Mount Saint Helens Revisited: A Missing Forest
My last post reported on Miocene (23-5.3 Ma) volcanic rocks on the eastern flank of Mount Saint Helens. Those rocks predate the creation of Mt St Helens, however; we reached our destination and, before exploring a lava tube called Ape Cave, we examined some interesting geology that is part of the most recent eruptive stage of this active stratovolcano. The Spirit Lake stage began about 4500 years ago. There were three earlier stages, beginning about 40,000 years ago; each lasted less than 5000 years.
Figure 1. About 1900 years ago, a large amount of basalt lava flowed from a fissure on the south flank of the volcano (indicated by a square in the inset map of Fig. 2). The lava was hot (~1200 C or 2200 F) and set the forest on fire; when the wood had been turned to charcoal, the lava cooled to leave casts of the trees. My wife is taking a photo of a small-diameter tube we’ll examine it more closely below.
Figure 2. Mount Saint Helens is about 70 miles south of Tacoma (Home in the right map), but the route we followed, around the north and east flanks, takes 3.5 hours to drive. The yellow areas in the inset map are mostly andesite lava flows older than 5 Ma. The circle is where we looked at them in the last post.
Figure 3. These holes were everywhere, forming a hazard for people walking, so a walkway was constructed over the area where the tree holes are densest. They haven’t been cleaned out and most are 3-4 feet deep.
Figure 4. This is the cast of a fallen log. The entrance is shown in Fig. 1; visitors are encouraged to crawl through it, about 40 feet, but it was too tight for us. However, several children I met there had braved the dark, tight tunnel.
Figure 5. This photo was taken a couple-hundred yards from the missing forest. The background reveals the leading edge of a lava flow that’s about ten-feet high. The foreground shows a stream being incised into the landscape, probably created along a collapsed lava tube. Regrowth of the forest is slow in the lava surface; however, there was no mention of whether or not this area was logged in the last century–it probably was, given the documented greed of the forest industry when it came to cutting down trees. However, I didn’t see any large stumps, so maybe it wasn’t worth the effort.
Figure 6. This is a mound of lava projecting up to 8 feet above the surrounding landscape. Several features are worth mentioning: 1) it is circular in plan and about 30 feet in diameter; 2) the upper-center of the image shows concentric bands of ropy lava known as pahoehoe, from its common occurrence in Hawaii; and 3) there is a small cave beneath it where lava ran out of the hardened surface. We’ll see a lot more of that in my next post.
Final Thoughts
Our journey along the backroads took us through a vast terrane of andesitic volcanism created more than five-million years ago. Then, about forty-thousand years ago, a new phase of volcanism began and Mount Saint Helens was created from this rugged ground.
Stratovolcanoes don’t just erupt at their summit, even though that is exactly what Mt St Helens did in 1980; more often they leak lava from the myriad faults and fissures surrounding them, especially in an active subduction zone where the earth’s crust is being compressed, twisted, and warped by tectonic forces.
Life is difficult in such an environment and we are fortunate to have a moment in time frozen for us to contemplate how immense the forces are that constantly reform the surface. Eruptions like the one that destroyed this forest are unlikely to kill many people, but they are crucial in reforming the environment. A new forest grows, possibly inhabited by different species of fauna and flora, and life goes on.
My next post will examine this same eruption event, but at a scale that dwarfs what we saw today.
Mount St. Helens Revisited: Miocene Volcanic Rocks
I couldn’t stay away from this fascinating active volcano. I reported on the recovery of the north flank, after the 1980 eruption, in a previous post. Today I visited the eastern and southern flanks, which were spared the devastation of an enormous explosion.
Figure 1. Mount Saint Helens National Volcanic Monument is about three-hours from Tacoma (Home in the left plate). We took back roads and circumnavigated the volcano today, following NF 25 (seen in the right plate), which took us through a volcanic terrain constructed during the last 23 million years. The circled area is the focus of this post. The rock types vary widely, but they are predominantly andesitic flows, ash layers, and breccias. The usual mixed bag of volcaniclastic rocks we expect in a subduction zone plate margin.
Figure 2. This photo reveals a series of thin beds that suddenly dip towards the road. They are highly fractured to the right of the image. Obviously, these were not recently erupted; they have been deformed in the last twenty-million years.
Figure 3. This image shows layers of volcanic ash that are weathering to reveal how thin the laminae are.
Figure 4. This photo dramatically reveals how much can happen in 10-20 my (million years). It was taken a few hundred yards from the previous photo. To the left are layers of ash that dip away from the camera–juxtaposed with steeply dipping layers that curve to the right and become almost horizontal (in the plane of the image) in the upper-right image quadrant.
Figure 5. This image, taken less than a mile from Fig. 4, reveals thick layers of ash and flows. I didn’t examine them closely, but the middle-right of the photo shows a substantial change in bedding.
Final Thoughts
Mount Saint Helens is part of the Cascades range, an elongate series of volcanoes that have been active for the last 60 my because oceanic crust is being subducted beneath the North American tectonic plate. The rocks we saw today are from an earlier phase of volcanism; they were buried to depths of several miles, deep enough to become cemented, but not deep enough to become ductile. Thus, they failed in brittle fracture as they were compressed by the huge pile of volcaniclastic rocks created along the ocean margin.
What comes up must go down. This simple phrase means that the earth’s upper mantle (including the subducting ocean plate) melted and produced a lot of magma, which rose because of its lower density and high pressure, filling every fracture, expanding them into magma chambers. The mantle collapsed because of these voids and the weight of the recently extruded magma. A balloon being repeatedly inflated and deflated.
Meantime, the compression was inexorable. The recently buried volcanic rocks broke along faults, creating the juxtaposition of volcaniclastic material we see in Fig. 4.
These aren’t geologically old rocks. This is a continuous process that we are able to witness in real time throughout the world.
We’ll see this continuous process in closer detail with my next post.
Review of “Raft” by Stephen Baxter
This is a review that I’m glad to write because, despite my often scathing criticism of what I consider half-finished books, Stephen Baxter finished the job. I don’t particularly like science fiction that borders on fantasy, but he keeps his wildly speculative physics consistent to the end; of course, he has a lot of leeway. The cover photo gives the reader a hint of what’s coming–flying trees?
The story that unwinds checks all the boxes: simple plot with plenty of action; good character arcs that aren’t too extreme; exposition written into dialogue in a very believable way; no extraneous characters or side plots confusing the story; a romantic subplot; a surprising ending, despite the reader knowing what’s coming; and, best of all, he does it in 245 pages.
The writing style is solid and the story is easy to follow. Furthermore, the author doesn’t seem to grow tired of the story after the half-way point, probably because he kept the length reasonable. Science fiction doesn’t have to require 400 pages to be understandable and believable. This reminds me of books written in the 60s and 70s; tell the story with enough background to make it comprehensible, but don’t share all of the notes that went into the final draft.
I recommend this novel to anyone who is willing to see what others can imagine.
Stormwater Project: Planting some grass
We stopped by the PNW garden at Pt. Defiance to see some local plants in the wild, but the gate was locked; so we went to Portland Ave. Nursery to view a wide selection of good base plants for the rain garden. We resisted temptation and only selected a few large grasses for now; I dug some holes and we got them in the ground with a quality planting soil.
I better record the names of the plants as I go or I’ll forget them for sure. The one closest to the camera is Sundowner New Zealand Flax (Phormium ‘Sundowner’); it is an evergreen plant that grows 5 ft. tall, 4-6 ft. wide, and blooms in summer. The two in the middle of the photo are Pampas Grass (Cortaderia ‘Silver Feather’); they grow 5-8 ft. high, 2-3 ft. wide, and bloom in summer to winter. The plant in the background is Cabaret Japanese Silver Grass (Miscanthus sinensis ‘Cabaret’); it will grow 7 ft. high and 4 ft. wide; coppery plumes appear in early fall.
This view shows our new plants, with some potted flowers we found earlier in the summer. They fit in well and should make the back yard look good in the near future.
Wing Luke Museum: A Guided Tour of an Immigrant Hotel
Wing Luke was a pioneering Chinese American lawyer, civil rights advocate, and the first Asian American elected to public office in Washington State. When he died in a small aircraft accident in 1965, the community formed the Wing Luke Museum in his honor. It celebrates Asian-American history and culture, and owns a hotel it purchased to display the lives of early immigrants.
The Yick Fung Corporation was formed by a group of Chinese immigrants because they were legally forbidden from owning property in Washington. This store served as a supplier to restaurants throughout Washington.
South Weller Street led directly to the tidal flats where the church steeple stands today. As part of a downtown reshaping, several hills were flattened and the soil used to fill in the nearshore area.
In addition to supplying regional restaurants, you could buy a third-class ticket to Hong Kong (or maybe Shanghai) for $1500 in today’s money. The store remained open until 2008.
To circumvent some of the financial restrictions, the Chinese immigrants formed associations of people from the same villages back in China. This is the meeting room of one such group. They assisted newcomers and planned civic activities. It was kind of like the YMCA.
This is the game room, where people played mahjong and other games.
The hotel contained about 180 apartments, but some of them had up to three rooms. This was the home of a family with eight children. The hotel remained a center of immigrants until it was closed in 1974 because of updated fire codes (after the deaths of twenty or so inhabitants in about 1972). The Wing Luke Museum purchased it and is renovating it as part of the display.
Every room was required to have a door and window. Most of the rooms were small. That is the light shaft out the window; it didn’t lead anywhere and only extended to the second floor, just for light and air.
Living out of your suitcase?
Here’s the light shaft. During reconstruction the building was modified and reinforced.
The museum also had exhibits displaying artwork and pictorial histories of many Asian immigrants, including Hawaiians. Overall, it was very interesting and worth the price of admission. I think it was $22 for a senior like me.
Fort Steilacoom Park and Lake Waughop
After spending the last five days walking around the back yard, digging the rain garden, I drove my FJ40 to Lakewood to take a look at Fort Steilacoom Park.
This play area was the only fort I saw.
But there were several old barns in various levels of disrepair. Apparently, Fort Steilacoom was the first U.S. military post in Washington, built in 1849 during the dispute with Britain over sovereignty. These barns are remnants of agriculture and the Western State Hospital, a psychiatric facility. The hospital superintendent from 1880 to 1897 was Dr. John Waughop, who turned the site into a botanical garden for non-native plants as part of his rehabilitation program.
The Coast Redwood isn’t native to the Tacoma area, along with many other ornamental species planted by John Waughop.
Lake Waughop was named after the hospital’s most popular superintendent. It is a kettle lake, created from the melting of a huge block of ice after the last ice age while sediment collected around it.
This invasive species is common to Washington. It is bull thistle (Cirsium vulgare). I also saw several thriving thickets of Himalayan Blackberry along the trail. These plants were not part of John Waughop’s ornamental plant garden.
Another ecosystem within the park is the oak savannah. It is the remnant of a native woodland that has been altered for thousands of years by the indigenous people of the PNW. The trees are Garry oak (Quercus garryana), the only native oak species in Washington. This area would have become a conifer forest if not for controlled burning by the local people.
After a three-mile circumnavigation of Fort Steilacoom Park, I finally made it back to my vehicle; unfortunately, there wouldn’t be AC for the ride home on this warm afternoon.
Ready to Plant
I amended the soil with 15 cubic feet (~1/2 cubic yard) of Tacgro compost at about 1:1. That’s the darker soil in the bottom of the pond. The original mulch was spread out 4-6 inches deep, sufficient to cover the grass and weeds; it’s ready for planting.
That’s not my department, unless a hole has to be dug in the stony, original soil.
The total time for this project was about 20 hours. The only cost was 14 bags of compost, less than $100.
Sisyphus and the Stone
I finished the surface today, and dug down about 10 inches to mix in compost for the central planting area. Along the way I encountered this boulder, which weighed a couple hundred pounds. I was able to roll it up the slope, but now what do I do with it? I’ll be using a compost created from yard waste collected by the city of Tacoma to amend the silty soil. The hole ended up deeper than I like, so I’ll need a lot more than four bags…
These are all the stones I could easily remove from the soil I removed and that to be amended by compost. Hauling them in a steel bucket may seem inefficient (it is), but carrying fifty pounds at a time is a lot easier than rolling the wagon up the hill, which is about six-feet higher than the job site. I estimate that I lost 10-15% of the soil volume, which will be replaced by compost.
Excavation Update
Five hours of digging finished the major excavation–six inches of soil removed, cleaned, and spread around the site. I’ll remove another 6-8 inches along the center next and knock the sides down to a 30 degree slope. I had to transport most of the pebbles and cobbles up the hill, but some of it filled the inflow sluice (to the right in the image).
I found this soil tamper in the shed, left by the last owner. It does a great job compacting the relocated soil and isn’t too much work to use. And it’s a lot more efficient than walking around in circles to use my body weight.
Excavation Begins
I worked four hours today and made a lot of progress. This photo makes it clear how shallow the rain garden pond is going to be; the areas that have been excavated to 6-8 inches aren’t going to be any deeper. There will be a deeper (18 inches before backfilling with compost-amended soil) thalweg along the center of the pond, and I’ll cut a slope of about 30 degrees from the edge to the center line. The piece of siding is covering the infiltration hole–a sure ankle breaker for someone like me stumbling around with shovel-fulls of soil. Better safe than sorry.
I definitely have more pebbles/boulders than I need. I’m dumping the excess in a quiet corner of the yard. I’ll figure out what to do with it later. I’ve been using this area to dump soil removed to plant a few shrubs and small trees, so the new material fits right in.
This is my version of being a sculptor, but I work with earth rather than clay.
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