0:00:04 > 0:00:08Two thirds of Planet Earth is covered by ocean.
0:00:08 > 0:00:11We need this water to sustain life.
0:00:11 > 0:00:17But water can also be one of the most destructive forces on this planet.
0:00:17 > 0:00:22Tsunamis, or giant ocean waves, have wreaked havoc throughout history.
0:00:24 > 0:00:28The forces that create such massive waves are incredible.
0:00:31 > 0:00:33What's more, as a geologist,
0:00:33 > 0:00:36I find the stories about tsunamis truly astounding.
0:00:38 > 0:00:41So, if you don't know which great civilisation
0:00:41 > 0:00:45may have been devastated by a tsunami...
0:00:45 > 0:00:51how a father and son managed to surf the highest wave ever recorded and survive...
0:00:52 > 0:00:56..or why millions of Americans could be at risk from a mega-tsunami,
0:00:56 > 0:00:58then stay around as I reveal
0:00:58 > 0:01:0210 things you didn't know about tsunamis.
0:01:15 > 0:01:18I'm here on La Palma, one of the Canary Islands.
0:01:18 > 0:01:22Most people come to the Canaries to get away from it all and relax,
0:01:22 > 0:01:23but not me.
0:01:23 > 0:01:29I've come here because this little island might one day generate a massive tsunami...
0:01:29 > 0:01:30A mega-tsunami.
0:01:30 > 0:01:32We'll explore that story later,
0:01:32 > 0:01:35but first I've got nine other tsunami stories
0:01:35 > 0:01:37to cover from around the world.
0:01:37 > 0:01:41We'll begin with one tsunami that's burnt into all our memories,
0:01:41 > 0:01:43it's certainly etched into my mind,
0:01:43 > 0:01:46and that's the Boxing Day tsunami of 2004
0:01:46 > 0:01:49which caused destruction around the Indian Ocean.
0:01:53 > 0:01:57On the morning of December 26th, 2004,
0:01:57 > 0:02:01a huge underwater earthquake ripped apart the seafloor
0:02:01 > 0:02:03northwest of Sumatra, Indonesia.
0:02:09 > 0:02:12When it subsided, no-one had any idea
0:02:12 > 0:02:15that the tremors had generated something even more deadly -
0:02:15 > 0:02:17a tsunami.
0:02:19 > 0:02:22A chain of waves fanned out across the Indian Ocean,
0:02:22 > 0:02:25travelling at the speed of a jet plane,
0:02:25 > 0:02:29hitting coastlines all around the Indian Ocean.
0:02:31 > 0:02:35The images of waves and death were unforgettable.
0:02:35 > 0:02:37I watched these images,
0:02:37 > 0:02:41amazed at how easily people's lives and homes were swept away.
0:02:41 > 0:02:45The tsunami had hit the nearest shores with such force
0:02:45 > 0:02:50it rose to over 60 feet, and surged inland for up to three miles.
0:02:50 > 0:02:52It destroyed everything in its path.
0:02:58 > 0:03:00Leaving a devastated Sumatra behind,
0:03:00 > 0:03:03the tsunami continued towards Thailand.
0:03:10 > 0:03:12SHOUTING
0:03:15 > 0:03:18The waves arrived faster than people could run,
0:03:18 > 0:03:21hurling them against buildings and trees
0:03:21 > 0:03:24and then snatching them out to sea.
0:03:29 > 0:03:33Meanwhile, the westbound waves roared across the Indian Ocean,
0:03:33 > 0:03:38slamming into Sri Lanka and even as far as the East African coastline.
0:03:39 > 0:03:42What's incredible is that the tsunami didn't stop there.
0:03:42 > 0:03:47It was so powerful that it travelled around the whole world for 40 hours.
0:03:47 > 0:03:53By the end, the Boxing Day tsunami had claimed more than 225,000 lives,
0:03:53 > 0:03:55in 11 different countries,
0:03:55 > 0:03:58from as far afield as Indonesia and South Africa.
0:04:17 > 0:04:21So, just what makes tsunami waves so different
0:04:21 > 0:04:25and so much more destructive than ordinary storm waves?
0:04:26 > 0:04:31Well, an ocean wave is caused by the effect of the wind on the surface of the sea.
0:04:36 > 0:04:40But a tsunami is triggered when a huge volume of water,
0:04:40 > 0:04:47not just on the surface but right down to the ocean floor, is shifted in one sudden violent motion.
0:04:47 > 0:04:53This rapid movement can happen after a volcanic eruption or a landslide,
0:04:53 > 0:04:56or an underwater earthquake.
0:05:00 > 0:05:04When an earthquake, for example, cracks the ocean floor,
0:05:04 > 0:05:06one side of the fault is thrust up.
0:05:06 > 0:05:11This then pushes up the whole body of water above the fracture as well,
0:05:11 > 0:05:15creating a wave on the surface of the sea that becomes a tsunami.
0:05:19 > 0:05:23In mid-ocean, the ripples of a tsunami have a small wave height
0:05:23 > 0:05:25and a very long wavelength.
0:05:25 > 0:05:29That's the distance from the front of the wave to the back of the wave
0:05:29 > 0:05:33and this can be hundred of miles long.
0:05:33 > 0:05:35But as the tsunami reaches land,
0:05:35 > 0:05:38it goes through a frightening transformation.
0:05:38 > 0:05:42From the shore, the first sign that something is wrong may be the water
0:05:42 > 0:05:46along the beach being sucked back toward the source of the tsunami.
0:05:46 > 0:05:49This is called "drawback".
0:05:50 > 0:05:53Then, as the tsunami itself nears land,
0:05:53 > 0:05:56the shallow water acts like a brake,
0:05:56 > 0:05:59slowing the front of the wave dramatically,
0:05:59 > 0:06:03but the back of the wave, hundreds of miles behind, is still travelling fast.
0:06:03 > 0:06:05It now catches up,
0:06:05 > 0:06:09causing the front of the wave to rear up into a wall of water.
0:06:10 > 0:06:15But there is worse to come. Instead of breaking onshore,
0:06:15 > 0:06:18the whole length of the wave sweeps onto land,
0:06:18 > 0:06:21engulfing everything in its path.
0:06:21 > 0:06:25And that's what happened on Boxing Day 2004.
0:06:35 > 0:06:37A few weeks later, I visited Thailand,
0:06:37 > 0:06:42one of the worst hit areas, and I was shocked by what I found there.
0:06:42 > 0:06:45I guess it was the first time I realised the devastation
0:06:45 > 0:06:48that can be caused by a wall of water.
0:06:48 > 0:06:51For a geologist like me, it was obvious that some truly
0:06:51 > 0:06:55catastrophic geological event had happened to create a tsunami.
0:06:55 > 0:06:59And indeed it was caused by a huge earthquake.
0:06:59 > 0:07:02But this was no ordinary earthquake.
0:07:04 > 0:07:07And to understand just how different this earthquake was,
0:07:07 > 0:07:12a group of scientists set off across the Indian Ocean to study it.
0:07:12 > 0:07:16They wanted to find actual evidence of the earthquake on the sea floor
0:07:16 > 0:07:20to work out how it had caused such a huge tsunami.
0:07:20 > 0:07:24What they were to discover on this expedition would shock them.
0:07:25 > 0:07:30But first, they would have to actually find the fracture in the Earth's crust.
0:07:33 > 0:07:37Below the ship lies a vast undersea chain of mountains,
0:07:37 > 0:07:39as high as the Alps.
0:07:39 > 0:07:41They've been pushed up over millions of years
0:07:41 > 0:07:45by the movement between two giant tectonic plates.
0:07:47 > 0:07:51Tectonic plates are slabs of the Earth's crust colliding together,
0:07:51 > 0:07:54and they're often the cause of deep ocean earthquakes,
0:07:54 > 0:07:57where one plate is pushed underneath the other.
0:07:58 > 0:08:00Somewhere below this spot, the sea bed
0:08:00 > 0:08:05ruptured for many hundreds of miles on Boxing Day 2004.
0:08:05 > 0:08:09This is where the tsunami was born.
0:08:09 > 0:08:11Using remote equipment,
0:08:11 > 0:08:15scientists are now able to scan the ocean bed in great detail.
0:08:15 > 0:08:17Oh, we came down.
0:08:17 > 0:08:20BEEPING We are at the bottom.
0:08:20 > 0:08:24It didn't take long before they quickly identified
0:08:24 > 0:08:26a dramatic geological feature.
0:08:28 > 0:08:30The line they had found
0:08:30 > 0:08:34looked like it could be a fracture caused by an earthquake.
0:08:41 > 0:08:43As they edged forward,
0:08:43 > 0:08:46the sonar image revealed something very large, dead ahead.
0:08:46 > 0:08:49- Look at the sonar.- Yeah.
0:08:51 > 0:08:54We got a big target in front of us now, about eight metres out.
0:08:58 > 0:08:59Oh, my God.
0:09:02 > 0:09:06It was a sheer vertical cliff thrust out of the sea bed.
0:09:06 > 0:09:09A wall large enough to have displaced a huge amount of water
0:09:09 > 0:09:13and the physical evidence of a massive earthquake.
0:09:16 > 0:09:19But to be sure this wasn't an ancient fault,
0:09:19 > 0:09:22they needed to inspect the top.
0:09:23 > 0:09:26If it showed a sharp, saw-toothed edge,
0:09:26 > 0:09:28it would prove this was a recent fault.
0:09:28 > 0:09:30OK, here we go, here we go up.
0:09:36 > 0:09:41And at the top, there it was - a rough, saw-toothed edge,
0:09:41 > 0:09:44proof that this cliff had been formed recently.
0:09:44 > 0:09:48The scientists had found the Boxing Day earthquake fault.
0:09:49 > 0:09:52But no-one was expecting what they discovered next.
0:09:52 > 0:09:58As they climbed higher, something else loomed out of the darkness -
0:09:58 > 0:10:03a second cliff beyond the first, and this one was enormous.
0:10:14 > 0:10:17These two sheer cliff faces were the evidence that proved
0:10:17 > 0:10:22to the scientists that this had been no ordinary earthquake.
0:10:22 > 0:10:26This was what they call a mega-thrust earthquake.
0:10:26 > 0:10:29Unlike ordinary earthquakes, mega-thrust earthquakes
0:10:29 > 0:10:33rupture over many hundred of miles and are always over a magnitude 9.
0:10:33 > 0:10:36They're the largest earthquakes in the world.
0:10:36 > 0:10:38And what most people don't realise,
0:10:38 > 0:10:41is that when this type of earthquake happens,
0:10:41 > 0:10:43it will create a far bigger tsunami.
0:10:45 > 0:10:48Having seen this dramatic evidence of uplift on the sea floor,
0:10:48 > 0:10:53the scientists were now able to outline the exact chain of events
0:10:53 > 0:10:55that devastated so many lives.
0:10:59 > 0:11:02Deep under the Indian Ocean, two tectonic plates
0:11:02 > 0:11:05had been pushing against each other for hundreds of years.
0:11:05 > 0:11:08The edges of these plates were locked together,
0:11:08 > 0:11:11building enormous stresses and bending the upper plate
0:11:11 > 0:11:13like a giant spring.
0:11:13 > 0:11:16And on Boxing Day 2004,
0:11:16 > 0:11:20this pressure reached breaking point.
0:11:28 > 0:11:33It happened with such enormous power that it was a mega-thrust event.
0:11:37 > 0:11:42The fault started to rupture, shooting upwards by as much as 40ft.
0:11:44 > 0:11:47At twice the speed of a bullet,
0:11:47 > 0:11:52the plates unzipped over a distance of more than 750 miles.
0:11:52 > 0:11:56It lifted the sea bed and the entire ocean above.
0:11:57 > 0:11:59Billions of tons of seawater,
0:11:59 > 0:12:02forced upward by the movement of the sea bed
0:12:02 > 0:12:05now flowed away from the fault.
0:12:05 > 0:12:08On the surface, the displaced water fanned out
0:12:08 > 0:12:10as a series of giant ripples.
0:12:11 > 0:12:16The tsunami began to travel at up to 500 mph.
0:12:19 > 0:12:23And so what triggered the Boxing Day tsunami was no ordinary earthquake -
0:12:23 > 0:12:25it was a rare mega-thrust earthquake
0:12:25 > 0:12:29that had set in motion this wave of destruction.
0:12:37 > 0:12:42The violence of the Indian Ocean tsunami showed us just how destructive these waves are.
0:12:42 > 0:12:48But this tsunami did one further unexpected thing that had nothing to do with destruction -
0:12:48 > 0:12:51it created a moment of revelation.
0:12:51 > 0:12:55In one brief instant, the remains of an ancient city
0:12:55 > 0:12:59lost just off the coast of India were revealed.
0:12:59 > 0:13:02And that's the subject of my next story -
0:13:02 > 0:13:07the legend of Mahabalipuram, the lost temples and the tsunami.
0:13:16 > 0:13:20Mahabalipuram is a beautiful complex of temples
0:13:20 > 0:13:24that sits near an ancient port city on the east coast of India.
0:13:24 > 0:13:27Built around the seventh century,
0:13:27 > 0:13:31only a precious few of the original temples have stood the test of time.
0:13:31 > 0:13:36One of the remaining temples is known as the Shore Temple,
0:13:36 > 0:13:39as it sits dangerously close to the coastline.
0:13:39 > 0:13:43Local fishermen tell an interesting story about this temple.
0:13:44 > 0:13:47The legend says that the Shore Temple is in fact
0:13:47 > 0:13:51the seventh temple of a series, called The Seven Pagodas.
0:13:51 > 0:13:54These temples are said to have once lined the shore,
0:13:54 > 0:13:56and according to the myth,
0:13:56 > 0:14:00they were so beautiful that the Gods grew jealous, and they sent a flood
0:14:00 > 0:14:03that submerged six of the temples below the waves.
0:14:06 > 0:14:12This left only one temple still standing on the coast - the Shore Temple that we can see today.
0:14:12 > 0:14:16But this wasn't to be the last we would hear of the six lost pagodas.
0:14:19 > 0:14:22On the morning of Boxing Day 2004, the tsunami reached
0:14:22 > 0:14:26the East Indian coastline and reared up on Mahabalipuram.
0:14:26 > 0:14:30Standing near the beach was a group of fishermen.
0:14:30 > 0:14:34They looked on as the sea retreated for up to half a kilometre,
0:14:34 > 0:14:40drawing back in the characteristic way just before a tsunami strikes.
0:14:40 > 0:14:44In the few short minutes that it took for the sea to retreat from the shore,
0:14:44 > 0:14:48tourists and fishermen stared spellbound
0:14:48 > 0:14:51by what the receding waters had revealed.
0:14:51 > 0:14:56They swore they had seen the six lost temples of Mahabalipuram.
0:15:08 > 0:15:10The onlookers claim that for several minutes,
0:15:10 > 0:15:14the lost temples had been revealed by the receding ocean.
0:15:16 > 0:15:20And then they were gone, as the wave swept up the shoreline
0:15:20 > 0:15:23engulfing everything these people had seen.
0:15:27 > 0:15:31Leaving everyone wondering, I guess, if they'd dreamt it all.
0:15:36 > 0:15:38So no-one is able to say for sure
0:15:38 > 0:15:42if the tsunami had revealed the lost temples of the myth.
0:15:42 > 0:15:44But I'd like to believe it's true,
0:15:44 > 0:15:49that for a few magical moments, those people on the beach
0:15:49 > 0:15:53saw the remaining temples of The Seven Pagodas.
0:15:53 > 0:15:56Whatever they saw, it's now under the water,
0:15:56 > 0:15:59and presumably out of sight for ever.
0:16:03 > 0:16:06Our next tsunami takes us way back in time,
0:16:06 > 0:16:09back to the age of the dinosaurs.
0:16:09 > 0:16:14And it wasn't triggered by an earthquake or any other natural force on THIS planet,
0:16:14 > 0:16:16the trigger for my next tsunami...
0:16:16 > 0:16:18came from outer space.
0:16:29 > 0:16:33Long, long ago, in fact 65 million years ago,
0:16:33 > 0:16:38one of the most catastrophic events this planet has ever seen happened.
0:16:40 > 0:16:43An enormous meteor struck the earth -
0:16:43 > 0:16:45a meteor the size of San Francisco.
0:16:59 > 0:17:03This is the meteor that many believe wiped out the dinosaurs
0:17:03 > 0:17:05by creating massive climactic change.
0:17:13 > 0:17:17But my story isn't about whether or not the meteor wiped out
0:17:17 > 0:17:20the dinosaurs or even whether it caused any change in the climate.
0:17:22 > 0:17:28The surprising detail that most people don't realise about this meteor strike
0:17:28 > 0:17:31is that it must have created a gigantic tsunami.
0:17:31 > 0:17:36And that's because when it hit the Earth, it struck not on land but on the water.
0:17:36 > 0:17:39It must have been the mother of all tsunamis.
0:17:45 > 0:17:50In 1991, scientists discovered the meteor's ancient impact site
0:17:50 > 0:17:52near the Gulf of Mexico.
0:17:52 > 0:17:56It had struck just off the coast of Mexico's Yucatan Peninsula.
0:17:57 > 0:18:00The crater dug into the ocean floor,
0:18:00 > 0:18:03was 112 miles across
0:18:03 > 0:18:05and 20 times as deep as the Grand Canyon.
0:18:09 > 0:18:14The meteor must have been six miles wide.
0:18:15 > 0:18:19So what kind of tsunami did this impact cause?
0:18:19 > 0:18:24Well, it would've created something very different from an ordinary tsunami.
0:18:26 > 0:18:30Travelling at over 700 miles a minute, the meteor impact
0:18:30 > 0:18:36would've created an incredible fireball, equivalent to billions of Hiroshima bombs exploding.
0:18:39 > 0:18:43The sheer force of the impact will have vaporised the water,
0:18:43 > 0:18:48releasing steam that will have blown a hole in the ocean.
0:18:51 > 0:18:55The meteor carved out this huge cavity in the sea floor.
0:18:55 > 0:18:59And then the sea that rushed in to fill the crater rose up,
0:18:59 > 0:19:02creating a colossal wall of water.
0:19:06 > 0:19:09When this wall of water then collapsed,
0:19:09 > 0:19:13it sent out a very unusual kind of tsunami wave,
0:19:13 > 0:19:16as high as the seafloor was deep.
0:19:16 > 0:19:20What's different is that it will have created a rather unique chain of tsunamis.
0:19:20 > 0:19:25And that's because the process will have continued oscillating inside the cavity,
0:19:25 > 0:19:28like the water sloshing around in a bath,
0:19:28 > 0:19:32creating not one but many gigantic tsunami waves.
0:19:39 > 0:19:44This chain of waves will then have radiated out, hitting coastlines thousands of miles away
0:19:44 > 0:19:48and travelling up to 100 miles inland,
0:19:48 > 0:19:51destroying everything in its way.
0:20:01 > 0:20:06We'll never know how many dinosaurs were killed by the tsunami itself
0:20:06 > 0:20:10rather than the climate change that would have followed.
0:20:10 > 0:20:14But one thing's for sure - this wasn't just one of the biggest meteor impacts,
0:20:14 > 0:20:17this was most likely one of the largest tsunamis ever.
0:20:17 > 0:20:21It must have created the most unbelievable spectacle.
0:20:21 > 0:20:23And who witnessed it? The dinosaurs.
0:20:37 > 0:20:41Our next story takes us to the myth of Atlantis,
0:20:41 > 0:20:44the legendary tale which Plato wrote
0:20:44 > 0:20:48about a magnificent civilisation which sank below the sea.
0:20:48 > 0:20:54Some scientists believe that they've found the island which might've been the inspiration for Plato's story.
0:20:54 > 0:20:59And, of course, at the heart of the tale is a gigantic tsunami.
0:21:05 > 0:21:07Over 2,000 years ago,
0:21:07 > 0:21:12the Greek philosopher Plato wrote a story about a super civilisation
0:21:12 > 0:21:15which lived on the mythical island of Atlantis.
0:21:15 > 0:21:19In Plato's story, the Atlantians ruled the Mediterranean.
0:21:19 > 0:21:22But, "In a single day and night of misfortune",
0:21:22 > 0:21:26Atlantis and all its inhabitants were swallowed by the sea.
0:21:30 > 0:21:33But could there be a true catastrophic event from history
0:21:33 > 0:21:37that prompted Plato to invent the story of Atlantis?
0:21:37 > 0:21:39Well, perhaps.
0:21:41 > 0:21:45Some scientists now believe that Plato may have been inspired
0:21:45 > 0:21:48by what happened to the Minoans on the island of Crete.
0:21:49 > 0:21:53The Minoans were the first great European civilisation.
0:21:53 > 0:21:58They flourished 5,000 years ago, long before Plato.
0:21:58 > 0:22:01They built palaces of the finest architecture
0:22:01 > 0:22:03and were ruled by powerful kings.
0:22:03 > 0:22:07Minoan artists recorded their lives in stunning frescoes.
0:22:07 > 0:22:11What's more, their fleet ruled the Mediterranean.
0:22:11 > 0:22:16But about 3,500 years ago, it all came to an abrupt end.
0:22:19 > 0:22:21Over a few generations,
0:22:21 > 0:22:25this great civilisation was wiped from the pages of history.
0:22:25 > 0:22:29For archaeologists, it had always been a complete mystery.
0:22:29 > 0:22:35What had happened to the Minoans? No-one could understand why they had disappeared so abruptly.
0:22:36 > 0:22:40But then they found an unexpected clue on the hill sides of Crete.
0:22:42 > 0:22:45High above sea level, they discovered sea shells.
0:22:45 > 0:22:47Wow, look at that!
0:22:47 > 0:22:51They found shells in places they should never have been.
0:22:52 > 0:22:55They guessed that a tsunami could have put them there.
0:22:55 > 0:22:58So they set about looking for the geological event
0:22:58 > 0:23:01that could have caused such a tsunami.
0:23:02 > 0:23:08They dated the organic matter in the surrounding sediment and came up with a very interesting date -
0:23:08 > 0:23:11around 1630 BC.
0:23:11 > 0:23:14That's 3,500 years ago.
0:23:14 > 0:23:17At this moment, the penny dropped.
0:23:17 > 0:23:21Because this date is about the time of one of the most cataclysmic
0:23:21 > 0:23:24geological events of the ancient world.
0:23:24 > 0:23:26An event we know created a huge tsunami -
0:23:26 > 0:23:30the eruption of the volcano in Santorini.
0:23:37 > 0:23:41Over the course of a few days, this monstrous volcano
0:23:41 > 0:23:46belched ash, gas and rock up to 25 miles into the atmosphere.
0:23:51 > 0:23:56Eventually the huge magma chamber collapsed, and the sea rushed in.
0:24:01 > 0:24:05The result was an even more cataclysmic explosion,
0:24:05 > 0:24:10now considered one of the most explosive volcanic eruptions in history.
0:24:15 > 0:24:18All the debris eventually plunged into the sea.
0:24:18 > 0:24:21As it hit the water, the sea will have risen up,
0:24:21 > 0:24:23creating a massive wall of water.
0:24:32 > 0:24:35This colossal wave must have then raced across the sea,
0:24:35 > 0:24:38consuming anything in its way.
0:24:42 > 0:24:46In only 20 minutes, it will have reached the island of Crete,
0:24:46 > 0:24:49lying directly south of the volcano.
0:24:50 > 0:24:53The Minoan people will have heard the explosions,
0:24:53 > 0:24:57but will have no idea what was heading towards them.
0:24:57 > 0:25:00There would have been no chance of escape.
0:25:19 > 0:25:23When it hit the shore, it reared up 60ft in the air
0:25:23 > 0:25:26and engulfed everything in its path.
0:25:32 > 0:25:36It would have instantly drowned tens of thousands of people,
0:25:36 > 0:25:38swallowing them up in one enormous wave
0:25:38 > 0:25:41then dragging them back out to sea.
0:25:53 > 0:25:56It must have devastated the island.
0:25:56 > 0:26:00And yet it won't have wiped the Minoans out all together.
0:26:00 > 0:26:02There would have been survivors.
0:26:03 > 0:26:06Many of them will have run to high ground.
0:26:06 > 0:26:10But the wave will have affected them in a more sinister way -
0:26:10 > 0:26:13it will have covered the fields in salt water
0:26:13 > 0:26:15and the crops will have failed.
0:26:15 > 0:26:17The Minoans could not have fished
0:26:17 > 0:26:21as the volcano may well have polluted the sea.
0:26:23 > 0:26:27Many would have starved and fought with each other to survive.
0:26:28 > 0:26:31We know that within a short time of this event,
0:26:31 > 0:26:34the Minoans had disappeared completely.
0:26:34 > 0:26:38The end of Europe's first great civilisation
0:26:38 > 0:26:41devastated by one natural disaster.
0:26:43 > 0:26:47So, if the dramatic ending of the Minoans was indeed linked to the massive eruption
0:26:47 > 0:26:51at Santorini and the huge tsunami that followed,
0:26:51 > 0:26:56then maybe it was the story that inspired Plato to write the tale of Atlantis.
0:26:56 > 0:27:00I would say this is as good an explanation, of how an island civilisation
0:27:00 > 0:27:03can be lost to the sea, as we will ever get.
0:27:09 > 0:27:12So far we've covered stories from around the world,
0:27:12 > 0:27:16but actually 80% of tsunamis happen just in the Pacific.
0:27:16 > 0:27:20So if you happen to be an island in this vast ocean with these forces
0:27:20 > 0:27:24of destruction let loose all around you, you're in deep trouble.
0:27:24 > 0:27:30That's why the tsunami capitals of the world are Hawaii and Japan.
0:27:36 > 0:27:40Most of us think of tsunamis as being rare random events
0:27:40 > 0:27:42that can happen anywhere, in any ocean.
0:27:42 > 0:27:47But surprisingly, some places are constantly bombarded by them.
0:27:49 > 0:27:51Of all the oceans of the world,
0:27:51 > 0:27:54the Pacific has the most frequent tsunamis.
0:27:54 > 0:27:58In fact, four out of every five tsunami happen in the Pacific Ocean.
0:28:06 > 0:28:09So just why is the Pacific so prone to tsunamis?
0:28:11 > 0:28:16Well, unlike all the other oceans of the world, the basin of the Pacific Ocean is encircled
0:28:16 > 0:28:20by a zone of frequent earthquakes and volcanic eruptions.
0:28:20 > 0:28:26These are the result of the shifting and colliding of the Earth's plates in this particular area.
0:28:26 > 0:28:29They call it the Pacific Ring of Fire.
0:28:29 > 0:28:33When there's an earthquake or a volcanic eruption along this rim,
0:28:33 > 0:28:38it can trigger a tsunami that will then rip across the entire ocean.
0:28:46 > 0:28:49And if you're an island in the middle of the Pacific,
0:28:49 > 0:28:53you'll be bombarded by all of these waves from every direction.
0:28:54 > 0:28:57And that's what happens to one set of islands
0:28:57 > 0:29:00right in the middle of the danger zone.
0:29:00 > 0:29:05Hawaii may be a paradise on Earth for surfers and sun worshippers,
0:29:05 > 0:29:10but they have been struck by an unbelievable 137 tsunamis
0:29:10 > 0:29:13in the past 200 years, from all directions.
0:29:15 > 0:29:21These are rare images of a tsunami that hit Hawaii in 1946.
0:29:21 > 0:29:27It was caused by an earthquake in Alaska, 2,500 miles away.
0:29:27 > 0:29:28Within five hours,
0:29:28 > 0:29:31it had sped across the Pacific Ocean and hit Hawaii,
0:29:31 > 0:29:34killing 159 people.
0:29:36 > 0:29:40Within 12 years, Hawaii was struck three more times.
0:29:46 > 0:29:50In 1960, the largest earthquake ever recorded
0:29:50 > 0:29:53occurred off the coast of Chile.
0:29:54 > 0:29:59It generated a tsunami that headed straight across the Pacific towards Hawaii.
0:30:02 > 0:30:04Within 15 hours of the earthquake,
0:30:04 > 0:30:08this tsunami crashed into the Hawaiian coastline,
0:30:08 > 0:30:11killing 61 people.
0:30:12 > 0:30:17These events happen so frequently, it's no wonder that Hawaii is called
0:30:17 > 0:30:20one of the tsunami capitals of the world.
0:30:23 > 0:30:25But Hawaii has one advantage.
0:30:25 > 0:30:29Because of its location, right in the middle of the Pacific,
0:30:29 > 0:30:32it takes tsunamis several hours to reach it.
0:30:32 > 0:30:38Which means that Hawaii has usually got enough time to issue a warning and clear the coastal areas.
0:30:38 > 0:30:43But that's not the case for Japan which, for one key reason,
0:30:43 > 0:30:46often only gets a few minutes' warning.
0:30:47 > 0:30:50And this is because Japan sits almost on some of the most
0:30:50 > 0:30:53active faults lines in the Pacific Ring of Fire.
0:30:53 > 0:30:57These faults are so close to Japan that if an earthquake happens here,
0:30:57 > 0:31:02it can create a tsunami that will hit Japan within minutes.
0:31:03 > 0:31:07This means those living near to the coast are given little warning,
0:31:07 > 0:31:10and often the wave arrives before they have time to run away.
0:31:20 > 0:31:25And this is why the Japanese death toll from tsunamis is one of the world's highest.
0:31:25 > 0:31:29Tragically, tens of thousands of people have lost their lives
0:31:29 > 0:31:31to tsunamis since records began.
0:31:32 > 0:31:35It's no wonder the Japanese people
0:31:35 > 0:31:38are now perhaps the most mindful of the power of the ocean.
0:31:42 > 0:31:45Having been regularly bombarded by tsunamis,
0:31:45 > 0:31:50Hawaii and Japan have become the centre of advanced warning systems,
0:31:50 > 0:31:53systems that have already saved many lives.
0:31:53 > 0:31:57Within minutes of an earthquake anywhere in the Pacific,
0:31:57 > 0:31:59scientists can assess the size of the quake,
0:31:59 > 0:32:05calculate the risk of a tsunami and, if necessary, issue a warning.
0:32:12 > 0:32:16But even with a warning system, both these island communities
0:32:16 > 0:32:20will always be in the path of every tsunami that has crossed the Pacific.
0:32:25 > 0:32:30In the end, these islands will always be in the wrong place,
0:32:30 > 0:32:31at the wrong time.
0:32:34 > 0:32:37And now for a real rarity.
0:32:37 > 0:32:40A tsunami that happened in a place where they never normally occur.
0:32:40 > 0:32:43It happened in Britain.
0:32:43 > 0:32:48It was one of Britain's worst natural disasters and at the time,
0:32:48 > 0:32:49it was a media sensation.
0:32:49 > 0:32:53In fact, the only reason we know so much about it,
0:32:53 > 0:32:56is because it was the first tabloid coverage of a tsunami.
0:32:56 > 0:33:01But it wasn't in the 20th century, or even in the 19th -
0:33:01 > 0:33:03it was 400 years ago.
0:33:10 > 0:33:13Who would have thought that we in Britain
0:33:13 > 0:33:15may have had our own tsunami?
0:33:15 > 0:33:20In fact, they're so rare here that we've only ever had three in recorded history.
0:33:20 > 0:33:24And this is because Britain sits in a fairly safe geological area.
0:33:24 > 0:33:29But in 1607, we were hit by what scientists believe
0:33:29 > 0:33:32was either a tsunami or a massive storm surge.
0:33:32 > 0:33:35It caused a media sensation,
0:33:35 > 0:33:38and this was how the media of the time covered it.
0:33:50 > 0:33:54These pamphlets reveal the full horror of the wave
0:33:54 > 0:33:58that struck the counties of Somerset, Gwent and Monmouthshire,
0:33:58 > 0:34:03along the Bristol Channel on January 20th, 1607.
0:34:07 > 0:34:11But what on earth caused this rare disaster off our shores?
0:34:11 > 0:34:15Some scientists believe a fault line that's rarely active
0:34:15 > 0:34:17shifted off the coast of Ireland.
0:34:22 > 0:34:25It displaced enough water to generate a tsunami.
0:34:27 > 0:34:31Moving at speed, the wave would have started to head
0:34:31 > 0:34:33in the direction of the Bristol Channel.
0:34:38 > 0:34:42We know from the pamphlets that it happened at dawn.
0:34:42 > 0:34:45People were just waking and starting their days.
0:34:49 > 0:34:54At nine o'clock, their lives were thrown into chaos.
0:34:56 > 0:34:59A huge wall of water hit the shores
0:34:59 > 0:35:01and surged inland towards their villages.
0:35:16 > 0:35:21Eyewitness accounts in the pamphlets report that the wave travelled faster
0:35:21 > 0:35:24than a greyhound can run.
0:35:29 > 0:35:35It was a time when very few people knew how to swim and many drowned.
0:35:43 > 0:35:46The survivors clung to the steeples of churches
0:35:46 > 0:35:49and to the roofs of the few buildings that were left standing.
0:35:52 > 0:35:56It swamped entire villages, people and livestock.
0:35:58 > 0:36:02It had swept inland for up to 200 square miles
0:36:02 > 0:36:05and took the lives of 2,000 people.
0:36:05 > 0:36:08News of the disaster travelled fast.
0:36:08 > 0:36:10And just like today,
0:36:10 > 0:36:12the first to arrive at the scene were the media...
0:36:12 > 0:36:14hungry for a story.
0:36:14 > 0:36:17Then, as now, disaster sells.
0:36:26 > 0:36:29In these cruel waters, many men, women and children lost their lives...
0:36:29 > 0:36:33..an overflowing of water and forcible breaches made into the firm land...
0:36:33 > 0:36:37The sudden terror whereof struck such an amazed fear into all the inhabitants...
0:36:37 > 0:36:39Flocks of sheep are destroyed...
0:36:39 > 0:36:44Everyone prepared himself ready to entertain the last period of his life...
0:36:44 > 0:36:47Dead bodies float to the surface and are continually taken up...
0:36:47 > 0:36:49The whole country shall feel the smart.
0:36:51 > 0:36:56Today, we're now able to explain the causes of tsunamis with science.
0:36:56 > 0:37:00But it's clear from these pamphlets what the media at the time
0:37:00 > 0:37:02believed caused the event.
0:37:02 > 0:37:07To their minds, God had sent this as an act of retribution.
0:37:07 > 0:37:11For them, God sends weather and God sends waves.
0:37:14 > 0:37:18Divine vengeance or not, these pamphlets have allowed us
0:37:18 > 0:37:21to piece together the awful events of that morning.
0:37:21 > 0:37:24And the 17th century media coverage
0:37:24 > 0:37:28recorded one of the worst ever natural disasters to hit our shores.
0:37:34 > 0:37:39My next story is one of the best kept wartime secrets from World War Two.
0:37:39 > 0:37:42It reads like the plot line of a James Bond novel.
0:37:42 > 0:37:45But I assure you it's not fiction.
0:37:45 > 0:37:48This is a story of the development of a bomb.
0:37:48 > 0:37:52But not just any old bomb - a bomb that would trigger a tsunami.
0:38:03 > 0:38:04The war in the Pacific.
0:38:06 > 0:38:09For several years during the Second World War,
0:38:09 > 0:38:11much of the Pacific was a battleground,
0:38:11 > 0:38:15with fierce fighting between the Allies and the Japanese,
0:38:15 > 0:38:16not just on the mainland,
0:38:16 > 0:38:20but also on many of the thousands of tiny islands
0:38:20 > 0:38:22scattered across the Pacific Ocean.
0:38:22 > 0:38:25The Japanese had captured many of these islands
0:38:25 > 0:38:30and were so well entrenched, it felt like they couldn't be defeated.
0:38:30 > 0:38:33The terrain was difficult and there were huge casualties.
0:38:34 > 0:38:37So the Allies were keen to explore new ideas about how to fight,
0:38:37 > 0:38:41without risking so many of their troops.
0:38:41 > 0:38:46They wondered if there was a way of fighting the Japanese here which didn't involve soldiers at all.
0:38:48 > 0:38:53It was in 1944 that the idea first began to dawn on allied generals
0:38:53 > 0:38:56that there might be a simpler way to wipe out the enemy.
0:38:56 > 0:39:00That it might be possible to create artificial tsunamis
0:39:00 > 0:39:02by exploding bombs in the ocean.
0:39:02 > 0:39:06The plan was that these man-made tsunamis could be set off
0:39:06 > 0:39:08in the direction of the Japanese-occupied islands
0:39:08 > 0:39:11and drown enemy soldiers.
0:39:14 > 0:39:20Codenamed Project Seal, this plan was considered so significant at the time
0:39:20 > 0:39:24that the Allies classified these documents as "top secret".
0:39:24 > 0:39:27And they have only been recently revealed.
0:39:27 > 0:39:29The mastermind of this project
0:39:29 > 0:39:32was to be an Australian, Professor Thomas Leech.
0:39:32 > 0:39:35And he became obsessed with building a tsunami bomb.
0:39:37 > 0:39:41He was convinced he could create a wave 40 feet high
0:39:41 > 0:39:43that would travel three miles inland,
0:39:43 > 0:39:47swamping enemy-held beaches and drowning the enemy.
0:39:47 > 0:39:49And so the experimenting began.
0:39:52 > 0:39:55His team didn't just use explosives out at sea,
0:39:55 > 0:39:59they also built a special pond as a laboratory to test their bomb.
0:40:02 > 0:40:06It was thought that at a certain depth, underwater explosions
0:40:06 > 0:40:09might generate surface waves much larger than usual.
0:40:09 > 0:40:15So they planted underwater explosives and detonated them.
0:40:16 > 0:40:21But on the first day, this idea was blown right out of the water.
0:40:23 > 0:40:27No matter what the depth, the waves formed were negligible.
0:40:29 > 0:40:32Professor Leech then came up with a new idea.
0:40:32 > 0:40:37He decided the best way was to detonate explosives on a raft on the surface of the water.
0:40:37 > 0:40:39EXPLOSION
0:40:39 > 0:40:44And when they tried it, it did produce a few encouraging waves.
0:40:47 > 0:40:51But as he started to increase the size of the explosions,
0:40:51 > 0:40:54he found little increase in the size of the waves.
0:40:54 > 0:40:58And from then on, as the experiments continued to fail,
0:40:58 > 0:41:04Professor Leech's science and data also became suspect.
0:41:09 > 0:41:11By the end of seven months,
0:41:11 > 0:41:14he'd carried out an incredible 4,000 experiments.
0:41:14 > 0:41:17But again, every single one of them failed.
0:41:17 > 0:41:23Not one explosion did any more than agitate the upper levels of the pond.
0:41:23 > 0:41:28Finally, our Professor Leech decided on the biggest experiment of all.
0:41:28 > 0:41:33He planned to carry out a huge test with 2,000 tons of explosives
0:41:33 > 0:41:38in an inlet with the exact same conditions as Tokyo Bay.
0:41:42 > 0:41:45But this experiment never happened.
0:41:45 > 0:41:51Top military scientific advisers were by now deeply concerned by the failure of his experiments.
0:41:51 > 0:41:54They looked over Leech's calculations
0:41:54 > 0:41:56and could see they were flawed.
0:41:56 > 0:41:59Some of his crucial equations were wrong.
0:41:59 > 0:42:02One adviser said the amount of explosives needed to create
0:42:02 > 0:42:07a tsunami were so vast that it would be impractical and would never work.
0:42:10 > 0:42:13Project Seal was closed down.
0:42:17 > 0:42:20The failure of the project was kept a secret...
0:42:20 > 0:42:22until now.
0:42:23 > 0:42:27And that was the end of one of the most unlikely tsunami stories that I've ever come across.
0:42:34 > 0:42:37Many of us are brought up on tales from the Bible.
0:42:37 > 0:42:41And my next story is a biblical tale that we're all familiar with -
0:42:41 > 0:42:44it's the story of Moses.
0:42:44 > 0:42:48But what some people may not know is that it's been linked to a tsunami.
0:42:55 > 0:42:58According to the Exodus story,
0:42:58 > 0:43:04around 35,000 years ago, Moses led his people out of slavery in Egypt.
0:43:04 > 0:43:07But as the Hebrews left Egypt,
0:43:07 > 0:43:09Pharaoh changed his mind about letting them go.
0:43:11 > 0:43:15So Pharaoh sent an army of 600 chariots in pursuit.
0:43:15 > 0:43:18And here's the part we all remember in the Bible.
0:43:18 > 0:43:21So as to save Moses and his followers,
0:43:21 > 0:43:26God parted the Red Sea so they could all escape across dry land.
0:43:26 > 0:43:28And then the waters returned.
0:43:28 > 0:43:32The sea closed over Pharaoh's army and drowned them.
0:43:35 > 0:43:37That's the Bible story we all know,
0:43:37 > 0:43:40but there's a twist to the Moses story.
0:43:41 > 0:43:45Some experts now believe that instead of crossing the Red Sea,
0:43:45 > 0:43:49Moses and his followers actually crossed a marshy area
0:43:49 > 0:43:52north of that once known as the Reed Sea.
0:43:52 > 0:43:56It was thought to be just east of the Nile Delta
0:43:56 > 0:44:00and most importantly, near the coast of the Mediterranean Sea.
0:44:00 > 0:44:03If you read the Bible in the original Hebrew,
0:44:03 > 0:44:05the word 'red' is mistranslated.
0:44:05 > 0:44:09In the Hebrew bible, Moses and his people
0:44:09 > 0:44:13cross the "Yam Suph" - this means the Sea of Reeds.
0:44:14 > 0:44:16So, not the Red Sea, but the Reed Sea.
0:44:16 > 0:44:21And not a narrow seaway, but a shallow, marshy area near the Mediterranean coast.
0:44:23 > 0:44:26Now you would think that parting the Reed Sea and then flooding it again
0:44:26 > 0:44:29could only be achieved through divine intervention.
0:44:34 > 0:44:38But there is a way that nature can perform exactly the same thing.
0:44:38 > 0:44:41And of course, it involves a tsunami.
0:44:42 > 0:44:45And this is how nature can do it.
0:44:48 > 0:44:54One of the largest of all volcanic eruptions took place 3,500 years ago,
0:44:54 > 0:44:57around the time that some experts date the Moses story.
0:44:57 > 0:45:01It was that massive volcanic eruption at Santorini,
0:45:01 > 0:45:04the one that devastated the Minoan civilisation on Crete.
0:45:07 > 0:45:12The eruption and collapse of Santorini would've been so violent,
0:45:12 > 0:45:15it would've displaced a huge body of water, creating tsunamis.
0:45:16 > 0:45:20But crucially, when the sea rushed in to fill the void,
0:45:20 > 0:45:24it would've sucked water in from all the surrounding coastlines...
0:45:24 > 0:45:25even from the Nile Delta.
0:45:27 > 0:45:32It's the drawback effect that happens just before a tsunami hits.
0:45:32 > 0:45:36As the sea was sucked away from coastal areas, billions of gallons
0:45:36 > 0:45:40of water would have been siphoned off the marshy Reed Sea in Egypt,
0:45:40 > 0:45:43drying it out for up to 20 minutes.
0:45:43 > 0:45:47It would have created the same effect as God parting the waves.
0:45:51 > 0:45:55Then suddenly, the tsunami itself would have arrived on the shore,
0:45:55 > 0:45:59flooding several miles inland and gushing up the river valleys.
0:46:06 > 0:46:12Creating exactly the same effect as the waters returning and drowning Pharaoh's army.
0:46:13 > 0:46:18If the Santorini eruption really did produce this type of tsunami in Egypt,
0:46:18 > 0:46:21it would have been remembered for generations,
0:46:21 > 0:46:25and may well have been the inspiration for this great story.
0:46:27 > 0:46:30But it's also an example of how the forces of nature
0:46:30 > 0:46:33can achieve an effect so unbelievable
0:46:33 > 0:46:35that it seems like an act of God.
0:46:38 > 0:46:41My next tsunami is truly extraordinary
0:46:41 > 0:46:44because it's the highest wave ever recorded,
0:46:44 > 0:46:47higher than any skyscraper on Earth -
0:46:47 > 0:46:50it was half a kilometre high.
0:46:50 > 0:46:54What's even more incredible is that a father and son, out on their boat,
0:46:54 > 0:46:56not only witnessed the wave,
0:46:56 > 0:46:59they surfed it and lived to tell the tale.
0:47:11 > 0:47:13It all happened in a peaceful-looking inlet
0:47:13 > 0:47:17on the northeast shore of the Gulf of Alaska.
0:47:17 > 0:47:20This is the scene of the highest wave ever recorded.
0:47:20 > 0:47:26The cause of the wave turned out to be something that took scientists completely by surprise.
0:47:26 > 0:47:30The wave reached an astonishing 520m,
0:47:30 > 0:47:33higher than the tallest building on Earth.
0:47:33 > 0:47:36And what's more, there were witnesses.
0:47:39 > 0:47:42On a clear and calm summer evening in 1958,
0:47:42 > 0:47:47Howard Ulrich and his son were on their boat inside this bay.
0:47:47 > 0:47:49The date was...
0:47:49 > 0:47:52July 9th, 1958.
0:47:53 > 0:47:57We came into Lituya Bay about eight o'clock in the evening.
0:47:57 > 0:47:59My son was with me.
0:48:00 > 0:48:04I was eight years old at the time and being a child like I was,
0:48:04 > 0:48:06I was halfway asleep as well.
0:48:09 > 0:48:10At approximately 10.15pm,
0:48:11 > 0:48:15there was a large rumbling noise from up at the head of the bay.
0:48:26 > 0:48:28It was like a big loud noise from...
0:48:28 > 0:48:32over in this direction towards the mountains over there.
0:48:40 > 0:48:42There was a slight pause.
0:48:42 > 0:48:45I thought that everything was over with...
0:48:45 > 0:48:49but some movement caught my attention out of the corner of my eye
0:48:49 > 0:48:55and so I looked directly up there and what I observed was a, er...
0:48:55 > 0:48:57like an atomic explosion.
0:49:13 > 0:49:16After this big flash came a huge wave.
0:49:16 > 0:49:18It looked like just a big wall of water.
0:49:25 > 0:49:29He threw me a life preserver and he said, "Son, start praying."
0:49:31 > 0:49:34You're looking at death and this is exactly my first thought.
0:49:46 > 0:49:50When the wave hit us, I did feel the boat all of a sudden
0:49:50 > 0:49:53start shooting upwards, skywards.
0:49:58 > 0:50:04I had 40 fathoms of anchor chain and it started running out off the boat.
0:50:04 > 0:50:08Came to the end of the 40 fathoms, just snapped it like a string.
0:50:11 > 0:50:15And then we were free, but we were still on the front of the wave.
0:50:18 > 0:50:22We were swept up over the land and up above the trees.
0:50:22 > 0:50:25That's where I assumed that we were going to end up.
0:50:26 > 0:50:29But instead, they rode the front of the tsunami
0:50:29 > 0:50:33as it carried them high above the trees for hundreds of metres,
0:50:33 > 0:50:36before washing them back into the bay.
0:50:36 > 0:50:39We still have the original 1958 conversation
0:50:39 > 0:50:42between Howard Ulrich and the coastguard after it was all over.
0:51:03 > 0:51:09I had never heard or seen of anything like this. It was unbelievable.
0:51:09 > 0:51:12I couldn't imagine what could have caused anything.
0:51:12 > 0:51:17I kept wondering just what mechanism could cause something like that.
0:51:22 > 0:51:27A scientist flew over Lituya Bay the following day and filmed this footage of the devastation.
0:51:27 > 0:51:30When he finally saw what had caused the wave,
0:51:30 > 0:51:32it came as a complete surprise.
0:51:35 > 0:51:4090 million tons of rock and ice had fallen in a massive landslide
0:51:40 > 0:51:42into the head of the bay.
0:51:42 > 0:51:45Amazingly, scientists had never before realised
0:51:45 > 0:51:48landslides could cause a tsunami.
0:51:48 > 0:51:52This cascade hit the water with a mighty impact
0:51:52 > 0:51:57and released enough energy to create a wave surge so high and powerful,
0:51:57 > 0:52:02it stripped trees and soil for up to half a kilometre up the slopes.
0:52:03 > 0:52:08At this height, the wave would have swamped the tallest skyscraper on Earth.
0:52:08 > 0:52:1150 times higher than a normal tsunami,
0:52:11 > 0:52:14it was greater than any wave heard of in history.
0:52:14 > 0:52:17This wall of water surged down the bay,
0:52:17 > 0:52:19picking up Howard Ulrich's boat.
0:52:19 > 0:52:23Surfing the front of the highest wave ever recorded,
0:52:23 > 0:52:28father and son unbelievably got away with their lives.
0:52:33 > 0:52:38The Lituya Bay tsunami taught us that massive landslides can cause tsunamis.
0:52:38 > 0:52:42That might mean we can work out where big tsunamis might happen.
0:52:42 > 0:52:46Which is why scientists are looking around the world's coastline
0:52:46 > 0:52:49for places where there are unstable slopes
0:52:49 > 0:52:52that might send giant landslides into the ocean.
0:52:52 > 0:52:55And that's why I'm here on La Palma in the Canaries.
0:52:55 > 0:52:58Because there's some evidence that that...
0:52:58 > 0:53:03whole slope of the volcano behind me might one day collapse into the sea.
0:53:03 > 0:53:08How it will happen is the subject of my final story.
0:53:15 > 0:53:18The Canary Islands are a chain of volcanic islands
0:53:18 > 0:53:22lying just off the coast of North Africa in the Atlantic Ocean.
0:53:22 > 0:53:25One of the most active of these is the island of La Palma.
0:53:25 > 0:53:29And it's this very landscape that some scientists say
0:53:29 > 0:53:34will one day cause havoc and devastation across the Atlantic.
0:53:35 > 0:53:38These scientists predict that this side of the island
0:53:38 > 0:53:40will collapse into the ocean,
0:53:40 > 0:53:44creating a tsunami of titanic proportions,
0:53:44 > 0:53:47far bigger than anything ever witnessed before.
0:53:47 > 0:53:50The island is made up of two volcanoes.
0:53:50 > 0:53:53This one in the south is called the Cumbre Vieja,
0:53:53 > 0:53:56and is not only still active, but very unstable.
0:54:01 > 0:54:04We know this because of something that happened
0:54:04 > 0:54:08after the last eruption of this volcano in 1949.
0:54:18 > 0:54:22About a week or so after the eruption in 1949,
0:54:22 > 0:54:24something extraordinary happened here.
0:54:24 > 0:54:29There were several very strong earthquakes, and this crack began to open.
0:54:29 > 0:54:34The west side of the volcano, over here, started to collapse and slide towards the sea,
0:54:34 > 0:54:37which is something you don't normally see on a volcano.
0:54:37 > 0:54:41What it means is that the volcano is unstable,
0:54:41 > 0:54:44which is why some scientists believe that this whole side of the volcano
0:54:44 > 0:54:49may one day, during an eruption, fall into the sea.
0:54:49 > 0:54:54But scientists can't tell how many more times this volcano has to erupt
0:54:54 > 0:54:58before its western flank finally collapses.
0:54:58 > 0:55:04But if it does happen, it would be one of the worst natural disasters in human history.
0:55:05 > 0:55:07A huge section of southern La Palma,
0:55:07 > 0:55:13weighing half a trillion tons, would fall into the Atlantic.
0:55:39 > 0:55:42The impact of this colossal landslide
0:55:42 > 0:55:45would displace a vast body of water.
0:55:47 > 0:55:50It would unleash much more than just a tsunami.
0:55:50 > 0:55:53It would be a mega-tsunami -
0:55:53 > 0:55:56a wave that would start out well over half a kilometre high.
0:56:12 > 0:56:16The wave would then radiate out across the Atlantic,
0:56:16 > 0:56:18racing towards North America,
0:56:18 > 0:56:22reaching the east coast in just eight hours.
0:56:22 > 0:56:25The La Palma mega-tsunami, this mighty wall of water,
0:56:25 > 0:56:28would hit Boston, New York,
0:56:28 > 0:56:32then all the way down the coast to Miami and the Caribbean.
0:56:34 > 0:56:36If you were standing on a beach,
0:56:36 > 0:56:40the very first effects you'd probably see is drawback.
0:56:40 > 0:56:44The ocean would suddenly just pull away. But in the background,
0:56:44 > 0:56:49you'd be looking at a wall of water that would keep coming towards you.
0:57:05 > 0:57:09It would engulf the whole US east coast,
0:57:09 > 0:57:15sweeping away everything in its path up to 14 miles inland.
0:57:15 > 0:57:19Every city on the shoreline would be destroyed.
0:57:27 > 0:57:31So when will this catastrophic event happen?
0:57:31 > 0:57:36Nobody knows. Nobody knows even when the next eruption will happen,
0:57:36 > 0:57:42and it'll probably take many more eruptions before this flank of the volcano finally collapses.
0:57:42 > 0:57:44So scientists can't say when,
0:57:44 > 0:57:49but some are convinced that one day it will really happen.
0:57:49 > 0:57:51If this event were ever to occur,
0:57:51 > 0:57:56it would create a tragedy on an unimaginable scale.
0:57:56 > 0:57:59Just because we've never experienced such an event,
0:57:59 > 0:58:01we believe it'll never happen to us.
0:58:02 > 0:58:05But from the age of the dinosaurs to the present day,
0:58:05 > 0:58:07the tsunami stories I've told you
0:58:07 > 0:58:11have shown us that they've always happened.
0:58:11 > 0:58:13So, there's one thing we can be sure of -
0:58:13 > 0:58:16tsunamis will continue to strike us at any time...
0:58:18 > 0:58:19..and from anywhere.
0:58:44 > 0:58:46Subtitles by Red Bee Media Ltd
0:58:46 > 0:58:48E-mail subtitling@bbc.co.uk