Researchers at Oregon State University think they have figured out why Mt. Hood doesn’t erupt with the same bang and violence as other Cascade volcanoes.
From a distance, Mount Hood looks like the rest of the Cascades volcanoes. But if you look closely around the base of the mountain, you don’t find big deposits of ash and pumice typical of volcanoes in the northwest. Alison Koleszar, a researcher at OSU, says the absence of that type of rock, called tephra, indicates that Hood has never experienced a violent eruption. The mountain tends to ooze, instead of explode.
“Most of the eruptions at Hood over the past 30,000 years have all occurred in about the same way, and that’s lava oozes up, so it forms a big lava dome, a blister of lava, near the top of the volcano,” Koleszar says.
Koleszar studied crystals that form in volcanic rock. She learned that before eruptions at Mt Hood, hot material rises from deep beneath the mountain, mixing with the cooler magma directly under Hood. The warmer, less viscous mix is pushed up out of the volcano more easily, explaining Hood’s history of polite eruptions.
A lava block that was ejected from Mount Hood during an eruption approximately 1,500 years ago.
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