Kinney Point

Kinney Point is the southern tip of Marrowstone Island and is actually a Washington State Park. It has no upland access, but it does host a Washington Water Trails campsite.  On my long walk around the south end of the island, this was the final turn before the home stretch back to the car.

Kinney Point is a double point, with a little notch in between.  As with so much of this end of the island, most of the upper bluff is glacial drift, but the bottom few feet is older sedimentary rock. I think the shape of the point reflects a change in the resistance of the toe to wave action.  A layer of sandstone anchors the eastern bump of the point, but it dips to the west and vanishes below beach level, exposing what appears to be a more erodible, finer grained unit (mudstone?) on the western bump.  At the same time, the amount of water seeping out over this unit increases significantly in the same direction and maybe that also affects erosion patterns.

Google Maps:  AERIAL VIEW
Ecology Coastal Atlas:  2006 AERIAL PHOTO

On the western side of the point, both the till and the older rocks seem pretty messed up, and my gut told me they were suggesting a more complicated story than the previous several miles of fairly predictable layer cake geology.

There are plenty of things that influence the shape of the coastline.  Around here, the primary factor is the basic form it inherited from the glacier.  But wave action, the resistance of the shoreline to erosion, and the width/height of the beach (which buffers the effect of wave action), are all important in controlling relative erosion rates and therefore the evolution of the shoreline. Here on the south end of Marrowstone, the overall shape reflects its glacial origins, but it seems like the geology of the bluff toe (largely influenced by the presence and type of harder pre-glacial sediments) is an important factor in some of the secondary bumps and wiggles.

Heading back northwest, the beach changes dramatically.  The bluff vanishes entirely at the campsite and there is even peat and wood exposed on the beach, probably the abandoned relic of the marshy swale still seen at the modern shoreline. Continuing north, the beach grows to become a barrier beach that extends 500 meters along the shoreline before reconnecting with the bluffs downdrift.

Google Maps:  AERIAL VIEW
Ecology Coastal Atlas:  2006 AERIAL PHOTO

Posted by Unknown

Tweet