This is an eyewitness report of ecological renewal at the volcano that erupted 32 years ago.
This past Saturday, August 4, a group of about 60 people hiked the Johnston Ridge trail to view Mt. St. Helens and hear about its geology and ecology. The event, advertised on DoNotBeDeceived.org, was organized with help from members of the Design Science Association of Portland and 7 Wonders Museum on highway 504 west of Mt. St. Helens. The event featured geologist Dr. Steven A. Austin, who personally researched the volcano in the weeks and years after its May 18, 1980 eruption and has hiked the area numerous times. Dr. Austin had even scuba-dived into Spirit Lake to view the patterns of tree deposition after sonar his team towed under a boat revealed trees sinking into the bottom in upright positions, analogous to the petrified forests of Specimen Ridge. He also discovered a 1/4oth scale “miniature Grand Canyon” carved by a mudflow in 1982. This canyon (left center in photo) was the destination of the hike.
Geology: The volcano is very stark, with most of the surroundings still highly impacted by the eruption 32 years ago. Two deep gorges, Loowit Canyon, headed with a large waterfall, and Step Canyon, 600 feet deep, descend from the crater and flow into the North Fork of the Toutle River. Mudflow damage along this river is still visible for miles west Mt. St. Helens. In the vast landslide debris field below the crater, the “Little Grand Canyon” becomes visible after about 1.5 miles on the trail. In many ways (except for color) the 200′ deep canyon resembles its larger namesake: it has stratified layers, round-headed side canyons and sharp gullies entering from both sides. There is a small stream flowing through it reached after a descent down Truman Trail, after 4.6 miles of hiking (requires off-trail permit).
What makes this little canyon fascinating and relevant to catastrophist geology is that we know exactly how and when it formed. The main eruption on May 18, 1980 deposited a thick layer of landslide debris. In June, a pyroclastic flow deposited 25 feet of sediments that show remarkable laminations at both large and small scales – a surprise to pre-eruption geological thinking. Finally, on March 19, 1982, a mudflow that poured from the crater deposited mud on top of the other flows, then overtopped a debris dam, causing rapid downcutting and upstream cutting through the three layers. While it might appear that the stream carved the canyon, we know from this highly-monitored volcano that the stream is a mere relic that had nothing to do with the canyon’s rapid, catastrophic formation….
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