(note: this report has been edited for example purposes)
This report is on the Olympic Coast’s marine geologic rocks, coastal processes, evidence of glaciers, and large landslides. Large amounts of marine deposits have been uplifted and are now visible along the Olympic coastline. More inland around the Olympic Mountains, evidence of large glaciers and the remains of them can be seen such as Lake Quinault. Examples of these will be described in field observations as well as pictures.
Leaving the Centralia College campus, we drove north on I-5 to exit 88. We then exited onto US-12 to follow the Chehalis River downstream. After a short rest stop at Aberdeen, we continued along US-101 towards the Olympic Coast. Stop 1 brought us to a landslide along SR-107 at Montesano. Continuing along US-101, we arrived at stop 2 at Lake Quinault. Further following US-101 along the coast, we arrived at Ruby Beach for stop 3. On our way back, we took stop 4 at Beach 4. Our final stop before heading home and before stopping to get food was at Klaloch for stop 5.
The first field site is about 4 mi south of Montesano on SR 107. We proceeded up the hill towards an outlook point to view the landslide. It extended for ~100m across and was roughly 30-50 meters high. A ledge over an 8m-tall headscarp was paved with grey gravel. The geologic material was a light brown clayish rock which appeared to be weak, possibly being the cause of the landslide. The landslide obviously carved a path through the trees toward the river after passing the road due to a slanted nature of the trees. In between them was a large V-shape suitable for the mass wastage to proceed.
Lake Quinault sits along the Olympic Mountains in a large U-shaped valley. The mountains show evidence of being heavily eroded and carved by the ice during the glaciation (figure 1).
Ruby Beach is located ________. Along the beach, medium sized rocks ~.5-3 inches in diameter were plentiful whereas sand was scarce (figure 2). Large stacks are scattered throughout the beach, as well as extending into the ocean. Most of the stacks seemed fairly consistent, being a dark gray to brownish color (figure 5). Around the bottom they appeared to be eroded and smooth (figure 3), whereas the top was rough and craggy. Along the bottom of these stacks I found large mineral grains and even some veins of a clear/whitish (possibly quartz or calcite) crystalline mineral (figure 4).
Upon arrival at Beach 4, a student pointed out a whale surfacing ~150-300 meters offshore. This distracted us for awhile from the large folded sedimentary bedrock we were standing on, which was vertically layered (figure 6). The grains in this rock were obviously sediments, seemingly ranging from fine grained silt to sand, ~1/64th – 1/16th (figure 7). With closer observation, proof that these were tilted upward and beyond was shown by graded beds in these sedimentary features. Large holes, almost looking vesicular, were scattered around the rocks on most sides (figure 8). Above the beach berm, the cliffs showed even more of these bedrocks tilted upwards. About 10 meters up, there appeared to be a large deposition of sediment, and a foot or so higher than that, horizontal layers could be seen (figure 9).
After leaving Beach 4, we traveled south on US-101 towards Kalaloch. When walking along the beach, the normally visible tilted bedrock was no where to be seen. Along the cliffs were graded beds below a mass amount of soil, which must have taken a lot of time to develop. Along this beach there was much more sand than at Ruby Beach.
Our field trip to the Olympic coast cleared up a lot of hazy imagery of our local geologic history. Having not traveled there for years… I couldn’t really remember any formations or what I had seen. Viewing photos in class helps a little, however walking out on the beach and being there really brings it into perspective.
The brownish sediments and rocks seen at the landslide’s weakness did turn out to be the cause of the landslide. Having no cementation or strong enough bonds, these rocks and sediments absorbed enough moisture to cause them to create the land slide.
The U-shaped valley seen at Lake Quinault in the Olympics is a popular characteristic of glacial erosion. As the glacier sat in that valley, it deposited a moraine, which is what dammed the lake. The stacks seen at both Ruby Beach and Beach 4 were jagged towards the top because that is the way they were created, and bottom was heavily eroded from wave action.
At Beach 4, a folding process
caused rocks that were originally horizontal to be completely vertical and
slightly beyond that. The seemingly vesicular holes seen throughout the rocks
were not that. Having vesicles would suggest that these rocks are igneous,
which they weren’t. They were sedimentary rocks. Perplexed, I later found out
that small grains of sand would get caught in this bedrock and would be worked
around by the wind enough to create these large holes, which were ~1 inch in
diameter. On the cliff facing the ocean, the layers of bedrock had a large
amount of sediments deposited on top of it, with layers above that. This was a
perfect example of an unconformity. A geologic gap in time happened after the
folding of this bedrock. After pointing it upwards, sediments were deposited
on top of it and later more horizontal layers on top of that.
The bedrock, not visible at Kalaloch, was folded in the same process as the other, however at a much lower depth. Traveling south from Ruby Beach, the bedrock gets lower and lower.
(if there were any, my grade would have been higher!)
This image barely shows Lake Quinault through the overgrown trees. Beyond the lake are the Olympic Mountains.
This is the exit of the Ruby Beach path on to the beach. Shown in the center is a large sea stack.
Here is a heavily eroded
example of the stacks.
Here is a large clear/whitish vein in the lower part of one of the stacks. Lens cap for scale.
Two students sit atop a large
sea stack. The bottom has clearly been partially eroded from waves.
An avid Geology student
examines the tilted sandstone bedrock exposed at Beach 4. Note the
angular unconformity of the overlying horizontal beds.
Up close, grains can be visible in this exposed sedimentary bedrock at Beach 4. Near the bottom, there are larger grains then there are at the top, suggesting a graded bed typical of a turbidity current.
Holes can be seen scattered
throughout the bedrock are honeycomb weathering in a Seastack at Beach 4.
Ms. Avid Student is shown climbing atop the exposed overturned Miocene-age bedrock exposed at Beach 4. Seen in the center of the image is an angular unconformity separating the sedimentary bedrock and other sedimentary layers.