Huge volcanic super-eruptions with the power to destroy civilisations take just hundreds of years to form, geologists believe. So-called 'super-eruptions', more than 100-times as large as the Mount Saint Helens incident, can spew gas, ash and rock over whole continents and cause the world to endure volcanic winters that can last decades.
It is thought that one Indonesian super eruption 74,000 years ago was so large it almost destroyed the whole human race. The cause of super eruptions is believed to be a massive magma pool that is created a few miles under the earth's surface.
Previously, it was thought that this process takes 100,000-200,000 years until it is ready to erupt.
But researchers at Nashville's Vanderbilt University suggest a study published in the Public Library of Science ONE journal that in it might only take a few hundred years until it erupts.
Director of the research and assistant professor of earth and environmental sciences at Vanderbilt University, Guilherme Gualda, says, "Our study suggests that when these exceptionally large magma pools form they are ephemeral and cannot exist very long without erupting."
Researchers examined the remains of the Bishop Tuff, Long Valley super eruption in California around 760,000 years ago.
They dated the magma formation process using the latest instruments and discovered several indications that the magma pool was created within a few thousand or even hundred years before it erupted and covered half of North America with red-hot ash.
Magna pools are often formed in pancake shapes and can be up to 25 miles across and three miles deep. Bubbles and crystals begin to form and alter its chemical make-up.
Experts think that currently no giant magma pool could produce a super eruption, but this might be because they exist for a much shorter period than assumed before.
Previous timespan calculations were based upon the fact that geologists used zircon crystals, which are often found in volcanic rock, in the measurements, says professor Gualda.
They include tiny amounts of radioactive uranium and thorium that decay to lead at a fixed rate, so researchers can discover when the crystals were originally created. They also survive many geological changes.
But because they can stand up to heat and other forces in the magma they are not very effective in showing the age of magma bodies that do not have many crystals.
So, instead, the team calculated the rate that crystals formed in quartz, which is also freely available in Bishop Tuff volcanic rock.
They tested them in four ways that showed the process took under 10,000 years and more likely 500-3,000 years until the eruption occurred.
The team believes that zircon crystals show the alterations in the earth's crust before the magma bodies are created.
As a result of the findings, geologists should be monitoring regions where super eruptions might occur, including Yellowstone National Park, in America, so they know if massive magma pools are forming.
The Geological Society of London said in 2005 that scientists could not stop a super-eruption, but they could work at predicting them and warning society.
Also working on the study was Vanderbilt doctoral student Ayla S. Pamukcu, Mark S. Ghiorso, from OFM Research, and Alfred T. Anderson Jr., Stephen R. Sutton and Mark L. Rivers of the University of Chicago. It was funded by the National Science Foundation.