About this transcript: This is a full AI-generated transcript of America in Danger: Yellowstone, San Andreas and the Next Great Disaster - Full Documentary from Easy Documentary, published November 15, 2026. The transcript contains 15,655 words with timestamps and was generated using Whisper AI.
"The 21st century started off with a bank, as volcanoes erupted all over the world. Iceland, the Canary Islands, southern Japan, and off the coast of Tonga, blasted by the most powerful eruption of the century so far. While these volcanoes can cause death and mayhem, they pale in comparison to the..."
[00:00:00] Speaker 1: The 21st century started off with a bank, as volcanoes erupted all over the world. Iceland, the Canary Islands, southern Japan, and off the coast of Tonga, blasted by the most powerful eruption of the century so far. While these volcanoes can cause death and mayhem, they pale in comparison to the supervolcanoes that some believe drove some of the Earth's mass extinctions and could happen again.
[00:00:26] Speaker 2: The worst possible consequences of a supereruption would be an existential threat to human beings.
[00:00:33] Speaker 1: We are nothing in comparison to death. One of the most powerful supervolcanoes on Earth sleeps in the very heart of the United States, in Yellowstone National Park. Its origin dates back some 2 billion years. So far, it has detonated three supereruptions around 700,000 years apart, and it's about due for the next one.
[00:00:52] Speaker 3: Yellowstone is definitely a big system. It is really massive. The caldera is huge. It's tens of kilometers across, but also in terms of its depth.
[00:01:02] Speaker 1: The Yellowstone supervolcano churns with the largest reservoir of magma on Earth. That has scientists' concern. Its seismic and geothermal activity have been rumbling for the last 10 years. Does that mean the giant is beginning to stir? If Yellowstone does erupt, what would happen? The answer is indisputable and inconceivable. If the supervolcano exploded today, it would destroy a huge part of North America and disrupt life on Earth for centuries. Chaos. It would be a major ecological and human disaster. What would the end of the world as we know it look like? Pyroclastic flows, breaking at hundreds of kilometers per hour, annihilating everything in their path. Huge amounts of ash smothering thousands of square kilometers across the North American continent. And then, magmatic gases, triggering volcanic winter around the world for decades to come.
[00:02:00] Speaker 4: Basically, there's no escape. There's no way of preventing it. You just got to kind of prepare for it.
[00:02:07] Speaker 1: Preparation is easier said than done. Yellowstone is the most powerful and potentially the most dangerous supervolcano on Earth. An eruption would be a million times more cataclysmic than the bombing of Hiroshima. Would humanity survive it? Would we even want to? After the apocalypse, what kind of world would be left? Volcanologists agree. The question is not whether the Yellowstone volcano will awaken, but when. It is one of the most beautiful and best-preserved natural sites in the world. But potentially, one of the most dangerous, Yellowstone National Park. Straddling the states of Wyoming, Idaho, and Montana, its sumptuous landscape covers more than a million hectares. Over an area 88 kilometers long and 95 kilometers wide.
[00:03:21] Speaker 3: There are lots of special places on Earth, and Yellowstone, I think, is one of those.
[00:03:26] Speaker 5: It hasn't been altered as strongly as most areas of the world.
[00:03:30] Speaker 3: It's wonderland on its own. It's almost impossible to believe.
[00:03:36] Speaker 1: Yellowstone National Park is the oldest national park in the world, and the most visited in the United States. After being discovered by a member of the famous Lewis and Clark Expedition in 1806, President Grant signed a protection order in 1872. It was listed as a UNESCO World Heritage Site in 1979. Here, the wildlife roams freely across more than 9,000 square kilometers of vast plains amid picture postcard landscapes located at an average of 2,400 meters above sea level. It is home to more than half of the world's geothermal phenomena, producing energy below the surface of the Earth. For many millennia before becoming a park, this vast territory was already inhabited by Native Americans. The Nez Perce, or Blackfeet tribes, gathered around geysers and collected obsidian stones from ancient lava flows. Being very much in touch with nature, they could sense the stirrings in the depths of Yellowstone.
[00:04:33] Speaker 3: It was known to be a volcanic system because even some of the early explorers had learned from some of the indigenous peoples of the area that there was perhaps a volcano somewhere up near the headwaters of the Yellowstone River.
[00:04:46] Speaker 4: They recognized that there were a lot of volcanic deposits in the area, so they kind of had an inkling of it was a large volcanic system.
[00:04:55] Speaker 1: While the Native Americans were aware of living in a sometimes hostile natural environment, Yellowstone Park was initially not regarded as an area of interest to geologists. But a tragic event awakened the attention of scientists around the world. It all began with a deadly earthquake in the late 1950s.
[00:05:16] Speaker 4: There was a magnitude 7.3 earthquake. We call that the Hebgen Lake earthquake. And that happened just west of the park, just outside of the park. That's the largest earthquake that has ever been recorded in the Intermountain West of the United States. The biggest effects, of course, were out where the earthquake occurred, out by Hebgen Lake, where you had a lot of damaged roads, where roads were blocked, people were trapped. And it caused a big landslide to occur. And that landslide came down on a campground and buried 28 people.
[00:05:47] Speaker 3: It killed a large number of people. It dammed a river and created a brand new lake. That created all kinds of damage in Yellowstone National Park as well, damage to roads with landslides. And the shaking from that event caused a large number of new geysers to form, and existing geysers to change their behavior.
[00:06:06] Speaker 1: The following day in the park, just a few kilometers away, to the astonishment of all, 289 hot springs exploded into the sky in the form of geysers. Later, cracks in the ground appeared, releasing plumes of toxic gases. There could be no doubt that the earthquake at Lake Hebgen had triggered a great deal of underground activity in Yellowstone. And yet the area is not located on the edge of a tectonic plate. What exactly was going on in the heart of the United States?
[00:06:34] Speaker 3: There were a lot of seismometers that were put in the area, a lot of research that was done into earthquake activity. And it was found that Yellowstone is actually one of the most seismically active areas in the United States.
[00:06:45] Speaker 1: These earthquakes were of volcanic origin, triggered by an accumulation of underground magma. Scientists also discovered that the region is active because it is located on a hotline. It is a thermal anomaly. Starting some 2,900 kilometers below the surface, a hot spot brings up fragments of magma, producing the volcanic and seismic activity seen at ground level.
[00:07:09] Speaker 6: And you can imagine this as a bit of a torch that is fixed. The North American continent is moving, is drifting toward the west.
[00:07:17] Speaker 3: And so you'll get little volcanoes, and the blowtorch pops through every now and then, and you'll get a chain of these volcanoes.
[00:07:25] Speaker 5: Volcanoes kind of pimple upward along the Snake River plain in southern Idaho. If you go to the most western side of Idaho, you get to the oldest volcanism, and then it gets younger and younger as you progress up towards Yellowstone today.
[00:07:39] Speaker 1: The three million plus tourists who come here every year are blissfully unaware that they are walking across a ticking time bomb of unimaginable power. Visitors are oblivious to the secret that lurks beneath Yellowstone Park, the invisible volcano that may one day erupt, and in doing so, profoundly disrupt human activity.
[00:08:00] Speaker 2: We have to bear in mind that what we call supervolcanoes can also produce small eruptions.
[00:08:06] Speaker 6: Yellowstone is an example. Most of the eruptions are actually very small, and there were three large eruptions.
[00:08:12] Speaker 1: Yellowstone has experienced three major volcanic eruptions. The oldest and most powerful occurred some 2.1 million years ago at Huckleberry Ridge. It would have covered Texas with 4.5 meters of volcanic ash. The second, 1.3 million years ago, was at Mesa Falls. Finally came the third eruption, at Lava Creek, some 640,000 years ago. These events produced astonishing quantities of magma, up to 2,450 cubic kilometers in each case. These extraordinary magma flows and the violence of the explosions make Yellowstone a supervolcano.
[00:08:49] Speaker 2: A supervolcano is really a volcano which has been able to produce an unusually large eruption. Unusually large, in this case, means several hundred, maybe a thousand times larger than a common eruption that we've seen in historical time.
[00:09:04] Speaker 7: The VI, Volcano Explosivity Index, is a scale that volcanologists use to measure the explosiveness of an eruption. So a supereruption has a VI8.
[00:09:16] Speaker 8: On a planetary scale, these eruptions have a huge impact on the ecosystem and on humanity.
[00:09:23] Speaker 1: The number of supervolcanoes can be counted on the fingers of one hand. Over the past 2 million years, there have been about 15 supereruptions worldwide. Today, most of these supervolcanoes are dormant. But for how long? The Yellowstone supervolcano was formed during its last supereruption. Its collapse created the current caldera, a crater which today extends over 65 kilometers or one-third of the national park.
[00:09:49] Speaker 7: A caldera is a large depression that has formed because of the collapse of a magma chamber.
[00:09:56] Speaker 8: Yellowstone Park is actually in the caldera. This caldera is so huge that it cannot be seen in the landscape.
[00:10:01] Speaker 2: The calderas can be so large that you can build entire towns and cities inside them.
[00:10:07] Speaker 7: They can have diameters in between 1 and 100 kilometers.
[00:10:11] Speaker 2: It's not recognized that you're actually inside a volcano. This is why trying to raise awareness of what a supervolcano is, or a large caldera is, can be very difficult because they don't look like a stereotypical volcano that you would see in, say, a film from Hollywood.
[00:10:29] Speaker 1: At first sight, the uniform nature of the landscape offers few clues. So what does an exploding caldera look like? And what exactly happened? The series of events leading to a supervolcano eruption is always the same. Several kilometers below the Earth, the magma chamber begins to liquefy under the effect of very high heat. The magma then fragments and rises a few dozen meters toward the surface. The pressure from the chamber eventually weakens the Earth's crust, splitting it open. The immense pressure and very high temperatures produce an explosion, causing the volcano to collapse in on itself, giving rise to a 4,000 square kilometer caldera.
[00:11:10] Speaker 3: And when that magma chamber emptied, the surface fell into the space that was created, the space that was vacated by all of that magma that erupted, and that left this structure that we call a caldera.
[00:11:20] Speaker 5: It's kind of like a piston cylinder plummeting down into a liquid, which then pushes more material outward and makes this very flat surface.
[00:11:28] Speaker 6: The area of the caldera gives us some idea of the surface occupied by the magma reservoir that is at the base of this volcanic system.
[00:11:39] Speaker 3: A lot of that hole that was created by the big explosion has been filled by lava flows and by glacial debris and by lake sediment. It's not necessarily clear you're looking at a volcanic area unless you know the features that you are looking at.
[00:11:56] Speaker 1: After each supereruption, the magma chambers fill up again and the Yellowstone caldera now has the largest amount of magma of any in the world. For scientists, the threat is ongoing and a constant worry. But volcanologists have another cause for concern. If we take the dates of the past three supereruptions, the calculation is simple. The park's dormant volcanic system seems to wake up every 700,000 years or so. Given that the last supereruption took place 640,000 years ago, another is due. Scientists now anticipate another major eruption, but the question is, when? And what will be its magnitude?
[00:12:38] Speaker 8: Yellowstone's three previous supereruptions are huge indications of what might happen in the case of a fourth. We know the volume, we know the surface areas, we know the quantities.
[00:12:49] Speaker 1: The signs are clearly visible in the heart of the caldera. The impressive forest of dead trees testifies to the presence of sulfur in the soil and in the streams. Scientists at the Yellowstone Volcano Observatory closely monitor the caldera. The slightest variation or change in physiognomy is a warning sign of a potential eruption.
[00:13:10] Speaker 2: As that pressure increases, it causes the ground to move. Now the movement may be just a few centimeters, but we can detect that with satellite measurements, global GPS measurements, but also from traditional surveying technique.
[00:13:25] Speaker 1: In the 1970s, while hiking through the park, a seismologist noticed that the landscape had changed. On the south shore of the lake, the bases of tree trunks had become submerged in water. The only explanation was that the opposite bank had risen and the slope had changed.
[00:13:44] Speaker 3: Between the 1920s and the 1970s, it was seen that the land actually rose in Yellowstone Caldera by over 70 centimeters. And Yellowstone sort of goes up and down all the time on its own, typically at a rate of two to three centimeters a year or so. Now, before an eruption, we might expect to see very dramatic uplift.
[00:14:04] Speaker 8: When the magma rises, when an eruption is imminent, tiny earthquakes occur. Micro earthquakes have a magnitude of only one or two, which is very weak. They barely register, but there are hundreds or even thousands of them every day.
[00:14:15] Speaker 2: It is the local, very localized, breaking of rock as pressure builds up underneath the volcano.
[00:14:22] Speaker 8: The classic sign of an imminent eruption is a combination of swelling and micro-seismicity. If we have between 100 and 1,000 micro earthquakes per day, allied to swelling of just a few millimeters or a few centimeters, the signs are worrying, the magma is moving and swelling. The situation then becomes critical.
[00:14:41] Speaker 4: We record on average about 1,500 to 2,500 earthquakes a year, so it's a very seismically active area. They don't always happen on a regular basis either. We get what we call swarms of earthquakes. For example, there's kind of an east-west band of seismicity between the Hebgen Lake area and Norris Geyser Basin, where we see most of the earthquakes in Yellowstone.
[00:15:02] Speaker 1: The Norris Geyser Basin is the park's most dynamic geothermal area. This is the visible part of 115,000 years of seismic activity. It is the oldest and the hottest spot, with temperatures hitting 237 degrees Celsius in some springs. The water here is acidic, and in this post-apocalyptic landscape, you get a sense of the volcano breathing, swelling, and purging itself of the pressure just below the surface.
[00:15:27] Speaker 4: There's always kind of weird things going on there that we're learning how hydrothermal systems work.
[00:15:32] Speaker 3: Sometimes I like to think of geyser plumbing systems as like the plumbing in an old house. You know, maybe the plumbing is sort of rotting away. The plumbing is very tight because of all the minerals that have precipitated around the plumbing on the inside of the pipes. And if you shake that, pipes are going to break here and there, and things just aren't going to work very well, right? That's sort of what Yellowstone is like. And so when you have these large earthquakes shaking the plumbing system, it's going to break and you'll see geysers doing all kinds of weird things. So that's really the hazard that I think will impact this area on a human time scale.
[00:16:08] Speaker 1: Scientists are acutely aware of the threat posed by the Yellowstone supravolcano. Since the installation of seismographs in the caldera, volcanologists have been scrutinizing seismic disturbances and their intensity has increased sharply since the turn of the century. Correct interpretation of these seismic phenomena makes it possible to better predict eruptions and thus save precious time in evacuating the area. Everyone remembers what happened at Mount St. Helens. After several weeks of seismic disturbances, fractures and deformation, on May 18, 1980, at 8:32 a.m., the volcano erupted. It was the most traumatic in the history of the United States.
[00:16:46] Speaker 7: The 1980 eruption of Mount St. Helens is the most catastrophic eruption in the United States.
[00:16:58] Speaker 9: It began with a kind of landslide.
[00:17:02] Speaker 8: The summit of a volcano collapsed and it decapitated itself, releasing the bagma below, which gushed out in the form of fast-moving pyroclastic flows in a mixture of gas and ash. Then a column rose up into the stratosphere, up to 27 kilometers high. In just a few minutes, this vertical column developed into a huge 25-kilometer-wide mushroom cloud.
[00:17:34] Speaker 1: The winds coming in from the Pacific pushed the voluminous cloud of ash towards the east of the United States at a speed of 100 kilometers per hour. Eleven states were affected by the ash, which even fell on Oklahoma, some 2,000 kilometers away.
[00:17:50] Speaker 7: It killed about 60 people, but it also destroyed hundreds of houses, hundreds of kilometers of roads, let's say infrastructure.
[00:18:01] Speaker 5: The eruption of Mount St. Helens is actually a huge revolution for the field of volcanology. It really changed our whole perspective on how volcanoes work.
[00:18:10] Speaker 8: It's a reference point. It happened in a technologically advanced country with lots of data.
[00:18:15] Speaker 7: That taught us also many lessons in terms of prevention, in terms of monitoring volcanoes, in terms of emergency crisis. We always have something to learn from volcanic eruptions, so we build our knowledge on starting new eruptions.
[00:18:36] Speaker 1: Scientific studies around this previous eruption still serve as a solid working basis for volcanologists. But the explosion of gas and rock, the volcanic purge that occurred at St. Helens, pales in comparison to the volume that could potentially erupt from Yellowstone.
[00:18:52] Speaker 8: A few cubic kilometers were released, so compared to a super eruption, the ratio is something like 1:500 or 1:1,000.
[00:19:00] Speaker 4: Yellowstone volcano is about 2,500 times larger than Mount St. Helens.
[00:19:05] Speaker 1: Sometimes the imminence of eruptive events becomes clear within a few months, as in Mount St. Helens, but sometimes it's just a few days. That's the worrying aspect of the Yellowstone caldera. What if the time elapsing between eruptions is shorter than expected? It is a vital question in anticipating possible disasters, because the Yellowstone caldera has the largest magma chamber on Earth.
[00:19:29] Speaker 6: If Yellowstone is reawaking now, how long is it going to take? How much time do we have before we need to take some sort of action? For this, we rely on crystals that are contained inside the magma.
[00:19:46] Speaker 1: It is vitally important to understand the warning signs of an imminent and massive eruption. The information locked in the crystals of Yellowstone's ancient lava flows provide clues about the conditions and processes that preceded the eruptions. Crystals are taken from the magma of the super eruption that occurred 2.2 million years ago, an eruption described as apocalyptic. If such an event were to be repeated in Yellowstone today, it would cover two-thirds of the United States in ash and kill millions of people within minutes. The explosive energy would be 22 times greater than that of the H-bomb. The objective of these analyses is to determine the time elapsing between the first signs of an eruption and the caldera exploding.
[00:20:31] Speaker 6: When magma cools, it generates crystals. Crystals are small particles inside the magma. So what we need to do, we go in the field, we collect a rock that is cooled magma that has been erupted.
[00:20:45] Speaker 5: And then we break them apart and look at the crystals and see, well, what did they record? And so essentially crystals can record all sorts of changes that happen within magma. So essentially they're like little recorders of the processes that are happening within the magma chamber.
[00:21:00] Speaker 6: This is important because it tells us something about how much magma was coming into the system before the eruption occurred.
[00:21:09] Speaker 1: Crystals ejected during a past super eruption allow scientists to establish the chronology of an explosion and define the time that elapsed between the fusion of magma in the chamber and its eruption. Using these direct witnesses to the cataclysm, scientists then attempt to predict the next awakening of Yellowstone.
[00:21:29] Speaker 5: The rock record is our best understanding of really what happened, especially for historic eruptions where we don't get to see them in real time.
[00:21:37] Speaker 6: It's a little bit like looking at what happened in the past to try to understand what will happen in the future. These sort of studies have been done for Yellowstone and some part of the community speaks about reactivation times of months.
[00:21:55] Speaker 1: For now, measurements show that the caldera remains stable. But what happens when the pressure generated by the magma beneath the caldera reaches a critical point?
[00:22:07] Speaker 8: Magma is a thick liquid that forms at a depth of less than 100 kilometers. It then rises to a depth of less than five kilometers and forms a magma chamber.
[00:22:16] Speaker 2: We call a magma chamber that last stage of storage. That's the place where the magma was immediately before the eruption. At the moment under Yellowstone, the geophysical surveys suggest that there's something like 15,000 cubic kilometers of molten rock.
[00:22:34] Speaker 5: The top part of this chamber is probably around 4 kilometers at depth, and it can extend up to maybe 8 or 10.
[00:22:43] Speaker 4: It's what's providing all the heat and energy that's fueling the hydrothermal system. Most of that magma chamber is actually solid. It's hot, but it's solid. Typically, to get magma to mobilize and to move, it has to be at least 50% melt, and we're only at about 15 to 20% melt. That's not to say that there might be small pockets within there that have a higher percentage of melt. So that's kind of one thing that we're looking at if we can get better resolution images of part of the magma reservoir. But right now we have kind of an overall average over the whole thing.
[00:23:17] Speaker 1: Its presence just a few kilometers from the surface may be cause for concern. Scientists are closely monitoring any possible change in the state of the magma in the chamber. The more it liquefies, the more dangerous it becomes. The discovery of a new model of the interior of the magma chamber is precisely what now worries volcanologists.
[00:23:37] Speaker 7: The change from a quiescent state to an eruptive state implies the migration of magma from depth to the surface.
[00:23:46] Speaker 6: So for a long time we have imagined a magma chamber, a volume filled with magma. This magma chamber, we conceive it as embedded in an elastic medium. So it's like blowing into a balloon that is inside a wood box. When you blow inside, you feel the pressure increasing. And we thought that the injection of magma was the parallel for blowing inside the balloon. The pressure would increase and then the eruption would occur. As we see today at Yellowstone, we think that there are little pockets or smaller pockets of magma embedded in a system that is a bit like a sponge. When these systems are separated, the pressure inside is not sufficient to feed an eruption. Now we think that if each of these pockets, the magma tends to go up, this may lead to these pockets getting connected. And if these pockets get connected, the pressure inside a connected system increases a lot.
[00:24:47] Speaker 1: The conclusions of this model of the magma chamber are crucial because these connections of magmatic pockets would generate zero or very few signs of seismicity. The magma would penetrate silently from one pocket to another, increasing the pressure before triggering a gigantic eruption.
[00:25:09] Speaker 6: We think that this process of connecting the various pockets could be itself the process that triggered the eruption. I think one of the biggest question is how big the next eruption will be in a sort of system like Yellowstone.
[00:25:25] Speaker 1: While seismic activity may not be the most reliable clue preceding an eruption, others need to be studied closely. Geysers, pools, hot springs, boiling mud, fumaroles, all as spectacular as they are potentially dangerous, are in fact indicators of underground activity constantly being monitored by scientists.
[00:25:44] Speaker 3: We like to say that there's 10,000 thermal features in Yellowstone.
[00:25:49] Speaker 5: Yellowstone has half of the world's hydrothermal features or geysers in the world.
[00:25:54] Speaker 1: The best known in the caldera is the geyser known as Old Faithful. For more than a century, it has been spurting out eruptions more than 40 meters high every 90 minutes or so. It is the park's star attraction. These geothermal phenomena act as a thermometer for the rise in heat within the magma chamber. When the underground hot water source reaches 100 degrees Celsius, a gas bubble forms and expels the hot water in the form of a column tens of meters high. But if the temperature rises excessively, the geyser could change its cycle and sound the alarm. This is precisely what happened in the Norris Basin geyser area with Scheme Boat, the world's largest geyser. With unpredictable eruptions, it suddenly woke up in 2018 after eight years of inactivity, triggering a 120-meter-high column of water.
[00:26:44] Speaker 6: These volcanoes are active. They always do something. They always inflate, deflate, they emit gas, they have airquakes continuously. One of the bigger problems is to understand at which time do we have to start worrying.
[00:26:57] Speaker 1: One striking feature of the landscape around the Yellowstone hydrothermal system is the forests of dead trees, collateral victims of degassing and real sources of danger. Grand Prismatic is the largest hot spring in America. The size of a football field and as deep as a ten-story building, the pool is composed of sulfur and iron dioxide and its temperature rises to 70 degrees Celsius. The hydrothermal explosions associated with these basins, caused by underground water suddenly turning into steam, represent a threat. When water transforms, it expands rapidly, creating a very large volume that needs to escape. If the steam remains confined, it explodes.
[00:27:41] Speaker 3: These sorts of hydrothermal explosions could happen just about anywhere that there's hot water moving around beneath the surface. In fact, in 2018, there was a small pool called Ear Spring and it suddenly started erupting as a geyser. It hadn't done that since I think at least the 1950s. Why did that happen in 2018? We don't know the answer to that and that's something that we're really trying to focus on, to understand these small changes.
[00:28:07] Speaker 2: Ground movement, earthquakes, the arrival of a magmatic gas, those are really the three components or the three factors that we will rely on most for deciding whether or not eruptions likely.
[00:28:20] Speaker 1: The unpredictable and uncontrollable nature of these gigantic volcanic systems is a source of great anxiety for scientists. Seismic alerts and geothermal thrusts are not enough to flag a catastrophic eruption. The intervals between explosions need to be closely examined too. The past three super eruptions at Yellowstone suggest that the rate of recurrence is approximately once every 700,000 years. So are we dangerously close to the end of a cycle?
[00:28:50] Speaker 8: There seems to be periodicity but a statistic based on just three eruptions has no real value. What we can say though is that a super eruption is possible sometime in the millennia to come or within the next 300,000 years.
[00:29:03] Speaker 5: The cycle nature of these systems is so challenging because I think in every system where you have these periods where you have more vulcanism and then less vulcanism, you're always trying to figure out are you at the end of a cycle, at the beginning of a new cycle, like where are you in the cycle?
[00:29:19] Speaker 3: It's entirely possible that we're not only at the end of the current cycle of Yellowstone activity but there may not be that much in the future. That's a possibility. Unfortunately, I suppose, we won't ever be able to answer that question because we're never going to see it.
[00:29:35] Speaker 1: The caldera's huge dimensions, plus the danger lurking within Yellowstone's active magma chamber, allied to the resurgence of earthquakes beneath the park, are all alarming indicators. The real question being asked by scientists around the world is not whether or not the eruption will take place, but what the nature of the event will be when it does. As with many alarming possibilities, scientists may be unable to provide an accurate timeline, but they can imagine the potential consequences of an eruption, but will they be able to give the alert in time? The prospect is undoubtedly a frightening one. A super eruption at Yellowstone would quite simply be a geological event that disrupts social organization throughout the northern hemisphere, and in the worst case scenario, wipe out the entire human race. The major danger of this type of explosive eruption is the phenomenal amount of energy expelled by the volcano as it purges itself. The most important factor is the volume emitted. One cubic kilometer of magma ejected during a regular eruption would bury the entire Paris region beneath its ashes. In the case of Yellowstone, we are talking about 1,000 cubic kilometers of magma, or 1,000 times more energy.
[00:30:51] Speaker 8: It's all about scale. As I tell my students, an eruption of 1 cubic kilometer already has a huge impact. Increase that 100-fold, 1,000-fold, up to 1,000 or even 10,000 cubic kilometers, and the event becomes absolutely catastrophic.
[00:31:04] Speaker 1: The energy that the Yellowstone caldera could potentially generate in the event of an explosion is simply unimaginable. Predictive models show that a super eruption at Yellowstone would be of unprecedented violence.
[00:31:21] Speaker 8: It starts with a normal eruption shooting a plume of ash and fragments into the air. Then, as the eruptive conduit widens, so the magnetic flow increases. And all of a sudden, the magma projections increase dramatically, and you have what are called ignimbrites, coming from the Latin word meaning "fire rain."
[00:31:40] Speaker 2: These eruptions expel clouds of gas and fragments of broken up magma. Some of these clouds and fragments, they spread out over the ground, and they can travel at hurricane speeds up to, well, tens of kilometers away from the volcano.
[00:31:57] Speaker 8: It's actually a burning cloud of ash, gas and fragments traveling at 600 kilometers an hour, at temperatures of 600 to 700 degrees, hot enough to immediately fuse into rocks. The curls of ash unleashed with lightning in the plumes are like the wrath of the gods, the fury of Zeus or Jupiter.
[00:32:16] Speaker 6: The super eruption could cover several thousand square kilometers. And because the pressure decreases in the reservoir, this becomes a sort of vacuum cleaner that is sucking new magma coming in. And if this process keeps going, eventually a caldera collapse can start. And when the roof of the caldera pushes on the reservoir, it makes the magma come out from the fractures around the caldera. And then these especially produce pyroclastic flows.
[00:32:45] Speaker 1: Gigantic, extremely high temperature fiery clouds, composed of ash, gas and rocks, roll down the slopes of a volcano, seeping into the surrounding terrain, petrifying the landscape.
[00:32:58] Speaker 6: Pyroclastic flows destroy everything that is on their way there and reach 500, 600 degrees centigrade.
[00:33:06] Speaker 7: For sure, pyroclastic flows would be the most devastating phenomena associated with the super eruption. Basically, there's no escape from pyroclastic flows.
[00:33:15] Speaker 1: Life on the ground then would be sacrificed. But there is no escape in the skies above either. Without evacuation, the explosion would instantly kill any sentient being within 1,600 kilometers around the caldera, as it expels 1,000 billion tons of matter into the atmosphere. Then, a few days after the explosion, comes the most formidable enemy of all, volcanic ash.
[00:33:40] Speaker 6: Volcanic ash is glass. It's like if you take your window glass, you break it with a hammer, you make a little powder, and then you throw it into the atmosphere. Previous eruption of Yellowstone have covered in ash essentially the entire North American region.
[00:33:58] Speaker 5: In the immediate vicinity around Yellowstone, for instance, we're supposed to get over a meter of ash. And that goes all the way down to Salt Lake City, over to Billings, Montana. It's a huge extent of a meter of ash, which is a crazy amount of material.
[00:34:11] Speaker 7: But most of the death associated with the volcanic ash is related to the collapse of buildings. Because you can accumulate a lot of ash on the roof of a building that can collapse.
[00:34:25] Speaker 1: In addition to destroying cities, the ash mantle contains still glowing residues of magma, causing forest fires and destroying crops and herds as it falls to the ground. The ecosystem necessary for human life is swept away. Wildlife is threatened. All of America would then be plunged into darkness. No more electricity, no more drinking water. Particles of volcanic gases then escape. As they reach the stratosphere, they threaten the entire planet.
[00:34:59] Speaker 6: These gases are liberated into the atmosphere and sulfur, for example, can produce aerosols in the atmosphere.
[00:35:07] Speaker 8: These sprays filter the sun's rays, meaning fewer solar rays reach the surface of the earth. They form an opaque veil, triggering cooling on the ground of anything from a few tenths of a degree to a few degrees, in the case of the very strong eruptions. This is what generates volcanic winters. A volcanic winter is a significant drop in temperature following a major eruption, a super eruption, which radically disrupts the climate.
[00:35:31] Speaker 2: This is a major problem. It's chaos. A major ecological and human disaster.
[00:35:36] Speaker ?: Far from fantasy,
[00:35:37] Speaker 2: Volcanoes are a few years later. It's a major disaster. This is a major disaster. It's a major disaster. It's a major disaster. It's a major disaster. It's a major disaster.
[00:35:54] Speaker 8: And it's a major disaster.
[00:35:56] Speaker 1: It's a major disaster.
[00:35:58] Speaker ?: It's a major disaster.
[00:36:00] Speaker 1: It's a major disaster. The meteorology researchers are constantly studying every eruptive event on the planet, in an attempt to anticipate any looming crisis at Yellowstone. The study of previous explosions can help produce predictive models. But the problem with Yellowstone is the scale. Compared to the eruptions in Iceland or the Philippines, the effects would be a thousand times worse.
[00:36:22] Speaker 8: There was a famous eruption in Iceland in the spring of 2010 when the Eyjaflöj volcano erupted.
[00:36:32] Speaker 7: It was a moderate eruption. It had a volcanic explosivity index of three.
[00:36:37] Speaker 8: Then in April, the magma migrated to another place beneath the glacier. From that moment on, everything changed.
[00:36:45] Speaker 1: The hot lava coming into contact with the frozen glacier caused a huge plume of steam to rise ten kilometers into the atmosphere. At the same time, an anticyclone in the north of Iceland pushed the plume right across Europe. European air spaces were closed down, costing billions of euros in just a few days. Iceland isolated itself. This major eruption went on for two weeks, with no deaths or injuries. But this ordinary event, coupled with unfavorable winds, showed the fragility of our society.
[00:37:20] Speaker 7: Eyjaflöjökull demonstrated how vulnerable we are, even to a small eruption.
[00:37:25] Speaker 8: Compared to a super eruption in Yellowstone, what happened in Iceland in 2010 is a ratio of one to a thousand.
[00:37:30] Speaker 7: So if the A7 had to happen now, in the world as we have it now, the impact would be devastating.
[00:37:39] Speaker 1: What's in store for Yellowstone and the surrounding area is far worse. The Icelandic eruption was not from a supervolcano and had no impact on the climate. The same was true of the dramatic eruption at Pinatubo in the Philippines, the most significant disaster of the 20th century.
[00:37:58] Speaker 2: So if we want to have sort of some idea of what might happen after super eruption, we could think, what were the consequences of one of the biggest explosive eruptions of the 20th century? And by that I mean the eruption of Pinatubo in 1991.
[00:38:12] Speaker 1: The terrible rumbling from Mount Pinatubo has been going on for six days now. A new three-kilometer-long crack has appeared on the southern slope. In late 1991, having been dormant for 500 years, the Mount Pinatubo volcano exploded. The consequences were catastrophic and affected the entire planet.
[00:38:31] Speaker 2: The explosions sent fine particles of magma, ash, and sulfur-rich gases into the stratosphere.
[00:38:39] Speaker 1: All life was wiped out in a 14-kilometer radius around Mount Pinatubo. Collapsed roofs claimed many victims. 300,000 people were evacuated and nearly 900 people died. So many of them were contaminated. So many of them were floating in the soil. So many of them were contaminated. So many of them were contaminated.
[00:38:55] Speaker ?: So many of them were contaminated.
[00:38:55] Speaker 1: So many of them were contaminated. So many of them were contaminated. So many of them were contaminated. So many of them were contaminated. So many of them were contaminated. So many of them were contaminated. So many of them were contaminated. So many of them were contaminated. So many of them were contaminated.
[00:39:04] Speaker 2: So many of them were contaminated. And they were contaminated. at a global scale of a fraction of a degree centigrade over the following few years. So this gives us an idea that such a small eruption can have an impact on climates.
[00:39:18] Speaker 1: Luminosity was reduced by 10% across the surface of the Earth, a colossal figure. The ash circulated around the globe for three whole years, resulting in torrential rains and unusual flooding in the United States. The subsequent hole created in the ozone layer took 30 years to fill.
[00:39:37] Speaker 2: This erupted a few cubic kilometers of magma, so already several hundred times, if not a thousand times, smaller than a super eruption.
[00:39:46] Speaker 6: So for an eruption like the size of Yellowstone, this could have an impact and generate a few years of volcanic winters, at least what we think.
[00:39:57] Speaker 1: Learning from previous disasters is one way for volcanologists to anticipate and better prepare populations in the event of an eruption. But some visionary scientists are playing the Sorcerer's Apprentice and trying to find other preemptive solutions. NASA, for example, decided to take things further. After the eruption at Mount Pinatubo in 1991, they began working on a plan of action that could be rapidly implemented. Given that a volcanic eruption is a way of purging the pressure that builds up in the magma reservoir, the engineer's idea was to schedule regular mini-purges.
[00:40:40] Speaker 2: Let's just take it seriously for a minute, okay? So the idea would be, could we, is it possible, for example, to put a drill hole down towards the magma body and maybe allow gases to escape gently so you reduce the pressure and prevent the molten rock, in fact, eventually coming to the surface? That really is still in the realms of science fiction, I'm afraid.
[00:41:07] Speaker 3: The NASA study to drill the volcano and cool it down was not realistic. It was, it was basically a calculation. It was sort of the thing you do on the back of a napkin in a bar.
[00:41:17] Speaker 6: And this will take tens of thousands of years, and even with the risk of generating phreatic eruption.
[00:41:25] Speaker 3: But it didn't account for the fact that there's always more heat coming in.
[00:41:30] Speaker 2: Once you start to trigger the formation of gases, there is a risk that it's a self-heating process. And once you start it, you won't just control the creation, the release of gas, which then increases the pressure, which then leads to an eruption.
[00:41:46] Speaker 6: Yellowstone is already water-cooled. This is why there is a, there is a geyser system that is continuously releasing heat from this system.
[00:41:55] Speaker 5: We can't even essentially make a lava flow go into a different direction many times. There's no way we're going to stop a super eruption from going if it wants to go.
[00:42:03] Speaker 4: There's no way of preventing it. You just got to kind of prepare for it.
[00:42:08] Speaker 6: So our scientific responsibility is to mitigate the impact, not to change nature.
[00:42:13] Speaker 7: Our responsibility is to avoid that this natural phenomena becomes an impact on the population.
[00:42:20] Speaker 5: We just have to monitor it, understand the system, how it works, what we might expect to see in terms of hazards, and then essentially make a response plan based on that information.
[00:42:32] Speaker 1: Volcanologists around the world collaborate with each other. Depending on their various areas of research and expertise, they pool their work to better understand what is happening at the center of the earth. The challenge for crisis cells all over the world is to ensure the earliest possible evacuation of populations around volcanic areas.
[00:42:51] Speaker 6: There are more than 800 million people living around 10 kilometers of an active volcano, so it's a big part of the global population, so we need to take care about this.
[00:43:00] Speaker 7: A volcano goes through cycles. Sometimes we can think that a volcano is extinct because it hasn't shown any sign for many years. People get used to it and can start also building houses close to volcanoes. And then all of a sudden, a volcano can reawake after hundreds of years. And this is why these type of volcanoes can be particularly dangerous for people.
[00:43:27] Speaker 8: The most worrying and the most boring result for a volcanologist is a non-eruption. It's already happened. All the signs are red, an eruption seems imminent, the area is evacuated and nothing happens.
[00:43:39] Speaker 3: There are an awful lot of examples of volcanic crises where populations were evacuated and nothing happened, and then the population tends to lose trust in the scientists.
[00:43:52] Speaker 6: If they lose the trust, this could be very dangerous, because perhaps then something happened two years after, when everybody is back.
[00:43:59] Speaker 8: We volcanologists are spectators. We try to understand what the volcano decides.
[00:44:06] Speaker 1: Volcanologists know that the only solution is increased monitoring of volcanic systems, such as Yellowstone. In 2015, researchers from the University of Utah made a discovery as spectacular as it was unexpected when they located a gigantic, undetected magmatic reservoir.
[00:44:27] Speaker 6: The Yellowstone plumbing system, it was not limited to the very large 10,000 cubic kilometer reservoir that is somewhere in the upper crust in the first 10 kilometers, but there was a much deeper reservoir where about 46,000 cubic kilometer of magma are stored.
[00:44:46] Speaker 1: Lying beneath the already-known magma chamber at a depth of some 45 kilometers, this reservoir is an alarming discovery. 19 kilometers high, 64 kilometers long and 40 kilometers wide, it contains 46,000 cubic kilometers of magma, enough to bury an area the size of Texas beneath 15 meters of material. It is currently the largest magma chamber on Earth.
[00:45:09] Speaker 2: That is a place where magma can reside for much, much greater intervals of time, much longer than for a single eruption. So that is really the reservoir that can last the lifetime of the volcano.
[00:45:21] Speaker 1: While the rocks are not completely melted, most are in a solid, spongy state, and they are extremely hot, with pockets of liquid. Scientists have calculated that on average 9% of the magma in the known chamber is molten, with a further 2% in this new reservoir below.
[00:45:38] Speaker 6: From this place there are little volumes of magma that keep the system that is in the last 10 kilometers alive.
[00:45:48] Speaker 3: And it is possible at some point that it might inject some of that lower viscosity magma into the upper magma chamber. That may be the kind of thing that would cause a rejuvenation. It might be able to melt some of that stagnant upper magma chamber.
[00:46:05] Speaker 6: So the thing that this show us is that even if Yellowstone is not erupting now, it's an active system.
[00:46:13] Speaker 1: The discovery of this reservoir helps explain why the carbon dioxide emitted by Yellowstone soil and geothermal springs exceeds the volume that the only known chamber could be expected to produce. scientists now have a better understanding of the complexity of the Yellowstone magmatic system.
[00:46:33] Speaker 3: Yellowstone is definitely a big system. It is really massive, not only in terms of its aerial extent, right? The caldera is huge, it's tens of kilometers across, but also in terms of its depth. And the evidence for that is all around us, not only in the geysers and the hot springs, but in all of the volcanic rocks we see, not just here, but trending all the way across southern Idaho. This has been a long-lived and very large volcanic system.
[00:47:00] Speaker 1: On a human time scale, the eruption of the Yellowstone caldera remains a very rare occurrence. The risk is comparable with that of the Earth colliding with a meteorite. The super eruption fantasy is part of an irrational fear particular to the human race, the only species aware of its own death.
[00:47:21] Speaker 4: You don't necessarily, like, live in fear from these things, because what can you do about it, right? It's just part of the way the Earth works.
[00:47:29] Speaker 8: The Earth is neither nice or nasty. The same is true of volcanoes. Humans are, of course, dependent on nature.
[00:47:36] Speaker 4: So you can plan on it, you can model, you can prepare, and you can gain knowledge on the system so we can better disseminate that knowledge to people who live in the area and be well-prepared for certain events.
[00:47:49] Speaker 1: If NASA's purge technique, or some other as yet unknown solution, fails to work, it is likely that a supervolcano such as Yellowstone will one day wake up and trigger a mega explosion and global cataclysm.
[00:48:03] Speaker 2: The worst possible consequences of a super eruption might actually get close to those that we might imagine Hollywood would come up with. And that would be an existential threat to human beings, mainly because of a continued famine. So there are, have been, uh, ideas that it could lead to the, uh, uh, end of the, uh, uh, species. But that really is an extreme case. It will certainly, uh, end up with the, the, the, a complete change in our civilization, that is for sure.
[00:48:40] Speaker 6: I'm a, I'm optimist in this case. I don't think a super eruption will cancel us from, uh, I think we are much more capable to do that by ourselves than, than an eruption. But, um, obviously it will have an impact.
[00:48:54] Speaker 1: While the Yellowstone supervolcano is one of the most beautiful representations of nature, it is perhaps also its most remarkable paradox. The raw beauty of the landscapes, the geothermal diversity, and the purity of its colors conceal a frightening reality. Here, many kilometers below one of the Earth's rarest and best-preserved ecosystems, lurks a volcanic complex, which, should it ever erupt, would completely reshuffle the cards of human activity.
[00:49:23] Speaker 2: We're making progress in forecasting when an eruption will occur, but we're a long way behind in forecasting how it will occur and how big it will be.
[00:49:34] Speaker 6: These, these are the big questions we ask ourselves for any volcano on Earth.
[00:49:38] Speaker 1: In Yellowstone, the paradise visible on the surface exists alongside and above the hell down below. This unique system, forged by fire and water over many millions of years, allows researchers to observe, study, and understand the evolution of our planet.
[00:49:54] Speaker 3: The scientific opportunities here are amazing, and the lessons we learn at Yellowstone, even if it's not going to erupt, we can apply to other caldera systems around the world.
[00:50:04] Speaker 4: There's always something new. It's such a dynamic place. It's always changing. Every year, something happens, all of it integrated together gives us a better idea of how the Earth works.
[00:50:15] Speaker 1: The long history of the universe is littered with examples of physical phenomena such as extinction, climate change, cosmic collisions, and dead planets. The disasters of the past are etched into our DNA, and maybe, as some believe, in a collective ancestral memory.
[00:50:34] Speaker 7: Any eruption teaches us that we are very small in front of nature, so we think that we are in control, but we are not in control. We can study as much as we can, but at the end, we need to study to be able to respect nature, not to control it.
[00:50:51] Speaker 6: So this is why we should take care and use super eruption as a demonstration of the supreme power of nature. We are nothing in comparison to that, so we should have a little bit more respect for nature than what we do now.
[00:51:11] Speaker 1: California, home to 40 million people, and the sprawling megacities of Los Angeles and San Francisco. In the last century, the most populated state in the U.S. has grown 50-fold. Yet the region faces a terrible threat: the Earthquake of the Century.
[00:51:42] Speaker 10: We call it the big one because we expect the next San Andreas earthquake to be in the upper magnitude 7s to a magnitude 8, which is a very large earthquake.
[00:51:52] Speaker 8: Magnitude 8 in a highly populated area can cause a huge amount of damage.
[00:51:57] Speaker 11: But how much is it going to cost, how many lives are going to be lost when we have another big earthquake? It's going to be tens of billions of dollars and hundreds, if not thousands, of lives lost.
[00:52:08] Speaker 1: To blame: a gigantic crack in the Earth's crust spanning more than 1,200 kilometers between the two megacities.
[00:52:15] Speaker 12: Here, we're in the San Andreas Fault area, in one of the very few places where you can actually see and touch it. Literally, on either side of this fault, you have different tectonic plates.
[00:52:27] Speaker 13: Anytime you can sort of go up on a hike and be high, looking over the big city down below, you're standing on top of an active fault.
[00:52:36] Speaker 1: For over 40 years, the fault has been ominously quiet. Everyone knows that the big one is coming. Even overdue. So when will it happen? What will it look like? How can we prepare? Is it even possible to predict it? To answer these questions, scientists study the geological history of the fault. So we date the different layers, and then we can determine when earthquakes occurred in the past. Every meter of the fault is mapped out, every movement scrutinized. Scientists have developed an ultra-sophisticated warning system.
[00:53:20] Speaker 14: With seismometers, we have approximately 1,400 of them spread across the West Coast.
[00:53:27] Speaker 8: Every time we can gain a few seconds, we can save lives, and that's important.
[00:53:33] Speaker 1: When the big one strikes, what shape will it take? You're about to see the two most likely scenarios envisioned by scientists. One in the San Francisco Bay Area.
[00:53:48] Speaker 11: What you're supposed to do is drop, cover, hold on, get under a table, get under something sturdy, and wait.
[00:53:54] Speaker 1: And the other in Los Angeles.
[00:53:58] Speaker 8: It's quite spectacular to see how the seismic waves can liquefy the ground. Entire apartment blocks can sink several feet into the ground.
[00:54:06] Speaker 14: So if you think of some jello, and you hit it on the side with a knife or a spoon, then the jello jiggles. If you think of some jello, imagine the Valentine last hand as well shaking out a hole with each other.
[00:54:20] Speaker 1: These earth-shaking scenarios foretell catastrophic consequences. Hundreds of lives lost. Thousands injured and homeless. The big one is coming. But there is no doubt and no stopping it. Is California ready? October 17th, 1989. A peaceful late afternoon in San Francisco. Most people are at home so as not to miss the start of the baseball World Series final. Two Californian teams are vying for the title: San Francisco and Oakland.
[00:55:05] Speaker 15: At home for the Giants, one of the most spectacular vistas on this continent, any continent, downtown San Francisco, in the background, and we zoom in to Cable Stick Park.
[00:55:18] Speaker 1: Jason, too, is in front of a screen, waiting for the game to start.
[00:55:23] Speaker 16: So I was sitting there watching the World Series, very excited. The game hadn't started yet, and then, poof, everything goes off the air. I'm like, what is going on here?
[00:55:33] Speaker 17: What's wrong? And he fails to get Dave...
[00:55:35] Speaker 1: 5:04 p.m., the broadcast is suddenly interrupted.
[00:55:38] Speaker 17: Open A's, take it, take it. I'll tell you what, we're having a group...
[00:55:45] Speaker 1: A 6.9 magnitude earthquake shakes the entire region. More than 15 seconds of panic.
[00:56:01] Speaker 18: I remember the noise very much, it was so loud. And then, all the large windows started to fall out onto the sidewalk. It was moving a lot. I remember grabbing the table in front of me, and I thought, oh, no, this is it. I don't know what that means, if this is the big one or if this is the end, I don't know. I don't know.
[00:56:25] Speaker 4: How is it an emergency? Cypress, the West Grand Freeway has come down. The Cypress Central has collapsed. We have 238, we have a major injury accident.
[00:56:33] Speaker 16: And I walked out onto the street, as did a lot of other people, and it was like looking over a war zone.
[00:56:41] Speaker 14: There were fires, the marina, right over there, it was pretty much all on fire.
[00:56:55] Speaker 16: There was a huge fire, a big, huge flame, and around the city, there were pockets of flames.
[00:57:01] Speaker 1: The earthquake started in an area called Loma Prieta, more than 100 kilometers away from San Francisco. The seismic waves spread through the entire area in less than a minute, before reaching the San Francisco Bay area. San Francisco is on fire. 63 lives are lost, and more than 3,000 people are injured. A few years later, barely back on its feet, California is shaken again by a 6.7 magnitude earthquake.
[00:57:32] Speaker 17: For 15 million people in Los Angeles, this was yet another 30 seconds of terror.
[00:57:39] Speaker 1: A few years after that, another earthquake hits, this time in Napa Valley, Northern California. Since the start of the 20th century, hundreds of earthquakes, both minor and major, have been occurring along a line that crosses California from south to north, cutting the state in half. This line is known as the San Andreas Fault.
[00:58:09] Speaker 13: If you are flying, anytime you fly from Los Angeles to San Francisco, you're going up San Andreas almost the whole time. So, if you sit on the correct side of the plane, you can just watch it. Mostly, if you want to look west, usually outside of the plane.
[00:58:22] Speaker 14: It is about 1,200 kilometers long, and so in places you'll see a little hill created that will actually show where the fault is located. And that could be through showing potentially ripples, and that is where it shows. And so pictures that you see in textbooks show that sort of rippled landscape.
[00:58:43] Speaker 1: The path followed by the fault endangers more than two-thirds of California's population. That is, almost 30 million people.
[00:58:52] Speaker 8: Along the San Andreas Fault, there are several major cities. Obviously, in the south, you have San Diego and Los Angeles. Los Angeles represents more than 10 million people. And further north, you have San Francisco. And so, it triggers extremely powerful earthquakes, with magnitudes of over seven or eight, in very populated areas.
[00:59:18] Speaker 14: I've been in many big earthquakes in my life. And we live in earthquake countries, so we're always thinking about these things. Earthquakes are going to happen. It's not a matter of if, it's just a matter of when they're going to happen.
[00:59:30] Speaker 1: California is one of the most seismic areas in the world, but also one of the most populated. When will the big one happen? And how strong will it be? These questions have been asked since the early 20th century, when an unexplained giant earthquake destroyed California's largest city, San Francisco. 1906. The city is booming, its streets teeming with people and incessant activity. But a few hours later, everything will change.
[01:00:04] Speaker ?: 5:10 PM. The earth starts to shake.
[01:00:06] Speaker 1: More than 40 seconds of terror for the city's sleeping residents. At 7:00 AM, San Francisco is in total chaos. Uncontrollable fires rage for two days. Water is scarce, and people flee in panic. The entire country is traumatized. How can a city this size have been destroyed in just a few seconds? The scientific community wants to understand what caused the earthquake, and especially whether it can happen again.
[01:00:44] Speaker 14: The earthquake occurred about 50 years after California became a state in 1850. And it affected the most industrialized, largest city on the west coast, San Francisco. And so it really sort of figures in history as impacting a really important place and where a lot of people were affected.
[01:01:03] Speaker 13: And because it was felt over such a big area and had such a huge impact on San Francisco, the scientists went out to study that to understand how long is this fall? How far does it extend?
[01:01:15] Speaker 1: A team of scientists is rapidly put together, led by Andrew Lawson, a researcher at the University of Berkeley.
[01:01:29] Speaker 19: It's the first time that scientists go out into the field with their little notebooks, et cetera, and they start mapping the fault. So that's a major shift. And that happened because it was California. Earthquakes have always happened, but when they happen deep in the steppe, in Asia, in the 20th century, there's no one to talk about it.
[01:01:51] Speaker 11: It was more than taking pictures. It was really assembling a team of scientists and very carefully documenting everything about the earthquake. So yes, people went out and walked along the fault line and mapped the earthquake rupture in great detail and took a lot of pictures.
[01:02:13] Speaker 1: By roaming the area and analyzing photos, the team of researchers quickly realized that this earthquake is unlike any other.
[01:02:20] Speaker 11: So with all the mapping that they did, Andrew Lawson and colleagues, they were able to see that along the fault, there were displacements of as much as seven meters, right?
[01:02:35] Speaker 20: And what really surprised him was this fault move sideways, totally different than all the faulting that he had thought before, or he always thought faults occur up and down, but this one occurred sideways.
[01:02:49] Speaker 19: That's actually the first time that we realized the earth was being deformed. That's when it clicked.
[01:02:58] Speaker 1: The San Francisco earthquake shifted the earth from north to south. Huge areas of land literally slid past each other.
[01:03:10] Speaker 21: And what does he see?
[01:03:11] Speaker 19: Mainly fences, roads, sometimes even natural objects like a riverbed that were shifted by the fault. He knew that far away from the fault line, things were moving. So he developed this so-called elastic rebound theory, where the earth deforms far from the fault, but the fault is locked because of friction until crack. There's this elastic rebound.
[01:03:38] Speaker 12: It's like stretching an elastic before it snaps. You can stretch it for a long time before it snaps. And so the fault works in almost the same way. It can deform over many years and at one point, which we would all like to predict, it will rupture in an almost immediate earthquake.
[01:04:04] Speaker 1: But why does the earth's crust move? At the time, nobody knows. Scientists decide to index every earthquake around the world. Their aim? To see whether their location can give any clues on their mechanisms. They discover something surprising. Earthquakes are triggered along very precise lines. These imaginary lines mark out large plates more than 15 kilometers deep, also known as tectonic plates. These plates move very slowly in relation to each other.
[01:04:43] Speaker 8: A century ago, we didn't know about plate tectonics. We didn't know about plate boundaries. And so, we've made a great deal of progress since we now know that more than 90 or 95% of destructive earthquakes occur along plate boundaries.
[01:05:02] Speaker 19: You have these rigid plates moving whichever way they can, and all of these plate boundaries are formed by faults. So, you have subduction faults, you have extension faults, and you have places where the plates slide along each other, essentially horizontally, like the San Andreas Fault.
[01:05:25] Speaker 1: The San Andreas Fault concentrates the continuous movement of two huge plates over 1,200 kilometers.
[01:05:31] Speaker 14: The San Andreas Fault is actually the boundary between the Pacific plate on the west and the North American plate on the east. And what's happening is that the western part is moving north. So, if you look at your thumbnail, and you imagine that it grows about 50 millimeters per year. So, imagine your thumbnail growing, and that's how fast Los Angeles is getting closer to San Francisco every year. It's about 50 millimeters.
[01:06:04] Speaker 13: The main driver is that the whole time the tectonic plates are always moving. They're locked at the faults, but then far away from the faults, they're always moving. So, you're always accumulating that energy that you need to release in an earthquake.
[01:06:16] Speaker 8: You accumulate tectonic forces, as they're called, and then you reach breaking point, and that breaking point is an earthquake. And this earthquake will level out the two sides of the fault. Then, a new seismic cycle will start, with a new accumulation of tectonic forces that will lead to new earthquakes.
[01:06:42] Speaker 1: Scientists understand that the fault is locked in California, while the huge tectonic plates continue to move in the middle of the Atlantic Ocean to the east, and all the way to Russia in the west.
[01:06:58] Speaker 19: We can measure the speed at which these faults move, so we know the slip deficit that is accumulated along these faults. And we have already exceeded the amount of slip released in previous major earthquakes, so basically, it's ready to happen again.
[01:07:15] Speaker 14: And so, the concern is that there's going to be an earthquake, a big one, as we refer to, which is the high magnitude 7 earthquakes, like magnitude 7.8, which is sort of the typical large earthquake on the San Andreas.
[01:07:33] Speaker 1: An earthquake of this magnitude could, according to experts, cause hundreds of people to die, thousands to be injured or homeless, and millions of dollars of damage. The stakes are colossal. This is why scientists have only one thing in mind: being able to predict when exactly the "big one" will happen.
[01:07:55] Speaker 8: The "when" depends on the time scale you consider. If you're talking centuries, yes, we can predict it. We know there will be a very large earthquake in the coming century, but that's not what interests us from a societal point of view. I always talk about the time scale of insurance companies who want us to predict earthquakes with a three-day window. Otherwise, if you move a population like that of Los Angeles for more than three days, the financial cost is so high that it isn't profitable, and they're better off compensating people for the damage. It's a bit of a cynical calculation, but that's how you've got to think.
[01:08:30] Speaker 1: In order to predict the next earthquake, we need to know the fault's movements down to the very last detail. Scientists have thoroughly mapped out its 1,200 kilometers and obtained a precise plot of the path it takes. It starts on the shores of the Salton Sea in Southern California. It then heads up north, skirting Los Angeles, before continuing through the valleys around Pasadena.
[01:09:07] Speaker 14: We are standing on top of two tectonic plates at the boundary of these plates. On this side is the Pacific plate, and on this side is the North American plate. And so if there is an earthquake here, an interesting thing will happen. To my right, there is a university. And if we were here during the earthquake, this university would move, in a few seconds, 10 meters that direction. That's a pretty big distance.
[01:09:35] Speaker 1: It then curves and forms steep mountains. It fractures the Earth's crust in the Carizzo Plain, lifting the ground and compressing it.
[01:09:48] Speaker 12: We're very close to the San Andreas Fault. And you can see here a perfect example of how the Earth deforms because of the colossal pressure and forces at play around fault lines.
[01:10:00] Speaker 1: It makes its way in a straight line to San Francisco, which it cuts in half before finally flowing into the sea, a few dozen kilometers further. By analyzing the fault, scientists discover that it doesn't move the same way everywhere.
[01:10:22] Speaker 13: So the San Andreas Fault is interesting because it does have three sections. The southernmost and the northernmost are always locked until they're having an earthquake. And then they release all of that tectonic strain that's been developing. The middle section is sort of unique, for much of California at least, in that it sort of keeps up with the tectonic rate of the plates.
[01:10:45] Speaker 10: Which means it's constantly moving a little bit every year. And so because of that, it doesn't build up elastic strain energy. It doesn't build up, you know, the rocks don't bend and build up that elasticity to the point where they break and snap back into shape.
[01:11:04] Speaker 1: The south of the fault in San Francisco and the north in Los Angeles are therefore the most seismic areas. But the rest of California is no better protected, as what scientists discover is not reassuring.
[01:11:19] Speaker 10: The San Andreas isn't really just a single fault, it's a system of faults. And in fact, we're out on one of the branches in southern California called the Elsinore Fault. And the San Andreas is really the biggest player, but it's by no means the only fault that could produce significant damage.
[01:11:37] Speaker 11: So here in the San Francisco Bay Area, we have at least four other faults that are named and are considered capable of producing their own great earthquakes. So that's mainly the Hayward Fault that goes right here through the university campus. The Calaveras Fault across the East Bay Hills and several other faults.
[01:12:00] Speaker 20: The fault seems to be everywhere. There's a piece of the main San Andreas, maybe a quarter mile to the right. There's more pieces of it, splays of it, back here to the left. That's a composite of a whole bunch of different segments of faults that are roughly parallel, running very near each other and connecting with each other.
[01:12:21] Speaker 1: A map gradually emerges. California is crossed by a multitude of faults, with the most important at its center. San Andreas.
[01:12:33] Speaker 19: One actually is an earthquake. It's a fracture that spreads. But if I start looking at the point where it breaks, there are all sorts of little cracks before it gives way completely. The earth's crust is the same. If you look closely at a fault, you'll see a branch here and here and here.
[01:12:51] Speaker 10: So we really live on a very active plate margin, which is also very broad. So it's distributed out over tens to hundreds of kilometers. In fact, there's faults that go all the way to the east.
[01:13:04] Speaker 1: The San Andreas Fault and its multiple ramifications worries seismologists. How can they precisely predict the time and location of the next earthquakes? To answer this, researchers have decided to index past earthquakes and see whether any cycle is repeated.
[01:13:24] Speaker 10: This is the main fault for the Elsinore Fault, and it separates Pliocene sandstone from these Quaternary alluvial fan deposits, which are about 40,000 years old. And these have been translated about 60 to 70 meters to the northwest relative to the sandstone. So this is the primary slip surface right there. Most of the slip will occur right along that fracture. And there are stria on this that are horizontal. So you can tell the motion, the direction of motion on this fault is virtually pure strike slip. But this is what we call the principal slip surface. That's beautiful.
[01:14:08] Speaker 1: By digging trenches perpendicular to the fault, scientists can go back in time.
[01:14:15] Speaker 10: So we excavate trenches across the fault, and we study the interaction between fault motion and sedimentation. So we like to find sites where you're having deposits of silt and sand and clay periodically put across the fault. And so the game is to identify where was the ground surface during a large earthquake. So we date the different layers, and then we can determine when earthquakes occurred in the past.
[01:14:43] Speaker 8: It helps determine or date past earthquakes, and that gives us an idea of what we can expect in the future. If we know the recurrence times of a given fault, we can reasonably believe they'll be similar going forward.
[01:15:03] Speaker 1: Each earthquake fractures the earth's crust. Then, as the years pass, a layer of sediment is deposited until the next earthquake, which again fractures the ground, which again is covered in sediment, and so forth. It is therefore possible to go back in time over millennia and determine the dates and magnitudes of major past earthquakes.
[01:15:28] Speaker 10: So if you look at all the studies that we've done along the San Andreas Fault system in California, northern and southern California, we can develop a chronology to tell how often they occur and some degree of variability.
[01:15:43] Speaker 13: Technically, we see that the average is 100 to 150 years, depending on where you are. And it's been 100 to 300 years since we've had a major earthquake.
[01:15:54] Speaker 10: So, you know, when we say the fault is now beyond its average recurrence time, you know, that's a concern. That's why we say we're waiting for the big one.
[01:16:05] Speaker 1: But what worries researchers the most are the earthquake cycles.
[01:16:12] Speaker 19: If you start looking in detail, you notice that there are what we call earthquake storms. It's more of an image, but there are moments when it's best not to be in a certain area, because the entire fault ruptures and ruptures several times, and then there are moments of calm.
[01:16:30] Speaker 1: This is the case of the San Francisco Bay Area. Before 1906, there were more than 11 major earthquakes in 75 years, against only one since.
[01:16:41] Speaker 11: So eight million people also moved to the Bay Area in a time that was unusually quiet when it comes to the occurrence of earthquakes. So now we might be getting back to a more normal frequency of earthquakes. And that would suggest there should be a magnitude six or bigger earthquake every decade or so, every two decades, rather than having had many decades of almost none of them.
[01:17:12] Speaker 13: You know, if you have a rupture, and then just 10 years later, when you're finally sort of coming back together, and you've done all this rebuilding, and you have another earthquake on the next section, then you're back at square one. So there's a different kind of challenge, rather than the sort of immediacy of one big earthquake, is having them in close enough succession that societally, economically, culturally, you're just getting over one earthquake when the next one happens. And that's kind of a different...
[01:17:40] Speaker 1: How do they start? Are there any warning signs? Scientists decide to study an earthquake in real time. But first, they need to know where the next one will happen. The solution may lie in Parkfield.
[01:18:10] Speaker 9: Parkfield is a small town.
[01:18:12] Speaker 12: Not many people live there. But it's located bang on the San Andreas Fault, in a place that generates magnitude six earthquakes, every 20 years or so, with a factor two. And so, it gives the opportunity to each generation of scientists to test the latest ideas, the latest models, and to check whether or not we can predict earthquakes.
[01:18:36] Speaker ?: The next one is going to occur in the late 1990s.
[01:18:38] Speaker 10: In 1922, 1934, and 1966, the earthquakes at Parkfield all started under Middle Mountain. And we have seismograms for them, so we know where they started. And the seismograms are identical, virtually identical.
[01:18:53] Speaker 1: Parkfield earthquakes occur regularly. The next one is expected in the late 1990s.
[01:19:00] Speaker 19: One of the difficulties when it comes to earthquakes is actually the duration of observation. Human life is a little too short to be able to observe several major earthquakes on the same fault line, and to check how regularly they happen, which is what we call recurrence. We don't live long enough. But Parkfield had this particularity of generating earthquakes that weren't necessarily of the greatest magnitude, but they were extremely regular.
[01:19:27] Speaker 11: And so, scientists said, "Oh, these earthquakes happen so regularly, there's going to be a big earthquake in 1988, which is 22 years after the last one in 1966. It's going to be a magnitude 6 again, and we should put out all the instrumentation possible, and if we do that, we're going to catch something that will allow us to understand how to predict earthquakes."
[01:19:54] Speaker 1: From 1989, scientists set up a drilling station to penetrate the Earth's crust as deep as possible, and collect rock samples from close to the fault.
[01:20:05] Speaker 14: What's really great about this experiment is that they were actually able to dig deeper into the Earth quite over a mile to find out what's happening down there, to get a sense of what does the fault look like at depth, and to understand what does the rock look like, what's the composition of the rock, how is it hot, is it cold, what's happening. So that particular study gave us a glimpse into what's actually happening deep inside the Earth, which is not, we don't get that very often.
[01:20:34] Speaker 1: They drill down to approximately three kilometers under the Earth's surface, collecting rocks in several places in order to analyze them. Could these rocks change after an earthquake and provide us with more information? We'll need to wait and see. So they put all sorts of instruments around Parkville,
[01:20:56] Speaker 20: and they held their fingers and their ears waiting for it to go off. Except disaster.
[01:21:05] Speaker 19: The last predicted earthquake didn't happen. Or at least it didn't happen in the predicted time frame.
[01:21:13] Speaker 12: It happened in 2004, and it didn't start like the others. It started 20 kilometers further south. So it did the opposite of every previous earthquake.
[01:21:25] Speaker 11: Nothing happened in the days, hours, weeks before the earthquake that anybody could claim could have allowed us to predict the earthquake. So that was a big reality check.
[01:21:40] Speaker 1: Nothing happened as expected.
[01:21:44] Speaker 14: It turns out that that experiment, the Parkfield experiment, as I was referring to, didn't end up being an earthquake prediction opportunity. We were expecting to be able to say that earthquakes happen over these time periods, repeat over certain periods of time. And the interval was something in the order of every 20 or so years, and it didn't work out for us.
[01:22:08] Speaker 19: So we realized that this accumulation of four or five earthquakes that had been kind enough to happen at regular intervals was more of a coincidence, or that there may have been a physical reason we didn't understand. But it certainly wasn't a set rule.
[01:22:28] Speaker 1: But all is not lost. Scientists analyze the hard rocks around the fault. They have literally been crushed and subjected to very high temperatures. Where does this heat come from?
[01:22:43] Speaker 12: Earthquakes are frictional contacts between solids, so they generate heat. It's the same principle as warming up your hands by rubbing them together when you're cold. Temperatures can change by several hundred degrees for a few seconds. And there are questions as to whether these temperature rises could explain the propagation of earthquakes or their nature. And so, to try and predict earthquakes, we need to understand the role of temperature.
[01:23:10] Speaker 1: The friction of the plates generates heat. The rocks are damaged and crumble. The plates slide. The movement accelerates. The heat increases. The cycle climaxes and ends in an earthquake. Could temperature be the first sign of an earthquake?
[01:23:28] Speaker 20: The material analysis, by looking at the amount of heat that's built up along the fault, the amount of heat that's stored, the amount of liquidity that's down in depth along this fault, is going to be an important piece of information that comes from it. And there's a long ways to understanding what stresses have to build up before an earthquake flattens San Francisco again or Los Angeles.
[01:23:57] Speaker 1: For now, everything is up in the air. Parkfield seems to have been abandoned while we wait for the next earthquake. The instruments are in place and other avenues are being considered.
[01:24:09] Speaker 8: Some people think that electromagnetic signals are emitted before an earthquake. There are also chemical signals such as the emission of certain gases like radon. Temperature is one example among many, but honestly, I'm not sure it's very reliable yet.
[01:24:28] Speaker 11: My sense is that that will improve our understanding of the earthquake system. It will be relatively unlikely to allow us to actually predict earthquakes with any confidence.
[01:24:43] Speaker 14: So what we want is something that we say that can happen over certain defined periods of time. And if you start applying exceptions and start saying, well, under these conditions it does this, under those conditions it does that, then it ceases to be a really good model to predict earthquakes.
[01:25:02] Speaker 1: The San Andreas Fault is ready to shake. Scientists have known this since 1906, but have so far been unable to give a precise date or detect any early warning signs.
[01:25:18] Speaker 11: By its nature, earthquakes are chaotic, meaning even the littlest change in the system, right? The butterfly effect, even just a little kink in a fault or a certain aspect of an earthquake when it happens, changes the system enough that it's never going to be predictable. That no matter how sophisticated a simulation you build, it will never truly allow you to predict what's going to come next.
[01:25:53] Speaker 12: To be clear, today we don't know how to predict when earthquakes will happen. We test, we have a lot of ideas, but we're not yet capable of making quantitative predictions. In terms of prediction, we're a little stuck.
[01:26:07] Speaker 10: I'd say when I got into this business 40 years ago, there were a lot of people that thought we were just on the cusp of predicting earthquakes. I'd say now we know we're farther away from that point than we thought we were 40 years ago.
[01:26:25] Speaker 1: Seismologists have reached an impasse, and California's population continues to increase. As does its construction, creating more and more megacities. It is vital to be able to warn residents. So, scientists have come up with a solution.
[01:26:44] Speaker 12: We have access to a lot of data. We know the seismic history of many faults around these cities. And so, we're able to make certain statistical risk predictions. Some models are sophisticated enough to be able to assign a probability of occurrence of a certain magnitude earthquake over a certain time period.
[01:27:07] Speaker 14: And so, we choose, say, 30 years, because it's a time that we can all deal with. Human generations are like 30 years. Home mortgage is 30 years.
[01:27:20] Speaker 10: We can write a probability distribution that, in the next 30 years, has a 10% chance of rupturing. In the next 50 years, it might be 20%. In the next 300 years, it might be 80%.
[01:27:35] Speaker 13: So, they all come down into those final numbers, and there's many different models that are used, and you sort of weight them based on how confident you are about that model, or that sub-model.
[01:27:48] Speaker 1: What's going to happen in the next 30 years around the San Andreas Fault? Which city is most likely to experience the big one? In San Francisco, Los Angeles, Santa Cruz, the population must be made aware of the incurred dangers living in California. In the San Francisco Bay Area, there is a 70% chance of the earthquake of the century happening in the next 30 years. Seismologists have even detailed the probability on every active fault, each one threatening a major city.
[01:28:26] Speaker 11: That allows us to say, well, in the next 30 years, the probability of an earthquake on the Hayward Fault is about 31%. We know it had one in 1868, that was a magnitude 7, and it's right stretching along the most populated area, really, in all of California. So, it's a major player.
[01:28:51] Speaker 1: But there is also the Rogers Creek Fault near Santa Rosa, with a population of 170,000, or the San Gregorio Fault that runs along Santa Cruz with a 10% risk.
[01:29:04] Speaker 10: If you just say, oh yeah, it's got a 10% chance in the next 30 years, that means maybe a 90% chance that it won't rupture. So, you know, a lot of people will think, ah, I'm not going to worry about it. But you should worry about it. Because some of these faults now are well beyond their average recurrence times. And the probabilities are really quite high from a geologic perspective for the San Andreas in particular. So, that is the one we really worry about. And when it does rupture in a large earthquake, it will be a big one.
[01:29:40] Speaker 1: Further south, around Los Angeles, there is a 75% risk of a giant earthquake of magnitude 7 or more.
[01:29:49] Speaker 14: And that's a magnitude 7.8 earthquake, which occurred along a 300-kilometer-long segment of the fault. That earthquake would affect almost all of Southern California and cause all kinds of disruptions from, you know, people being injured to critical infrastructure being affected and that kind of thing.
[01:30:10] Speaker 1: Ultimately, there's a greater than 99% chance of a big one happening somewhere in California in the next 30 years.
[01:30:21] Speaker 13: But a forecast has a really important societal value because there are 30-year forecasts and that helps you decide what infrastructure you're going to repair first.
[01:30:32] Speaker 12: We need to protect our infrastructure, our hospitals, our schools, and so we need to make informed decisions.
[01:30:38] Speaker 13: So, I was just talking to a city today that was describing how they haven't updated any of their fire stations in decades. And so, you might say, well, we have high odds of an earthquake here. We should probably have fire stations that can withstand the earthquake and then be able to help people after it.
[01:30:59] Speaker 1: These figures are a terrible reminder of the threat to Californians.
[01:31:06] Speaker 14: Really, it's one thing to understand that you live in earthquake country and that things are going to happen, earthquakes are going to happen. But it's having an emergency supplies kit, like with water and with food and medical, your prescriptions and having some money because ATMs are not going to work after an earthquake. Yes, we should always be prepared for an earthquake in California.
[01:31:31] Speaker 8: It's going to happen, for sure. And because it's going to happen, the idea is that we have to be prepared. The population needs to be educated. And we need to try and reduce the impact of the earthquake on infrastructure and the number of victims.
[01:31:46] Speaker 1: Preparing for the worst. Scientists are not throwing in the towel and will deploy all the technology at their disposal to protect residents as best they can. To do so, they will start by deploying one of the most sophisticated earthquake warning systems in the world.
[01:32:05] Speaker 14: The idea was that if you could detect an earthquake quickly enough, meaning once that earthquake reaches the surface of the earth, which sometimes then you take that information and you move it to a place where you can figure out like where is the earthquake located and how much is it going to shape.
[01:32:21] Speaker 1: The idea is therefore to capture seismic waves triggered by the earthquake using ultra-sensitive seismographs.
[01:32:28] Speaker 19: When the rupture spreads, it emits different types of waves. First, it emits so-called compressional waves, like sound waves, that travel very fast. These are also known as P waves.
[01:32:43] Speaker 20: They're traveling ridiculously fast, five miles a second. They hit. And then a couple seconds later, the S waves, which are totally different. Instead of being compression waves, they're shear waves, and they're going to hit you.
[01:33:01] Speaker 11: And that's much stronger, and it moves a little bit more slowly. And so if we feel the shaking from that P wave, that actually gives you also a little bit of time to maybe protect yourself because the much stronger shaking is still to come.
[01:33:18] Speaker 1: First, the P waves reach the surface of the Earth and spread extremely rapidly. A few seconds later, the S waves emerge, moving in such a way that they spread less fast than the first waves. It's this delay between the two wave trains that will allow scientists to develop a warning system.
[01:33:40] Speaker 19: The first compressional wave is the one that sensors will detect immediately. Even you, if you're in bed, you'll feel something. And if you're a seismologist, that's when you start counting. Because you know the propagation speed of the waves, and you wait to feel the second tremor before saying, okay, that's X many seconds, so X speed, so X distance. In the context of the big one, I think you'll be shaken pretty hard by the first wave, and you'll have better things to do than start counting.
[01:34:10] Speaker 1: Seismologists will capture the first waves, the P waves, in order to sound the alarm before the more devastating second wave train hits the city.
[01:34:19] Speaker 14: Think of Earthquake Early Warning like a race, and we're trying to outrun the seismic waves, trying to get information out ahead of those waves that are moving through the Earth.
[01:34:32] Speaker 1: This race against seismic waves comes down to the second. In order to win it, scientists have deployed more than 1,500 seismometers along the San Andreas Fault and the secondary faults. But that's not all.
[01:34:46] Speaker 14: That information is moved to the processing center, so essentially the brains of the operation are these processing centers. In fact, here in Pasadena, this is one of the processing centers right here that are located. And it all happens in a matter of just a few seconds. And that's the important thing, is that this is one of the key innovations. We've been using seismometers for years, but the ability to process that information super fast is the real innovation here.
[01:35:15] Speaker 11: Just a month ago, I got a warning on my watch, and it was a magnitude 5 earthquake just south of here. But I got the warning before the earthquake happened, and I was in a meeting, and we dropped, covered, and held on, and it worked. So when a much larger earthquake will happen, and it will happen, it's probably going to make a big difference.
[01:35:43] Speaker 12: It's the airbag analogy, right? You can't predict an accident three days ahead, but when it does happen, you're glad you have an airbag.
[01:35:50] Speaker 1: A warning, even just a few seconds before the waves hit, can save lives.
[01:36:00] Speaker 14: There have been some earthquakes recently where you've collected a lot of data from close-circuit televisions, and you've understood what people do when they feel shaking. And one of the major responses is people just freeze. They don't do anything. And so what we want people to do is not to freeze, but we want them to actually take that protective action, to do something about it, to protect themselves.
[01:36:25] Speaker 1: Preparing the population, anticipating, knowing what to expect. These are the challenges facing scientists. How fast will the waves spread? How long will residents have to protect themselves? Will the buildings hold up? To answer these questions, seismologists have simulated the most probable Big One scenarios in California's two most-at-risk megacities. Up north, the Hayward Fault represents the greatest danger. Several million people live and work nearby. Major earthquakes occur every 150 to 220 years, and the last one dates back to 1868. At zero seconds, the fault ruptures in the extreme southern part of the bay. The warning systems detect the first waves.
[01:37:23] Speaker 14: So the earthquake starts in the Earth, reaches the surface in about one second. Information is moved from the sensor to the processing center in about one second. And then the processing center works on it, say, for about three seconds. And then it makes that information available to other people who then deliver alerts. That could take an additional three seconds.
[01:37:45] Speaker 1: Seven seconds after the earthquake is detected, the warning goes out. But the earthquake has already wrought havoc at its epicenter, Fremont, a city of 220,000 people.
[01:37:57] Speaker 8: If you're close to the epicenter, there is what we call a blind zone, where the warning system isn't much use because the P waves and the S waves hit almost simultaneously.
[01:38:10] Speaker 14: One of the major factors is how far they're away from the epicenter. So distance matters. The idea is if you're farther away, then you'll have a little bit more time.
[01:38:21] Speaker 1: The P waves spread towards Oakland and Richmond. Five seconds later, the more devastating S waves hit and caused the buildings to shake for more than 30 seconds.
[01:38:31] Speaker 19: The idea of the early warning system is to set a certain number of criteria based on the sensors in order to say something is happening that is abnormally strong. So we'll activate a certain number of security processes without even thinking. Typically, we'll shut down high voltage electricity lines because we know that the wavetrain is coming and we'll shake everything up, causing live wires to touch and cause a short circuit.
[01:39:01] Speaker 21: We'll shut down gas supply.
[01:39:04] Speaker 19: You can go through every red light. Everyone stops.
[01:39:09] Speaker 11: Automated systems that shut down industrial manufacturing or open up fire station doors. There, even a second might make a big difference.
[01:39:22] Speaker 1: San Francisco is hit 26 seconds later, but the worst is yet to come.
[01:39:31] Speaker 8: It's often the secondary effects of earthquakes that cause the most victims. There are issues of water supply, issues of epidemics. There's a whole sequence of catastrophes that can happen. For example, very often major earthquakes cause absolutely huge fires.
[01:39:53] Speaker 9: There are no more people who are in the middle of the city.
[01:39:54] Speaker 1: There are no more people who are in the middle of the city. There are no more people who are in the middle of the city. There are no more people who are in the middle of the city.
[01:39:58] Speaker ?: There are no more people who are in the middle of the city. There are no more people who are in the middle of the city.
[01:40:00] Speaker 1: There are no more people who are in the middle of the city. There are no more people who are in the middle of the city. There are no more people who are in the middle of the city. There are no more people who are in the middle of the city. There are no more people who are in the middle of the city. There are no more people who are in the middle of the city. There are no more people who are in the middle of the city. There are no more people who are in the middle of the city. There are no more people who are in the middle of the city. There are no more people who are in the middle of the city. There are no more people who are in the middle of the city. There are no more people who are in the middle of the city. There are no more people who are in the middle of the city. There are no more people who are in the middle of the city. There are no more people who are in the middle of the city. There are no more people who are in the middle of the city. There are no more people who are in the middle of the city. There are no more people who are in the middle of the city.
[01:40:21] Speaker ?: There are no more people who are in the middle of the city. There are no more people who are in the middle of the city.
[01:40:23] Speaker 1: Another scenario, worse but also the most likely. Starting at the south end of the fault, its consequences are catastrophic. The earthquake is triggered around the Salton Sea. It is immediately detected by the warning system. The stopwatch starts.
[01:40:43] Speaker 14: So we did a scenario of the fault breaking all the way from the Salton Sea all the way up to the northwest part of Los Angeles County. It's called a shakeout scenario. And it takes about 90 seconds for that rupture to move 300 kilometers. That's pretty fast.
[01:40:59] Speaker 1: Los Angeles marks the halfway point. The first waves hit at 35 seconds. But what will play against the city is its relief.
[01:41:08] Speaker 8: Los Angeles is built in a basin.
[01:41:12] Speaker 19: It's essentially a big bowl. If you send waves in there, the waves hit. But that's not all. Unfortunately, they're reflected everywhere.
[01:41:21] Speaker 12: We're going to have waves spreading in the Los Angeles basin for several minutes. When they've already been and gone everywhere else. And so that creates waves that are bigger and last longer. Long enough, unfortunately, to bring down buildings.
[01:41:38] Speaker 14: And what happens with seismic waves when we hit these basins is they slow down and they get bigger. That means that things shake a lot more. So if you think of some jello and you hit it on the side with a knife or a spoon and the jello jiggles. Imagine Valentine Los Angeles shaking on that bowl of jello.
[01:42:02] Speaker 1: The waves bounce around the basin creating another much more devastating phenomenon.
[01:42:11] Speaker 21: If you have a basin, you have a basin filled with sediment. And that means that you aren't on solid ground. You're on soil, on loose sediment.
[01:42:26] Speaker 19: And that doesn't particularly enjoy being shaken.
[01:42:29] Speaker 8: When you shake the ground, the ground becomes liquid. It's kind of like when you're at the beach and you shake a stick in the sand. The water comes up and the ground softens. The same thing happens in sediment basins. It's quite spectacular to see how the seismic waves can liquefy the ground. And that's a problem.
[01:42:49] Speaker 19: Because even if you constructed your building extremely well, if it ends up like this, it might not crumble, but it will fall down.
[01:42:58] Speaker 1: The city will be shaken for several long minutes before the earth calms down again. Is California ready for these earthquakes of unprecedented intensity in its ultra-industrialized cities? Everything is set up to warn the population, save lives, and protect infrastructure. Efforts and research are ongoing in this race against time. And the predicted big one.
[01:43:40] Speaker ?: The people that are in the sea. The people that are in the sea. The people that are in the sea. The people that are in the sea. The people that are in the sea. The people that are in the sea. The people that are in the sea. The people that are in the sea.