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East Coast vs. West Coast

September 29, 2010

This past weekend I went to the Jersey shore (not the regrettable tattoo and binge drinking part).  Looking at maps of the coastline there and all the way down the eastern seaboard, down to Florida, made me think about the differences between the East Coast and the West Coast. Not just the good summer tomatoes vs. readily available avocados part, or hurricanes and nor’easters vs. earthquakes, or Minor Threat vs. Black Flag. But the shoreline itself. Why do the East Coast and the Southeast have barrier islands?

The Georgia coast:

And the West Coast doesn’t?

Southern California:

I don’t know.

Not that it’s surprising that they look different. They’re really far away from each other.

As big as California’s shoreline is, there are a lot of rocks just off the coast, but not that many islands. (Geologists, please forgive me for being really really basic here. If I get anything wrong, or you want to explain in more detail, please have at it!) California’s eight Channel Islands in Southern California were formed by tectonic forces, volcanic activity, and sedimentary deposits. The four northern Channel Islands are like the top of a mountain ridge sticking out of the ocean. They were never attached to the mainland.

Anacapa Island, one of the Channel Islands

Ano Nuevo Island between Santa Cruz and Half Moon Bay was the tip of a peninsula until relatively recently; Spanish explorers did not record it as an island when they were here. The Farallones, off of San Francisco, are made of the same magma as the Sierra Nevada. And the islands in the San Francisco Bay are hilltops that remained above water level after the mouth of the Sacramento and San Joaquin Rivers was flooded.

Back to Georgia (courtesy of NOAA).

The barrier islands on the Atlantic, at least the ones on the Georgia coast, which are the ones I’ve been reading about (and the ones I grew up visiting) are remnants from a much lower sea level. As the sea rose, it inundated low-lying land behind the islands, creating salt marshes and the intercoastal waterway.

Sapelo Island. By Flickr user http://www.flickr.com/photos/k1000/

Also, one last thing, because I mentioned New Jersey and growing up: ECFU (in case you are in an office without headphones or you are 12, this video has language that we would not use in public radio).

The Natural History of the Islands of California
was helpful for half of this post. The Georgia stuff I scrounged up online.

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5 Comments leave one →
  1. September 30, 2010 1:21 pm

    This is off the top of my head, but the things I think about regarding your question include:

    (1) The significant difference between the style of continental margin on east vs. west coast. If you look at GoogleEarth and zoom out a bit note the width of the continental shelf. As you go offshore at some point the seafloor drops off very steeply into much deeper water. The edge of the continental shelf on the west coast varies quite a bit but, in general, is much closer to the shoreline as compared to the east coast. Additionally, the slope of the continental shelf along the west coast is steeper. As you noted, the rocky coastline of California is a testament to this different style of regional topography.

    This physiography has an effect on the shoreline sedimentary systems. Very large barrier island systems cannot develop because of the highly variable topography. We do have some systems like that but they are quite small and develop only at the mouths of rivers.

    (2) The climatic/oceanographic condition. Admittedly, I know less about this, but I’d guess the strong seasonality of summer beach construction vs. winter beach destruction has a big effect on where/when the sediment that would build a barrier island system gets redistributed.
    hope that helps

    • mollysamuel permalink
      September 30, 2010 2:35 pm

      Thanks, I was hoping you might weigh in. I thought the shape and location of the continental shelf could be related. And regarding the climate angle, I wonder if it’s simply good luck that there are barrier islands in places susceptible to hurricanes, or if there’s a a connection.

  2. tom a-m permalink
    October 13, 2010 8:19 pm

    Three things:
    1. The West Coast get more porous as you go north into its BC and Alaskan parts. How is that?

    2. More important, public radio-unfriendly commentary on this topic: GBTC. Are there Canadian pop songs that play east against west, I wonder.

    3. You got another shout out in the Editor’s Note of the current issue of High Country News (Oct. 11). Here’s the video:
    http://flipnote.hatena.com/js/flipplayer_s.swf

  3. tom a-m permalink
    October 13, 2010 8:26 pm

    I’ll never learn my H-T-M-Ls. For that last bit, try this: PG.

  4. mollysamuel permalink
    October 14, 2010 9:47 am

    Hi Tom! I nominate you to find the answer to the question of a Canadian rivalry. Nova Scotia vs. Vancouver Island?

    I am completely baffled by that video. Thanks.

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