Overview
- U.S. Geological Survey and Cascades Volcano Observatory researchers say lahars are the Cascades’ single most threatening volcanic hazard and pose a direct danger to towns downslope of Mount Rainier.
- Mount Rainier’s ~25 major glaciers hold far more ice and snow than other Cascade peaks, so small melts, landslides, heavy rain or minor quakes can mobilize very large, fast-moving mudflows.
- Scientists estimate a sudden “no-notice” lahar could travel from the mountain to Orting, Puyallup and Sumner in roughly 30 minutes, putting about 60,000 people inside mapped lahar paths at acute risk.
- Agencies have built real-time monitoring networks, run computer models and used a large experimental flume to study lahar behavior, but experts say prediction of sudden flows remains highly uncertain.
- Emergency planners have run large evacuation drills involving over 45,000 students and staff to test warnings and foot-escape routes, yet limited roads and potential traffic jams mean residents could still be trapped if a rapid lahar occurs.