Yesterday, I suggested that perhaps a reason for Cape Blanco's prominence out into the ocean was a tough armoring of gravel from a former stream drainage. That may play a minor role, but I doubt it's of any real importance, for three reasons. First, the terrace deposits are only partially consolidated- I wouldn't describe them as "lithified" by any stretch of the imagination. Second, erosion of the terrace surface is inconsequential in terms of the overall erosion and diminishing of Cape Blanco; wave erosion at sea level is pretty obviously the overwhelming agent in that process. Third, that
Otter Point greywacke- which is incredibly indurated and tough for a clastic rock (it
has been somewhat metamorphosed) is what's actually taking the brunt of the pounding by the surf. As you can see in the photo, the terrace deposits only extend down about a third of the way to the shore. They're consolidated enough to hold a significant slope, but they wouldn't stand up to the surf at all. Despite my off-the-wall
conjecture after noticing the
imbrication of the gravel in these deposits, I think it's unlikely the resistance to erosion by the coarse material makes much difference to the prominence of Cape Blanco.
Photo unmodified. May 7, 2013.
FlashEarth location.
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