Scientists Identify Third-Largest Eruption in Earth’s History

palouse river, eruptions — The Palouse River cliffs in Washington state were formed by lava flows that occurred over 16 million years ago. B.E. Butler / Getty Images

In southeastern Washington state, the Palouse River dives 200 feet (60 meters) off cliffs created by lava flows that occurred over 16 million years ago. While this in itself is impressive, researchers recently discovered something even more astounding about these cliffs: They were created by the third-largest eruption in Earth's history.

The research by Washington State University, funded by the National Science Foundation, appears in the journal Geology and details a thousand-year span during which an explosion of sulfuric gas blocked out the sun and chilled the Earth.

"This would have been devastating regionally because of the acid-rain effect from the eruptions," John Wolff, a professor in the WSU School of the Environment said in a university statement. "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."

Lava Flows Created Cliffs

About 16.5 million years ago, lava began to be released from vents in southeast Washington and northeast Oregon. The flow, laden with toxic gases, traveled nearly to the Canadian border and also found its way to the Pacific Ocean. In the process, the fiery lava carved out gorges and created cliffs like those along the Palouse River in Washington state.

The researchers estimate that, over tens of thousands of years, the flows put out between 242 and 305 billion tons (219 and 277 billion metric tons) of sulfur dioxide. Some of the gas remained trapped in crystals near the volcanic vents, which were analyzed in the WSU study by doctoral student Klarissa Davis, Michael Rowe, now at the University of Auckland, and Owen Neill, now at the University of Michigan.

This huge eruption in the Pacific Northwest is bested only by two other basalt floods — characterized as large stretches of land or ocean floor covered by lava. The Siberian Traps in Russia and the Deccan Traps in India may have led to two of Earth's major extinctions. A similar eruption today, said Wolff, "would devastate modern society globally."