Deadly Pacific (Full Episode) | Drain the Oceans

Deep below the Pacific Ocean lies a tectonic monster. You know how we told you not to panic? Well, that's all off. Panic, run for your life. The world's biggest tsunami machine, its dangers hidden from view until now. Imagine if we could empty the oceans, letting the water drain away to reveal the secrets of the seafloor. Now we can, using the latest underwater scanning technology, piercing the deep oceans and turning accurate data into 3D images. This time, is the world's next mega earthquake brewing off the coast of Seattle? We can have the big one right now as we speak. Why has the discovery of an underwater volcano just 44 miles from Tokyo got seismic experts so worried? And what do scientists caught up in an undersea earthquake learn about the dangers facing New Zealand? The front of it would have a huge amount of energy. The scale is just immense. Drain the oceans reveals the secrets of the deadly Pacific. The Pacific Ocean, the planet's largest and deepest. 500 million people live around its coast. But deep beneath the waves lurks a terrifying monster that threatens all of them. The planet's largest and most dangerous seismic zone, the Ring of Fire. 90% of all earthquakes strike here. And when they do, the consequences are devastating. March 11, 2011, Tohoku, northeastern Japan. A magnitude 9 earthquake violently shakes the region. The quake causes buildings to collapse and people to flee for their lives. But that's not the end of the destruction. A defining characteristic of the Ring of Fire is that the biggest earthquakes here shake not just the land, but the seabed as well, generating huge surges of water, deadly tsunamis. In Japan, almost 16,000 people are killed. And geologists are certain it will happen again somewhere around the Pacific Ring of Fire. But when and where? Pulling the plug on the Pacific Ocean reveals a glimpse of one of its most terrifying secrets, just off the west coast of America. Not the infamous San Andreas Fault in California, but something close to the teeming cities of Portland, Seattle, and Vancouver. Something far more menacing. It's known that it's an active structure. It could happen now, and that's truly the source of fear. This region of North America is known as Cascadia, one of the most beautiful and peaceful in North America. It's also home to 10 million people. They feel safe here. And why wouldn't they? In all recorded history, there's been no trace of any natural disasters in the region. But on the 18th of May, 1980, everything changes. There is no question at all that the volcanic activity has begun. Mount St. Helens, 50 miles from Portland. Huge eruptions blast a 1,300-foot crater in the summit of a volcano, long thought to be dormant. It is the biggest eruption ever recorded of Mount St. Helens so far. I think it does not look good for people in that area now. It's the worst volcano disaster in US history, claiming 57 lives. Scientists are now forced to ask a tough question. Is it scaled to look at tsunamis? Does the eruption of the supposedly inactive Mount St. Helens mean the 10 million inhabitants of Cascadia are now sitting on a seismic time bomb that just started ticking? To find out, scientists launch an urgent investigation on land and deep under the sea. Off the coast of Cascadia, the latest scanning technology reveals something extraordinary and terrifying. Based upon their exact data, for the first time, we can pull the plug on the Pacific Ocean to reveal their shocking discovery. As the water drains away, a vast world no human has ever seen before is laid bare. For mile after mile across its heart, the Pacific Ocean floor is a vast, flat, featureless plain until suddenly the landscape changes. Here, just 150 miles from the great cities of the Pacific Northwest, a dramatic transformation takes place, revealing a fractured, broken sea floor, brooding, menacing. One of the best analogies I can think of is looking at the front end of a car that's been in a head-on collision, dented and corroded and corrugated into this complex mess. The scale of this geological fender bender is truly epic. Colossal cliffs almost twice the height of the Grand Canyon, some deep enough to hide six Empire State buildings stacked on top of each other, all of it stretching 700 miles along the Cascadian coastline. This titanic rupture in the Earth's crust is what geologists call a subduction zone. At the core of our planet is a boiling cauldron of molten iron surrounded by a thick mantle of rock. That outer crust is divided into huge tectonic plates that are constantly in motion. When they collide, they thrust mountains upwards and carve deep trenches into the ocean floor as one plate drives the other back inside the Earth. If the plates lock together, tremendous pressure begins to build. Only in subduction zones, where the plates are compressing together and there's this lock between the plates, those are the only fault zones that have the potential to create magnitude 9.0 and higher events. But that's not all. Subduction zones, because they are underwater, can generate not just earthquakes, but huge tsunamis. Written history suggests that Cascadia's subduction zone has been inactive for centuries. But does written history go back far enough? Is this monster really as sleepy as it seems? Scientists scour the landscape around Cascadia in search of answers. And in the banks of coastal rivers like this, they find an alarming pattern. It's very much like a chocolate cake. You slice a chocolate cake, and there's a layer of brown frosting, and then down below, there's another layer of brown frosting. And the Washington Coast looks very much like that. But there's nothing sweet about these layers of peat and sand. Each of these buried soil layers on the Washington Coast reflected times when the coast had been jerked downwards by the occurrence of an earthquake. In the layers of peat, David Yamaguchi and geologist Brian Atwater unearth evidence of seismic devastation stretching back over thousands of years, quakes that scarred the entire coastline of Cascadia. The question now is, when was the last one, and how big was it? The Copalis River, Washington State. Scientist David Yamaguchi is on a quest. He and his fellow scientists already suspect that the 10 million inhabitants of Cascadia are living on a seismic time bomb. But when did it last go off, and how big was it when it did? Three miles inland, he comes across a haunting sight. This is what's left of a once mighty forest of red cedar and spruce trees, thousands of petrified corpses scattered over hundreds of miles along Cascadia's coast. And the mystery here is, what killed the trees, and when did they die? Sampling dozens of the trees, Yamaguchi analyzes their age rings, and what he finds is a new mystery. The trees were fine and healthy in 1699. Then the following summer, the trees that would normally have produced another annual ring were nearly all dead. What happened to kill an entire forest in one instant? And why did it do that? Another scientist thinks the answer could lie deep in the geological car crash of the Cascadia subduction zone, just 100 miles away. Chris Goldfinger is an underwater earthquake detective, seeking evidence in core samples taken from deep under the seafloor. Studying the layers of sediment reveals when and where earthquakes struck in the past and how powerful they were. Sediment settles to the seafloor, but it got there somehow. From some storm, an earthquake, even a volcanic eruption will leave a deposit on the seafloor. And so it's just a very precise three-dimensional tape recorder just recording every single thing that happens. Well, this is a core sample from the seafloor off of Cascadia. And it's about 2,000 years worth of sediment. In the middle of the sample, dating to roughly 300 years ago, Goldfinger finds the classic signs of a large earthquake. Well, in fact, the shells like this turn out to be shallow water fossils. But this is a deep water core. So these things were carried down from shallow water to deep water. What this points to is a fairly dramatic kind of event. That dramatic event was an earthquake that triggered a vast underwater landslide. And it all happened around the same time that Yamaguchi's trees died. Next, he compares core samples of the same date taken along the 700 miles of the Cascadia subduction zone. Core after core reveals the same disturbed layer all occurring at the exact same time. This is evidence of no ordinary earthquake, but a monster. Cascadia, through the study of past earthquakes, has shown that it's capable of generating earthquakes that run the full length, roughly 1,000 kilometers. In 1700, the Cascadia subduction zone generated a cataclysmic quake along its entire length with a magnitude that Goldfinger and other scientists calculate as level eight. But that's not all. This was more than just an earthquake. Japan has a long history of earthquakes and tsunamis, with written evidence going back 1,400 years. Among these historical records, in accounts written by samurai and merchants, researchers uncover reports of a 16-foot tsunami that arrives from far out in the Pacific, swamping the eastern coast. It destroys houses and causes villagers to flee to higher ground. The date of these reports? 1700. They proposed that our earthquake was magnitude nine. A magnitude eight was not big enough to produce a wave that's that wide. In addition, based on the arrival times of the waves in Japan, the earthquake must have happened here on January 26, 1700, at 9 o'clock at night. Yes, local time. The Cascadia megaquake was so powerful that it generated a tsunami that hit Japan 4,500 miles away. Using the combined insights of experts from both sides of the Pacific and the extraordinary drained landscape of the subduction zone, it's now possible to visualize the titanic events of January 1700 and its deadly trail of destruction. The entire subduction zone shakes very hard. The ground motion is big. And it's over a big area. So it's going to shake a lot of sediment loose. There are going to be hundreds of landslides. They're going to all come tumbling down the slope and leave a deposit. The quake also triggers a huge tsunami, which smashes into the coast of Cascadia, flooding the land with seawater, including the Red Cedar Forest and everything else in its path. Although there is no written history of the 1700 earthquake and tsunami in Cascadia, native peoples of this region do hold haunting memories of these terrible events. The First Nation peoples had oral histories about the great battle of Thunderbird and Whale. It had a lot of shaking of the ground, washing away of villages. The great Thunderbird finally carried the whale to its nest. There were a shaking, jumping up, and trembling of the earth beneath, and a rolling up of the great waters. Once these stories came to light, the Native Americans essentially said, why didn't you just ask us? We knew all about that. The story had a moral, and the moral was don't build your village too close to the beach. But evidently, no one was listening. Today, 10 million people live along the coast of Cascadia and in the cities of Seattle, Portland, and Vancouver. And the question is, how likely is it that the monster will roar again? It's not at all like a clock, but the average time between the earthquakes is on the order of 400 years. If the Cascadia subduction zone repeats its 400-year cycle, then its next megaquake could be imminent. We know the strain is building, and we know one day it's going to be released, and that could happen any day. So what will happen when the monster wakes? In a subduction zone earthquake, energy is stretched out not 10 seconds or 20 seconds, more like three minutes. The shaking's not incredibly violent, but it lasts for a long time, and it's a very long rolling motion. For tall buildings, that's not good news. With buildings collapsing and infrastructures shattered, it will be hard for the population to escape from the coastal area, the worst place to be trapped. You know that if you get a giant earthquake, you better assume you're about to get a giant tsunami. The tectonic plate's sudden release of pressure forces a massive swell in the ocean above. So the wave height initially might only be a couple of meters, but it might be 200 kilometers long. And it heads out at the deep water wave speed, which is very fast. So it's jetliner speed, 500 or 600 miles an hour. Everything we've seen in Japan, we can expect basically the exact same thing in Cascadia. 30 meters of water rushing in at 10 meters a second kind of velocities, it just scours everything off the surface of the Earth. Within 20 minutes, the tsunami will approach the coast of Cascadia. When that wave starts feeling bottom, like all other waves do, it gets compressed from 200 kilometers down to a kilometer or two. It's like an enormous tide happening very quickly. A Cascadia megaquake is predicted to be North America's worst ever natural disaster. The fatalities could be fairly large. We're looking at a few tens of thousands of people, at least, on our coastline. We know the strain is building. That's quite harrowing to know that we can have the big one right now as we speak. But Cascadia is not the only populated region in the Ring of Fire danger zone. As the waters of the Pacific continue to drain away, they reveal another sleeping giant near the east coast of New Zealand, where scientists discover traces of an epic seismic event that reshaped the southern hemisphere and ask, when will it happen? Again. The islands of New Zealand lie directly on the Ring of Fire. Small earthquakes shake the ground here every week. In 2011, the country's second largest city, Christchurch, is devastated by a magnitude 6.3 quake. I can confirm that there have been deaths. Killing 185 people. 100 miles from Christchurch is the town of Kaikoura. Kia ora. Welcome aboard. A peaceful holiday resort that's popular with nature lovers. Keep looking out there. You can see they're just out in front of us there. It's deep, nutrient-rich waters entice whales close to the shore. This is the beautiful ocean. While these leviathans are Kaikoura's star attraction, geologists now come here for a very different reason. New Zealand's geologists constantly monitor the threat posed by the faults and fissures that run under the islands, trying to discover where the next big quake might strike. Ground surveys can help, but investigating under the waves has always been a challenge. Until now, because the latest multiple beam sonar technology is opening up a hidden world. It's multiple beams of sound energy being released from the instrument on the vessel, and we time how long it takes for that beam to come back. We do what we call mowing the grass. And we're just collecting this continuous image of what the shape of the seabed is. And the shape of the seabed near Kaikoura is not what they expected. As the data comes in, it slowly reveals something astonishing and potentially lethal. Pulling the plug on the Pacific Ocean exposes the remarkable site. Just a half mile from the town of Kaikoura, as the water drains away, it reveals the plunging walls of a vast undersea chasm, the Kaikoura Canyon. The Kaikoura Canyon, it comes within a really short distance of the coastline out here, less than a kilometer. And from there, it drops down at 30, 40 degrees, down to about 600 meters water depth. Then it carries on down to about 2,000 meters water depth. Stretching for over 37 miles, the canyon forms part of one of the deepest sea channels in the world. The walls nosedive over 6,000 feet, the depth of the Grand Canyon. Geologists wonder at the immense geological forces involved to create such a huge canyon, but also ask themselves, does it pose a threat to those living on the nearby coast? Geologists know that landslides triggered by earthquakes in underwater canyons can generate lethal tsunamis. Could the Kaikoura Canyon do the same? On board the research ship Tangaroa, they investigate. Using perspex tubes, they gather evidence from the sedimentary layers on the canyon's floor, looking for signs of seismic activity in the past. This is core two. But then, just as they're studying history, they get the chance to make some. Midnight, November 14, 2016. We are undergoing a fairly dense earthquake at the moment. So please just get to somewhere where you are safely under some protection. I can honestly say I doubt that I'll be able to stay in the chair for much longer. The 7.8 magnitude quake rips apart the Earth, creating giant crevices and billions of dollars of damage. Geologist Joshua Mountjoy has never seen anything like it. The key thing was that it just covered such a large geographic area, and it was right on our coastline. The quake rattles the ground for two minutes, causing thousands of landslides across 3,800 square miles. Just north of Kaikoura is the biggest. 800 million cubic feet has shaken to the ground, exposing a virgin cliff face almost a mile wide. Grass and tussock we're standing on was connected to that grass and tussock up there. And then the whole block slid right down to bring it down to where it is now. So this has happened during the earthquake. We call that co-seismic. And there's actually a fault line running through here that runs right down to the coastline. The shaking is so severe that it thrusts the foreshore of Kaikoura upwards by three feet in just one second. We look out here, we can see a whole lot of seaweed that's stranded above the tideline. Before the earthquake, that would have been down below the sea level. But Joshua Mountjoy isn't only interested in how the earthquake tears apart the land. As soon as the earthquake begins, he wants to know the effect it's having deep under the ocean, in the newly scanned Kaikoura Canyon. Mountjoy makes contact with the research ship Tangaroa, which is mapping the very far end of the canyon. We requested that they divert their energy to focus on doing some earthquake response. That response is to immediately gather core samples from the floor of the canyon before the dust has settled. So we already had an unprecedented opportunity to assess, well, what is the aftermath of a major earthquake? If the crew responds in time, they can achieve a world first, recording the impact of an earthquake in a deep sea canyon as it happens. Within minutes of the earthquake, the crew retrieves precious core samples from the sea floor. They collected the sedimentary deposit that had only just happened. So they were pouring it while it was probably still settling out of the ocean. And what marine geologist Alan Orpin discovers is intriguing. There's some kind of trichophy. I'm not quite sure of it. What we found was a very soupy, fluidized mud that was lying on the seabed. As we moved south, what we found was compelling evidence, core after core, for a thickness of material that had spilled down through the channel. The more samples they take, the clearer the picture becomes. The shaking of the quake has created a secondary and truly spectacular undersea upheaval. No one's ever been able to observe one of these huge landscape scale canyon flushing events to show exactly what effect it had on the canyon itself. Using the data gathered by the crew of Tangaroa and the remarkable drained seascape, the impact of a large earthquake on a gigantic underwater canyon can now be visualized for the very first time. The seabed shudders ominously as huge tectonic forces power through the Earth's crust. This dislodges a top layer of sediment, becoming a gigantic canyon flushing landslide. Rock and sediment tumble down the steep walls. 850 million tons of debris roars through the canyon, gouging 160 feet out of the floor. It's really like a powder snow avalanche. The front of it would have a huge amount of energy moving at about 70 kilometers an hour and maybe 400 meters high. It's spreading tens of kilometers across the ocean floor. It's just going to take over everything that's down there. The landslide travels with such velocity, it carves a path across the seafloor for an astonishing 435 miles. A landslide of this ferocity has the potential to generate a tsunami that could devastate Kaikoura. When a landslide creates a tsunami, you need a large chunk of material to slide down slope. And what happens is it's coupled to the water above it and actually pulls it down with it. And then as that water rebounds, then you create your wave. This time, Kaikoura is lucky. In the wake of the tsunami, no large objects fall off the canyon rim. Next time, the town may not be so fortunate. And the dramatic events of 2016 draw the geologist's attention to an even bigger tsunami threat nearby. By continuing to drain the ocean off the northeast coast of New Zealand, we can see the reason for their fear. Lurking just north of the canyon and frighteningly close to the New Zealand capital of Wellington, the Hikurangi subduction zone, 2,174 miles of seismic trouble. Geologists recently learned that stress has been building at its southern end for hundreds of years. And they believe that the 2016 earthquake has ratcheted the pressure up even further. Understanding what's happening here has become an international priority. 100 ocean floor seismic measuring devices and support scientists recently arrived from Japan. They're here to monitor and record the mounting stresses in the hope of discovering the true danger of Hikurangi. Geologists delve deep into the subduction zone's tectonic past, and their results are astounding. It hasn't fractured recently, but deep in its past, it produced something bigger than anyone had imagined. Now, using the geologist's data, it's possible to reconstruct, for the first time, a tectonic event that reshaped a hemisphere, the Ruatoria avalanche. Just 200 miles from what today is New Zealand's bustling capital, Wellington, the epicenter of one of the biggest seismic events in the history of the Earth. 170,000 years ago, the Australian plate is bearing down on its Pacific neighbor, grinding down everything in its path. Even a towering volcanic cone, six times the volume of Mount Fuji, becomes collateral damage. The resulting seismic shock triggers an underwater landslide on a scale rarely seen. Moving a swath of broken rock, the equivalent of 3 quarters the size of the Grand Canyon. So the Ruatoria avalanche is the second biggest submarine landslide in the world. It's absolutely enormous, 3,000 cubic kilometers. And if you can try and visualize a cubic kilometer, that's a kilometer high by a kilometer long by a kilometer wide, 3,000 of them. Nobody knows when the Hikurangi subduction zone will fracture again. But when it does, geologists estimate the tsunami wave from the megaquake will take only seven minutes to reach New Zealand's capital city, Wellington, and its half a million residents. And such a huge tsunami wouldn't only impact New Zealand. There would be an ocean wide alert as the waves fan out into the Pacific. The last time a tsunami on this scale hit the southern arc of the Ring of Fire was December 26, 2004, devastating 14 countries and killing 230,000 people. A terrible reminder of the power of the deadly Pacific. Continuing to drain away the Pacific Ocean reveals a very different kind of seismic threat 5,000 miles away, right next to one of the most densely populated cities on the planet. Just 44 miles from bustling Tokyo, a mysterious underwater feature has scientists on the edge of their seats. The island nation of Japan suffers from its position on the Ring of Fire. The country accounts for about 20% of the world's earthquakes of magnitude 6 or greater. Its biggest city, Tokyo, has been hit by nine mega earthquakes in the past 95 years. But just 44 miles off the city's shoreline, geologists have recently discovered a new and very different tectonic troublemaker. The first discovery is made by scientist Ken Tani. He's heading out to test his new underwater remotely operated vehicle, or ROV, in the waters just off the island of Oshima, south of Tokyo Bay. Until now, the waters here have been considered safe passage for one of the busiest shipping lanes into the port of Tokyo, with 400 vessels passing through here every day. But that is about to change. 44 miles from Tokyo Bay, Ken Tani prepares an underwater survey using an ROV. Passing over a rocky mound on the seafloor, he discovers something extraordinary, a seismic beast that has lain hidden for hundreds of thousands of years. Using Ken Tani's own data, draining away the Pacific Ocean reveals what is lurking below the waves. As the water recedes, it exposes a large, flat plateau. Near its center, what looks like an ordinary hole in the seafloor. But on closer inspection, the frightening truth emerges. It's the vent of an undersea volcano. Thousands of years ago, it very likely had a towering cone. But erosion and wave action has worn it down, which is why no one discovered it before. But is it as dormant as it appears? Ken wastes no time in exploring the crater. So that's the sea surface. Testing the water temperature around the outlet with a submarine thermometer. And what he finds surprises everyone. We found this very active high-temperature hydrosomal vent, which suggests even more that it's volcanically active. We first got very excited. But at the same time, we started to get concerned about the potential hazards if it erupts in the near future. The smoldering undersea volcano is named Umuradashi, 44 miles south of Tokyo, placing at risk the lives of thousands of mariners in the shipping lanes above. In 1952, an underwater volcano like Umuradashi erupts 260 miles south of Tokyo. Superheated magma reacts with water to produce what's called a fredomagmatic explosion, an underwater steam bomb. A nearby ship is engulfed in the explosion, killing all 31 on board. The big problem with the submarine volcano, it can erupt any time. And even from a small eruption, if the boats were going above it, it can cause severe maritime safety issue. A stirring volcanic giant is not just a danger to shipping. A major eruption could send tsunami waves racing towards Tokyo, population 38 million. Even from a very small eruption, it can cause severe impact. Ken decides he needs to keep Umuradashi under surveillance. Nothing happens for five years. Then, when he returns to gather fresh samples, Umuradashi has another unpleasant surprise for him. Returning to the drained ocean floor reveals his next shocking discovery. In addition to the crater, five more volcanic cones. That's five more possible outlets for the volcano. Only one is currently active, but all could become so. And if the volcano keeps growing, Umuradashi could become an even greater threat by breaking the surface and spewing toxic ash into the sky. Active volcanoes can do this astonishingly quickly. It took Nishinoshima, Japan's latest volcanic island, just two years to grow from a flat-topped underwater summit to this tectonic monster, measuring one square mile and 443 feet high. But Nishinoshima is nearly 600 miles from Tokyo. Umuradashi is only 44. Once out of the water, any major eruption of Umuradashi could shower Tokyo in choking volcanic ash. Despite the dangers, Kentani and his team continue to monitor Umuradashi. Any increase in the volcano's activity could signal impending disaster for the thousands living on nearby islands and threaten the safety of millions in nearby Tokyo. Draining the ring of fire has revealed hidden geological wonders and terrors, exposing new evidence of this immense power of plate tectonics and its ability to create and destroy.