Researchers Document One of Earth's Largest Volcanic Eruptions

Only two other eruptions — the basalt floods of the Siberian Traps and the Deccan Traps — were larger, and they led to two of the Earth’s great extinctions.

WSU researchers sampled sulfur dioxide trapped in rock near lava vents to gauge how much gas was put in the air by massive basalt flows 16.5 million years ago. The inset map shows the extent of the flows, with the region in the black line showing the Wapshilla Ridge flow that emitted more than 200 billion tons of sulfur dioxide.

Credit: WSU

“This would have been devastating regionally because of the acid-rain effect from the eruptions,” said John Wolff, a professor in the WSU School of the Environment. “It did have a global effect on temperatures, but not drastic enough to start killing things, or it did not kill enough of them to affect the fossil record.”

The research, which was funded by the National Science Foundation, appears in Geology, the top journal in the field. Starting 16.5 million years ago, they say, vents in southeast Washington and northeast Oregon put out a series of flows that reached nearly to Canada and all the way to the Pacific Ocean. The flows created the Wapshilla Ridge Member of the Grande Ronde Basalt, a kilometer-thick block familiar to travelers in the Columbia Gorge and most of Eastern Washington. The researchers say it is “the largest mapped flood basalt unit on Earth.”

The researchers estimate that, over tens of thousands of years, the floods put out between 242 and 305 billion tons of sulfur dioxide. That’s more than 4,000 times the output of the 1815 Mount Tambora eruption in present-day Indonesia. That eruption blanketed the Earth in an aerosol veil, creating the “Year Without A Summer” and food shortages across the northern hemisphere.

The volume of gas emitted from the Wapshilla Ridge lavas, said the researchers, “is equivalent to a Tambora eruption every day for 11 to 16 years.”

The Grande Ronde lava flows created the largest mapped flood basalt on Earth. New research shows that its Wapshilla Ridge flow produced massive amounts of sulfur dioxide, obscuring the sun and cooling the planet.

Contacts and sources:
John Wolff