1 00:00:03,031 --> 00:00:08,783 Earth, a 4.5- Billion-year-old planet, still evolving. 2 00:00:08,783 --> 00:00:17,325 As continents shift and clash, volcanoes erupt, glaciers grow and recede, 3 00:00:17,325 --> 00:00:21,909 the Earth's crust is carved in countless fascinating ways, 4 00:00:21,909 --> 00:00:25,368 leaving a trail of geological mysteries behind. 5 00:00:26,368 --> 00:00:27,410 Water. 6 00:00:27,410 --> 00:00:30,494 One of the most powerful forces on the planet. 7 00:00:30,494 --> 00:00:35,995 It plays a crucial role in creating life and destroying it, 8 00:00:35,995 --> 00:00:41,121 in forging landscapes and in breaking apart the Earth. 9 00:00:41,121 --> 00:00:48,079 In its most dramatic form, it becomes a killer wave known as a tsunami. 10 00:00:48,079 --> 00:00:52,164 Until recently, predicting when these monsters may next strike 11 00:00:52,164 --> 00:00:53,539 has been impossible. 12 00:00:55,748 --> 00:01:00,915 But today, scientists are starting to understand these giant waves. 13 00:01:00,915 --> 00:01:07,791 By connecting clues as varied as ancient Japanese writings and landslides, 14 00:01:07,791 --> 00:01:13,167 ancient corals and buried Native American settlements, 15 00:01:13,167 --> 00:01:17,001 the secrets of tsunamis are finally being unlocked. 16 00:01:25,210 --> 00:01:30,420 Tsunamis. One of the most deadly forces of nature. 17 00:01:30,420 --> 00:01:35,003 Giant waves that travel faster than a jet plane, 18 00:01:35,003 --> 00:01:38,838 they can cross entire oceans in just hours. 19 00:01:41,671 --> 00:01:46,505 They have the power to smash buildings, vehicles, anything in their way. 20 00:01:49,089 --> 00:01:52,298 MAN: By itself, you wouldn't think that water just streaming 21 00:01:52,298 --> 00:01:55,756 into the coast would necessarily cause so much damage. 22 00:01:55,756 --> 00:02:01,965 But in fact, they are very fast moving and they pick up everything in its path, 23 00:02:01,965 --> 00:02:07,050 so it's not the water by itself, it's what comes with the water 24 00:02:07,050 --> 00:02:09,634 that is also a part of the big hazard. 25 00:02:11,050 --> 00:02:14,675 A tsunami isn't over in just a few seconds, 26 00:02:14,675 --> 00:02:18,510 it is a torrent of raging water that keeps coming. 27 00:02:19,968 --> 00:02:22,386 The main thing about a tsunami is the persistence. 28 00:02:22,386 --> 00:02:27,636 It comes on and on and on, and just when you think it has to quit, 29 00:02:27,636 --> 00:02:31,804 it keeps coming, and it's the power plus the... the duration 30 00:02:31,804 --> 00:02:34,179 that is unstoppable, really. 31 00:02:35,429 --> 00:02:39,805 Tsunamis have ravaged the Earth for billions of years. 32 00:02:41,472 --> 00:02:46,013 When the Earth was first created, the moon was much closer. 33 00:02:46,013 --> 00:02:47,514 It filled the sky. 34 00:02:48,765 --> 00:02:51,432 Its gravitational pull was much stronger, 35 00:02:51,432 --> 00:02:55,682 and it generated towering waves over half a mile high 36 00:02:55,682 --> 00:02:58,683 that raced across the primeval oceans. 37 00:03:01,308 --> 00:03:03,349 MAN: Oh, my God! 38 00:03:03,349 --> 00:03:04,808 (SCREAMING) 39 00:03:04,808 --> 00:03:08,933 Today, tsunamis are still a threat to coastlines all over the world. 40 00:03:11,226 --> 00:03:15,268 MOONEY: Tsunamis will always occur, and have always occurred, 41 00:03:15,268 --> 00:03:16,602 throughout Earth's history. 42 00:03:16,602 --> 00:03:20,894 But it's only been more recently, as population densities have increased 43 00:03:20,894 --> 00:03:24,686 and people have moved and migrated to the coastal regions, 44 00:03:24,686 --> 00:03:28,561 that we've become much more aware of the tsunami hazards. 45 00:03:28,561 --> 00:03:32,562 The investigation into what caused these monster waves 46 00:03:32,562 --> 00:03:35,021 began over a thousand years ago 47 00:03:35,021 --> 00:03:37,730 on the islands of Japan. 48 00:03:37,730 --> 00:03:40,897 This country is the world's tsunami hotspot. 49 00:03:40,897 --> 00:03:44,064 Its coasts have been pounded with these enormous waves 50 00:03:44,064 --> 00:03:46,273 more than anywhere else on the planet. 51 00:03:48,148 --> 00:03:51,440 Evidence for this is the word tsunami itself. 52 00:03:51,440 --> 00:03:56,066 It is Japanese and literally means "harbour wave". 53 00:03:58,983 --> 00:04:04,109 Japan has the longest written tsunami record of anywhere in the world. 54 00:04:04,109 --> 00:04:09,151 The records go back as far as 684 A.D. 55 00:04:10,151 --> 00:04:13,110 By studying these records, it is possible to work out that, 56 00:04:13,110 --> 00:04:18,069 on average, this country has been struck nearly every seven years. 57 00:04:19,278 --> 00:04:21,778 Samurai writings speak of people living on the coasts 58 00:04:21,778 --> 00:04:26,029 running for higher ground as soon as they felt an earthquake. 59 00:04:26,029 --> 00:04:29,863 The Japanese knew this was a clue, 60 00:04:29,863 --> 00:04:33,030 a warning sign that a deadly tsunami would soon follow. 61 00:04:33,030 --> 00:04:35,571 But despite their attempts to escape, 62 00:04:35,571 --> 00:04:40,739 tsunamis have continually brought death and destruction to these islands. 63 00:04:42,322 --> 00:04:46,157 In 1896, a wave that hit Honshu in the northeast 64 00:04:46,157 --> 00:04:50,199 claimed the lives of 27,000 people. 65 00:04:51,532 --> 00:04:55,824 In 1933, the same area was smashed again. 66 00:04:55,824 --> 00:04:59,116 This time, 3,000 people were swept away. 67 00:05:00,242 --> 00:05:05,576 And in 1993, the island of Okushiri was rocked by an enormous earthquake 68 00:05:05,576 --> 00:05:08,868 measuring 7.8 on the Richter scale. 69 00:05:08,868 --> 00:05:15,078 Buildings were levelled and fires raged. But worse was to come. 70 00:05:15,078 --> 00:05:17,412 Minutes after the shaking had subsided, 71 00:05:17,412 --> 00:05:22,454 an ominous white crest appeared on the horizon - a tsunami. 72 00:05:22,454 --> 00:05:27,079 A gigantic wave swept in, flattening any buildings still standing. 73 00:05:31,288 --> 00:05:34,747 In Japan, the locals had already worked out the connections 74 00:05:34,747 --> 00:05:37,289 between earthquakes and tsunamis. 75 00:05:37,289 --> 00:05:41,332 But there's another hotspot on Earth where tsunamis regularly strike - 76 00:05:41,332 --> 00:05:43,790 the Hawaiian islands. 77 00:05:43,790 --> 00:05:48,916 But very few of them were preceded by an earthquake. 78 00:05:48,916 --> 00:05:51,000 The city of Hilo on the Big Island has been dubbed 79 00:05:51,000 --> 00:05:54,208 the Tsunami Capital of the World. 80 00:05:54,208 --> 00:05:58,584 Dozens of these enormous waves have hit these beautiful islands, 81 00:05:58,584 --> 00:06:00,876 and the mystery is why. 82 00:06:00,876 --> 00:06:02,626 With no natural warning to go on, 83 00:06:02,626 --> 00:06:04,293 the people of Hawaii must rely 84 00:06:04,293 --> 00:06:07,585 on the world's biggest tsunami monitoring station. 85 00:06:08,918 --> 00:06:13,503 Set up in 1949, it is connected to a network of buoys 86 00:06:13,503 --> 00:06:15,628 spread across the Pacific Ocean. 87 00:06:15,628 --> 00:06:19,295 These buoys provide important clues. 88 00:06:19,295 --> 00:06:21,588 They monitor changes in sea level 89 00:06:21,588 --> 00:06:25,796 that indicate the approach of any potential tsunamis. 90 00:06:28,964 --> 00:06:33,381 In 1960, scientists got the breakthrough they were looking for. 91 00:06:33,381 --> 00:06:35,590 They were finally able to work out the type of event 92 00:06:35,590 --> 00:06:39,465 at the root of Hawaii's mystery tsunamis. 93 00:06:39,465 --> 00:06:43,632 An enormous quake on the coast of Chile, the biggest recorded of all time, 94 00:06:43,632 --> 00:06:47,341 with a factor 9.5 on the Richter scale, 95 00:06:47,341 --> 00:06:52,008 triggered a tsunami that swept across the entire Pacific Ocean 96 00:06:52,008 --> 00:06:54,342 in just a few hours. 97 00:06:54,342 --> 00:07:01,218 The islands of Hawaii were thousands of miles away, directly in its path. 98 00:07:01,218 --> 00:07:05,177 The Tsunami Warning Center was monitoring its progress, 99 00:07:05,177 --> 00:07:08,969 revealing for the first time that a single massive wave 100 00:07:08,969 --> 00:07:12,136 crossed thousands of miles of ocean. 101 00:07:12,136 --> 00:07:14,970 The warning centre was a success. 102 00:07:14,970 --> 00:07:18,679 They were able to evacuate the communities closest to the shore 103 00:07:18,679 --> 00:07:20,805 before the wave struck. 104 00:07:20,805 --> 00:07:24,013 But the homes they left behind were decimated. 105 00:07:24,013 --> 00:07:30,681 In Hilo, the tsunami was so strong it even bent parking metres in half. 106 00:07:30,681 --> 00:07:33,765 The wave continued past Hawaii to Japan. 107 00:07:33,765 --> 00:07:36,681 It had lost none of its power. 108 00:07:36,681 --> 00:07:40,558 Pacific-wide, this tsunami cost more than 2,000 lives 109 00:07:40,558 --> 00:07:43,932 and caused millions of dollars' worth of damage. 110 00:07:46,183 --> 00:07:47,642 Devastating as it was, 111 00:07:47,642 --> 00:07:52,226 the 1960 event was a turning point in the study of tsunamis. 112 00:07:52,226 --> 00:07:56,102 It was the first time that scientists could accurately measure 113 00:07:56,102 --> 00:07:58,810 how the size of an underwater earthquake 114 00:07:58,810 --> 00:08:02,353 directly affected the size of a tsunami. 115 00:08:02,353 --> 00:08:05,727 And conclusive proof that a tsunami can travel 116 00:08:05,727 --> 00:08:08,811 thousands of miles across the Earth. 117 00:08:08,811 --> 00:08:12,645 And It was with this Chilean earthquake that we really could prove 118 00:08:12,645 --> 00:08:16,813 that the, uh, undersea motions associated with the earthquake 119 00:08:16,813 --> 00:08:19,771 are generating these huge effects. 120 00:08:20,896 --> 00:08:24,106 Now scientists had the evidence to confirm 121 00:08:24,106 --> 00:08:28,939 that undersea earthquakes were directly responsible for tsunamis. 122 00:08:28,939 --> 00:08:34,149 The ancient Japanese suspicion was now scientific fact. 123 00:08:34,149 --> 00:08:40,649 In terms of modern tsunami study, the 1960 wave was year zero. 124 00:08:40,649 --> 00:08:43,692 MOONEY: The Chilean earthquake was, you might say, the perfect storm, 125 00:08:43,692 --> 00:08:46,775 it's when scientific understanding had advanced to the point 126 00:08:46,775 --> 00:08:52,110 where scientists had begun to see the link connecting everything, 127 00:08:52,110 --> 00:08:54,526 so it's a new science, we're talking about something 128 00:08:54,526 --> 00:08:57,444 which is really only less than 50 years old. 129 00:08:58,485 --> 00:09:02,611 There are more tsunamis in the Pacific Ocean than any other. 130 00:09:02,611 --> 00:09:06,236 So in 2004, the world was taken by surprise 131 00:09:06,236 --> 00:09:09,445 when one of the largest recorded tsunamis of all time 132 00:09:09,445 --> 00:09:12,820 took place in the Indian Ocean. 133 00:09:14,405 --> 00:09:17,155 On December 26th, 2004, 134 00:09:17,155 --> 00:09:21,780 Indonesia was rocked by the second largest recorded earthquake ever, 135 00:09:21,780 --> 00:09:25,197 9.2 on the Richter scale. 136 00:09:26,198 --> 00:09:27,906 Minutes later, 137 00:09:27,906 --> 00:09:31,782 a 90-foot tsunami slammed into the South-East Asian coastline. 138 00:09:33,991 --> 00:09:39,658 225,000 men, women and children lost their lives. 139 00:09:44,409 --> 00:09:47,492 The Indonesian earthquake had as much energy in it 140 00:09:47,492 --> 00:09:51,535 as the total energy consumption in the United States in one year. 141 00:09:53,410 --> 00:09:58,077 This enormous burst of energy had been released in just seconds. 142 00:09:58,077 --> 00:10:01,328 Once again, the world had been reminded 143 00:10:01,328 --> 00:10:03,161 of the Earth's awesome power. 144 00:10:04,579 --> 00:10:09,621 In the last 50 years, scientists were finally able to confirm a solid link 145 00:10:09,621 --> 00:10:12,621 between earthquakes and tsunamis. 146 00:10:13,664 --> 00:10:17,456 By monitoring the size of the Chilean earthquake in 1960, 147 00:10:17,456 --> 00:10:20,915 scientists were able to prove conclusively that earthquakes 148 00:10:20,915 --> 00:10:23,998 triggered these gigantic waves. 149 00:10:25,081 --> 00:10:28,791 By following the path of this tsunami, they were able to prove 150 00:10:28,791 --> 00:10:33,166 that a tsunami could travel thousands of miles from its origin. 151 00:10:34,958 --> 00:10:38,750 Monitoring the earthquakes that cause this incredible devastation 152 00:10:38,750 --> 00:10:41,834 involves looking many miles underground. 153 00:10:43,375 --> 00:10:47,418 By investigating the power at the root of these giant waves, 154 00:10:47,418 --> 00:10:53,294 scientists can begin to figure out when and where these waves may strike next. 155 00:10:56,252 --> 00:10:58,544 These dramatic pictures of the aftermath 156 00:10:58,544 --> 00:11:05,837 of the 2004 Indian Ocean tsunami show the havoc a tsunami can unleash. 157 00:11:05,837 --> 00:11:08,546 It's almost impossible to imagine something like that 158 00:11:08,546 --> 00:11:11,839 happening here in the Pacific Northwest. 159 00:11:11,839 --> 00:11:17,214 But Professor Brian Atwater believes that events like the 2004 tsunami 160 00:11:17,214 --> 00:11:20,465 could one day happen right here too. 161 00:11:20,965 --> 00:11:22,424 He was intrigued 162 00:11:22,424 --> 00:11:26,216 by early settlers' accounts of Native American folklore tales 163 00:11:26,216 --> 00:11:29,216 that spoke of great waves sweeping inland. 164 00:11:29,466 --> 00:11:33,967 They convinced him that huge, locally generated tsunamis 165 00:11:33,967 --> 00:11:36,634 have struck here before, and could strike again, 166 00:11:36,634 --> 00:11:39,676 posing a threat to tens of thousands of people 167 00:11:39,676 --> 00:11:42,759 living on the Pacific Northwest coast. 168 00:11:43,926 --> 00:11:49,094 To find out if he was right, he needed to uncover evidence of past giant waves 169 00:11:49,094 --> 00:11:51,052 hidden in this landscape. 170 00:11:52,053 --> 00:11:56,303 To be really sure it's a tsunami, though, he would also have to find evidence 171 00:11:56,303 --> 00:11:59,137 of the earthquake that caused it. 172 00:11:59,137 --> 00:12:03,221 Atwater's starting point is the Copalis River in Washington State, 173 00:12:03,221 --> 00:12:06,346 just a couple of miles from the long sandy beaches 174 00:12:06,346 --> 00:12:09,597 that make this area a thriving tourist resort. 175 00:12:10,847 --> 00:12:15,973 In the banks of this estuary lie buried thousands of years of history. 176 00:12:18,640 --> 00:12:22,057 This is one of the dirtiest jobs in science. 177 00:12:22,057 --> 00:12:27,183 Hunting for evidence of earthquakes is a muddy business, but it's worth it. 178 00:12:27,183 --> 00:12:31,475 Atwater has found signs of a potential tsunami. 179 00:12:31,475 --> 00:12:37,434 There's a clue in this bank that nature has provided, it's this notch. 180 00:12:37,434 --> 00:12:39,560 And notches like this are common 181 00:12:39,560 --> 00:12:42,602 where tsunamis have laid out sheets of sand 182 00:12:42,602 --> 00:12:44,603 and then later currents 183 00:12:44,603 --> 00:12:46,477 and... and waves come along 184 00:12:46,477 --> 00:12:50,728 and they pluck the sand grains out of the bank, but they leave the mud. 185 00:12:52,561 --> 00:12:56,395 Atwater has to dig deeper to find what he is looking for, 186 00:12:56,395 --> 00:13:01,646 a layer of sand that could have been swept miles inland by a tsunami. 187 00:13:03,104 --> 00:13:08,648 OK, so now you can see the sand. What deposited this sand? 188 00:13:08,648 --> 00:13:11,398 Maybe it was a tsunami. 189 00:13:11,398 --> 00:13:14,523 To prove that this was sand from a tsunami, 190 00:13:14,523 --> 00:13:18,191 Atwater's muddy quest must continue. 191 00:13:18,191 --> 00:13:21,441 He also needs to find proof that the land here around the river 192 00:13:21,441 --> 00:13:25,275 has moved up or down - a sure sign of an earthquake. 193 00:13:26,317 --> 00:13:30,109 After some hard work, Atwater finds what he has been looking for - 194 00:13:30,109 --> 00:13:33,568 clear evidence of both an earthquake and a tsunami. 195 00:13:33,568 --> 00:13:36,985 This time, there was a human cost as well. 196 00:13:37,985 --> 00:13:41,860 Here we have evidence for abrupt lowering of land, 197 00:13:41,860 --> 00:13:44,569 and we also have evidence for the associated tsunami. 198 00:13:44,569 --> 00:13:47,653 In this case, humans are involved - this was a fishing camp. 199 00:13:47,653 --> 00:13:50,237 Here you have the remains of that fishing camp 200 00:13:50,237 --> 00:13:52,654 in the form of fire-cracked rocks which were... 201 00:13:52,654 --> 00:13:55,821 The rocks were used to heat water, mainly. 202 00:13:55,821 --> 00:14:00,405 OK, so fishing camp, overrun by tsunami. 203 00:14:00,405 --> 00:14:03,030 Because the land dropped after the tsunami, 204 00:14:03,030 --> 00:14:07,406 the tides came in and covered the fishing camp site 205 00:14:07,406 --> 00:14:09,823 and made sure that people wouldn't use it again. 206 00:14:11,615 --> 00:14:14,824 The land the fishing camp was built on was dragged down 207 00:14:14,824 --> 00:14:16,574 during the earthquake. 208 00:14:16,574 --> 00:14:19,699 The tsunami deposited sand over the remains, 209 00:14:19,699 --> 00:14:22,616 and finally, the tide covered the settlement with mud, 210 00:14:22,616 --> 00:14:26,534 where it remained undisturbed - until now. 211 00:14:26,534 --> 00:14:29,284 Atwater finally had the proof he needed. 212 00:14:29,284 --> 00:14:35,077 His Native American myths of giant waves were no mere legend. 213 00:14:36,660 --> 00:14:39,786 But what was it that caused the earthquake? 214 00:14:39,786 --> 00:14:46,203 The prime suspect lay 50 miles offshore - the Cascadia fault. 215 00:14:46,203 --> 00:14:50,454 Cascadia is a major weakness in the Earth's crust. 216 00:14:50,454 --> 00:14:54,205 Although the Earth may seem to be a solid sphere, 217 00:14:54,205 --> 00:14:56,955 beneath the oceans and continents it is divided 218 00:14:56,955 --> 00:15:02,205 into eight major and many minor segments known as tectonic plates. 219 00:15:02,205 --> 00:15:08,040 Where they meet, they can grind and jostle against each other at fault lines, 220 00:15:08,040 --> 00:15:09,998 causing earthquakes. 221 00:15:11,290 --> 00:15:14,582 Geologists had long thought that the Cascadia fault line 222 00:15:14,582 --> 00:15:17,541 was incapable of generating a major quake. 223 00:15:17,541 --> 00:15:22,875 But Atwater's investigation has proved that it was highly active. 224 00:15:22,875 --> 00:15:25,292 The big worry for Atwater and the thousands of people 225 00:15:25,292 --> 00:15:29,043 who live in this region is that the Cascadia fault line 226 00:15:29,043 --> 00:15:34,835 bears an uncanny resemblance to another highly active fault line, 227 00:15:34,835 --> 00:15:36,711 the Sunda Megathrust. 228 00:15:38,002 --> 00:15:41,670 It was an earthquake along this fault that was responsible 229 00:15:41,670 --> 00:15:47,129 for the Indian Ocean tsunami that killed nearly a quarter of a million people. 230 00:15:47,129 --> 00:15:49,212 Where we get two tectonic plates coming together, 231 00:15:49,212 --> 00:15:52,338 such as the case of the Indonesian tsunami in 2004, 232 00:15:52,338 --> 00:15:54,422 one plate pushes beneath the other plate 233 00:15:54,422 --> 00:15:57,089 and creates lots and lots of friction and tension 234 00:15:57,089 --> 00:15:59,797 and drags the upper plate down with it, 235 00:15:59,797 --> 00:16:01,589 and that process can take hundreds of years, 236 00:16:01,589 --> 00:16:03,131 even thousands of years. 237 00:16:03,131 --> 00:16:04,674 It's a very slow process. 238 00:16:04,674 --> 00:16:08,091 But eventually the pressure of this one trying to push back up again wins, 239 00:16:08,091 --> 00:16:10,091 and it flips like that. 240 00:16:11,925 --> 00:16:15,133 And that creates a megathrust, a sudden movement of the seabed, 241 00:16:15,133 --> 00:16:18,550 and that's what creates a phenomenal tsunami. 242 00:16:18,550 --> 00:16:23,342 Two factors made this Sunda Megathrust earthquake so deadly. 243 00:16:23,342 --> 00:16:25,093 The first was its size. 244 00:16:25,093 --> 00:16:27,343 At factor 9.2 on the Richter scale, 245 00:16:27,343 --> 00:16:31,802 this was the largest in nearly 50 years. 246 00:16:31,802 --> 00:16:37,137 The second was that it took place not far below the surface. 247 00:16:37,137 --> 00:16:38,928 BOXALL: When we talk about a megathrust, 248 00:16:38,928 --> 00:16:42,137 that's really where the seabed is disturbed dramatically. 249 00:16:42,137 --> 00:16:44,470 Sometimes, if the earthquake is deep in the Earth's crust, 250 00:16:44,470 --> 00:16:47,846 then you see very little surface manifestation of that earthquake. 251 00:16:47,846 --> 00:16:50,472 If it's quite close to the surface or very intense, 252 00:16:50,472 --> 00:16:52,930 then quite often you'll see the seabed itself moving, 253 00:16:52,930 --> 00:16:56,098 and that's what creates a powerful tsunami. 254 00:16:57,765 --> 00:17:00,515 Investigating the ocean floor after the quake 255 00:17:00,515 --> 00:17:04,849 revealed that more than 1,000 miles of fault line had fractured 256 00:17:04,849 --> 00:17:07,683 and sprung up by 60 feet. 257 00:17:07,683 --> 00:17:12,058 This massive jolt pushed up billions of tons of water, 258 00:17:12,058 --> 00:17:17,309 enough to cover Manhattan to a depth of nearly five miles. 259 00:17:20,018 --> 00:17:22,893 The rift zone itself was about a thousand miles long. 260 00:17:22,893 --> 00:17:26,602 We had this entire stretch of subsea moving, 261 00:17:26,602 --> 00:17:28,603 which creates a huge wave. 262 00:17:28,603 --> 00:17:31,937 So the whole thing was a phenomenal size 263 00:17:31,937 --> 00:17:34,603 and certainly one of the biggest tsunamis in living memory. 264 00:17:35,812 --> 00:17:39,895 Atwater's determined research showed that the Pacific Northwest 265 00:17:39,895 --> 00:17:43,105 was at risk from this level of devastation too. 266 00:17:44,105 --> 00:17:48,439 But he didn't want to unnecessarily alarm the coastal inhabitants 267 00:17:48,439 --> 00:17:51,398 until he had collected all the evidence he could. 268 00:17:51,398 --> 00:17:56,815 Atwater needed to find out precisely when this tsunami struck this coastline 269 00:17:56,815 --> 00:17:59,065 to see if there could be more. 270 00:17:59,065 --> 00:18:03,816 He first tried radiocarbon dating the soil along the Copalis River. 271 00:18:03,816 --> 00:18:06,774 But the result could only take him so far. 272 00:18:06,774 --> 00:18:09,275 They showed that the earthquake and tsunami occurred 273 00:18:09,275 --> 00:18:13,734 somewhere between 1680 and 1720. 274 00:18:13,734 --> 00:18:19,526 More importantly, Atwater still needed precise evidence of how big it had been. 275 00:18:20,985 --> 00:18:26,569 But so far, his investigation has uncovered two extraordinary facts. 276 00:18:26,569 --> 00:18:29,945 By unearthing the abandoned fishing camp, 277 00:18:29,945 --> 00:18:32,653 Atwater could see that a Cascadia earthquake here 278 00:18:32,653 --> 00:18:35,404 had caused the land to drop. 279 00:18:35,404 --> 00:18:37,779 The notch in the bank was proof 280 00:18:37,779 --> 00:18:41,071 that this same earthquake had generated a tsunami. 281 00:18:41,071 --> 00:18:46,530 But what these clues didn't tell Atwater was just how big the tsunami was. 282 00:18:46,530 --> 00:18:51,907 He had no way of pinning down the size of the threat to the Pacific Northwest. 283 00:18:51,907 --> 00:18:55,990 His investigation was about to take an unexpected turn, 284 00:18:55,990 --> 00:19:00,032 with clues coming from not only thousands of miles away, 285 00:19:00,032 --> 00:19:03,116 but also from hundreds of years ago. 286 00:19:05,658 --> 00:19:10,910 Japan has the oldest record of tsunamis of anywhere in the world. 287 00:19:10,910 --> 00:19:15,327 Samurai writings told of a huge tsunami in 1700 288 00:19:15,327 --> 00:19:18,452 that had swept over the east coast of Japan. 289 00:19:18,452 --> 00:19:23,578 It hit without warning, and destroyed entire settlements. 290 00:19:23,578 --> 00:19:27,620 Japanese scientists were baffled as to where this wave had come from. 291 00:19:27,620 --> 00:19:33,204 There had been no earthquake to warn the villagers to make for higher ground. 292 00:19:33,204 --> 00:19:37,329 The mystery wave was dubbed an orphan tsunami. 293 00:19:40,205 --> 00:19:41,663 Back in the U.S., 294 00:19:41,663 --> 00:19:45,580 Brian Atwater's investigation into the mysterious Cascadia earthquake 295 00:19:45,580 --> 00:19:47,998 and tsunami needed more evidence. 296 00:19:49,999 --> 00:19:55,916 He had no accurate way to pin down either the size or the date of the event. 297 00:19:57,083 --> 00:20:03,334 All he knew was that it had taken place sometime between 1680 and 1720. 298 00:20:03,334 --> 00:20:08,042 But Atwater's dates were a revelation to the Japanese scientists. 299 00:20:08,042 --> 00:20:14,210 Could this event be the birthplace of their 300-year-old orphan tsunami? 300 00:20:14,210 --> 00:20:16,752 And they said, "By the way, we have this tsunami 301 00:20:16,752 --> 00:20:20,670 "we've been trying to, uh, find a home for in 1700, 302 00:20:20,670 --> 00:20:24,129 "so we think your... your earthquake happened in 1700, 303 00:20:24,129 --> 00:20:27,754 "specifically in the evening of the 26th of January 1700, 304 00:20:27,754 --> 00:20:29,795 "and it was of magnitude nine." 305 00:20:31,671 --> 00:20:35,588 A Cascadia earthquake that produced a wave with enough power 306 00:20:35,588 --> 00:20:38,297 to cross the entire Pacific Ocean to Japan 307 00:20:38,297 --> 00:20:42,172 would have had to be a factor nine at the very least. 308 00:20:43,214 --> 00:20:48,340 This is roughly equivalent to the enormous Indian Ocean earthquake. 309 00:20:49,965 --> 00:20:52,633 Earthquakes like this have so much power 310 00:20:52,633 --> 00:20:58,134 that they can send a tsunami across an entire ocean with ease. 311 00:20:58,134 --> 00:21:00,926 BOXALL: The amount of energy involved is very hard to estimate, 312 00:21:00,926 --> 00:21:04,592 and it's hard to put it into sort of terms that people can understand. 313 00:21:04,592 --> 00:21:08,302 We are looking at the phenomenal forces of several Hiroshimas, 314 00:21:08,302 --> 00:21:10,427 hundreds of Hiroshimas, in fact. 315 00:21:11,469 --> 00:21:17,095 But tsunamis are not just a very big wave, they're fast. 316 00:21:17,095 --> 00:21:19,011 The big difference is the scale of the wave - 317 00:21:19,011 --> 00:21:22,804 it's typically three or four hundred miles long. 318 00:21:22,804 --> 00:21:24,720 It's also not very high - 319 00:21:24,720 --> 00:21:28,388 when it starts off life, it's usually about two or three foot high. 320 00:21:28,388 --> 00:21:30,179 But it's moving very fast. 321 00:21:30,179 --> 00:21:33,347 It moves at a speed determined by the water depth. 322 00:21:33,347 --> 00:21:35,263 The deeper the water, the faster it moves, 323 00:21:35,263 --> 00:21:40,848 so in the deep ocean, this wave is moving at over 500 miles an hour. 324 00:21:40,848 --> 00:21:44,390 Deceptively, as a tsunami speeds through deep water, 325 00:21:44,390 --> 00:21:48,516 it may appear completely harmless and scarcely detectable. 326 00:21:49,849 --> 00:21:53,350 Close to shore, the wave becomes a deadly killer. 327 00:21:53,350 --> 00:21:58,725 It is only then that a tsunami's true power becomes clear. 328 00:22:00,184 --> 00:22:02,559 As the wave gets to shallower and shallower water, 329 00:22:02,559 --> 00:22:05,768 as it approaches a coastline, the wave slows down. 330 00:22:05,768 --> 00:22:08,935 The shallower the water, the slower the wave, so it goes from 500, to 400, 331 00:22:08,935 --> 00:22:10,853 to 300, to 200, much, much slower. 332 00:22:10,853 --> 00:22:12,853 The back of the wave is still going full speed, 333 00:22:12,853 --> 00:22:17,604 and so the whole thing piles up, and that's why tsunamis are so destructive. 334 00:22:21,312 --> 00:22:25,896 It is this immense speed and power that reveals how events here in Cascadia 335 00:22:25,896 --> 00:22:29,647 could devastate a coastal village in Japan, 336 00:22:29,647 --> 00:22:34,064 how an earthquake in Chile could decimate Hawaii, 337 00:22:34,064 --> 00:22:36,147 and how the Indian Ocean earthquake 338 00:22:36,147 --> 00:22:39,857 could kill almost a quarter of a million people. 339 00:22:39,857 --> 00:22:43,732 If a quake like this happened in Cascadia, 340 00:22:43,732 --> 00:22:47,899 the damage it would do to the Pacific Northwest coastline 341 00:22:47,899 --> 00:22:49,649 would be catastrophic. 342 00:22:50,691 --> 00:22:53,192 But to be sure about the scale of this threat, 343 00:22:53,192 --> 00:22:56,109 Brian Atwater has to be 100% certain 344 00:22:56,109 --> 00:23:00,193 that the dates of the two tsunamis were the same. 345 00:23:00,193 --> 00:23:03,735 After fully exploring the estuary of the Copalis river, 346 00:23:03,735 --> 00:23:08,069 he found one site that might hold the information he was looking for - 347 00:23:08,069 --> 00:23:10,777 a ghost forest. 348 00:23:10,777 --> 00:23:15,154 This spruce root marks the remains of a forest 349 00:23:15,154 --> 00:23:17,487 that includes the ghost forest behind us, 350 00:23:17,487 --> 00:23:21,738 dropped down into tidewater during the Cascadia earthquake. 351 00:23:24,530 --> 00:23:26,822 This ghost forest is made up 352 00:23:26,822 --> 00:23:30,156 of the standing dead trunks of western red cedar, 353 00:23:30,156 --> 00:23:34,615 and they were killed on account of the land here dropping, 354 00:23:34,615 --> 00:23:38,698 and then tides coming in and surrounding these trees 355 00:23:38,698 --> 00:23:40,990 and bringing in saltwater. 356 00:23:41,991 --> 00:23:45,783 This area would once have been covered with a dense forest. 357 00:23:47,200 --> 00:23:51,867 But today, only the bleached trunks of the rot-resistant western red cedar 358 00:23:51,867 --> 00:23:54,243 remain in place. 359 00:23:54,243 --> 00:23:58,785 When Atwater and expert tree ring specialists cut them open 360 00:23:58,785 --> 00:24:01,035 and studied the lines of growth inside, 361 00:24:01,035 --> 00:24:06,036 they finally cracked the 300-year-old tsunami puzzle. 362 00:24:07,120 --> 00:24:10,078 The dates of the Japanese and Cascadia events 363 00:24:10,078 --> 00:24:11,828 were exactly the same - 364 00:24:11,828 --> 00:24:14,371 January 1700. 365 00:24:14,371 --> 00:24:19,330 The Japanese orphan tsunami finally had a parent. 366 00:24:19,330 --> 00:24:21,746 Maybe there's a certain amount of justice to it 367 00:24:21,746 --> 00:24:25,497 that... that a place that doesn't have written records 368 00:24:25,497 --> 00:24:28,831 has these outstanding geological records. 369 00:24:28,831 --> 00:24:31,498 The link between the two events made it certain 370 00:24:31,498 --> 00:24:36,749 that the Cascadia earthquake had been at least an awesome magnitude nine. 371 00:24:36,749 --> 00:24:40,332 And ominously, it is almost certainly not the only time 372 00:24:40,332 --> 00:24:43,041 that Cascadia has rocked this area. 373 00:24:44,708 --> 00:24:48,750 Atwater believes he has found proof of a whole series of tsunamis 374 00:24:48,750 --> 00:24:51,709 stretching back 5,000 years. 375 00:24:52,793 --> 00:24:57,168 Each layer of sand in this sample represents a separate tsunami. 376 00:24:59,127 --> 00:25:02,920 There are places at Cascadia where I've seen nine stacked up 377 00:25:02,920 --> 00:25:06,337 in a column about 20 feet long. 378 00:25:06,337 --> 00:25:09,837 Uh, nine buried soils, some of them coated with little sand sheets. 379 00:25:09,837 --> 00:25:11,712 And... and they, you know, you... you say, 380 00:25:11,712 --> 00:25:16,255 "OK, it's... it's not a question of if, but it's just a matter of when." 381 00:25:18,714 --> 00:25:21,922 Atwater's tireless detective work alerted officials 382 00:25:21,922 --> 00:25:24,339 to the increased tsunami threat. 383 00:25:25,589 --> 00:25:29,340 As a result, the towns along the Washington State coast 384 00:25:29,340 --> 00:25:32,507 have been able to prepare for this potential catastrophe. 385 00:25:33,924 --> 00:25:38,050 If a Cascadia quake occurred, the first waves could arrive here 386 00:25:38,050 --> 00:25:40,091 in just 25 minutes. 387 00:25:41,091 --> 00:25:45,842 Tsunami warning signs line the roads, and sirens stand ready to warn 388 00:25:45,842 --> 00:25:48,301 of an approaching wave. 389 00:25:48,301 --> 00:25:54,469 The lives of thousands of people are safer thanks to the work of Atwater, 390 00:25:54,469 --> 00:25:57,969 and to some 300-year-old Japanese writings. 391 00:25:59,010 --> 00:26:03,970 This is a hazard that shows its face often enough for us to take precautions, 392 00:26:03,970 --> 00:26:06,679 to fasten the seatbelt against it. 393 00:26:06,679 --> 00:26:11,304 By dating the ghost forest along the Copalis River to precisely 1700, 394 00:26:11,304 --> 00:26:15,888 Atwater had the final proof that Cascadia was capable of creating 395 00:26:15,888 --> 00:26:18,805 a Pacific-wide tsunami. 396 00:26:18,805 --> 00:26:22,723 Uncovering the multiple layers of tsunami debris in the riverbank 397 00:26:22,723 --> 00:26:26,182 dating back 5,000 years show that monster waves 398 00:26:26,182 --> 00:26:28,516 have struck here many times. 399 00:26:28,516 --> 00:26:31,099 This is an ongoing threat. 400 00:26:32,349 --> 00:26:34,849 Atwater knows that another earthquake is due here, 401 00:26:34,849 --> 00:26:39,433 but he has no way of knowing exactly when. 402 00:26:39,433 --> 00:26:41,475 Back in the Indian Ocean, 403 00:26:41,475 --> 00:26:45,352 the site of the world's most lethal tsunami in 2004, 404 00:26:45,352 --> 00:26:50,185 one man has taken the investigation of tsunamis to a new level. 405 00:26:50,185 --> 00:26:53,894 He believes that he has found a way to make the Earth's fault lines 406 00:26:53,894 --> 00:26:58,145 give up their secrets and accurately predict when the next deadly tsunami 407 00:26:58,145 --> 00:27:01,187 could be on its way. 408 00:27:04,896 --> 00:27:10,355 The idyllic looking Mentawai island chain in Indonesia hides a violent secret, 409 00:27:10,355 --> 00:27:14,981 one that makes it today one of the most dangerous places on Earth. 410 00:27:16,356 --> 00:27:19,940 These islands lie directly on top of the Sunda Megathrust, 411 00:27:19,940 --> 00:27:22,732 south of where the enormous Indian Ocean earthquake 412 00:27:22,732 --> 00:27:25,732 triggered the 2004 tsunami. 413 00:27:25,732 --> 00:27:30,191 The Sunda Megathrust is one of the largest fault lines on the planet. 414 00:27:30,191 --> 00:27:33,691 Since it caused the 2004 earthquake, 415 00:27:33,691 --> 00:27:36,817 it has also become one of the most notorious. 416 00:27:39,650 --> 00:27:41,735 Predicting earthquakes here is tricky, 417 00:27:41,735 --> 00:27:45,776 but Professor Kerry Sieh has a good track record. 418 00:27:45,776 --> 00:27:51,153 He has successfully forecast two along the Sunda Megathrust already. 419 00:27:52,903 --> 00:27:56,320 The key to successful tsunami prediction is to forecast 420 00:27:56,320 --> 00:27:59,029 when and where earthquakes will strike. 421 00:27:59,029 --> 00:28:03,696 And to do this, scientists must look into the past. 422 00:28:03,696 --> 00:28:05,863 SIEH: If you want to answer questions about earthquakes 423 00:28:05,863 --> 00:28:07,863 that only happen every few hundred years 424 00:28:07,863 --> 00:28:09,655 or few thousand years, 425 00:28:09,655 --> 00:28:13,322 well, you've got to find some... some geological instrument 426 00:28:13,322 --> 00:28:16,323 that allows you to see those earthquakes. 427 00:28:16,323 --> 00:28:18,490 Professor Sieh has found an unusual way 428 00:28:18,490 --> 00:28:23,699 to unlock the secrets of the Sunda Megathrust's turbulent history. 429 00:28:23,699 --> 00:28:25,741 Corals. 430 00:28:25,741 --> 00:28:28,283 These coral atolls are built from the limestone skeletons 431 00:28:28,283 --> 00:28:30,825 of millions of tiny creatures. 432 00:28:30,825 --> 00:28:35,117 Each generation builds on the remains of the last. 433 00:28:35,117 --> 00:28:38,701 Over time, the atoll gets bigger and bigger. 434 00:28:38,701 --> 00:28:42,410 As long as the corals remain underwater, they flourish, 435 00:28:42,410 --> 00:28:45,785 but once they're above water, they die. 436 00:28:45,785 --> 00:28:50,161 Earthquakes are responsible for killing all the coral stranded 437 00:28:50,161 --> 00:28:52,745 above water on this beach. 438 00:28:54,412 --> 00:28:57,495 This beach contains corals of many different ages. 439 00:28:57,495 --> 00:29:01,329 Altogether, Professor Sieh has nearly a thousand years of history 440 00:29:01,329 --> 00:29:03,538 at his fingertips. 441 00:29:03,538 --> 00:29:06,747 But to unlock the secret history the corals contain, 442 00:29:06,747 --> 00:29:11,539 he and his team have to take a less than delicate approach. 443 00:29:11,539 --> 00:29:15,707 We're looking at a sawcut that we just made through a coral micro atoll. 444 00:29:15,707 --> 00:29:18,749 And the great thing about this head is it records a sudden drop 445 00:29:18,749 --> 00:29:21,749 of about a foot and a half down to here. 446 00:29:21,749 --> 00:29:24,041 It died down to here, because the island rose. 447 00:29:24,041 --> 00:29:25,792 The new low tide is way down here. 448 00:29:25,792 --> 00:29:29,000 Everything that was so bold as to grow up this high dies. 449 00:29:30,959 --> 00:29:34,334 The shape of the coral records the fall of the Mentawai islands 450 00:29:34,334 --> 00:29:38,585 as they are literally pulled down by the Sunda Megathrust. 451 00:29:39,585 --> 00:29:43,252 But, crucially, the corals also record the moments 452 00:29:43,252 --> 00:29:48,920 when the islands are thrust up out of the water during an earthquake. 453 00:29:48,920 --> 00:29:52,962 Between quakes, the islands are once again pulled down by the fault 454 00:29:52,962 --> 00:29:55,171 in a never-ending cycle. 455 00:29:57,379 --> 00:29:59,963 You have to imagine that rocks actually are elastic. 456 00:29:59,963 --> 00:30:03,130 Take a diving board, the diver... the diver walks out on the platform 457 00:30:03,130 --> 00:30:04,756 and it... it bends like this, 458 00:30:04,756 --> 00:30:07,548 and then he jumps and he springs up and he jumps off. 459 00:30:07,548 --> 00:30:10,507 And when he jumps off, the diving board doesn't stay here, 460 00:30:10,507 --> 00:30:12,840 it doesn't go like... it doesn't go like this, 461 00:30:12,840 --> 00:30:15,757 you know, the diving board springs back up, it's elastic. 462 00:30:15,757 --> 00:30:18,424 Well, rocks are the same, rocks are elastic too, 463 00:30:18,424 --> 00:30:22,924 so when the Indian Plate goes down it pulls the Sumatran section down too, 464 00:30:22,924 --> 00:30:25,175 and then later, it fails. 465 00:30:25,175 --> 00:30:27,467 So it just springs up like a diving board. 466 00:30:28,509 --> 00:30:31,176 By analysing corals all over this beach, 467 00:30:31,176 --> 00:30:35,427 Professor Sieh has discovered a regular pattern to this cycle. 468 00:30:36,427 --> 00:30:41,136 A major earthquake rocks these islands roughly every 200 years. 469 00:30:43,261 --> 00:30:47,553 What we have here in Sumatra with the corals is what I call the Holy Grail 470 00:30:47,553 --> 00:30:50,679 of, uh... of earthquake science, of... of palaeoseismology, 471 00:30:50,679 --> 00:30:54,388 and that is a long record that has many cycles in it, 472 00:30:54,388 --> 00:30:57,680 a thousand-year-long history of earthquakes. 473 00:30:57,680 --> 00:31:00,264 But when the geologist looked even closer, 474 00:31:00,264 --> 00:31:02,973 he saw that the cycle was more complex. 475 00:31:04,347 --> 00:31:07,306 When we cut a slab, we can see it in much more exquisite detail 476 00:31:07,306 --> 00:31:09,432 because we can see what we call the stratigraphy, 477 00:31:09,432 --> 00:31:11,224 or the... the... the layering 478 00:31:11,224 --> 00:31:14,307 and how the layering relates to the changes of the tide, 479 00:31:14,307 --> 00:31:18,724 so what we can see over here, then, is the annual bands of growth, right here, 480 00:31:18,724 --> 00:31:24,184 so there's about ten years between this earthquake and this earthquake. 481 00:31:26,100 --> 00:31:29,476 Professor Sieh had discovered a major clue. 482 00:31:29,476 --> 00:31:34,269 The corals record that, not only does a major earthquake and tsunami hit here 483 00:31:34,269 --> 00:31:37,436 every 200 years, but that they are always accompanied 484 00:31:37,436 --> 00:31:40,728 by a number of smaller quakes. 485 00:31:40,728 --> 00:31:45,354 This is a cycle within a cycle, a supercycle. 486 00:31:46,646 --> 00:31:49,438 And by counting back the layers of growth within the coral, 487 00:31:49,438 --> 00:31:53,938 the geologists can put an exact date on all of these earthquakes. 488 00:31:53,938 --> 00:31:56,397 We know there's a sequence in the 1350s, 1370s, 489 00:31:56,397 --> 00:32:00,939 we know there's a sequence in the 1560s, 1600s... 1600, 490 00:32:00,939 --> 00:32:04,690 we know there's a sequence 1797, 1833. 491 00:32:04,690 --> 00:32:08,523 Those sequences are about 200, to 200... yeah, 230 years apart. 492 00:32:09,941 --> 00:32:14,608 This is crucial information for the people of the Mentawai islands, 493 00:32:14,608 --> 00:32:16,900 who have no written history. 494 00:32:16,900 --> 00:32:19,484 But Professor Sieh's work doesn't stop here. 495 00:32:19,484 --> 00:32:22,901 By uncovering their history in the corals, 496 00:32:22,901 --> 00:32:26,693 he believes that he can now predict the future for these islands. 497 00:32:28,027 --> 00:32:30,943 And he's already had some success. 498 00:32:30,943 --> 00:32:34,569 Professor Sieh began his work here in 1993, 499 00:32:34,569 --> 00:32:38,070 and soon realised an earthquake was imminent. 500 00:32:38,070 --> 00:32:42,862 The Mentawai islands were about to start their next deadly supercycle. 501 00:32:44,238 --> 00:32:46,738 MAN: OK! Experienced an earthquake! 502 00:32:46,738 --> 00:32:50,030 In September 2007, he was proved right, 503 00:32:50,030 --> 00:32:54,239 when an earthquake shook the islands just enough to generate a small tsunami 504 00:32:54,239 --> 00:32:56,823 that wrecked homes and schools. 505 00:32:59,740 --> 00:33:03,699 History is repeating itself, exactly as he predicted it would. 506 00:33:04,948 --> 00:33:07,074 A much bigger earthquake 507 00:33:07,074 --> 00:33:11,283 and more dangerous tsunami could be due any day. 508 00:33:12,366 --> 00:33:15,117 SIEH: One section hasn't failed since 1797, 509 00:33:15,117 --> 00:33:18,992 so, since George Washington was President of the United States. 510 00:33:18,992 --> 00:33:21,701 We know we're now in a sequence of at least three giant earthquakes, 511 00:33:21,701 --> 00:33:23,327 we're expecting another one. 512 00:33:23,327 --> 00:33:25,327 The question is whether the earthquake and tsunami 513 00:33:25,327 --> 00:33:28,244 will be in the next 30 minutes or the next 30 years. 514 00:33:29,453 --> 00:33:31,786 Thanks to Sieh's research, 515 00:33:31,786 --> 00:33:34,745 the people of these islands have had time to prepare. 516 00:33:34,745 --> 00:33:37,953 When the wave comes, they will be ready. 517 00:33:37,953 --> 00:33:40,537 Earthquakes are forecastable. 518 00:33:40,537 --> 00:33:43,413 If you... if you have enough information about how they've behaved 519 00:33:43,413 --> 00:33:46,580 over the last thousand years, or two or three or four cycles, 520 00:33:46,580 --> 00:33:48,663 you can really make a significant forecast 521 00:33:48,663 --> 00:33:51,539 that people living in the area actually can do something about. 522 00:33:53,498 --> 00:33:56,248 Education is key. 523 00:33:56,248 --> 00:33:57,915 Children here are now taught 524 00:33:57,915 --> 00:34:00,831 that as soon as they feel the shaking of an earthquake, 525 00:34:00,831 --> 00:34:02,832 they should run for higher ground. 526 00:34:05,208 --> 00:34:09,791 Newly built roads snake up steep hills from waterside villages 527 00:34:09,791 --> 00:34:12,501 to allow rapid escape from the deadly waves. 528 00:34:13,626 --> 00:34:17,834 I'll bet that young children alive today, if they... certainly if they live to be 60, 529 00:34:17,834 --> 00:34:19,627 they're gonna see that earthquake. 530 00:34:19,627 --> 00:34:22,793 In fact, I think there's a better than 50% chance that it'll happen in... 531 00:34:22,793 --> 00:34:24,294 ...within the next 30 years. 532 00:34:24,294 --> 00:34:28,044 By analysing the shape of the corals on the Mentawai islands, 533 00:34:28,044 --> 00:34:33,545 Sieh has proved that a major tsunami cycle starts here every 200 years. 534 00:34:33,545 --> 00:34:38,337 By dating the lines within the coral, he can be even more exact. 535 00:34:38,337 --> 00:34:43,088 They show that these cycles contain not just one, but several deadly tsunamis. 536 00:34:44,255 --> 00:34:48,214 The Sunda Megathrust is the clear culprit for tsunamis here. 537 00:34:49,214 --> 00:34:53,006 But not every tsunami is generated by an earthquake. 538 00:34:53,006 --> 00:34:58,924 A rarer, different type of wave is out there - a megatsunami. 539 00:35:04,758 --> 00:35:08,842 Although earthquakes are by far the most common cause of tsunamis, 540 00:35:08,842 --> 00:35:14,052 there is another source for these deadly waves - landslides. 541 00:35:14,052 --> 00:35:17,551 And these tsunamis have the potential to be so big 542 00:35:17,551 --> 00:35:21,177 that they have been called megatsunamis. 543 00:35:22,428 --> 00:35:26,762 Scientists had long suspected that waves could be generated in this way, 544 00:35:26,762 --> 00:35:32,512 but conclusive photographic proof wasn't available until 1958. 545 00:35:33,846 --> 00:35:37,679 A landslide into Lituya Bay in Alaska triggered a wave 546 00:35:37,679 --> 00:35:41,138 that reached heights of several thousand feet. 547 00:35:42,431 --> 00:35:45,472 This footage, shot just after the tsunami struck, 548 00:35:45,472 --> 00:35:48,181 shows the wave's enormous power. 549 00:35:48,181 --> 00:35:52,765 The trees here once stretched all the way down to the shores of the bay, 550 00:35:52,765 --> 00:35:55,974 but were ripped off the slopes by a wall of water, 551 00:35:55,974 --> 00:35:59,558 leaving nothing but bare exposed rock. 552 00:36:01,099 --> 00:36:04,475 The tsunami was generated when a relatively small earthquake 553 00:36:04,475 --> 00:36:06,683 triggered a single enormous landslide 554 00:36:06,683 --> 00:36:09,768 of rocks and debris into the bay. 555 00:36:11,642 --> 00:36:15,185 The resulting wave was higher than the Empire State Building 556 00:36:15,185 --> 00:36:19,019 and stunned scientists around the world. 557 00:36:19,019 --> 00:36:22,978 Tsunamis on this scale are incredibly rare. 558 00:36:25,061 --> 00:36:26,853 But another megatsunami, 559 00:36:26,853 --> 00:36:31,104 triggered by a rockfall 10,000 times bigger than Lituya Bay, 560 00:36:31,104 --> 00:36:36,438 could be on its way from a small island across the Atlantic Ocean. 561 00:36:37,938 --> 00:36:39,981 The Canary Islands, off the coast of Africa, 562 00:36:39,981 --> 00:36:43,189 are formed from a series of volcanoes. 563 00:36:45,356 --> 00:36:48,023 The youngest is the island of La Palma. 564 00:36:48,023 --> 00:36:51,107 It is formed from two volcanic ridges. 565 00:36:51,107 --> 00:36:56,524 The first is the extinct Cumbre Nueva to the north of the island. 566 00:36:56,524 --> 00:37:01,359 The younger, active Cumbre Vieja lies to the south. 567 00:37:02,775 --> 00:37:06,151 It erupted as recently as 1971. 568 00:37:09,276 --> 00:37:12,902 Geologist Dr Simon Day's research was crucial 569 00:37:12,902 --> 00:37:15,694 in developing the La Palma megatsunami theory. 570 00:37:15,694 --> 00:37:18,444 It began with an unusual rift 571 00:37:18,444 --> 00:37:23,112 that had opened up during a major volcanic eruption in 1949. 572 00:37:25,528 --> 00:37:31,530 We're standing here in the fault and it runs way down to the south 573 00:37:31,530 --> 00:37:34,363 along the crest of the volcano for two and a half miles, 574 00:37:34,363 --> 00:37:37,073 so it's one continuous long structure. 575 00:37:38,198 --> 00:37:42,615 Day believes this fault is evidence of a geological time bomb, 576 00:37:42,615 --> 00:37:46,074 the beginning of a giant landslide. 577 00:37:47,490 --> 00:37:51,033 What we see here to my right are layers of... of volcanic rocks, 578 00:37:51,033 --> 00:37:54,116 volcanic blocks here and layers of volcanic ash. 579 00:37:54,116 --> 00:37:57,700 And on the west of the fault, we see the same layers of blocks 580 00:37:57,700 --> 00:38:00,951 and ash and those, before the fault moved, were joined up 581 00:38:00,951 --> 00:38:03,201 and then when the fault moved, they were separated 582 00:38:03,201 --> 00:38:06,951 and the rocks to my left moved down and to the west. 583 00:38:06,951 --> 00:38:10,827 What we think will happen in some future eruption 584 00:38:10,827 --> 00:38:13,869 is that this fault will have gotten bigger 585 00:38:13,869 --> 00:38:19,579 and the whole of this western side will slide away in a giant landslide 586 00:38:19,579 --> 00:38:22,037 into the ocean to create the tsunami. 587 00:38:23,704 --> 00:38:28,497 This landslide would send the entire southwest section of La Palma, 588 00:38:28,497 --> 00:38:32,789 one sixth of the island's total mass, crashing into the Atlantic Ocean 589 00:38:32,789 --> 00:38:35,997 in a single giant landslide. 590 00:38:35,997 --> 00:38:38,664 What we envisage is the whole of this coastline 591 00:38:38,664 --> 00:38:42,207 and the slope extending up all the way to the crest of the volcano 592 00:38:42,207 --> 00:38:45,999 that is now in the clouds, all of that mass of rock would slide away 593 00:38:45,999 --> 00:38:49,458 in a single massive landslide into the ocean 594 00:38:49,458 --> 00:38:54,792 and pushing the water up in front of it to create the tsunami wave. 595 00:38:54,792 --> 00:38:58,376 Initially, this wave would be over 30 times bigger 596 00:38:58,376 --> 00:39:04,960 than the 2004 Indian Ocean tsunami, more than 3,000 feet high. 597 00:39:04,960 --> 00:39:06,210 (EXPLOSION) 598 00:39:06,210 --> 00:39:10,794 The 1980 eruption of Mount St Helens was proof that a volcano could collapse 599 00:39:10,794 --> 00:39:13,919 in this terrifying fashion. 600 00:39:13,919 --> 00:39:17,295 This was impressive, but the collapse of the Cumbre Vieja 601 00:39:17,295 --> 00:39:21,254 would be 200 times the volume of this. 602 00:39:22,337 --> 00:39:23,671 (LOUD RUMBLING) 603 00:39:23,671 --> 00:39:30,714 1,200 billion tons of rock would hurtle towards the ocean at top speed. 604 00:39:31,964 --> 00:39:36,339 The resulting wave would head straight out into the Atlantic. 605 00:39:36,339 --> 00:39:38,465 DAY: That wave, of course, would then spread out 606 00:39:38,465 --> 00:39:40,882 and separate out into smaller waves, 607 00:39:40,882 --> 00:39:47,008 but even so, after crossing the Atlantic and piling up again on, 608 00:39:47,008 --> 00:39:50,050 for example, the eastern seaboard of the United States or in the Caribbean 609 00:39:50,050 --> 00:39:53,801 or in northern Brazil, the waves there, we predict, 610 00:39:53,801 --> 00:39:56,801 would still be between 30 and 100 feet high. 611 00:39:56,801 --> 00:40:00,885 So that's as large as, if not larger, 612 00:40:00,885 --> 00:40:05,011 than the tsunami that struck Sumatra in 2004. 613 00:40:07,261 --> 00:40:08,803 Boston... 614 00:40:13,929 --> 00:40:15,470 New York... 615 00:40:19,096 --> 00:40:24,222 ...and even Miami could all be under threat from the giant waves. 616 00:40:29,972 --> 00:40:31,806 This was a bold prediction. 617 00:40:31,806 --> 00:40:35,556 Day needed more evidence to back up his theory. 618 00:40:35,556 --> 00:40:39,891 As he was about to see, the rift in La Palma's landscape 619 00:40:39,891 --> 00:40:43,141 was far worse than he expected. 620 00:40:43,141 --> 00:40:49,100 The 1949 eruption had left a different type of geological scar on the island. 621 00:40:50,976 --> 00:40:53,852 Evidence of a more serious weakness within La Palma 622 00:40:53,852 --> 00:40:58,144 came from a series of eerie-looking lava flows dotted across the island. 623 00:41:00,894 --> 00:41:04,728 One of the characteristics of the 1949 eruption that's unusual 624 00:41:04,728 --> 00:41:09,020 is that, instead of starting at one vent and just continuing there, 625 00:41:09,020 --> 00:41:13,771 a series of volcanic vents opened up in different parts of the island. 626 00:41:13,771 --> 00:41:16,105 When Day plotted these weaknesses on a map, 627 00:41:16,105 --> 00:41:18,730 he came to a frightening conclusion. 628 00:41:18,730 --> 00:41:22,480 The rift was far bigger than he had first suspected. 629 00:41:23,523 --> 00:41:27,689 The area that's potentially affected is very much greater 630 00:41:27,689 --> 00:41:31,607 than the length of the fault at the crest of the volcano would indicate, 631 00:41:31,607 --> 00:41:36,274 extending out, um, 10 or 15 miles from the crest out to sea. 632 00:41:37,483 --> 00:41:39,358 This growing body of evidence proved 633 00:41:39,358 --> 00:41:43,775 that the rift wasn't just a mere crack in the surface of La Palma, 634 00:41:43,775 --> 00:41:46,483 but a deep fissure that reached hundreds of feet 635 00:41:46,483 --> 00:41:49,276 down into the island's foundations. 636 00:41:49,276 --> 00:41:54,194 It is La Palma's volcanic heritage that is the key to this tsunami threat. 637 00:41:55,443 --> 00:41:57,986 The big hazard here isn't the eruptions themselves, 638 00:41:57,986 --> 00:42:00,903 it's the fact that the volcano is building up and building up over time 639 00:42:00,903 --> 00:42:05,362 and becoming more and more unstable, so that will eventually lead to a collapse. 640 00:42:06,362 --> 00:42:10,321 And it seems that this is not the first time a La Palma eruption 641 00:42:10,321 --> 00:42:12,863 may have triggered a giant landslide. 642 00:42:12,863 --> 00:42:17,489 Proof lies in the north of the island in these sheer cliff faces, 643 00:42:17,489 --> 00:42:20,489 formed 65,000 years ago. 644 00:42:21,573 --> 00:42:26,490 What we see in the north of La Palma is the landslide scar left 645 00:42:26,490 --> 00:42:30,032 when the old volcano in the north of La Palma 646 00:42:30,032 --> 00:42:33,283 experienced a giant collapse 647 00:42:33,283 --> 00:42:36,575 and produced a giant landslide off to the west. 648 00:42:38,242 --> 00:42:39,867 So that was a huge collapse - 649 00:42:39,867 --> 00:42:43,701 it removed as much as 100 cubic miles of rock 650 00:42:43,701 --> 00:42:47,118 and deposited it out into the ocean, so it's the sort of event 651 00:42:47,118 --> 00:42:49,160 that we think is going to happen again 652 00:42:49,160 --> 00:42:51,702 in the future at the... at the Cumbre Vieja. 653 00:42:53,118 --> 00:42:56,619 This ancient collapse of the old Cumbre Nueva volcano 654 00:42:56,619 --> 00:43:01,245 is almost certain to have generated a gigantic wave. 655 00:43:03,329 --> 00:43:07,413 And the next collapse might not be that far away. 656 00:43:07,413 --> 00:43:10,247 This tsunami could strike in our lifetime. 657 00:43:15,497 --> 00:43:17,456 DAY: Even though it seems so extraordinary 658 00:43:17,456 --> 00:43:19,165 when we consider it in human terms, 659 00:43:19,165 --> 00:43:22,415 and we talk about a tsunami striking the east coast of North America 660 00:43:22,415 --> 00:43:26,582 and causing huge devastation on the scale of the Sumatra tsunami, 661 00:43:26,582 --> 00:43:29,332 but this is what happens in the geological record, 662 00:43:29,332 --> 00:43:32,542 this is what Earth does. 663 00:43:33,708 --> 00:43:37,500 Although tsunamis have been documented for thousands of years, 664 00:43:37,500 --> 00:43:41,418 it is only in the last century that geologists have been able to prove 665 00:43:41,418 --> 00:43:44,459 how they are connected to the movements of the Earth. 666 00:43:46,460 --> 00:43:50,669 By analysing data from the great Chilean earthquake of 1960, 667 00:43:50,669 --> 00:43:55,169 scientists were finally able to firmly link earthquakes with tsunamis. 668 00:43:55,169 --> 00:43:58,295 Unearthing buried Native American settlements 669 00:43:58,295 --> 00:44:02,420 proved that the Cascadia fault line in the Pacific Northwest 670 00:44:02,420 --> 00:44:05,129 was an active tsunami threat. 671 00:44:05,129 --> 00:44:09,964 Corals in the Indian Ocean proved that some earthquake-generated tsunamis 672 00:44:09,964 --> 00:44:15,048 follow a pattern, and strike the same area with regular intervals. 673 00:44:15,048 --> 00:44:19,507 And the giant rift in La Palma's landscape shows that tsunamis 674 00:44:19,507 --> 00:44:25,758 generated by landslides are also a very real threat, megatsunamis, 675 00:44:25,758 --> 00:44:30,092 which could prove to be the biggest waves that threaten our coastline. 676 00:44:31,133 --> 00:44:32,967 Tsunamis are an inevitable part 677 00:44:32,967 --> 00:44:35,509 of Earth's dynamic structure. 678 00:44:35,509 --> 00:44:37,801 Their capacity to destroy 679 00:44:37,801 --> 00:44:39,177 is awesome, 680 00:44:39,177 --> 00:44:40,593 but, as scientists 681 00:44:40,593 --> 00:44:42,051 begin to understand more 682 00:44:42,051 --> 00:44:43,676 about the origins of tsunamis, 683 00:44:43,676 --> 00:44:46,177 they are coming closer to predicting 684 00:44:46,177 --> 00:44:49,302 where and when these monsters may strike.