Flaming Geyser State Park
The park is located at the upstream end of Green River, where it enters a gorge. This is one of the best places I’ve seen anywhere for taking a stroll through nature; the path is moist but not muddy, and well trimmed, with breathtaking natural scenes like this. A veritable Garden of Eden. This post is an overview of the park; I discuss the geology and flora in other posts.
With a name like that, I’m expecting a spectacular show…
I’ll summarize what you can read if you zoom in on the information presented in this billboard. An exploratory well was drilled here about 100 year ago, looking for coal–they found it, along with methane (natural gas) and other gases produced by decaying vegetation at several hundred feet below the surface. The small well produced a flammable gas that has burned intermittently since it was first lit by a geologist.
Flaming geyser wasn’t very active when we visited, but it was burning. To repeat, this is NOT a natural seep, but the result of a well drilled a century ago. Nevertheless it has become a local tradition, and it is relit whenever it goes out.
Bubbling geyser is a lot more fun. This video shows small bubbles of methane, as well as hydrogen sulfide and other, unnamed, gases. Methane is odorless, but this area smelled strongly of H2S, which is added to natural gas to help detect leaks.
This is a beautiful example of survival. The surface roots have all been exposed by erosion, but the tree is thriving; its roots have turned into separate trunks. I read somewhere that these conifers in the PNW send their roots out for hundreds of feet, far beyond their canopies.
This is where Green River Valley turns into Green River Gorge. The water was perfectly clear, with a slight green tinge, even though there is no algae visible. It reminds me of Commencement Bay, which is also devoid of aquatic plants. And it is all natural, simply a unique ecosystem.
If you wear waders, you can walk on water here.
Final Thoughts
This is a place you have to visit for yourself, especially on such a gorgeous summer day. The temperature was in the mid-seventies, the sky was clear, and people were filling the huge number of picnic areas, carrying their supplies and tubes, ready for a fun day of floating down one of the best rivers I’ve ever seen.
You’ve got to see it for yourself.
The Foothills Trail along Carbon River, Pierce County, Washington
This post is a humorous (I hope) addendum to my posts on the geology and flora of Carbon River. I have noticed a lot of quirky, regional trends, both in decoration and signage, here in the Pacific Northwest (PNW) during our nature walks. The Foothills Trail was no exception.
There are several access points to the trail, but this was the only sign. It ends with a serious warning: Use at your own risk. What lies ahead in that darkness?
A couple miles downstream from the “official” trailhead, we stopped along the Carbon River. This is a piece of ubiquitous columnar andesite that was apparently placed here as a decorative piece. Unfortunately the sign is long gone.
The trail is wide and easy to access on foot. I don’t know about a wheel chair although it is flat all the way.
We saw several of these marker stakes along the trail. I looked it up and, to the best of my knowledge, this is indicating a tree where a pair of Marbled Murrelets are nesting. They are an endangered species and extremely difficult to locate, but there is an ongoing survey program. That sounds reasonable to me; the sign gives both a distance and compass heading to the tree.
The trail intersected the Franklin Bridge, which is indefinitely closed to traffic.
We climbed a steep slope, with the help of sturdy handles attached to wire rope, and took some photos on the bridge.
After we finished on the bridge, we passed the concrete blocks obstructing the road. Several signs made it clear that the bridge is closed to cars, bicycles, and pedestrians. Apparently someone disagreed with the DOT restrictions, and modified the sign. Don’t ask me why the figure is carrying a gas can that says, “Oh ya fuck ya.” I guess they’re thumbing their nose at anyone who would dare condemn what looks like a perfectly useful bridge — at least for people and wild animals.
We walked the three miles back to our car along the abandoned road. There were several rock falls and damage to the guardrails. In this image, a large boulder smashed through the eroded roadbed. It was like a post-apocalypse movie. Pretty cool … and quiet.
These relatively new signs were posted randomly on trees on the hill of the road. Hazards. Not hazard. Maybe Western Rattlesnakes, poison ivy or … dare I say it? Bigfoot. Stay out of the woods. But we just walked three miles through the woods. Damn!
These opposite-pointing signs were on a curve. Nevertheless, I have to wonder why the guardrail stops in the middle of the curve, but reflective signs were felt necessary. Short sightedness? Budget constraints? Stupidity?
The Flora of Carbon River, Pierce County, Washington
Plate 1. Our first stop was at Carbonado, where the Carbon River exits the canyon that has constrained it from its origin on Mt. Rainier. It immediately forms multiple channels as it cuts through glacial till on its circuitous path to Commencement Bay.
Plate 2. This lovely flower is red clover (Trifolium pratense), a common wildflower along rivers.
Plate 3. CoPilot and I argued too long about this one, but, after some back and forth, I decided it might be a genus of Spiraea. They are another common shrub in this ecosystem, but they aren’t in flower in July. Note the shriveled flowers in the right image. Too late to be sure. That’s why I’ve always ignored these bushes.
Plate 4. Cow parsnip (Heracleum maximus) is a common wildflower in meadows and roadsides in Washington.
Plate 5. Tansy (Tanacetum vulgare) is a common wildflower along the Carbon River corridor.
Plate 6. I thought, when putting this post together, that this was red clover (Plate 2), but CoPilot identified it as Canada thistle (Cirsium arvense). It loves disturbed areas like river edges. I did detect some spines when I zoomed in on the second photo. Why am I not surprised? If it’s pretty it will have spikes ready to draw blood from any inquisitive passers by.
Plate 7. This view is looking downriver from Franklin bridge, which is permanently closed. I’ll now describe some of the flora we encountered as we followed the river along a steep slope.
Plate 8. I (kinda) got this one right. This is a wild rose, Nootka rose (Rosa nutkana). This is another plant that waits for an opening in the forest canopy to grow, and then it colonizes like crazy — until the forest canopy catches up with it. Moist but well-drained soil pretty much sums up Carbon River canyon.
Plate 9. This familiar flower is foxglove (Digitalis purpurea), introduced from Europe; but it is so naturalized that it behaves like a native plant, similar to Cascade penstemon (see Plate 11), thriving in disturbed ground at the edge of conifer forests and in temporarily sunny areas.
Plate 10. Besides white flowers, I am also fixated on thorns; however, I don’t know anything about thorns except that roses have them, as well as many of the shrubs I’ve encountered on my nature walks. This is probably Himalayan blackberry (Rubus armeniacus), an invasive species to Pierce County. I guess that’s why it isn’t called Washington blackberry, or some such. I checked a previous post from Point Defiance, and there it was! Invasion of the forest snatchers.
Plate 11. This purple wildflower is probably Cascade penstemon (Penstemon serrulatus), a native to the PNW. It is what CoPilot calls an ecotone plant — one that thrives where a conifer forest is encroaching on a prairie environment. We encountered it where the conifers hadn’t yet blocked out the sun along the trail.
Plate 12. I’m easily fooled by white flowers. This non-woody shrub is False Solomon’s seal (Maianthemum racemosum). It grows in the understory of a conifer forest, which is a good description of Carbon River canyon.
Plate 13. This is the first triplet I’ve seen from a nurse log. These young hemlocks will certainly compete for sun and nutrients. There can be only one survivor.
Plate 14. I thought this was cow parsnip, but CoPilot identified it as ocean spray (Holodiscus discolor). The white flowers were all I needed to see, but this tall, woody shrub (6-12 feet) is completely different from the weed in Plate 4.
Final Thoughts
The only thing I can add to the photos is that Carbon River is part of a transitional ecosystem, not unlike Mima Mounds. I Imagine this borderland environment is also alternating between a lowland/prairie and an upland/conifer forest, depending on conditions. However, much to my disappointment, the plants here were different from those we saw before. Furthermore, there were far more species along the Carbon River corridor. We were fortunate to visit when many of the flowers were in bloom.
I enjoy taking pictures of flora and learning about the ecosystem, but this is too complex for me. I’m only a simple geologist.
Geological Survey of the Columbia River Gorge
The popular route east from Portland, Oregon, is I84 following the Columbia River, which cuts across the Cascades range. There are plenty of scenic views and geology to examine, but few safe places to stop. Thus we followed the Washington shoreline along state route 14.
The inset map shows the distribution of volcanic rocks within Washington and Oregon. The oldest are predominantly andesites erupted from volcanoes (triangles) within the Cascades between about fifty and five million years ago (Ma), shown in light brown. The bright green represents the Columbia River Basalt Group, which flowed from fissures between seventeen and five Ma. The youngest rocks are primarily andesite erupted from volcanoes within the last million years (e.g. Rainier, St. Helens, Hood, Baker). The rectangle shows the area we are traversing, which contains a mixture of these rocks.
We stopped frequently, but I’ve lumped the photographs into four areas: 1) Beacon Rock is near the beginning of Columbia River Gorge; 2) Lake Bonneville and 3) Hood River give a good picture of the central canyon; and 4) Columbia Hills is where the river enters the gorge before cutting through the thickest section of volcanic rocks.
1. Beacon Rock
This photograph looks east towards Beacon Rock, which has an interesting origin. It was originally injected into a cinder cone volcano about 60 thousand years ago (Ka). Subsequent, multiple glacial floods eroded the loose material away, leaving the core, which is called a neck. This region was never covered by continental glaciers, although there is evidence of alpine glaciers like those still existing on the high volcanoes (e.g. Rainier or Hood). During numerous advances and retreats of continental glaciers into Canada, large lakes formed and periodically drained catastrophically. These floods, which were as deep as 1000 feet, naturally followed the Columbia River to the Pacific Ocean.
This low road cut reveals a thick layer of volcanic rock (basalt, according to Wikipedia) overlain by volcaniclastic rocks, which are loosely cemented. That’s why the DOT placed netting over the friable layer. These are sedimentary rocks consisting of volcanic ejecta as well as material transported by water.
According to Wikipedia, Beacon Rock is 848 feet tall and there is a trail to the top that is popular with hikers. It doesn’t look that high from the bottom, but I’m glad I didn’t trust my first impression and climb it; as stubborn as I am, I would have made it–and wished I hadn’t for the next week. It looks a little pale to be basalt, including the boulder visible at the bottom of the image; in a terrain with continuous volcanism, spanning the gamut from rhyolite to basalt, for 50 Ma, you just can’t tell from surface features. Some basalt is a little lighter colored and some andesite is darker–it’s a spectrum based on mineralogy, not color.
This eroded slope got my attention because it reveals an interesting juxtaposition of an exposed basalt outcrop that is rounded (unlike the earlier exposures we saw) and light-colored boulders of much smaller size (less than three feet). These rocks are too uniformly light in color to be weathering of basalt or andesite. There is some rhyolite (a leucocratic extrusive rock found within the Cascades) in the region, but an alternative explanation is that these are flood deposits from the aforementioned glacial lakes. There are many deposits from these mega floods within the gorge, but I couldn’t (easily) find a map of them. Anyway, this is what I would expect to find in such a sedimentary deposit–mixed rock types that are rounded by transport tens, if not hundreds, of miles during flooding episode. The bedrock would be rounded by collisions with these boulders. If the shoe fits…
2. Lake Bonneville
The central part of Columbia River Gorge is characterized by several broad valleys with sediments filling the margins of the canyon. This is a typical exposure from this area. The rock looks like basalt to me; the map (see first plate) shows a mingling of volcanic rocks along the river, which would have been a low point for lava to flow towards. However, this is not a volcaniclastic deposit as we saw before; instead, there are several, heavily weathered (i.e. smooth) flows of lava (3-10 feet thick). The lowest layer seems to be dipping towards the camera as if flowing down a steep slope. Maybe…
3. Hood River
This location is close to the eastern entrance to Columbia River Gorge, where flood basalts erupted from multiple fissures in the crust. In other words, there are no nearby volcanoes and steep slopes; thus, the basalt flowed over a relatively flat landscape, forming rolling hills. This photo reveals basalt flows that gently slope to the left, as seen in the middle-right and background of the image. These massive flows partially blocked the river many times–long before glaciers dominated the landscape. The island in the center of the channel is a remnant of one. I haven’t heard of any glacial lakes in this area, however, so the blockage must have been partial–these thick sequences of basalt didn’t occur at one time, but over millions of years, giving the ancient Columbia River time to erode passages through them.
4. Columbia Hills
Columbia Hills is the eastern end of the gorge, where the Columbia River ends its meandering path to the Pacific. The rocks are basalts erupted from many fissures between 17 and 5 Ma. According to the latest interpretation, these rocks were ejected from the same mantle plume that now underlies the Yellowstone caldera in NW Wyoming. They have nothing to do with subduction or the Cascades volcanic belt, even though the much younger Mt. Hood (in the background) towers over them.
We are now in Eastern Washington, a climatic zone with completely different characteristics than west of the Cascades. This volcanic range creates a rain shadow and resulting precipitation is less than 20 inches here; and it shows in the scrubland ecosystem. These extensive basalt flows are no longer covered by younger andesites from the high Cascades (the young volcanoes like Mt. Hood).
The volcanic layers are thin and extensive (see the map at the beginning of this post). They include columnar joints as I described in a previous post. The textures seen in this photo reveal the variability of lava coming from a single source; for example, individual, blocky layers cap this exposure whereas the rock presents a ropy texture lower down (middle-right of the photo).
Summary
The Pacific Northwest (PNW) didn’t exist before the Tertiary period, which began at 65.5 Ma. However, Pangea began to split apart at about 200 Ma, which should have created plate collisions here because the N American plate would have necessarily overrun the plates comprising the ancient Pacific Ocean. The west coast of N America was located approximately at the WA-ID boundary. So why don’t we see Jurassic and Cretaceous volcanoes and their associated volcanic deposits in the PNW?
This question has perplexed geologists for decades. After carefully collecting data from far and wide, a still-controversial theory has evolved: For more than 100 million years, this tectonic collision was accommodated by transform faults (e.g. the San Andreas fault system in California). A tectonic plate collision is not a conveyer belt as shown in schematic representations.
This schematic profile of the PNW shows several transform faults, which misalign the Pacific mid-ocean ridge (note the misalignment of the dark, Juan De Fuca Ridge. This tectonic scenario didn’t develop until those transform faults, which were not perpendicular to the mid-ocean ridge, could no longer accommodate the displacement of these microplates with N America. That apparently happened about sixty-million years ago. Some of these slivers of volcanic terrain have probably become exotic terranes that are now part of Alaska.
That is probably why we didn’t encounter any Mesozoic ((251-65.5 Ma) volcanic rocks within the Columbia River Gorge. Instead, we discovered a Tertiary volcanic landscape dominated by andesite/basalt lava flows, preserved because the transform faults had stopped absorbing the collisional, crustal tectonics. A real subduction zone emerged from this chaos and created the Cacades.
Superimposed on this was the unexpected (tectonically speaking) effusion of basalts as the westward-propagating N American plate rode over a mantle plume, which buried the evidence for this slipping history beneath miles of volcanic rocks. I can’t say anything else about this because I’m not actively researching the PNW’s geologic history.
My last word is that I can’t wait to see what new discoveries the PNW holds for me.
A Day Trip to Yakima
We wanted to see what was on the other side of the mountain, so we headed east from Tacoma and crested the Cascades at Chinook Pass. It was snowing at the pass and fog/clouds obscured what were probably majestic views. We pushed on to Yakima and found the Cowiche Canyon recreation and conservancy area.
This is a typical view from the trail, which follows an old rail line that was used for seventy years to haul apples out of the area. I have discussed the columnar basalts and vegetation in previous posts. It was late spring and all of the plants were showing their color while water rushed past in the creek at the bottom of the canyon.
This undulating columnar basalt caught my eye because of the color and its wavy appearance.
The Burlington Northern railroad wasn’t afraid to use explosives to create a path through what was described at the time as, “A dry, rocky canyon good for nothing except a railroad.” The rails have been removed, but the eleven bridges required to construct a rail line to cover the 3 miles of the trail system are mostly still in place.
Here’s one that didn’t last. It was replaced by a pedestrian bridge constructed by the Cowiche Canyon Conservancy and the Bureau of Land Management.
We took a more circuitous route back to Tacoma using US12 through White Pass. It didn’t snow, and we got a look of one of the many water falls in Washington.
This was the best angle I could get, and I still couldn’t see the bottom! It turns out that Washington has more than 3000 catalogued water falls, more than any other U.S. state. Clear Creek is rather small at only 300 feet, so I guess there is some more air down there.
It was a beautiful day in the Pacific Northwest, including the snow flurries. A ten-hour day trip took us from coastal Washington, over a 6000 foot pass, into dry eastern Washington, where we hiked through a canyon filled with native plants and rocks (hahaha), and back over the Cascades past a magnificent water fall in Wenatchee National Forest.
This is undoubtedly the most beautiful place I have ever lived…
Volcanic Rocks at Cowiche Canyon
Introduction
Burlington-Northern Railroad built a line through Cowiche Canyon in 1913 to transport apples, but it was abandoned in 1984 and the land was acquired by the Cowiche Canyon Conservancy for a non-motorized vehicle trail system. The main trail extends 2.9 miles along the South Fork Cowiche Creek, crossing the 11 bridges constructed for the railroad line.
The left panel shows the distribution of Columbia River flood basalts, deposited between 16 and 6 Ma. Yakima and Cowiche Canyon are outlined by a rectangle. These volcanic rocks were erupted in overlapping flows with erosion and landslides occurring between individual layers, which are irregular and not shown in this map. The ages from the USGS national geologic map are Tertiary (66-2.6 Ma). Tacoma is marked by a smiley face.
The right panel shows the Cowiche Canyon trail system and the specific area discussed in this post. The stream itself hosts a riparian habitat whereas the uplands comprise a shrub-steppe environment.
Observations
The canyon walls consist of a series of ledges like this with eroded slopes between them. The ledges are erosional margins of basalt flows and the slopes consist of talus and fine sediments weathered from the mafic rocks.
As we traveled west up the canyon, columnar-jointed basalt began to appear in the ledges overlooking the trail. Several pieces had rolled down the slope into the stream bed; these were about three-feet in diameter. Columnar jointing results from slow cooling of a uniform basalt flow, which causes joints to form hexagonal blocks like these because of thermo-mechanical failure during a decrease in volume.
These semi-circular blocks got my attention because, if you look closely, they appear to be eroded hexagons I estimate to be more than six feet in diameter. These are very large basalt columns that have either toppled or…
The top of this photo shows a birds-eye view of columnar basalt blocks because of their horizontal position. The size varies from smallest on the left to the largest blocks on the right. I reported on similar, horizontal columnar joints in a previous post and proposed that the lava flowed down a slope before solidifying.
The lower-right part reveals columnar basalt in a vertical position. This juxtaposition suggests (if my model is correct) that the lava from multiple flows covered an irregular landscape–sometimes flowing into canyons like Cowiche Canyon, and somtimes over fairly level ground.
This remarkable set of columnar joints got my attention because of their undulating form. I’ve never seen anything like this before. This style of jointing (supposedly) results from uneven cooling and weathering; for example, a heavy load on the layer during cooling leads to pinching and swelling at fairly uniform spacing. That sounds reasonable to me.
Another weathering feature of these rocks is the fissile structure revealed in this image. More solid blocks are interspersed with flaky layers, possibly (I’m speculating here) associated with necked and wider segments of an individual column. For example, the wider sections might undergo shear during stretching, resulting in microscopic shear layers within the minerals comprising the original lava. These weak layers would permit water to penetrate and weather the mafic minerals of which basalt is made.
These highly weathered columns are more than six-feet in height. They suggests an alternative mechanism, shear from flowing as the basalt cooled; this might disrupt the microscopic structure without interrupting the macroscopic jointing process. Maybe…
This photo really got my attention. It reveals horizontal columnar joints abutting vertical ones in the upper-center of the image. There’s a lot going on as hot lava flows over an irregular landscape, but I think this is a vent where more magma flowed out; not a large eruption, but enough to have a separate cooling history from the rock it penetrated. I should note that the Columbia River basalts flowed from fissures rather than point sources like volcanoes. The entire area shown in the map above was cut by fissures that led to a shallow magma chamber, which is still down there although it has probably solidified by now. Or not…
I like this picture because it reveals how much weathering can change the appearance of what was once molten lava in only a few million years. Note the layer of angular blocks sandwiched between weathered columns.
Conclusions
This is a typical basalt column that isn’t as weathered as some of the others. All those shards I’m standing on resulted from the breakdown of the rock by water seeping into its internal structure, where it altered the mafic minerals (e.g. pyroxene, plagioclase feldspar, biotite), which are susceptible to chemical weathering. This is where all the mud in the world comes from.
It was a great day to drive over the Cascades at Chinook Pass, where it snowed on us (in June), and explore the Columbia plateau. I’ve never seen so much variability in basalts before. The magma chamber underlying central Washington was a giant chemical reactor that released pressure by erupting a mix of fluids that cooled to form minerals and then these magnificent rocks. These rocks tell us how the magma chamber evolved over several million years; and once they were exposed to the atmosphere, they began to record the slow process of being reduced back to their basic constituents (fine-grained minerals like clay), which can remain suspended in water and begin their long and perilous journey to their final resting place–sometimes a lake but, ultimately, the ocean.
Everything eventually returns to the sea…
Mount St Helens After Forty-Five Years
Introduction
I was a geology student at Arizona State University in May, 1980, when Mount St. Helens made the headlines. It is the largest volcanic eruption in North America, and when one-cubic-mile of mountain collapsed, it became, and remains, the largest landslide in human history. I followed the progress of geological investigation into the eruption with interest as I pursued my education, but progress was slow. It isn’t easy to reconstruct an event that occurred in a few minutes. The area was too dangerous to approach for more than a year because of gas explosions from within the pile of debris, which reached 600 feet in thickness.
Mount St. Helens faded from memory for decades, eventually becoming just another geologic event in a long chain of cataclysms covering billions of years. I never thought about it until I found myself living less than 100 miles from ground zero. I had to check it out. This post is a brief summary of what I found when I visited Mount St. Helens National Volcanic Monument. I hope I can convey some of the excitement I felt at stepping on ground that was literally on fire less than fifty years ago.
Figure 1. I arrived at about 10:30 in the morning and got this image before low clouds settled in, accompanied by fog later in the day. The characteristic volcanic cone is missing; the top of the mountain slants slightly upward to the right in the center of this image. That isn’t a lake in front of St. Helens, just fog collecting in the valley that feeds the Toutle River.
Figure 2. Mount St. Helens is about 2.5 hours from Tacoma. The closest you can drive is Hummocks Trail, but a four-mile hike will take you to the rim of the caldera. Maybe another time.
Older Volcaniclastic Rocks
Figure 3. Mount St. Helens is less than forty-thousand years old, but it is constructed on a thick sequence (~2 miles thick) of volcanic rocks as old as 300-thousand years. Beneath these Pleistocene volcaniclastic rocks mixed rocks of uncertain age that comprise “bed rock” in this area; however, these igneous and sedimentary rocks are much older–spanning the Oligocene epoch (~34-23 Ma). I stopped to look at several road cuts along the new Highway 504 (the original is buried under debris).
A. Exposure of andesite volcanic rocks showing a complex eruption history, which includes ash layers and what looks like tuff (ash so hot it melted together to form a glass-like volcanic rock).
B. Close-up from the left side of (A) showing a layer of volcanic breccia that is now vertical. Individual clasts are visible but there is very little matrix. The dashed line indicates the approximate bedding plane of the layer. The rounded block labeled with ?? is about 12 feet in diameter. This is a puzzling structure. My guess is that there was a collapse of one or more volcaniclastic layers into a ravine after deposition. A jumble of material.
C. Photo of a complicated structure separating the left side of the exposure (tilted beds and blocks) from the right side (horizontal ash layers). The dash line is meant as a reference to the vertical beds in (B), but it was difficult to determine orientation. However, a clear change in texture suggests a depression, which may have been a conduit for volcanic material to erupt. The BLOCK/PLUG label reflects this interpretation. Within this “BLOCK” there is a discrete region of thin, irregular bedding that I’ve labeled (for convenience) as a CHANNEL? The question mark reflects my doubts about this identifier. Nevertheless, this road cut exposes a sequence of events: lava and ash being erupted onto an irregular volcanic landscape; probable surface erosion for some period of time; physical disruption and collapse, probably while still hot, of some part of later volcanic material. I don’t have enough experience with volcaniclastic sediments to say anymore than that.
D. The pushpin shows the location of this road cut. The blue ribbon is Coldwater Lake, where Hummocks Trail is located (see Fig. 2); this exposure is more than ten miles from the caldera, and hundreds of feet above the valley floor.
Figure 4. This post-eruption road cut is a mile or more further from the caldera. The solid line was a striking lineation that could be a fracture or possibly a contact between eruption beds. The dash-dot lines are apparent bedding planes between andesite flows. There is no ash present at this location. The dash lines delineate what I’m calling a BRECCIA because there is no evidence of bedding and the overall appearance is irregular; also, some large blocks were evident, although they could be a result of differential weathering. Lava flows are notoriously difficult to trace any distance laterally. Nevertheless, this exposure is similar in appearance to Fig. 3 with respect to the discontinuity between identifiable volcaniclastic deposits.
Figure 5. This road cut is located (see inset map) in an area the geologic map (Rock D) identifies as volcaniclastic rocks of Oligocene age (33.9-23.04 Ma). This is a smaller exposure than seen in Figs. 3 and 4, but it is also very different in appearance. That could be an optical illusion; close examination of the photo (I took it from my vehicle stopped in the middle of the road) suggests to me that this is ash that was so hot it formed what is called a welded tuff when it fell, after being blown into the atmosphere by an eruption. The light color suggests a magmatic composition more like granite than gabbro, or even diorite. That wouldn’t be surprising in the complex magmatic environment of a subduction zone, where partially melted, oceanic crust (e.g. gabbro and basalt) chemically mixes with continental crust (e.g. granite and diorite).
This completes my survey of older volcanic rocks near Mount St. Helens. There are no rocks exposed that explain the apparent hiatus in volcanism between about 23 and 2 million years ago. That is a story for another day…
Volcaniclastic Deposits from May 1980 Eruption
Figure 6. Photo A was taken a few days before the eruption in May, 1980. Image B was taken a few days afterward. The pre-eruption volcano was 9677 feet tall, but the obliterated peak is only 8365 feet. The total volume of material displaced exceeded one cubic mile, most of which was rock that collapsed during the rock slide preceding the actual eruption. The flat area fronting the volcano in (B) is a large fraction of the previous peak, which filled in several channels originating at the volcano. Note the holes in (B), which are probably blow-outs of gases trapped in the debris.
Figure 7. (A) This plaque was located along Hummocks Trail. I’ve supplemented it with the map of volcaniclastic deposits shown in (B). I will focus on the three major volcaniclastic deposits I encountered at Hummocks Trail (blue circle in B), which are numbered 1-3 in both figures.
The first stage was collapse of the north flank of Mount St. Helens (brown in A and cross-hatched in B). This was a run-of-the-mill massive landslide that followed existing drainage, until stage two occurred.
When the rock containing the highly pressurized magma was removed. The resulting release of pressure created an explosion equivalent to 10-50 megatons of TNT; although a volcanic eruption is not analogous to a nuclear explosion, the energy released was roughly 1600 times the energy of the Hiroshima atomic bomb. It moved a lot of rock. This blast occurred seconds after stage 1 began; the hot gases overtook the rock slide, driving rock and debris up the sides of the valley, removing everything, including top soil, within a few miles of the volcano. The orange area in B shows how widespread this explosion was.
Stage 3 was a pyroclastic flow (red in B), which was limited to the immediate vicinity of the caldera; however, what goes up must come down, so several inches of ash were deposited as far as Spokane, Washington–400 miles distant.
Video 1. This video shows debris from the landslide (Stage 1) that was pushed at least 300 feet from the original valley floor to the ridge by the unimaginable blast of Stage 2. The main slide followed Toutle River (North Fork), but with this impetus, debris was launched over the canyon walls. That’s what this video shows. It’s like the heavy stuff collected at the top of the ridge whereas the sand/gravel-sized debris was blown miles further.
Figure 8. This photo is looking south towards Mount St. Helens from Hummocks Trail (see Figs. 2 and 7B for location) along the Toutle River (North Fork), which is more than a hundred feet lower, even after being filled with debris from the 1980 eruption. Note the difference between this scene and the deposit from Video 1. It’s difficult to comprehend the dynamics of a blast (Stage 2) capable of pushing rock (Stage 1) up this slope; when the explosion lost energy it simply dumped its load, creating a surreal landscape. The debris has very little clay and is thus non cohesive; thus slumps like this are common. Note the small hill and “ridge” in the middle of the photo. This terrain makes no sense, other than erosion has been etching it for 40 years.
Figure 9. This layer of ash I encountered along the Hummocks Trail is a remnant of a vast sheet originally deposited during Stages 2/3–breaking such a continuous eruption sequence into stages is useful but not particularly elucidating. It all happened too fast to comprehend. You might call this an “over-bank” deposit, like when a river tops its natural levee and deposits fine-grained sediment on its floodplain.
Figure 10. Hummocks Trail followed a small stream through a bizarre landscape comprising multiple small ponds like this one. A dam constructed of eruption debris (left-to-right in the center of the photo) has blocked the stream flow, creating a meandering channel during low-water conditions; but I can imagine all those dormant grasses erupting later this spring. I encountered several of these marshes, each one defined by water trying to find a way out of this labyrinth. According to Fig. 2, this is the outflow from Coldwater lake; the eruption partially blocked its path but nature is finding a way through this discombobulated landscape.
Figure 11. This photo perfectly captures the topography of Hummocks Trail. This is the northern end of the trail, which is a little higher; the Toutle River (North Fork) is more distant and the cliffs we saw in Fig. 8 have receded, replaced by moderate slope; however, note the fine-scale nature of the hummocks here. They are ubiquitous but contain only a few scattered boulders.
Figure 12. This is a view of Coldwater Lake from the visitor center, looking south towards Mount St. Helens. There are two things to note from this image: 1) the Toutle River valley is a broad, flat plain because it was filled with debris from Stage1; 2) the overflow deposits (e.g. Video 1) have blocked the lake and raised its level. The source of water we saw in Fig. 10 is evident in the center of the photo. This isn’t a sedimentary dam, created by flood deposits, or even a glacial dam produced from the debris scraped up by thick ice sheets. The shoreline was modified when Mount St. Helens collapsed and then exploded with unbelievable violence.
Final Thoughts
The eruption of Mount St. Helens in 1980 gave geologists a rare opportunity to see how Earth produces sausage. Let me explain my metaphor.
Ocean crust is denser than continental crust it encounters at a convergent plate boundary, and at a lower elevation. It is thus overridden by the continent, forcing it to dive into denser and hotter rocks at depths of hundreds of miles. This obviously displaces hot and ductile rocks, heating the subducting rocks even more; the sausage-making operation has begun. Still pushed from behind by the conveyor belt of oceanic crust being subducted, this basalt/gabbro mixture heats enough to boil off the water contained in its sedimentary cover as well as any constituents with a reduced melting point (e.g. silicon-rich minerals). This superheated material rises through tens-to-hundreds of miles of crust, heating it and producing a mixture of oceanic and continental crust.
Plate tectonics keeps turning the crank on the sausage machine for tens (even hundreds) of millions of years. The molten mass of magma keeps rising because it is less dense than the rocks through which it is passing, until the pressure has decreased enough for it to find cracks in the solid crust. The magma fills these cracks, which often lead to fissures in the surface; the magma erupts. The magma cools and begins to solidify, forming a pluton at depths of several miles to tens of miles.
This process keeps operating, in fits and starts, until the tectonic plates change direction. In the meantime, the upper crust has been filled with multiple plutons (solidified magma chambers), sometimes squeezed into the volcanic rocks from previous eruptions. Individual magma chambers/plutons are about one mile in diameter, although they take many shapes, and remain active for less than one-hundred-thousand years (often much less). These are injections of fluid rising through weak points in the crust, driven by pressure paths–not missiles launched from the mantle. They are like the sweat on your brow after a hard workout.
Mount St. Helens has released a lot of pressure, although it is still very dangerous at human scales. Chances are that this magma chamber will solidify within the next hundred-thousand years; but the unstoppable sausage machine will continue cranking out more mixed material in a molten form until it has filled every nook and cranny in the upper crust. That’s how mountain ranges like the Sierra Nevada were formed. It takes a really long time.
Mount St Helens probably won’t erupt again at the scale of the 1980 event, but that doesn’t mean much if you happen to be camping near the caldera when a smaller eruption occurs. After all, the magma chamber is still extruding lava in an unsteady process that is currently pretty slow. However, we humans can’t see fractures in bed rock; thus, the next and the next, etc, magma chamber could appear anywhere from Northern California to British Columbia. There are plenty of young volcanoes in the Cascades that haven’t blown their tops yet.
Who’s next?
The Olympic Peninsula: Quinault Rainforest to Cape Flattery
This is the first in what I hope will become a regular series of blogs from my travels around the Pacific Northwest (PNW) as well as trips throughout the world. This series accompanies my main blog, Rocks and (no) Roads, which reports on the geology of various places to which I travel. You could see I’m expanding my horizons; in addition to posting about general sights in this post, I will also be including environmental and ecological observations that are of interest to me. My background is in geology, but I’ve become aware of a lot more since moving to the PNW. So this is a learning experience, thanks in large part to the availability of expert assistance from CoPilot, Microsoft’s version of ChatGPT. I’ll be turning to it to identify plants and evidence of animal activity in future posts.
This is the base map I’ll be using in many of my posts from the PNW. The star indicates my base in Tacoma. Today’s post describes a two-day trip to circumnavigate the Olympic Peninsula. Although this area is the wettest in the contiguous United States, with annual rainfall up to twelve-feet, it was clear for the duration of my visit. The labeled areas indicate where the photos described below were taken.
Location A: Quinault Rainforest. Photographs can’t do justice to the experience of being surrounded by a temperate rainforest. There are many trails of different lengths, but I followed a shorter one (about one mile) that followed Willaby Creek for a while before turning into the depths of the forest. This image shows the creek rushing by about 50 feet below the trail as it races to the south shore of Lake Quinault.
Location A: Quinault Rainforest. This rotted log is about six-feet in diameter. It is representative of the ongoing decay and rebirth of the forest. I’ll talk more about that in another post. Note the ferns growing out of the decaying wood.
Location A: Quinault Rainforest. There are at least half-a-dozen species of giant evergreen trees in the rainforest, and I can’t identify any of them; but CoPilot suggests it might be a Coast Redwood, part of a local population found in this area. This example is typical in an area known for its “Champion Trees”. We’ll get to that in the next photo.
Location A. Quinault Rainforest. This is the world’s largest Spruce tree. It is 191 feet tall and about 1000 years old. It is one of the six champion trees located in Quinault Valley. The other champion trees are: the world’s largest Western Red Cedar, Douglas Fir, and Mountain Hemlock; and the largest Yellow Cedar and Western Hemlock in the U.S. This tree is growing in a wetland area at the NE end of Lake Quinault.
Halfway between Sites A and B. During my day-trips around the area, I’ve noticed a what appears to be a regional interest in post-industrial art, including but not limited to large concrete facilities that have been left to decay in place, as well as small sculptures and other curiosities scattered throughout the cities and forests. I don’t know if this is intentional or not: the roof of the information board collapsed (no doubt because of 12 feet of rain per year) and was set aside, possibly as a monument to nature?–or evidence of the poor funding and mismanagement of the National Park Service.
Location B: Kalaloch Lodge. This is the view from the deck of the lodge where I spent the night. Kalaloch Creek meanders as it approaches the coast and enters the Pacific Ocean here. An impenetrable pile of driftwood (actually logs and entire trees) has collected on a sand spit deposited on bedrock.
Location B: Beach 4 at Kalaloch. Steep bluffs of glacial till front a wide beach with many exposures of rock, which I’ll discuss in my next post.
Location C: Ruby Beach. This was the last beach before US 101 turned inland for ten miles. I took a video because a series of photos can’t possibly convey the beauty of this location as the sun was rising. Note all the rocks protruding from the water at low tide. The rocks are rising from the earth as we make our way north.
Location C. This selfie demonstrates how chilly it was, with the temperature below 40F. Rock formations like this are called stacks; they are erosional outliers as the coast recedes over millions of years, pounded day and night by rocks carried by waves; and tides that exceed nine feet–twice a day! You have to time your visit accordingly or all you’ll see is water.
Location D: Point Flattery. This is the extreme tip of the contiguous United States. The bedrock we saw further south, at Ruby Beach, now forms wave-cut cliffs that tower 40-80 feet above the waves. The top of the bluffs is 330 feet above sea level. The view from the catwalks is breathtaking. Vancouver Island, BC, is visible in the background, with peaks around 6000 feet.
More PNW Humor. All of the toilets we saw along the coast were constructed over septic tanks, with warnings about what to put in them. Someone with a sense of humor modified just one word of the official message…
If you get the chance, I strongly recommend visiting Olympic National Park, but you’re going to want to spend a week unless you live nearby in the PNW.
Gravel Beaches on Vashon Island
This photo of the gravel/mud beach at Fern Cove Nature Preserve reveals a marine delta, fed by Shinglemill Creek. Unlike the mud/sand delta we saw at Dash Point, the sediment here is dominated by rounded gravel and small boulders. Mud, sand and silt form the matrix. All of this material is available from the glacial till that comprises Vashon Island.
The inset map (right) shows the two sites I visited today. Fern Cove is located near the northern tip of Vashon Island whereas Maury Island Marine Park occupies the SE side of an island that is connected to Vashon by a fill zone about 200 yards across (which is eroding away as I type).
Fern Cove Nature Preserve
Vashon Island was logged out, so the beautiful evergreen forests that cover most of the island are all second growth. The state is trying to restore the original habitat, and Fern Cove is a good example; they don’t allow dogs!
I’ve noticed that people in the Pacific Northwest (PNW) appreciate industrial art of a practical nature. I found an example here, in a threatened habitat that is actively being restored. I guess this old truck body isn’t hurting anything; I’ve also noticed that communities in the PNW don’t waste money on unnecessary actions.
This photo shows how the gravel is localized within the delta, forming low nearshore gravel bars. The intervening areas are muddier than I found at Dash Point.
These gravel bars do more than concentrate larger rock fragments. Acorn barnacles encrust the larger ones, which are several inches in diameter. The tidal range is about 7 feet here and the beach is inundated twice daily, so I think these are living. I’ve seen barnacles on large boulders before, but I didn’t know they grew on stones. I guess the wave energy isn’t high enough to disturb them over a life cycle; their larvae must hang around after a storm and find a new rock to inhabit.
On all the beaches I’ve reported on for Rocks and (no) Roads, I’ve never seen this before. This is an active feeding area for sea birds. These are mussels, which the birds grab from a nearby mussel colony on the shallow delta front and drop on exposed gravel during low tide. The shells break open and the birds feast, leaving their dirty dishes behind.
This Western skunk cabbage is just emerging from the wetland surrounding Shinglemill Creek. It will grow leaves up to two feet long, but it makes a beautiful display in the unseasonably warm late winter we’re having in the PNW.
Maury Island Marine Park
On the opposite side of Vashon Island, I visited a gravel quarry that operated for about seventy five years, before being purchased by the state as a park. This is another example of letting nature recover without interference.
This photo looks SSE towards Dash Point. Commencement Bay and Tacoma are visible in the background; a little sunlight is shining on the bay. The cliff has been quarried for 75 years, so the 400-foot vertical face is now a steep incline with a trail that utilizes many switchbacks to reach the shoreline. Let’s see what I found…
There is no mud or sand visible on this beach. I thought that might be a side-effect of so much gravel quarrying, so I walked beyond the limit of the quarry; the substrate didn’t change, but there must be lingering effects after so many decades of preferential sand removal.
After what I saw at Fern Cove, I thought I was prepared for whatever I might find; but I never expected to see clam shells with the hinge lineament intact; this shell even closed after the bird (e.g. gull or crow) has eaten the soft tissue. The shell actually snapped shut after the animal was eaten. Amazing!
This spectacle gives driftwood a whole new meaning. Someone even built a crude shelter in the background from the logs that have collected over the years. There are a lot of trees in the PNW and many of them fall into Puget Sound, ending up all over the place. This looks like what coastal geologists might call a “hot spot”, a location where waves converge during storms.
After a hot climb, even in 45F temperatures, I made it back to the top of the cliff. This area was a barren wasteland in 1975, when the state took over; park authorities and volunteers have worked tirelessly to not only allow recovery, but to keep out invasive species. I think they’re doing a pretty good job.
Summary and Acknowledgments
I learned more biology on this day trip than in my entire life. For example, sea birds eat mussels on muddy beaches and clams on cobblestone ones. They carry the hard shells in the air and drop them on rocks, breaking them open to reveal the animal hiding within. Apparently I arrived at these two beaches just after lunch, when the tide hadn’t cleaned up the dishes yet.
I’m going to pay more attention to fauna and flora in my future posts.
I don’t know anything about biology, so all plants and animals identified in this post came from CoPilot (AKA ChatGPT). I didn’t check their identifications because it wasn’t worth the hours that would have required. This is not a research paper. I’m just going out into the world and observing through my dirty, discolored glasses.
But now I can see living things…
Pinnacle Peak Park: Miocene Andesitic Volcanism
Introduction.
This post examines some of the rocks we discovered while climbing Pinnacle Peak (Fig. 1), a small shield volcano created during the Miocene epoch, between 23 and 5.3 Ma (millions of years ago determined by radiometric dating). The wide range of dates suggests that this volcano remained active for a very long time, producing volcanic material of different types as it released pressure from the magma chamber feeding it. I can’t pin down the dates any better, although they are better known within the geological literature. Thus, my discussion and the model that follows are meant to apply to the entire period of activity.
Figure 1. Pinnacle Peak is about 1000 feet in height. This photo reveals the characteristic low profile of a shield volcano, making it appear smaller because the summit is more than a mile distant; however, note that it is slightly asymmetrical because the southern (right side) slope is lower than the north side.
Figure 2. (A) The Pacific Northwest (PNW) base map I will refer to in this series of posts. Tacoma is indicated by a star and Pinnacle Peak park by the circle. It was less than an hour drive on a weekend at 0800; traffic picked up substantially and, by the time we left at about 1130, there was a traffic jam throughout the area because the access roads are small. Go early! (B) The geological map from RockD shows several volcanoes of similar Miocene age standing out in an ocean of glacial till. Note the presence of a deposit of till on the southern slope of the mountain. This was difficult to identify because the main trails followed old logging roads that had been covered with gravel, probably from this till and the White River flood plain below, in which there was active quarrying on the day of our visit. Note the blue arrows at the summit because they will be referred to below.
Observations.
We walked up the Pinnacle Peak Loop Trail counterclockwise, taking photos and noting the geology along the path. However, this is not a geological report but only a casual observation. All dates and rock types are from RockD, a compilation of geological maps produced by uncountable numbers of geologists engaged in active geological field and laboratory research. Thank them for the accessibility of their data, and blame me for any errors in interpreting it.
Figure 3. This photo was taken about half-way up the volcano where a road-cut revealed volcaniclastic sediments like we saw at Snoqualmie Falls. This nice exposure reveals a fine matrix of dark material including irregular, but rounded, boulders up to a few feet in diameter. These are volcanic bombs, semi-molten lave blown out of the vent by gas pressure which landed hundreds of feet from the summit.
Figure 4. (A) This boulder of volcanic breccia was placed in the parking lot, probably as an example for public viewing. It is about 3 feet in diameter and contains numerous volcanic bombs, as well as fine lamination near what was its original bottom, as labeled in the figure. These would have been layers of ash with alternating chemical properties that gave them different colors. (B) Close-up showing the contrast between the lighter colored ash matrix and an andesite bomb. Imagine this semi-molten, andesite bomb flying hundreds of yards and landing in still-hot ash. The number of bombs visible in (A) suggest that this was part of a very explosive event.
Figure 5. (A) Close-up of a boulder within a semi-hidden exposure of andesite near where Fig. 4 was taken. (B) This close-up reveals phenocrysts (solid mineral crystals) and vesicles (pockets left by escaping volcanic gases). I cannot identify the minerals comprising the phenocrysts, but common ones within andesite are pyroxenes, plagioclase (high-calcium feldspar), hornblende, and biotite. These are all dark minerals that crystallize at higher temperatures than high-silica (Si02) minerals. The specific mineralogy tells volcanologists about the chemistry of the magma chamber feeding the volcano. The vesicles of gas (e.g. CO2, CO, water vapor, sulfur compounds, H2S) are a crude indication of how explosive the magma was; more vesicles implies more explosive potential, especially in andesites, which are more viscous than basalt.
Figure 6. View from near the summit looking south toward the White River. This is a very different perspective of Pinnacle Peak than Fig. 1. The river valley is filled with glacial till (< 1 million years old) that covered all of the volcanic material from the volcano, which stands out today because it was never covered by ice.
Figure 7. Photo taken on the SE side at the top of Pinnacle Peak (blue arrow in Fig. 2A). These horizontal rocks are not boulders, but instead the ends of columnar joint blocks of andesite. They are less than one foot in diameter; most of them are hexagonal, but irregular shapes are also present. They form when lava cools slowly enough to allow this kind of crystallization to occur, but rapidly enough that the lava doesn’t form massive beds.
Figure 8. Photo of columnar andesite near the summit on the NNW side. These are much larger in diameter than those seen in Fig. 7. Columnar jointing is usually oriented with the ends vertical, but this isn’t necessarily required because gravity is not the dominant force; chemical bonds between the individual minerals determines the development and size of columnar joints. As long as the “top” of the lava flow (facing the camera in this photo) is exposed to the atmosphere, they can form. I reported on incredible examples of this in my post on Organ Pipes National Park near Melbourne, Australia.
Figure 9. This exposure, from further down the south slope of Pinnacle Peak, reveals blocky lava that seems to be bedded, with bedding planes dipping away and to the right of the camera. No columnar jointing is visible, and the rocks are solid. This could be an outcrop of sandstone if it weren’t for the grayish color. Maybe limestone?
Figure 10. (A) Exposure of andesitic lava that looks much the worse for wear than anything I’ve seen before on this field trip. (B) Close-up of the exposure outlined in (A) that reveals a jumbled mass of lava that reveals several secondary textures: contamination and preferential erosion along “bedding” planes (fissility); irregular and tilted bedding planes; fine-scale fracturing and weathering (fractured); and blocks with a hint of hexagonal form (columnar joints). This was near the bottom of the volcano and the rocks are presumably older than those seen in Figs. 3, 7, 8, and 9; in other words this photo implies that eruption style was not uniform throughout this volcano’s lifetime. I further suggest that, over the lifetime of this volcano’s active period, the magma chamber became more stable, and thus the eruptions more predictable.
Figure 11. All of the textures, mineralogy, and fabric of the rocks comprising Pinnacle Peak fall within the expected composition of a shield volcano, except for the horizontal columnar jointing seen in Figs. 7 and 8, which point in opposite directions (NW and SE) even though the lava erupted directly from a rather small outlet (~200 feet in diameter). I didn’t understand what I saw at Organ Pipes National Park, but I let it go; now that I’ve encountered similar textures again, I want to have at least a naive understanding of how lava can form structures similar to a wilted plant. This is my model. The purple represents thousands of lava flows, volcaniclastic deposits, etc; the red is the lava just before the eruption(s) represented by Figs. 7 and 8; and the yellow is a thin layer of viscous lava that flowed out over a slightly older deposit. This last eruption wasn’t immediately covered by more lava and it cooled according to the laws of thermodynamics. In other words, it formed columnar joints, which are represented by the squiggly lines. The red arrows point to toward the “top” of the flow at every point; as you can see, the “top” isn’t always pointing towards the sky. This model is based on simple thermodynamics and mineralogy–I assume that the lava is a homogeneous mixture of the components of andesite (e.g. quartz, feldspar, pyroxene), which are cooled only by their exposure to the atmosphere. The different diameters in the columns (compare Figs. 7 and 8) suggests that this is an oversimplification. Nevertheless, it makes sense to me.
SUMMARY.
I had a great time climbing Pinnacle Peak and I learned something new from the rocks that surround and support us. A large mountain range like the Cascades doesn’t appear overnight. Subduction along the NW coast of N. America continued, interrupted by collisions with offshore continents, from 200 Ma to the present, creating multiple mountain ranges which created the Pacific Northwest. A small volcano like Pinnacle Peak would have burned out in a few million years. The range in age is based on stratigraphy, and the absence of funding/geologists to date rocks from every minor volcano in a major subduction zone, leaves me to apply common sense.
Pinnacle Peak erupted about 5 Ma, based on the physical status of the summit. It sputtered for a few hundred-thousand years as the magmatic system decompressed; eventually the magma chamber, or a subsystem of pathways, gave a last gasp. The columnar jointing we saw today suggests that this final eruption consisted of some spitting and then the appearance of timid lava, flowing a few-hundred yards from the summit (Fig. 11). That is what we saw on today’s field trip.
That’s my story…
Timothy R. Keen 
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