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Yellowstone Is a Supervolcano?
Creators of a British Broadcasting Company (BBC) science program first aired on February 3, 2000, gathered U.S. and British geologists, anthropologists, geneticists, paleontologists and others to talk about “supervolcanoes”, which was also the name of the resulting documentary. Available online, this well-written, medium-length transcript is an astonishing synthesis of post-modern knowledge about historical Earthly events virtually unknown to most people*. It is truly required reading for any person interested in the ultimate impact of a catastrophic disaster on human behavior. Throughout the BBC documentary, the scientists focus on Yellowstone National Park, underneath which lies one of the largest known supervolcanoes in the world. This caldera volcano is overdue to erupt. Highlights from the documentary follow.
1. How do supervolcanoes differ from regular volcanoes? “Normal volcanoes are formed by a column of magma, molten rock, rising from deep within the Earth, erupting on the surface and hardening in layers down the sides. This forms the familiar dome or cone-shaped mountains…Most people's idea of a volcano is a lovely symmetrical cone and this involves magma coming up, reaching the surface, being extruded either as lava or as explosive eruptions as, as ash and these layers of ash and lava gradually accumulate until you're left with a, a classic cone shape…Vulcanologists know this smooth flowing magma contains huge quantities of volcanic gases, like carbon dioxide and sulphur dioxide. Because this magma is so liquid these gases bubble to the surface, easily escaping. There are thousands of these normal volcanoes throughout the world. Around 50 erupt every year, but supervolcanoes are very different in almost every way. “First, they look different. Rather than being volcanic mountains, supervolcanoes form depressions in the ground. Despite never having seen a supervolcano erupt, by studying the surrounding rock scientists have pieced together how supervolcanoes are formed. Like normal volcanoes they begin when a column of magma rises from deep within the Earth. Under certain conditions, rather than breaking through the surface, the magma pools and melts the Earth's crust turning the rock itself into more thick magma. “Scientists don't know why, but in the case of supervolcanoes a vast reservoir of molten rock eventually forms. The magma here is so thick and viscous that it traps the volcanic gases building up colossal pressures over thousands of years. When the magma chamber eventually does erupt its blast is hundreds of times more powerful than normal draining the underground reservoir. This causes the roof of this chamber to collapse forming an enormous crater. All supervolcano eruptions form these subsided craters. They are called calderas. The exact geological conditions needed to create a vast magma chamber exist in very few places, so there are only a handful of supervolcanoes in the world. The last one to erupt was Toba [Sumatra] 74,000 years ago. No modern human has ever witnessed an eruption. We're not even sure where all the supervolcanoes are. Yellowstone National Park, North America [is one]. Ever since people began to explore Yellowstone the area was known to be hydrothermal. It was assumed these hot springs and geysers were perfectly harmless, but all that was to change.”* 2. How old is the Yellowstone supervolcano? “Volcanic activity began in the Yellowstone National Park region a little before about 2 million years ago. Molten rock (magma) rising from deep within the Earth produced three cataclysmic eruptions more powerful than any in the world's recorded history. The first caldera-forming eruption occurred about 2.1 million years ago. The eruptive blast removed so much magma from its subsurface storage reservoir that the ground above it collapsed into the magma chamber and left a gigantic depression in the ground- a hole larger than the state of Rhode Island. The huge crater, known as a caldera, measured as much as 80 kilometers long, 65 kilometers wide, and hundreds of meters deep, extending from outside of Yellowstone National Park into the central area of the Park. “The most recent caldera-forming eruption about 650,000 years ago produced a caldera 53 x 28 miles (85 x 45 kilometers) across in what is now Yellowstone National Park. During that eruption, ground-hugging flows of hot volcanic ash, pumice, and gases swept across an area of more than 3,000 square miles. When these enormous pyroclastic flows finally stopped, they solidified to form a layer of rock called the Lava Creek Tuff. Its volume was about 240 cubic miles (1,000 cubic kilometers), enough material to cover Wyoming with a layer 13 feet thick or the entire conterminous United States with a layer 5 inches thick. The Lava Creek Tuff has been exposed by erosion at Tuff Cliff, a popular Yellowstone attraction along the lower Gibbon River. “The eruption also shot a column of volcanic ash and gases high into Earth's stratosphere. This volcanic cloud circled the globe many times and affected Earth's climate by reducing the intensity of solar radiation reaching the lower atmosphere and surface. Fine volcanic ash that fell downwind from the eruption site blanketed much of North America. This ash layer is still preserved in deposits as far away as Iowa, where it is a few inches thick, and the Gulf of Mexico, where it is recognizable in drill cores from the sea floor. Lava flows have since buried and obscured most of the caldera, but the underlying processes responsible for Yellowstone's tremendous volcanic eruptions are still at work.”** 3. Is the Yellowstone volcano extinct? No. Geologist Robert Christiansen said, “I first came to Yellowstone in the mid-1960s to be a part of a major restudy of the geology of Yellowstone National Park, but at that point [we] had no idea of what we were to find. [We] noticed many rocks were made of compacted ash. But [we] could see no extinct volcano or caldera crater, there was no give-away depression. We realised that Yellowstone had been an ancient volcanic system. We suspected that it had been a caldera volcano, but we didn't know where the caldera was or specifically how large it was. As [we] searched throughout the Park looking for the volcanic caldera [we] began to wonder if [we were] mistaken. Then [we] had a stroke of luck. NASA decided to survey Yellowstone from the air. The Space Agency had designed infrared photography equipment for the moon shot and wanted to test it over the Earth. NASA's test flight took the most revealing photographs of Yellowstone ever seen. What was so exciting about looking at the remote sensing imagery was the sense that showed it in one, one sweeping view of what this truly was. [We] hadn't been able to see the ancient caldera from the ground because it was so huge. It encompassed almost the entire Park. “[We were] determined to find out when Yellowstone had last erupted. [We] began examining the sheets of hardened ash, dozens of metres thick blasted from the ground during the eruption. What [we] found [were] 3 separate layers. This meant there had been 3 different eruptions. When [we] dated the Yellowstone ash [we] found something unexpected. The oldest caldera was formed by a vast eruption 2 million years ago. The second eruption was 1.2 million years old and when [we] dated the third and most recent eruption [we] found it occurred just 600,000 years ago. The eruptions were regularly spaced. Quite amazingly we realised that there was a cycle of caldera-forming eruptions, these huge volcanic eruptions about every 600,000 years. Yellowstone was on a 600,000 year cycle and the last eruption was just 600,000 years ago. Yet there was no evidence of volcanic activity now. The volcano seemed extinct. That reassuring thought was about to change.” 4. Have researchers located a magma chamber beneath Yellowstone? Yes.Geologist Bob Smith used his 22 seismographs located throughout Yellowstone to document a huge, bulging magma chamber approximately four miles underground (seismographic waves travel more slowly through magma than rock). “The magma chamber we found extends basically beneath the entire caldera. It's maybe 40-50 kilometres long, maybe 20 kilometres wide and it has a thickness of about 10 kilometres. So it's a giant in volume and essentially encompasses a half or a third of the area beneath Yellowstone National Park. 5. What will happen to humankind when this magma chamber erupts? “A terrible truth underlies all mankind's efforts to understand the vast mechanisms [that define supervolcano] eruptions. Ultimately trying to find out what makes supervolcanoes work may be pointless. Consider the last one. 74,000 years ago a supervolcano erupted…in Sumatra. It would have been the loudest noise ever heard by man. It would have blasted vast clouds of ash across the world. The resultant caldera formed Lake Toba, 100 kilometres long, 60 kilometres wide…We're talking about 3,000 cubic kilometres of material coming out of that volcano. That's about 10,000 times the size of the 1980 Mount St. Helens eruption which people think of as a large eruption…It was, in short, colossal. Scientists are only now beginning to understand the effects of so much ash on the planet's climate…”* Chemical analysis of 35 centimeters of ash located in the floor of the Indian Ocean approximately 2,500 kilometers from the Toba volcano tells us that “this eruption was rich in sulphur, [which] would have released a tremendous amount of sulphur dioxide and other gases into the stratosphere which would have turned into sulphuric acid aerosols and affected the climate of the Earth for years…The fine ash and sulphur dioxide blasted into the stratosphere reflects solar radiation back into space and stops sunlight reaching the planet. This has a cooling effect on the Earth…[T]he temperature change after Toba in degrees Celsius would have been about a 5 degree global temperature drop, very significant, very severe global cooling…causing Europe's summers to freeze and triggering a volcanic winter. Five degrees globally would translate into 15 degrees or so of summer cooling in the temperate to high latitudes. The effects on agriculture, on the growth of plants, on life in the oceans would be catastrophic.” In fact, human geneticists have learned through the study of accumulation of mutations in mitochondrial DNA that the human species was almost wiped out approximately 70,000-80,000 years ago. Probably only five or ten thousand people worldwide managed to survive. “As for what caused this dramatic reduction in population the geneticists had no idea. Dr. Henry Harpending began touring universities to talk about the bottleneck. He was invited by anthropologist Stanley Ambrose to give a lecture to his students. [Ambrose] sat in on the lecture and [when Harpending] started talking about this human population bottleneck…I thought what could have caused it [the eruption of Toba] and at that point I broke out into a sweat. I went up to Henry and said I've just read a paper [about the super eruption of Toba in Sumatra], and it's on the top of my desk now, that may have an explanation for why this population bottleneck occurred. Harpending said, ‘I didn't read [the paper] till a week later and when I read it you know it was like somebody kicking you in the face. There it was.’” “Th[e] team of scientists believe the bottleneck occurred between 70 and 80,000 years ago, although this date is hotly debated. Toba erupted in the middle of this period, 74,000 years ago. If there really is a connection this research has terrifying implications for a future Yellowstone eruption. It could well be of a similar size and ferocity to Toba. Like Toba, it would have a devastating impact, not just on the surrounding region, North America, but on the whole world. If Yellowstone goes off again, and it will, it'll be disastrous for the United States and eventually for the whole world. Vulcanologists believe it would all start with the magma chamber becoming unstable. You'd start seeing bigger earthquakes, you may see parts of Yellowstone uplifting as magma intrudes and gets nearer and nearer the surface. And maybe an earthquake sends a rupture through the brittle layer, you've broken the lid of the pressure cooker. This would generate sheets of magma which will be probably rising up to 30, 40, 50 kilometres sending gigantic amounts of debris into the atmosphere. Where we are right now would be gone. We would be instantly incinerated. “Pyroclastic flows will cover that whole region, maybe kill tens of thousands of people in the surrounding area. You're getting a, an eruption which we can barely imagine. We've never seen this sort of thing. You wouldn't be able to get within 1,000 kilometres of it when it was going like this. The ash carried in the atmosphere and deposited over large areas of the United States, particularly over the great plains, would have devastating effects. The area that would be affected is the bread basket of North America…and…produces an enormous amount of grain on a global scale really. That's, that's, that's the problem and you would see nothing. “The harvest would vanish virtually overnight. All basic economic activity would certainly be impacted by this and let alone changes in the climate that could possibly be induced. The climatic effects globally from that eruption will be produced by the plume of material that goes up into the atmosphere. That'll spread worldwide and will have a cooling effect that will probably knock out the growing season on a global basis. We can't really overstate the effect of these huge eruptions. Civilisation will start to creak at the seams in a sense. The fact that we haven't seen one in historic time or documented means the human race really is not attuned to these things because they're such a rare event. It's really not a question of if it'll go off, it's a question of when because sooner or later one of these large super eruptions will happen.” Editor’s Note: Editor’s Note: Supervolcanoes are relevant to a recent disaster. The Toba supervolcano is in quite close proximity to the recent earthquake and tsunami off the coast of Sumatra (please see photos below).
Sources: *http://www.bbc.co.uk/science/horizon/1999/supervolcanoes_script.shtml ** http://vulcan.wr.usgs.gov/Volcanoes/Yellowstone/OFR95-59/OFR95-59.html Accessed July 6, 2005 |
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