1 00:00:02,607 --> 00:00:08,327 Earth, a 4.5- Billion-year-old planet, still evolving. 2 00:00:08,327 --> 00:00:16,887 As continents shift and clash, volcanoes erupt, glaciers grow and recede, 3 00:00:16,887 --> 00:00:21,487 the Earth's crust is carved in countless fascinating ways, 4 00:00:21,487 --> 00:00:24,923 leaving a trail of geological mysteries behind. 5 00:00:25,927 --> 00:00:26,967 Water. 6 00:00:26,967 --> 00:00:30,087 One of the most powerful forces on the planet. 7 00:00:30,087 --> 00:00:35,567 It plays a crucial role in creating life and destroying it, 8 00:00:35,567 --> 00:00:40,727 in forging landscapes and in breaking apart the Earth. 9 00:00:40,727 --> 00:00:47,687 In its most dramatic form, it becomes a killer wave known as a tsunami. 10 00:00:47,687 --> 00:00:51,767 Until recently, predicting when these monsters may next strike 11 00:00:51,767 --> 00:00:53,120 has been impossible. 12 00:00:55,367 --> 00:01:00,527 But today, scientists are starting to understand these giant waves. 13 00:01:00,527 --> 00:01:07,407 By connecting clues as varied as ancient Japanese writings and landslides, 14 00:01:07,407 --> 00:01:12,767 ancient corals and buried Native American settlements, 15 00:01:12,767 --> 00:01:16,601 the secrets of tsunamis are finally being unlocked. 16 00:01:24,847 --> 00:01:30,047 Tsunamis. One of the most deadly forces of nature. 17 00:01:30,047 --> 00:01:34,647 Giant waves that travel faster than a jet plane, 18 00:01:34,647 --> 00:01:38,481 they can cross entire oceans in just hours. 19 00:01:41,327 --> 00:01:46,162 They have the power to smash buildings, vehicles, anything in their way. 20 00:01:48,727 --> 00:01:51,927 MAN: By itself, you wouldn't think that water just streaming 21 00:01:51,927 --> 00:01:55,407 into the coast would necessarily cause so much damage. 22 00:01:55,407 --> 00:02:01,607 But in fact, they are very fast moving and they pick up everything in its path, 23 00:02:01,607 --> 00:02:06,727 so it's not the water by itself, it's what comes with the water 24 00:02:06,727 --> 00:02:09,287 that is also a part of the big hazard. 25 00:02:10,727 --> 00:02:14,327 A tsunami isn't over in just a few seconds, 26 00:02:14,327 --> 00:02:18,161 it is a torrent of raging water that keeps coming. 27 00:02:19,647 --> 00:02:22,047 The main thing about a tsunami is the persistence. 28 00:02:22,047 --> 00:02:27,327 It comes on and on and on, and just when you think it has to quit, 29 00:02:27,327 --> 00:02:31,487 it keeps coming, and it's the power plus the... the duration 30 00:02:31,487 --> 00:02:33,876 that is unstoppable, really. 31 00:02:35,127 --> 00:02:39,484 Tsunamis have ravaged the Earth for billions of years. 32 00:02:41,167 --> 00:02:45,727 When the Earth was first created, the moon was much closer. 33 00:02:45,727 --> 00:02:47,206 It filled the sky. 34 00:02:48,447 --> 00:02:51,127 Its gravitational pull was much stronger, 35 00:02:51,127 --> 00:02:55,367 and it generated towering waves over half a mile high 36 00:02:55,367 --> 00:02:58,404 that raced across the primeval oceans. 37 00:03:01,007 --> 00:03:03,047 MAN: Oh, my God! 38 00:03:03,047 --> 00:03:04,527 (SCREAMING) 39 00:03:04,527 --> 00:03:08,645 Today, tsunamis are still a threat to coastlines all over the world. 40 00:03:10,927 --> 00:03:15,007 MOONEY: Tsunamis will always occur, and have always occurred, 41 00:03:15,007 --> 00:03:16,327 throughout Earth's history. 42 00:03:16,327 --> 00:03:20,607 But it's only been more recently, as population densities have increased 43 00:03:20,607 --> 00:03:24,407 and people have moved and migrated to the coastal regions, 44 00:03:24,407 --> 00:03:28,287 that we've become much more aware of the tsunami hazards. 45 00:03:28,287 --> 00:03:32,287 The investigation into what caused these monster waves 46 00:03:32,287 --> 00:03:34,767 began over a thousand years ago 47 00:03:34,767 --> 00:03:37,487 on the islands of Japan. 48 00:03:37,487 --> 00:03:40,647 This country is the world's tsunami hotspot. 49 00:03:40,647 --> 00:03:43,807 Its coasts have been pounded with these enormous waves 50 00:03:43,807 --> 00:03:46,037 more than anywhere else on the planet. 51 00:03:47,887 --> 00:03:51,207 Evidence for this is the word tsunami itself. 52 00:03:51,207 --> 00:03:55,837 It is Japanese and literally means "harbour wave". 53 00:03:58,727 --> 00:04:03,887 Japan has the longest written tsunami record of anywhere in the world. 54 00:04:03,887 --> 00:04:08,915 The records go back as far as 684 A.D. 55 00:04:09,927 --> 00:04:12,887 By studying these records, it is possible to work out that, 56 00:04:12,887 --> 00:04:17,836 on average, this country has been struck nearly every seven years. 57 00:04:19,047 --> 00:04:21,567 Samurai writings speak of people living on the coasts 58 00:04:21,567 --> 00:04:25,807 running for higher ground as soon as they felt an earthquake. 59 00:04:25,807 --> 00:04:29,647 The Japanese knew this was a clue, 60 00:04:29,647 --> 00:04:32,807 a warning sign that a deadly tsunami would soon follow. 61 00:04:32,807 --> 00:04:35,367 But despite their attempts to escape, 62 00:04:35,367 --> 00:04:40,521 tsunamis have continually brought death and destruction to these islands. 63 00:04:42,127 --> 00:04:45,967 In 1896, a wave that hit Honshu in the northeast 64 00:04:45,967 --> 00:04:50,006 claimed the lives of 27,000 people. 65 00:04:51,327 --> 00:04:55,647 In 1933, the same area was smashed again. 66 00:04:55,647 --> 00:04:58,923 This time, 3,000 people were swept away. 67 00:05:00,047 --> 00:05:05,407 And in 1993, the island of Okushiri was rocked by an enormous earthquake 68 00:05:05,407 --> 00:05:08,687 measuring 7.8 on the Richter scale. 69 00:05:08,687 --> 00:05:14,887 Buildings were levelled and fires raged. But worse was to come. 70 00:05:14,887 --> 00:05:17,247 Minutes after the shaking had subsided, 71 00:05:17,247 --> 00:05:22,287 an ominous white crest appeared on the horizon - a tsunami. 72 00:05:22,287 --> 00:05:26,917 A gigantic wave swept in, flattening any buildings still standing. 73 00:05:31,127 --> 00:05:34,607 In Japan, the locals had already worked out the connections 74 00:05:34,607 --> 00:05:37,127 between earthquakes and tsunamis. 75 00:05:37,127 --> 00:05:41,167 But there's another hotspot on Earth where tsunamis regularly strike - 76 00:05:41,167 --> 00:05:43,647 the Hawaiian islands. 77 00:05:43,647 --> 00:05:48,767 But very few of them were preceded by an earthquake. 78 00:05:48,767 --> 00:05:50,847 The city of Hilo on the Big Island has been dubbed 79 00:05:50,847 --> 00:05:54,047 the Tsunami Capital of the World. 80 00:05:54,047 --> 00:05:58,447 Dozens of these enormous waves have hit these beautiful islands, 81 00:05:58,447 --> 00:06:00,727 and the mystery is why. 82 00:06:00,727 --> 00:06:02,487 With no natural warning to go on, 83 00:06:02,487 --> 00:06:04,167 the people of Hawaii must rely 84 00:06:04,167 --> 00:06:07,443 on the world's biggest tsunami monitoring station. 85 00:06:08,807 --> 00:06:13,367 Set up in 1949, it is connected to a network of buoys 86 00:06:13,367 --> 00:06:15,487 spread across the Pacific Ocean. 87 00:06:15,487 --> 00:06:19,167 These buoys provide important clues. 88 00:06:19,167 --> 00:06:21,447 They monitor changes in sea level 89 00:06:21,447 --> 00:06:25,679 that indicate the approach of any potential tsunamis. 90 00:06:28,847 --> 00:06:33,287 In 1960, scientists got the breakthrough they were looking for. 91 00:06:33,287 --> 00:06:35,487 They were finally able to work out the type of event 92 00:06:35,487 --> 00:06:39,367 at the root of Hawaii's mystery tsunamis. 93 00:06:39,367 --> 00:06:43,527 An enormous quake on the coast of Chile, the biggest recorded of all time, 94 00:06:43,527 --> 00:06:47,247 with a factor 9.5 on the Richter scale, 95 00:06:47,247 --> 00:06:51,927 triggered a tsunami that swept across the entire Pacific Ocean 96 00:06:51,927 --> 00:06:54,247 in just a few hours. 97 00:06:54,247 --> 00:07:01,127 The islands of Hawaii were thousands of miles away, directly in its path. 98 00:07:01,127 --> 00:07:05,087 The Tsunami Warning Center was monitoring its progress, 99 00:07:05,087 --> 00:07:08,887 revealing for the first time that a single massive wave 100 00:07:08,887 --> 00:07:12,047 crossed thousands of miles of ocean. 101 00:07:12,047 --> 00:07:14,887 The warning centre was a success. 102 00:07:14,887 --> 00:07:18,607 They were able to evacuate the communities closest to the shore 103 00:07:18,607 --> 00:07:20,727 before the wave struck. 104 00:07:20,727 --> 00:07:23,927 But the homes they left behind were decimated. 105 00:07:23,927 --> 00:07:30,607 In Hilo, the tsunami was so strong it even bent parking metres in half. 106 00:07:30,607 --> 00:07:33,687 The wave continued past Hawaii to Japan. 107 00:07:33,687 --> 00:07:36,607 It had lost none of its power. 108 00:07:36,607 --> 00:07:40,487 Pacific-wide, this tsunami cost more than 2,000 lives 109 00:07:40,487 --> 00:07:43,877 and caused millions of dollars' worth of damage. 110 00:07:46,127 --> 00:07:47,607 Devastating as it was, 111 00:07:47,607 --> 00:07:52,167 the 1960 event was a turning point in the study of tsunamis. 112 00:07:52,167 --> 00:07:56,047 It was the first time that scientists could accurately measure 113 00:07:56,047 --> 00:07:58,767 how the size of an underwater earthquake 114 00:07:58,767 --> 00:08:02,327 directly affected the size of a tsunami. 115 00:08:02,327 --> 00:08:05,687 And conclusive proof that a tsunami can travel 116 00:08:05,687 --> 00:08:08,767 thousands of miles across the Earth. 117 00:08:08,767 --> 00:08:12,607 And It was with this Chilean earthquake that we really could prove 118 00:08:12,607 --> 00:08:16,807 that the, uh, undersea motions associated with the earthquake 119 00:08:16,807 --> 00:08:19,765 are generating these huge effects. 120 00:08:20,887 --> 00:08:24,087 Now scientists had the evidence to confirm 121 00:08:24,087 --> 00:08:28,927 that undersea earthquakes were directly responsible for tsunamis. 122 00:08:28,927 --> 00:08:34,127 The ancient Japanese suspicion was now scientific fact. 123 00:08:34,127 --> 00:08:40,647 In terms of modern tsunami study, the 1960 wave was year zero. 124 00:08:40,647 --> 00:08:43,687 MOONEY: The Chilean earthquake was, you might say, the perfect storm, 125 00:08:43,687 --> 00:08:46,767 it's when scientific understanding had advanced to the point 126 00:08:46,767 --> 00:08:52,127 where scientists had begun to see the link connecting everything, 127 00:08:52,127 --> 00:08:54,527 so it's a new science, we're talking about something 128 00:08:54,527 --> 00:08:57,439 which is really only less than 50 years old. 129 00:08:58,487 --> 00:09:02,647 There are more tsunamis in the Pacific Ocean than any other. 130 00:09:02,647 --> 00:09:06,247 So in 2004, the world was taken by surprise 131 00:09:06,247 --> 00:09:09,487 when one of the largest recorded tsunamis of all time 132 00:09:09,487 --> 00:09:12,843 took place in the Indian Ocean. 133 00:09:14,447 --> 00:09:17,167 On December 26th, 2004, 134 00:09:17,167 --> 00:09:21,807 Indonesia was rocked by the second largest recorded earthquake ever, 135 00:09:21,807 --> 00:09:25,243 9.2 on the Richter scale. 136 00:09:26,247 --> 00:09:27,927 Minutes later, 137 00:09:27,927 --> 00:09:31,840 a 90-foot tsunami slammed into the South-East Asian coastline. 138 00:09:34,047 --> 00:09:39,724 225,000 men, women and children lost their lives. 139 00:09:44,447 --> 00:09:47,527 The Indonesian earthquake had as much energy in it 140 00:09:47,527 --> 00:09:51,600 as the total energy consumption in the United States in one year. 141 00:09:53,487 --> 00:09:58,127 This enormous burst of energy had been released in just seconds. 142 00:09:58,127 --> 00:10:01,407 Once again, the world had been reminded 143 00:10:01,407 --> 00:10:03,238 of the Earth's awesome power. 144 00:10:04,647 --> 00:10:09,687 In the last 50 years, scientists were finally able to confirm a solid link 145 00:10:09,687 --> 00:10:12,679 between earthquakes and tsunamis. 146 00:10:13,727 --> 00:10:17,527 By monitoring the size of the Chilean earthquake in 1960, 147 00:10:17,527 --> 00:10:21,007 scientists were able to prove conclusively that earthquakes 148 00:10:21,007 --> 00:10:24,079 triggered these gigantic waves. 149 00:10:25,167 --> 00:10:28,887 By following the path of this tsunami, they were able to prove 150 00:10:28,887 --> 00:10:33,278 that a tsunami could travel thousands of miles from its origin. 151 00:10:35,047 --> 00:10:38,847 Monitoring the earthquakes that cause this incredible devastation 152 00:10:38,847 --> 00:10:41,919 involves looking many miles underground. 153 00:10:43,487 --> 00:10:47,527 By investigating the power at the root of these giant waves, 154 00:10:47,527 --> 00:10:53,397 scientists can begin to figure out when and where these waves may strike next. 155 00:10:56,367 --> 00:10:58,647 These dramatic pictures of the aftermath 156 00:10:58,647 --> 00:11:05,967 of the 2004 Indian Ocean tsunami show the havoc a tsunami can unleash. 157 00:11:05,967 --> 00:11:08,687 It's almost impossible to imagine something like that 158 00:11:08,687 --> 00:11:11,967 happening here in the Pacific Northwest. 159 00:11:11,967 --> 00:11:17,327 But Professor Brian Atwater believes that events like the 2004 tsunami 160 00:11:17,327 --> 00:11:20,607 could one day happen right here too. 161 00:11:20,607 --> 00:11:22,047 He was intrigued 162 00:11:22,047 --> 00:11:25,847 by early settlers' accounts of Native American folklore tales 163 00:11:25,847 --> 00:11:28,847 that spoke of great waves sweeping inland. 164 00:11:28,847 --> 00:11:33,367 They convinced him that huge, locally generated tsunamis 165 00:11:33,367 --> 00:11:36,007 have struck here before, and could strike again, 166 00:11:36,007 --> 00:11:39,087 posing a threat to tens of thousands of people 167 00:11:39,087 --> 00:11:42,159 living on the Pacific Northwest coast. 168 00:11:43,327 --> 00:11:48,487 To find out if he was right, he needed to uncover evidence of past giant waves 169 00:11:48,487 --> 00:11:50,443 hidden in this landscape. 170 00:11:51,447 --> 00:11:55,727 To be really sure it's a tsunami, though, he would also have to find evidence 171 00:11:55,727 --> 00:11:58,527 of the earthquake that caused it. 172 00:11:58,527 --> 00:12:02,647 Atwater's starting point is the Copalis River in Washington State, 173 00:12:02,647 --> 00:12:05,767 just a couple of miles from the long sandy beaches 174 00:12:05,767 --> 00:12:08,998 that make this area a thriving tourist resort. 175 00:12:10,247 --> 00:12:15,401 In the banks of this estuary lie buried thousands of years of history. 176 00:12:18,047 --> 00:12:21,487 This is one of the dirtiest jobs in science. 177 00:12:21,487 --> 00:12:26,607 Hunting for evidence of earthquakes is a muddy business, but it's worth it. 178 00:12:26,607 --> 00:12:30,927 Atwater has found signs of a potential tsunami. 179 00:12:30,927 --> 00:12:36,887 There's a clue in this bank that nature has provided, it's this notch. 180 00:12:36,887 --> 00:12:39,007 And notches like this are common 181 00:12:39,007 --> 00:12:42,047 where tsunamis have laid out sheets of sand 182 00:12:42,047 --> 00:12:44,047 and then later currents 183 00:12:44,047 --> 00:12:45,927 and... and waves come along 184 00:12:45,927 --> 00:12:50,159 and they pluck the sand grains out of the bank, but they leave the mud. 185 00:12:52,007 --> 00:12:55,847 Atwater has to dig deeper to find what he is looking for, 186 00:12:55,847 --> 00:13:01,126 a layer of sand that could have been swept miles inland by a tsunami. 187 00:13:02,567 --> 00:13:08,127 OK, so now you can see the sand. What deposited this sand? 188 00:13:08,127 --> 00:13:10,847 Maybe it was a tsunami. 189 00:13:10,847 --> 00:13:14,007 To prove that this was sand from a tsunami, 190 00:13:14,007 --> 00:13:17,647 Atwater's muddy quest must continue. 191 00:13:17,647 --> 00:13:20,927 He also needs to find proof that the land here around the river 192 00:13:20,927 --> 00:13:24,761 has moved up or down - a sure sign of an earthquake. 193 00:13:25,807 --> 00:13:29,607 After some hard work, Atwater finds what he has been looking for - 194 00:13:29,607 --> 00:13:33,047 clear evidence of both an earthquake and a tsunami. 195 00:13:33,047 --> 00:13:36,483 This time, there was a human cost as well. 196 00:13:37,487 --> 00:13:41,367 Here we have evidence for abrupt lowering of land, 197 00:13:41,367 --> 00:13:44,087 and we also have evidence for the associated tsunami. 198 00:13:44,087 --> 00:13:47,167 In this case, humans are involved - this was a fishing camp. 199 00:13:47,167 --> 00:13:49,727 Here you have the remains of that fishing camp 200 00:13:49,727 --> 00:13:52,167 in the form of fire-cracked rocks which were... 201 00:13:52,167 --> 00:13:55,327 The rocks were used to heat water, mainly. 202 00:13:55,327 --> 00:13:59,927 OK, so fishing camp, overrun by tsunami. 203 00:13:59,927 --> 00:14:02,527 Because the land dropped after the tsunami, 204 00:14:02,527 --> 00:14:06,927 the tides came in and covered the fishing camp site 205 00:14:06,927 --> 00:14:09,361 and made sure that people wouldn't use it again. 206 00:14:11,127 --> 00:14:14,367 The land the fishing camp was built on was dragged down 207 00:14:14,367 --> 00:14:16,087 during the earthquake. 208 00:14:16,087 --> 00:14:19,247 The tsunami deposited sand over the remains, 209 00:14:19,247 --> 00:14:22,127 and finally, the tide covered the settlement with mud, 210 00:14:22,127 --> 00:14:26,047 where it remained undisturbed - until now. 211 00:14:26,047 --> 00:14:28,807 Atwater finally had the proof he needed. 212 00:14:28,807 --> 00:14:34,598 His Native American myths of giant waves were no mere legend. 213 00:14:36,207 --> 00:14:39,327 But what was it that caused the earthquake? 214 00:14:39,327 --> 00:14:45,767 The prime suspect lay 50 miles offshore - the Cascadia fault. 215 00:14:45,767 --> 00:14:50,007 Cascadia is a major weakness in the Earth's crust. 216 00:14:50,007 --> 00:14:53,767 Although the Earth may seem to be a solid sphere, 217 00:14:53,767 --> 00:14:56,527 beneath the oceans and continents it is divided 218 00:14:56,527 --> 00:15:01,767 into eight major and many minor segments known as tectonic plates. 219 00:15:01,767 --> 00:15:07,607 Where they meet, they can grind and jostle against each other at fault lines, 220 00:15:07,607 --> 00:15:09,563 causing earthquakes. 221 00:15:10,847 --> 00:15:14,167 Geologists had long thought that the Cascadia fault line 222 00:15:14,167 --> 00:15:17,127 was incapable of generating a major quake. 223 00:15:17,127 --> 00:15:22,447 But Atwater's investigation has proved that it was highly active. 224 00:15:22,447 --> 00:15:24,887 The big worry for Atwater and the thousands of people 225 00:15:24,887 --> 00:15:28,647 who live in this region is that the Cascadia fault line 226 00:15:28,647 --> 00:15:34,407 bears an uncanny resemblance to another highly active fault line, 227 00:15:34,407 --> 00:15:36,318 the Sunda Megathrust. 228 00:15:37,607 --> 00:15:41,247 It was an earthquake along this fault that was responsible 229 00:15:41,247 --> 00:15:46,727 for the Indian Ocean tsunami that killed nearly a quarter of a million people. 230 00:15:46,727 --> 00:15:48,807 Where we get two tectonic plates coming together, 231 00:15:48,807 --> 00:15:51,927 such as the case of the Indonesian tsunami in 2004, 232 00:15:51,927 --> 00:15:54,047 one plate pushes beneath the other plate 233 00:15:54,047 --> 00:15:56,687 and creates lots and lots of friction and tension 234 00:15:56,687 --> 00:15:59,407 and drags the upper plate down with it, 235 00:15:59,407 --> 00:16:01,207 and that process can take hundreds of years, 236 00:16:01,207 --> 00:16:02,727 even thousands of years. 237 00:16:02,727 --> 00:16:04,287 It's a very slow process. 238 00:16:04,287 --> 00:16:07,727 But eventually the pressure of this one trying to push back up again wins, 239 00:16:07,727 --> 00:16:09,718 and it flips like that. 240 00:16:11,567 --> 00:16:14,767 And that creates a megathrust, a sudden movement of the seabed, 241 00:16:14,767 --> 00:16:18,167 and that's what creates a phenomenal tsunami. 242 00:16:18,167 --> 00:16:22,967 Two factors made this Sunda Megathrust earthquake so deadly. 243 00:16:22,967 --> 00:16:24,727 The first was its size. 244 00:16:24,727 --> 00:16:26,967 At factor 9.2 on the Richter scale, 245 00:16:26,967 --> 00:16:31,447 this was the largest in nearly 50 years. 246 00:16:31,447 --> 00:16:36,767 The second was that it took place not far below the surface. 247 00:16:36,767 --> 00:16:38,567 BOXALL: When we talk about a megathrust, 248 00:16:38,567 --> 00:16:41,767 that's really where the seabed is disturbed dramatically. 249 00:16:41,767 --> 00:16:44,127 Sometimes, if the earthquake is deep in the Earth's crust, 250 00:16:44,127 --> 00:16:47,487 then you see very little surface manifestation of that earthquake. 251 00:16:47,487 --> 00:16:50,127 If it's quite close to the surface or very intense, 252 00:16:50,127 --> 00:16:52,607 then quite often you'll see the seabed itself moving, 253 00:16:52,607 --> 00:16:55,758 and that's what creates a powerful tsunami. 254 00:16:57,447 --> 00:17:00,167 Investigating the ocean floor after the quake 255 00:17:00,167 --> 00:17:04,527 revealed that more than 1,000 miles of fault line had fractured 256 00:17:04,527 --> 00:17:07,367 and sprung up by 60 feet. 257 00:17:07,367 --> 00:17:11,727 This massive jolt pushed up billions of tons of water, 258 00:17:11,727 --> 00:17:17,006 enough to cover Manhattan to a depth of nearly five miles. 259 00:17:19,687 --> 00:17:22,567 The rift zone itself was about a thousand miles long. 260 00:17:22,567 --> 00:17:26,287 We had this entire stretch of subsea moving, 261 00:17:26,287 --> 00:17:28,287 which creates a huge wave. 262 00:17:28,287 --> 00:17:31,647 So the whole thing was a phenomenal size 263 00:17:31,647 --> 00:17:34,286 and certainly one of the biggest tsunamis in living memory. 264 00:17:35,487 --> 00:17:39,607 Atwater's determined research showed that the Pacific Northwest 265 00:17:39,607 --> 00:17:42,804 was at risk from this level of devastation too. 266 00:17:43,807 --> 00:17:48,127 But he didn't want to unnecessarily alarm the coastal inhabitants 267 00:17:48,127 --> 00:17:51,087 until he had collected all the evidence he could. 268 00:17:51,087 --> 00:17:56,527 Atwater needed to find out precisely when this tsunami struck this coastline 269 00:17:56,527 --> 00:17:58,767 to see if there could be more. 270 00:17:58,767 --> 00:18:03,527 He first tried radiocarbon dating the soil along the Copalis River. 271 00:18:03,527 --> 00:18:06,487 But the result could only take him so far. 272 00:18:06,487 --> 00:18:09,007 They showed that the earthquake and tsunami occurred 273 00:18:09,007 --> 00:18:13,447 somewhere between 1680 and 1720. 274 00:18:13,447 --> 00:18:19,238 More importantly, Atwater still needed precise evidence of how big it had been. 275 00:18:20,727 --> 00:18:26,287 But so far, his investigation has uncovered two extraordinary facts. 276 00:18:26,287 --> 00:18:29,687 By unearthing the abandoned fishing camp, 277 00:18:29,687 --> 00:18:32,407 Atwater could see that a Cascadia earthquake here 278 00:18:32,407 --> 00:18:35,167 had caused the land to drop. 279 00:18:35,167 --> 00:18:37,527 The notch in the bank was proof 280 00:18:37,527 --> 00:18:40,807 that this same earthquake had generated a tsunami. 281 00:18:40,807 --> 00:18:46,287 But what these clues didn't tell Atwater was just how big the tsunami was. 282 00:18:46,287 --> 00:18:51,647 He had no way of pinning down the size of the threat to the Pacific Northwest. 283 00:18:51,647 --> 00:18:55,767 His investigation was about to take an unexpected turn, 284 00:18:55,767 --> 00:18:59,807 with clues coming from not only thousands of miles away, 285 00:18:59,807 --> 00:19:02,879 but also from hundreds of years ago. 286 00:19:05,447 --> 00:19:10,687 Japan has the oldest record of tsunamis of anywhere in the world. 287 00:19:10,687 --> 00:19:15,087 Samurai writings told of a huge tsunami in 1700 288 00:19:15,087 --> 00:19:18,247 that had swept over the east coast of Japan. 289 00:19:18,247 --> 00:19:23,367 It hit without warning, and destroyed entire settlements. 290 00:19:23,367 --> 00:19:27,407 Japanese scientists were baffled as to where this wave had come from. 291 00:19:27,407 --> 00:19:33,007 There had been no earthquake to warn the villagers to make for higher ground. 292 00:19:33,007 --> 00:19:37,125 The mystery wave was dubbed an orphan tsunami. 293 00:19:40,007 --> 00:19:41,447 Back in the U.S., 294 00:19:41,447 --> 00:19:45,367 Brian Atwater's investigation into the mysterious Cascadia earthquake 295 00:19:45,367 --> 00:19:47,801 and tsunami needed more evidence. 296 00:19:49,807 --> 00:19:55,723 He had no accurate way to pin down either the size or the date of the event. 297 00:19:56,887 --> 00:20:03,167 All he knew was that it had taken place sometime between 1680 and 1720. 298 00:20:03,167 --> 00:20:07,887 But Atwater's dates were a revelation to the Japanese scientists. 299 00:20:07,887 --> 00:20:14,047 Could this event be the birthplace of their 300-year-old orphan tsunami? 300 00:20:14,047 --> 00:20:16,567 And they said, "By the way, we have this tsunami 301 00:20:16,567 --> 00:20:20,487 "we've been trying to, uh, find a home for in 1700, 302 00:20:20,487 --> 00:20:23,967 "so we think your... your earthquake happened in 1700, 303 00:20:23,967 --> 00:20:27,607 "specifically in the evening of the 26th of January 1700, 304 00:20:27,607 --> 00:20:29,643 "and it was of magnitude nine." 305 00:20:31,527 --> 00:20:35,447 A Cascadia earthquake that produced a wave with enough power 306 00:20:35,447 --> 00:20:38,127 to cross the entire Pacific Ocean to Japan 307 00:20:38,127 --> 00:20:42,006 would have had to be a factor nine at the very least. 308 00:20:43,087 --> 00:20:48,207 This is roughly equivalent to the enormous Indian Ocean earthquake. 309 00:20:49,807 --> 00:20:52,487 Earthquakes like this have so much power 310 00:20:52,487 --> 00:20:58,007 that they can send a tsunami across an entire ocean with ease. 311 00:20:58,007 --> 00:21:00,807 BOXALL: The amount of energy involved is very hard to estimate, 312 00:21:00,807 --> 00:21:04,447 and it's hard to put it into sort of terms that people can understand. 313 00:21:04,447 --> 00:21:08,167 We are looking at the phenomenal forces of several Hiroshimas, 314 00:21:08,167 --> 00:21:10,317 hundreds of Hiroshimas, in fact. 315 00:21:11,327 --> 00:21:16,967 But tsunamis are not just a very big wave, they're fast. 316 00:21:16,967 --> 00:21:18,887 The big difference is the scale of the wave - 317 00:21:18,887 --> 00:21:22,687 it's typically three or four hundred miles long. 318 00:21:22,687 --> 00:21:24,607 It's also not very high - 319 00:21:24,607 --> 00:21:28,287 when it starts off life, it's usually about two or three foot high. 320 00:21:28,287 --> 00:21:30,087 But it's moving very fast. 321 00:21:30,087 --> 00:21:33,247 It moves at a speed determined by the water depth. 322 00:21:33,247 --> 00:21:35,167 The deeper the water, the faster it moves, 323 00:21:35,167 --> 00:21:40,767 so in the deep ocean, this wave is moving at over 500 miles an hour. 324 00:21:40,767 --> 00:21:44,287 Deceptively, as a tsunami speeds through deep water, 325 00:21:44,287 --> 00:21:48,439 it may appear completely harmless and scarcely detectable. 326 00:21:49,767 --> 00:21:53,247 Close to shore, the wave becomes a deadly killer. 327 00:21:53,247 --> 00:21:58,640 It is only then that a tsunami's true power becomes clear. 328 00:22:00,087 --> 00:22:02,487 As the wave gets to shallower and shallower water, 329 00:22:02,487 --> 00:22:05,687 as it approaches a coastline, the wave slows down. 330 00:22:05,687 --> 00:22:08,847 The shallower the water, the slower the wave, so it goes from 500, to 400, 331 00:22:08,847 --> 00:22:10,767 to 300, to 200, much, much slower. 332 00:22:10,767 --> 00:22:12,767 The back of the wave is still going full speed, 333 00:22:12,767 --> 00:22:17,557 and so the whole thing piles up, and that's why tsunamis are so destructive. 334 00:22:21,247 --> 00:22:25,847 It is this immense speed and power that reveals how events here in Cascadia 335 00:22:25,847 --> 00:22:29,607 could devastate a coastal village in Japan, 336 00:22:29,607 --> 00:22:34,007 how an earthquake in Chile could decimate Hawaii, 337 00:22:34,007 --> 00:22:36,087 and how the Indian Ocean earthquake 338 00:22:36,087 --> 00:22:39,807 could kill almost a quarter of a million people. 339 00:22:39,807 --> 00:22:43,687 If a quake like this happened in Cascadia, 340 00:22:43,687 --> 00:22:47,847 the damage it would do to the Pacific Northwest coastline 341 00:22:47,847 --> 00:22:49,599 would be catastrophic. 342 00:22:50,647 --> 00:22:53,167 But to be sure about the scale of this threat, 343 00:22:53,167 --> 00:22:56,087 Brian Atwater has to be 100% certain 344 00:22:56,087 --> 00:23:00,167 that the dates of the two tsunamis were the same. 345 00:23:00,167 --> 00:23:03,727 After fully exploring the estuary of the Copalis river, 346 00:23:03,727 --> 00:23:08,047 he found one site that might hold the information he was looking for - 347 00:23:08,047 --> 00:23:10,767 a ghost forest. 348 00:23:10,767 --> 00:23:15,127 This spruce root marks the remains of a forest 349 00:23:15,127 --> 00:23:17,487 that includes the ghost forest behind us, 350 00:23:17,487 --> 00:23:21,719 dropped down into tidewater during the Cascadia earthquake. 351 00:23:24,527 --> 00:23:26,807 This ghost forest is made up 352 00:23:26,807 --> 00:23:30,167 of the standing dead trunks of western red cedar, 353 00:23:30,167 --> 00:23:34,607 and they were killed on account of the land here dropping, 354 00:23:34,607 --> 00:23:38,687 and then tides coming in and surrounding these trees 355 00:23:38,687 --> 00:23:40,996 and bringing in saltwater. 356 00:23:42,007 --> 00:23:45,795 This area would once have been covered with a dense forest. 357 00:23:47,207 --> 00:23:51,887 But today, only the bleached trunks of the rot-resistant western red cedar 358 00:23:51,887 --> 00:23:54,247 remain in place. 359 00:23:54,247 --> 00:23:58,807 When Atwater and expert tree ring specialists cut them open 360 00:23:58,807 --> 00:24:01,047 and studied the lines of growth inside, 361 00:24:01,047 --> 00:24:06,075 they finally cracked the 300-year-old tsunami puzzle. 362 00:24:07,167 --> 00:24:10,127 The dates of the Japanese and Cascadia events 363 00:24:10,127 --> 00:24:11,847 were exactly the same - 364 00:24:11,847 --> 00:24:14,407 January 1700. 365 00:24:14,407 --> 00:24:19,367 The Japanese orphan tsunami finally had a parent. 366 00:24:19,367 --> 00:24:21,807 Maybe there's a certain amount of justice to it 367 00:24:21,807 --> 00:24:25,527 that... that a place that doesn't have written records 368 00:24:25,527 --> 00:24:28,887 has these outstanding geological records. 369 00:24:28,887 --> 00:24:31,567 The link between the two events made it certain 370 00:24:31,567 --> 00:24:36,807 that the Cascadia earthquake had been at least an awesome magnitude nine. 371 00:24:36,807 --> 00:24:40,407 And ominously, it is almost certainly not the only time 372 00:24:40,407 --> 00:24:43,080 that Cascadia has rocked this area. 373 00:24:44,767 --> 00:24:48,807 Atwater believes he has found proof of a whole series of tsunamis 374 00:24:48,807 --> 00:24:51,765 stretching back 5,000 years. 375 00:24:52,847 --> 00:24:57,238 Each layer of sand in this sample represents a separate tsunami. 376 00:24:59,207 --> 00:25:03,007 There are places at Cascadia where I've seen nine stacked up 377 00:25:03,007 --> 00:25:06,407 in a column about 20 feet long. 378 00:25:06,407 --> 00:25:09,927 Uh, nine buried soils, some of them coated with little sand sheets. 379 00:25:09,927 --> 00:25:11,807 And... and they, you know, you... you say, 380 00:25:11,807 --> 00:25:16,358 "OK, it's... it's not a question of if, but it's just a matter of when." 381 00:25:18,807 --> 00:25:22,007 Atwater's tireless detective work alerted officials 382 00:25:22,007 --> 00:25:24,441 to the increased tsunami threat. 383 00:25:25,687 --> 00:25:29,447 As a result, the towns along the Washington State coast 384 00:25:29,447 --> 00:25:32,598 have been able to prepare for this potential catastrophe. 385 00:25:34,047 --> 00:25:38,167 If a Cascadia quake occurred, the first waves could arrive here 386 00:25:38,167 --> 00:25:40,203 in just 25 minutes. 387 00:25:41,207 --> 00:25:45,967 Tsunami warning signs line the roads, and sirens stand ready to warn 388 00:25:45,967 --> 00:25:48,407 of an approaching wave. 389 00:25:48,407 --> 00:25:54,607 The lives of thousands of people are safer thanks to the work of Atwater, 390 00:25:54,607 --> 00:25:58,077 and to some 300-year-old Japanese writings. 391 00:25:59,127 --> 00:26:04,087 This is a hazard that shows its face often enough for us to take precautions, 392 00:26:04,087 --> 00:26:06,807 to fasten the seatbelt against it. 393 00:26:06,807 --> 00:26:11,447 By dating the ghost forest along the Copalis River to precisely 1700, 394 00:26:11,447 --> 00:26:16,047 Atwater had the final proof that Cascadia was capable of creating 395 00:26:16,047 --> 00:26:18,967 a Pacific-wide tsunami. 396 00:26:18,967 --> 00:26:22,887 Uncovering the multiple layers of tsunami debris in the riverbank 397 00:26:22,887 --> 00:26:26,327 dating back 5,000 years show that monster waves 398 00:26:26,327 --> 00:26:28,647 have struck here many times. 399 00:26:28,647 --> 00:26:31,241 This is an ongoing threat. 400 00:26:32,487 --> 00:26:35,007 Atwater knows that another earthquake is due here, 401 00:26:35,007 --> 00:26:39,607 but he has no way of knowing exactly when. 402 00:26:39,607 --> 00:26:41,647 Back in the Indian Ocean, 403 00:26:41,647 --> 00:26:45,527 the site of the world's most lethal tsunami in 2004, 404 00:26:45,527 --> 00:26:50,367 one man has taken the investigation of tsunamis to a new level. 405 00:26:50,367 --> 00:26:54,047 He believes that he has found a way to make the Earth's fault lines 406 00:26:54,047 --> 00:26:58,327 give up their secrets and accurately predict when the next deadly tsunami 407 00:26:58,327 --> 00:27:01,364 could be on its way. 408 00:27:05,087 --> 00:27:10,527 The idyllic looking Mentawai island chain in Indonesia hides a violent secret, 409 00:27:10,527 --> 00:27:15,157 one that makes it today one of the most dangerous places on Earth. 410 00:27:16,527 --> 00:27:20,127 These islands lie directly on top of the Sunda Megathrust, 411 00:27:20,127 --> 00:27:22,927 south of where the enormous Indian Ocean earthquake 412 00:27:22,927 --> 00:27:25,927 triggered the 2004 tsunami. 413 00:27:25,927 --> 00:27:30,407 The Sunda Megathrust is one of the largest fault lines on the planet. 414 00:27:30,407 --> 00:27:33,887 Since it caused the 2004 earthquake, 415 00:27:33,887 --> 00:27:37,038 it has also become one of the most notorious. 416 00:27:39,847 --> 00:27:41,927 Predicting earthquakes here is tricky, 417 00:27:41,927 --> 00:27:46,007 but Professor Kerry Sieh has a good track record. 418 00:27:46,007 --> 00:27:51,365 He has successfully forecast two along the Sunda Megathrust already. 419 00:27:53,127 --> 00:27:56,527 The key to successful tsunami prediction is to forecast 420 00:27:56,527 --> 00:27:59,247 when and where earthquakes will strike. 421 00:27:59,247 --> 00:28:03,927 And to do this, scientists must look into the past. 422 00:28:03,927 --> 00:28:06,087 SIEH: If you want to answer questions about earthquakes 423 00:28:06,087 --> 00:28:08,087 that only happen every few hundred years 424 00:28:08,087 --> 00:28:09,887 or few thousand years, 425 00:28:09,887 --> 00:28:13,567 well, you've got to find some... some geological instrument 426 00:28:13,567 --> 00:28:16,567 that allows you to see those earthquakes. 427 00:28:16,567 --> 00:28:18,727 Professor Sieh has found an unusual way 428 00:28:18,727 --> 00:28:23,967 to unlock the secrets of the Sunda Megathrust's turbulent history. 429 00:28:23,967 --> 00:28:26,007 Corals. 430 00:28:26,007 --> 00:28:28,527 These coral atolls are built from the limestone skeletons 431 00:28:28,527 --> 00:28:31,087 of millions of tiny creatures. 432 00:28:31,087 --> 00:28:35,367 Each generation builds on the remains of the last. 433 00:28:35,367 --> 00:28:38,967 Over time, the atoll gets bigger and bigger. 434 00:28:38,967 --> 00:28:42,687 As long as the corals remain underwater, they flourish, 435 00:28:42,687 --> 00:28:46,047 but once they're above water, they die. 436 00:28:46,047 --> 00:28:50,447 Earthquakes are responsible for killing all the coral stranded 437 00:28:50,447 --> 00:28:53,007 above water on this beach. 438 00:28:54,687 --> 00:28:57,767 This beach contains corals of many different ages. 439 00:28:57,767 --> 00:29:01,607 Altogether, Professor Sieh has nearly a thousand years of history 440 00:29:01,607 --> 00:29:03,807 at his fingertips. 441 00:29:03,807 --> 00:29:07,047 But to unlock the secret history the corals contain, 442 00:29:07,047 --> 00:29:11,847 he and his team have to take a less than delicate approach. 443 00:29:11,847 --> 00:29:16,007 We're looking at a sawcut that we just made through a coral micro atoll. 444 00:29:16,007 --> 00:29:19,047 And the great thing about this head is it records a sudden drop 445 00:29:19,047 --> 00:29:22,047 of about a foot and a half down to here. 446 00:29:22,047 --> 00:29:24,327 It died down to here, because the island rose. 447 00:29:24,327 --> 00:29:26,087 The new low tide is way down here. 448 00:29:26,087 --> 00:29:29,284 Everything that was so bold as to grow up this high dies. 449 00:29:31,247 --> 00:29:34,647 The shape of the coral records the fall of the Mentawai islands 450 00:29:34,647 --> 00:29:38,879 as they are literally pulled down by the Sunda Megathrust. 451 00:29:39,887 --> 00:29:43,567 But, crucially, the corals also record the moments 452 00:29:43,567 --> 00:29:49,247 when the islands are thrust up out of the water during an earthquake. 453 00:29:49,247 --> 00:29:53,287 Between quakes, the islands are once again pulled down by the fault 454 00:29:53,287 --> 00:29:55,517 in a never-ending cycle. 455 00:29:57,727 --> 00:30:00,287 You have to imagine that rocks actually are elastic. 456 00:30:00,287 --> 00:30:03,447 Take a diving board, the diver... the diver walks out on the platform 457 00:30:03,447 --> 00:30:05,087 and it... it bends like this, 458 00:30:05,087 --> 00:30:07,887 and then he jumps and he springs up and he jumps off. 459 00:30:07,887 --> 00:30:10,847 And when he jumps off, the diving board doesn't stay here, 460 00:30:10,847 --> 00:30:13,167 it doesn't go like... it doesn't go like this, 461 00:30:13,167 --> 00:30:16,087 you know, the diving board springs back up, it's elastic. 462 00:30:16,087 --> 00:30:18,767 Well, rocks are the same, rocks are elastic too, 463 00:30:18,767 --> 00:30:23,287 so when the Indian Plate goes down it pulls the Sumatran section down too, 464 00:30:23,287 --> 00:30:25,527 and then later, it fails. 465 00:30:25,527 --> 00:30:27,836 So it just springs up like a diving board. 466 00:30:28,847 --> 00:30:31,527 By analysing corals all over this beach, 467 00:30:31,527 --> 00:30:35,805 Professor Sieh has discovered a regular pattern to this cycle. 468 00:30:36,807 --> 00:30:41,517 A major earthquake rocks these islands roughly every 200 years. 469 00:30:43,607 --> 00:30:47,927 What we have here in Sumatra with the corals is what I call the Holy Grail 470 00:30:47,927 --> 00:30:51,047 of, uh... of earthquake science, of... of palaeoseismology, 471 00:30:51,047 --> 00:30:54,767 and that is a long record that has many cycles in it, 472 00:30:54,767 --> 00:30:58,047 a thousand-year-long history of earthquakes. 473 00:30:58,047 --> 00:31:00,647 But when the geologist looked even closer, 474 00:31:00,647 --> 00:31:03,366 he saw that the cycle was more complex. 475 00:31:04,727 --> 00:31:07,687 When we cut a slab, we can see it in much more exquisite detail 476 00:31:07,687 --> 00:31:09,807 because we can see what we call the stratigraphy, 477 00:31:09,807 --> 00:31:11,607 or the... the... the layering 478 00:31:11,607 --> 00:31:14,687 and how the layering relates to the changes of the tide, 479 00:31:14,687 --> 00:31:19,127 so what we can see over here, then, is the annual bands of growth, right here, 480 00:31:19,127 --> 00:31:24,599 so there's about ten years between this earthquake and this earthquake. 481 00:31:26,487 --> 00:31:29,887 Professor Sieh had discovered a major clue. 482 00:31:29,887 --> 00:31:34,687 The corals record that, not only does a major earthquake and tsunami hit here 483 00:31:34,687 --> 00:31:37,847 every 200 years, but that they are always accompanied 484 00:31:37,847 --> 00:31:41,127 by a number of smaller quakes. 485 00:31:41,127 --> 00:31:45,757 This is a cycle within a cycle, a supercycle. 486 00:31:47,047 --> 00:31:49,847 And by counting back the layers of growth within the coral, 487 00:31:49,847 --> 00:31:54,367 the geologists can put an exact date on all of these earthquakes. 488 00:31:54,367 --> 00:31:56,807 We know there's a sequence in the 1350s, 1370s, 489 00:31:56,807 --> 00:32:01,367 we know there's a sequence in the 1560s, 1600s... 1600, 490 00:32:01,367 --> 00:32:05,127 we know there's a sequence 1797, 1833. 491 00:32:05,127 --> 00:32:08,961 Those sequences are about 200, to 200... yeah, 230 years apart. 492 00:32:10,367 --> 00:32:15,047 This is crucial information for the people of the Mentawai islands, 493 00:32:15,047 --> 00:32:17,327 who have no written history. 494 00:32:17,327 --> 00:32:19,927 But Professor Sieh's work doesn't stop here. 495 00:32:19,927 --> 00:32:23,367 By uncovering their history in the corals, 496 00:32:23,367 --> 00:32:27,155 he believes that he can now predict the future for these islands. 497 00:32:28,487 --> 00:32:31,407 And he's already had some success. 498 00:32:31,407 --> 00:32:35,047 Professor Sieh began his work here in 1993, 499 00:32:35,047 --> 00:32:38,527 and soon realised an earthquake was imminent. 500 00:32:38,527 --> 00:32:43,317 The Mentawai islands were about to start their next deadly supercycle. 501 00:32:44,687 --> 00:32:47,207 MAN: OK! Experienced an earthquake! 502 00:32:47,207 --> 00:32:50,487 In September 2007, he was proved right, 503 00:32:50,487 --> 00:32:54,727 when an earthquake shook the islands just enough to generate a small tsunami 504 00:32:54,727 --> 00:32:57,321 that wrecked homes and schools. 505 00:33:00,207 --> 00:33:04,166 History is repeating itself, exactly as he predicted it would. 506 00:33:05,447 --> 00:33:07,567 A much bigger earthquake 507 00:33:07,567 --> 00:33:11,765 and more dangerous tsunami could be due any day. 508 00:33:12,847 --> 00:33:15,607 SIEH: One section hasn't failed since 1797, 509 00:33:15,607 --> 00:33:19,487 so, since George Washington was President of the United States. 510 00:33:19,487 --> 00:33:22,207 We know we're now in a sequence of at least three giant earthquakes, 511 00:33:22,207 --> 00:33:23,847 we're expecting another one. 512 00:33:23,847 --> 00:33:25,847 The question is whether the earthquake and tsunami 513 00:33:25,847 --> 00:33:28,759 will be in the next 30 minutes or the next 30 years. 514 00:33:29,967 --> 00:33:32,287 Thanks to Sieh's research, 515 00:33:32,287 --> 00:33:35,247 the people of these islands have had time to prepare. 516 00:33:35,247 --> 00:33:38,487 When the wave comes, they will be ready. 517 00:33:38,487 --> 00:33:41,047 Earthquakes are forecastable. 518 00:33:41,047 --> 00:33:43,927 If you... if you have enough information about how they've behaved 519 00:33:43,927 --> 00:33:47,087 over the last thousand years, or two or three or four cycles, 520 00:33:47,087 --> 00:33:49,207 you can really make a significant forecast 521 00:33:49,207 --> 00:33:52,085 that people living in the area actually can do something about. 522 00:33:54,047 --> 00:33:56,767 Education is key. 523 00:33:56,767 --> 00:33:58,447 Children here are now taught 524 00:33:58,447 --> 00:34:01,367 that as soon as they feel the shaking of an earthquake, 525 00:34:01,367 --> 00:34:03,358 they should run for higher ground. 526 00:34:05,727 --> 00:34:10,327 Newly built roads snake up steep hills from waterside villages 527 00:34:10,327 --> 00:34:13,046 to allow rapid escape from the deadly waves. 528 00:34:14,167 --> 00:34:18,367 I'll bet that young children alive today, if they... certainly if they live to be 60, 529 00:34:18,367 --> 00:34:20,167 they're gonna see that earthquake. 530 00:34:20,167 --> 00:34:23,367 In fact, I think there's a better than 50% chance that it'll happen in... 531 00:34:23,367 --> 00:34:24,847 ...within the next 30 years. 532 00:34:24,847 --> 00:34:28,607 By analysing the shape of the corals on the Mentawai islands, 533 00:34:28,607 --> 00:34:34,127 Sieh has proved that a major tsunami cycle starts here every 200 years. 534 00:34:34,127 --> 00:34:38,887 By dating the lines within the coral, he can be even more exact. 535 00:34:38,887 --> 00:34:43,677 They show that these cycles contain not just one, but several deadly tsunamis. 536 00:34:44,807 --> 00:34:48,800 The Sunda Megathrust is the clear culprit for tsunamis here. 537 00:34:49,807 --> 00:34:53,567 But not every tsunami is generated by an earthquake. 538 00:34:53,567 --> 00:34:59,517 A rarer, different type of wave is out there - a megatsunami. 539 00:35:04,487 --> 00:35:08,567 Although earthquakes are by far the most common cause of tsunamis, 540 00:35:08,567 --> 00:35:13,807 there is another source for these deadly waves - landslides. 541 00:35:13,807 --> 00:35:17,287 And these tsunamis have the potential to be so big 542 00:35:17,287 --> 00:35:20,916 that they have been called megatsunamis. 543 00:35:22,167 --> 00:35:26,527 Scientists had long suspected that waves could be generated in this way, 544 00:35:26,527 --> 00:35:32,284 but conclusive photographic proof wasn't available until 1958. 545 00:35:33,607 --> 00:35:37,447 A landslide into Lituya Bay in Alaska triggered a wave 546 00:35:37,447 --> 00:35:40,883 that reached heights of several thousand feet. 547 00:35:42,207 --> 00:35:45,247 This footage, shot just after the tsunami struck, 548 00:35:45,247 --> 00:35:47,967 shows the wave's enormous power. 549 00:35:47,967 --> 00:35:52,527 The trees here once stretched all the way down to the shores of the bay, 550 00:35:52,527 --> 00:35:55,767 but were ripped off the slopes by a wall of water, 551 00:35:55,767 --> 00:35:59,316 leaving nothing but bare exposed rock. 552 00:36:00,887 --> 00:36:04,247 The tsunami was generated when a relatively small earthquake 553 00:36:04,247 --> 00:36:06,487 triggered a single enormous landslide 554 00:36:06,487 --> 00:36:09,559 of rocks and debris into the bay. 555 00:36:11,447 --> 00:36:14,967 The resulting wave was higher than the Empire State Building 556 00:36:14,967 --> 00:36:18,807 and stunned scientists around the world. 557 00:36:18,807 --> 00:36:22,766 Tsunamis on this scale are incredibly rare. 558 00:36:24,847 --> 00:36:26,647 But another megatsunami, 559 00:36:26,647 --> 00:36:30,927 triggered by a rockfall 10,000 times bigger than Lituya Bay, 560 00:36:30,927 --> 00:36:36,240 could be on its way from a small island across the Atlantic Ocean. 561 00:36:37,767 --> 00:36:39,807 The Canary Islands, off the coast of Africa, 562 00:36:39,807 --> 00:36:43,004 are formed from a series of volcanoes. 563 00:36:45,167 --> 00:36:47,847 The youngest is the island of La Palma. 564 00:36:47,847 --> 00:36:50,927 It is formed from two volcanic ridges. 565 00:36:50,927 --> 00:36:56,367 The first is the extinct Cumbre Nueva to the north of the island. 566 00:36:56,367 --> 00:37:01,202 The younger, active Cumbre Vieja lies to the south. 567 00:37:02,607 --> 00:37:05,997 It erupted as recently as 1971. 568 00:37:09,127 --> 00:37:12,727 Geologist Dr Simon Day's research was crucial 569 00:37:12,727 --> 00:37:15,527 in developing the La Palma megatsunami theory. 570 00:37:15,527 --> 00:37:18,287 It began with an unusual rift 571 00:37:18,287 --> 00:37:22,963 that had opened up during a major volcanic eruption in 1949. 572 00:37:25,367 --> 00:37:31,367 We're standing here in the fault and it runs way down to the south 573 00:37:31,367 --> 00:37:34,207 along the crest of the volcano for two and a half miles, 574 00:37:34,207 --> 00:37:36,926 so it's one continuous long structure. 575 00:37:38,047 --> 00:37:42,487 Day believes this fault is evidence of a geological time bomb, 576 00:37:42,487 --> 00:37:45,923 the beginning of a giant landslide. 577 00:37:47,367 --> 00:37:50,887 What we see here to my right are layers of... of volcanic rocks, 578 00:37:50,887 --> 00:37:54,007 volcanic blocks here and layers of volcanic ash. 579 00:37:54,007 --> 00:37:57,567 And on the west of the fault, we see the same layers of blocks 580 00:37:57,567 --> 00:38:00,847 and ash and those, before the fault moved, were joined up 581 00:38:00,847 --> 00:38:03,087 and then when the fault moved, they were separated 582 00:38:03,087 --> 00:38:06,847 and the rocks to my left moved down and to the west. 583 00:38:06,847 --> 00:38:10,727 What we think will happen in some future eruption 584 00:38:10,727 --> 00:38:13,767 is that this fault will have gotten bigger 585 00:38:13,767 --> 00:38:19,487 and the whole of this western side will slide away in a giant landslide 586 00:38:19,487 --> 00:38:21,921 into the ocean to create the tsunami. 587 00:38:23,607 --> 00:38:28,407 This landslide would send the entire southwest section of La Palma, 588 00:38:28,407 --> 00:38:32,687 one sixth of the island's total mass, crashing into the Atlantic Ocean 589 00:38:32,687 --> 00:38:35,887 in a single giant landslide. 590 00:38:35,887 --> 00:38:38,567 What we envisage is the whole of this coastline 591 00:38:38,567 --> 00:38:42,127 and the slope extending up all the way to the crest of the volcano 592 00:38:42,127 --> 00:38:45,927 that is now in the clouds, all of that mass of rock would slide away 593 00:38:45,927 --> 00:38:49,367 in a single massive landslide into the ocean 594 00:38:49,367 --> 00:38:54,727 and pushing the water up in front of it to create the tsunami wave. 595 00:38:54,727 --> 00:38:58,287 Initially, this wave would be over 30 times bigger 596 00:38:58,287 --> 00:39:04,887 than the 2004 Indian Ocean tsunami, more than 3,000 feet high. 597 00:39:04,887 --> 00:39:06,127 (EXPLOSION) 598 00:39:06,127 --> 00:39:10,727 The 1980 eruption of Mount St Helens was proof that a volcano could collapse 599 00:39:10,727 --> 00:39:13,847 in this terrifying fashion. 600 00:39:13,847 --> 00:39:17,247 This was impressive, but the collapse of the Cumbre Vieja 601 00:39:17,247 --> 00:39:21,206 would be 200 times the volume of this. 602 00:39:22,287 --> 00:39:23,607 (LOUD RUMBLING) 603 00:39:23,607 --> 00:39:30,683 1,200 billion tons of rock would hurtle towards the ocean at top speed. 604 00:39:31,927 --> 00:39:36,287 The resulting wave would head straight out into the Atlantic. 605 00:39:36,287 --> 00:39:38,447 DAY: That wave, of course, would then spread out 606 00:39:38,447 --> 00:39:40,847 and separate out into smaller waves, 607 00:39:40,847 --> 00:39:46,967 but even so, after crossing the Atlantic and piling up again on, 608 00:39:46,967 --> 00:39:50,007 for example, the eastern seaboard of the United States or in the Caribbean 609 00:39:50,007 --> 00:39:53,767 or in northern Brazil, the waves there, we predict, 610 00:39:53,767 --> 00:39:56,767 would still be between 30 and 100 feet high. 611 00:39:56,767 --> 00:40:00,887 So that's as large as, if not larger, 612 00:40:00,887 --> 00:40:05,005 than the tsunami that struck Sumatra in 2004. 613 00:40:07,247 --> 00:40:08,805 Boston... 614 00:40:13,927 --> 00:40:15,485 New York... 615 00:40:19,087 --> 00:40:24,207 ...and even Miami could all be under threat from the giant waves. 616 00:40:29,967 --> 00:40:31,807 This was a bold prediction. 617 00:40:31,807 --> 00:40:35,567 Day needed more evidence to back up his theory. 618 00:40:35,567 --> 00:40:39,927 As he was about to see, the rift in La Palma's landscape 619 00:40:39,927 --> 00:40:43,167 was far worse than he expected. 620 00:40:43,167 --> 00:40:49,117 The 1949 eruption had left a different type of geological scar on the island. 621 00:40:51,007 --> 00:40:53,887 Evidence of a more serious weakness within La Palma 622 00:40:53,887 --> 00:40:58,165 came from a series of eerie-looking lava flows dotted across the island. 623 00:41:00,927 --> 00:41:04,767 One of the characteristics of the 1949 eruption that's unusual 624 00:41:04,767 --> 00:41:09,047 is that, instead of starting at one vent and just continuing there, 625 00:41:09,047 --> 00:41:13,807 a series of volcanic vents opened up in different parts of the island. 626 00:41:13,807 --> 00:41:16,167 When Day plotted these weaknesses on a map, 627 00:41:16,167 --> 00:41:18,767 he came to a frightening conclusion. 628 00:41:18,767 --> 00:41:22,521 The rift was far bigger than he had first suspected. 629 00:41:23,567 --> 00:41:27,727 The area that's potentially affected is very much greater 630 00:41:27,727 --> 00:41:31,647 than the length of the fault at the crest of the volcano would indicate, 631 00:41:31,647 --> 00:41:36,323 extending out, um, 10 or 15 miles from the crest out to sea. 632 00:41:37,567 --> 00:41:39,407 This growing body of evidence proved 633 00:41:39,407 --> 00:41:43,847 that the rift wasn't just a mere crack in the surface of La Palma, 634 00:41:43,847 --> 00:41:46,567 but a deep fissure that reached hundreds of feet 635 00:41:46,567 --> 00:41:49,367 down into the island's foundations. 636 00:41:49,367 --> 00:41:54,282 It is La Palma's volcanic heritage that is the key to this tsunami threat. 637 00:41:55,527 --> 00:41:58,087 The big hazard here isn't the eruptions themselves, 638 00:41:58,087 --> 00:42:00,967 it's the fact that the volcano is building up and building up over time 639 00:42:00,967 --> 00:42:05,438 and becoming more and more unstable, so that will eventually lead to a collapse. 640 00:42:06,447 --> 00:42:10,407 And it seems that this is not the first time a La Palma eruption 641 00:42:10,407 --> 00:42:12,967 may have triggered a giant landslide. 642 00:42:12,967 --> 00:42:17,567 Proof lies in the north of the island in these sheer cliff faces, 643 00:42:17,567 --> 00:42:20,604 formed 65,000 years ago. 644 00:42:21,687 --> 00:42:26,607 What we see in the north of La Palma is the landslide scar left 645 00:42:26,607 --> 00:42:30,127 when the old volcano in the north of La Palma 646 00:42:30,127 --> 00:42:33,407 experienced a giant collapse 647 00:42:33,407 --> 00:42:36,683 and produced a giant landslide off to the west. 648 00:42:38,367 --> 00:42:39,967 So that was a huge collapse - 649 00:42:39,967 --> 00:42:43,807 it removed as much as 100 cubic miles of rock 650 00:42:43,807 --> 00:42:47,247 and deposited it out into the ocean, so it's the sort of event 651 00:42:47,247 --> 00:42:49,287 that we think is going to happen again 652 00:42:49,287 --> 00:42:51,847 in the future at the... at the Cumbre Vieja. 653 00:42:53,247 --> 00:42:56,767 This ancient collapse of the old Cumbre Nueva volcano 654 00:42:56,767 --> 00:43:01,397 is almost certain to have generated a gigantic wave. 655 00:43:03,487 --> 00:43:07,567 And the next collapse might not be that far away. 656 00:43:07,567 --> 00:43:10,400 This tsunami could strike in our lifetime. 657 00:43:15,647 --> 00:43:17,607 DAY: Even though it seems so extraordinary 658 00:43:17,607 --> 00:43:19,327 when we consider it in human terms, 659 00:43:19,327 --> 00:43:22,567 and we talk about a tsunami striking the east coast of North America 660 00:43:22,567 --> 00:43:26,727 and causing huge devastation on the scale of the Sumatra tsunami, 661 00:43:26,727 --> 00:43:29,487 but this is what happens in the geological record, 662 00:43:29,487 --> 00:43:32,684 this is what Earth does. 663 00:43:33,887 --> 00:43:37,687 Although tsunamis have been documented for thousands of years, 664 00:43:37,687 --> 00:43:41,607 it is only in the last century that geologists have been able to prove 665 00:43:41,607 --> 00:43:44,644 how they are connected to the movements of the Earth. 666 00:43:46,647 --> 00:43:50,847 By analysing data from the great Chilean earthquake of 1960, 667 00:43:50,847 --> 00:43:55,367 scientists were finally able to firmly link earthquakes with tsunamis. 668 00:43:55,367 --> 00:43:58,487 Unearthing buried Native American settlements 669 00:43:58,487 --> 00:44:02,607 proved that the Cascadia fault line in the Pacific Northwest 670 00:44:02,607 --> 00:44:05,327 was an active tsunami threat. 671 00:44:05,327 --> 00:44:10,167 Corals in the Indian Ocean proved that some earthquake-generated tsunamis 672 00:44:10,167 --> 00:44:15,247 follow a pattern, and strike the same area with regular intervals. 673 00:44:15,247 --> 00:44:19,727 And the giant rift in La Palma's landscape shows that tsunamis 674 00:44:19,727 --> 00:44:25,967 generated by landslides are also a very real threat, megatsunamis, 675 00:44:25,967 --> 00:44:30,324 which could prove to be the biggest waves that threaten our coastline. 676 00:44:31,327 --> 00:44:33,167 Tsunamis are an inevitable part 677 00:44:33,167 --> 00:44:35,727 of Earth's dynamic structure. 678 00:44:35,727 --> 00:44:38,007 Their capacity to destroy 679 00:44:38,007 --> 00:44:39,407 is awesome, 680 00:44:39,407 --> 00:44:40,807 but, as scientists 681 00:44:40,807 --> 00:44:42,287 begin to understand more 682 00:44:42,287 --> 00:44:43,887 about the origins of tsunamis, 683 00:44:43,887 --> 00:44:46,407 they are coming closer to predicting 684 00:44:46,407 --> 00:44:49,524 where and when these monsters may strike.