RICHLAND, Wash. – Around 17-million years ago the tectonic plates underneath Oregon shifted and ripped a giant tear in the Earth’s surface. That’s according to a new model by two researchers at the University of California, San Diego. They say, magma then poured out for about two million years – the blink of an eye in geological terms. The researchers think all that activity created the Columbia River Flood Basalt. Basalt is a type of igneous rock formed from lava.
You can try to picture it this way, says geophysics professor Dave Stegman: the amount of lava coming out of this tear was a million times bigger than the 1980 Mount St. Helens eruption.
“Flood basalt is one of the most impressive geologic phenomena in all of Earth’s history. The amount of lava that pours out on the surface is astronomical,” says Stegman.
The Columbia River Flood Basalt formation has always mystified scientists. Stegman says this model should clear up questions about how the massive geological area was created.
Both this new model and previous models show large amounts of magma flowing to the surface – they just attribute different causes. This new model focuses more on pressure created by the giant tear in the Earth’s surface. Stegman says flood basalts in other parts of the world formed differently. Researchers considered that when creating this model.
“We weigh the evidence for each flood basalt, and this particular mechanism works best to explain this particular flood basalt,” Stegman says. “But [with] other flood basalts, both of us agree, that the evidence points to a mantle plume, a large mushroom-shaped plume head, as the origins for the giant out pouring of magma in those settings.”
The researchers say one of the key points to their new model is the tectonic plate location. They say the new model lines the plates up correctly with their location today. That also corresponds with volcanic eruptions in the area. Stegman says the initial giant tear happened at Steens Mountain in southeastern Oregon, where the Columbia River Flood Basalt first began to form.
Researcher Lijun Liu says the new model is more sophisticated than previous ones. He says interdisciplinary work also helped further this model.
“We didn’t use the Columbia River geology, whatsoever, to constrain the model in the first place. But it’s almost like a prediction, and that’s why we have confidence in this story,” Liu says.
The researchers believe this model could help predict future volcanic eruptions caused by shifting plates in places like Alaska, South America and the Pacific.
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