The weather today was great overcast all day, best weather for hiking for my perspective. I took a bus to Discovery Park, trying to find out the South Cliff in this park. I heard from our professor that there would be evidence of glaciation on that cliff. Specifically, there are different layers of sediments showing that glacier was there long time ago.
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| Figure 2, a closer view of the Olympia Formation, Lawton Clay, and a little bit of Esperance Sand |
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| Figure 3, my sketching of the bluff |
As I went closer to the bluff, everything seemed more clear to me. From the bottom up, I could see the Olympia formation, Lawton Clay, and a tiny bit of Esperance Sand that I could barely see. You might be wondering where the Vashon Till layer is. However, Vashon Till layer is not in this bluff. According to the USGS Seattle Soils Map, there is only a tiny piece of Vashon till in the southern park of Discovery Park and there is basically no till on this bluff at all. As for sand layer, it was also hard for me to see. After talking to my professor, I learned that I would've seen it if I had been to the top of this bluff. Maybe sometimes I will go there again and observe the sand layer.
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| Figure 4, the Olympia formation |
My favorite layer among these four is the Olympia formation. Just looking at its streaks, how gorgeous it is! This layer was formed even before the Vashon ice sheet came 14,000 years ago. It was made up of mostly clay. Those parallel streaks were the evidence of moving water. So, it was supposed to be a lake or something that was running by the Olympia formation before the Vashon ice sheet came into Puget Trough. In class, my professor told us the lake was called Lake Russell. Thanks to Lake Russell, such pretty formation like the Olympia formation was created. Lake Russell was the lake before the Vashon ice sheet came while Lake Bretz was the one after the Vashon ice sheet was gone.
Since clay is the smallest particle among sand, gravel, silt, and clay, it can be carried by slow moving water for the longest distance. That also explains why I could only see Esperance sand at the top of the bluff. Since sand particles are bigger than clay particles, they can't be carried by slow-moving streams. So, they end up being on higher position than clay is. In Discovery Park, Lawton Clay is the layer right above the Olympia formation. However, there is a bad news about clay layer. Because clay is impermeable to water, when it gets wet, it could become really slippery. Figure 3 could be an example of clay falling down during landslide. Seattleites should be aware of this potential danger, not building any houses at the top of clay layers or sand layers. One of the causes for Oso disaster is actually the impermeability of clay. If we had paid attention to those layers beneath our houses, the disaster could have been avoided.
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| Figure 6, a closer view of clay |
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| Figure 7, some blackberries are able to grow |
I noticed that some plants were growing on the bluff. For example, as shown in Figure 7, harsh-environmental-adapted Himalayan blackberries are growing out of those falling clay. In fact, not only can Himalayan blackberries grow here, but some other species are also able to survive here (I found some horsetails growing there too). However, I couldn't identify most of them by using my field guide.
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| Figure 8, newly-grown red alder in the restoration project site |
On my way back, I found a restoration project called Capehart Forest Restoration Project. It had already torn down a tract of military housing and was planting native plant species such as Douglas fir, lodgepole, red alder and so on. I'm happy to see that people are caring about the environment and trying to make it better.
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