Scientists Name Mt Rainier America's Most Dangerous Volcano

Lahars are unusual among volcanic hazards because they do not require an eruption to occur. According to the United States Geological Survey (USGS) and the Cascades Volcano Observatory (CVO), Rainier's 25 major glaciers hold more than five times as much snow and ice as all other Cascade volcanoes combined. A heavy rainstorm, a sudden thaw, or even a dam failure can loosen this material and trigger a "no-notice" lahar that grows hundreds of feet tall and travels more than 50 miles. Former CVO geophysicist Andy Lockhart described such silent flows as "the thing that goes bump in the night." Volcanologist Lizeth Caballero García noted that lahars are complex phenomena: they can grow, dilute, and change shape as they move downhill.

The dangers are not theoretical. In November 1985, a lahar from Colombia's Nevado del Ruiz volcano buried the town of Armero and killed more than 23,000 people within minutes. To prevent a similar tragedy, the CVO has installed a network of seismic monitors throughout the Cascade Range to detect lahars and earthquakes and alert emergency responders. Two years ago, more than 45,000 students and staff from over 20 schools west of Rainier took part in one of the world's largest lahar evacuation drills. Officials say the exercises confirmed what previous studies have long shown: in the short minutes a lahar allows, fleeing on foot — and uphill — remains the most effective way to escape its path.