Washington: Life on Earth could be facing 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, 2,900 km beneath the Pacific Ocean, researchers say.
"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," said seismologist Michael Thorne, the study`s principal author and an assistant professor of geology and geophysics at the University of Utah.
However, disaster is "not imminent," he adds, "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 new study, published in the journal Earth and Planetary Science Letters, said the activity is creating a Florida-sized zone of partly molten rock that may be the root of either of two kinds of massive eruptions far in the future.
Hotspot plume supervolcano eruptions like those during the past 2 million years at Wyoming`s Yellowstone caldera, which covered North America with volcanic ash.
Gargantuan flood basalt eruptions that created "large igneous provinces" like the Pacific Northwest`s Columbia River basalts 17 million to 15 million years ago, India`s Deccan Traps some 65 million years ago and the Pacific`s huge Ontong Java Plateau basalts, which buried an Alaska-sized area 125 million to 199 million years ago.
"These very large, massive eruptions may be tied to some extinction events," Thorne said. The Ontong eruptions have been blamed for oxygen loss in the oceans and a mass die-off of sea life.
Since the early 1990s, scientists have known of the existence of two continent-sized "thermochemical piles" sitting atop Earth`s core and beneath most of Earth`s volcanic hotspots - one under much of the South Pacific and extending up to 20 degrees north latitude, and the other under volcanically active Africa.
Using the highest-resolution method yet to make seismic images of the core-mantle boundary, Thorne and colleagues found evidence the pile under the Pacific actually is the result of an ongoing collision between two or more piles.
Where they are merging is a spongy blob of partly molten rock the size of Florida, Wisconsin or Missouri beneath the volcanically active Samoan hotspot.
The study`s computer simulations "show that when these piles merge together, they may trigger the earliest stages of a massive plume eruption," Thorne said.