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GSOC Field Trip to Ape Cave, Mt. St. Helens, Washington
by Janet Rasmussen
The annual Geological Society of the Oregon Country (GSOC) picnic was held on August 13 this year at Mt. Tabor Park. The following weekend, Doug, Forrest, and I drove up to Mt. St. Helens for a tour of Ape Caves and surrounding volcanic features, led by Ken Cameron.
Clay Kelleher was the grillmaster at the picnic, which was complemented by some wonderful potluck dishes.
GSOC member Tara Schoffstall brought crafts materials for geologic art projects for young and old. I made a flowerpot decorated with many beautiful rock specimens donated by Taylor Hunt.
Larry Purchase brought these 10 million year old shell fossils which he found on the previous GSOC field trip to the Oregon Coast.
On the following Saturday, over 40 people participated in the Ape Cave field trip. Organizers Bev and Bart are here with Ken Cameron, who is on the left.
Ken gives some preparatory remarks about the geology of the lava tube caves near Mt. St. Helens, and provides us all with digital elevation maps. The lava that created this cave flowed about 1900 years ago.
We climb down the stairs into the cave. At first, the cool air is refreshing. But by the end, I was really getting cold, even with a heavy sweatshirt.
Forrest was the youngest person on the tour. He enjoyed getting ahead of the crowd into the dark cave with his flashlight.
The walls of the cave had been remelted after later lava flows came through. The textures were varied and beautiful.
We stopped occasionally for Ken to explain some of the features seen, and to keep the large group together. One thing I had never thought of: the lava tube meandered back and forth, going slightly downhill in the direction of flow for 3/4 mile (it also went 1 1/4 mile in the opposite direction uphill, but that was a rougher walk that we didn't take). He said the lava coming from the mountain flowed down a river channel, seeking the lowest ground as a fluid would. Therefore, the cave traces the path of a river.
This was a remarkable sight: flowing lava had buoyed up these loose fragments, which were rounded, and then they cooled enought to become welded to the gap in the ceiling.
After lunch at the Trail of Two Forests trailhead, we strolled down to look at these tree holes which were caused by lava flowing over and around trees, which then burned or rotted away. Some of these were standing trees, and some were either knocked over by the flow or were already down.
Doug has climbed down a short ladder into one standing treehole, and then enters a horizontal treehole that can be climbed through.
These are my feet, I'm following Doug through the horizontal tunnel. You can see the shape of the bark of these ancient trees in the walls. I went through without a light, and really couldn't see anything at the time.
I came out through another tunnel that intersected with the first (two downed trees lying over one another). But Doug was intrigued to see if he could fit through the narrowest opening. He could, but nearly got stuck.
