Saturday, August 11, 2018

The Disappointing Cape: Land's End and Rock Pillows



Just over 200 years ago, the first expedition of Americans reached the Pacific Ocean after following the Missouri River over the Rocky Mountains and down the Columbia River. Lewis and Clark and their crew arrived in November of 1805, and they knew they could not make the return trip until the winter snows abated.

They explored the area around the mouth of the Columbia for an decent campsite to stay in several months. They ultimately settled on the south side of the river at Fort Clatsop, but for a time they spent a week at "that dismal little nitch" on the north side of the river. They explored around the rocky peninsula that had already been given the name Cape Disappointment by fur trader John Meares who, because of a storm, turned his ship around in 1788, just missing the mouth of the Columbia. The credited discovery was four years later, although we know that history has a serious bias; the river was discovered more than 10,000 years ago by humans.

The peninsula is today a state park, and it has a well-developed campground complex that fronts a wide sandy beach, with a more modest sandy cove on the east side called Waikiki Beach (it memorializes a Hawaiian seaman who perished during a shipwreck).

The winter encampment of the Lewis and Clark expedition at Fort Clatsop was largely a miserable affair with constant hunger and lack of supplies. They had hoped to flag down a sailing ship coming down the coast to trade for supplies, but their fort was a couple of miles from the beach and they missed ships for lack of a good lookout point. One might wonder why they didn't set up camp on the wide sandy beaches of Cape Disappointment. The answer is pretty straightforward: the beach didn't exist when they were there. It was a rocky peninsula as can be seen on their sketched map (below)

The mouth of the Columbia River is a nightmare for shipping. The discharge is more than enough to support even large freighters as far upstream as Portland, but the river carries vast amounts of sand and silt, and the shifting bars have caused vast numbers of shipwrecks. In an effort to stabilize the shifting sand bars, jetties were constructed in 1886. One extends for several miles from Cape Disappointment. Although the rock wall helps to keep the river channel clear, it also serves as a barrier to the southward movement of sand along the coast north of the Cape. The sand started backing up immediately forming the wide flat beaches that can be explored today (see the map below...sand is the yellow unit marked "Qb").
Source: US Geological Survey and https://nwgeology.wordpress.com/the-fieldtrips/pillow-lava-sites-in-washington/pillows-in-the-crescent-formation-cape-disappointment-state-park/

One of the coolest things about exploring Cape Disappointment is the privilege to actually see the rocks. The wave-carved cliffs are not totally covered by vegetation as is so often the case in western Washington. And the rocks are weird. They are not layered, and instead are marked by strange globular masses of what turns out to be weathered and oxidized orange basalt (we would normally expect basalt to be black like the lava flows in Hawaii). How did they get this way?
Note the cormorant for scale (upper left)
When basalt erupts underwater, it forms these globs that are about the size of thick down pillows. It looks like toothpaste being squeezed out and then getting pinched off. Although these rocks are on land today, they were once on the bottom of the Pacific Ocean. They formed in eruptions at the mid-ocean ridge on the seafloor. They traveled like a conveyor belt for hundreds of miles (at the stunning rate of several inches a year) and were scraped off and added to the edge of the continent in the subduction zone that forms the western boundary of the North American Plate in Washington and Oregon. These rocks, the Crescent Formation, are Eocene in age (around 40 million years ago).

Cape Disappointment is a fascinating place to explore (it's neither dismal or disappointing). Watch the weather, though. Not only for the incessant rain, but for fog. It's said to be the foggiest place in the country which helps explain why the peninsula has not one, but two lighthouses.