Sometimes when I travel outside the Pacific Northwest and meet people, they ask where I live. “Outside Seattle, near Mount Rainier,” I tell them. They often scrunch up their face and squint funny, replying, “Um, that’s an active volcano, right?” Yes, it sure is!
Mount Rainier boasts several vital signs of an active volcano. First is the frequent occurrence of earthquakes beneath and around the mountain, most of which are detected only by the instruments designed to record them. As this column went to press, park geologist Scott Beason had recorded 29 earthquakes around Mount Rainier in the last 30 days.
A second vital sign is the presence of gases—mostly carbon dioxide—that bubble up from the mountain’s underground “plumbing system” through mineral waters in the Longmire and Ohanapecosh areas in the park.
The third sign Mount Rainier is a living volcano is the steam vents high on the upper slopes that emit hot gases and vapors. These emissions, often reported by climbers as smelling like rotten eggs, signal activity deep within the mountain’s interior.
This is probably a good time for my disclaimer: I’m not a geologist. That said, I have spent untold hours tagging along after them, trudging up and stumbling down mountain slopes, asking questions and making notes, attending conferences and workshops, and reading and dissecting scientific papers. As my geologist friends would say, “You can trust me on this.”
Considering the spectacular 1980 eruption of a neighboring active volcano, Mount St. Helens, you’d be forgiven a moment of panic and the urge to check the real estate market in Peoria (Arizona or Illinois) or Omaha, Nebraska. But relax—there’s good news! Although Rainier and St. Helens are first cousins sitting just 50 miles apart on the spine of the Cascade Mountain Range, their volcanic tendencies differ. As Patrick Pringle explains in “Roadside Geology of Mount Rainier National Park and Vicinity”, the gas-trapping magma at St. Helens runs cooler and thicker. This favors the buildup of lava domes and eventually, large, catastrophic eruptions. Mount Rainier’s hotter and more fluid magma flows longer distances but without such dramatic eruptions. Its geologic history—which is the best predictor of future events—includes eruptions with ashfall (fine particles) and tephra (all sizes of rock and lava), some having occurred as recently as the mid-1800s. None has approached anything close to the magnitude of Mount St. Helens’ headlines-grabbing blow-ups.
That’s good news, right? You don’t have to worry about leaving behind this area’s eye-popping natural beauty and moving to the flatlands. And now, the bad news: In its 2018 update to the U.S. Geological Survey National Volcanic Threat Assessment, Mount Rainier scored a “very high threat” ranking, coming in third after Hawaii’s Kilauea (frequent and widespread lava flows) and Mount St. Helens (violent eruptions). Yikes! If Mount Rainier doesn’t pose the explosive threat of St. Helens, why list it as one of the most dangerous volcanoes in the country?
The answer lies at the intersection of the mountain’s geologic history and its nearness to large population centers. In “Postglacial Lahars from Mount Rainier Volcano, Washington,” pioneering geologist Rocky Crandell detailed over 55 debris flows called lahars that have rumbled down the mountain’s slopes and into river valleys over the last 10,000 years. A wet, concrete-like slurry that can top 40 miles per hour, a lahar engulfs everything in its path. The word lahar translates from the Indonesian word meaning “like a thousand stampeding water buffalo,” giving a vivid sense of the sound and power of these unstoppable forces of nature.
One of the world’s largest lahars — the Osceola Mudflow — began about 5,600 years ago (a finger-snap in time by geologic standards) when the upper northeast flank of Mount Rainier collapsed and rushed down the White and West Fork White Rivers. Adding rocks, trees, and other debris to its incredible bulk as it gushed down the valley at the height of a 50-story building, it tore across the Enumclaw Plateau, burying parts of present-day Enumclaw under 60 feet or more of lahar debris. Part of the flow poured west through present-day Buckley, eventually running out into Tacoma’s Commencement Bay, while another giant tongue of it flowed through today’s Kent and Auburn areas to fill in 60 square miles of Puget Sound. Its volume of nearly one cubic mile could have filled CenturyLink Field, home of our beloved Seattle Seahawks, over 2,000 times.
In an interesting side note, Green River Community College archaeology professor Gerald Hedlund oversaw digs from 1968 until the late 1970s at a Native American site two miles west of Enumclaw that had been overrun by the Osceola Mudflow. Students found fire hearths, earth ovens, and building posts. They recovered over 13,000 stone tool artifacts, many of them projectile points, scrapers, and knives. The age and number of items made it one of the most important collections of native artifacts in the Puget Sound region.
In addition to a rich history of lahars and the possibility of future ones, the other factor placing Mount Rainier in the survey’s top three of dangerous volcanoes is the many cities and towns situated in the valleys leading away from the mountain. Lahars follow the unrelenting laws of physics, flowing downhill and filling river valleys. A 2012 Washington Department of Natural Resources report by Recep Cakir and Timothy J. Walsh estimated that future lahars could jeopardize 1.2 million people and properties valued at $40 billion. These factors place Mount Rainier near the top of the list.
Yes, we live near an active volcano. But before you resume scanning real estate listings in Arizona, Illinois, or Nebraska, remember that nearly everywhere, people live with the potential for some kind of natural disaster. Earthquakes, fires, floods, hurricanes, tornadoes and other events all pose serious threats, depending on where you live. So breathe easy. In the next column, we’ll see that if you’re going to live near a volcano, Enumclaw is much safer than many other places. Until then, keep your boots dry and your spirits high.
Correction to the August column: Although the scattering of human ashes within Mount Rainier National Park is considered illegal without a permit, it’s now possible to receive a permit and do so legally.
Jeff Antonelis-Lapp is an educator, naturalist, and writer living in Enumclaw since 1982. Tahoma and Its People, his natural history of Mount Rainier National Park, was published this spring by Washington State University Press. Copies are available at https://jeffantonelis-lapp.com/. Jeff would love to hear from you about Mount Rainier. Send your questions and favorite stories to firstname.lastname@example.org, and subscribe to his blog, too.