Geologic Survey of the Northern Cascades: 4. Thrust Faulting within a Subduction Zone
Figure 1. This is my last post from our Cascades Loop drive. The geologic map shows a wide variety of rock types west of the Columbia River, some of which we’ve seen before. But we also see two unfamiliar lithologies: Tertiary basalts that erupted throughout eastern Washington between 17 and 6 million-years ago; and mixed Paleozoic/Mesozoic metamorphic rocks (539-66 ma), which appear as a sliver of gray pointing like an arrow towards Site 12. These older rocks have been thrust over younger Mesozoic metamorphic rocks along a thrust fault (dashed line with arrow indicating direction of relative movement).
Figure 2. Stop 11 is located along the Columbia River, where steep slopes conceal high-grade, metamorphic rocks generally assigned Mesozoic ages. This image shows a knob dissected by numerous intersecting dikes. Ages for metamorphic rocks indicate the time when they were transformed into gneiss, schist, etc. The description from the NGMDB map describes a jumble of rocks in complex interrelationships.
Figure 3. This outcrop is about 10 feet across (the tree is young); it shows what the geologic map’s metadata are saying. There is no continuity visible, yet thin layers of sandstone/mudstone are visible, adjacent to blocks of buff material in the lower left; meanwhile, the right side reveals quite different layering.
Figure 4. This image reveals an intrusive, igneous texture that has been modified into what I would call an orthogneiss. Large grains of feldspar have formed layers because dark minerals like amphibole and biotite have been remineralized into the dark laminae. None of these minerals (except perhaps an occasional zircon) is original. The entire outcrop appears to have been folded into a three-dimensional, origami form. The gray area exposes the core of this spheroidal structure.
Figure 5. These two photos from Stop 12 are so speculative that they could be considered as schematic. I included them to demonstrate the change in geomorphology when crossing something as subtle as a thrust fault. These images are from the intersection of US-2 and US-97; I don’t need GPS to know where I am. The NGMDB map shows a thrust fault crossing the Columbia River at this spot.
(A) This mountain forms steep, rock faces. It is composed of Mesozoic metamorphic and igneous rocks. (B) This mountain, only a few miles north, is predominantly covered with loose soil and has a few outcrops on the upper slope.
There is an identified thrust fault between them, pushing the northern rocks over the younger rocks to the south (some time in the past). At first glance, the two look alike but, on closer examination, we can identify differences even from a mile away. I should add that a thrust fault is not cut with a knife; instead, it is a general zone of brittle failure within colliding rock masses. The result is seldom obvious.
Figure 6. Stop 13 in East Wenatchee revealed deformed rocks similar to those at Chelan (Stop 11), which isn’t surprising; however, this road-cut revealed larger exposures that aren’t as criss-crossed by veins. The lighter colors are the result of illusive changes in chemistry that interact with the environment, but they seem to reflect subtle differences in lithology. Note the massive, layered section at the bottom that seems to have been cut off; perhaps this is an outcrop-scale expression of regional compression and thrust faulting.
Figure 7. This photo is difficult to explain. Thin layers of what was once an intrusive rock abut an intrusive rock that hasn’t been as altered. This is an opportunity to point out the fallacy of jumping to geological conclusions: this might look like a sedimentary rock laid down on a granite boulder, which once formed a shoreline–it is NOT.
Final Thoughts
These four posts have explored a subduction-zone orogen, from youngest to oldest. The rocks got progressively more complex during our transit. They tried to fool us repeatedly by revealing patterns that, at a glance, seemed familiar and could be mistaken for textbook schematic concepts.
The rocks are never wrong, but they are known to have a bit of fun at our expense.
Geologic Survey of the Northern Cascades: 2. The Central Orogen
Figure 1. This magnificent vista of Washington Pass, at an elevation of 5477 feet, is representative of the core of the Northern Cascades. Highway 20 has to change direction to get out of this dead end, created by glaciers among massive mountains of high-grade metamorphic rocks, some of which have been exhumed from depths greater than twenty miles. Some of the intrusive rocks were emplaced at much shallower depths. Remember that it took tens of millions of years for this striking rock-scape to evolve on the surface of a dynamic planet.
Figure 2. I have annotated this piece of the USGS national geologic map to give an overview of the terrain we traversed. Today’s post will only be discussing Sites 4-6, which fall within the core of the orogen. We saw low-grade metamorphic rocks in my last post. The bright-colored area represents rocks that are classified as orthogneiss–a mixture of non-plutonic rocks that were subjected to high pressure and heat. The dark-purple shades are Mesozoic intrusive rocks and the lighter hues are Tertiary. Site 6 is approximately where Fig. 1 was photographed.
Figure 3. Steep peaks like this one (near Site 4 in Fig. 2) replaced the ridges seen in the sedimentary prism rocks to the west. When you see spires and domes, it is safe to assume that you are looking at high-grade metamorphic/intrusive igneous rocks.
Figure 4. The Skagit River canyon between Sites 4 and 5 is filled with boulders and gravel, but there are no exposures. This boulder is interesting because it is composed of two lithologies with different properties. I think this is a piece from miles upstream; the irregular part looks like a coarse-grained intrusive rock like granite whereas the smoother component is probably an intrusive rock that filled cracks in the host rock.
Extreme physical erosion in the river has emphasized several sets of intersecting dikes that were filled at different times in this rock’s history.
Figure 5. (A) Photo looking north from Site 6 in Fig. 2. According to the geologic map, this mountain comprises Tertiary (~66-2.3 Ma) intrusive rocks that don’t contain a lot of quartz (e.g. diorite).
(B) This is a closer view of the rectangle in A, showing vertical lineations that form ridges in the steep face of the mountain. At first glance these structures remind me of columnar jointing in basalts, but similarity in appearance doesn’t indicate a common origin. These lineations are irregular and wavy in some places. They probably followed jointing that developed as the massive rock cooled…under a continuously changing stress environment; e.g., uplift from erosion of overburden, sliding along a transform fault just to the west of here, and a jumble of motion along numerous tensional and compressive faults.
Figure 6. This view is looking southward towards a mountain comprising Paleozoic-Mesozoic (~250-66 Ma) intrusive rocks. The pluton in Fig. 5 was injected into this mass of far-older rock with a similar composition. This difference is striking at this distance: these older rocks present a curvilinear pattern of joints and fractures. I could speculate about the complex, almost turbulent, flow suggested by this view–but I won’t.
These rocks are so much older than those in Fig. 5 that they experienced several lifetimes before the tectonic stress field of the Tertiary (~66-2.3 Ma) developed; nevertheless, they reveal the cumulative effects of continuous deformation associated with ocean crust subduction.
Figure 7. I included this high-resolution (~20x) photo as a baseline for some rocks we’ll see later. This is the Tertiary intrusive rock, but the fabric (i.e. mineralogy and structure) has been modified from the original magma. Most of the minerals are feldspar, but only chemical and microscopic analysis can differentiate potassium and sodium end members. The anomalously large, dark crystal is probably the result of solid-state diffusion after the magma cooled. There is quartz, identifiable as the amorphous gray areas, throughout but not at high concentrations.
The description in the geologic map covers a wide range of quartz-poor plutonic rocks, so I won’t try to name it. What matters is that this is not a rock that simply cooled and was frozen in time.
Final Thoughts
Driving through batholiths, which are built up over millions of years from multiple plutons, gives plenty of opportunities for panoramic photography, but the real geological story is buried within the minerals themselves.
Washington Pass has exposed the beating heart of the Northern Cascades. We’ll have to look at the periphery to learn more.
Ecology Notes from Tacoma Nature Center
Today’s field trip took us to the center of Tacoma, where the city operates a nature center focused on education and outreach programs.
We weren’t looking for birds, but this display showcases some of the birdhouses constructed within the area.
We walked the entire trail system, which is almost three miles, and noticed several signs indicating stops on different self-guided tours. Unfortunately we didn’t have a guidebook. This post is about learning from experience. (LOL!)
The trail climbed about 100 feet to a ridge that gave a great view of Mt. Tahoma (aka Mt. Rainier) on a beautiful day. Note the cloud trailing off the top of the mountain in a northerly wind.
Snake Lake was dry and the deciduous trees in the wetland were losing their leaves, so I didn’t take much interest in them. It wasn’t until we followed the Hilltop Trail that I began to notice the different ecosystems juxtaposed in this seventy-acre site. The rest of this post, therefore, will focus on trying to salvage something intellectual from what started as simply a walk in the woods.
Tacoma Nature Center supplies a catalogue of the flora and fauna located within its limits. I took a couple of photos and, when I got home, discovered the lists they supplied on their web page. Thus, instead of guessing what I’d seen, it was more like a homework assignment with a limited number of choices.
Trees
This is a list of the trees known to exist at Tacoma Nature Center. The ones I identified are in bold typeface.
- Sitka Alder
- Oregon Ash
- Cascara Buckthorn
- Black Cottonwood
- Douglas Fir
- Pacific Madrone
- Scouler Willow
- Garry Oak
(A) This young tree still had all of its leaves, so I used my copy of Pacific Coast Tree Finder to identify it. (B) The leaf shape and vein structure was critical. If I hadn’t already had a list of possible choices, however, this would have been a lot harder; in fact, my answer may well be incorrect.
I’ve seen enough Douglas Firs to guess these conifers, especially since it is the only native conifer found within the nature center; all of the old-growth forest was clear cut and this species planted because it grows fast and is a good source of lumber.
Shrubs
This is where my homework got very difficult. So I asked for some assistance from ChatGPT, but I fact-checked everything it said and, after a long discussion, we agreed on the final identifications. It may have read everything ever written, but it can’t see what isn’t visible in a photograph, and it is prone to making things up–just like people.
As with the trees, I’ve emphasized my answers in bold type.
- Baldhip Rose
- Beaked Hazelnut
- Black Twinberry
- Bracken Fern
- Clustered Wildrose
- Common Snowberry
- Creeping Snowberry
- Douglas Spirea
- Dwarf Oregon Grape
- Evergreen Huckberry
- False Lily-of-the-valley
- Indian Plum
- Oceanspray
- Orange Honeysuckle
- Red Elderberry
- Red Huckleberry
- Salal
- Sword Fern
- Tall Oregon Grape
- Trailing Blackberry
- Western Trillium
This bramble of shrubs contains five separate species of shrubs or ground cover from the list. I’ve circled examples of each and discussed them below. I supplied ChatGPT with close-up images to get its input. It was very useful, but not infallible. In fact, I identified (A) and (D) on my own, after taking a closer look at the photo–and using Wikipedia as a reference.
(A) Bracken Fern (Pteridium sp., family Dennstaeditaceae) is the oldest known fern, with fossils from the Eocene epoch (~55 my). If you zoom in on this area, you’ll notice that each branch has perpendicular stems, which then have perpendicular leafs. The entire plant reminds me of what I’ve heard about fractals in nature; a simple pattern repeating over and over.
(B) Baldhip Rose (Rosa gymnocarpa, family Rosaceae). There are two roses on the list, but their leaves are very different.
(C) Dwarf Oregon Grape (Mahonia nervosa, family Berberidaceae). Wikipedia redirected my reality check of ChatGPT’s identification to Berberis nervosa. The explanation was that Mahonia is an alternative scientific name to the accepted one. Not being a botanist, I don’t care about such subtleties. The name, Berberis, certainly fits the family lineage better. I’ll leave the name as is and include these notes.
(D) Western Sword Fern (Polystichum munitum, family: Dryopteridaceae). This more modern cousin (note the different family) of the Bracken Rose has a simpler leaf design: it has one broad leaf growing perpendicular to the main stalk. I didn’t notice such a blatant difference when the two plants were right in front of my eyes!
(E) Creeping Snowberry (Symphoricarpos mollis, family Caprifoliaceae) is my best estimate after a long conversation with ChatGPT, examining photos of several species, and comparing their growth habits. This example is more like ground cover than an erect, woody plant. I wouldn’t bother with the species name except that the catalogue lists two species. I’ll look for the other one next time I get to the nature center.
Final Thoughts
I hope that everyone who reads this takes more notice of the plants they encounter wherever they go. And you can always take a picture.
And don’t be afraid to ask a Large Language Model (e.g. ChatGPT, Claude, Gemini) for help identifying whatever you find. They are knowledgeable, unassuming, and fun to work with.
And they will readily admit when they are wrong…
Autumn at Kubota Garden
It was a beautiful fall morning that brought us to Kubota Garden in Seattle (https://www.kubotagarden.org; https://en.wikipedia.org/wiki/Kubota_Garden). Links aren’t working on WordPress so I inserted those two as references. The garden is 100 years old next year, but it has been a public park since 1987.
We wandered around the 20 acre area on meandering paths lined with every kind of shrub you would expect in a classic Japanese garden. I used ChatGPT to tentatively identify some of the plants.
ChatGPT had high confidence that this is Weeping Blue Atlas Cedar (Cedrus atlantica ‘Glauca Pendula’).
The park has a central pumping facility that recirculates water through several waterfalls and a dozen ponds, making for a very serene environment.
ChatGPT tentatively identified this reborn, small tree as Japanese Plum Yew (Cephalotaxus harringtonia). It was recently cut back, but it is growing vigorously now.
This is a fascinating hedge because only one of the bushes is being trimmed while the others protrude, almost like sculpture.
There were many pagodas and ponds with stone bridges and private spots, creating a sense of privacy in a public space.
Mahonia eurybracteata subsp. ganpinensis ‘Soft Caress’ is a fall-flowering plant.
Lacecap Hydrangea (Hydrangea serrata or a lacecap cultivar of Hydrangea macrophylla) has two sets of flowers; the typical hydrangea flowers, and an outer layer of decorative petals to attract pollinators.
There were red berries everywhere. I’ve had Euonymus several times over the years, but they were never as colorful as Burning Bush.
Weeping Conifer (likely a Weeping Hemlock) said goodbye at the exit, just as a Weeping Cedar greeted us. The aura of evergreen was overwhelming beneath its boughs.
Final Thoughts
Kubota Garden is a great place to spend a couple hours. There were a lot of visitors, and even a youth naturalist activity, but it didn’t feel crowded; however, the parking lot was full and we had to park a couple hundred yards up the street.
As part of my expanded interest in local sights here in the Pacific Northwest, I’m learning about plants. ChatGPT is an excellent assistant in this endeavor, but I can’t memorize a thousand species names. It referred to taxonomic FAMILY several times today, so I included this photo from Wikipedia as a memory helper. I will try to remember this when I report on ecology in the future. I will go as far up the plant family tree as I can in the future.
The only thing missing from this gorgeous fall morning in the park was a fresh cup of coffee. Alas, Kubota Garden is in a residential area and there isn’t even a Seven-Eleven nearby.
Later…
Reseña de “Short Stories in Spanish (for beginners)” por Olly Richards
Este libro es una colección de cuentos cortos en español escritos para principiantes. Cada cuento tiene tres capítulos con un resumen, un glosario y preguntas de opción múltiple. Pero las palabras en el glosario no son suficientes para mí. La autora sugiere que el lector debería saltarse las palabras desconocidas, pero hay demasiadas.
Sin embargo, yo disfruté leyendo los cuentos e intento leer más colecciones como esta. Es fácil de leer y no es tan difícil como las novelas. Además, los cuentos son divertidos.
Yo recomiendo este libro para principiantes como yo.
Yo no sé cuál es más difícil: leer los cuentos o escribir esta reseña…
The Olympic Mountains: Accretionary Wedge Geology
Introduction
A few months ago, we followed US101 along the Washington coast and reported on Eocene (56-34 Ma) sedimentary rocks that were deposited in the trench that fronts the Cascadia subduction zone. Today I am expanding my investigation into the heart of the Olympic Mountains, which comprise the northern extent of the sedimentary wedge known as the Coast Range (see Fig. 1).
Figure 1. This schematic representation of a subduction zone beautifully encapsulates the Olympic Mountains, which are labeled on it as well–even Olympic National Park. The Coast Range (shown in green) is the exhumed remains of the sedimentary wedge, as shown in purple and labeled as the Trench. It is useful to note that, as subduction has continued (at least since the Eocene), the trench moves seaward and older, previously buried, ocean sediments are pushed up over the subducting ocean plate. This motion is indicated by the white arrows on the front of the block diagram.
Figure 2. (A) Map showing Lake Crescent (outlined with a box) and Hurricane Ridge, the two locations I’ll be discussing in this post. I presented some of the geology of Victoria, British Columbia, and Vancouver Island in a previous post.
(B) Geologic map from RockD of the Lake Crescent area. Two rock types dominate the area: Eocene marine sediments and slightly younger basalt flows and volcanic breccia.
(C) Detail map of the area outlined in panel B, showing the Spruce Railroad Trail. The circle outlines the two locations discussed in the next section.
Lake Crescent
Figure 3. Lake Crescent fills a deep (~600 feet) valley created by glaciers over the last two-million years, which was blocked by a landslide several thousand years ago. The shoreline in this image is broken by a series of linear ridges. These are resistant layers of sedimentary rock that has been rotated to a high angle.
Figure 4. The entrance to McPhee tunnel has been reinforced with rock bolts, which can be seen throughout this bedding plane. The left side of the photo shows why the tunnel was dangerously unstable: the ridge through which it was cut is composed of thin layers of interbedded sand, silt and clay.
Figure 5. McPhee tunnel is only a couple hundred yards long (see Fig. 2C), but the exit reveals completely different rocks. There is a red line in the geologic map (Fig. 2B); this represents a contact between the marine sedimentary rocks (Fig. 4) and the volcanic rocks.
Figure 6. (A) Outcrop scale photo of basaltic rocks near the exit to McPhee tunnel. I have tentatively labeled one round boulder as a pillow basalt. Pillow basalts result when lava erupts on the sea floor in deep water (~1000 feet deep) because of the immense water pressure. When the rock weathers, they retain their shape because of a more homogeneous composition than the lava surrounding them.
(B) Detail showing the wide variation in clast size and shape. This mix of material, all of it basalt, is indicative of a tectonic breccia. Imagine what happens to undersea lava flows as they weather through seawater action and collapse into the trench (see Fig. 1).
Hurricane Ridge
Figure 7. This photo shows Hurricane Ridge (see Fig. 2A), which leads to Hurricane Hill at about 5500 feet above sea level. The next few photos show the kinds of rocks visible along Eagle Point trail, which leads to the summit.
Figure 8. These sedimentary rocks resemble those at McPhee tunnel’s entrance (Fig. 4). They are tilted to nearly vertical, consist of dark and bright layers (mud and sand/silt, respectively), and are fairly continuous; however, they have an additional feature that might escape one’s attention at first: some of the darker layers contain rounded forms that are brighter. If I’m right, these are boudins, concentrations of silica-rich minerals that result from the rocks being squeezed under high pressure.
Figure 9. (A) This outcrop (about 20 feet across), located a few hundred yards from Fig. 8, is dominated by sandy sediments. The surface is littered with angular blocks, which suggests that these rocks were subjected to intense deformation after they became lithified (turned to rock).
(B) Detail of area indicated by the rectangle in (A). Now we can see bedding planes, e.g. in the center of the photo. These beds are also nearly vertical. These are reminiscent of the sandstones we saw along the coast; I’ll bet they contain turbidites, layers of coarser sediment deposited by submarine landslides in deep water.
Figure 10. (A) These thin beds have been folded into a chevron. This implies extreme horizontal stresses.
(B) The bedding is almost obliterated in this exposure, where coarser sediment (lighter colored) is mixed with shale. Furthermore, the entire assemblage is fractured into small pieces like those lying on the ground.
Figure 11. This view from the top of Hurricane Hill is looking northward towards Vancouver Island, British Columbia. The main features seen here are the knobs that protrude from the summit of this adjacent ridge. Promontories like this were ubiquitous along the ridges comprising the Olympic Mountains. Compare this topography to the narrow ridge leading up to Hurricane Hill (Fig. 7). The fractured and folded rocks we saw along the trail (Figs. 9 and 10) have weathered faster than these, but what are they?
Figure 12. (A) Closer view of the left side of Fig. 11, showing several interesting features: a series of knobs to the left, then a deep ravine cutting across the ridge, then massif to the right. These are basalt that has not been as deformed as the sedimentary rocks we saw lower down the trail. Seafloor basalts erupt into layers of marine sediments, but they are harder and more resistant to both chemical and physical alteration during burial and deformation. These layers are unusually strong layers.
(B) Close-up of a knob on Hurricane Hill. I didn’t approach closer because signs asked visitors to remain on the trail, and it was a pretty steep slope into a deep canyon. I don’t see any possible basalt pillows (see Fig. 6A); instead, it seems to be fractured into rectangular blocks. However, some of the rounded boulders seen in the foreground look like lava pillows. RockD calls this formation, Crescent Formation, pillowed…
Final Thoughts
The Coastal Range extends from Alaska to Mexico but not as a continuous mountain range; instead, it comprises a series of mountain chains like the Olympic Mountains. These individual mountain chains are lumped together because they all formed during subduction of multiple tectonic plates underlying the Pacific Ocean during the last 200 million years. The Olympic Mountains are simply the most volcanically active area in recent times.
The subduction zone trench (see Fig. 1) is continuously filled with sediment eroded from the adjacent highlands in a process that doesn’t cease until plate convergence ends. Sediment is carried into the trench, buried, then exhumed ; there is simply more volume of sediment/rock than the trench can contain. Today the trench is approximately 100 miles west of Seattle whereas it was located within the Olympic Mountains between 55 and 34 million-years ago, a difference of about 70 miles; in other words, the subduction zone has moved about 30 miles westward in less than 60 million years.
I am bothered by one discrepancy, as I understand the picture of marine sedimentation and eruption of seafloor basalt in the westward-propagating trench: Where is the modern analog of the thick sequences of basalt that occur within the Olympic Mountains?
Things to consider (I don’t have the answers):
- Volcanism within the Cascades Range (see Fig. 1) is overwhelmingly andesitic, which results from mixing of the sinking ocean plate (gabbro and basalt) with continental crust (granitic) as magma rises.
- Massive outpourings of basalt occurred in eastern Washington between 17 and 5 Ma, known as the Columbia River Basalt Group.
- The North American plate has been moving over a hot spot in the upper mantle currently located beneath Yellowstone National Park.
- Pillow basalt is a definitive indicator of submarine eruption, as seen occurring today in Hawaii. Thus, these features are consistent with either (a) eruption of flood basalt in the trench or (b) collision of a sea mount with North America.
Every subduction zone is unique and overprinted with whatever else is going on in the earth’s crust and upper mantle. I wonder if the Olympic Mountains basalts are the result of mixing of marine sediments with flood basalts, and possibly incorporation of islands or seamounts.
Food for thought…
Addendum
After thinking about it a little longer, I want to add that the basalt breccias we saw (Figs 6 and 12) probably originated from the subducting ocean crust. It would have been covered by deep-sea sediments, including muds and limestone (from ocean phytoplankton). These would have been scraped off and mixed into sediments with a terrestrial source. That would explain layers of basalt intercalated with marine sediment; however, the question of pillow lavas remains controversial because they aren’t found at mid-ocean ridges, where ocean crust is created.
So, no flood basalts but probably a seamount is mixed into the Olympic Mountains.
The Olympic Mountains
The Olympic Peninsula is home to the last old-growth temperate rainforest in N. America. It is also dominated by the Olympic Mountains, a wilderness area only accessible on foot for the most part. However, the north side, facing Juan de Fuca Strait and Canada, is only a few miles from US 101 and Port Angeles; and less than three-hours from Tacoma.
It’s late September and the tourist season is about to end in Olympic National Park, so we fit in a weekend visit to the Log Cabin Resort on Lake Crescent.
The highest peak in the Olympic Mountains is Mount Olympia, standing at 7980 feet, and there are many peaks over 6000 feet. None of them are volcanoes, however; they were formed by collision of N. America with the tectonic plate underlying the Pacific Ocean. I’ll discuss that in another post.
Lake Crescent was created when a landslide blocked the outlet of a valley cut by alpine glaciers over the last couple million years. Its maximum depth is 600 feet, and it contains exceptionally clear water because of a low nitrogen content (no pollution) and thus no algal growth. It is twelve miles long and thus popular with sport boaters. I didn’t see anyone fishing, so maybe no algae means no fish.
We followed the Spruce Railroad Trail 1.7 miles to this tunnel, which is huge when you pass the smaller entrance; however, it is only a couple hundred yards long. Nevertheless, as the sign says, it is very dark inside, especially later in the day. It leads to a favorite site for visitors.
The Spruce Railroad Trail circumnavigates Lake Crescent (about 11 miles), but we didn’t go that far. Devils Punch Bowl is a deep hole with steep cliffs and a walkway. Adventurous young people were leaping into the cold water and sunning on the nearby rocks, but I didn’t see anyone jumping from the top of the cliff more than 60 feet above us.
This is the view from our back yard. I took some photos of the half-moon when it was still light, but this is my favorite because of the moon’s reflection on the still water of Lake Crescent.
We spent a very quiet night in our log cabin, which had a modern heating system and was very cozy, then drove to the Hurricane Ridge trail head. The trail was asphalt paved and climbed about 1000 feet in (supposedly) 1.8 miles. It was steep near the top but wide enough for wheelchairs to use easily. This is the view from the top, which was at an elevation of about 5500 feet; that’s Mount Olympia across a deep valley.
This is the view looking north. That’s Vancouver Island, British Columbia, across the cloud-covered Juan de Fuca Strait. The brighter area above the two peaks is Victoria. We were there last month.
This photo shows the trail we followed along a ridge like those seen in the background. The many sharp peaks are reminiscent of the Cascades Mountains, but these were formed by alpine glaciers in combination with a high uplift rate, rather than volcanic processes.
Final Thoughts
The weather in the Olympic Mountains was exceptionally nice this weekend. The drive was easy and traffic low because it was the last day of the season. Overall, I can’t think of a better place to spend a couple of days.
Try to make it if you’re ever in the Pacific Northwest…between April and September.
Port of Tacoma Tour
Every year, the Port of Tacoma and Pearce County operate a series of one-hour tours on a cruise ship. There is no charge and passengers have a timed ticket, so there are no long lines. It turned out to be a rainy day, but that didn’t dampen the enthusiasm of the Tacoma’s residents.
The Spirit of Seattle usually runs various tours around Seattle, operated by Argosy Cruises. It was only half full for the port tours so there was plenty of space to move around on the deck.
The first facility we saw is the tank farm, which temporarily stores refined petroleum products for distribution by tanker trucks. There is also a small refinery on the port, but the guide didn’t say anything about that.
This power plant was used to generate electricity for the port, but it is no longer operational. In fact, it is for sale.
This is s roll-on-roll-off ship that, as its name suggests, is used to transport vehicles that require no special handling. However, it also transports heavy equipment, some of which requires partial disassembly to fit into the ship’s hold.
These are the main cranes for handling container ships. The one in the foreground is unloading a ship (One Strength, registered in Singapore) that can carry about 14,000 TEUs–twenty foot equivalent cargo container–or about 7000 40-foot shipping containers. The largest container ships can carry 24,000 TEUs.
Along with storage facilities for cargo, an aluminum plant, and a couple of gypsum plants, there is a repair facility. It is currently preparing an ocean-going fishing ship for the upcoming season.
The Port of Tacoma also handles grains and cereals through a modern facility that can load these bulk ships in all weather. The corn, soy beans, etc arrives by trains that arrive practically year round, mostly from central and eastern Washington.
Final Thoughts
Dreary weather didn’t hamper my interest is seeing the Port of Tacoma up close. This place can handle everything a nation needs to import or export. Places like this are the real backbone of our economy, not computer chips and programmers.
But running a complex facility like this isn’t easy. The smelter that used to operate along Commencement Bay produced so much pollution that my back yard was part of an EPA Superfund site, and there is a current site along the eastern shore where an aluminum plant operated for decades. We have a long way to go, but the waters surrounding Tacoma are the cleanest I’ve ever seen in my life.
A Quick Visit to Portland
Mount Saint Helens is only 25 miles as the crow flies from Portland, so we stopped by our southern neighbor for a visit. It was raining, so we opted for indoor activities.
World Forestry Center
The World Forestry Center is next to the Oregon Zoo, and it was a dry place to wait for our next stop to open. It turns out that it is a children’s museum. A new exhibit had just opened so we toured Siberia by train, China by boat, the Amazon by a tree-top crane, and…
South Africa in a 1960s International Harvester Scout. I was ready to go, but the engine wouldn’t start.
Someone left a 22 caliber rifle in this tree back in the 60s, and it became one with nature.
This fake evergreen tree extends to the ceiling in the middle of the World Forestry Center. There were lots of activities for children of all ages, so this is probably a good place to visit with the family.
Japanese-American Museum of Oregon
After discovering forestry around the world, we went to the museum.
JAMO is small, but very interesting.
The early Japanese immigrants lived much like the Chinese, whose accommodations we saw in a previous post. By the 1930s they had established themselves throughout the West Coast, especially the PNW. This is a representative display of a general store.
There were dentists and all the trades because, despite being legal residents–many of them American citizens–they were prevented from fully participating in the American dream.
They lived in nice homes, owned businesses, spoke English better than most of their fellow citizens, but…
There weren’t enough of them to overwhelm the government’s demographers (unlike the German and Italian Americans), so they were rounded up in a show of national security; they were shipped to places where, if they were lucky, they shared a room like this with their entire family.
The JAMO has a lot of documents to read, but I focused on physical objects because I forgot my “museum glasses”, which focus at six feet. You’ll need to visit the museum yourself to learn the true history of the Japanese-Americans.
One brave activist violated curfew after release from a detention center, and found himself in jail for nine months. He eventually won in the courts, but at a high personal cost.
This terrible injustice wasn’t as horrific as what was done to the Native Americans, but it was pretty bad. The U.S. government eventually apologized, in the 1990s, but that was little consolation to those Americans who lost everything during a period of national paranoia. Some of them actually received a few thousand dollars in reparations (I guess they used 1940s dollars, not adjusted for inflation).
Mount Saint Helens Revisited: Ape Cave
We made it to our destination (Fig. 2) and explored a rare lava tube at Mount Saint Helens. This lava was erupted 1900 years ago as part of the same sequence that destroyed the forest a short distance away.
A full discussion of this fascinating natural feature is available from Washington Department of Natural Resources.
Figure 1. This lava tube is a lot larger than the tree casts we described in the last post. This immense cavern, which is more than 2.5 miles long, was created when a single basaltic lava finger flowed over the landscape. The outer material cooled in the air and insulated the interior, like an oven, allowing the remaining lava to exit the end of the tube. This left a void to be filled by subsequent lava flows. According to the information displayed at the site, the entire eruption lasted about 100 days.
Figure 2. Ape Cave is presumably named after the first eruption sequence of Mount Saint Helens, dated about 40 Ka. I didn’t find an explanation for this confusion, but it might have something to do with the Bigfoot legend associated with Ape Canyon, not far away. At any rate, the lava tube is indicated by the square in (B).
This video captures the scale of one of the many chambers better than any image. My narration isn’t very technical.
Figure 3. These parallel ridges running along the bottom of the cave near its terminus are the remnant of the last flow to use this conduit to reach open air.
Figure 4. A block of basalt transported through this narrow passage became stuck where the walls of a previous flow almost meet, leaving it stranded. It looks like it partially melted into the walls, however.
Figure 5. This view of the ceiling reveals a joint pattern caused by cooling of the outer layer of lava. Several generations of fractures occur throughout the cave, created as individual flows cooled differentially.
Figure 6. This is the end of the tube as it exists today. Apparently, there is no modern opening; it probably collapsed during the last 1900 years.
Figure 7. As a retired sedimentologist, I immediately noticed the layer outlined by the dash lines. This looks like cross-bedding; the layer fills a depression below the line, and is truncated by an overlying flow. This is interesting because cross-bedding is associated with particles being transported by wind or water; how it appears in a lava flow is an intriguing problem–perhaps heavy minerals like pyroxenes and lighter plagioclase feldspar?
Figure 8. This is a good time to briefly explain how the ledges seen in Figs 1, 4, and 6, and the video, were formed.
Once the lava tube was created by cooling of the surface of the original flow, subsequent flows ran through, but didn’t fill, an insulated tube. Their surface was usually below the original ceiling. The coolest parts of this conduit would have been the sides (heat dissipates more quickly through older, cooler basalt than the superheated air above the lava river). Thus, ridges like these formed where the molten basalt hardened. Of course, these subsequent flows were of different volumes and the rules of stratigraphy cannot be applied. Geologists have worked out these relationships but that is beyond the scope of this report.
Let’s just say that many rivers of magma flowed through this channel, like stormwater through a sewer pipe–some larger than others.
Figure 9. This is an enigmatic photograph because I don’t remember which wall it was on. I didn’t notice the detail when I took the photo, and now I can’t say if this is an excellent example of cross-bedding (always tilts downstream) as in Fig. 7. or a total mystery. My only excuse is that it was TOTALLY BLACK in the cave and I was disoriented the entire time.
Figure 10. We made it out without spraining an ankle or hitting our heads. This cave-in is the only entrance/exit for the downstream part of the tube. There is another one 1.5 miles upstream, but that route is difficult (according to the park information).
Final Thoughts
The Ape Cave lava tube, and the missing forest from my previous post, are part of the Spirit Lake eruption phase of Mount Saint Helens, which began about 1900 years ago and continues to this day. The magma chamber didn’t erupt at the center of the stratovolcano, but instead found an opening along one of the many cracks in the thick pile of volcanic rock that had accumulated during at least 50 million years.
Lava tubes present a unique eruption environment. Ground water that finds its way into the magma chamber cannot escape, thus pressurizing the conduit and altering the lava’s behavior. Imagine lava as thin as water surging through this passage, sloshing around, encountering obstacles, rushing headlong downhill towards what apparently was a small opening, if Fig. 6 is any indication of the narrowing channel.
It was a great drive through a wild terrain to reach Mount Saint Helens, and the destination was worth the effort.
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