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  • Our planet is capable of unleashing extreme chaos.

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    Volcanoes, earthquakes, hurricanes and floods can cause untold devastation. We may think we've seen the worst Mother Nature can throw at us, but scientists struggling to understand these disasters are discovering evidence that even more extreme events have struck in the past.

    So, this is about 13 times more powerful than the Pompeii eruption. They're uncovering clues that the worst catastrophes in history could strike again. This is one of the largest eruptions in the last 10, years. No one knew the source of the eruption. The clues are here, buried and hidden all around the world. Now, scientists come together to scour our volatile earth, to solve the mystery of Killer Volcanoes, right now, on NOVA.

    Of all the forces of nature, volcanoes are among the most dangerous. They have the power to kill millions and disrupt the fabric of modern life.

    Volcanoes can have a global impact. Today, there are more than 1, active volcanoes on Earth. About 50 erupt every year. Many are well known, like Vesuvius, in Italy, and Mount St. Helens, in Washington State, but could there be other slumbering giants that we have never heard of? Volcanoes that were once even more powerful and destructive than today's monsters? That's what a series of clues is suggesting. Scientists working across the world have begun to find evidence of a cataclysmic event, a mysterious eruption that could have been one of the largest in human history, and the trail starts in a very unexpected place.

    Here, in the heart of London, archaeologists uncover a surprise. While excavating a medieval cemetery, they happened upon a series of mass graves, on the edges of the burial ground. Over 4, men, women and children, packed into large pits. The cause of death was not obvious. So, what killed so many people? And why were they all buried together? When we find mass burial pits, we know that there's been a lot of people dying very quickly, and something has gone very wrong.

    As a first step to identifying the killer, archaeologist Don Walker and his team conducted radiocarbon tests to find out how long ago they died. The hope was that they could tie their deaths to some historical event, but what they found merely deepened the mystery.

    The victims all died around in the Common Era. That ruled out one of the most notorious mass killers of the past, the Black Death, which ravaged Europe about a century later, in So, what could have caused this mass killing?

    Don Walker heads to the British Library, to consult ancient historical records from the period. This manuscript is a history of England, over years old. It was written in Latin by a monk named Matthew Paris. Among these chronicles, one account stands out, a description of bitterly cold weather around London in the spring and early summer ofthat kills crops and livestock and leads to a deadly famine. It says, "Owing to the scarcity of wheat, a large number of poor people died and dead bodies were found in all directions, swollen and livid.

    Then Walker discovers a description that seems to match the discovery of the mass graves. Mary Spital, where they were digging these huge pits. According to this text, the famine killed over 15, people in London. That's 30 percent of the city's population, at the time. You're talking about something that was perhaps nearly as deadly as the Black Death. And possibly as widespread, too. Other sources reveal the far-reaching impact of the extreme weather and its disastrous effect on crops. There are various records from this period—,—in various parts of Europe and as far as Japan, that do attest to extreme impacts in terms of famine, in particular.

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    Something devastating was plunging much of the Northern Hemisphere in a pattern of bitter winters and summers blighted by torrential rain. We thought perhaps this was something to do with some catastrophic event.

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    Only one type of natural disaster could have such a widespread impact on the climate: But which volcano was the culprit? The closest volcanoes are a thousand miles away in Iceland.

    Inwhen a volcano known as Eyja erupted, it sent an ash cloud over Europe that disrupted air travel for weeks, stranding people all over the world. And historical records reveal that ineruptions from the Laki volcano caused mass deaths across Europe. It seems like an Icelandic volcano could be to blame for the mysterious 13th century event. But Walker came across another possibility. He became intrigued by one of the most massive eruptions in recorded history, even though it occurred just years ago and was located much farther away: Mount Tambora, in Indonesia.

    In Aprileyewitness accounts record that Mount Tambora erupted explosively. And this is one of the largest eruptions of the last 10, years. It's estimated over 60, people died in the shadow of this volcano. But the eruption had an even more far-reaching impact. In northern Europe and North America, the year after the eruption,is known as the "year without a summer. In Europe, cold weather led to the worst famine for a century.

    The climate change caused agricultural failures, poor harvests; it pushed up grain prices, with many people perishing from malnourishment. So, perhaps another powerful eruption could have caused the year without a summer in We began to think that perhaps this might be something to do with what had happened back in the 13th century; perhaps this was why the people starved.

    But to pinpoint the location of the mysterious volcano, they needed to know more about its size and type of eruption. They look at one of the largest volcanic events in recent memory, the eruption of Mount Pinatubo in the Philippines. Unlike volcanoes that erupt by pouring out rivers of molten lava over a long period of time, Pinatubo erupted suddenly and violently, when water and gases trapped inside the magma exploded with tremendous force, shattering the rock into millions of tiny particles and sending them high into the atmosphere.

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    Explosive eruptions like this are the most dangerous of all. Pinatubo killed people, locally, and left overhomeless. But, as with the other big Indonesian volcano, Mount Tambora, this eruption also had far-reaching effects.

    NASA's satellites were able to monitor the eruption. Pinatubo blasted out one-cubic-mile of superheated ash, but it also ejected hundreds of millions of tons of volcanic gases, in a plume 22 miles high. The ash and the gases are dispersed through the atmosphere by the wind, and they can travel thousands of kilometers, tens of thousands of kilometers.

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    But unlike heavy ash that soon falls out of the atmosphere, the lightweight gases persist for much longer. The most impactful gases are the sulfur-rich gases. And those gases will form little droplets of sulfuric acid in a large cloud. The tiny drops of sulfuric acid are called "aerosols," and in a large cloud, high in the upper atmosphere, these aerosols caused enough sunlight to reflect out into space to cool the planet.

    The satellite data revealed that this sulfuric acid mist had a much more dramatic impact than the ash. It blocked enough sunlight to cool the entire planet by one degree Fahrenheit for two years. That doesn't sound very much, but it actually masks much stronger regional variations, and that translates into real impact on the ground in terms of crop yields.

    Inthe temperature drop was much greater than caused by Pinatubo. This suggests that whatever triggered this medieval disaster could have been much bigger. That indicated that a big event occurred somewhere in, in the world, but there was no record of a massive volcanic eruption. For volcanologists, it was the biggest mystery for us. So where could the culprit volcano have been? And, after more than years, could this killer volcano be found?

    It seemed the trail had gone cold, until a clue appeared frozen in the polar ice. About a thousand miles from the North Pole, researchers for the Greenland Ice Sheet Project are taking core samples from deep in the ice. This ice sheet was built, layer by layer, as snowfall accumulated overyears. The deeper into the ice the scientists drill, the farther back in time they can look.

    The samples arrive for analysis at the Desert Research Institute, in Nevada. Glaciologists Nelia Dunbar and Joe McConnell are preparing to analyze an Arctic ice core sample that contains snowfall from the mid-thirteenth century.

    The core comes from 1, feet below the surface of the ice sheet. They will be looking for sulfuric acid, evidence of an intense eruption. If there were a big volcanic eruption that produced a lot of sulfur, that sulfur should be preserved in this ice. And that's what we're interested in studying. Where is this from, and what's the age of it? So, this piece is from aroundA. This represents about three years.

    So, this is roughly one year, roughly one year and roughly one year. These ice cores hold an incredible record of past climate. In between the snow crystals, are little pockets of atmosphere that are little time capsules that represent the composition of the atmosphere at the time the snow fell.

    Over time, more snow will fall on the ice sheet and that record is locked in. Up to the right, and then up to there. But to unlock the record, scientists have to destroy it, inch by inch. Okay, so now we're ready to start the analysis.

    As each layer of ice melts down, the meltwater passes through a mass spectrometer. The results start to come through, and the team immediately sees a telltale spike. So, we're seeing the responses come up on all the various instruments, right now. So this would beand you can see the acid, now, has just skyrocketed: So, it's certainly pointing to volcanism. Okay, so that must have been a really big volcanic event.

    The sulfur locked inside the ice layer tells the story of a powerful volcanic eruption.

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    And though the sulfur was washed out of the atmosphere in rain and snow inthe eruption itself likely occurred the year before. Now, keep in mind that it takes a while for the sulfur to make it from the volcano, through the atmosphere and be deposited on the ice sheet.

    And so this event, it probably occurred in, in maybe mid- to late And the amount of sulfur ejected by this eruption was vast by comparison with that produced by the other known eruptions captured in the ice cores. Of that, that we just measured again in this, in this new ice core, we can see that its huge. When you compare it to Tambora, here, inits, you know, something like more than twice as big. So, this is a really, really big event. And, at least in this composite, it's the biggest event over the last 2, years, very clearly.

    So, this eruption seems to have been large enough to account for the freak climate disaster across the northern hemisphere inincluding London's deadly famine. It was hard to really pin down one event and say, "This was the result of a volcanic eruption," but I think, in this case, the evidence is quite strong.

    You can imagine living in medieval London. You know that you haven't got enough food to live, your crops are failing, the weather's very bad, but you'd have no idea the true cause of what was going on. The true cause was that somewhere on the planet, ina volcano exploded and blasted its contents, including poisonous gas and ash, high into the atmosphere, where it dimmed the sun for months, if not years.

    But where was this killer? The mystery that remains is what was the volcano that was responsible for this big volcanic eruption? More than 1, volcanoes have been active in the last 10, years, so pinpointing which of these causes such a massive disruption in is a huge challenge.

    The first place to look is a string of volcanoes known as the Pacific Ring of Fire. The continents we live on ride atop giant tectonic plates made of rock.

    Where plates collide or slide under each other gives rise to volcanoes, making this one of the most geologically active regions of the world. But the Ring of Fire extends for thousands of miles. How can scientists work out which volcano is the culprit? In her lab at the New Mexico Bureau of Geology, Nelia Dunbar examines some distinctively shaped mineral particles, lodged in a section of ice from a different Greenland ice core.

    The particles also date towhen the sulfur concentrations are highest. Could these particles be possible clues to the volcano's identity? At 50,times magnification, it's clear that the mineral particles are actually microscopic pieces of volcanic ash.

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    These particles are smaller than a human hair. The ash particles are fragments of shattered pumice, produced when magma cools rapidly during an eruption. And their chemical composition is unique to each volcanic eruption. Just like a human fingerprint allows a suspect to be identified, the chemical composition of an ash layer allows the source volcano to be identified. This unique signature didn't match any known volcano. But it did show up in one other surprising place, at the exact opposite end of the world, in ice cores taken from the South Pole.

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    These cores also contained a significant spike in sulfuric acid corresponding to the eruption in This means that the monster darkened not only the Northern Hemisphere, but the Southern Hemisphere as well, smothering the entire world in a blanket of sulfuric acid. Climatologist Michael Mills believes the size of this global cloud can help pinpoint the place where the volcano erupted. He uses satellite data to map how clouds of sulfuric acid aerosols disperse around the world.

    Let's look at what happens when you have an eruption in the Northern Hemisphere. Inwe had several eruptions, and the aerosol stays in the Northern Hemisphere. Now look at what happens when you have an eruption in the Southern Hemisphere: But how could an aerosol cloud reach both hemispheres? For that, an eruption has to occur within a narrow band around the middle of the globe.

    This is Pinatubo in June ofin the Philippines. It starts spreading throughout the tropics, and from there it spreads into the Northern Hemisphere and to the Southern Hemisphere. Within a year after the eruption, the aerosol has covered the globe from pole to pole, affecting temperatures globally. The mystery eruption of also spread a cloud of sulfuric acid over both poles, so, it too must have erupted near the equator.

    But that still leaves over possible volcanoes as suspects, like Mount Tambora that led to the year without a summer; Krakatoa, that also erupted in Indonesia in ; and El Chichon, in Mexico, that erupted in Any one of hundreds of tropical volcanoes could have caused thousands of deaths on the other side of the planet, but which one?

    And could it strike again? It's still a needle in a haystack to find the one volcano, the one eruption that, that triggered all of this, because there are so many volcanoes. Even if you narrow it down to the tropics, where do you start? It seemed an impossible mystery to solve, but then a French geographer named Franck Lavigne decided to take it on. For me, it looks a bit strange that nobody found this eruption, so I decided to take up the challenge.

    He approaches it as a detective. Trying to find the identity of this mystery volcano was like a crime scene, so, we needed to investigate, to look for culprits, to look for clues. Volcanologist Jean-Christophe Komorowski joins the investigation. It's a very large eruption, it's an unknown eruption, so it has to be in a, in a country where there are many, many volcanoes. Most of them, perhaps, have not been studied. Share this article Share What we do know is that there are several causes that are more likely to occur than any other.

    Pilot error As aircraft have become more reliable, the proportion of crashes caused by pilot error has increased and now stands at around 50 per cent. Aircraft are complex machines that require a lot of management.

    Equipment failures still account for around 20 per cent of aircraft losses. Bad weather accounts for around 10 per cent of aircraft losses. About 10 per cent of aircraft losses are caused by sabotage.

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    The remaining losses are attributed to other types of human error, like mistakes made by air traffic controllers, dispatchers, loaders, fuellers or maintenance engineers. Because pilots actively engage with the aircraft at every stage of a flight, there are numerous opportunities for this to go wrong, from failing to programme the vital flight-management computer FMC correctly to miscalculating the required fuel uplift.

    While such errors are regrettable, it is important to remember that the pilot is the last line of defence when things go catastrophically wrong.

    With no power, the captain, Chesley Sullenberger, had to weigh up a number of options and act quickly. Using his extensive flying experience and knowledge of the plane's handling qualities he elected to ditch the aircraft in the Hudson River. The passengers were not saved by computers or any other automated system.

    They were saved by the two pilots — the very components that techno-enthusiasts claim can be replaced by computers and ground controllers. Sabotage remains responsible for only one in ten airline crashes. There are several causes more likely to be behind this kind of tragic event stock picture of airliner pictured In January an Airbus A hit a flock of geese over New York City.

    Using his extensive flying experience and knowledge of the plane's handling qualities he elected to ditch the aircraft in the Hudson River 2. Mechanical failure Equipment failures still account for around 20 per cent of aircraft losses, despite improvements in design and manufacturing quality. While engines are significantly more reliable today than they were half a century ago, they still occasionally suffer catastrophic failures.

    Ina disintegrating fan blade caused the number one left-hand engine of a Belfast-bound British Midland Boeing to lose power. Hard-to-read instrumentation contributed to the pilots' misreading of which engine was losing power.

    Confused, the pilots shut off the number two right-hand engine. With no power, the aircraft crashed short of East Midlands Airport's Runway 27, killing 47 and injuring many, including the captain and first officer. More recently, a Qantas A carrying passengers and crew suffered an uncontained engine failure over Batam Island, Indonesia.

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    Thanks to the skill of the pilots, the stricken aircraft landed safely. Sometimes, new technologies introduce new types of failure.