A recent study, published in the journal Nature Geoscience, indicated that the risk of a "Supervolcano" eruption could be between 10 to 100 times more likely than previously thought.
Scientists originally assumed that seismic activity was necessary to crack open the earth's crust and trigger a supervolcano eruption, but evidence now suggests that it is the build up of pressure from contained magma that ultimately causes it to break through and escape onto the surface in a cataclysmic explosion.
Supervolcano eruptions are hundreds of times more powerful than standard volcanoes, and have the potential to cause mass-extinction level events on earth. These bubbling underground cauldrons of magma are ticking time bombs, which, in terms of their threat to life on the planet, are second only to a direct hit from a sizeable asteroid from space. Past eruptions have resulted in mass extinctions of various species and have had a significant, long-term impact on the world's climate. Scientists predict that a supervolcanic eruption would result in a 10C drop in average global temperatures for a decade or more, a dramatic reduction that would change life on earth as we know it.
Scientists believe that the last supervolcano erupted 70,000 years ago, on the site of what is now Lake Toba in Sumatra, Indonesia. This eruption emitted such a profusion of volcanic ash that the sun was blocked out for up to eight years, which subsequently lowered temperatures across the globe for over one thousand years.
One of the most well-known supervolcanoes lies under Yellowstone Park in Wyoming. This massive volcano has not erupted for over 600,000 years, when it spewed out over 1000 cubic kilometers of lava and dust into the atmosphere and covered an entire continent in ash. The volcano is known to erupt every 600,000 years, so the buzzer could sound at any time for the next explosion.
It was an analysis of the molten lava beneath the currently dormant volcano at Yellowstone that provided the latest revelations; researchers analysed magma from the huge Yellowstone caldera, an enormous underground cavern measuring 55 miles across and containing between 200 and 600 cubic kilometres of molten rock, and recorded its reactions to variations in pressure and temperature. The team was led by Wim Malfait and Carmen Sanchez-Valle of ETH Zurich (Switzerland) and comprised scientists from the Paul Scherrer Institute in Villigen (Switzerland), Okayama University (Japan), the Laboratory of Geology of CNRS, Université Lyon 1 and ENS Lyon (France) and the European Synchrotron (ESRF) in Grenoble (France).
Using X-ray technology from the European Synchroton Radiation Facility in Genoble, France, the scientists were able to determine that the density of the magma reduced in response to the extreme underground pressures and temperatures. The French X-ray machine was able to take accurate density measurements at temperatures of up to 1,700C and pressures 36,000 times greater than normal atmospheric pressure. The results indicated that these variations in density, occurring between magma and the rock that contains it, could create enough pressure for the lava to burst through the earth's surface.
“The results reveal that if the magma chamber is big enough, the overpressure caused by differences in density alone are sufficient to penetrate the crust above and initiate an eruption,” said Professor Carmen Sanchez-Valle of the Swiss Federal Institute of Technology (ETH) in Zurich, who led the study.
“The difference in density between the molten magma in the caldera and the surrounding rock is big enough to drive the magma from the chamber to the surface,” added Jean-Philippe Perrillat of the National Centre for Scientific Research in Grenoble. “The effect is like the extra buoyancy of a football when it is filled with air underwater, which forces it to the surface because of the denser water around it. If the volume of magma is big enough, it should come to the surface and explode like a champagne bottle being uncorked.”
Other research teams focused on a comparison of normal and supervolcano eruptions, and attempted to simulate the conditions required for each type of eruption to take place. Luca Caricchi of the University of Geneva, Switzerland, and his colleagues simulated 1.2 million eruptions of varying sizes, and applied a varying a number of different factors including the average flow of new lava and the pressure change required to erupt.
Ordinary eruptions occur when an jet of magma is fired into the volcanic chamber, quickly increasing pressure and prompting an explosion, whereas supervolcanoes have larger chambers, with heated and flexible walls, which expand when new magma enters and contract as it cools. This means that takes a much longer time for the magma chambers of supervolcanoes to accumulate enough pressure to erupt, as the magma chambers of supervolcanoes fill much more slowly with hot magma over many thousands of years. The large volume of hot magma is less dense than the cooler crust around it, but, will eventually bursts through the surface over a much larger area, like a beach ball held under water and bursting back through the surface.
Malfait's team recreated these conditions in the lab by squeezing magma-like materials between two diamonds, while heating them, causing the samples to reach extremely high pressures. The X-ray machine was used to measure the density of the liquid silicates and compared with the density of solid rocks at Earth's surface. The difference, they found, was so great that large volumes of liquid silicates could push through solid rock above it, just as suggested by Caricchi's team. "They come more or less to the same conclusion – that buoyancy is the only real trigger that can work in very large magma chambers," says Malfait. "They are very much in agreement."
"One thing we can do is estimate the thickness of this magmatic body and see if the pressure is potentially compatible with an eruption, " said Caricchi.
What cannot be determined is the rate at which magma enters the chamber, however, which is not always predictable. At Yellowstone, for example, there is known to be a higher influx of magma than at other sites.
"We need to go around the globe and estimate the magma flux," added Caricchi." This information should reduce the frequency of eruptions predicted by the model."
This new information does not provide scientists with the means to prevent an eruption, but they may help them to make more accurate predictions of impending events, removing the element of surprise from future eruptions, and at least allowing for evacuations to take place.
Meanwhile, in Indonesia, Mount Sinabung erupted 77 times over the weekend, causing mass panic and the hurried evacuations of around 20,000 people. The evacuation zone is five to seven kilometers from the crater, but the authorities are preparing for a worst case scenario and are considering extending the zone to a full ten kilometers.
Sinabung has beenactive since September last year, and is currently on the second highest alert level in Indonesia's four level system.
Volcanoes serve to remind us that we live in a volatile and ever-evolving environment. To keep up-to-date with the latest significant events from the edge of this world, and beyond, subscribe to Unknown Country today!