The CNN original series “Violent Earth with Liev Schreiber” explores harrowing weather events like hurricanes and wildfires, which are increasingly frequent in our changing climate. The final episode airs at 9pm ET/PT on Sunday.
The snow-capped peak of Mount Rainier, which rises 4.3 kilometers (2.7 miles) above sea level in Washington state, has not produced a significant volcanic eruption in the last 1,000 years. Still, more than Hawaii’s bubbling lava fields or the extensive supervolcano of Yellowstone, It’s Mount Rainier this worries many US volcanologists.
“Mount Rainier keeps me up at night because it poses a major threat to surrounding communities. Tacoma and South Seattle were built on ancient 100-foot-thick mudflows from the eruptions of Mount Rainier,” said Jess Phoenix, volcanologist and ambassador for the Union of Concerned Scientists, on an episode of “Violent Earth With Liv Schreiber.” , a CNN original series.
The sleeping giant’s destructive potential lies not in its fiery lava flows, which, in the event of an eruption, would be unlikely to extend more than a few kilometers beyond the boundaries of Mount Rainier National Park in the Pacific Northwest. And most of the volcanic ash would likely dissipate downwind to the east, away from population centers, according to the U.S. Geological Survey.
Instead, many scientists fear the prospect of a lahar — a fast-moving mud of water and volcanic rock originating from ice or snow quickly melted by an eruption that picks up debris as it flows through valleys and drainage channels.
“What makes Mount Rainier resilient is that it’s very tall and it’s covered in ice and snow, so if there’s any kind of eruptive activity, the hot stuff…will melt the cold stuff and a lot of water will start coming in. down,” said Seth Moran, a research seismologist at the USGS Cascades Volcano Observatory in Vancouver, Washington.
“And there are tens if not hundreds of thousands of people who live in areas that could potentially be affected by a large lahar, and it could happen very quickly.”
A lahar is a fast-moving debris flow
The deadliest lahar in recent memory occurred in November 1985, when the Nevado del Ruiz volcano in Colombia erupted. Just a few hours after the eruption began, a river of mud, rocks, lava and icy water swept through the town of Armero, killing more than 23,000 people in a matter of minutes.
“When it comes to rest… you have this hardened, almost concrete substance that can be quicksand when people are trying to get out of it,” Bradley Pitcher, a volcanologist and professor of Earth and environmental sciences at Columbia University, said in a episode of CNN’s “Violent Earth.”
Pitcher said Mount Rainier has about eight times the amount of glaciers and snow that Nevado del Ruiz had when it erupted. “There is potential for a much more catastrophic mudflow.”
In the U.S. Geological Survey report latest threat assessment 2018the federal agency considered Hawaii’s Kilauea the most dangerous volcano in the US – no surprise given how many people live near it and how often it erupts. Mount St. Helens, which erupted cataclysmically in May 1980, was ranked second most dangerous, ahead of Mount Rainier in third place.
Previous eruptions reveal multiple mudflows
Lahars typically occur during volcanic eruptions, but can also be caused by landslides and earthquakes. Geologists have found evidence that at least 11 large lahars from Mount Rainier reached the surrounding area, known as the Puget Lowlands, within the last 6,000 years, Moran said.
Scientists have not linked the most recent of these lahars, which occurred about 500 years ago, with any type of volcanic activity. A large landslide on the western flank of the mountain may have caused the flow event, researchers said.
Loose, weak rocks remain at that location, and it is the threat of a similar spontaneous lahar, triggered by a landslide, that particularly worries Moran and other volcanologists.
“We now know that the volcano is potentially capable of doing this again. And so we’re in this world where it could happen at any time,” Moran said.
“If it’s the same size, it’s 10 minutes to the nearest places where people live and 60 minutes to the nearest large communities. And these are really tight deadlines,” she added.
A 2022 study modeled two worst-case scenarios. In the first simulation, a 260 million cubic meter, 4 meter deep (9.2 billion cubic feet, 13 feet deep) lahar would originate on the west side of Mount Rainier. The debris flow would be equivalent to 104,000 Olympic-size swimming pools, according to Moran, and could reach the densely populated plains of Orting, Washington, about an hour after an eruption, where it would travel at a speed of 13 feet (4 meters). per second.
A second area of “pronounced danger” is the Nisqually River Valley, where a huge lahar could displace enough water from Alder Lake to cause the 100-meter-tall (330-foot-tall) Alder Dam to overflow, according to with the simulation. .
Surviving a lahar
Mount St. Helens, a cousin of Mount Rainier further south in the Cascade Range, unleashed a devastating lahar when it erupted four decades ago, although it did not reach any densely populated areas.
Venus Dergan and her then-boyfriend, Roald Reitan, were caught in the Mount St. Helens lahar while camping and are two of the few people known to have survived being swept away by a debris flow.
“I tried to hold on as we were swept downstream, the bark on the trees was just scraping. … I could feel it in my legs, in my arms,” she recalled during an interview with CNN’s “Violent Earth.”
“And at one point, I went under the logs and the mud and just resigned myself to thinking that was it. I wasn’t going to get out of this and I was going to die.”
Reitan managed to pull her out of the mudflow and they headed downriver on a huge log. When the log stopped, they jumped into a ravine and climbed a slope, where they were rescued. It took Dergan two years to fully recover from his injuries.
The world’s largest lahar evacuation exercise
After the eruption of Mount St. Helens, the U.S. Geological Survey created a lahar detection system on Mount Rainier in 1998which has been updated and expanded since 2017.
Around 20 locations on the slopes of the volcano and in the two paths identified as most at risk of lahar now have broadband seismometers that transmit data in real time and other sensors, including trip wires, infrasound sensors, webcams and GPS receivers.
The system is aimed both at detecting a lahar if the volcano wakes up in the future and at the specific scenario of a lahar triggered by a landslide, Moran said.
The original system had low bandwidth and low power requirements due to the limitations of 1990s technology, which meant data was only transmitted every two minutes.
There is a lack of historical reference data, as there are not many lahars around the world that monitoring stations have recorded, so a wider range of instruments will help determine whether a seismic signal received from one of the stations is actually from a debris flow. and not from an eruption or earthquake, Moran said.
Infrasound instruments, for example, would tell researchers that there was a disturbance at the surface of the ground, rather than deeper into the earth.
In March, about 45,000 students from Puyallup, Sumner-Bonney Lake, Orting, White River and Carbonado, Washington, participated in a Lahar evacuation exercise. It was the first time multiple school districts practiced on the same day, making it the largest lahar exercise in the world, according to the USGS.
About 13,000 students walked up to 3.2 kilometers (2 miles) to designated locations outside the mapped lahar zone, while the remainder in schools located outside the lahar zone practiced sheltering in place.
Moran said the failsafe parts of the lahar detection system are located about 45 minutes from the nearest large community, making that the time frame communities had to work with.
“Most of what happens at volcanoes is close by, which is why you try to keep people away, because things happen quickly, but lahars can travel a long way from the volcano and have a big impact.”
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