Mega Disasters - Mountain Tsunami

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the chance of seeing an alpine landslide in its moment of creation is too good to miss but for thousands who live in the shadow of Europe's tallest an unaware of the unfolding spectacle it's already too late I immediately thought - dammit for me death is very Joseph ham do you think you're going to die investigators uncover an astonishing plan to control an unstable mountainside and unlock the shocking truth violent is completely and that mate assassin the whole thing was just primed to go disasters don't just happen there a chain of critical events unravel the clues and count down those final seconds from disaster northern Italy the viand Valley October the 9th 1963 workers from Italy's national electric energy agency are having lunch on top of the violent dam today like every day they're watching the slopes enjoying a fantastic natural spectacle as chunks of Montauk slip towards the reservoir locals are also aware of the creeping landslide 11 year-old Jevon Atsuko lives in castle a tiny hamlet directly opposite mount talk people saw the cracks on Montauk and I could see that the adults were alarmed I was worried too a week before my mother told me that she dreamed of suffocating in the water [Music] six kilometers from the dam is the Soviets in a power station where water released from the reservoir turns four giant turbines luigia Vivi's his deputy manager of the plant and has been charting the daily slippage of the mountainside today's movements are so big he wonders if there's been a mistake I got the data about the landslides movement I was surprised and I asked for confirmation from the control room they could see blocks of rock and soil falling into the water what this edci must he seen that in fact the chart showed that the landslide was about to fall anticipating the final slip into the lake dam operators have lowered the water level so that any waves thrown up by the collapse will be contained by the dam wall along the slopes of Mount talk power company officials insist farmers move their animals off the mountainside local priest Don Carlo Honorine II senses the anxiety of the villages she said people react order we knew something but they were all rumors we didn't know if talk would fall much might fallen or even if the dam might collapse in the late afternoon jer vasya's mother sets out to move the families counts my mother I was used to going up with her to stay at home with your granny's and I'll be back tomorrow morning in longer only a small town just two kilometers from the bottom of the dam another school girl Mikayla Coletti is eating supper with her family the atmosphere had been a bit different for a while you could hear strange rumors Michaela's father works at the dam and her mother has been alarmed by what he's told her I heard my mother saying it is better to send children away what did we do that our mum wants to get rid of us my dad replied if we must die because the dam collapses it is better to die together on that Sadie's here at 6 p.m. we were told that the landslide was about to fall meaning and we were asked to go up key personnel from the Power Station are invited to join the engineers on top of the dam to monitor the sly but Luigi has worked to finish I wanted to go off but I told my colleague look unfortunately I need to do this so I stayed well he went up from their privileged position on top of Europe's tallest an Luigi's colleagues expect to be eyewitnesses to the creation of a tsunami like wave up to 20 meters high as the landslide slips into the water in the valley below any rumors about the dam have been forgotten for the night the bars in longer oñate are filled with football fans watching a European Cup game between Real Madrid and Glasgow Rangers [Music] in castle high above the damn chair Vasya is fast asleep the house is engulfed by a terrifying noise it was not like you were hearing the noise from the other side of the mountain you were actually inside it was something immense you know my grandma said it's the end of the world in the village church giancarlo on Irini here is the same overwhelming sand I could see a searchlight lighting up the whole top I saw a black thing it was a shadow of a tall shadow it was rising we're investing a lot of the water blooms reached the top of the bell tower Rochard rain down avvocato I fell to my knees shopping with beer fearing their house may be destroyed Joe vasya's brother tries to save his family he grabbed me by the shoulders and threw me down the stairs took me to the back door and pushed me out Casso is more than 250 meters above the reservoir but is swamped running like crazy because I was really frightened now my instinct telling we do head upwards what're you you think you're going to die below the dam in longer oni street lights go out michaela Coletti is in bed I was pretending to sleep waiting for a kiss from my mom you know my grandmother came into the room and said I'm going to close the shutters a storm is approaching my bed folding in half Miha and I was inside picked up a terrifying speed a 70 meter high wall of water swamps longer Oni and sweeps on down the valley flattening buildings killing hundreds 20 minutes later the floodwater is gone leaving longer Oni a death strewn landscape until medicine I was totally buried in rubble I felt the need to make an effort and lift my arms to touch my face I don't remember much after that longer own a has-been whiteout a rescue effort begins but few survivors are found houses roads the railway line have been swept away or buried in debris yeah I was found sometime after 2:30 a.m. then when they found me completely buried little better with just a hand and foot sticking out michaela is one of 30 children rescued the only one of her family to survive the total loss of life that night is more than 2,000 including 60 workers from the Power Company show no sorry t propio perky they went up to be there when it happened but we were no camicazi they wind up I never came back they died in value in the light of dawn rescue workers are staggered to see that rock and mud have now filled the huge reservoir and a ghostly M shaped scar of freshly exposed limestone identifies where Farland had been just hours earlier fifty years later the landslide scar is still visible and still a focus for geologists struggling to unravel the mechanisms that brought destruction on such a massive scale we are almost at the top of the landslide and this is the failure surface we can see also the other lateral boundary of the landslide that is a big fault and from here to there there is a 1.8 kilometers professor monica karate leads the latest research team the goal of my research is to obtain a three-dimensional model of the landslide to better understand what happened in 1963 even now I am astonished geology will shed light on the landslide mechanism but one thing is already clear the disaster is rooted in man's recent intervention in this valley professor David Pedley leads an international effort to investigate predict and prevent catastrophic landslides understanding the viol disaster has been one of the most important challenges of his career if I aren't in terms of loss of life is the biggest last eye disaster in Europe in the last century or so and it has probably been the most important landslide of all time because it raised our awareness the whole series of issues peddler's findings are unequivocal violent is completely a man-made disaster there's no doubt at all that the violent disaster would not have happened if humans hadn't been involved now by going deep into these investigations we can reveal why 270 million cubic meters of mountainside slid into the violent reservoir and how it managed to kill more than 2,000 people pet li will retrace the steps of the original engineers as they attempted to understand the geology of the valleys and he'll identify the critical mistakes that led to disaster [Music] in 1956 excavation begins for the foundations of the vianden it will block a precipitous gorge to creates one of the deepest man-made lakes in the world and generate hydroelectricity to power Italy's post-war economic boom the chief engineer is Carlos Samantha a world renowned Dam builder this will be his final project before he retires and he knows it'll is spectacular dolomite mountain range offers a unique opportunity the dome lights are a part of the Alps and they basically consist of big lumps of limestone that have been pushed up to form towering pits the steep slopes of the violent valley appear to make it the ideal location for a dam the dam could be relatively narrow and therefore relatively small in terms of width obviously very very tall and hold just from vast volumes of water in the valley behind Samantha and his team of geologists take great care surveying the location where the dams foundations will be built but they pay little attention to the valley upstream that will eventually be flooded in the 1950s the emphasis was very much on getting the engineering design of the dam itself correct and really very little effort was put into understanding the upstream geology it was considered that wasn't really relevant to the dam or to the reservoir Pedley finds their casual attitude all the more alarming given the region's well known geological instability between the mountains in the valleys are much weaker rocks or the sands and clays and shales and the whole system is folded and faulted so it's quite disturbed and that's the classic environment for creating landslides none of this is news to the local population they're constantly vigilant for signs of Rock Falls and landslides [Music] and Matt talk adjacent to the site of the dam has even earned a nickname the walking Mountain construction continues for two years and the 261 meter high dam is almost complete when on March the 22nd 1959 a new reservoir at nearby pontus a suffers a huge landslide creating a 20 meter high tsunami like wave drowning one worker and over topping the dam this was the first time there was an understanding that there was a potentially really damaging effect of big landslides in its center seismic shock through the reservoir industry in northern Italy and it was just this mechanism that caused death and destruction in bay on the mountainside slid into the lake generating a massive tsunami the dam remained intact but the wave swept over it swampy the valley below the hydro industry had underestimated the potential consequences of flooding a valley as a reservoir fills slopes that have been drained into a deep valley for thousands of years become waterlogged for the first time with surprising results rock that appears solid is often made of separate blocks held in place by gravity and friction you have to think of a block rock on the hillside be a bit like about when water level increases the block starts to float it doesn't completely float it just becomes more buoyant and as it becomes more buoyant the friction force the resistance to movement decreases and that makes land sliding much more fearing a repeat of the fatal landslide and tsunami in Pontus a the power company commissioners survey of the banks have we proposed reservoir in the violent valley the project's chief geologist is Professor Leopold Miller and he employs Eduardo Samantha the chief engineer's son and a recently qualified geologist to take on the survey Eduardo walks every inch of the valley making observations of the rock formations when he sees evidence of ancient large-scale movement in the steep slopes close to the dam it looks like the power company's worst fears are confirmed and while those cimento was convinced that there was a big old landslide located on the south bank of the reservoir an old landslide has already moved so the rocks at the base of last night are likely to be much much weaker eduardo fears that flooding the valley could reactivate the landslide which in turn could lead to a catastrophic tsunami repeating the deadly pontus a event on a mega scale the landslide mass that he'd identified was within 100 metres of the dam site itself if Eduardo is correct that it could cause the whole dam project to be abandoned for Eduardo's father Carlos immense ax the news is devastating and he initiates a more detailed investigation if this is the site of a giant ancient landslide evidence will exist in the underground rock strata Engineers dig three balls into the mountainside in the danger zone identified by Eduardo and the geology team look for signs of previous movement shattered rock or unstable layers of clay despite drilling up to 170 meters into the rock they find no evidence of an ancient landslide project leader Carlos immense ax is relieved his chief geological adviser professor Muller is confident the slopes some made of solid immovable blocks of limestone the damn designers come to conclusion that but although there was the potential for small landslides on the banks of the reservoir there was no real danger for large failures in February 1960 with the threat of a destructive landslide discounted Samantha green lights the next phase of the project before handing the dam over to the power company they must confirm its structural integrity by filling the reservoir to the top by October the reservoir is 170 meters deep 91 meters below maximum and the dam is holding up perfectly [Music] but then a setback farmers discover a huge em shaped crack directly above the reservoir [Music] look at the crack that opened up is really large it's about 1,700 meters long it's widening at about three centimeters or so per day it must have been a terrible surprise for the team the power company's fears are realized just days later when a slab of mountainside the size of six football pitches falls into the violent reservoir creating a wave two meters high fortunately nobody is hurt but the rest of this colossal landslide is still in motion and the record reveals a new sense of urgency at the power company from Eduardo's earlier analysis of the rock strata they believe the remaining unstable ground probably penetrates up to 250 meters into the slope making a total volume equivalent to 90 city blocks of 30 story skyscrapers chief engineer Carlo Samantha needs to tame this mountainside before the whole unstable mass slams into the lake and swamps the valley below Samantha's engineering team can think of no way to stop the slide it sheer size makes it impractical to pin it to the mountainside with concrete piles but professor moolah has a hunch he can control how fast the landslide slips into the reservoir and prevent a devastating tsunami he believes that if raising the water level activated the slide lowering the level should slow it down [Music] Carlo Samantha immediately puts Mulas idea to the test and opens floodgates to reduce the water depth moolies theory is simply the dropping the reservoir level will let water drain out of the slopes increasing the friction and anchoring the floating limestone blocks back onto the slope over the next two months the rate of creep slows from three centimeters a day to barely one millimeter a day this big massive landslide slowed down and eventually stopped the consequence was that Muller and cement sir are quite confident that raising the level of Lake again would induce movement and dropping it again would reduce a movement even if they can't permanently stop the landslide the two men are convinced they can control how quickly it slips into the valley Samantha and Muller proposed to ease the giant massive rock into the lake using the depth of water in the reservoir like the accelerator and brake on a car leaving the dam free to begin power generation it's a simple plan but pet li is aghast their understanding of the geology and the mechanisms of movement of of this big mass were were really very poor and yet despite that lack of knowledge they embarked upon this extraordinarily bold plan to try to induce movement the landslide by raising and lowering the lake level Mira's geology team is confident they can detach the whole mass gradually without causing a dangerous tsunami but Carlos immense ax is more cautious he insists on expanding the plan to deal with the worst case scenario where the whole of the landslide falls into the lake in one catastrophic event and a tsunami is created Samantha Commission's a study to find out the maximum safe depth of the reservoir a water level leaving enough damn wall exposed to contain the biggest possible tsunami some ENSO was trying to ensure that the tsunami wouldn't go over the top of the dam but this is 1961 and there are no computers to run a tsunami simulation Carlos team builds a scale model of the dam and runs a series of physical simulations to see a big wave to be the initial experiments suggest the worst case tsunami height of 20 meters so Samantha fixes a maximum reservoir depth leaving the dam with 25 meters of exposed concrete protecting the valley below at last he thinks he has all bases covered Carlos amends ax was still to refine his calculations but before he was able to do so he died suddenly from a brain hemorrhage without the leadership of its visionary chief engineer the scheme is plunged into crisis and the power company puts together a new team to execute the plan and save Samantha's legacy project September the 26th 1963 in the two years since the bypass tunnel was completed the reservoir level has been systematically raised and lowered to coax the landslide down into the flooded Valley and so far the plan has worked two weeks before the disaster the landslide has moved a total of three meters the dam operators are now really quite confident about their ability to control the downslide the reservoir is now the highest it's ever be 245 meters above the base of the dam a fall 10 meters higher than Samantha's maximum safe level there's not much doubt they were genuinely trying to get themselves to a point where the landslide slipped into the lake so really they were pushing the level of the lake as as high as they thought they could get away with their high-risk strategy appears to be paying off and the entire slide is picking up speed flood gates are opened to get the lake down to a safe level before the final form dam operators expect that as seen previously lowering the water level will also slow the slide but this time it's different actually the landslide continued to accelerate this is exactly what they didn't expect so they were really quite baffled by what was going on if the mountain side Falls now their simulations guarantee a tsunami that will spill over the dam wall for two tense weeks the reservoir level is dropped as fast as the operators there without adding to the stresses in the slopes but the landslide continues to accelerate [Music] by October the 9th the mountainside is moving 30 centimeters a day but the reservoir has now dropped to leave 25 meters of exposed concrete and dam operators breathe a sigh of relief sure there's enough wall to catch any wave because the lake level was now below that maximum size of a tsunami that they'd identified they considered the situation was completely safe so safe the power company managers are invited to witness the creation of the tsunami and local people are not alerted to any danger [Music] but instead of the predicted 20 meter tsunami the wave towered over 200 meters above the dam an astonishing 10 times bigger than expected now our investigators reveal why the plan to control the landslide by adjusting the reservoir level was such a huge error of judgment right from the start of the movement of this landslide their model of the way that it's behaving was wrong their geological investigation has failed to identify but located within the limestone there were thin bands of play and those soft play layers produced a sign of weakness the geology teams bore holes meant to search for evidence of a weak sliding surface never went deep enough to find the clay and you're looking for a clay layer that could be a 250 metres below the surface but maybe only a centimeter thick but it's that centimeter thick layer but determines whether this lands like a move or not the extraordinary properties of this clay layer ultimately led to the whole side of the mountain detaching at once at incredible speed Monica karate survey of man talk has revealed the clay deposits that Mira steam missed these are the clays on which the 1963 landslide smooth it is a continuous layer when this layer failed the mass moved but Garrity's investigation focuses on another quirk of this thin layer of clay this case an impermeable material that doesn't permit water to pass a waterproof layer suggests an entirely new mechanism for the slide never considered by Mulla rain water from high on Montauk could drain into the rock below the clay have become trapped the increase in pressure pushing on the clay from below could destabilize the slight surface but it would need an enormous volume of trapped water to shift the landslide mass crucially kuratas team have gathered evidence that rainwater from the entire upper part of Montauk collected in the limestone isolated below the landslide after heavy rain a vast amount of water was trapped beneath the clay with nowhere to go the pressure below the clay spiked and the landslide got an extra job it's clear to the arathi but in attempting to control the landslide by simply changing the level of the reservoir they were missing a crucial element it wasn't a good plan because Miller didn't considered the existence of play inside the slope and so it it controlled only the lake lattice but not the rainfalls it was in the hopeless project if the original geology team had known about the clay Pat Lee believes history would have taken a different path plenty was known about the fact that clay is a weak material and so if they'd known that the clay layers were present they almost certainly would have walked away from the site at that point when pet Lee returns to the archive he realizes just how close Miller came to identifying the clay layer in 1961 Muller installed four water pressure gauges called piezo magis to monitor the water level in the rock he wanted to be sure the limestone slope was behaving the way his theory predicted three of the devices confirmed Mulas expectation that the water level in the rock followed the level in the reservoir but hidden in the data from the fourth piece ometer Pedley finds devastating evidence of a clay layer the water level in that fourth hole didn't really respond at all well - to the level of water in the lake the pedometer gave a high water reading whatever the level of water in the reservoir this is probably an indication that actually the clay layers were trapping water at high pressure underneath the landslide mass but Miller assumed the fourth bassam eater was faulty and its data was wrong because the behavior of this borehole didn't really conform to their preconceptions of the way that the outside was operating it was ignored for fedley the seeds of the disaster were sown in this systemic failure to understand the geology of Montauk what it shows is that if the model that you're operating doesn't actually explain some of the behavior that you're seeing then your model is wrong it's not that the landslide is doing something wrong and failing to develop your model to that point means that you actually potentially allow a large landslide like that Pedley now understands why the landslide happened but one final mystery surrounds the vile disaster why was the tsunami so much bigger than anyone expected [Music] professor Pedley turns his attention to Samantha's tsunamis simulation experiments the model that they constructed suggested that the tsunami would be relatively small 20 meters or less the actual landslide generated his basement wave that was more than 200 meters above the height of the dam the meticulous scale models should have given an accurate indication of the size of the tsunami tied to one critical factor the outcome of the model completely depends upon the speed at which the landslide moves the experiments tested the effect of landslides across a range of slump times from slow up to the fastest they could expect the slide to move the engineering team take an educated guess that one minute would be the quickest the real landslide could possibly fall correlating to just over four seconds in the simulation but when Pat Lee examines data from the night of the disaster he discovers that the entire collapse took just 45 seconds although just 15 seconds less than their estimate this 25 percent error is enough to totally change the outcome of the simulation the model they constructed was actually very sensible and very good but in computer modeling we we often use the phrase garbage in garbage out unfortunately in this case because the assumption was that the landslide would move slowly they put garbage into the model and the result of that was that they got misleading results out implementing the spurious results of the simulation had very real consequences the incredible speed of the final slump has baffled scientists for nearly five decades the acceleration is is really very dramatic it's like the acceleration of a Formula One car within a few seconds this louse I went from moving at a few centimeters per hour to only about a hundred and ten kilometers per hour Pedley now believes he has solved the mystery of this phenomenal final acceleration and once again the answer is in the clay and it's extraordinary behavior when compressed deep underground you've got to imagine there's 200 meters of solid limestone sitting above this clay layer Pedley has shown that when buried beneath millions of tons of rock the normally soft clay becomes hard the material is essentially brittle it's hard and it's strong for millennia the deep play had been undisturbed but filling the reservoir for the first time created enormous stresses in this thin layer that allows the clay to starts to form and as it deforms it generates what we call micro cracks tiny little cracks fractures build up in the clay the surprising behavior of these micro cracks is the key to the final acceleration of the slide as the landslide continued to move these little cracks grew they extended outwards to form big cracks and as those big cracks joined together they formed a single surface through the whole of the clay once the micro cracks had spread throughout the whole of the M shaped site surface total collapse was inevitable eyewitnesses report the final collapse took just 45 seconds but pet Lee's analysis shows this final irreversible phase began much earlier the 45-second event is just the bit we've received but in fact this final acceleration of the landslide didn't occur in 45 seconds it occurred over around about 60 days 60 days before the final collapse the water was at its highest level to date just 25 meters below the top of the dam up to this point the rise and fall of a lake has been causing the spread of micro cracking but now the cracks have penetrated so much of the clay a chain reaction begins and the cracks spread by themselves the micro cracking now controls the movement of the landslide and at that point the operators genuinely had no control on the behavior of the landside even though they thought they did one by one the few remaining patches of uncracked clay shear faster and faster and the landslide accelerates as a classic runaway failure the whole thing was was just primed to go after 50 years of uncertainty we can reveal how the construction of Europe's tallest man led to a tsunami that wiped out an entire community October the 9th 1963 four and a half hours to disaster damn operators have been preparing for the entire landslide detaching in one giant event and have reduced the reservoir level to lead 25 metres of exposed concrete two minutes to disaster in the belief the 20 meter high tsunami that the Power Company is expecting will be caught by the dam wall the local population is not warned about the imminent collapse of the landslide and Power Company workers watch the spectacle from a privileged position on top of the dam one minute to disaster unknown to the dam operators tens of meters below the mountain surface a vast brittle layer of clay has been shattering uncontrollably for two months and now only one small patch is left unbroken 45 seconds to disaster the clay shears and a landslide the size of 90 city blocks purfles towards the reservoir accelerating as fast as a Formula One car the impact creates a tsunami over 200 metres high thirty million tonnes of waterfalls 261 meters blasting a hole 40 meters deep in the valley floor the narrowing valley accelerates a 70 meter high column of water and it punches across the valley at around 140 kilometres an hour [Music] longer Oni is destroyed in less than two minutes I look down from the helicopter and saw the place with a wave had come down the whole valley disappeared Valley vanished a violent demonstrates the folly of humans and their failure to manage and understand natural systems [Music] their model for how to manage this landslide was completely wrong and in fact led to the catastrophe that finally occurred in 1971 two people were convicted of multiple manslaughter including the chief engineer who took over from Carlos amantha he was sentenced to two years in prison the power company was ordered to pay compensation to the victims [Music] the viand damn little is celebrated engineering masterpiece never generated power again and remains a relic in the landscape [Music] today engineers and geologists must always examine the slopes of proposed reservoirs and explain why they are safer than the slopes of the violent Valley [Music]

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Channel: Mega Disasters

Views: 205,811

Rating: 4.673152 out of 5

Keywords: Mega, Disasters, Mountain, Tsunami

Id: bpPGI-7E_aQ

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Length: 44min 58sec (2698 seconds)

Published: Sat Oct 08 2016

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