There is a king in the Pacific Northwest, his brow crowned in glittering ice.
Mount Rainier starts to rise only about 25 miles from the Seattle-Tacoma metropolitan area. Today this beautiful Cascades stratovolcano, towering 14,410 feet above Puget Sound, dominates the skyline of towns and cities that sit on material that once made Rainier almost 2000 feet taller.
About 5600 years ago, around the time when the ancient Egyptians were getting organized, Mount Rainier’s northeast flank and summit collapsed. It was dramatic even as described by scientists, who say that a cubic mile (4 cubic kilometers) of flank and summit material (now called the Osceola Mudflow):
…washed across Steamboat Prow and Glacier Basin and then ran up to about the 6400-foot level of Goat Island Mountain and Sunrise Ridge. It then descended the White River valley 80 to 150 m (260- 490 ft) deep, spread out over 210 km2 (82 mi2) of Puget Sound Lowland 70-100 km (44-62 mi) from source, and flowed into Puget Sound, moving underwater up to 20 km (12.4 mi) to the present sites of Tacoma and the Seattle suburb of Kent. The contemporaneous phreatic and phreatomagmatic explosive eruptions blew hydrothermal clay and mud northeastward across Sunrise Ridge and spread pumice across an arc from south to northeast of the volcano. The Osceola edifice collapse left a horseshoe-shaped crater open to the northeast at Mount Rainier, much like the open crater formed at Mount St. Helens in 1980.
Geologists believe that this collapse happened because the rock had been weakened by the circulation of hot, acidic water inside the volcanic structure. Over time, through many eruptions, Rainier built itself back up into the majestic but dangerous structure everyone today knows and loves.
The USGS says it has seen no change in the pattern and expects Rainier to continue growing, erupting and collapsing.
Today, about 80,000 people are at risk from a potential mudflow, also known as a lahar, from Mount Rainier, say experts at the United States Geological Survey (PDF). This could be triggered by the sort of volcanic activity that the USGS monitoring network would pick up, but it might also happen without warning as another flank collapse. Such a collapse, say the geologists, could reach Orting, Washington, in as little as 40 minutes.
For this urgent need, an acoustic network now surrounds Rainier. Pierce County, Washington, also is developing a specific volcanic hazard plan (PDF) for Mount Rainier.
No one wants to live in fear when there is so much beauty and wonder about this monarch of the Cascades. Having recognized its dangers, people are working to minimize them so that everybody can continue to enjoy this beautiful mountain.. This requires a lot of work but, as shown in Jayson Yogi’s video of a 2011 Rainier summit climb via the Emmons Glacier, difficult struggles have their own special rewards.
Update, July 17, 2014: “Detailed imaging of Mount Rainier shows subduction zone in glorious detail.” Scott Johnson, Ars Technica.
Front Page Image of Mount Rainier is by Michael Lehenbauer.
“Mount Rainier,” United States Geological Survey: Volcano Hazards Program.
“Mount Rainier – Living Safely With A Volcano In Your Back Yard.” (PDF) USGS Fact Sheet 2008-3062
“Timeline — B.C.” Air War College: Contents of 12,000 Year Timeline.
“Volcanoes of the Cascades: Their Rise and Their Risks.” Richard L. Hill. Globe Pequot Press, Guilford, Connecticut. 2004.