Tacoma’s Ticking Time Bomb: The Dangerous Reality of Mount Rainier’s Lahars

When Mount Rainier erupts, it is not the lava and ash flows that pose the greatest threat to populated areas, but rather the fast-moving mixture of water and volcanic rock that comes from melting snow and ice. The snow-covered peak of Mount Rainier, 4,300 m high in Washington state, USA, has had no major eruptions in the past 1,000 years. However, surpassing the boiling lava fields in Hawaii or the Yellowstone super volcano, Rainier worries American volcanologists the most.

According to volcanologist Jess Phoenix, “Rainier keeps me up at night because it poses such a huge threat to the surrounding community. Tacoma and South Seattle are built on 100 feet of ancient mudflow from Mount Rainier’s eruptions.” Many scientists worry about lahars – fast-moving streams of water and volcanic rock that originate from melting snow and ice from volcanic eruptions.

What makes Rainier so dangerous is that it is very high and covered with snow and ice. So if any eruption occurs, the hot material will melt the cold material and a huge amount of water will begin to form. There are tens, even hundreds of thousands of people living in areas that could potentially be affected by a major lahar, and it could happen quite quickly. According to Bradley Pitcher, a lecturer in Earth and environmental sciences at Columbia University “A much more catastrophic mud flood is at risk of happening.”

The USGS established a lahar detection system at Mount Rainier in 1998 then upgraded and expanded it in 2017. About 20 locations on the volcano’s slopes were identified as having a high risk of lahars. In March of this year, about 45,000 students from various areas of Washington state participated in a lahar evacuation drill