On March 21, 2024, more than 45,000 students in communities south of Seattle and west of Mount Rainier participated in the world’s largest lahar evacuation drill. Although the Regional Lahar Evacuation Drill is held every two years, this year’s was the largest ever. The East Pierce Interlocal Coalition (EPIC) Emergency Management Team coordinates the drill, with support from local government officials, school districts, first responders, emergency managers, volunteers, and state and federal agencies, such as the U.S. Geological Survey. Students from Puyallup, Sumner-Bonney Lake, Orting, White River and Carbonado, Washington participated in the event. 

What is a Lahar?

Lahar is an Indonesian term that describes this mixture of mud, water, rock fragments, and debris that flows down the slopes of a volcano and typically enters a river valley.  A moving lahar looks like a churning slurry of wet concrete as it rushes downstream. Lahars can travel quickly at hundreds of miles per hour on places like the steep slopes of Mount Rainier and tens of miles per hour through nearby valleys. Lahars can be hundreds to thousands of feet tall and travel over fifty miles away from their starting point. Lahars are a common hazard found around volcanoes like Mount Rainier; they often occur during volcanic eruptions but can also be caused by landslides and earthquakes. In the Cascade Range of the Pacific Northwest, smaller flows that do not travel far from a volcano are typically referred to as "debris flows" to distinguish them from the larger and more dangerous lahars that can threaten communities far downstream. Lahars are common at Mount Rainier, because its cap of snow and ice provides water when melted, and parts of the upper flanks of the volcano contain abundant loose, weak, hydrothermally altered rock.

Why are lahars at Mount Rainier concerning? 

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Geologists have found evidence that at least 11 large lahars from Mount Rainier have reached into the surrounding area, known as the Puget Lowlands, in the last 6,000 years. A recent USGS study estimated that over 90,000 people live within Mount Rainier lahar hazard zones. Infrastructure damage in the surrounding areas could impact millions of people in the region. Therefore, evacuation drills prompt critical emergency preparedness conversations within and outside the lahar hazard zones.

Geologic evidence tells us that most large lahars occur during Mount Rainier eruptions. However, scientists have found no evidence of eruptive activity associated with the most recent large lahar, the Electron Mudflow, that occurred about 500 years ago. It is believed to have been caused by a large landslide off the west flank of Mount Rainier. USGS and other scientists have documented there is enough hydrothermally altered rock remaining on the west flank to produce another similar event. Locally, communities refer to this scenario as a “no notice lahar”; in this scenario, the closest communities would have tens of minutes to evacuate, illustrating why monitoring, warning, and evacuation planning are so important. 

Communities respond and prepare for lahar hazards 

After the 1980 eruption of Mount St. Helens, communities near other Cascade volcanoes sought more information on lahar hazards. When USGS research and modeling indicated that a large lahar from Mount Rainier was possible without a volcanic eruption, community members wanted to prepare. In response, Pierce County Department of Emergency Management (PCDEM), USGS, Washington State Emergency Management Division (WA EMD) and other local and county emergency-management agencies initiated a multi-agency effort in 1995 to develop a lahar warning system for the Carbon and Puyallup River valleys. The system became operational in 1998 and is still in operation today.

Schools, USGS and other partners help prepare students for success 

The D-CLAW model, developed by USGS scientists in collaboration with university researchers, indicates a large lahar could reach the community of Orting in as little as 50 minutes. Starting in the early 1990s, Orting schools and Orting Valley Fire and Rescue initiated evacuation drills to assess schools' response capabilities within this short timeframe. Since then, this drill has grown steadily to today’s massive effort involving over 50 facilities. This year’s drill was the first time that multiple school districts evacuated on the same day, requiring the activation of three Emergency Operations Centers to ensure the safe movement of students. 

Of the 45,000 participating students, around 13,000 walked up to 2 miles (3.2 km) each way to designated locations outside of the mapped lahar zone. The remaining 32,000 participating students attend schools situated outside the lahar zone and shelter in place. While students who sheltered in place at school would be safe there during a lahar, their homes, routes to and from school, and other essential community locations may still be within the lahar zone. Participating in the drill in any form, walking or sheltering, demonstrates to parents that students are safe and accounted for, and encourages emergency preparedness conversations at home. 

To prepare for the drill, the USGS and City of Puyallup hosted an outreach education event at the Puyallup Library on March 18th. On March 19th and 20th staff from the USGS, the Federal Emergency Management Agency, the National Park Service, WA EMD, and Washington State Department of Natural Resources partnered together to present information about geologic hazards and emergency preparedness in 11 schools to over 2,000 students. 

Year after year, these students prove that evacuating on foot is not only possible, but the most effective way to evacuate the community in the potentially short timeframes. These drills enhance community readiness for when the next lahar hazards occur at Mount Rainier. 

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