ModeratorThe snowcapped peak of Mount Rainier, which towers 4.3 kilometers (2.7 miles) above sea level in Washington state, has not produced a significant volcanic eruption in the past 1,000 years. Yet, more than Hawaii’s bubbling lava fields or Yellowstone’s sprawling supervolcano, it’s Mount Rainier that has many US volcanologists worried.
“Mount Rainier keeps me up at night because it poses such a great threat to the surrounding communities. Tacoma and South Seattle are built on 100-foot-thick (30.5-meter) ancient mudflows from eruptions of Mount Rainier,” Jess Phoenix, a volcanologist and ambassador for the Union of Concerned Scientists, said on an episode of “Violent Earth With Liv Schreiber,” a CNN Original Series.
The sleeping giant’s destructive potential lies not with fiery flows of lava, which, in the event of an eruption, would be unlikely to extend more than a few miles beyond the boundary of Mount Rainier National Park in the Pacific Northwest. And the majority of volcanic ash would likely dissipate downwind to the east away from population centers, according to the US Geological Survey.
Instead, many scientists fear the prospect of a lahar — a swiftly moving slurry of water and volcanic rock originating from ice or snow rapidly melted by an eruption that picks up debris as it flows through valleys and drainage channels.
“The thing that makes Mount Rainier tough is that it is so tall, and it’s covered with ice and snow, and so if there is any kind of eruptive activity, hot stuff … will melt the cold stuff and a lot of water will start coming down,” said Seth Moran, a research seismologist at USGS Cascades Volcano Observatory in Vancouver, Washington.
“And there are tens, if not hundreds of thousands of people who live in areas that potentially could be impacted by a large lahar, and it could happen quite quickly.”
A lahar is a fast-moving debris flow
The deadliest lahar in recent memory was in November 1985 when Colombia’s Nevado del Ruiz volcano erupted. Just a couple hours after the eruption started, a river of mud, rocks, lava and icy water swept over the town of Armero, killing over 23,000 people in a matter of minutes.
“When it comes to rest … you’ve got this hardened almost, like, concrete substance that can be like quicksand when people are trying to get out of it,” Bradley Pitcher, a volcanologist and lecturer in Earth and environmental sciences at Columbia University, said in an episode of CNN’s “Violent Earth.”
Pitcher said that Mount Rainier has about eight times the amount of glaciers and snow as Nevado del Ruiz had when it erupted. “There’s the potential to have a much more catastrophic mudflow.”
In the the US Geological Survey’s most recent threat assessment from 2018, the federal agency considered Hawaii’s Kīlauea the most hazardous US volcano — no surprise given how many people live near it and how frequently it erupts. Mount St. Helens, which cataclysmically erupted in May 1980, ranked as second most hazardous before Mount Rainier in third place.
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