0:00:11 > 0:00:1416th of August 2004.
0:00:15 > 0:00:19A freak storm strikes the village of Boscastle in Cornwall.
0:00:19 > 0:00:24Without warning, a wall of water tears through the village,
0:00:24 > 0:00:28destroying houses and sweeping 80 cars into the sea.
0:00:30 > 0:00:33The damage will run into millions.
0:00:36 > 0:00:39Nearly 100 people are airlifted from their flooded homes,
0:00:39 > 0:00:43their lives saved by 21st-century technology.
0:00:51 > 0:00:56400 years earlier, the peoples of the Bristol Channel were less fortunate.
0:00:57 > 0:01:04On the 20th January 1607, another freak wave swept across the lowlands of the south-west.
0:01:10 > 0:01:15It too came without warning and left 2,000 dead in its wake.
0:01:16 > 0:01:21Yet for centuries this apocalyptic flood has been forgotten
0:01:21 > 0:01:26and only now are scientists piecing together the evidence left behind.
0:01:26 > 0:01:28Was it just a huge storm?
0:01:28 > 0:01:33Or was the killer wave of 1607 in fact a British tsunami?
0:02:01 > 0:02:04It is the winter of 1607.
0:02:04 > 0:02:11The Stuart dynasty is not yet four years old and Britain is at last a united kingdom under James I.
0:02:17 > 0:02:22This year will see the premiere of Shakespeare's Anthony and Cleopatra.
0:02:22 > 0:02:27In the new North American colonies, Pocahontas will save John Smith's life.
0:02:29 > 0:02:32In London, the Thames will freeze over.
0:02:33 > 0:02:38The most remarkable event, however, will be forgotten -
0:02:38 > 0:02:41the greatest flood in Britain's history.
0:02:43 > 0:02:52On Tuesday 20th of January, as dawn breaks over the villages and hamlets of Somerset, Gwent and Monmouthshire,
0:02:52 > 0:02:54there is no sign of an impending tragedy.
0:02:55 > 0:03:02In these backwaters of the Bristol Channel, life is dominated by the steady rhythms of agriculture.
0:03:03 > 0:03:07Sheep and cattle farming are the lifeblood of the local economy.
0:03:12 > 0:03:17The people are relatively prosperous, hardworking and God-fearing.
0:03:20 > 0:03:27Around nine o'clock in the morning, this simple, ordered life will be thrown into chaos.
0:03:36 > 0:03:44In Llanwern, Monmouthshire, four miles from the sea, the servants of Mistress Van prepare her lunch.
0:03:48 > 0:03:55In Goldcliff, of Gwent, William Tapp, church warden, makes ready for morning service.
0:03:58 > 0:04:01In Berrow, Somerset, a milkmaid heads for work.
0:04:03 > 0:04:07In the same village, John Stoles,
0:04:07 > 0:04:12father of five, wakes late, unaware he will not survive the day.
0:04:14 > 0:04:16No-one has any warning.
0:05:07 > 0:05:10In an age when few people knew how to swim,
0:05:10 > 0:05:14any caught in the freezing waters will be lucky to survive.
0:05:23 > 0:05:30One Mistress Van, a gentlewoman of good sort, her house being four miles from the sea,
0:05:30 > 0:05:34having seen the approaching waters, was surprised by them and destroyed
0:05:34 > 0:05:38even before she could get into the higher rooms of her house,
0:05:38 > 0:05:40such was the speed of the waters.
0:05:51 > 0:05:54There was a maid that went to milk her cows in the morning
0:05:54 > 0:05:58but before she had fully ended her business, the vehemence of the waters increased
0:05:58 > 0:06:02and so suddenly environed her, she could not escape thence
0:06:02 > 0:06:07but was forced to make shift up to the top of a high bank to save herself.
0:06:19 > 0:06:22John Stoles was thrown down by the water.
0:06:22 > 0:06:26He himself, with three or four of his children, drowned.
0:06:28 > 0:06:32His wife and one of her sons were found the next day and survived.
0:06:36 > 0:06:42According to eyewitness accounts, the dead perished in a mountainous wall of water
0:06:42 > 0:06:47and that after the wave came a torrent that swept across the fields,
0:06:47 > 0:06:52creating an inland sea of over 200 square miles.
0:06:55 > 0:06:59The waters have washed many onto the rocks of poverty and misery.
0:06:59 > 0:07:03But so have they brought some profit,
0:07:03 > 0:07:08for seafaring men, I might call them thieves, come daily now in boats
0:07:08 > 0:07:12and get richly laden with goods which they find swimming in the waters.
0:07:14 > 0:07:17Many dead persons are sadly found floating
0:07:17 > 0:07:20and as yet cannot be known who they are.
0:07:21 > 0:07:27When the waters receded ten days later, they left behind a scene of devastation.
0:07:27 > 0:07:302,000 dead.
0:07:30 > 0:07:33Hundreds of thousands of sheep and cattle drowned.
0:07:33 > 0:07:37The local economy destroyed.
0:07:39 > 0:07:43Men that were rich in the morning when they rose from their beds
0:07:43 > 0:07:46were made poor before noon of the same day.
0:07:48 > 0:07:56To this day, 20th of January 1607 remains the largest and most destructive flood in British history.
0:08:04 > 0:08:10But until now, a full explanation for the disaster has not been scientifically researched.
0:08:10 > 0:08:15Just why so many lost their lives remained a mystery.
0:08:15 > 0:08:22When I was young I remember seeing in some books in a library some woodcuts of the flood -
0:08:22 > 0:08:27pictures of people stranded up on top of high trees, on top of roofs,
0:08:27 > 0:08:32rabbits even clinging to the back of sheep as they were floating along.
0:08:32 > 0:08:40Very dramatic scenes which I've shown in my lectures to students for, well, getting on for ten years,
0:08:40 > 0:08:43as a good example of what a storm can do.
0:08:43 > 0:08:48Simon Haslett is a professor of geography from Bath Spa University College.
0:08:48 > 0:08:51He grew up with the folklore of the flood.
0:08:51 > 0:08:57You can't really imagine what it must have been like, other than the human tragedy of it.
0:08:57 > 0:09:02Quite catastrophic and how people actually dealt with that is amazing.
0:09:02 > 0:09:08For most of his life, Simon has accepted the conventional explanation of 1607.
0:09:08 > 0:09:15A lot of the commentators on the 1607 flood have put it down to a storm coming in
0:09:15 > 0:09:21and as a child you just accept what you're being told by the scientists and the historians
0:09:21 > 0:09:23and you don't really question it.
0:09:26 > 0:09:30Attributing the flooding of 1607 to a storm makes sense.
0:09:30 > 0:09:32The area is famous for them.
0:09:33 > 0:09:36- NEWS REPORTER: - The sea defences have been breached
0:09:36 > 0:09:39at more than a dozen points along the coast
0:09:39 > 0:09:42and there's now concern about tonight's high tide.
0:09:42 > 0:09:44On December the 13th 1981,
0:09:44 > 0:09:49the sea defences along the Somerset coast were breached by a storm-driven tidal surge
0:09:49 > 0:09:54and the lowlands behind them were inundated, as they had been in 1607.
0:09:54 > 0:09:57As the waves swept through seaside villages during the night,
0:09:57 > 0:10:00they carried away cars and parts of houses.
0:10:00 > 0:10:04Officials say it was a miracle no-one was killed or seriously injured.
0:10:04 > 0:10:08The lowlands of the Bristol Channel have always been prone to flooding.
0:10:08 > 0:10:15Much of the area is below high-tide mark and has been protected by sea walls for 600 years.
0:10:15 > 0:10:20This weakness is exposed when heavy storms coincide with high tides.
0:10:20 > 0:10:24It's exactly what happened in 1981.
0:10:24 > 0:10:26Low pressure over the Irish Sea
0:10:26 > 0:10:29drew a huge volume of water to the mouth of the Bristol Channel.
0:10:29 > 0:10:32A combination of high tide and strong winds
0:10:32 > 0:10:37then forced the swollen waters back against the Somerset coast.
0:10:37 > 0:10:40What should have been just a high seasonal tide
0:10:40 > 0:10:43became a storm surge.
0:10:44 > 0:10:47As a local man, Simon is well aware of the dangers.
0:10:47 > 0:10:52If you live on the Levels, you're always aware of the vulnerability.
0:10:52 > 0:10:56Although it looks tranquil, it actually has a record of disaster
0:10:56 > 0:11:00and if a big event comes in, a big flood comes in,
0:11:00 > 0:11:05then it can actually tragically lead to a huge loss of life.
0:11:08 > 0:11:11Fascinated by the scale of the 1607 disaster,
0:11:11 > 0:11:15Simon decides to meet with witnesses of the 1981 flood -
0:11:15 > 0:11:17the biggest in living memory.
0:11:21 > 0:11:25Ken Burrell lives in the same house he did 23 years ago.
0:11:25 > 0:11:30In those days there was a bathroom down there and that's about a foot lower than this room.
0:11:30 > 0:11:35My daughter was going to take a bath and water was actually coming through the bath panel.
0:11:35 > 0:11:38I thought it was a burst pipe, so we said forget about that.
0:11:38 > 0:11:40Came in and maybe...
0:11:40 > 0:11:4520 minutes, half an hour later, that's when I started looking out through here.
0:11:45 > 0:11:50Coming dusk and the first thing I saw was a row of black things coming towards me.
0:11:50 > 0:11:53And that was actually the leaves being picked up by the water,
0:11:53 > 0:11:57not that fast, maybe a fast walking pace.
0:11:57 > 0:12:02Stood here and saw the water deepening and then getting a little bit deeper
0:12:02 > 0:12:04and then it started to come up to the window.
0:12:04 > 0:12:07That's when I said to my wife and kids, "Time to get upstairs."
0:12:07 > 0:12:10And what damage did it do to your property?
0:12:10 > 0:12:13Apart from knocking furniture about,
0:12:13 > 0:12:16it just brought in a slow, steady flood level.
0:12:16 > 0:12:18A flood level I marked on the doorjamb the day after.
0:12:18 > 0:12:24I carved that mark in the doorjamb which was the height of the water throughout this room.
0:12:24 > 0:12:30Further up the coast, Simon meets Thelma Blake, a farmer at the front line of the storm.
0:12:32 > 0:12:37Much of Thelma's land is below high-tide level and is only protected by the sea defences.
0:12:37 > 0:12:44It just come cascading down the bank and on through, like.
0:12:44 > 0:12:49I mean you just had to make sure all the cattle run was all right, you know.
0:12:49 > 0:12:54- So just hoping it wasn't going to get any deeper.- Right.
0:12:54 > 0:12:57Thelma lost just six sheep in the flood that night.
0:12:59 > 0:13:041981 was the worst tidal surge flooding in 100 years.
0:13:04 > 0:13:09Yet the church in Kingston Seymour reveals how little damage it actually did.
0:13:10 > 0:13:16In the 1981 flood, the church here wasn't flooded. It was dry.
0:13:16 > 0:13:21In 1607, the water was five feet high here in the church
0:13:21 > 0:13:27and most of that water actually was here on the ground for about ten days afterwards.
0:13:29 > 0:13:36The level of the 1607 flood is recorded in five other churches on both sides of the Bristol Channel -
0:13:36 > 0:13:41all record flood levels that make 1981 pale in comparison.
0:13:41 > 0:13:471607 was a local disaster unlike any other before or since.
0:13:48 > 0:13:51News of the catastrophe spread fast.
0:13:51 > 0:13:57As the waters retreated, the media of the day arrived to report on the event.
0:13:57 > 0:14:01The waters as they did come down on their first entry.
0:14:01 > 0:14:04So much did happen. So much terrible devastation.
0:14:04 > 0:14:08They recorded the graphic accounts of destruction and lives lost
0:14:08 > 0:14:13that appear in six different pamphlets written and published at the time.
0:14:13 > 0:14:20It is from these eyewitness accounts that the full horror of the 1607 flood unfolds.
0:14:21 > 0:14:26Upon Tuesday, being the 20th of January last past,
0:14:26 > 0:14:31there happened an overflowing of waters and forcible breaches made into the firm land,
0:14:31 > 0:14:37the sudden terror whereof struck such an amazed fear into the hearts of all the inhabitants
0:14:37 > 0:14:43that everyone prepared himself ready to entertain the last period of his life's destruction.
0:14:43 > 0:14:48The pamphlets revel in the details of death and destruction.
0:14:52 > 0:14:57Then, as now, disaster sells.
0:14:57 > 0:15:02It may be the case that the pamphleteers exaggerate in order to profit,
0:15:02 > 0:15:07although I don't think we really know enough about the 17th-century book trade
0:15:07 > 0:15:09to be certain that the bigger the lie you told,
0:15:09 > 0:15:11the more copies you would sell.
0:15:11 > 0:15:14That might be an attitude we're importing from the 21st century
0:15:14 > 0:15:16back into the 17th century.
0:15:16 > 0:15:22The quantity of detail about local geography for example, suggests that this just isn't made up.
0:15:22 > 0:15:26One pamphlet is clearly written by a local as a pamphlet.
0:15:26 > 0:15:32He has written it to present a local testimony about the flood and the damage done.
0:15:36 > 0:15:38This is a direct communication
0:15:38 > 0:15:43from an author who was, if not an eyewitness, at least close to eyewitnesses.
0:15:43 > 0:15:46These pamphlets are published upon occasion
0:15:46 > 0:15:50and they're published because something sensational has happened.
0:15:50 > 0:15:55Usually what we find reported is based upon fact.
0:16:02 > 0:16:06Page by page, they set out a chilling roll call of the villages
0:16:06 > 0:16:10struck by the wave and of the lives lost.
0:16:13 > 0:16:18In Brean Down stood nine houses and of those seven were consumed
0:16:18 > 0:16:21and with them 21 persons lost their lives.
0:16:21 > 0:16:25All the counties along on both sides of the River Severn,
0:16:25 > 0:16:30from Gloucester to Bristol, which is about some 20 miles, were all overflown.
0:16:32 > 0:16:38In some places six miles over. In some places more, in some less.
0:16:41 > 0:16:4526 parishes in Monmouthshire were inundated
0:16:45 > 0:16:49and in these cruel waters many men, women and children lost their lives.
0:16:51 > 0:16:56There happened such an overflowing of waters into the boroughs of Monmouth, Glamorgan, Carmarthen
0:16:56 > 0:17:00and diverse and sundry other places in South Wales.
0:17:00 > 0:17:07In Bristol, all the houses standing upon the quay near the waterside were all overflown with water.
0:17:07 > 0:17:11Everything lies melted and soaked in grime and salt water.
0:17:16 > 0:17:18Taken in their entirety,
0:17:18 > 0:17:22the pamphlets reveal an unparalleled chronicle of disaster
0:17:22 > 0:17:25and the full extent of the flood.
0:17:25 > 0:17:29Over 200 square miles of land lost to the sea.
0:17:32 > 0:17:38With this information, scientists at the Proudman Oceanographic Laboratory in Liverpool
0:17:38 > 0:17:43can model the precise storm conditions needed to produce the 1607 flood.
0:17:43 > 0:17:441607 is a fascinating event.
0:17:44 > 0:17:48Although we've observed surges in the Bristol Channel before,
0:17:48 > 0:17:50we've never seen one of that magnitude.
0:17:50 > 0:17:55The data is excellent because it allows us to piece together the extent of the flooding
0:17:55 > 0:17:58and also the depth of the flooding at many locations.
0:17:58 > 0:18:05Critical to interpreting the 17th-century measurements is the height of the tide that day.
0:18:06 > 0:18:12The morning of the event, we have a very big tide. It's almost eight metres above ordnance datum.
0:18:12 > 0:18:15That's one of the biggest tides you can get in the Bristol Channel.
0:18:15 > 0:18:20So we know that there was a massive tide on that particular morning.
0:18:20 > 0:18:28Kevin can transform this tide into a storm surge by adding hurricane winds of 80 miles an hour.
0:18:28 > 0:18:33Only then do the flood waters of 1607 become a computer reality.
0:18:33 > 0:18:35The warm colours, the reds and the oranges,
0:18:35 > 0:18:40represent a metre and a half to two metres of extra water due to the surge.
0:18:40 > 0:18:43You can see how that amplifies into the Bristol Channel.
0:18:43 > 0:18:51Ten metres of water above normal sea level. Two billion tons of water were probably involved in the flood.
0:18:53 > 0:19:01Was it this cruel coincidence of high tide and hurricane winds that made 1607 the most deadly of storm surges?
0:19:15 > 0:19:22It seems to be proof positive of the assumptions that for years Simon Haslett took as fact.
0:19:23 > 0:19:27But in 2002, Simon made his own discovery
0:19:27 > 0:19:33and it has forced him to consider a more shocking explanation for the 1607 flood.
0:19:35 > 0:19:42Today, Simon is meeting again with the Australian geologist Ted Bryant, with whom he made that discovery.
0:19:42 > 0:19:45- Hey, hi, Ted. How are you?- Not bad.
0:19:45 > 0:19:47- Easy journey? - Yeah, oh, till we got to Bangkok.
0:19:47 > 0:19:48Yeah? Oh.
0:19:49 > 0:19:54Over the next two weeks they intend to collect evidence from around the Bristol Channel
0:19:54 > 0:19:57that will substantiate their revolutionary theory -
0:19:57 > 0:20:00a theory sparked by a chance discovery in a country church.
0:20:04 > 0:20:10There it is, what we saw two years ago, "The great flood, AD1606".
0:20:10 > 0:20:13Yeah, that's still as impressive as the first time I saw it.
0:20:15 > 0:20:21The date reads 1606 because at the time, the new year did not begin until March.
0:20:21 > 0:20:25Above the inscription, over five foot off the ground,
0:20:25 > 0:20:28is a mark showing the level of the floodwaters.
0:20:28 > 0:20:32But it was what they found inside that really stunned them.
0:20:32 > 0:20:35As they thumbed through a history of the church,
0:20:35 > 0:20:41they came across an extract from one eyewitness account recorded in the pamphlets.
0:20:41 > 0:20:44They describe these waves as mountainous and the line was,
0:20:44 > 0:20:47"Such a smoke as if mountains were on fire
0:20:47 > 0:20:51"and to the view of some it seemed as if myriads of thousands of arrows
0:20:51 > 0:20:53"had been shot forth all at one time."
0:20:53 > 0:20:57So there's obviously sparks coming off this wave.
0:20:57 > 0:21:01After we read this, we looked at each other and said, "That's not a storm."
0:21:01 > 0:21:03That's a description of a tsunami.
0:21:12 > 0:21:15Suddenly, the pamphlets had new significance.
0:21:15 > 0:21:17They may be the only eyewitness accounts
0:21:17 > 0:21:22of one of the world's most destructive natural phenomena striking Britain -
0:21:22 > 0:21:23a tsunami.
0:21:23 > 0:21:28It would explain why the victims of the killer wave of 1607 never stood a chance.
0:21:30 > 0:21:36The terrifying reality of a tsunami stunned the whole world on Boxing Day 2004.
0:21:49 > 0:21:56The Asian tsunami, known to have killed 300,000, was triggered by a submarine earthquake.
0:22:02 > 0:22:09Giant underwater landslides and collapsing volcanoes can also unleash similar disasters.
0:22:11 > 0:22:12For the last 15 years,
0:22:12 > 0:22:18Professor Ted Bryant has been defining the unique character of tsunamis across the globe.
0:22:18 > 0:22:20A tsunami surges over the land,
0:22:20 > 0:22:23so there's an enormous volume of water brought onto the land
0:22:23 > 0:22:26and you don't see that under storm waves.
0:22:26 > 0:22:33Even thousands of miles away from its source, a tsunami can have terrifying destructive power.
0:22:33 > 0:22:40In 1960, a massive earthquake off Chile generated a tsunami ten metres high.
0:22:40 > 0:22:44It travelled across the Pacific Ocean at the speed of a Boeing 707.
0:22:44 > 0:22:45600km an hour.
0:22:53 > 0:22:58And when it got to the other side of the ocean - Japan - that's half a hemisphere away,
0:22:58 > 0:23:03it had enough force to wreck buildings, to drive ships onto the shore
0:23:03 > 0:23:08and there was massive damage right around the whole rim of the Pacific Ocean in 1960
0:23:08 > 0:23:13because of that earthquake-generated tsunami back on the coastline of Chile.
0:23:16 > 0:23:22The eyewitnesses of some tsunamis have observed a strange and distinctive phenomenon.
0:23:22 > 0:23:27They describe the crest of the waves as sparkling with strange lights.
0:23:27 > 0:23:34The last such account was from survivors of the Papua New Guinea tsunami in 1998.
0:23:34 > 0:23:37In Papua New Guinea, the tsunami came at twilight,
0:23:37 > 0:23:43and again there were reports of flames. There were sparks coming off the top of the wave.
0:23:43 > 0:23:45For Ted, the echoes of 1607 are uncanny.
0:23:45 > 0:23:51The Redwick church one is about nine in the morning, it would have been daylight
0:23:51 > 0:23:53and still there's this description of sparks.
0:23:53 > 0:23:56We don't know what causes the sparks
0:23:56 > 0:23:59but it is a characteristic of tsunami waves
0:23:59 > 0:24:04and for Redwick people to see sparks on the top of the wave in broad daylight,
0:24:04 > 0:24:08they were looking at some incredible phenomena coming towards them.
0:24:12 > 0:24:16To Ted Bryant, the pamphlets are clearly describing a tsunami.
0:24:16 > 0:24:20The size, speed and strange sparkling of the wave all fit.
0:24:22 > 0:24:26It seemed as if millions of thousands of arrows had been shot forth all at once...
0:24:26 > 0:24:30Those who saw the mighty torrent approaching say that the waters afar off
0:24:30 > 0:24:36looked to be many yards above the earth and with such smoke as if all the mountains were on fire.
0:24:36 > 0:24:41The like have never, ever been seen or heard of in the memory of man.
0:24:44 > 0:24:48The pamphlets provide a foundation case for a tsunami
0:24:48 > 0:24:53but Simon and Ted need physical proof to back up these chilling voices from the past.
0:24:55 > 0:24:59They set out to scour the coast of the Bristol Channel for evidence.
0:25:01 > 0:25:06At Dunraven Bay in South Wales, hundreds of boulders lie at the foot of the cliffs.
0:25:06 > 0:25:12Some have obviously just dropped off the face but others are less easy to explain.
0:25:12 > 0:25:16Which ones have we done? We've done that one over there, that one over there.
0:25:16 > 0:25:19Have we done that one? All right?
0:25:19 > 0:25:22To the untrained eye, all boulders look the same
0:25:22 > 0:25:27but to Simon, each rock gives up clues to the events of the past.
0:25:27 > 0:25:31This particular boulder has, I'm pretty sure, been moved off the beach.
0:25:31 > 0:25:36It's got some fossils in it, which you don't normally associate with the older limestones
0:25:36 > 0:25:38which you find on the cliffs here,
0:25:38 > 0:25:42so it looks like this quite big boulder has come from over there on the beach.
0:25:42 > 0:25:50The force of water needed to move seven-ton boulders could easily be produced by a tsunami.
0:25:50 > 0:25:54The way the boulders are lying gives Simon and Ted another clue.
0:25:56 > 0:25:59OK, that's 270 degrees west.
0:25:59 > 0:26:03We're finding a lot of these boulders are actually sloping back
0:26:03 > 0:26:07because they come to rest in an orientation
0:26:07 > 0:26:10that offers least resistance to the flow going over the top of them
0:26:10 > 0:26:13and we've got a lot of these boulders over here
0:26:13 > 0:26:16which all point back in the same or similar direction.
0:26:16 > 0:26:19A storm operates in splashes.
0:26:19 > 0:26:23You've got a wave breaking and storms can move the odd boulder
0:26:23 > 0:26:25and can fling boulders up onto the top of cliffs
0:26:25 > 0:26:30but given that we've got so many boulders in a train - what we call a boulder train -
0:26:30 > 0:26:37and they're all pointing back in the same direction. That suggests to us a constant flow over time.
0:26:39 > 0:26:42By measuring the size and shape of the boulders,
0:26:42 > 0:26:46Ted can estimate what height of tsunami would have been required to move them.
0:26:46 > 0:26:51The equation we have is one that says, "This boulder is sitting at the edge of the beach.
0:26:51 > 0:26:53"About water level.
0:26:53 > 0:26:56"What force is required to lift it up and move it?"
0:26:56 > 0:27:02And we have equations that relate that to the depth of the water and the height of the tsunami.
0:27:02 > 0:27:08Ted reckons it would only have taken a five-metre tsunami wave to shift these boulders.
0:27:08 > 0:27:14For a storm to do the same thing, they calculate it would have taken a wave at least 20 metres high.
0:27:14 > 0:27:16Over 60 feet.
0:27:16 > 0:27:21Yet the very idea of a tsunami laying waste to the Bristol Channel
0:27:21 > 0:27:26goes against every assumption we have about Britain being geologically safe.
0:27:26 > 0:27:34The widely held view is that storms batter us all the time but tsunamis never come anywhere near Britain.
0:27:34 > 0:27:37But in fact, they do.
0:27:41 > 0:27:477,000 years ago, the entire east coast of Scotland was battered by a mega tsunami.
0:27:47 > 0:27:50It was triggered by a gigantic landslide off Norway.
0:27:50 > 0:27:54On an area of the continental shelf called Storegga,
0:27:54 > 0:27:59billions of tons of sediment plunged from the shallows into the deep.
0:27:59 > 0:28:03The scar of the landslide is still visible in sonar surveys
0:28:03 > 0:28:09and from this evidence Norwegian scientists have calculated the size of the tsunami created by Storegga.
0:28:11 > 0:28:16The wave that hit Scotland 7,000 years ago was 70 foot high.
0:28:20 > 0:28:24Nor are British tsunamis confined to prehistory.
0:28:26 > 0:28:33In 1755, an earthquake off the coast from Lisbon sent a series of tsunamis out into the Atlantic.
0:28:33 > 0:28:37The south-west tip of Cornwall was hit by a three-metre wave.
0:28:37 > 0:28:42If a third tsunami did hit the Bristol Channel in 1607,
0:28:42 > 0:28:46the evidence should be extensive and not just on the shoreline.
0:28:47 > 0:28:51Ted and Simon decide to investigate Rumney Wharf.
0:28:53 > 0:28:5620 years ago, a survey of the marshes by a local archaeologist
0:28:56 > 0:28:59revealed a strange anomaly in the sediment deposits.
0:29:02 > 0:29:07Simon and Ted are hoping it might offer more evidence for a tsunami.
0:29:10 > 0:29:14Well, the marshes here are very muddy and they've been like that for centuries
0:29:14 > 0:29:18but back in the 1980s there was a survey done
0:29:18 > 0:29:23that actually documented a sand layer within the mud deposits.
0:29:25 > 0:29:31If the old survey is correct, the layer of sand should be visible on exposed sections of the marshes.
0:29:31 > 0:29:36The same survey also proposed that the sand layer was left behind
0:29:36 > 0:29:41by a massive surge of water from the sea around 400 years ago.
0:29:41 > 0:29:4320 years on, is the sand layer still there?
0:29:43 > 0:29:47And if so, what clues will it yield to Ted and Simon?
0:29:47 > 0:29:51OK, Ted, I think I've got a dark layer here.
0:29:51 > 0:29:52It's got...
0:29:54 > 0:29:57It's coarse. It's quite sandy.
0:29:58 > 0:30:02It's quite thin, here. It's coming to about ten centimetres.
0:30:02 > 0:30:06Is there any pebbles in it at all? Can we see here?
0:30:06 > 0:30:11No. No. No, but let's follow it round and see if it thickens.
0:30:14 > 0:30:17Just around the corner, they find what they're looking for.
0:30:17 > 0:30:19Gosh, it's got lots of pebbles in it.
0:30:19 > 0:30:22And bits of shell.
0:30:22 > 0:30:24This is heaps thick.
0:30:24 > 0:30:27Not only is it sand but within it you have...
0:30:27 > 0:30:33Well, just here small pebbles and also the little white flecks that you can see in here,
0:30:33 > 0:30:39that's broken-up shell. Shell that's been smashed up and brought in here with the sand and been deposited.
0:30:49 > 0:30:55Whatever force brought the sand here was an event of enormous power.
0:30:55 > 0:30:58And for Ted, the sea shells rule out a storm.
0:30:58 > 0:31:00Yeah, it's a good one.
0:31:00 > 0:31:03It's a pipi, I think.
0:31:03 > 0:31:08In these type of deposits you get them. You might be able to track it back to a source.
0:31:08 > 0:31:10You look around you and there's no beach for miles,
0:31:10 > 0:31:15so that's an indication that this stuff has been transported considerable distance.
0:31:15 > 0:31:21The way some of the flow behaves, it will not abrade the material, so to find something very fragile
0:31:21 > 0:31:26like this in this type of deposit is an indication that we're dealing with tsunami flow.
0:31:27 > 0:31:32Microscopic analysis will provide more evidence of where the sand comes from
0:31:32 > 0:31:34and how it got dumped onto the marshes.
0:31:37 > 0:31:44To calculate the volume of sand deposited, Simon and Ted check how far the layer extends inland.
0:31:44 > 0:31:46That's it. Right.
0:31:52 > 0:31:55- Let's take this up really slow. - Yeah.
0:32:02 > 0:32:04OK, let's see what we've got.
0:32:06 > 0:32:08Sand.
0:32:08 > 0:32:10More sand.
0:32:10 > 0:32:11And then clay.
0:32:11 > 0:32:15So it was about 20cm thick here.
0:32:15 > 0:32:22So it's tapering from whatever that was there, about 40, 45cm thick to about 20 here
0:32:22 > 0:32:26and we peter out inland across the marshes.
0:32:27 > 0:32:30For me, that layer - that layer of sand -
0:32:30 > 0:32:34is such a stark difference to the rest of the estuary.
0:32:34 > 0:32:36The waters of the estuary are full of mud.
0:32:36 > 0:32:40The Severn is one of the muddiest estuaries in Europe and we have marshes.
0:32:40 > 0:32:45That sand layer is out of place. It couldn't have got here unless we had this high-energy event.
0:32:45 > 0:32:51If I came here and we couldn't find our sand layer than I'd have doubts that the tsunami didn't exist.
0:32:51 > 0:32:52It was probably a storm surge.
0:32:52 > 0:32:57But having seen those sand layers, the tsunami's sitting in the back of my mind well and truly.
0:33:00 > 0:33:03At another site, 20 miles away, they find similar evidence.
0:33:03 > 0:33:06Have a look at that.
0:33:06 > 0:33:09And that's sitting right on that land surface.
0:33:09 > 0:33:12We've got to explain how that got there.
0:33:12 > 0:33:15- Well, you wouldn't get that just by floating in.- No.
0:33:15 > 0:33:22In total, Simon and Ted take samples from five separate locations around the Bristol Channel.
0:33:22 > 0:33:28At all five sites, they find sand or gravel deposits and all in a single layer.
0:33:28 > 0:33:32If the occurrence of sand layers in these marshes is due to storms,
0:33:32 > 0:33:34you might expect to find more than one,
0:33:34 > 0:33:37given that we do experience storms quite frequently.
0:33:37 > 0:33:41But we have only got the one layer, which is interesting.
0:33:43 > 0:33:47Back in his lab, Simon can examine the samples in more detail.
0:33:47 > 0:33:52He is looking for microscopic evidence of where the sand originated.
0:33:54 > 0:34:00Meanwhile, Ted heads out to Sully Island, a small outcrop of rock just off Cardiff.
0:34:00 > 0:34:06It would have taken the full brunt of a tsunami moving up the Bristol Channel.
0:34:06 > 0:34:09That's a major erosion.
0:34:09 > 0:34:15Look at the big block over there that's collapsed in and the other rocks straight ahead.
0:34:18 > 0:34:23Once again, big boulders seem to have been picked up and shoved against one another
0:34:23 > 0:34:29by a massive movement of the water and on the headland, the top layer of rock has been eroded away -
0:34:29 > 0:34:33exactly the sort of thing a tsunami could do.
0:34:35 > 0:34:38So the tsunami will bash into this cliff, full force
0:34:38 > 0:34:42and it could carve through the hardest rock.
0:34:42 > 0:34:46It will carve through granites and salicified sandstones -
0:34:46 > 0:34:48very resistant rock.
0:34:48 > 0:34:49It just means nothing to it.
0:34:49 > 0:34:52It just erodes them and it erodes it very quickly.
0:34:52 > 0:34:55And this is as good as any evidence I've seen in New South Wales.
0:34:55 > 0:34:58It's incredibly exciting.
0:34:58 > 0:35:03However, dating the erosion on Sully Island back to 1607 is impossible.
0:35:03 > 0:35:08Dramatic as this big-scale evidence is, it's far from conclusive.
0:35:10 > 0:35:14But at a microscopic level, Simon has made a breakthrough.
0:35:15 > 0:35:17These tiny spiral shells
0:35:17 > 0:35:22are typical of the species that grow in the shallow waters inside the Bristol Channel.
0:35:24 > 0:35:28But these shells are only found at much greater depths -
0:35:28 > 0:35:33out in the open ocean, over 50 miles away from where they were deposited.
0:35:33 > 0:35:37One of the sand layers that we're looking at here is from North Devon
0:35:37 > 0:35:43and it's full of species of microfossils that have come from the Continental Shelf,
0:35:43 > 0:35:47so this sand layer has been transported from out on the open ocean.
0:35:48 > 0:35:50All of Simon and Ted's evidence -
0:35:50 > 0:35:54the boulder movements, the sand deposits and the erosion of headlands -
0:35:54 > 0:35:58reveals the 1607 flood in greater detail than ever.
0:35:58 > 0:36:00Yet they have a problem.
0:36:00 > 0:36:04None of it is unique to a tsunami.
0:36:04 > 0:36:09At the Proudman Laboratory, the same evidence fits their explanation for 1607.
0:36:09 > 0:36:13A storm surge is going to provide some billion tons of water
0:36:13 > 0:36:15rushing across the flood plain
0:36:15 > 0:36:18that's more than capable of picking up enormous rocks
0:36:18 > 0:36:20and large amounts of sediment
0:36:20 > 0:36:22and depositing them a long way from their origin
0:36:22 > 0:36:25and as far as rocks and sediments are concerned,
0:36:25 > 0:36:29they can't distinguish between one large, rushing volume of water and another.
0:36:29 > 0:36:35And whilst the storm surge modelled at the Proudman Laboratory is of record proportions,
0:36:35 > 0:36:40history and the pamphlets themselves do not rule out such a freak event.
0:36:44 > 0:36:51The morning of January the 20th 1607 would indeed have been one of the highest tides on record.
0:36:51 > 0:36:58Furthermore, three of the pamphlets begin their story of the flood by describing stormy weather.
0:36:58 > 0:37:06In the month of January last past, upon a Tuesday, the sea being very tempestuously moved by the winds,
0:37:06 > 0:37:10overflowed his ordinary banks and did drown 26 parishes...
0:37:10 > 0:37:15And upon the highest of the spring, the wind blowing very hard at south-west,
0:37:15 > 0:37:21there was such a flood of tide as the like was never seen in this town.
0:37:21 > 0:37:26But not all of the pamphlets describe the weather of that day as being stormy.
0:37:26 > 0:37:30One of the most detailed reports actually states it was a sunny morning.
0:37:32 > 0:37:37About nine of the clock in the morning, the sun being most fairly and brightly spread,
0:37:37 > 0:37:43the farmers overseeing their grounds and looking to their cattle perceived far off
0:37:43 > 0:37:47huge and mighty hills of water tumbling one over the other.
0:37:49 > 0:37:52Simon has been through the pamphlets time and time again
0:37:52 > 0:37:57and believes the very brevity of their weather descriptions is significant.
0:37:57 > 0:38:01In the pamphlets the weather only gets one or two lines,
0:38:01 > 0:38:05so it seems to me that it wasn't of spectacular proportions.
0:38:05 > 0:38:09There doesn't seem to be an overall impression of a huge storm,
0:38:09 > 0:38:14one that would be necessary to actually cause the flooding that we have recorded.
0:38:14 > 0:38:21Instead, the thing that really stands out for Simon is the detail with which they describe the wave.
0:38:21 > 0:38:25There is an overall theme running through all the pamphlets
0:38:25 > 0:38:32of a destructive event, very violent, disastrous, on a scale that is unprecedented.
0:38:33 > 0:38:40The waters ran with a swiftness so incredible that no greyhound could have escaped by running before them.
0:38:40 > 0:38:43Whole houses were removed from the ground where they stood
0:38:43 > 0:38:46and were floating up and down like ships half sunk,
0:38:46 > 0:38:53which came in such swiftness that the fowls of the air could scarcely fly so fast.
0:38:53 > 0:38:56In contrast, observers of the 1981 storm surge
0:38:56 > 0:39:00remember the flood waters advancing at only a fast walking pace.
0:39:02 > 0:39:04It's a different character altogether.
0:39:04 > 0:39:10Much more violent in 1607, with waters rushing inland at a velocity...
0:39:10 > 0:39:14You know, some of the accounts say faster than a greyhound can run.
0:39:14 > 0:39:21Nowhere is the comparison between the storm surge of 1981 and possible tsunami of 1607
0:39:21 > 0:39:24starker than at the village of Uphill.
0:39:24 > 0:39:31In 1981, the biggest storm floods of the last 100 years barely broke a window.
0:39:31 > 0:39:35In 1607, the same village caught the full force of the wave,
0:39:35 > 0:39:39as recorded in the fate of local landowner, John Good.
0:39:42 > 0:39:47The gentleman with his wife and children got up to the highest room of the house.
0:39:47 > 0:39:53There they sat comforting each other in their misery, hoping they might but go away with their lives.
0:39:53 > 0:39:57Yet even that very desire for life put the gentleman
0:39:57 > 0:40:02in mind to preserve something by which afterwards they might live
0:40:02 > 0:40:08and that was a box of writing, wherein were certain bonds and all the evidence of his lands.
0:40:08 > 0:40:11This box he got with much danger
0:40:11 > 0:40:15and tied it with cords fast to a rafter, hoping there it would be safe.
0:40:21 > 0:40:29But alas, in the midst of his gladness, the sea fell with such violence upon the house
0:40:29 > 0:40:35that it bore away the whole building, rent it in the middle from top to bottom.
0:40:35 > 0:40:38The gentleman in this whirlwind of waves got to a beam
0:40:38 > 0:40:43and clinging to that was carried against his will for some three or four miles.
0:40:45 > 0:40:48There he crept up and sat pouring out his tears
0:40:48 > 0:40:51and to make him desperate in his sorrows
0:40:51 > 0:40:58the tyrannous stream presented him with the tragedy of his dear wife and dearest children,
0:40:58 > 0:41:01wrenched to their deaths by the torrent.
0:41:04 > 0:41:11To the 17th-century mindset, such tragedy was evidence of nothing less than an apocalypse.
0:41:11 > 0:41:14The readers of these pamphlets are not asking themselves,
0:41:14 > 0:41:18"Was this a tidal wave? Was this the consequence of global warming?"
0:41:18 > 0:41:24because the cause for the authors and for the readers is the same.
0:41:24 > 0:41:27This is God. God has sent this. God sends weather. God sends waves.
0:41:27 > 0:41:30So the root cause is the same and that's what's significant.
0:41:30 > 0:41:34SHE SOBS
0:41:36 > 0:41:40A BELL TOLLS
0:41:43 > 0:41:49What is true for them is that this happened
0:41:49 > 0:41:54and that this is a visitation by God. A warning of some kind.
0:41:58 > 0:42:04In these cruel waters, many men, women and children lost their lives.
0:42:04 > 0:42:09Dead bodies float hourly to the surface and are continually taken up.
0:42:10 > 0:42:13Countless flocks of sheep are utterly destroyed.
0:42:15 > 0:42:19The whole country shall feel the smart.
0:42:22 > 0:42:26For Simon and Ted, the apocalyptic character of a tsunami
0:42:26 > 0:42:31matches the testimony of 1607 far more convincingly than a storm surge.
0:42:31 > 0:42:36But without a credible explanation for what triggered the tsunami in the first place,
0:42:36 > 0:42:39Simon and Ted will struggle to persuade others.
0:42:45 > 0:42:50They had assumed that their tsunami was triggered by a submarine landslide
0:42:50 > 0:42:52but they are out of luck.
0:42:52 > 0:42:58Detailed surveys of the continental shelf around Great Britain reveal no evidence of a landslide.
0:42:58 > 0:43:01Their next best hope
0:43:01 > 0:43:06is the possibility that an earthquake on its own could have triggered the tsunami.
0:43:06 > 0:43:13At the British Geological Survey, Dr Roger Musson, head of seismic hazards, assesses that likelihood.
0:43:13 > 0:43:15We're really driven to the conclusion
0:43:15 > 0:43:19that it must have been an earthquake that was quite large
0:43:19 > 0:43:23and produced a tsunami by actually breaking through the sea floor
0:43:23 > 0:43:25and causing a vertical displacement.
0:43:25 > 0:43:29The big surprise is that the sea bed off the south-west tip of Ireland
0:43:29 > 0:43:32is far less stable than commonly imagined
0:43:32 > 0:43:38and is the location of an ancient but massive fault line.
0:43:38 > 0:43:41We still have this old weakness in the crust here
0:43:41 > 0:43:45and it's been suggested that this is exactly the sort of place
0:43:45 > 0:43:49where you could get an anomalously large earthquake happening.
0:43:49 > 0:43:52It's not just an idle theory.
0:43:52 > 0:43:58On the 8th of February 1980, sensors recorded an earthquake from exactly this area.
0:43:58 > 0:44:01It was 4.5 on the Richter Scale -
0:44:01 > 0:44:06not enough to lift the sea floor but violent enough to give fresh impetus to the tsunami theory.
0:44:06 > 0:44:12So we know from geological grounds that this is a probable likely place
0:44:12 > 0:44:17for getting an extra-large earthquake if we're going to get one anywhere around Britain
0:44:17 > 0:44:22and we know from seismological evidence that we've actually had an earthquake here,
0:44:22 > 0:44:25so there is a fault which is moving. It's active.
0:44:25 > 0:44:33So putting a hypothetical large historical earthquake in this spot is not so fanciful.
0:44:33 > 0:44:38To the oral history of the pamphlets, and the geological evidence they've discovered,
0:44:38 > 0:44:42Simon and Ted can finally add a possible cause.
0:44:42 > 0:44:46The final piece of their tsunami theory is in place.
0:44:46 > 0:44:51This, now, is how they believe the killer wave may have struck 400 years ago.
0:44:52 > 0:44:55On the morning of the 20th of January 1607,
0:44:55 > 0:44:59an ancient fault line off the coast of Ireland shifted violently,
0:44:59 > 0:45:04displacing enough water to generate a tsunami.
0:45:14 > 0:45:19Moving at close to 100 miles per hour, the tsunami rushed up the Bristol Channel,
0:45:19 > 0:45:24its force magnified by the high tide and the funnelling effect of the geography.
0:45:24 > 0:45:27As it roared towards its unsuspecting victims,
0:45:27 > 0:45:33it eroded headlands and pushed boulders aside like pebbles.
0:45:39 > 0:45:46A wall of water up to ten metres high rushed over the low-lying sea defences either side of the Channel.
0:45:57 > 0:45:59Now travelling at 30 miles an hour,
0:45:59 > 0:46:03the killer wave bore down on the villages of Somerset and Monmouthshire.
0:46:23 > 0:46:31In one giant slab of water, billions of gallons kept coming with terrible violence.
0:46:36 > 0:46:40The people caught in its path had next to no warning.
0:46:42 > 0:46:48And the force of the waters was such that even those who thought they were safe in their houses,
0:46:48 > 0:46:52they were swept away also and the numbers and numbers of...
0:47:02 > 0:47:05I'm doubly excited now about what we've found.
0:47:05 > 0:47:07We've managed to go right round the estuary
0:47:07 > 0:47:13and we've seen the physical evidence that supports the historical accounts.
0:47:13 > 0:47:17There's nothing at odds there at all and everything is very consistent.
0:47:20 > 0:47:23Whether it's sand on the salt marsh or it's pebbles in the clay
0:47:23 > 0:47:29or it's erosion on the headlands or boulders piled up in key spots, you go for the simplest explanation
0:47:29 > 0:47:35and I can put down most of the signatures we've seen in the past week very easily by one way,
0:47:35 > 0:47:39one process, one point in time, and that's the simplest explanation.
0:47:39 > 0:47:41I think it's a colossal event.
0:47:41 > 0:47:45If it is a storm, it's a big one but if it's a tsunami,
0:47:45 > 0:47:49it could be well within what we've experienced elsewhere in the world.
0:47:49 > 0:47:51We're just not used to it here.
0:47:54 > 0:47:56For the people struck down by the killer wave,
0:47:56 > 0:48:00there is still no definitive answer as to why they died.
0:48:00 > 0:48:04But their fate is not just a historical curiosity,
0:48:04 > 0:48:08for what is not in doubt is the vulnerability of the Bristol Channel lowlands.
0:48:08 > 0:48:15Where once there were only farms and hamlets are now modern towns and many thousands of people.
0:48:15 > 0:48:17Tsunami or storm surge -
0:48:17 > 0:48:19both could happen again.
0:48:19 > 0:48:22Another freak storm would give us some warning.
0:48:22 > 0:48:24A tsunami would not.
0:48:24 > 0:48:27Subtitles by BBC Broadcast 2005
0:48:27 > 0:48:30E-mail us at subtitling@bbc.co.uk