Washington, Oct 11 (PTI) The Pacific Northwest was hometo one of the Earth's largest known volcanic eruptions, amillennia-long spewing of sulphuric gas that blocked out theSun and cooled the planet 16.5 million years ago, according toa study.
Only two other eruptions - the basalt floods of theSiberian Traps and the Deccan Traps - were larger, and theyled to two of the Earth's great extinctions, researchers said.
"This would have been devastating regionally because ofthe acid-rain effect from the eruptions," said John Wolff, aprofessor at the Washington State University in the US.
"It did have a global effect on temperatures, but notdrastic enough to start killing things, or it did not killenough of them to affect the fossil record," Wolff added.
Starting 16.5 million years ago, vents in southeastWashington and northeast Oregon put out a series of flows thatreached nearly to Canada and all the way to the Pacific Ocean,researchers said.
The flows created the Wapshilla Ridge Member of theGrande Ronde Basalt, a kilometre-thick block familiar totravellers in the Columbia Gorge and most of EasternWashington.
It is "the largest mapped flood basalt unit on Earth,"they said.
The study, published in the journal Geology, estimatesthat, over tens of thousands of years, the floods put outbetween 242 and 305 billion tonnes of sulphur dioxide.
That is more than 4,000 times the output of the 1815Mount Tambora eruption in present-day Indonesia.
That eruption blanketed the Earth in an aerosol veil,creating the "Year Without A Summer" and food shortages acrossthe northern hemisphere, researchers said.
The volume of gas emitted from the Wapshilla Ridge lavas,is equivalent to a Tambora eruption every day for 11 to 16years, they said.
Most of the lava's gases were released during theeruptions, but some of the gas remained trapped in crystalsnear the volcanic vents.
Researchers put the eruption into one of three classes ofcataclysms, the other two being a caldera eruption like theYellowstone volcano and the impact of an asteroid.
A similar eruption today "would devastate modern societyglobally," said Wolff. PTI APA MHN SARMHN.
This is unedited, unformatted feed from the Press Trust of India wire.