In the Path of a Killer Volcano 1993 - Documentary

Foreign [Music] begins to stir. These scientists are responsible for predicting whether or not this means a deadly eruption is near. Should they order an evacuation? [Music]

Typhoon bearing down and eruptions becoming more frequent, the order goes out. Can they survive in the path of a killer volcano? [Music]

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Foreign [Music] volcano that really erupts in a large eruption is obviously for a geophysicist or volcanologist, a very exciting and dramatic event. [Music] Be right there at the time. What waves of azure coming through within Thomas balls are falling on your head and you're feeling a lot of earthquakes? Is that the calderas forming and the roof of the over the magma chamber is collapsing into the hole and things like that are really, you know, that that's the stuff that really turns us on and and gets us very excited about this whole business. And at the same Dave Harlow is a seismologist with the United States Geological Survey. When one of the world's big volcanoes becomes restless, USGS specialists like Harlow are typically among the first on the scene. And not just because they find it exciting. One of their jobs is to predict if an eruption is going to occur and when, so they can advise people when to get out of the volcano's path. [Music] That's the most important thing to my way of thinking is is knowing when to get out of the way and being able to tell other people who who aren't volcanologists that they're in the way and they should leave. Unfortunately, volcanologists have never distinguished themselves as forecasters. Even at Mount St. Helens, where they successfully predicted the time of the eruption, they did not anticipate either the size or the lateral direction of the blast. But in the decades since Mount St. Helens, the development of new theories of how volcanoes work and better instruments for studying them has convinced many experts that they are ready to make truly accurate forecasts. [Music]

Spring 1991. Mount Pinatubo in the Philippines. A series of explosions rocks the mountain, which had not erupted in recorded history, driving thousands of terrified Aeta tribes people from their homes. There was a rumbling like a bulldozer and Iran, and it rumbled again and again. And the third time it rumbled like a bulldozer exploded. We were splashed with mud from the sky, and I thought it was my time to die. Meanwhile, in Manila, where only a few experts even know that Pinatubo is a volcano, no one is aware of the explosions. The news arrives two days later when a nun working with the Aeta shows up at PHIVOLCS, the Philippine Institute of Volcanology. After hearing about the explosions, director Ray Punungbayan immediately orders an aerial survey of Pinatubo. From the air, three explosion craters and four columns of steam are clearly visible. But the survey team decides there's nothing to worry about. The blasts, they conclude, were simply the mountain letting off steam. But I said, why only now? Why are we having this steam explosion? And they cannot give me any good answer. So Punungbayan orders a portable seismometer taken to the mountain. In less than two days, it records over 400 earthquakes beneath the still steaming summit. Now genuinely concerned, Punungbayan places a call to friends at the U.S. Geological Survey to ask for help. Worldwide, there are 50 or so volcanic eruptions a year. Because of limited funds, the USGS can send scientists to only a few. But over 10 million people and two huge American military bases sit in the shadow of Mount Pinatubo. Subic Bay Naval Station is 25 miles away, and Clark Air Base, just 10. [Music]

Less than three weeks after Pinatubo starts showing signs of life, U.S. volcanologists are working alongside Filipinos, trying to figure out what's going on. Under the mountain, abilities exist, one of which magma rising from the Earth's crust could be catastrophic. What is that? What's happening? Or is the mountain simply letting off excess steam, which would be insignificant? Or are the earthquakes being produced by tectonic stresses caused by shifting in the Earth's crust? This might cause local damage but little more. [Music] I'll tell you what I could probably do as far as setting up seismographic spots. Strike, probably sets you here. You guys might have to hike up here. I have to walk a half a mile or a quarter mile up to the right and set it up right up here. But from right here, should be line to sight back to Clark. By early May, seven seismic stations surround the mountain. These transmit data by radio to a tiny room at Clark Air Force Base. Their afternoon grandly as the Pinatubo Volcano Observatory, or PVO. The seismic stations record earthquakes five miles beneath the surface. Earthquakes this deep are a sign of more than a mountain just letting off steam. The least threatening possibilities quickly eliminated. Next, using an instrument called a correlation spectrometer, or COSPEC, the team measures the amount of sulfur dioxide, or SO2, coming out of the mountain. If magma, molten rock from deep within the Earth, is rising, SO2 and other gases should be escaping into the atmosphere through cracks in the rock above the magma chamber. The first measurements we got were about 500 tons a day, which is a pretty substantial amount of SO2 to come out. And that increased with each successive measurement until by the end of the month, it was 5,000 tons a day, which is a lot of SO2 to be coming out. And and we couldn't see any possibility that that was a tectonic phenomenon. It must be magma, and it must be magma rising up underneath the volcano. But is this mountain, which hasn't erupted in hundreds of years, really about to blow? High SO2 levels and seismic activity don't guarantee an eruption. It is not unusual for magma to rise for a while and then stop. And if an eruption is coming, how big will it be? Particularly with a volcano that doesn't have any uh historic activity, your best guide to what it may do is the is what it's done in the past. And and that is recorded in the deposits that have been produced by past eruptions. I flew over with Dave Harlow, and as we were flying to the Philippines, we were able to look down on on Katmai from 33,000 feet and see the ash flow sheets and the pyroclastic flows and and the whole uh laying the land down there. And and we were impressed. And then we got to uh to Pinatubo, and we flew around, and and Dave Dave and I turned to each other and said, wow, that looks like Katmai. You know, this is bad. Heavily eroded volcanic ash and rock deposits extend for miles on all sides of Pinatubo. Strong evidence that when this volcano does go off, it goes off big. Looking for details from Pinatubo's past, Newhall, Hoblitt, and their Filipino colleagues unearthed charcoal remnants of trees incinerated by previous eruptions. These are radiocarbon dated. They indicate the mountain has erupted only four or five times in the last two thousand years. Volcanoes that erupt infrequently almost always erupt violently. This violence can take many forms. The volcanoes produce lava flows, rivers of molten rock. [Music] [Applause] Others eject past quantities of ash and rock into the air. As this material falls to Earth, it can completely smother the countryside. [Applause] Fall, and you might get a hot mud flow or lahar, which can bury a town in minutes. [Music] This devastation at Mount St. Helens was caused by a tremendous lateral blast, triggered when a massive landslide weakened the volcano's wall. [Music] And then there are the hot, dense avalanches of ash, rock, and gas called pyroclastic flows. These can roar down a mountain at 100 miles per hour, burning everything in their path. Most of these are possibilities at Pinatubo. Though by late May, it's still not clear Pinatubo will erupt at all. Geologist Rick Hoblitt is a veteran of Mount St. Helens. While in the Philippines, he keeps a detailed diary of life at PVO. Journal entry, 28 May, Tuesday. Up at 05:30. Shower. Get ready for COSPEC flight in a Huey. Ask Harlow to watch the drums while we're at the crack. Fly past summit to west side. God, look at the old pyroclastic deposits. Land. Grab a few samples of old dome fragments. Fly back to base. Seismicity quiet. 31 May, Friday. Wake up feeling awful. Something bit me on the forehead. Earthquakes today. Impulsive, small, low-amplitude tremor-like signal at two stations in net. Andy says vents showing low vigor. A little steam today. Andy and I go to commissary. We're the only people in the place with beards. As we drive around the base, we see a sign for some show called The Last Days of Pompeii. Dinner tonight at Colonel Ander eggs. I sense they would like to be reassured, but we can't tell them it will all go away. Something was going on, but it was in kind of a steady state. The number of earthquakes per day that we were locating ranged between 40 and 150, which is high, but it's not not enormous. Um, the what was a little bit worrisome is is that the locations of those earthquakes were spread over a wide area, um, some five or six kilometers in in diameter. So the footprint of what was going on was big, and that was of concern to us. Journal entry, 2 June, Sunday. Activity event is up. More ash coming out. Some puffs to a thousand feet above the summit. Dave, Andy, John, and I discussed the situation after breakfast. We're not sleeping well because of nerves. Is it possible that a catastrophic eruption could occur with no warning? I think that this is possible. Depressing subject. Not sure what the probability is. My best seat-of-the-pants estimate is something between one and ten percent. This may be paranoid, but blame it on St. Helens. Journal entry, 3 June, Monday. 1941. A big event comes in. Probably an explosion. Harmonic tremor larger than we've seen on all stations. [Music] Like so many others, this message from the mountain sparked speculation and debate at PVO. I was talking to Dave, and he says, well, what do you think? I said, [Music] You know, Dave, I think maybe we're witnessing the the precursor to uh to a historic eruption. And he says, don't talk like that. I want to hear that. Volcanologists use four levels of alert to warn people of the danger posed by a restless mountain. [Music] Oh, as the likelihood of an eruption grows, the team declares a Level Two alert, and a limited evacuation begins. On June 3rd, Ray Punungbayan orders 20,000 Filipinos living within six miles of Pinatubo to evacuate their homes. Meanwhile, on Clark, it's four miles beyond the Level Two evacuation zone. The crisis facing the base begins to sink in. We had millions of dollars worth of airplanes, helicopters, millions and millions of dollars of supplies. We had about 14,500 or so people to move in short order. All of their belongings are very important to them. Their pets are very important to them. We had a 200-bed hospital, a lot of babies. I have to tell you that if you took all of that and tried to do it in one big bite, it becomes very mind-boggling and obviously just scares the hell out of you. You know, everybody wants to know, well, do we evacuate now? And it's it's an it's an incredible sort of weight to bear. And all you can do is say, well, we think it's gonna do this, but there's maybe only a sixty percent probability of that. And people don't want probabilities, they want black and white. Yes, no. It's going to erupt, it's not. It's going to be big, it's it's not. We should move, we shouldn't. It's a that was uh for me, the the worst part. And uh and I didn't even have the uh that sort of awesome responsibility that was uh, you know, Dave Harlow and and Rick Hoblitt. Stress load was intense. [Music] There was an awful lot riding on our interpretations, and if we if we drop the ball, it would be very unpleasant. When a volcano prediction is wrong, the consequences can be tragic. In 1986, one day after scientists had decided it posed no immediate threat, Nevado del Ruiz in Colombia erupted, sending a hot mud flow roaring down upon the sleeping town of Armero. Twenty-two thousand people were killed. [Music] On the other hand, predicting an eruption that doesn't happen is rarely forgiven. In 1982, USGS volcanologists issued warnings affecting the resort community of Mammoth Lakes, California. When nothing happened, townspeople, concerned about lost tourist dollars and threatened property values, reacted with anger. Scientists' lives were threatened, and bitter feelings have persisted for years. No one at PVO wanted to relive either of these experiences. I don't think any of us were sleeping very well. I certainly was not sleeping very well during during this period. It was a kind of thing where the volcano then picked up and and just it was a sense that this thing was really grinding away on you personally. It was you want an adversary in this particular case where we had to get it right and and make the forecast. Journal entry, 5 June, Friday. Seismicity has changed. We're now getting more quakes under the vent rather than to the Northwest. We're also getting many B-type events. Today's COSPEC is 260 tons per day. Very low. Bad news. System is not degassing. More discussion about going to Alert Level Three. Andy Ewert and I leaning toward a three. Harlow not quite there yet. PJ says if we do go to a three, the Filipinos will expect an eruption in two weeks, meaning we only have one chance before we lose credibility.

The tension around PVO hits a new peak with the sighting of that blob or spine of new magma. The decision is made to go to Alert Level Three. A meeting is scheduled to explain to Clark's top officers the implications of this new development. Hoblitt will fly over the summit at dawn, just before the crucial meeting, to double-check the presence of fresh magma on the mountain. Journal entry, 6 June, Thursday. Fly to summit. Quite clear. White steam plume hangs over summit. Good view of the vent and suspected spine. It's only an erosional remnant. Take two more passes. No doubt I should have confirmed this before we went public. Return to flight line. I call PVO. Get Dave. Give him the news. What to do? I say, "Have a nice day." As he walks into the lion's den. There was a morning meeting where I needed to present basically a story about how the the um volcano's increasing inactivity. But by the time that I went into the meeting, the activity had decreased. And I said that, sort of swallowed my words that I had made this announcement that things were going on. In fact, they were not. Journal entry, 6 June, Thursday. Dave was in a bad spot during the briefing. Gotta slough it off. When I returned back to our observatory from the meeting, the our normal background activity went from something like this to to something like this. And and here I I just finished telling everybody that this thing was not as active as we thought it was. And here it was cranking out. And, you know, part of the drama is like, not do I rush back over there and tell everybody, no, no, the thing's cranking up again? Or is this another one of these little fluctuations? And if I wait it out long enough, it's going to go away? Well, it turned out that it didn't go away and didn't go away. And and basically, I was holding my breath. Um, and and about in here, we can see all of this the activities, you know, getting the earthquakes are getting bigger and bigger and more and more frequency, and the background noise is picking up. That's when I I cracked. I just couldn't take it any longer. I called them again and said that this thing is really now cranking up. Um, and we need to be really concerned about this. And by the time somebody came over, it was now back down to background level again. It was an incredible roller coaster. I think Hoblitt described it as riding the tiger. For for periods of hours, the volcano was was looking like it was gonna, you know, go totally non-linear and erupt, and we would not be at a high enough level of alert. And at other times, the volcano would would be fairly quiescent, and we'd and just after we'd gone to a higher level of alert, we'd say, oh no, what did what did we do? Are we are we uh jerking these people around? You know, the military and and the Philippine government, you know, just what's going on? Journal entry, 7 June, Friday. At 15:22, continuous or nearly continuous earthquakes on UBO. Hi, yes, Sam peaks at three to four Hertz. Can't reach Ray by phone. Send fax warning of increase. Dave says he's about to call a four based on amplitude continuity of seismicity. Colonel Grime says, you know, once you declare a four, the end of the world happens. Dave makes the declaration. Alert Level Four means an eruption could come within 48 hours. The evacuation of everyone within 12 miles of the mountain. 120,000 people leave their homes for temporary evacuation centers. A well within the evacuation zone, General Studer knows his people are not yet ready to leave. He is well aware of premature evacuation could cause dangerous panic. Convince the volcanologists can give him at least six hours warning. General Studer decides the Air Force will for the moment stay put. Journal entry, 7 June, Friday. York says, if you put a frog in cold water and slowly turn up the heat, he'll stay there till he dies. But if you throw him into hot water, he'll jump out. You know, if someone had just plunked this down in the situation on on June 7th, we would have uh run screaming from the area or something. You know, because we, you know, you look at something and you say, wow, it's really obvious that uh that it's getting hot here and then we should leave. Whereas if you're sort of slowly working into the situation, you say, yeah, it's a little worse than yesterday, but we made it through yesterday and we're still here. And uh well, we can probably stay a little longer. There's, you know, you get the familiarity breeds contempt or something, and you get uh you get used to the situation. You begin to think that, you know, maybe you're going to be luckier than you are. Perhaps this kind of overconfidence is what led to tragedy in Japan earlier that same week. Through the spring, magma had been rising beneath Mount Unzen. By late May, molten rock was visible through cracks on the mountain summit. In early June, the summit gives way. [Music] For a while, the resulting pyroclastic flows behave exactly as expected. So a group of volcanologists and journalists move in for a closer look. Suddenly, a flow changes course, trapping 43 people who burn to death. Journal entry, 8 June, Saturday. 07:51. Fly back east to inspect the vent area. That's uh that's coming up out of the ground. We've got a we've got a series of, well, if you want us to keep flying around looking at it, or uh, yeah, we got to make sure what it is. Um, let's, let's drop down a bit. Okay, coming down. Standard using throttles. All right. We don't we don't have to snuggle up real close to it. We'll take a look at it from a little bit farther out. I can appreciate your bravery. Make a close pass. See a dome. Take several passes to make sure it's for sure. Call Dave immediately. Give him the news. He's happy. As we observed a dome, in other words, a little slug of magma, you know, cold, relatively cold magma squirting out on the ground. And when you see this domal structure, that's indicative of a kind of magma that's very explosive. So then suddenly, the the equation changed dramatically. The stuff that came out on the ground, although none of us cared to walk up and whack off a sample of this stuff, looked and for all intensive purposes with the same stuff. I mean, the ash samples indicate it's the same stuff that, you know, had come out previously, been around the previous scene, these huge pyroclastic flow sheets. Um, and and at that time, we began began to come become very concerned. On June 8th and 9th, General Studer goes with Rick Hoblitt on his surveillance flights over the volcano. You have the sound of the helicopter, which is a is that thump, thump, thump, that all of us remember from Southeast Asia. The doors are open, you know, you hear the wind, and you see how big it is, and you're so close to it, you feel like you could reach out and touch it, but you're afraid that if you did, it'd burn your hand. There was no doubt that there was something going on underneath this ground, and that it wasn't happy. It was not a happy camper. On the morning of June 10th, General Studer orders a full evacuation of Clark, leaving behind only a 1500-person security force. The top priority for Clark officials this morning was getting people safely out of the area. Staging areas were set up on the park flight line to make the evacuation of over 14,000 people as smooth as possible. Have a safe trip. Thank you. We just got here 12 days ago. They didn't tell us we were going to do this. You have a good day. Thank you. Bye-bye. [Music]

The evacuation is now underway, affecting hundreds of thousands of people. Scientists know they have risked a lot predicting an eruption at Pinatubo. Every hour that passes without one heightens the tension at PVO. That was a period of falling off in our spirits. We were then beginning to really second-guess ourselves. We were fundamentally sure something was going to happen, but then we started asking the what if. What if this waits a long time? What if it doesn't go? What if we, you know, made a huge mistake? [Music]

Foreign [Music] [Music] [Music] 48 hours after Clark is evacuated, Pinatubo erupts. All remaining personnel hastily retreat to the far side of the base. Hey, I was up at the wall and I got that, okay. I seen that thing started going, and that was gone. I think my underwear is about two and a half miles that way. I came straight up yet about this fast. Did you hear any sound or anything? [Music] [Applause] [Music] [Applause] But when that first big blast happened on on the 12th of June, there were several Airmen around us just, you know, looking at this thing. And, you know, this is, you know, just being awed by this. Where I was, you know, I was jumping. Yeah, cool. All right. That's great. I mean, it was more of an emotional release. You know, one, it was a spectacular blast, and second, our, you know, what we have been saying was was right on about this. The volcano that that we have really nailed it. And it was a lot of excitement about that. [Music] You know, people after after the first eruption would come and say, was that the big one? Was that the big one? It was like, no, I don't think that was the big one. That was, you know, you try and make a make an analogy or metaphor. You know, that was like a throat clearing, uh, thing or, you know, event clearing phase. You know, we knew that June 12th wasn't the the big guy. That was just the, uh, the volcano saying, okay, I'm gonna do it. I'm ready. And this is, you know, these are appetizers. This first eruption covers the once green area near the summit with a thick blanket of gray ash, and there's lots more where that came from. This sucker's huge. This time, we got to get out of here pretty soon. That stuff's gonna come down right on us. This time. Contagious scale eruptions and accompanying retreats to the far side of the base continue day and night for the next 48 hours. [Music] With each eruption, communities as far as 50 miles from the volcano are showered with ash and sand. [Music] While all this is going on, a major typhoon is heading straight to the central Philippines. It will reach the Pinatubo area within the next 36 hours. Journal entry, 14 June, Friday. Been here 19 days, I think. Seems like forever. 06:45. Call Ewert. Ask what's happening. He says it's still rocking and rolling. Wonders what's keeping the lid on. 21:00. Dave calls a meeting. It doesn't work. People are too beat. 22:17. Go to bed exhausted. [Music]

On the 15th, Pinatubo serves up the main course. From 2 A.M. on, there is a continuous eruption punctuated by massive explosions that send ash 100,000 feet into the air. Oh, at daybreak, when the eruption becomes visible, it appears to be over 10 miles wide. Pyroclastic flows roar down from the summit in all directions. Even from 15 miles away, these flows overwhelm the horizon. [Music] The 6 A.M. explosion is the fifth of the morning. It is large enough to create lightning as part of its own weather system. At 6:30, rain from the leading edge of Typhoon Yunya hits the area. General Studer calls it quits. He orders all remaining personnel to abandon the base. For 7:20, essentially monochromatic, one Hertz tremor, rail to rail. 07:25. Pack our stuff and split. We're the last ones out. [Music] Five miles. So we decided that we would then, lacking in courage and and proper, you know, objective viewpoint, the things weren't really that that bad. Can you tell us what the situation is like now? And we're, uh, been discussing what to do, and we expect to go back right now. And so we returned to the base and got our equipment all going again and started looking at these eruptions. And by that time, the eruptions were having with with increasing frequency. There was a low-level wind shear from from this typhoon that was blowing ash right over Clark Air Base, and where we were. So there are periods of 15 or 20 minutes when we were just dark. It's like the middle of the night. It was raining. It was raining pieces of pumice that were that ranged in size from two or three inches to five or six inches big. Those kinds of things were coming down. And if you went outside, it came down on you. Um, but the biggest thing was you could not see. You could not hear. And what you could see was scaring out of you. I suppose the best way of describing it is that the events were biblical. We've gotten this, uh, it's a little bit larger than ash is what's falling right now from Mount Pinatubo, which has been erupting, uh, steadily all afternoon. We've also had a number of earthquakes and even some thunderstorms on a wild afternoon in the Philippines. In about 15 minutes of two, about 1:45 in the afternoon, it was just a blast. As we stood and we just watched our instruments for half an hour, and they were just pegged. They're just going as hard as they could. And then finally, our instrument sites between the mountain, Clark Air Base, just ceased to function. When we lost the instruments, the last instruments up close to the volcano, our thought was that they were probably knocked out by pyroclastic flows. And of course, there was the possibility that they could have been moving towards us because of that. Some people moved to the center of the building for a while. If we were hit, that might afford a little bit more protection. I don't know. We had, you know, four cinder block walls between us and the and the mountain. And, you know, the way the the ash clouds come down, you know, it's it's great, sort of hurricane force wind and rocks and just, uh, just an awful mess. And, uh, you know, you figure if you hunker down behind the wall, maybe you'll maybe you'll you'll come through it. And, and, you know, the roof will come off and a lot of debris will fly around, but, you know, maybe you'll be okay. We had some calm, frightened moments. Nobody could decide what to do, what to think, really. Andy Lockhart just made some popcorn, and John looks over and sees Andy eating popcorn and says, "What are you doing on eating popcorn at a time like this?" And then he says, "I I always eat popcorn at this part of the movie." Pebbles finally, the decision is made to leave. Six months later, General Studer remembers that moment at a conference in San Francisco. What what led me to make the decision on the 15th of June to get in the last 30 or so of us out of Clark and head up toward the agricultural college was a guy by the name of Andy who ran past me saying, "General, you better put jam in your pockets because we're all about to be touched." Lines. I'm gonna. I walked out and, um, opened up a door to a carry-all, and there was a there was a driver in there crossing himself. And I said, [Music] Do you know how to get to this place? And he said, no. So I closed the door and chose another video. Raining mud, pumice balls, that side bouncing off the car. And, and by that time, it was it was, um, is like like our our dignities were still in place. We we're not completely panicked. It was an orderly, um, but, uh, a retreat that we were very confident that we were doing the right thing. There was a, there was no question about any anybody's courage left anymore. I don't, I don't regret leaving at all. And I think if I was put in that situation again, I'd I might have left sooner. Um, uh, no, no, I don't, I don't regret, uh, I don't regret leaving at all. It was, uh, it was a huge eruption. And I think, uh, just psychologically, I was I was just happy to get away, to go anywhere else as long as it was away from where that eruption was happening. I think if I'd still been on the base and I started feeling these earthquakes, uh, I don't know, you know, I might have come unglued. As it was, it was, you know, it was a week of almost no sleep and and incredible stress. And, and then to have this sort of constant earthquake activity was unnerving. As it turned out, some of us had the best sleep we'd had in a week, that night, being rocked to sleep by these things, and knowing that we were that we were away, away from, uh, well, we were a little bit further away. We didn't know if we were far enough away, but we were, you know, it was just important to leave. Uh, and if I, if I'd been on base, uh, when that seismicity kicked in, I don't know, it would have been, it would have been bad. Thanks to the prediction, virtually everyone within 15 miles of Pinatubo was evacuated before the cataclysmic eruption. But the huge blast, coupled with the typhoon, spreads devastation far beyond the evacuation zone. [Music] [Music] All right, thank you. [Music] [Applause] [Music]

Towns like Angeles and Olongapo are buried in ash up to a foot deep. [Music] Roofs collapse under the weight of rain-soaked ash and the near constant shaking from earthquakes. While tens of thousands of Filipinos suffer in the aftermath of Pinatubo, the evacuation has kept the death toll to under 500. [Music]

The first photographers who venture into the area near the mountain discover a surreal, monochromatic landscape. [Music]

[Applause] [Music] Even miles from the summit, the countryside is blanketed with ash. [Music] [Applause] [Music] As far as 50 miles away, farm fields and pastures are buried. In the weeks and months to come, one half of the region's farm animals die. No estimates about the impact on wildlife are available. [Music] Weeks after the cataclysmic eruption of June 15th, Mount Pinatubo is still spewing forth ash and rock. It is now recognized as the largest volcanic eruption in 80 years. [Music] The total volume of products produced by the eruption can only be broadly estimated. It's somewhere in the neighborhood of five to maybe eight cubic kilometers of of ash deposits of various kinds. And but it's approximately an order of magnitude, roughly 10 times the size of the Mount St. Helens eruption in 1980. Driven by atmospheric winds, material from Mount Pinatubo circles the globe within weeks. It will remain in the atmosphere for years, filtering out enough sunlight to reduce average global temperatures for more than a full degree for up to five years. For the Filipinos, however, there are immediate problems to deal with. Three weeks after the eruption, the number of people displaced by Pinatubo is put at one quarter of a million. Four months later, two hundred thousand are still in evacuation centers. Their return home complicated by the problem of volcanic mud flows, or lahars. The eruption filled the valleys up on the volcano with a very large volume, estimated four to seven cubic kilometers of pyroclastic flow deposits. That's fairly loose ash and and pumice fragments that fill the valleys in places, in at least one place up to more than 200 meters thick, over large areas, 30 to 50 meters thick. And these are very loosely consolidated. Once during the pan, they are easily remobilized. [Music] Come down the slope at the rate of about 15 to 20 kilometers, and the density is about equivalent to that of flowing concrete. [Music] [Applause] [Music]

Throughout the month following the eruption, Philippine authorities fight a losing battle to keep rivers free of sediment. Once the channels are filled in, every new lahar results in widespread flooding. [Music] [Applause] [Music] Assistant, the estimates are about 650,000 people lost their jobs, and about 50,000 families have permanently lost their homes. This consists of 10,000 Aetas, which are our cultural minorities, our indigenous people, and about 40,000 lowland families. These lowland families, their places of residences have either been turned into riverbeds or they have been covered with one meter to four meters thick of lahar. Yeah, the damage at Clark was so extensive, the Air Force decided not to rebuild the base. [Music] Subic Bay was also heavily damaged, but the Navy decided it was too valuable to abandon. Millions were spent to make it operational again. [Music] But less than six months later, the Philippine Senate refused to renew the Navy's lease, effectively ending America's 100-year military presence in the Philippines. While no one expects another major blast, Mount Pinatubo has not yet gone down for its much awaited 600 years sleep. Eruptions still happen. Most are quite small, but some would require the evacuation of tens of thousands of Filipinos, and there has been loss of life. Property damage caused by mud flows may continue for a decade. [Music] Today, over a year since 1991's climactic eruption, Mount Pinatubo is generally quiet. This huge new crater and lake serve as a powerful reminder of the violent potential of the natural world. [Music] For the scientists who had successfully predicted the eruption and helped save thousands of lives, there was real satisfaction, tinged perhaps with just a touch of melancholy. [Music] It's kind of strange because, you know, I'm, uh, I'm 33, and I've I've had this incredible, incredible experience. And you got to kind of wonder, okay, well, you know, what do you do for an encore? What else, what do you go to that's that's bigger, you know? Oh. [Music] [Applause] [Music]

Funding for Nova is provided by Lockheed, America's Aerospace company, supporting math, science, and engineering education for national technology leadership, and Johnson and Johnson, the signature recognized around the world for commitment to quality healthcare products for the entire family. Major funding for Nova is provided by The Corporation for Public Broadcasting and by the financial support of viewers like you. [Music] [Applause] [Music]