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Rosetta Stones

Rosetta Stones

Adventures in the good science of rock-breaking.

Friday Photos: Whidbey Island Erosion

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Whidbey Island, Washington is a fantastic place to see glacial deposits while you enjoy some seascapes.

Bluff at Penn Cove, Monroe Landing, on Whidbey Island. The bluff is chock full of glacial deposits. The beach is a delightful jumble of rocks, mud flats, and sand, where you can break up your geological investigations by amusing yourself with little crabs, clams, and if you're very lucky, a live shrimp.

You can also see excellent evidence of why it's not a good idea to build on a bluff. We didn't actually mean to see those. My intrepid companion and I meant to go see a fine example of a clastic dike. I should have remembered lessons learned from Doctor Who: "Turn Left." If I had, we'd have ended up at Blowers Bluff as intended. But, like Donna, we turned right, and will have to get it right (left?) on a second go.

No matter. It turned out to be a happy little accident. There's enough in the bluff that is not Blowers Bluff to keep a person interested in both geology and sea critters happy for hours. And it has some textbook examples of erosion.

Root ball in eroding bluff. This tree is going to find itself slip-siding down onto the beach, if it hasn't already.

These glacial sediments are quite firm, even hard, but they're more like dried mud than rocks: classic unconsolidated sediments, which haven't had the opportunity to turn to stone just yet. And between the waves from Puget Sound and the gargantuan amounts of rain we get here in the winter, they have a habit of eroding rapidly.

Erosion. You can see in this photo that parts of the bluff are well on their way to becoming beach, and it looks like there's some slumping going on to the right. Chunks of the bluff are sloughing off.

This is why Scenic Heights Road is endeavoring to become Scenic Lows Road.

Erosion undermining the road.

There were moments photographing this bluff when I questioned the wisdom of standing beneath it. This closeup of the eroded bit of road should explain why:

Closeup of erosion undermining the road.

The US Geological Survey estimates that 51% of Island County's shorelines are unstable (pdf). All around Puget Sound, you can see signs of mass wasting. Waves make the bluffs too steep, while soaking rains cause the compacted sediments to lose cohesion, leading to landslides and debris flows. It can get rather exciting round here in the winter.

Before I began my geological adventures, I used to think I'd like a nice house on the seashore, probably perched up high with a view of the ocean. These days, I'm content living inland. Don't get me wrong: I liked The Little Mermaid, but I'd rather not have "Under the Sea" stuck in my head because that's where my house landed.

 

References:

Tucker, Dave (2010): "Blowers Bluff, Whidbey Island." Northwest Geology Field Trips.

Crucher, Suzanne (2008): "Determination of Shoreline Erosion Rates of Double Bluff." University of Washington Earth & Space Sciences.

Shipman, Hugh (2004): "Coastal Bluffs and Sea Cliffs on Puget Sound, Washington." U.S. Geological Survey Professional Paper 1693.

The views expressed are those of the author and are not necessarily those of Scientific American.

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