Mima Mounds Natural Area Preserve
It was unbelievably gorgeous weather here in the Pacific Northwest (PNW), with a high of 74 F, so we took a look at a couple of nearby natural areas.
Mima Mounds
This exceptional area isn’t unique but it is an unsolved geological problem. It is also peculiar in being a transition zone between active prairie and forest ecosystems. I’ll try to explain this with photos, and some help from CoPilot, Microsoft’s version of ChatGPT. However, I won’t solve the geological conundrum, which may never be fully explained.
The Mima Mounds are about 16500 years old. They formed as the last continental ice sheet retreated from Washington. The mounds you see in this photo sit atop a gravel surface created at the southern extremity of this glacier. People, including the native Americans who have lived here for tens of thousands of years, have been perplexed by this bizarre topography.
There is a 1.9 mile trail that goes through the area; however, when European Americans first came here, this topography extended for more than twenty miles. Most of it has been demolished.
This is a portion of the information board at the interpretive center. (A) The Mima Mounds were constructed after the ice sheets began to retreat for the last time. The inset map shows the location of the NAP relative to the glacier and modern cities. This was the absolute furthest south of thick ice, but that doesn’t mean it was warm. (B) This is a rare photo of a cross-section through a mound. The dark soil is organic-rich and excellent potting soil. The subjacent glacial outwash is gravel. (C) This is a photo from the air, which shows their regular spacing. This is the geological problem. How could they have formed over about 400 square miles?
There are many theories for the origin of the Mima Mounds, and other mounds found in N. America and elsewhere. These are summarized on the Wikipedia page. I included this photo because it was on the poster; and the size/shape of these blocks of permafrost from Scandinavia are a good match to the mounds we saw. And they are in a similar, post-glacial environment.
Prairie Ecosystem
I’m discussing both the geology and ecology of Mima Mounds together in this post because they are inextricably connected. There are two ecosystems competing for space in this lumpy prairie environment. The result is there for anyone to see, if they ask the right questions.
This low shrub was identified by CoPilot as snowberry, which is a staple of the prairie. I only saw them on the mounds, their roots in good soil, but apparently they also do well in the sandy glacial soil. From my perusal of the internet, I can’t disagree.
My ignorance is hilarious. I thought this was some kind of wildflower … but CoPilot identified it as a Douglas fir seedling. They were growing only on the mounds, sometimes in clusters. This is evidence (to me and CoPilot) that this is a dynamic transitional environment where forest species coexist with prairie flora.
This fern caught my eye because it is not a natural inhabitant of a prairie ecosystem. However, the mounds are near a forest, so … CoPilot thinks it is a bracken fern, which is native to the area but not a prairie environment. It often behaves as an aggressive colonizer in disturbed edge habitats. That last phrase gets my attention because this preserve is at the edge of a mature forest.
This lovely flowering shrub was identified by CoPilot as a species of Lotus, commonly called Spanish Clover, deervetch, or trefoil. It grew in the sandy areas between the mounds. My quick check can neither confirm nor deny this identification, but this common variety of clover is native to the PNW.
This mound is populated by bracken ferns, crowding onto the area with good soil.
I don’t know what species this copse of young trees is, but it is obviously encroaching on the prairie ecosystem.
You never know what you’re going to find when you go outdoors. According to CoPilot, this is probably the result of NAP’s policy of not removing human artifacts that don’t interfere with the environment. Manpower shortages, policy priorities, etc. Mima Mounds was established in 1976, so it’s fair to say that this structure is at least that old. I guess NAP hasn’t gotten around to it yet, which fits my nascent sense of priorities in the PNW.
Bill Frank Jr. Nisqually National Wildlife Refuge
We stopped for a quick visit, which turned into a one-mile death march (for me, after walking 4 miles on uneven ground), to see where the Nisqually River empties into Puget Sound. It originates from the face of an alpine glacier above 6000 feet on Mt. Rainier. This is a tributary stream that forms a series of algae-covered ponds.
Here we are, less than a mile from the Nisqually River’s delta in Puget Sound. There is a lot of downcutting and the creation of sand bars, but no boulders or even cobbles. This glacial river has been tamed by nature over a distance of about eighty miles, but it is still flowing pretty fast. We didn’t make it to the delta … maybe next time.
Summary
This was a great day trip to a fascinating and beautiful area, where the prairie and the forest compete for space on the top of mounds of top soil whose origin is a mystery. This back-and-forth movement of plants on timescales of years to decades suggests that the PNW is alive and well, the flora responding to minute changes in soil and air temperature/moisture, precipitation, wind, etc. Let’s hope these two thriving ecosystems can continue their dance without further human interference.
I have my own hypothesis about the formation of the Mima Mounds, which is consistent with the facts. 1) As the glacier melted and retreated, over thousands of years, shallow lakes developed in local depressions. These lakes were shallow, perhaps twenty feet deep, and limited in extent. 2) Fine-grained sediment (i.e. mud) and organic debris settled in them to depths of no more than ten feet. They were ice covered for part of the year. 3) As the glacier retreated further, streams began to superimpose their beds onto this landscape, but they weren’t like a glacial river (e.g. Nisqually River). These were weak streams flowing over a post-glacial landscape, meandering and not cutting new channels. 4) This mild erosion was superimposed on a landscape dominated (in this area) by an antecedent pattern like that seen in the Arctic (see above photo). Fine-grained sediment was removed, following a suture pattern until only irregular bumps remained. 5) This process of sheet-flow erosion continued to the present day, leaving us with these paradoxical mounds.
I am a sedimentologist, so I think in terms of turbulence and flow as interconnected processes that alter a landscape slowly, one grain of sand at a time. There wasn’t enough turbulence to strip away the veneer of clay over this basin in the time allowed, so it chipped away at the weak edges of lumps of soil that were probably held together by the roots of plants.
In other words, the thawing of permafrost created the pattern, and turbulent flow polished it to what we see today.
Prove me wrong…
The Geology of Franklin Falls
Washington has more than 3000 catalogued waterfalls, so we stumble onto them regularly. Waterfalls form wherever there is a change in the lithology of the crustal rocks: along crustal faults, which naturally create vertical planes; where weaker rocks lie beneath strong ones and are reached by a downcutting river; and of course where glaciers have sculpted the land. These natural features create spectacular views as well as revealing glimpses of deep time.
Plate 1. Franklin Falls is about 70 feet high. The reddish rocks forming the cliff are Eocene sandstones and volcanic rocks (56 – 34 Ma). The park follows the South Fork of the Snoqualmie River along I-90. The parking lot is quite large and we found a parking space, even though it was great weather; more than one million people visited the site in June.
The rocks in this photo don’t reveal well-defined bedding although there is a suggestion of bedding to the right side of the image. However, I think the bedding marker is the vertical, dark streak that is slightly wavy. This curvature suggests that these rocks were deformed while ductile (buried deep enough to bend rather than break). The geologic map identifies an anticline in the area, and I think I found it.
Plate 2. Franklin Falls is located just west of Snoqualmie Pass, at an elevation of about 3000 feet. The Northern Cascades are very rugged and access is limited, especially in the winter. The topography shown in this map reveals steep slopes, especially through this pass, which I assume is the easiest route through this rugged terrain.
Plate 3. The geologic map from Rock D shows three distinct rock units, which reveal the general geological history of this area. The oldest rocks are part of the Jurassic melange belt (201 Ma), comprising metasedimentary and metavolcanic rocks that were originally deposited in deep water, possibly on a submarine fan. These sediments were buried and then scraped off the subducting ocean plate. This process deformed them as if they were put in a blender; hence the name, melange.
Almost 150 million years are missing before Eocene volcanic and sedimentary rocks were deposited in a continental setting, possibly a river or lake not too close to mountains; the rocks seen in Plate 1 don’t contain any large boulders like we see in the modern river bed below them.
Granodiorite is an intrusive igneous rock containing light-colored feldspars like albite, and slightly less quartz than granite. This batholith was emplaced during the Miocene (23-5.3 Ma) into rocks much like the Eocene rocks exposed along the river (Plate 1). However, granodiorite magma does not produce andesite, which is the most common volcanic rock in the Cascades. All those plutons being shoved into the upper crust exhibit a lot of chemical variety because the magma mixes with continental crust as it rises.
The final piece of the puzzle is the normal fault shown on the geologic map. The NW block of melange is labeled with a “U” to indicate that it moved upwards relative to the SE block of sandstone/volcanics. This displacement brought the older (Jurassic) rocks upward, eroding the rocks that were deposited above them. The fault isn’t shown as extending into the granodiorite, however; it is very difficult to identify a fault (usually by displaced stratigraphic units) in relatively uniform intrusive rocks, which contain no layering. If the field geologist saw evidence of this fault extending into the granodiorite, they would have used a dash line to indicate uncertainty. This line stops cold…
Plate 4. This photo is looking NW, across the fault, towards the melange. This peak is a block of Jurassic rock that was once tumbled in the accretionary wedge after it was scraped off the subducting ocean crust. The peak further back is Denny Mountain, Oligocene (34-23 Ma) volcaniclastic deposits. They are older than the granodiorite. We couldn’t hike around these mountains to see the rocks up close, but fortunately, gravity has made our job easier.
Plate 5. These are small boulders of the Jurassic Melange that rolled down the steep slope (i.e. face of the fault) and landed in the river bed (see Plate 1). (A) Mud deposited in the deep-sea trench was buried deeply enough to squeeze quartz and feldspar into veins (thin white lines in the image). However, it is probable that the thick layer of light-colored minerals were injected along weak points when the Miocene granodiorite was emplaced. Note that the vein becomes more orange to the right of the sample; this is probably a local concentration of K-feldspar (e.g. sanidine). (B) This sample looks like it was spun in a blender because the thin layers of light-colored minerals are twisted rather than approximately following original bedding (which has been obliterated).
Plate 6. This rounded boulder of granodiorite is about 18 inches in diameter. The large, white phenocrysts are plagioclase feldspar with a low Ca content whereas the darker ones with blurred sides are hornblende. The matrix is fine-grained plagioclase with a higher Ca content (feldspar composition varies with potassium-sodium-calcium). Calcium is associated with dark, potassium with pink, and sodium with white-colored crystals.
Summary
Today’s field trip was a unique opportunity to integrate the large scale observations (Plates 1 and 4) with hand samples (Plates 5 and 6) using a geologic map (Plate 3) as a guide to understanding the geologic history of the Cascades Range. Let’s try to create a simple, plausible geological history from what we know.
I’m going to list a series of geologic events because I don’t feel like finding/creating schematic cross-sections to pictorially demonstrate what I’m saying. I’ll start from oldest and proceed to the youngest.
- About 200 Ma: Muddy sediments were deposited in a subduction trench, which was approximately aligned N-S along the axis of the later Cascades range. Over the next 10-20 Ma these sediments were buried miles beneath younger erosional debris, until they were snagged by the overlying NA tectonic plate and deformed like putty.
- Between 120 and 60 Ma: It is unclear exactly what occurred, but subduction ceased, probably because several large crustal blocks slid to the NW along a series of transform faults. The melange we see in Plates 4 and 5 missed the boat and remained buried, slowly inching their way to the surface.
- About 60 Ma: Subduction resumed and a series of volcanoes produced lava, which mixed with sandy sediments in a continental environment. Volcanism continued for 30 Ma, creating a mixture of fresh lava and sandy sediments, which were buried while erosion continued — a delicate balance of tectonic uplift and isostatic sinking.
- Between ~30 and 23 Ma: Tectonic uplift increased, bringing the Jurassic melange and Eocene rocks (Plate 3) into the crust’s brittle fracture zone, driven by a combination of subducting plate dynamics and upwelling magma, as the ocean plate melted. This agglomeration of different rock types began to fracture along contacts, while still deforming plastically internally. The normal fault seen in Plate 3 would have occurred along such a seam during this complex exhumation process.
- A series of hot, rising plumes of magma originating at the top of the subducting ocean slab eventually reached these rocks, possibly within a few miles of the surface, between 23 and 5 Ma. The granodiorite filled every fracture and fault, creating the complex pattern seen in Plate 3. The thick veins of quartz/feldspar seen in Plate 5A would have been injected during this interval.
- Exhumation has continued, from 5 Ma to the present, modified by glacial scouring of the ancestral Snoqualmie River canyon. Today we see these rocks conveniently frozen in time, from our perspective.
Identifying the contacts between these many rock facies is a laborious task that will take decades, if not centuries, to complete. Nevertheless, it is obvious that a lot has occurred in the last few million years. The earth’s surface is a conveyor belt on which the pile of soil/rock is constantly removed by wind/rain/snow/ice…
That’s my story…
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.
Ecological Notes from Cowiche Canyon
Cowiche Canyon Recreation Area is located on US12 just west of Yakima, Washington. The region receives 9-14 inches of rain per year, making it a dry area; thus, the trail system includes both shrub steppe (uplands) and riparian (along Cowiche Creek) habitats. We followed the main trail along the path of a rail line that was in use between 1913 and 1984 along the creek; however, the wetland is very narrow, in places constricted to less than 100 yards. Thus, I encountered plants from both environments.
The canyon walls are composed of a series of basalt ledges with intervening slopes covered by talus and colluvium, which are part of the shrub-steppe habitat. I discussed the geology of the area in another post.
The recreation area is maintained by the Cowiche Canyon Conservancy in partnership with Bureau of Land Management. This stone is a piece of the columnar basalt that lines the canyon.
It’s fortunate that I visited this area during spring, which lasts a little longer here in the Pacific Northwest. As always, I used CoPilot (AKA ChatGPT) for identification while I try to remember scraps of the huge amount of information presented in this mixed environment.
This is Asclepias speciosa, also known as showy milkweed. It is native to Yakima county and is a host species for Monarch butterflies.
The leafy shrub with dark leaves is snowberry–Symphoricarpos albus (or possibly S. oreophilus, which also occurs around Yakima).
The low, brightly colored shrub with straight stalks is probably wax currant (Ribes cereum). The bright green is small leaves and the small patches of pink–barely visible in the photo–are the flowers. These are both native plants.
CoPilot wasn’t so sure about this, but it might be Creek or Red-osier Dogwood (Cornus sericea). This specimen was growing in the bottom of the canyon, not far from Cowiche Creek, which is a natural location for this native riparian species. It will probably become a small tree.
This is my favorite from the walk. Silky lupine (Lupinus sericeus) is one of the signature wildflowers of eastern Washington. I sure am glad we caught them in bloom.
This looks like Pale‑stem buckwheat (Eriogonum heracleoides), another native wildflower to the shrub-steppe habitat.
My untrained eye thought this was Pale-stem buckwheat, but CoPilot pointed out the different leaf pattern and color. This is (probably) Sulphur Buckwheat (Eriogonum umbellatum), another common wildflower to Yakima County’s uplands.
Antelope bitterbrush (Purshia tridentata) is a foundation species of the steppe. This young one had lots of flowers, but the old ones have bare branches; and groups of them grow and die together in cohorts after a disturbance like a wildfire. Yet another native plant.
After some discussion, and sharing a close-up, CoPilot swears (hahaha) this is Woods’ rose (Rosa woodsii). However, its justification fits what I see with my own, somewhat confused eyes.
Here’s a close-up of the fruit. The shrub is covered with small nuts that have a distinctive shape, and are definitive for a wild rose. This is another native species to the steppe habitat of Eastern Washington.
This photo, looking across Cowiche Creek, puts it all together for me. On the other side of the canyon we see columnar jointed basalt, several plant species similar to snowberry, bitterbrush, and buckwheat. Along the creek are dogwood and wild rose; and in the foreground is (maybe) big sagebrush (Artemisia tridentata).
When I took this picture, all I saw was a bunch of plants. After carefully examining them with CoPilot, it has become a mixed riparian-shrub-steppe habitat. However, I didn’t see/hear any birds or other animals, even though it was a cool day with temperatures in the mid-sixties.
CoPilot was a great help, but it is not infallible–more like working with someone who has studied some biology/ecology. After all, it is only a Large Language Model, not an AI system trained on recognizing plant species. Nevertheless, it was a great collaborator and I learned a lot from our collaboration.
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…
Ecology Notes from Vancouver, British Columbia
Every time I go outside here in the Pacific Northwest I find something new and mysterious, so I’ll keep posting these notes on my discoveries. This time I crossed the border and entered our northern neighbor, Canada. It’s only a three-hour drive, not counting the time spent at the border patrol station.
There is no old-growth forest in this part of British Columbia but that doesn’t mean the forest has died. It is regrowing and adapting to a more urban environment. We were strolling through Stanley Park, on the waterfront of Vancouver, when this bizarre tree caught my eye. The tree looks dead, including no crown and a trunk that appears ready to fall over; but near the top a curved branch has appeared. It is almost as large as the trunk and has a thick canopy. Unbelievable!
This tropical appearing plant is Gunnera manicata, also known as giant rhubarb (according to CoPilot). It is originally from Brazil, but it does well in the PNW because of the wet climate and mild winters.
We drove a little up a fjord to Shannon Falls and discovered that nurse-log trees occur here as well as in Washington. This one is probably a Western Hemlock growing from a stump comprising multiple roots from clumped trees that merged into one. That’s why it looks like a bamboo thicket.
This Sooty Grouse didn’t seem to mind being photographed as it poked around this water hole in Squamish and Chief Viewpoint park.
This reminded me of the tree I saw in Stanley Park, a dead stump with curved growth full of foliage. I asked CoPilot about it and, surprisingly, it had a plausible explanation. It is so damp in the coastal PNW that trees don’t just grow out of stumps, they can actually grow from dead trees well above the ground. Apparently, the young tree has sent roots down through the decaying stump to reach the ground…another biological wonder. Simply awesome!
I thought these bright flowers looked familiar, but I don’t trust my intuition on biological matters (all yellow flowers are the same); as it turns out, according to CoPilot these are Western Skunk Cabbage–the same plant I saw in a wetland along the Olympic Peninsula. I was right…but I had forgotten the name. LOL!
I enjoyed this trip and writing this post, thanks to CoPilot. Its identifications may be wrong but they are better than mine. I think of its comments as those of someone who took a biology class in college.
I hope you enjoyed it too.
Cretaceous Intrusive Rocks in British Columbia
This post finds me in British Columbia (Fig. 1), where I explored fjords cut into mostly intrusive rocks that form an immense batholith composed of many overlapping plutons. The tectonic regime of this area is collision between the many small plates that comprised the Pacific Ocean as well as any island arcs and microcontinents that got in the way of N. America on its westward journey, which began about 200 million years ago (Ma). A collision between ocean crust and the N. American tectonic plate would have created a subduction zone, in which the denser ocean crust was driven beneath the continent. However, recent work suggests that this process was interrupted for uncertain intervals when islands collided with N. America; furthermore, there is evidence for a lot of strike-slip fault movement along transform faults. You can learn more about this complex history at Nick Zentner’s web page.
Figure 1. (A) Regional map showing the location of the study area in SW British Columbia, about 230 km (140 miles) north of Tacoma (starred location). (B) Detail map of the inlet (I couldn’t find a name for it), showing the location of the Sea-to-Sky gondola I rode to Squamish and Chief Viewpoint park. (C) Geologic map from RockD, showing the fairly uniform occurrence of diorite intrusive rocks intruded between 143 and 66 Ma (covering the entire Cretaceous geological period). The town of Squamish sits at the head of the fjord. Faults of unidentified type (i.e., normal, reverse, strike-slip) are common but don’t appear to control the location of major drainage basins, which have been excavated by glacial action during the Pleistocene epoch. The circle indicates the area reported on today, except for Fig. 2.
Figure 2. (A) Exposure of Late Cretaceous (100-66 Ma) sedimentary rocks at Stanley Park (bottom center of Fig. 1B). These rocks look unconsolidated, but they are actually well cemented. (B) Close-up showing lamination and sets of unidirectional cross-bedding, which indicates transport in a stream rather than a marine environment. Transport was generally to the left, but each set of cross-beds is a slice through a three-dimensional form like the bars seen in modern rivers.
Figure 3. View looking northward from Squamish and Chief Viewpoint park (circled in Fig. 1C). Besides offering a breathtaking view of the northern Rocky Mountains, this photo reveals several interesting geologic phenomena. The small peak in the foreground is solid diorite that was intruded between 143-66 Ma more than 20 km beneath the surface at that time. It has been uplifted as overlying rocks were removed by erosion. It may represent a single intrusive episode because typical plutons are 2-3 km in diameter; batholiths comprise multiple intrusions spanning millions, if not tens of millions, of years. Note the lineations running up the side. These reflect the scraping action of ice sheets during the last two million years as they flowed towards the sea. The valley in the background is the classic U-shape caused by the advance of glaciers. It has been filled in by glacial deposits very similar to those found in NW Washington. Glaciers in this area originated locally and were up to several kilometers in thickness. They flowed both towards the sea and inland to form a continental glacier.
Figure 4. (A) The rocks within the park are fairly uniform in composition because they were intruded as part of a single pluton. This boulder shows the typical salt-and-pepper appearance of dioritic rocks. This sample is relatively fine grained, which indicates that it wasn’t emplaced more than a few tens of kilometers deep; i.e., smaller crystals indicate faster cooling which occurs nearer the surface. (B) Close-up at the highest optical magnification available on my phone, about 5X. RockD generally describes the igneous rocks from this area as granodiorite, a type of diorite that contains 20-60% quartz (labeled Q in the photo), and primarily feldspar (labeled F) that contains sodium and calcium with little potassium. The dark minerals are amphiboles (labeled A), probably hornblende. These are typical granitoid rocks from a subduction zone.
Figure 5. (A) Surface showing a vein filled with a harder mineral that is probably quartz. The softer feldspar and hornblende has weathered more easily and been removed by the scraping of ice sheets containing rocks. Note the irregular shape of the vein; minerals like quartz have the lowest temperature to solidify and fill cracks in the slowly cooling magma. (B) This vein is straighter than that in A and is filled with minerals that have weathered more than the main rock. (C) This photo shows joints (X pattern in the center of image) and lineations (top to bottom) that indicate ice moving over the surface with embedded rocks that scratch the exposed rock. (D) This image shows a finer grained material filling a void in the original magma. The pebbled appearance of the coarser material results from preferential weathering of minerals like hornblende and feldspar. These images imply that the magma had solidified sufficiently to form joints as it cooled, but was then injected with more fluid. This isn’t surprising in a region where so many plutons were being created; there was certainly a lot of overlap in their intrusion.
Figure 6. This final photo shows two pointed peaks that result from ice cutting away at any rock that protruded above the main surface. Remember that the ice was up to three kilometers thick here whereas the peaks are less than two km above sea level. It is hard to imagine that much ice.
SUMMARY
This post describes only a small part of one pluton of the hundreds exposed within the Northern Rocky Mountains in British Columbia. The scale is difficult to visualize, but they represent only a tiny fraction of the immense volume of oceanic crust that was subducted beneath the nascent west coast of N. America during the Cretaceous period. Nevertheless, what we’ve documented shows that this was a continuous process that lasted almost 70 million years. And it is continuing to this day, as evidenced by volcanism within the Cascades Range of Washington, Oregon, and N. California.
Deep igneous intrusion doesn’t necessarily create volcanoes, however; surface eruptions occur when magma is emplaced at shallow depths, which was probably not the case for these rocks from the Cretaceous. We can’t know for sure because so much rock has been removed by wind, water, and glaciers during the uplift of these intrusive rocks, from tens of kilometers beneath the surface.
Even if our picture of the earth’s history in the Pacific Northwest is incomplete and mysterious, it is awe inspiring to look back in time and deep within the crust.
And it isn’t science fiction…
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?
Ecosystem Notes from Quinault Rainforest
Introduction
I’ve spent the past few months wandering the Olympic Peninsula with my attention fixed mostly on rocks—tilted beds, breccias, sea stacks, and the stories they tell about deep time. But along the way I’ve been noticing the living world with the same quiet fascination. I’m not a biologist and I don’t pretend to be; I can’t name any of the plants I pass. What I can see is how each organism plays a role in the larger system, the way geology shapes life and life responds in turn. These are simply notes from a wanderer paying closer attention.
I’ll try to remember to label these environmental posts as NOTES to avoid any confusion, especially on my part. This first post arises from a short walk on a semi-muddy trail through the Quinault Rainforest, on the Olympic Peninsula. I won’t have much to say about the photos, and all identification will come from CoPilot (aka ChatGPT). I’m certain its identifications will be better than mine after hours of searching the internet.
Quinault Rainforest in Olympic National Park
Plate 1. That raging stream about 50 feet below me is one of hundreds draining this temperate rainforest, which gets about 12 feet of rain per year. Note the ferns, which are everywhere, even in the temperate forests of northern Virginia. Ferns must be the most common plant in cooler forests. I am in a narrow strand of Olympic National Park that has never been logged. This is primordial nature, viewed by a geologist, but I’ll do my best.
Plate 2. Map of the Olympic Peninsula showing the areas I reported on in previous posts. I’m going to be focusing on Site A today, with a few photos from D.
Plate 3. I haven’t seen this anywhere else I’ve lived, not even northern Virginia, but they occur everywhere here in Washington. Apparently this is a common occurrence in rainforests, where the ground is a dangerous place for seeds. I couldn’t identify the species in this photo, but this practice is very common for hemlock.
Plate 4. This pile of debris is a large log turning into compost and supplying nutrients to a variety of plants. The top of the photo shows the base of a young tree growing out of all this chaos. According to CoPilot and the Olympic National Park map, this area has never been logged, so I am in wonder of this pile of “forest garbage”. Is that sandy soil I see? Where did it come from? I don’t know.
Plate 5. If you look close in the exact center of this photo, you’ll see daylight on the other side of the base of this unidentified tree. It’s about six-feet in diameter and covered with an epiphyte community of mosses and liverworts. Those aren’t leaves or fronds, but communities that mimic ferns–for their own reasons.
Plate 6. Here’s an example of a Western Red Cedar that has grown into a mature tree after being nursed by a stump. I guess it will eventually absorb the rotting stump and grow to full height, but this is the largest I’ve seen so far in the region.
Plate 6. This miniature ecosystem caught my eye, but I had to turn to CoPilot to get an idea of what’s going on. As a tree trunk decays it goes through five stages: 1) moss; 2) liverworts; 3) fungi; 4) shrubs; and 5) young trees. This one seems to be in stages 1-4. I didn’t see any seedlings on it. The shrub is probably huckleberry and the mushrooms a bracket fungus, probably Trametes or Stereum.
Plate 7. I am fascinated by these nurse trees after seeing species of fig trees in Australia that devour living trees, like a giant fungus or alien. These are nursing on dead trees, however, so it isn’t as gross; but this one is now standing on its own legs after the original stump has begun to collapse.
Plate 8. This is the largest Spruce tree in the world. It’s 191 feet tall and about 1000 years old. It is growing in a swampy wet land at the inflowing stream to a glacial lake, Lake Quinault.
Plate 9. I thought this was toxic waste until CoPilot took a look at the photo: this is a mass of frog eggs (probably northern red-legged frog). There were several more at the shallow, marshy wetland where a stream fed Lake Quinault. The water is so clear you can see the bottom, which is only a couple of feet down.
Kalaloch Beach in Olympic National Park
Plate 10. This one was a doozy. These objects are one-two inches long, thin, translucent, and oval in general shape. At first, CoPilot suggested insect wings (until I told it the size), then gull secondary feathers (until I said, “no way”), then settled on small fish cranial bones–e.g. the opercula, the bone that covers the gill. I asked for references, but it supplied me with titles and no links (how did it find them?). I spent longer on this photo than I wanted to. I don’t fault CoPilot for its ambiguous response because I found nothing when I looked very specifically. This phenomenon is either so common that no one bothers mentioning it, or infrequently observed that no serious beachcombers have stumbled across it. I’m going to have to agree (for now) with CoPilot that these are small bones from a school of fish that was decimated by either predation, coastal fishing, or disease and only these translucent cranial bones survived by floating, until waves concentrated them on this beach. This is the only beach where I saw them. I guess there are no easy answers to some questions–unless someone who reads this is a marine biologist.
Plate 11. I solved the mystery of the white objects on the beach (Plate 10). I spoke to an ecologist I know who suggested they are a Hydrozoa called Velella-velella, which floats on the ocean like a jellyfish. They are a colonial organism that is blown about by the wind. They don’t swim so they are easily blown onto a beach and carried by waves. (Here’s a good article about them.)
Cape Flattery
I reported on this amazing location in a previous post. You can scan that post to get an idea of where these photos were taken.
Plate 11. I don’t know if this living (it looked healthy to me) tree was stressed or not, but CoPilot thinks these are perennial bracket fungi, which favor environmentally stressed conifers. There were only a few on this tree. I noticed that this forest didn’t show nearly as many signs of decay as Quinault Rainforest, despite its exposed location.
Plate 12. I had to throw this photo in because the root growing out of the tree(s) on the left looks like a dog that got its head caught in a hole, and died there. Its limbs of limp. Overactive imagination, I know. Nevertheless, this is a bizarre image because the dog is lying on top of a mound of soil. I’d bet there was a stump there that has decayed because the trees visible in this image are both composed of multiple trunks. A large tree died here (like the dog) and these are its adopted offspring. I would add that Cape Flatters, which is part of the Makah Reservation, has never been commercially logged. This is old-growth forest and this is a naturally occurring phenomenon.
Summary
Moisture drives everything on the Olympic Peninsula, soaking old volcanic and sedimentary foundations until the forest grows straight out of its own decay. Fallen logs become elevated nurseries, their wood breaking down under fungi and mosses until they’re more sponge than tree. Hemlock, cedar, and huckleberry take root on these platforms, sending roots around stumps and into the thin soils draped over ancient bedrock. Even the beaches tell the same story: waves sorting bones, shells, and driftwood carved from headlands shaped by tectonics and storms. It’s an ecosystem built on slow collapse and constant renewal.
Acknowledgment
I am experimenting with using CoPilot (aka ChatGPT) to help as I pursue my growing interest in ecosystems. I have been up front about where it contributed. It has been a great help, as well as an inspiration; if not for CoPilot, I wouldn’t have had the time of inclination to add these ecosystem NOTES to Rocks and (no) Roads. In fact, I’m tired of this entire series of posts, for which I get no compensation other than sharing my observations of the world. As a final note, CoPilot wrote the Summary and I stand by it.
Now I have to think about more than just rocks…
Cape Flattery: Conglomerates at the End of the World
Figure 1. I ran out of road and land, ending up at Cape Flattery on the Makah Reservation. This is Location D in Fig. 2. A half-mile hike down a boardwalk took me to the end of the world, where the cliffs are about 80 feet above sea level. This photo is looking northward towards Vancouver Island, Canada, in the distance. Wave action has cut a wave terrace, a seen in the center of the image, and a series of sea caves.
Figure 2. Today’s post takes us to Site D, which is shown in a geologic map from Rock D in the inset map. The rocks are a mixture of sandstone and conglomerate of Eocene age (56-34 Ma). This is the same time that the lower Cascades were being created east of Puget Sound. Note the large number of faults (thin lines) shown in the inset map. Many of these are strike-slip faults with motion of the opposing crustal block to the left, which would explain why the sedimentary layers in seen in Fig. 1 are almost horizontal, dipping slightly towards the sea.
Figure 3. The sea stacks seen further south have been replaced with rocky islands like Tatoosh Island, which has a light house. Pacific Ocean seafloor (Juan de Fuca tectonic plate) is being actively subducted along the Washington-Oregon coast at about 2 inches/year, but the plate tectonic geometry is complex in this area. This could partly explain the large number of faults seen in Fig. 2 as well as the high elevation of bedrock. Maybe.
Figure 4. This photo was taken looking down towards the wave-terrace on the south side of the lookout point. For scale, the largest boulders are a couple of feet long, based on exposures at the surface of the trail. This is a textbook tectonic breccia. However, note that most of the rock fragments are rounded, so they have been transported some distance before reaching their final resting place. Some of the layers are relatively uniform with a few large boulders whereas others resemble the cobblestones we saw at Ruby Beach. Each bed might represent a single depositional event (like a landslide) or accumulation over years. These are marine rocks, deposited on a submarine fan, probably as turbidity flows. The process that created them is occurring now a few miles offshore, where the rocky outcrops we saw are eroding and supplying large and small fragments to a steep continental shelf.
Figure 5. This image looks like run-of-the-mill gravel like you see on pathways and drives, but it is Eocene rock, and I mean solid rock (Note the large, gray piece protruding from the cliff in Fig. 4). This angular slab is about a foot in length. There is no Pleistocene glacial till in this area, even if the ground looks the same. This is a picture frozen in time, where an angular piece of what looks like sandstone, but could be andesite, slid downslope along with smaller fragments.
Summary.
This is the last of my geology posts from a weekend excursion along a hundred-mile stretch of the Washington coast. This is a high wave-energy coast with a tidal range of about 10 feet, the beaches covered with sand and cobbles. Sea stacks protrude from the beach, culminating in cliffs made of 50 Ma conglomerates. Beneath our feet, ocean crust was being subducted at several inches per year, feeding a system of magma chambers that are actively venting through volcanoes like Mt. Saint Helens, Rainier, and Mt. Baker. Rainfall drops along this coast at up to 12 feet per year, feeding streams that carry immense quantities of sediment into the trench created by the subducting ocean crust.
Geology doesn’t get any realer than this…
Timothy R. Keen 
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