"Mountains are amongst the most spectacular and beautiful features of our planet, yet when you think about it, they're quite unusual." "Mountains are found only in a few parts of the world." "For many years geologists have been exploring the mountains trying to explain their origins, but only recently have they finally begun to understand how and why the world's great mountain ranges are formed." "Delphi in Greece is the place where the Ancient Greeks would come to find the answers to difficult questions." "One thing puzzled them - though it's doubtful they asked the Oracle." "They wondered why occasionally people would find seashells at the tops of mountains." "How could sea creatures get to the summit of a mountain?" "Today geologists are asking a much more fundamental question:" "why are there mountains in the first place?" "One geologist who's been wrestling with this problem is Philip England." "Over the last 20 years he's developed a radical new theory of how mountains are made." "It's a theory that sees mountains not as ancient and fixed, but as active and dynamic features of our planet and Greece is one of the most geologically active places in the world." "These are the earthquakes in Greece over the past 30 years or so." "What you can see in the middle here is a huge region 600 kilometers of a side absolutely covered with earthquakes, and that's what we 're interested in." "This pattern of earthquakes is a vital clue in the problem of how mountains are made." "The significance of these earthquakes started to become clear 35 years ago." "keynote of cordiality..." "In the early 60s the Soviets and the Western nations agreed to a partial ban on nuclear testing." "Tests in the atmosphere and underwater were banned." "...but the Russian refusal to allow inspection teams on their own territory has prevented any agreement on underground tests." "Just take a look at these pictures showing the upheaval of 12 million tons of earth in an American underground test." "Huge underground explosions like this are effectively man-made earthquakes." "So the US Air Force decided to keep an eye on the Soviets by setting up a global network of seismometers - the standard way of monitoring earthquakes." "This network detected nuclear explosions, but it also gave scientists the first global picture of where earthquakes occur." "Well of course we've known for centuries that earthquakes occur in certain zones." "People have had their houses knocked down by them and since the beginning of instruments, we've been monitoring earthquakes with instruments but it wasn't until we got this co-ordinated worldwide network of instruments which could talk to each other," "which could locate earthquakes accurately that we suddenly saw the whole picture and here it is." "Look at the thin line of epicenters of earthquakes all the way down the Atlantic sweeping round into the Indian Ocean and off into the Pacific." "The discovery of this extraordinary pattern of earthquakes was very exciting because it confirmed the new theory of plate tectonics." "The earthquakes clearly outlined the boundaries of the large plates which make up the planet's surface and which are constantly moving around the globe." "But significantly not all the earthquakes zones were so neatly defined." "There are parts of the world where the plate boundary isn't quite so simple and that's particularly the case where you come to the continental areas." "Look here." "Here's the edge of the plate through the Himalayan range off into the Mediterranean." "See there's a lot of earthquakes marking the edge of the plate, but there's a very broad zone here." "Something else is going on here." "And what they noticed was that these broad zones of earthquakes seemed to occur wherever there were high mountain ranges." "But what was the link between earthquakes and mountains?" "The most mountainous region in the world is the small Himalayan Kingdom of Nepal, jammed between the flat plains of India to the south and the very high plateau of Tibet to the north." "Since the 1960s geologists have been searching for clues linking the Himalayan earthquakes to the mountains." "Jean-Philippe Avouac has recently made a critical discovery." "But he doesn't work in the high mountains." "Instead, he spends his time in the foothills, where the rivers flow down from the high Himalayas on to the plains of India." "He is walking over the rounded pebbles of an old river bed which is now high and dry." "As you can see there is no more water flowing here." "And the reason for that is that the present river is far down below, to the right." "So the problem here was to understand what was going on." "And when he looked closely at the river bed he found charcoal - old pieces of wood." "Here you have a small piece of charcoal and this kind of matter can be dated." "For example this terrace was dated to be 4,000 years old and as you can see it overhangs the present river bed by about 20 meters." "So these pieces of charcoal show that water last flowed here on this ancient river bed several thousand years ago." "Now most people would imagine that this is the result of the river cutting down through the rocks." "But Jean-Philippe thinks something else has happened." "What we found is that the whole land around is rising, bringing up the old river bed while the valley stays at the same position." "Further upstream he has dated three older river beds even higher above the present river." "The top one is hidden by the trees." "So the rocks have been uplifted at about one centimeter per year on average, but actually that was not a continuous process." "The rock were uplifted by very large earthquakes such as the one that occurred in 1934, and during those earthquakes the rocks here are uplifted suddenly by about two meters." "Jean-Philippe's measurements show that the land here has been rising by a centimeter a year." "This is the fastest rate that's ever been measured." "But there are least 15 small earthquakes a day recorded here in Nepal." "Every single one represents land levels changing." "It's now clear that seismologists are actually watching mountains being built" "An earthquake basically is some kind of rock failure in the rocks at depth." "When the rocks fail, they break along fault that slips suddenly and each time a fault slips it's an earthquake." "Seismometers show not only where the rocks have slipped, but also by how much the rocks have been displaced." "And these displacements, when they accumulate over million of years, are creating the mountains." "Jean-Philippe's work here shows that the Himalayas are still very active, still growing." "The amazing conclusion is that vast mountain ranges can form in a relatively short period of geological time." "But if the earthquakes are creating the mountains then what are the forces creating the earthquakes?" "Bob Spicer and Leonore Hoke are exploring the mountains in western Nepal." "Leonore has worked in the high ranges of the Alps and the Andes." "Bob is an unusual combination - he's a botanist and a geologist." "They're trekking up to the high Himalayas searching for evidence of the fundamental forces creating these mountains." "This looks promising." "Yeah, it's quite dark which means that it's low oxygen conditions and preservation's likely to be quite good." "There's a nodule." "And so has it got the characteristic ammonite?" "No, it's just the shale." "There's quite a lot of them here." "Well we're here at 12'46" 3,600 meters above sea-level and where I am standing is, is black shale and in fact when you look close, closely there are nodules in here and in fact here is quite a nice one," "and if we 're lucky and we crack these nodules open," "some of these nodules contain fossils." "And here we have a beautiful coiled shell - in fact it's an ammonite - and this tells us that the sediment is marine and from the detailed structure of that ammonite" "We can tell the age of this sediment, which is about 150 million years old." "We want that one." "How much for this one?" "200." "200..." "Similar ammonites can be found along the entire length of the high Himalayas." "They're a sign of an ancient ocean which has long since vanished." "And it seems that most of the mountains here are made of rocks originally laid down on the floor of this ocean." "We 're in the purple stuff here aren't we?" "Yeah in there and that's been mapped as lower Jurassic, and it looks like limestone beds, quite uniformly dipping away from us." "Yeah and the beds seem to get thicker as we go up, and that's pretty much, pretty much what we see over there, so I think what we're dealing with is a very large fold." "I'll measure the inclination." "They seem to have an apparent dip of about 30 degrees." "These beds are incredibly contorted." "Immense forces must have squeezed and folded these ancient limestone beds - the remains of dead marine organisms - pushing them up from the ocean floor to make this part of the Himalayas." "Incredible to think that that's basically a beach that's up on end now." "It's vertical, is it?" "Yeah." "So how did these rocks get here?" "In the 1960s geologists could not have answered that question." "But then came the realization that the continents were moving around the globe." "India was once part of a continent called Gondwana which was located near the South Pole." "Around 85 million years ago," "India broke away and moved rapidly northwards towards Asia." "As it collided with Asia it buckled up the old ocean bed in front to form the Himalayas." "Here was the force that geologists were looking for." "It's this collision of continents which is causing all the earthquakes and creating the highest mountain range in the world." "So the first part of the answer to the mystery of mountains lies in the theory of plate tectonics." "As the continents collide they push up the mountains." "But it's the events after the collision which continue to puzzle scientists." "Mike Searle and Roberto Weinberg are trying to work out exactly when the Himalayas became so high." "To do this they need to understand the events which occur deep within the earth's crust as mountains are built." "The evidence they are looking for lies in the rocks close to the high and spectacular peaks around Mount Everest." "I'm standing here amongst the highest, some of the highest mountains of the world and in front of me I have the Nuptse Lhotse Ridge." "Nuptse is the mountain on the left and Lhotse is the highest peak on the right." "This ridge is continuously above 8,000 meters for about 6 or 7 kilometers." "In the distance underneath that mushroom cloud is the highest mountain of the world," "Everest, at 8,800 meters and as we swing around in the distance there we have Makalu, another giant 8,000 meter peak." "And, as we swing around further towards the south, here we have the magnificent face of 18'13" Ama Dablam." "It's only when they reach the glaciers below the towering peaks that they can start work." "This is where they find the rocks which show what happened after India collided with Asia." "Well, we've got some biacite." "Any garnet?" "One minute." "Yeah, this is the main granite piece on which is biacite, muscovite, garnet..." "But these are not rocks from the ocean floor." "They're finding granites, rocks which were once molten and these granites reveal a crucial aspect of the Himalayas that lies hidden deep underground." "Following the collision" "India continued to penetrate northwards into Asia deforming the rocks by squeezing them and thickening them." "Now this thickening process not only pushed rocks up, it also pushed rocks down." "And at the deepest levels that these rocks went the increased temperatures and pressures ultimately resulted in melting - the temperatures were high enough to melt this rock to form granites like we see in the high mountains around us here." "When mountains form they develop huge roots." "They're rather like icebergs with far more rock being pushed down than up." "As the rocks are forced down into the Earth's interior to form this mountain route, they melt." "Then, as the mountains continue to be built, this molten rock rises, cooling and solidifying to form granite." "But when did all this happen?" "What we are particularly interested in doing is dating the timing that this rock solidified to form this granite." "We have minute quantities of radioactive minerals which we can use for dating this rock, and when we do that we find that most of the granites in this area solidified around 20 million years ago." "And the amazing thing is that this 20 million year age is actually the same along the whole of the Himalayan chain." "So I think this probably marks the climax of mountain building along the Himalayas." "Mike Searle's work is confirming that since the first moments of the collision with Asia some 55 million years ago," "India has continued to plough its way northwards, moving at 5 centimeters per year." "And it wasn't until some 20 million years ago that the mountain building here reached its peak." "The picture of a mountain range formed by colliding continents seemed complete." "But impressive though the Himalayas are, the staggering fact is that they are just a small part of an even bigger mountain range." "By the mid 1970s most geologists accepted that the theory of plate tectonics could explain the creation of the Himalayas, but at the same time that the Himalayas were forming, there was forming to the north of them the vast plateau of Tibet " "and some geologists began to question whether plate tectonics could be the whole story." "The theory explained when and why mountains were formed but it had very little to say about how large and high these mountain ranges should be and it was this question that Philip England was determined to answer." "So let's look at the size of the object you 're dealing with." "Most people concentrate on the Himalaya, which run along the south of the Tibetan plateau here, but it's important to realise that these mountains are barely 200 kilometers wide, and stretching to the north of them is this vast plateau of Tibet." "The Tibetan plateau extends for nearly 2,000 kilometers to the north of the Himalayas, and it's very high - on average just as high as the Himalayas - well over 5 kilometers - and it's just as active." "There are earthquakes everywhere." "The problem was simply this:" "plate tectonics is a theory about the movement of large rigid plates over the surface of the earth and Philip realised that the collision of two rigid plates could not produce something the size and shape of Tibet." "Now we knew that plate tectonics was not the explanation for what we see so we thought why not abandon completely the idea of rigid plates and treat the continents as though they were some kind of fluid." "Now that doesn't seem to make a lot of sense perhaps because we 're accustomed to looking at the surface of the earth and seeing large rigid mountains hat you could build skyscrapers out of, but what we must hold on to is the understanding that" "below the earth's surface, and not very far below the earth's surface, we find rocks that are much more like fluids." "So what we thought is that could treat the continents as though the surface were being carried along by something that is much more fluid-like underneath." "But if the rocks are behaving like a fluid how does India pushing into Asia make the huge plateau of Tibet?" "If Asia really is fluid there are going to be two sets of forces acting." "First of all India is crunching up into Asia, moving northwards, shortening the crust, making it thicker and so making mountains, but at the same time the force of gravity is acting on this fluid tending to make it thin out," "to fall apart under its own weight and we can see how this might work if we take this blob of syrup here, drop it onto the bench and there you can see it's flowing away under it's own weight." "But now let's suppose that this spoon is India." "We move it into the fluid and you can see that we 're growing a small plateau in front of India and if we stop the movement we can see the fluid flowing away." "Now syrup obviously isn't a particularly good way of investigating the, the mountains and one should do this problem properly, write down the correct equations and solve them." "As it happens one needs to solve them inside a computer." "In the early 80s" "Philip and his colleagues wrestled with the problem of creating Tibet using the fundamental laws of fluid motion." "Could they get a fluid to look something like the vast ranges in Asia?" "It took them over 5 years working on the equations before they got a shape that resembled Tibet." "But in the end we were fairly pleased with this simple view of the, the deformation." "And here's the result of one of our experiments." "You can see that what we've grown is a plateau that's roughly the right size and shape and indeed is roughly the right height, about 5 kilometers." "As a result of this simple balance between the push of India crumpling the mountains up and the force of gravity to, to make them flow away." "So it looked like their fluid theory of mountains could explain the shape of Tibet." "But the theory also made an extraordinary prediction." "When the force pushing up the mountains stops, then the mountains will start to flow away and Philip England has found somewhere where mountains do appear to be flowing down " "Greece." "These are the ruins of the church where 2,000 years ago" "St. Paul preached to the Corinthians." "But it's not underwater because sea-levels are rising." "The ground here is sinking." "In fact the whole of Greece is slowly sinking into the sea" "and the way this is happening is clearly visible in the rocks." "This is incredibly smooth." "This is part of a, a fault that stretches 10 or 15 kilometers below our feet here" "and what you've got to imagine is that about a million years ago there was another piece of rock, just like this, jammed up against the fault and every time there's an earthquake a rock that was here slipped down about a meter," "a meter and a half, something like that." "This is what we call a normal fault and normal faults do the opposite of mountain-building." "The ground here is falling away, stretching apart." "Philip and his team have recently started to work out how fast Greece is moving and they had to climb to the top of almost every mountain to do their measurements." "18.9" "F" "Using GPS - global positioning satellites - they're measuring the hundreds of movements on the faults throughout Greece." "Right now the display on the receiver tells me that we're recording the distance to nine satellites." "What we can do to make the measurement more accurate is to leave the antenna above the mark on the ground for say 24 hours and measure the distance repeatedly to the satellites, so at the end of the day we might end up" "with say several thousand measurements of distance." "To give you an idea of how accurately we can do this, we 're about 100 kilometers now from Athens and we can measure that distance to 5 millimeters." "11.5." "One meter 11.5." "H." "One 11.5 One 11..." "Some of the survey points they're using were set up in the 1890s when the whole of Greece was surveyed extremely accurately." "We were very lucky to have these data." "We can come back now and find out how much each of these survey points has moved." "Up here in the north as you can see, not very much." "Down here in the middle where we are now there's been about 2 meters of mov, motion, and down here in the south-west 4 or 5 meters over the past 100 years." "This is as fast as India is moving into Asia." "But it looks as if Greece is flowing in one direction - towards the south west." "Notice that here the movement is 2 meters whereas here it's been 4 or 5 meters, so the ground is stretching." "It is all moving in one direction and for a reason." "Here's the deepest part of the ocean floor in the region and remember the syrup on a plate." "Well, here it is." "It's flowing downhill to the lowest piece of ground around and stretching as it goes." "This is the Gulf of Corinth, one of the places where Greece is stretching apart." "All the steep slopes disappearing into the distance are the normal faults that are doing the stretching." "The ground is dropping down as Greece sinks." "It is an incredible thought, but in a few million years' time this lovely country will have disappeared under the sea." "But despite all the successes of the fluid theory," "Philip England began to realise that there was a problem with it." "This first cropped up when geologists examined photographs of Asia taken from space." "This is a photograph from the Space Shuttle." "You can see the Himalaya running along the south of the plateau and here the plateau itself stretching off northwards, flat as you like." "The scale of the photograph is given by curvature of the Earth's surface here and here running smack into the north of the Himalya is a tremendous gash in the ground." "This gash is a normal fault." "And off to the north we can see several others." "These lakes are formed in the normal faults - here and here and here." "In fact they're all over the place." "Initially we thought that this wasn't particularly important, so we tended to neglect this kind of observation, to be honest." "These normal faults didn't fit with their fluid theory of mountain making because normal faults are found where mountains are sinking, like Greece." "They'd not predicted this for Tibet which they assumed was still rising." "Something strange was happening in Tibet." "When scientists were at last given permission to visit Tibet the problem became even more apparent." "Peter Molnar had also been puzzled by the normal faults in Tibet - but even he was surprised by what he found." "We're standing here in a valley, a valley extending over to a range of mountains over here and you'll notice that, although the mountains are dissected with deep valleys, the crests of ridges that reach back" "are all about the same height - you can see a whole string of these going along." "Some time in the past those ridges and this valley here were at the same elevation." "The valley has dropped relative to the ridges." "This is not unique." "There are hundreds of normal faults like this in Tibet today and this fault is active." "There's likely to be an earthquake on this, on, on this fault at any time." "Faced with this overwhelming evidence, geologists could no longer ignore these faults." "There was a paradox here." "Although India is still moving into Asia pushing up the mountains, it seemed that Tibet was sinking like Greece." "And then another clue emerged that something strange had happened to Tibet." "Every summer the Indian subcontinent is drenched by monsoon rains." "Climatologists now know that the monsoon is a direct result of the height of Tibet." "During the summer months, the plateau heats up warming the upper atmosphere drawing in moist air from the Indian Ocean." "As it passes over India and the Himalayas the moisture condenses as rain, giving rise to the annual downpour." "But climatologists have discovered that the rains were much less intense in the past." "The present monsoon only started about 10 million years ago." "The implications of this were startling - climatologists were suggesting that about this time" "Tibet must have suddenly increased in height." "What was exciting was that maybe this sudden increase in height could explain the normal faults in Tibet which had been puzzling Philip England and his colleagues." "If Tibet had suddenly risen 10 million years ago then maybe it had become too high to be supported, even by the relentless push from India and so it started to sink, creating the normal faults." "Then geologists started dating these normal faults." "They discovered that they were indeed about 10 million years old, so what was going on, what could possibly have caused Tibet to suddenly rise up?" "Philip England has recently had an ingenious idea." "He thinks something must have happened to the deep root under Tibet." "When Tibet was formed, just like any other mountain, there was an even bigger and thicker root of continental crust forming under the plateau pushing down into the mantle." "We've known for 100 years that mountains are a bit like icebergs, so we might draw a picture of the Tibetan plateau which looks a bit like this." "Here are the, the plains of India, here is the high Tibetan plateau about 5 kilometers high, and underneath that is the root of the iceberg, a thick layer of continental crust, perhaps 30 or 40 kilometers thick," "so the mountains are simply the tip of an iceberg of thick crust." "What we'd overlooked is that as well as thickening the crust when we thicken up the continents, we also thicken up a cold layer of mantle underneath and what we think happened is that this layer dropped off and you might think of that like a," "like an anchor dropping off the bottom, so it now, the continent up above rises up into the air." "His surprising conclusion is that the huge root under Tibet was acting like an anchor and holding Tibet down and 10 million years ago when Tibet lost the bottom of its root, it suddenly bobbed up." "When that happened it rose so far that it became too high to be supported by the push of India and so soon afterwards started to sink down again and flow away." "It was an extraordinary idea - many geologists were skeptical." "After all there was no way of telling exactly how the height of Tibet had changed in the past." "But then Bob Spicer realised that as a botanist he might be able to do this." "Rocks don't change with altitude, but plants do." "This is a monsoon forest and the reason why I'm here is that" "I'm interested in the leaves which are formed in this kind of situation." "Here where it's hot and very wet leaf size is quite large and the tip of the leaf has got a little projection on which sort of sheds the water off when it rains." "The other feature which is apparently suggestive of warm conditions is this margin." "Now there are no teeth on there, it's very, very smooth." "These are features which are adaptations to the very warm, very humid environment." "But that environment changes with altitude." "Driving up into the Himalayas the differences in vegetation are easy to spot." "2000 meters in altitude is like moving from the climate of North Africa to Britain." "I'm looking at the size and the shape and other features of the leaves such as these microscopic teeth and the pointed tips." "Now these features are, are fairly typical of leaves which are growing in quite cool environments." "We tend to find that vegetation reflects very, very strongly the climate in which it's growing." "And the same rules apply to fossil leaves." "Bob Spicer has been collecting fossils from different sites in Asia." "Here in lowland Nepal which is almost at sea-level he's found fossil leaves which are 11 million years old." "very slow..." "Very broad flat," "He's also collected leaves at altitude in the Himalayas and Tibet." "These fossil leaves come from the Tibetan plateau." "If we have a collection of leaves like this at a particular point we can work out what the mean annual temperature was." "In fact this collection of leaves comes from Tibet." "It's dated at 11 million years old and the temperature, which we get from the leaves, is about 10 degrees Celsius, or 50 degrees Fahrenheit for the mean annual temperature and we can do exactly the same thing" "for an assemblage that we collected from lowland Nepal." "Now that assemblage gives us a much warmer temperature." "It was near sea-level, so we've got that temperature at sea-level and we've got the temperature at this site and we can calculate the temperature difference and from that temperature difference we can calculate the altitude." "Now this site in Tibet was about 2'/2 kilometers above sea-level," "11 million years ago." "Now if you go to that site today you're 4'A kilometers above sea-level." "There are no trees, no leaves like these at all, so that means in the last 11 million years" "Tibet has risen by two kilometers." "It looks as if the ideas relating to the fluid theory are probably right." "What seems to have happened is that Tibet rose to about" "2'/2-3 kilometers 11 million years ago and then the bottom dropped off allowing Tibet to spring up rather suddenly." "The thought that Tibet sprang up quickly by such a huge amount " "2 kilometers - is quite staggering." "And just as intriguing is that this sudden growth is the reason Tibet is now collapsing." "but Tibet seems not to be unique." "This whole process appears to be part of the pattern of mountain building around the world." "In the western United States lies the Basin and Range province." "It's a vast area of mountains and deep valleys." "One of the valleys is particularly well known." "This is the infamous Death Valley of California." "It was given that name by some of the pioneers, the Forty-niners who tried to use it as a short-cut to the goldfields." "It's a long way from Tibet but from this valley and the surrounding mountains maybe scientists can get a glimpse of Tibet's future." "Death Valley is the lowest place in the western hemisphere." "It's 86 meters below sea-level." "But Death Valley hasn't always been below sea-level." "Some time in the past it was much higher and like Tibet, this area lost part of its mountain root." "The whole of the valley floor is sinking" "and it's not just Death Valley." "The same thing is happening over the whole of the Basin and Range province." "The entire region is spreading out sideways and sinking and this is happening quite rapidly." "How rapidly has recently been calculated by Jack Wolfe." "But there are some things that look like elm is it?" "Yeah, there 's an elm and yeah, that's one of the oaks." "That's the big tree sequoia of the Sierra Nevada." "And have you got dates on this?" "Yeah, there are several dates in the section and this would appear to be about 16 million." "So at 16 million years, how high do you think this was above sea-level?" "We generally have come down about 1500 meters." "In other word it was about 1500 meters higher at 16 million years ago than it is today." "For a whole mountain range to fall down 1/2 kilometers is quite something." "It seems probable that in a few tens of millions of years parts of Tibet, one of the highest places in the world, will be like Death Valley, one of the lowest." "In the last 30 years scientists have completely changed their view of how mountains are formed." "no longer do they see them as ancient and fixed, but as young and active features of our world." "Scientists now know that mountains are made when continents collide." "But what's been more surprising to learn recently is that mountains can ebb and flow." "In geological terms they are formed very rapidly and collapse just as rapidly." "The Himalayas and Tibet are just the latest of the high mountains to form during the long and turbulent history of our planet." "But as mountains are formed it has also become clear that they have had unexpected and far-reaching effects on the rest of the world." "As mountains rise and fall they've had a dramatic impact on the earth's climate." "And it's just that relationship between changes to the earth and changes to our climate that we're going to be looking at in our next programme." "Subtitles:" "Thor"