At almost 5,000 feet heklas distinctive cone towers above the landscape. Shes one of icelands most active volcanoes, erupting over 20 times in the last thousand years. Hekla last erupted in 2000 and recently her eruptions have been mild. But thors discovered a place that shows just how explosive she can be. And with hekla its all about ash. The snowcovered mountain in the background there is the hekla volcano itself. And here in the foreground this lightcolored layer there at the top was erupted from hekla 3,000 years ago. Narrator these ash layers tell thor a great deal about heklas explosive past. Thordarson the reason why we spend our time studying these ash layers is that we can get information about the nature of the eruption, its intensity, its explosive power, and how widely it affected the environment. Narrator hes discovered one particular eruption from hekla 3,000 years ago which threw out a tremendous amount of ash. If you look at the landscape around us, all the surface is covered with the ash, which is 15 feet thick. And it doesnt matter where you look, its all around you. That gives you a good indication of how powerful, how strong that eruption was. Narrator heklas explosive eruptions created this barren landscape. Its made of layer upon layer of ash, formed from pulverized magma. And its typical of heklas family of volcanoes the stratovolcanoes. Thordarson most stratovolcanoes around the world will produce big, explosive eruptions. Every so often we have a big bang. explosion man on walkietalkie now weve got an eruption down here. Narrator its exactly what happened in Washington State in may 1980. Mt. St. Helens, americas most famous stratovolcano, erupts. Rising magma triggers an earthquake and a vast landslide. Man on walkietalkie the whole northwest section blowed up. Narrator . Sending ash 80,000 feet high in just 15 minutes. This is far east as you can go. Narrator . And causing over 50 deaths. Man on walkietalkie i cant believe this. Doesnt look like any place ive ever been before. Narrator europes most famous stratovolcano is mt. Vesuvius. When it erupted 2,000 years ago, gases and hot ashes rained down on the towns of pompeii and herculaneum, asphyxiating an unsuspecting population and killing up to 25,000 people. But what thors discovered about heklas eruption 3,000 years ago makes mt. St. Helens, mt. Vesuvius and eyjas 2010 eruption pale in significance. Thordarson weve learned that this is one of the biggest eruptions from hekla, in the last 10,000 years. And the total volume of this material is between two and three cubic miles. It also sent ash plumes extending from greenland well into mainland europe. If we were standing exactly in this location 3,000 years ago when hekla erupted, the first thing we would have seen is a humongous column of ash rising up from the volcano. And from that plume, we have ash raining out. And along with that, you would have rocks like this one here flying through the air. This one is 20 pounds. So this eruption it would have killed you and you would have been buried in 15 feet of ash. Narrator when eyja erupted, her ash grounded aircraft for almost a week. But hekla could be far more disruptive. 3,000 years ago, hekla produced 75 times more ash. The concern is she might be about to do it again. Thordarson the pattern that we have detected is suggesting that right now it is at the end of a phase with eruptions diminishing in size, indicating that we might be entering a new phase which usually starts with a big, explosive eruption. So its possible that hekla might produce a very big, explosive eruption in the near future. Narrator what chaos might we expect if this happens . Claire witham has been asking the same question. Shes part of a Rapid Response team at the London Volcanic Ash Advisory Center at the uks met office. Its the first line of defense against volcanic ash for europes aviation industry. And when eyja erupted, it put the team through their paces. We hadnt seen anything that had really blown an ash cloud from iceland to our area in recent history, so it hadnt really got into peoples minds that that might happen. The eyjafjallajokull eruption went on for about 39 days. People were working around the clock here on a scale that we hadnt really experienced before. Narrator the minute an eruption occurs, observers in iceland contact the team. Witham we then have a race against time to get out an advisory. We then have to update that information every six hours until the end of the eruption. Narrator claire needs two key things to predict where the ash cloud is going. First, she needs an accurate weather forecast. Witham the weathers really vital because when the ash is erupted into the atmosphere, it then gets transported by the winds at those higher levels and gets taken wherever those winds are going. Narrator how forcefully the volcano erupted is also critical. Witham we need to know how high the eruption is and also how much has been emitted and how that changes with time. Narrator armed with this information in 2010, claire and her team used supercomputers to model the movement of ash from eyja. So what we can see is the start of the eruption, and then the ash is transported to the southeast and is then dispersed across the northern hemisphere. Narrator in the future, with the possibility of bigger eruptions, the teams predictions will be even more important. To see what might happen nova asks claire to make a model using heklas huge eruption 3,000 years ago, which belched up to three cubic miles of ash and the weather conditions when eyja erupted in 2010. So this simulation shows the first ever model run of a much larger eruption. And what we can see is that because this eruption was much bigger, so it went much higher in the atmosphere and produced considerably larger amounts of ash, the plume covers a much wider area, and the levels of ash in the plume are much greater, which is shown by this red color, spreading out over a much larger region of europe and also across the northern hemisphere. And what this tells us is that for a future eruption of a larger size, the potential for disruption is greater. Narrator whats worse is that we might not have time to prepare. Thordarson hekla does not give us much warning. Her temperament is such that she will flare up 30 minutes before it erupts, so she can surprise us. Narrator as scientists are learning icelands home to a group of deadly volcanoes eyja blew in 2010; laki sent a toxic cloud of sulfur circling around the northern hemisphere; and hekla, which could unleash millions of tons of ash without warning. But the greatest threat is from their restless neighbor. Rampino i would be more worried about a katlastyle eruption happening today. Narrator one that volcanologists cant afford to ignore. The concern with katla is that it might erupt any time. Narrator the volcano hidden under the ice. Katlas rumbling. Narrator some fear her eruption could be worse than lakis sulfur cloud and heklas ash put together. Katla erupts every 50 years on average. Her last major outburst was nearly a hundred years ago so an eruption is long overdue. All the signs that we detect from the volcano are telling us that it is building up to an eruption. Narrator recently scientists have detected swarms of earthquakes around her crater. Whether this threatening activity is because eyjas eruption has lit katlas fuse no one knows. To find out whats going on, Sigrun Hreinsdottir and Freysteinn Sigmundsson are making the threehour trip to the volcanos summit to set up monitoring stations. Hreinsdottir we are driving now up to the glacier and we need a guide because its a fairly rough environment and there are crevasses to worry about. Narrator its a treacherous journey. Katlas crater is over six miles wide, buried below the ice. Sigrun is looking for a specific site to set up one of her stations somewhere where katlas rim breaks through the ice. Hreinsdottir right on the top of the bedrock there. Its actually. The bedrock is the caldera rim sticking right out of the glacier. Sigmundsson what a fantastic site narrator its the perfect spot. This rocky outcrop connects to katlas Magma Chamber deep below. If the magma moves down there, so should the ground above it, here. Hreinsdottir this is just a simple antenna that is receiving data from the satellites that are travelling across the sky and we hook the antenna to a receiver and the receiver is logging the data. Narrator the satellites transmit signals to sigruns gps network stationed around katlas rim providing an extremely accurate fix on their positions. If katlas Magma Chamber inflates its rim pushes outwards, moving the receivers. Even a tiny shift of less than an eighth of an inch can be detected. 429point3. So magma, molten rock, is coming from great depth into the volcano and what we have is like a Magma Chamber, which is just like a balloon if you imagine you put air in a balloon and it inflates. We can actually sense that on the surface. Narrator and there are indications that katlas chamber is indeed inflating. Hreinsdottir so freysteinn, we can actually look at the data from the gps station that is right here at katla volcano. And we set this up during the eyja eruption. This is 2010 and now we are in 2012 and you can see that the overall trend here, that is up, so inflation of the Magma Chamber is almost eight centimeters. Its quite a bit. The Magma Chamber of katla volcano is inflating. Narrator the gps readings show katla could be building to an eruption. So whats the worst we can expect from her . Thors been investigating layers of black ash the volcano ejected in 934. What hes uncovering alarms him. So here we have the lower part of the deposit. Here is the bottom, and its fairly coarse grained. This is the one thing that we really want to worry about. Explosive events like this produce a lot of ash. Narrator volcanologists have measured the thickness and extent of these ash layers, allowing them to calculate the volume of material katla erupted a thousand years ago. The results tell us this eruption of katla in terms of volume of material is double the hekla eruption 3,000 years ago. Narrator the closest weve come to experiencing an eruption on that scale rocked the philippines in 1991 when mt. Pinatubo erupted. This, one of the largest eruptions in modern history, rumbled for just over a week sending an estimated 2. 5 cubic miles of ash into the atmosphere. But katlas ash reveals she can erupt for far longer. Thordarson there are many, many many layers there, which means that this eruption featured many, many explosive events. Its a complex eruption; it probably lasted for at least one year. Narrator if a yearlong eruption of ash wasnt threatening enough, katla also spewed 220 million tons of sulfur much more than laki in 1783. It is double that of laki. So it is the biggest eruption in icelandic history and it is the biggest volcanic pollutant in recent times on planet earth. Narrator its this acidic pollution that scientists fear the most. If katla erupts today, the devastation could trump the effects of eyja, laki and hekla combined. And the amount of sulfur produced would be far worse. Well, sulfur has a sort of a double whammy effect when its in the atmosphere. The little droplets of sulfuric acid or aerosol, as its called, stay in the upper atmosphere and cut out some of the sunlight that would come in and warm the earth so the result is that the earth gets cooler. Narrator katla has the power to change the worlds climate. Rampino a longduration eruption such as katla, if it happened today would cause quite a mess on a global scale. The numbers are about two degrees celsius cooler. It doesnt sound like much but its enough to cause a transformation of the landscape. Narrator the evidence is clear. Icelands volcanic eruptions could have global consequences producing enough ash and sulfur to change the worlds climate. But could we protect our economy if a less powerful eruption, like eyja in 2010, occurs in the near future . Its a vital question for the Airline Industry as aircraft will be the first to feel the effects. At 35,000 feet, ash particles are so fine they are invisible to the naked eye. So when eyja erupted thousands of planes were immediately grounded. Its a problem aircraft engineer ian davies has been grappling with. Davies well, we know ash and engines dont mix, because this modern turbo fan engine behind me basically takes in hundreds of cubic meters of air every second. Narrator any volcanic ash sucked into the engine which heats up to 2,000 degrees fahrenheit melts and sticks to vital parts. And when it does that, it will cause a surge stall, which is effectively a backfire, and in doing so we can get flames out the front and out the back of the engine. And ultimately it will shut down. Narrator fred prata, an imaging expert, is developing a unique system that could help. Its called avoid. Prata this instrument here is a fast sampling dual camera system measuring in the infrared. Infrared radiation is heat. Every molecule in the atmosphere thats vibrating emits infrared radiation. Narrator ash particles also emit infrared radiation at a particular wavelength. Prata now, they have a particular spectral signature in the infrared which is quite different to that of other things in the atmosphere like water clouds ice clouds, water vapor. Narrator the cameras, which can pick up infrared signatures, provide pilots with a picture of the sky up to 60 miles ahead, allowing them to distinguish between ash and clouds. Prata so now he can start to see where the ash is. If it is there and he sees it five or six minutes ahead of time, he can then make a small deviation and avoid it completely, safely and economically and land his aircraft. Narrator the new system could be the First Step Towards keeping planes in the air when ash next rises from iceland. And it could help pilots map and maneuver around invisible ash clouds while theyre flying, even reducing the need to ground planes. Still, the greatest threat would come not from katlas ash, but from her toxic sulfuric acid cloud. Faced with a giant volcanic eruption today, a major response would be needed to protect us. Grattan but how would they do that . Theyd do that by switching off the power stations that might be burning coal. Theyd do that by stopping us driving cars that are emitting pollution from the engines. Theyd do that by closing factories down. I think modernday society should very much be concerned with volcanism. I think were probably more susceptible to these types of events in the 21st century than we were even in the early 20th century. We think were immune to these things and frankly were not. Narrator those least able to protect themselves would be most affected. Grattan to be brutal about it, the vulnerable population will be culled from society the elderly, the sick, people with heart and lung conditions, the obese. We are going to see many, many people dying. Narrator today we have a society dependent on air travel. Davies the way we move food freight, people around the world now any disruption to that is devastating. Narrator a society thats delicately linked together. Grattan so a Massive Volcanic eruption is really going to disrupt this web of connectivity. All those networks are going to be fractured. Theyre not going to work anymore. Narrator lives were thrown into chaos when eyja a relatively small volcano awoke in 2010. How much worse will it be if and when one of icelands doomsday volcanoes erupts again . Neanderthals rediscovered. Who were these primitive cavemen from our prehistoric past . Man neanderthals have the mother of all image problems. Theyre brooding theyre stupidlooking they have no personality. New evidence paints a startling picture. This is the smoking gun. Man i think they had language. Man they were engineering their rocks. Decoding neanderthals, on nova next time. Major funding for nova is provided by supporting nova and promoting public understanding of science. And by the corporation for public broadcasting. And by contributions to your pbs station from additional funding is provided by Millicent Bell through the exploration continues on novas website, where you can watch this and other nova programs see expert interviews, interactives, video extras and more. Follow nova on facebook and twitter, and find us online at pbs. Org nova. This nova program is available on dvd. To order, visit shoppbs. Org, or call 1800playpbs. Nova is also available for download on itunes. Captioned by Media Access Group at wgbh access. Wgbh. Org bonneville i think in season 3, the mood changes and theres a lot of uncertainty still as time creeps forward. Lord grantham doesnt deal with the changes very well. He wants everything to maintain the same and of course, that will never happen. I refuse to be the failure. Bonneville robert isnt a natural businessman. I can tell you that there are some big financial problems on the horizon. We have my motherinlaw coming to stay. Robert, arent you going to kiss me . And any man who has a motherinlaw coming to stay knows that theres fireworks on the horizon. You americans never understand the importance of tradition. Yes, we do. We just dont give it power over us. Bonneville and of course, weve got the whole will they wont they . With mary and matthew. Im looking forward to all sorts of things. Dont make me blush. Shes still very adamant that things stay the same and that she wants to bring up her children at downton. And matthew is not quite decided upon that. What about us . What about our children . You know i would do anything for this family. Anything except help us. Bonneville will edith ever find proper love and happiness . I do hope to be seeing a bit more of you. Bonneville what will happen to mr. Bates . Anna one day, something will occur to us and well follow it up and the case against you will crumble. Do you never doubt . No. Bonneville and sybil and branson, of course. They come backan interesting sort of territory to play, because branson having been the chauffeur downstairs is now married to the daughter so that creates a whole social unease and how you cope with that. Branson no, i dont agree and i dont care who knows it is there any way to shut him up . Bonneville i suppose an overarching theme is the family trying to find its feet again after the upsets of the war. So, theres still plenty to play for. Ha ha