08/24/2026
So among all the other varied things I do for a living, I've spent the tourism season this year guiding bus tours to Mt. St. Helens for Adventure Day Touring. We get to create our own tour scripts; as long as they're relevant to the trip, it's all good. Since it's a long drive from the Port of Kalama where we pick up cruise ship passengers to the mountain itself, there's ample time for me to talk about the geology of MSH, the two months leading up to the 1980 eruption, and the eruption and aftermath. I like to wrap up the talk with pointing out the ecological recovery of the landscape there.
While the first thing people often think of with MSH is the twelve mile high ash cloud that lasted all day and then circumnavigated the globe over the next two weeks, that wasn't the longest-term impact of the eruption. No, that honor goes to the lahars, volcanic mudflows that formed when the heat of the eruption melted the mountain's entire snowpack all at once, sending almost four million cubic yards of mud, rock, and dead trees racing down the mountain.
But the lahars didn't stop there. They flooded the North Fork Toutle River, then the main Toutle, then the Cowlitz, and finally the Columbia, where they filled the 40 foot deep shipping channel to just 13 feet deep. Along the way they took out almost 200 homes and two dozen bridges, largely powered by a 600 foot wide logjam at the head of the flood. When the lahars finally came to a halt, they left up to 600 feet deep mud deposits along their path.
But the mud isn't going to stay put. The Toutle keeps eroding it away as it flows, moreso with seasonal rains and snowmelt. The dam referenced in the article was completed in 1987 to help keep the mud from filling the Columbia again, and was supposed to not be full until 2035. (It was full by 2012). The Army Corps of Engineers has had to raise the height of the dam twice, and they can only raise it so much more.
While the MSH National Volcanic Monument is being allowed to recover without human interference, so scientists can see how the land responds to such a massive disturbance over time, the area referenced in the article in the c0mments is outside that boundary. Most of the human changes have been of the "timber company planting new tree plantations" variety. But I am loving seeing this effort toward bringing in beavers as ecosystem engineers.
See, it's estimated that there were once as many as 400 million beavers across North America. Excessive trapping for their fur, castor glands, or simply to get them out of the way meant that they were extirpated from most of their range, and today they are still commonly classified as nuisance animals, meaning landowners can exterminate them at will. The North American population has rebounded to about 15 million, but that's a tiny fraction of their prior numbers.
What we are finding when we reintroduce them to their old habitats is that they very often have positive impacts. In this case, they are slowing flooding and helping native ecosystems return. Beavers are a pioneer species, and were among the first animals to return to MSH after the eruption. Even if reintroduced beavers head upstream to the National Volcanic Monument, increasing beaver density there, it's only a reflection of the return of these ecosystem engineers to more normal numbers.
