The geology of the Olympic coastline

Ruby Beach in Olympic fascinates with its impressive sea stacks and sand patterns in the back light of the sunset. The Pacific coastline in Washington is a tectonically very active region and is repeatedly struck by severe earthquakes and tsunamis. The reason for this is that deep-sea sediments are welded against the continent, while the ocean plate sinks below the continent.
Basalt is a dense and therefore heavy volcanic rock. The sea floor is composed of basalt in the form of pillow lavas. During the sea floor spreading process, the ocean plates grow older and hence accumulate thick layers of comparably lightweight sediments. The Juan de Fuca ocean plate subducts under the North American continent, which is relatively young being about 10 million years in age. The lightweight deep-sea sediments get scraped off the heavy volcanic ocean floor during the subduction process. This causes the sediments to steeply tilt into a tectonic mélange, called flysch, that is attached to seaward growing continent. Former deep sea ocean sediments become land in a geological process called accretion. This explains why the coastline of the Olympic peninsula exhibits the youngest rocks that are only 20 million years of age. The surf already erodes these former deep sea sediments that are now the headlands into sea stacks.