What happened when Mount St. Helens erupted — and the missing part of that story

The eruption of Mount St. Helens erupted after a massive avalanche of hot rocks triggered a change in the volcano’s position and sent out jets of molten rock and gas.

NASA research scientist Dave Karpf, who was an undergraduate at Oregon State University studying the volcanic ash and volcanic-entombing process in 1989, said the eruption is a textbook case of the “dome collapse process.”

In the event of an eruption, a long column of ash may well cover the surrounding area, with potentially disastrous consequences, Karpf said. In January of 1989, about 4,000 feet above Portland, Molten rock and gases rose from the ground, along with a massive lava dome of about 240 feet in diameter.

“I’m pretty sure it was 4,000 feet above the [Portland] Mayne Maroon, where you see that long, thin column of dust and ash,” he said. “The column was dropping and then suddenly it changed course and spiked upward.”

Karpf added: “It was like a giant pile driver, it was like, that mountain? Get the fuck out of here.”

Researchers have long theorized that a type of magnitude 7.0 earthquake could trigger the eruption of a single volcano. In the Mount St. Helens eruption, according to NASA, the earthquake came between two four-hour periods when magma was being pumped out of the volcano. That most likely sent molten rock and gases farther into the volcano’s surface than otherwise would be possible.

According to The New York Times, a 30,000-foot column of ash and volcanic gas rose straight into the sky on January 22, 1989. The ash eventually covered the entire 1,400-mile-long Cascade Range. In February, Mount St. Helens became one of the most lethal volcanoes in the world in terms of fatalities and injuries. More than a thousand people became sick, and 29 were killed, including 13 children and 11 miners. Some areas of Washington were still buried by 2 feet of ash up to a year later.

Today, Karpf is director of the Atlas Volcano Observatory at the University of Washington and research scientist in geophysics, working in collaboration with NASA’s Jet Propulsion Laboratory.

He has spent more than a decade developing techniques for studying ash and volcanic gases, and pinpointing when the ash or gases will blow or disappear. He said that timing is vitally important because not only do explosive events at Mount St. Helens yield a huge amount of ash but they also have a harmful affect on the quality of air over an extended period of time.

“You get rapid particle flow, an exceptionally high volume of particles, which not only enhance the density of the ash but will go all the way down to the very lowest clouds and the deepest layers,” he said. “So instead of just keeping the ash out of the atmosphere, it moves it around into higher layers of the atmosphere, which then is moving the gases and the moisture into our soil and our marine and ocean sediments. It’s not like the air in the west on a volcanic eruption day is going to be better quality than the air in the west every day during an ordinary day.”

Karpf’s research has helped NASA scientists forecast and predict volcanic eruptions, and helped forecasters hone a process that says when and where a volcano will erupt, and how to prepare for the experience. And earlier this year, he and lead author Jane Ward, associate professor of geology at the University of Alaska Fairbanks, wrote a study about how far a Volcano Watch alert should go before sounding the warning siren in order to get the attention of a human being on the ground.

Karpf added: “That was my first work with volcanoes, first work on this, to think that a volcano watch could send that far.”

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