LONDON, Aug. 8 (Xinhua) -- Large-scale volcanic eruptions started life 100 kms underground over millions of years, a new research published in the latest edition of Nature has revealed.
With super eruptions expected once every 20,000 years, one could even be due as the last massive volcano to erupt occurred 26,000 years ago, said Prof. Stephen Sparks, an experienced vulcanologist from the University of Bristol.
Sparks led an international research project in the Andes in northern Chile where a number of massive volcanic eruptions happened many years ago, aimed at giving early warning and forecast for volcanic eruptions.
"These eruptions happened a long time ago in the Andes. We could look at the whole process of how the magmas are generated and how they erupt. And we find these huge eruptions happen about every million years. So they're very rare events, but there's a certain regularity of them erupting," Sparks told Xinhua.
"We believe that reflects processes in the Earth which lead to periodic behavior in which large amounts of molten rock accumulated over very long periods of time, and then really quite rapidly in a geological sense, rise to the Earth's surface and erupt in one go," he said.
In the research, the researchers using radioactive isotopes dated tiny little crystals, which were erupted in the volcano, are up to two or three million years older than the age of eruption itself.
"That's telling us that the processes which lead up to these enormous eruptions is a very long process, and can easily be millions of year," Sparks said.
"It's somewhat unexpected. What we found was that before you really got much volcanism at all, magmas had been stored underground. They intruded into the shallow part of the crust, maybe ten or 20 kilometers depth, and accumulated there. And they had to build up enough energy for these enormous eruptions. And that seems to have taken a few million years to do that," he added.
The research in the Andes was part of a project supporting the mining company BHP who were exploring for copper. Deep drills through volcanic rocks in the northern part of Chile were taken as part of the exploration program.
He said what was now of great interest is how often eruptions of that scale happen.
"We've been studying the rates of these eruptions around the Earth and we find that roughly there's one every 20,000 years. So they're pretty unlikely to happen during any one human's lifespan. The last one we know about was in New Zealand about 26,000 years ago," he said.
Sparks said there are about 1,500 volcanoes which have known to be historically active on Earth, with about 50 so-called super eruption volcanoes.
On the impact of super volcano eruptions, Sparks said that locally they might damage areas of hundreds of thousands of square kilometers, either through big fast moving flows or a massive amount of volcanic ash falling on the ground.
He added: "Perhaps the biggest concern is that these eruptions pollute the Earth's atmosphere for several years. They put up a lot of dust and volcanic gases like sulphur. And these gases can perturb the climate because they actually produce global cooling rather than warming for several years."
Sparks says the new research will help experts better understand the causes of episodic volcanism.
"Volcanoes don't erupt all the time, they're quiet for very long periods of time, not doing very much. They're just basically a mountain that's causing no harm, and then suddenly they burst into life and explode and erupt and cause a lot of damage," he said.
"With the kind of study we've just published in Nature, we're starting to get insights into how volcanoes can behave in this way," he added.
"We think it's to do with the need for large amounts of molten rock to accumulate underground for long periods of time before enough energy is developed for this magma to rise up and erupt. And so we're starting to develop a theory of why volcanoes erupt episodically," said Sparks. ■
