Sunday, March 18, 2012

Cama Beach

I went back to Cama Beach Saturday morning to see how the landslide was evolving.  It's hard to tell how much new material is being added from the headwall, although small chunks kept falling during my visit.  The debris in the gully has continued moving on down to the beach, with new trees and large blocks of till perched on top.


The landslide itself is interesting enough - but I think I am most curious about how the beach responds to the slide.  The debris cone at the base projects out onto the beach, acting like a groin, and has resulted in the accumulation of a small wedge of beach up against the southern side of the landslide debris.  Some of this new material may be beach sediment from the south, while some is derived directly from the eroding toe of the slide.  Most wave action here comes from the south.  While I was on site today, a gentle northerly breeze gradually gave rise to stronger southerly waves over a period of several hours.

Fine grained sediment is being winnowed from the toe of the slide during high tides and moved way in suspension - there is turbid water along the water's edge and extending in a plume offshore.  What is less clear is how the coarser fraction - sand and gravel - is moving.  We'll watch this, qualitatively at least, over the next weeks and months to see if it leads any noticeable change in beach profiles or sediment texture in the vicinity.

The headwall of the slide remains scary, with the loud thump of falling blocks of till reminding me to stay back from the edge.  Too much is still moving and there are some significant overhangs.

I've posted more photos of the landslide at:
Photos:  March 7th
Photos:  March 17th

It was raining when I left Seattle shortly after 7:00.  It was slushing in Marysville.  But it stopped by the time I got to Cama.  And then the sun gradually worked its way out from behind the clouds. I posted some less geologic pictures at hshipman, for those less interested in landslides and dirt and more interested in new places to enjoy coffee and scones while overlooking the beach.

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