Monday, March 25, 2013

Chambers Bay

I think this beach is where I'll bring the class in May, since it's close to the classroom (which looks down on it from the top of the hill) and because it's a beach that looks like it can tell some interesting stories.  The challenge will be finding geologic stories that are relevant to other Puget Sound shorelines, not just stories unique to this strange anthropogenic coastline.

Just like Richmond Beach in the previous post, this site began as a late glacial delta, become a gravel pit (a very large one), and has ended up a park.

Previous post from here:  Pioneer:  October, 2010
Post from the active mine at Dupont, south of here:  Sequalitchew Delta, October 2011


A high bluff once rose steeply from this beach.  The beach itself probably ran in a fairly straight line, interrupted only by occasional clusters of large logs and downed trees.  The bluffs receded rapidly when the mining began and now they now lie 1000 meters to the east.

Beaches are active and often very young geologic landscapes.  The wave environment at this one probably hasn't changed much in the last 150 years, but much else has, and the beach has responded accordingly.  Resistant headlands have been imposed in the form of concrete structures, pier abutments, and coarse cobble lags leftover from loading operations, and these have altered the configuration of the beach. The original bluff sediment sources have been replaced by the beach itself, as one part erodes to supply another.  Transport patterns have changed to reflect the beach's new shape and the shifting sediment sources.

It's a wonderful beach, but also a very different one than the one that had gradually transgressed into the forested bluffs for thousands of years.  It tells some neat stories, but the most obvious have to do with its human history.

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