- 2 days ago
After a Colombian volcano erupted in 1985 killing 25,000 people, scientists have feverishly looked for an accurate way to predict eruptions. Now geophysicist Bernard Chouet may have found how to in the form of seismic signals given off by volcanoes.
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00:00An erupting volcano may be nature's most terrifying force.
00:15No one can predict exactly when it will strike.
00:21And its sudden fury can destroy thousands of lives.
00:27In Colombia, a single cataclysm wiped out an entire city.
00:42But there may be a way to prevent such disasters.
00:47For volcanoes issue a warning.
00:51A cryptic signal decoded after years of struggle by one man.
00:58Suddenly you realize the volcano is speaking to you.
01:03And you understand the language.
01:06Ignore the language at your peril as one group of scientists tragically learned.
01:13Monitoring a volcano high in the Colombian Andes.
01:20The scientists climbed into the crater of the rumbling giant.
01:24Just as it awoke.
01:30I have this awful memory of a few moments.
01:33Kind of tottering around.
01:35Thinking, okay, you've got to get down.
01:37You've got to get out of here right now.
01:39People were being killed all around me.
01:45And I thought, I'm not going to get out of this.
01:50I was sure I was going to die.
01:57Now, another more horrific disaster may be brewing.
02:04A volcano near Mexico City is sending the same ominous signal.
02:11It's like a red light flashing.
02:16Something important is happening.
02:18The volcano is telling you, well, okay, I'm under pressure here.
02:22I'm going to blow it to top.
02:24Will the message be ignored again?
02:29Volcano's deadly warning.
02:32Up next on NOVA.
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03:45After 70 years of tranquil sleep, the Mexican volcano, Popocatepetl, is restless.
04:03A plume of gas pours ominously from its summit.
04:10And daily tremors hint at its power.
04:16Of all the volcanoes in Latin America, this mountain may be the most deadly.
04:24Two million people live in its shadow.
04:31Their lives now under threat.
04:35But should they evacuate?
04:37And when?
04:42These questions are up to scientists to answer.
04:47Are we going to be heroes or are we going to be, you know, colossal goats in the end?
04:53And this is the kind of stuff that gives you gray hair and makes this business very tough.
05:00It can be a life or death decision.
05:10You're driven and motivated by saving lives.
05:15And at the same time, you don't want to make people miserable for nothing.
05:19It's also a double-edged sword.
05:24Force people to abandon their homes or leave them to risk the volcano's wrath.
05:33How can scientists make the right call?
05:38This is the holy grail of volcano science.
05:43And one man thinks he has found it.
05:46When one looks at this kind of natural phenomena, volcanic eruption,
05:52you always think of the impact on human lives.
05:58The ultimate quest is to understand enough about the activity in that volcano
06:06to be in a position to make a prediction, predict the occurrence of an eruption.
06:16Bernard Chouet believes he has a radical new way to predict eruptions,
06:22something no one has tried before.
06:27If his idea works, it could prevent a catastrophe
06:31like the one that devastated the Colombian town of Armaro.
06:35The greatest volcanic disaster in recent history began quietly in the winter of 1984.
06:47High in the Colombian Andes, a monstrous volcano called Nevado del Ruiz awoke, smoking and rumbling.
06:55It alarmed the local people who lived on the flanks of the mountain.
07:04They sensed danger.
07:06But no one anticipated the volcano's destructive potential.
07:10A small team of scientists ventured to the top of the volcano to investigate.
07:22Near the summit, they encountered thick clouds of sulfurous gas.
07:27Nevado del Ruiz had come alive for the first time in over 100 years.
07:37But would it erupt?
07:40And what would be the consequences?
07:43At the National Library, a young scientist named Marta Calvace made a frightening discovery.
07:53She trapped down manuscripts that describe Ruiz's fury in the past.
08:01Centuries ago, volcanic blasts had melted the mountain's ice cap,
08:07sending torrents of mud down the valleys, obliterating everything in their path.
08:14A lot of people died, and they described how they died.
08:18Some of them, they were in the mud, and people were not able to help them for several days, and they died there because of the lack of water and food.
08:30The details of the description were very frightening.
08:37Calvace's team drew up a hazard map showing the path of an eruption,
08:40and where the melted ice and debris would surge down the mountain.
08:45The gravest threat was to the volcano's eastern flank.
08:50There, a single valley was fed by two rivers.
08:55Each of the rivers would pick up mud and rocks.
08:59Then, they would meet, becoming one overwhelming deluge.
09:06Calvace traced the path of the raging waters to a town of 28,000 people.
09:13Armero.
09:16Armero was a generally peaceful town, unaffected by the guerrilla warfare that disrupted much of Colombia.
09:36Now, its townspeople were told that they risked annihilation from a volcano 40 miles away.
09:47They would say, no, it's not going to happen.
09:50It doesn't happen for more than a hundred years.
09:53Why is it going to happen now?
09:55It was easy to deny the mountain's violent potential.
10:00On the surface, Ruiz seemed relatively calm.
10:06Only the scientists had seen up close the brewing inferno.
10:11And volcanoes can steam and rumble for years without exploding.
10:18The authorities would agree to evacuate Armero only if they were told exactly when Ruiz would erupt.
10:26And how serious the eruption would be.
10:30But the scientists couldn't answer either of those questions.
10:35A volcano is incredibly complicated.
10:41And we were unable to give them a prediction.
10:44That is, we couldn't tell them how big the eruption would be.
10:48And we couldn't tell them when it would happen.
10:50The scientists feared that an evacuation, if it came at all, would come too late.
11:04There was undoubtedly a great sense of doubt.
11:08A fear of not knowing what was going to happen at all.
11:12So, yes, we felt impotent.
11:14In imminent danger, the town of thousands could only watch and wait.
11:29On November 13th, 1985, the waiting ended.
11:35It was very, very dark. It was rainy, rainy, very strongly.
11:41It was really, especially bad weather.
11:45The storm concealed a greater threat.
11:49Forty miles away, Ruiz had erupted.
11:54Around nine, when we were about to go to sleep, we began to hear sounds coming from the volcano.
12:11We went to the main door and looked towards the mountain.
12:14It was overcast, but explosions, like flashes of lightning, could be seen.
12:20The sound got louder, but all the time there was this muffled sound.
12:25Hot, volcanic gas was melting the ice cap,
12:35sending a torrential flood on its way down the valley.
12:49The next morning, the town of Armaro was buried under six feet of mud and water.
12:54And many of its 28,000 inhabitants were missing.
13:06It was really shocking to see that.
13:28It's like, you don't realize at the first time, well, those are bodies.
13:33And then, yes, you see one and you start to distinguish.
13:39But many, many, many, many, many, many bodies there.
13:44I think it was very, it was difficult.
13:54More than 25,000 people died.
13:57For the scientists who had foreseen the disaster, the reality was unbearable.
14:14It was a very difficult thing to face.
14:16It was absolutely devastating that we had warned the people that this could happen.
14:24But we were unable to tell them exactly when.
14:33They were tormented by the thought that the tragic loss of life might have been prevented.
14:38There had to be a better way to predict volcanic eruptions.
14:48The disaster sparked a new sense of urgency.
14:52The scientists involved with that, including me,
14:55were very impacted by that eruption and that failure.
14:59And there was a group of us that were resolved not to let that happen again.
15:04What makes volcanoes like Ruiz erupt?
15:11All volcanic explosions are fueled by one thing.
15:16Magma.
15:20Magma is molten rock that flows into a volcano through the Earth's crust.
15:26Magma and hot gas then rise toward the surface.
15:30If the top of the volcano is sealed, they have nowhere to go.
15:36Pressure mounts.
15:39And when it hits a critical point, the volcano will blow.
15:48That magma has to get to the surface.
15:50And so volcanologists and those monitoring volcanoes have the,
15:54one of their priorities is to identify that magma and to spot it as it moves up towards the surface.
15:59If it were possible to track the magma and tell how close it was to the surface,
16:07that might indicate when the volcano would erupt.
16:11The volcano would erupt.
16:21But how can scientists look inside a volcano?
16:24Seismographs create an indelible record of volcanic activity.
16:39When a volcano is on the brink of exploding, there may be hundreds, even thousands of small earthquakes each day.
16:53Seismology has been studied on volcanoes since the middle part of the 19th century.
17:00And it's critical because you don't get a volcanic eruption without seismic activity, without earthquakes.
17:06As scientists poured over thousands of signals, one stood out as the possible key to predicting volcanic eruptions.
17:16They called it the A-type.
17:20It was instantly recognizable.
17:23It had a clear beginning and tailed off quickly.
17:27It was the sound of rock breaking.
17:29A great hope was that these A-types would be, you know, the great predictor or forecaster of eruptions.
17:39And in that as this magma pushed itself closer to the surface, we see an ever-increasing number of A-type earthquakes or rock fracturing events.
17:49As magma forces its way up a volcano, it breaks through rock.
18:01Perhaps the A-type signals could reveal the location of the magma and how fast it was rising to the surface.
18:09In Colombia, scientists seized on the data from Ruiz, certain they would find a pattern of A-type seismic signals.
18:26The idea was that if we plotted those together, that the trends of those numbers would tell us something about the eruptive potential of a volcano.
18:36But this seismic blur revealed no consistent pattern to explain the eruption of Ruiz or any other volcano.
18:49Every volcano created its own pattern.
18:53And it was almost impossible to come up with a chart saying that this is the book that we're going to go by.
19:02It would take a scientist with an unusual eye to find the right signal hidden in the noise.
19:11He trained in aeronautics and physics.
19:18But then, intrigued by volcanoes, Bernard Chouet spent years trying to decipher their secret code.
19:28I realized that volcanoes were, although they had been looked at for a long, long time and people had always been fascinated by them, they were relatively poorly understood.
19:41And so this was a frontier that was worth exploring.
19:44When Chouet arrived in Colombia, he too went straight to the seismographs.
19:55He saw how other scientists had marked the A-types with red stickers, desperately searching for a pattern.
20:04But something else caught his eye.
20:16Hidden among the A-types was another signal.
20:20It was called the B-type.
20:23But no one knew what it meant.
20:28It was sort of a mystical sort of thing.
20:31We didn't really understand fully what it was, nor did we understand that we could use it.
20:37The B-types were a mystery.
20:41They had no clear beginning, and they tailed away slowly.
20:46Often they would merge with other signals, making them hard to detect at all.
20:53It was really difficult to separate them and say definitively, well, there was this type of event that would be helpful for forecasting.
21:04They were too messy.
21:07But Chouet saw something in them that everyone else overlooked.
21:12It stared you in the face.
21:15Wow, this is obviously different.
21:25Embedded in a record among all these A-type earthquakes were classic-looking quasi-monochromatic harmonic signature.
21:32Beautiful textbook example.
21:37Or, as he would put it more simply, a long-period event.
21:42Well, the easiest way to visualize the difference between these two types of events is to draw them.
21:46And so the A-type event is characterized by a sharp onset.
21:54This sharp onset here is the signature.
21:57It's the sound of rock breaking.
21:59In other words, we're seeing the brittle failure of rock material.
22:01On the other hand, if you look at the long-period event, it's characterized by this slow onset, gradual buildup of energy in the signal, and then slow decaying, single tone, which lasts for a while.
22:17What we're seeing here is resonance.
22:27All around us, we hear sounds that are resonating.
22:31These tones are nothing more than air, set into motion by a sudden pressure.
22:38We're here in this church because we have here a beautiful example of organ pipes.
22:49It's an instrument, a musical instrument, that is well known to everyone.
22:53And this is an excellent example of resonance and a resonator.
22:56In that case, you're talking about a pipe which is filled with air, and you're pumping air in that pipe, and the air vibrates, and you're hearing the sound of this vibration, that tone.
23:08As air is pumped across the base of an organ pipe, it triggers a resonating sound wave.
23:15We hear this vibration as a single tone that gently fades away.
23:20On a graph, its signature is unmistakable.
23:26A long-period event.
23:31Each time I press the key, I pump more air in that pipe.
23:36And so you hear the result of pumping air in the pipe, which is its resonance.
23:44Each time air is pumped across the base of the pipe, another resonating tone is heard.
23:50Another long-period event.
23:57Shue realized that a similar process was taking place in a volcano.
24:02Just like air in an organ pipe, magma and gas fill the cracks of volcanic rock.
24:11With each new injection of magma or gas, another wave will be triggered.
24:16Another long-period event.
24:19Another long-period event.
24:23But there is one crucial difference between a volcano and an organ.
24:29Air can escape from an organ.
24:34In a volcano, if the crater is closed at the top, the magma and gas have nowhere to go.
24:45Pressure builds and, eventually, the volcano will blow.
24:49The signal that no one else had understood was a secret warning that now revealed itself to Bernard Shuey.
25:05It's a defining moment because suddenly you realize the volcano is speaking to you.
25:12And you understand the language.
25:14The message hidden in the data from Ruiz was now clear.
25:33Scattered through the records were hundreds of long-period events.
25:42More and more as Ruiz got closer to erupting.
25:47The long-period events were a countdown to the eruption.
25:52If this had been understood, 25,000 lives might have been saved.
26:00Shuey hoped these warning signs could prevent future tragedy.
26:07But he needed to prove that his method worked.
26:11In December 1989, a volcano in Alaska put Shuey's idea to the test.
26:25The ice-covered colossus called Redout hit a fiery and quaking core.
26:32Seismic signals reached Shuey's colleagues in California.
26:36One of my colleagues approached me and they said,
26:40we're seeing the very rapid occurrence of these type of events.
26:44We don't know what they are.
26:46And it was obvious that all these events were long-period events.
26:51There were 4,000 long-period events in less than a day.
26:57To Shuey, the threat was obvious.
27:01Pressure was mounting in the volcano.
27:03But his colleagues were skeptical.
27:07I said, I think you have an eruption on your hand.
27:10And this came out of the blue for them, so they were a little taken aback,
27:15thinking, well, maybe he's a little bit cocky.
27:18Maybe he's joking or something.
27:20We don't really know what he's doing.
27:22So Shuey went straight to scientists in Alaska.
27:26I received a phone call from Bernard Shuey, who I did not know at the time.
27:30And Bernard said, introduced himself and said, Tom, I'd like to talk to you about readout.
27:37And Tom said, well, I can't speak now because readout is erupting.
27:41And Bernard said, oh, I thought it would. Okay, I'll talk to you later.
27:47Well, I had many duties to do right then, but I did not forget that.
27:51The eruption in a sparsely populated region of wilderness was relatively tame.
28:01But one more fiery blast could melt the massive ice cap.
28:05And a devastating mud flow would cascade down the volcano to a depot holding millions of tons of oil.
28:17The seismometers soon picked up another series of long period events,
28:23which Shuey interpreted as pressure rising sharply within the volcano.
28:27I told Tom, I think we're going to have a major eruption on our hands.
28:34The scientists tried to convince the oil company that within 24 hours,
28:41readout would erupt again.
28:43And they said, look, just a few hours ago, we took a helicopter trip.
28:47We flew over that dome, and it's very quiet.
28:52Just a little, you know, wisp of steam coming out.
28:56It looks totally dead.
28:58And we had to convince them that it wasn't as dead as they thought.
29:02And it could be very hazardous.
29:04And I think the clincher was Tom faxing them that sheet of paper
29:08that showed the very rapid increase in seismicity.
29:12And for them, it was enough.
29:13They realized something was shooting up, you know, to the sky,
29:17and maybe these people know what they're doing.
29:20At that point, they made a decision to evacuate the terminal.
29:24Shut everything down and evacuate.
29:29The evacuation was completed by 4 o'clock in the afternoon.
29:34At 5.30, the volcano erupted,
29:37sending ash and debris seven miles into the sky.
29:44A torrent of mud and smoldering pumice flooded the valley.
29:49But no lives were lost.
29:51And despite being buried by three feet of mud,
29:55the carefully sealed tanks were secure.
29:57They called Tom back and told him, you know,
30:02that they thought he was walking on water.
30:05So it was a great success.
30:08It worked. So we were quite happy.
30:10Yes, very happy.
30:11Bernard Shuey had successfully predicted an eruption.
30:19But all volcanoes are unique.
30:22Would his method work on others?
30:25I thought that if Redout would behave in this way,
30:28then I would expect that other volcanoes would behave similarly.
30:31And then it was just a question of actually going after the next one
30:33and seeing what happened.
30:38Shuey was nearing the ultimate goal of volcanology.
30:44With seismic signals,
30:46he could predict when a volcano would erupt.
30:54But other scientists remained unconvinced.
30:59They took another tack.
31:00Hunting for clues in volcanic gas.
31:05Stanley Williams' approach was radically different from Bernard Shuey's.
31:12He believed that to predict eruptions,
31:17you had to get up close,
31:19climbing right into the heart of the crater itself.
31:23Stan's a very aggressive scientist.
31:26He's produced some tremendous science.
31:28He believes passionately in monitoring volcanoes.
31:33It's his love.
31:35He loves to do that.
31:39Williams monitored gases like sulfur dioxide.
31:43Every day, an active volcano can produce thousands of tons of it.
31:48And in this veil of gas lies vital information.
31:52Developing an understanding about gases was sort of the key to sort of understanding volcanoes and perhaps even developing an ability to predict volcanic eruptions.
32:02As magma rises, it releases more and more gas, which escapes through holes on the surface of the volcano called fumaroles.
32:15What we're looking at now is called a fumarole.
32:19As you can see, it's a fairly hostile environment.
32:22As the volcano starts to heat up and magma comes closer to the surface, we're going to get a component of gas coming out of here, which is coming from the magma.
32:30It's going to have increased sulfur dioxide, increased HCl, the temperature is going to go up here, and all over here we're going to start to see a whole lot more gas come out.
32:41It's not an easy place to work.
32:44By measuring gas levels at these hot spots, Williams believed he could tell how close magma was to the surface.
33:02Williams was convinced that his method could be used to predict eruptions.
33:06He had witnessed rising gas levels before a number of volcanic explosions.
33:14Back in Colombia, his ideas would be tested against chueyes in a chain of events that would end in tragedy.
33:23Deep in southern Colombia, rises another volcano, Galeras.
33:41In the city of Pasto, 300,000 people live in its shadow, accustomed to its quiet rumblings.
33:49But in 1991, there were signs the volcano was growing more dangerous.
33:57Scientists flocked to Colombia.
34:00Among them, Stanley Williams and his colleague, John Sticks.
34:06They descended into the crater of Galeras.
34:10There were huge amounts of sulfur dioxide being emitted on the order of thousands of tons per day,
34:16which is a pretty good indicator that there was magma underneath the volcano.
34:25The levels of toxic gas confirmed that Galeras was becoming more active.
34:31Then, they discovered something even more alarming.
34:35A lava dome.
34:36When you see lava domes, well, you think, hmm, this isn't so good, because pressure can build underneath lava domes,
34:42and oftentimes, lava domes get blown out, blown out of craters.
34:46Lava domes are often the first stage in the build-up to an eruption.
34:51Fresh magma breaks through the crater and cools to create a dome.
34:55While it stays open, gas can escape.
34:59But if the dome seals, the gas is trapped.
35:03And if pressure rises enough, an explosion is guaranteed.
35:08The vast amounts of gas at Galeras suggested that magma streaming up the volcano would seal the dome.
35:21Williams and Styx said an explosion was a virtual certainty.
35:33But they were not the only scientists in Pasto.
35:37Bernard Chouet was there, too.
35:40He agreed that Galeras would erupt when the dome sealed.
35:45But he went further.
35:46He told the Colombians they would know the dome had sealed by looking at the seismographs.
35:53When the volcano began to pressurize, a tell-tale sign would appear.
35:58He had this idea that if the dome was sealed, we would see a particular kind of seismic signal.
36:08The signal would be a long period event.
36:18For a while, nothing out of the ordinary appeared on the seismographs.
36:27Life in Pasto continued as normal.
36:30Then, the scenario Chouet had envisioned began to unfold.
36:41Once, sometimes twice a day, the seismographs recorded an ominous trace.
36:48It was a long period event, and if Chouet was right, the countdown had begun.
36:59This was an indication that you were pressurizing the dome
37:04and that you're moving toward an explosion that would blow the dome apart.
37:07Four days later, Galeras erupted.
37:16It was a small blast, but powerful enough to blow open the lava dome
37:35and destroy a police station built on the crater rim.
37:48Both prediction methods seemed to work.
37:51Chouet's and Williams.
37:54But the next test would be tragically decisive, shattering reputations and lives.
38:05Six months after the eruption, Stanley Williams was back in Pasto.
38:18He was hosting an international conference on volcanoes.
38:21With Galeras still active, it seemed like an ideal case study.
38:27It was a good conference. I mean, I have to say, I was enjoying the conference very much.
38:34People were presenting interesting papers. It was lively.
38:38There's a sense of camaraderie, especially in a small field like that.
38:42There aren't that many volcanologists in the world.
38:48For Williams, the highlight of the conference was a field trip.
39:00He told local reporters that he planned to take a group of scientists deep into the crater.
39:07He was confident it was safe.
39:12Just before the conference, he had checked on the volcano,
39:19descending into the crater and measuring gas emissions.
39:22This time they were low, a reassuring sign that no eruption was imminent.
39:31But Galeras was anything but quiet.
39:37Warning signals were inking their way across the seismograph.
39:41A series of long period events.
39:44The two methods seemed to contradict each other.
39:50Gas measurements suggested Galeras was safe.
39:54The long period events spelled danger.
39:59The night before the field trip,
40:02Williams met with other scientists at their hotel
40:05to decide whether to venture into the crater or not.
40:09We were faced with a dilemma in a sense.
40:11Here was an active volcano, but a very quiet active volcano.
40:16Where were we going?
40:18And what were the seismic signals telling them?
40:22Some of the scientists were worried.
40:25We were concerned by these long period events
40:30and what had happened when we'd seen them before.
40:34But the seismic method was still relatively untested.
40:38There was a concern, but we didn't really understand what those events were telling us.
40:50One man who might have helped was missing.
40:54Bernard Shuey, like other U.S. government scientists,
40:58was not allowed to travel to war-torn Colombia.
41:01Williams and Styx decided to rely on the method they knew.
41:08Low levels of gas suggested that there was no immediate threat.
41:14There was a possibility that there could be explosive eruptions in the next weeks or months.
41:19And yet the activity compared to previously was extremely low.
41:29Volcano scientists are used to taking calculated risks.
41:34Every volcanologist who works on monitoring active volcanoes
41:39puts himself or herself in that situation at some point.
41:43They have to.
41:44The nature of the beast.
41:47The field trip would go ahead as planned.
41:51Early the next morning, an international team of scientists from Russia,
42:06Great Britain, the U.S., and South America set off for the volcano.
42:13By 9.30 a.m., they were on the summit of Golaris.
42:19We met different groups going up to the summit.
42:24And most of the people were very happy.
42:27There's a lot of anticipation, but first you couldn't see anything.
42:34And in fact, when we hiked down to the crater, you couldn't see the crater.
42:42Through a thick cloud of smoke, 12 scientists descended into the mouth of the volcano.
42:49They were joined by three Colombian tourists.
42:52Most of the people in the group were there to sample those fumaroles.
42:58So there was really a fairly big crowd of people around the fumaroles.
43:02They could not have known that at 9.47, the seismograph came to life.
43:13For four hours, the scientists worked quietly in the volcano.
43:24But then, everything changed.
43:31I remembered at that time hearing three rock falls in the space of about a minute.
43:37After a couple of them, I asked Stan, you know, you hear those rock slides?
43:47And as I remembered, it was right after that that the thing blew up.
43:53We heard boom.
43:54The eruption hurled rocks the size of refrigerators more than a mile into the air.
44:13I was looking up and, you know, I could see the plume going up and it was gray.
44:21And the fog around it was gray.
44:23And the blocks were gray.
44:25And I'm looking up, trying to see something.
44:27And I hear like three or four heavy impacts around me, the big blocks coming in that I'm not seeing.
44:33And I just think, well, this isn't going to work.
44:36I'm just going to have to run for it.
44:37I remember out of the corner of my eye seeing one of the tourists get hit by some big piece.
44:47And it, you know, I remember thinking at the moment he looked like, you know, a fence post getting driven into the ground.
44:54I mean, just horrendous.
44:55No way anybody could survive something like that.
44:58Some members of the group managed to escape.
45:01But others never had a chance.
45:05Not by themselves.
45:06You've got to set somebody down there.
45:10You know, I was running and falling, getting up, running and falling.
45:13I ran, I passed Jose Arlis.
45:15He was obviously dead.
45:17He was lying face down, not moving.
45:22And I fell down close to Stan.
45:24He had blood down the side of his face and sort of lifted his leg at me and said, you know, my leg is broken, it's broken, it's severed.
45:35I tried.
45:36I thought, well, there's only one thing I can do for him that's going to be meaningful and that's to pick him up.
45:42I tried to reach him and my legs weren't responding very well.
45:45And, you know, I was too weak.
45:48And I just thought, you know, if I try and do this, we're both going to get killed.
45:52And so I had to leave him there.
45:56And that was really awful because I thought, at the time, I thought, you know, I'm probably leaving him to die because I don't think, I don't think I'm going to make it.
46:05And he can't move.
46:06Rescue workers found Andrew McFarlane at the bottom of the crater, deep in shock with a fractured skull.
46:21Stanley Williams was also pulled out alive, but it would be two years before he would walk again.
46:36Both physically and emotionally shattered, Williams was unable to talk to Nova about the tragedy.
46:46Nine people died that day.
46:50Lives that would have been spared if the team of experts had interpreted the volcano's warning signs differently.
46:56In hindsight, there were two explanations for the low levels of volcanic gas that Stanley Williams measured before the conference.
47:08One was that the magma had dropped to a safe distance from the surface.
47:17The other was that the volcano's lava dome had again sealed.
47:22With gas trapped inside, Galaris had become a ticking bomb.
47:29The clearest signs of danger, long period events, silently making their way across the seismograph, were disregarded by the scientists.
47:40I think we can be a little myopic at times, where we focus in on the information that we feel, well, that we're experts on.
47:49We don't even feel it's the most important area, but that we're experts on.
47:52And at a science like volcanology, you have to be able to look at things collectively.
47:58It's always easy in hindsight.
48:00If I had been there, of course I'd looked at the records, and I would have seen immediately the parallel between July and December,
48:07and I would have started sounding bells, alarm bells in there, I know I would have done that.
48:14Whether I would have been successful in preventing people from taking a trip to the crater on that day,
48:19would have depend on how they would react to what I was saying.
48:29Not surprisingly, scientists have become more responsive to this new method of volcano prediction.
48:35Bernard Chouet's idea is being adopted throughout the world.
48:41Recently, it faced its most critical test yet.
48:54It happened at Popocatapital, right outside of Mexico City.
48:58This giant volcano has been active since 1993.
49:05For the two million people living nearby, its rumblings became part of daily life.
49:15Then, in the year 2000, Carlos Valdez and other scientists monitoring the volcano saw a change.
49:22Their seismographs recorded a new signal, a long period event.
49:29They had heard about Bernard Chouet's ideas and asked him to come and take a look.
49:36I told them about the significance of long period events, which they weren't aware of at the time.
49:43From then on, they carefully tracked these warning signs.
49:50It's like a red light flashing.
49:53When you see these signals, something important is happening.
49:57The signals began to occur more frequently.
50:06Pressure was building in the volcano.
50:11The volcano is singing its song.
50:13I mean, actually, this is like chirping, if you want, with these sustained waves from the long period event.
50:19But would the seismographs tell them what they desperately needed to know?
50:28When should people be evacuated?
50:31Valdez knew the consequences of a false alarm.
50:38If people abandoned their homes and nothing happened, they would be wary of leaving the next time.
50:44We feel so bad asking people to leave their homes.
50:49And you have to keep your mind in the scientific work and say,
50:54Look, other volcanoes have done this.
50:56The potential of this volcano is that these particular villages could be in danger.
51:04The scientists had to forecast exactly when the volcano would erupt.
51:09On December 16th, the number of long period events multiplied dramatically.
51:17The volcano's message was clear.
51:21This is a siren song, so to speak, because it's telling you,
51:24well, okay, I'm on the pressure here.
51:26I'm going to blow at the top.
51:30Valdez had to make a decision.
51:32We could clearly see that it would be in the afternoon of the 18th.
51:39The order was given.
51:422,000 soldiers raced to the most vulnerable areas to help get people out in time.
51:5030,000 people had to be evacuated in 24 hours.
51:54It was a monumental effort with an uncertain outcome.
52:01But a day later, the volcano erupted exactly as predicted on the 18th of December.
52:27Although moderate in size, it was the biggest eruption of this volcano in a thousand years.
52:34Finally, penetrating the mysteries of the volcano and understanding its hidden language,
52:51scientists were able to warn people with confidence and save lives.
53:01It takes somebody to say, look, we can really do this.
53:04We can go after this and understand what's going on in a volcano.
53:08Science goes in steps, and this is a big one.
53:13In volcanology, this is a biggie.
53:15It is too early to claim that there is now a foolproof method to predict all volcanic eruptions.
53:22But the work begun by Bernard Shouet offers new hope of avoiding tragedies
53:28when nature unleashes its most terrifying force.
53:32The science works through a painstaking process of research and testing and research and testing.
53:37They have to show that process is applicable to other volcanoes as well.
53:46Because there's infinitely more richness in nature than one can imagine.
53:52A volcano threatens to erupt.
53:59Who makes the call about whether and when to evacuate?
54:03Hear from the leader of a U.S.-based volcano SWAT team ready to assist at hot spots around the world
54:09at PBS.org or America Online keyword PBS.
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