Part of America's Yellowstone National Park was closed to visitors on July 23 this year and remains closed today due to high ground temperatures and increased thermal activity in the park. National Park Superintendent Suzanne Lewis said that "A portion of the Norris Geyser Basin on the west side of the park has been closed." 
On August 7, the United States Geological Survey (USGS) reported that scientists were planning to set up a temporary network of seismographs, Global Positioning System receivers and thermometers to monitor increasing hydrothermal activity in the Norris Geyser Basin and gauge the risk of a hydrothermal explosion. 
On August 10, the Denver Post reported that Liz Morgan, a U.S. Geological Survey research geologist had discovered a huge bulge underneath Yellowstone Lake that had risen 100 feet from the lake floor. The bulge is two thousand feet long and has the potential to explode at any time. Morgan was quoted as saying that "The inflated plain is a potential and serious hazard and possible precursor to a large hydrothermal explosion event." 
Then, on August 24th, the University of Utah Seismograph Station reported that a magnitude 4.4 earthquake occurred just 9 miles southeast of the southern entrance to Yellowstone National Park. USGS scientists agreed that the earthquake was "uncommon" in that it was a very shallow earthquake, occuring just 0.3 miles below the surface. 
Jacob Lowenstern, a researcher for the U.S. Geological Survey and scientist-in-charge of the Yellowstone Volcano Observatory said: "Our goal is to understand what's driving this volcanic system, and are there indications it could be moving into a period of unrest? 
This worrying situation was confirmed on September 8 by Dr. Bruce Cornet, a geologist and paleobotanist with the USGS, who explained: "Steam pressure is apparently building again in Yellowstone, and hydrothermal fluids and steam are working their way up through fractures and vents. If more steam vents appear, that means a continuous pathway for pressure release has been established to the magma chamber. If that happens, the pressure in the magma chamber will continue to drop until it reaches a critical stage when the superheated water within the magma explodes. Unfortunately, as the steam venting subsides, there will be a false sense of security. People will think it was just another cyclical event, and the danger is over. But that will be the farthest from the truth. It will be the quiet before the storm." 
Initially this should be of little or no consequence to anyone apart from those planning to visit Yellowstone . . . except for one thing. Lurking beneath Yellowstone National Park is one of the most destructive natural phenomena in the world: a massive supervolcano.
Only a handful exist in the world but when one erupts the explosion will be heard around the globe. The sky will darken, black acid rain will fall, and the Earth will be plunged into the equivalent of a nuclear winter. It could push humanity to the brink of extinction.
Volcanoes have always been a threat to humanity. The Tambora eruption in Indonesia in 1815 killed more than 90,000 people, while the Krakatau eruption in 1883, also in Indonesia, killed 36,000. The last supervolcano to erupt was Toba in Sumatra 74,000 years ago. It created a global catastrophe that dramatically affected life on Earth. Toba blasted so much ash and sulphur dioxide into the stratosphere that it blocked out the sun, causing the Earth's temperature to plummet, and possibly reducing the population on Earth to just a few thousand people. For a long time scientists have known that volcanic ash can affect the global climate. The fine ash and sulphur dioxide blasted into the stratosphere reflects solar radiation back into space and stops sunlight reaching the planet. Temperatures drop dramatically and nothing grows, causing mass starvation.
Bill McGuire, professor of geohazards at the Benfield Greig Hazard Research Centre at University College London, says that America's Yellowstone Park is one of the largest and most dangerous supervolcanoes in the world. "The Yellowstone volcano can be likened to a sleeping dragon," says Professor McGuire, "whose slow breathing brings repeated swelling and sinking of the Earth's crust in northern Wyoming and southern Montana."
Professor McGuire went on to explain that: "Many supervolcanoes are not typical hill-shaped structures but huge, collapsed craters called "calderas" that are filled with hot magma and are harder to detect. The Yellowstone supervolcano was detected in the Sixties when infra-red satellite photographs revealed a magma-filled caldera 85km long and 45km wide. It has been on a regular eruption cycle of 600,000 years. The last eruption was 640,000 years ago, so the next is long overdue."
Volcanologists have been tracking the movement of magma under the park and have calculated that in parts of Yellowstone the ground has risen over seventy centimetres, almost two and a half feet, since 1923, indicating a massive swelling underneath the park.
"The impact of a Yellowstone eruption is terrifying to comprehend." says Professor McGuire. "Magma would be flung 50 kilometres into the atmosphere. Within a thousand kilometres virtually all life would be killed by falling ash, lava flows and the sheer explosive force of the eruption. One thousand cubic kilometres of lava would pour out of the volcano, enough to coat the whole of the USA with a layer 5 inches thick. The explosion would be the loudest noise heard by man for 75,000 years."
The long-term effects would be even more devastating. The thousands of cubic kilometres of ash that would shoot into the atmosphere would block out light from the sun, making global temperatures collapse. This is called a nuclear winter. A large percentage of the world's plant life would be killed by the ash and the drop in temperature. The resulting change in the world's climate would devastate the planet, and scientists know that another eruption is due - they just don't know when.
Michael Rampino, a geologist at New York University, quoted in a BBC Horizon documentary on Supervolcanoes  three years ago explained: "It's difficult to conceive of an eruption this big. 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."
Professor McGuire says "There's nowhere to hide from the effects of a supervolcano. One day - perhaps tomorrow, perhaps in fifty years, perhaps in 10,000 - it will erupt; once again wreaking devastation across the North American continent and bringing the bitter cold of Volcanic Winter to Planet Earth. Mankind may become extinct."
So the rumblings currently going on underneath Yellowstone should be a warning not just to those who plan to visit the National Park, but to the whole world. If the increased thermal activity is the precursor to an eruption event, we may well be on the brink of the biggest catastrophe the modern world has ever witnessed.
 http://www.denverpost.com/Stories/0,1413,36%257E53%257 E1561852,00.html
 http://story.news.yahoo.com/news?tmpl=story&u=/ap/20030904/ap _on_sc/geyser_guessing
 http://www.earthchangestv.com/breaking/2003/september_2003/08 yellowstone.htm
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