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Violent volcanoes fuelled by 'highway from hell'

Short fuse A subterranean "highway from hell" enables some volcanoes to erupt at super-speed, a discovery that also throws up options for predicting the peril, according to a new study.

Volcanoes disgorge molten rock generated within the mantle, the layer sandwiched between Earth's crust and fiery core.

The magma gathers in a chamber beneath the volcano, progressively rising until the pressure -- detectable over time by rumblings at the surface -- becomes too great and an eruption occurs.

Conventional wisdom has it that the mantle magma creeps upwards before it reaches the chamber, lingering for long periods in a kind of halfway house several kilometres beneath the volcano.

But the new research, published in the journal Nature, suggests there are channels that run directly through the crust from the mantle to the magma chamber itself.

As a result, a volcano can be recharged and primed for action in a matter of months -- a blink of an eye in geological terms, and a clear danger to humans living nearby.

The evidence comes from traces of an eruption between 1963 and 1965 of Irazu, a Costa Rican stratovolcano located on the notorious Pacific Ring of Fire.

A team led by Philipp Ruprecht of Columbia University's Lamont-Doherty Earth Observatory in New York analysed ashes from an 2010 expedition to Irazu.

Nickel spikes

Buried in crystals of the volcanic mineral olivine were spikes of nickel, which is a trace element in the mantle.

The spikes were a telltale sign of an extraordinarily fast ascent -- a slower rise would have meant that the nickel would have melted and diffused through the crystals.

The magma charged 35 kilometres through the crust in just months, the team calculates.

"There has to be a conduit from the mantle to the magma chamber," says geochemist Terry Plank. "We like to call it the highway from hell."

Olivine with the signature nickel spikes has also been found in volcanoes in Mexico, Siberia and northwestern America, proving that this is not a local phenomenon, according to the researchers.

The findings may explain why seismologists have sometimes detected mysterious earthquakes occurring at great depths -- 20 to 30 kilometres -- several months before great eruptions.

These may herald mantle magma blasting its way through the hidden channels.

These examples include the 1991 eruption of Mount Pinatubo in the Philippines -- an event that disgorged so much ash into the atmosphere that it temporarily cooled the planet -- and the 2010 blowout of Iceland's Eyjafjallajokull, causing the famous ash cloud that resulted in widespread flight cancellations.

Vulcanologists, says the paper, should try to look for signs of deep quakes in the lower and middle crust. Giving a warning several months before an eruption, rather than days or weeks, would save lives and limit destruction to property.

But, say the authors, volcano prediction is still a tricky business. Scientists still have to learn what to look for and to translate the signals into a useable date of when the eruption will occur.