Ingalls Weather on Nostr: Basalt is the main bedrock of much of the Pacific Northwest, owing to the massive ...

Basalt is the main bedrock of much of the Pacific Northwest, owing to the massive Columbia River basalt flows over ten million years ago. This flood basalt province erupted from numerous vents in Eastern Washington, Eastern Oregon, and far Western Idaho with the largest eruptions flowing out to the Pacific Ocean.

Columbia River basalt underlies the Columbia Basin and the Columbia River’s path from there to where it meets the Pacific Ocean near Astoria. We can use it to see where the river used to flow, such as Crown Point near Troutdale and Tillamook Head north of Cannon Beach.

Basalt outcrops downstream of the Columbia Basin represent the old path of the river because the basalt would have flowed in the low point of existing valleys, shoving the Columbia River aside. These outcrops remain because basalt takes a long time to erode compared to other formations.

The Ginkgo Flow (orange) superimposed over other Columbia River Basalt Group flows (brown). The black line in Eastern Washington is where the Ginkgo Flow erupted from. (CWU)One interesting location with a basalt outcrop is Yaquina Head north of Newport on the Oregon Coast. This is where the Ginkgo Flow of the Columbia River Basalt Group reached the ocean. It is well south of other points where Columbia River basalt meets the Pacific.

The Ginkgo Flow erupted from a series of vents extending northwest and southeast from near Kahlotus, Washington. Evidently a low valley crossed the Coast Range east of here allowing the basalt to pass through.

Yaquina Head is the site of one of Oregon’s lighthouses. At the base of the outcrop are numerous tide pools. Basalt outcrops into the ocean often feature tide pools because of the rock’s resistance to erosion, allowing rocky shores to be exposed rather than wearing down into sand.

Basalt cobbles at Yaquina Head. (Personal photo)Between the tide pools and the base of the cliffs is a beach covered in basalt cobbles. These have been knocked off the cliff over time and then rolled around against other rocks by the water to become rounded and polished.

Yaquina Head is one of the more interesting geologic features of the Oregon Coast. It is accessible by car, though visiting the tide pools involves walking down (and back up) a long staircase. It is operated by the Bureau of Land Management and there is an interpretive center on site.

https://ingallswx.com/2024/09/07/eastern-washington-basalt-on-the-oregon-coast/

#Geology #Oregon