Wednesday, October 22, 2014

Geo 730: October 22, Day 660: Punchbowl Strata

All three major components of the stratigraphy at Devils Punchbowl are visible here: the Astoria Formation forms the bedrock of the punchbowl itself. Contemporaneous Columbia River Basalt forms Otter Rock, offshore, as well as the headland on the far right horizon. Finally, flat-lying, probably Pleistocene, terrace sands have created the eroding bluff along the right and bottom edges. The role of plant cover in assisting the latter unit maintain some degree of coherence is evident in the grassy slabs slowly sliding down the slope toward the maw of the punchbowl in the right middle. Where the sands are exposed, they erode quickly. However, the lush vegetation (naturally, not grass, but salal, ferns, and other low shrubs) is very effective at protecting it except along the edges of the eroding coastal cliffs.

Photo unmodified. July 15, 2014. FlashEarth Location.

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