Future Eruptions at Mount Rainier
The volcano is behaving about as it has over the last half-million years, so all evidence suggests that Mount Rainier will continue to erupt, grow, and collapse. When it does erupt again, volcanic activity may affect people living in the surrounding areas, those visiting Mount Rainier National Park, and potentially those flying overhead. Additionally, it will impact a scenic and natural resource that provides recreation, wildlife habitat, and water for drinking and power generation.
An eruption is likely to be preceded by days to months or more of small earthquakes centered beneath the volcano, by subtle deformation of the volcano, and by increases in volcanic gas emissions and temperatures. Detection of these natural precursors can allow communities to go to heightened levels of alert and take basic precautions against hazards.
New eruptions of Mount Rainier will most likely start with steam and ash explosions at the summit, and progress to the effusion of a small lava flow or the disintigration of steeply sloping lava flows as avalanches of hot rock and gas called a pyroclastic flow. Either type of eruption will probably create lahars that can reach heavily populated areas. Weak, hydrothermally altered rocks remain at high elevation on the volcano's west flank, and some of this material could be dislodged by earthquakes during an eruptive period. We cannot rule out the possibility that altered material could collapse due to its own weakness, without a triggering eruption or earthquake. Many people live in the river valleys downstream from Mount Rainier, so these eruptive and collapse events pose substantial hazards that are the reason for concerted scientific studies and cooperative measures with officials.