One feature of Mount Rainier that I haven’t covered yet and think is fascinating is its volcanic nature. More specifically, what would happen if it erupted before some of us ever get to stand on top.
The living model is Mount Saint Helens, which — as you probably know — erupted on May 1980. The eruption caused lahars (mudflows) to surge through a significant portion of the state of Washington. The news footage from the event makes me appreciate the various powers of earth, just as do other phenomena like glaciers, mountain slopes, rain storms and even sunshine. They all have a significant impact on the landscape.
While most think of lava, ash, and pumice as the biggest threats from Mount Rainier, it’s actually flooding and lahars. In fact, just a pressure explosion from trapped underground steam — rather than a major eruption involving lava — would melt the vast snow and ice reservoirs on the mountain sides in the form of glaciers, snowfall and snow fields. One of the largest glaciers, the Emmons alone is six miles long, two wide and several hundred feet deep. That’s a lot of water!
The glacier melting and mixing with the soil and rock on the mountain’s slopes would quickly overwhelm the surrounding area. It’s estimated that Orting, Washington would be struck by mudflows in one-to-two hours after a steam eruption. The town could be hit by a lahar 30 feet deep and be left buried in 15 feet of moist soil and debris. Though other estimates claim that Rainier has potential to send lahars that are 100 feet deep and they might move at a rate of 45 to 50 miles per hour.
Population-wise, the three-plus million residents around Puget Sound are the most at-risk from the mudflows that could come down the Carbon, Payallup, Nisqually and Green Rivers. 150,000 people live atop previous mudflows, and some of them having done excavating for a variety of reasons have said that they have dug up entire tree trunks and stumps in the ground. If an eruption were to occur, this group or residents would have to be notified to evacuate as quickly as possible as there will be little-to-no warning of an eruption of any kind based on current forecasting and technology. To help prevent greater impact to more people, there are attempts to limit community development in the at-risk paths.
In the end, Rainier won’t remain over two-and-a-half miles high. The Seattle skyline will have been changed and one of our classic climbing destinations will have been forever changed. While the odds are low for an eruption anytime soon, according to experts, when the event comes, it will be powerful.
Sources: 1) Filley, Bette, The Big Fact Book About Mount Rainier: Fascinating Facts, Records, Lists, Topics, Characters and Stories, Dunamis House, 1996; and 2) “Mount Rainier: Learning to Live with Volcanic Risk,” NationalAtlas.gov.