologists often disregard them. In July 2000, for example, an international group of scientists climbed Mt. Semeru, a volcano on the island of Java. The trip, which followed a volcanological meeting, had no particular scientific purpose, and there had been no plan to approach the active crater, but some of the scientists did so on the spur of the moment, without any kind of protective gear or other safety precautions. A small explosive eruption, similar to the one that killed Stanley Williams’s colleagues on Galeras, happened without warning while the scientists were standing on the edge of the crater. It killed two Indonesians and injured three Americans, one of them severely.

While this accident may have been the result of mere thoughtlessness, a culture of daredevilry still permeates the volcanological community. To take one example, the website of John Stix, one of the organisers of the 1993 Galeras meeting, shows a student posing Jackass-like in front of a spray of red-hot lava, while wearing no more protection than a cotton cap. It is as if some of the people who are drawn to do research on active volcanoes are exactly the ones who are psychologically ill-suited for the job.

Stanley Williams has remained professionally active, but both he and others have noted a sharp decline in his intellectual powers and productivity, which he attributes to his brain injury. Williams has had other travails in recent years, including a divorce and a bizarre episode in 2001 when he was briefly suspected (but quickly cleared) of involvement in a double homicide - an event that brought him another deluge of publicity.

Whatever the views of others, Williams himself (who didn’t respond to my requests for an interview) has steadfastly refused to accept any blame for the Galeras tragedy. ‘I do not feel guilty about the deaths of my colleagues,’ he wrote in his book. ‘There is no guilt. There was only an eruption.’