SUPERVOLCANO THREAT: 'MANTLE PLUMES'

Life on Earth could be at threat from a catastrophic "supervolcano" which seismologists believe is due to erupt – in 200 million years' time.

At least two "piles" of rock the size of continents are crashing together as they shift at the bottom of Earth's mantle, 1,800 miles (2,900km) beneath the Pacific Ocean.

In doing so they are creating a well of partially molten rock the size of Florida, raising the prospect of a rare eruption of disastrous proportions, seismologists claim.

But the danger is "not imminent" and is likely to occur between 100 million and 200 million years from now if at all, the team from the University of Utah added.

The piles of rock were initially discovered in the 1990s, lying just above the Earth's core below some of Earth's most active volcanic zones in the South Pacific and Africa.

But a new study using earthquake waves to generate images of the Earth's interior, in a similar way that X-rays are used on the human body, found that the piles are crashing into one another.

Dr Michael Thorne, who led the study, said: "What we may be detecting is the start of one of these large eruptive events that – if it ever happens – could cause very massive destruction on Earth.

"This is the type of mechanism that may generate massive plume eruptions, but on the timescale of 100 million to 200 million years from now. So don't cancel your cruises."

The first, a hotspot plume supervolcano eruption, could be of similar scale to three eruptions at Yellowstone in the US over the past two million years, which covered much of North America with ash.

Alternatively it could result in flood basalt eruptions which could bury entire regions under igneous rock.

The scientists detected the movement of the plates using data on 51 earthquakes which took place deep below the Earth's surface, examining changes in waves to detect variations in the rock sitting above the core.

Using computer simulators, they were able to determine the shape and size of the two piles, and identify "blobs" of semi-molten rock on their edges.

Dr Thorne said: "My study might be the first to show actual seismic evidence that the piles are moving. People who have done previous simulations have suggested this.

"They are sitting atop the core and getting pushed around by overlying mantle forces like subduction. They move around on the core somewhat like continental plates drift at Earth's surface."