FAQs

Although Mount Rainier has not produced a significant eruption in the past 500 years, it is potentially the most dangerous volcano in the Cascade Range because of its great height, frequent earthquakes , active hydrothermal system , and extensive glacier mantle. Mount Rainier has 25 major glaciers containing more than five times as much snow and ice as all the other Cascade volcanoes combined. If...

Debris flows ( lahars ) pose the greatest hazard to people near Mount Rainier . A debris flow is a mixture of mud and rock debris that looks and behaves like flowing concrete. Giant debris flows sometimes develop when large masses of weak, water-saturated rock slide from the volcano's flanks. Many of these debris flows cannot be predicted and may even occur independently of a volcanic eruption...

Eruptions of Mount Rainier usually produce much less volcanic ash than do eruptions at Mount St. Helens . However, owing to the volcano's great height and widespread cover of snow and glacier ice, eruption triggered debris flows ( lahars ) at Mount Rainier are likely to be much larger--and will travel a greater distance--than those at Mount St. Helens in 1980. Furthermore, areas at risk from...