Monday, April 28, 2014

Point Defiance

While Owen Beach was broad and stable and seemed well stocked with sediment, the situation changes as you walk north toward Point Defiance itself.  Much of this stretch consists of relatively high sandy bluffs, eroding over the top of clay layers exposed at beach level.  There's tilting to the beds, and some faulting, suggesting more structural activity than we typically see on Puget Sound bluffs. And as you approach the point the beach thins and there are dramatic ledges of older, more resistant materials outcropping at low tide. This stretch really deserves a post of its own, but this entry is actually about something else. 


The best part is on the western side of the tip of Point Defiance, where a dramatic divot has been taken out of the beach. The beach simply vanishes -- dropping off into the head of a deep submarine ravine. Locals said that it had cut back significantly just this past winter. There wasn't much room to get around and there was something pretty spooky about this spot. I'd love to see some high resolution bathymetry of this place.

Rounding the point and heading back south along the Tacoma Narrows, the beach changes completely.  There really isn't much beach on this side -- a combination, I suspect, of the steep topography/bathymetry and the strong tidal currents that probably carry most loose sediment off into deep water pretty rapidly.

Point Defiance is a distinctive feature in the geography of Puget Sound - something pretty special is going on here, most likely related to the underlying geology and its subsequent influence over glacial drainage patterns.

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