The photo above, which was taken from the deck of the house we rented just north of Yachats, shows a large area of beach containing sandstone formations. From the deck, they don’t really look that interesting, but a closer inspection reveals a number of fascinating formations, as shown in the photos at right.

The structures vary in size and shape. In some areas, the water has carved intricate maze-like patterns, while in other areas, the formations are more ribbon-like, gently rising out of the soft sand. And, as the last photo shows, some have even taken on a mushroom shape.

Curious about how these structures came to be, I approached my good friend Tim, who is, among other things, a geologist. And while he doesn’t often update his own blog (zing!), he was kind enough to help me out with this post.

Upon hearing that I had some photos for him to look at, he did what any self-respecting geologist would do: He asked me if I’d included an object for scale in the photos. You know — a coin, or, say, a pickaxe?

And while my answer was, of course, “No” — what can I say? I left the pickaxe at home during this vacation! — he was kind enough to examine the photos anyway. I asked him to offer his best guess at how these structures came to be:

These appear to be sandstone. The history of which is most likely:

Sand is deposited by waves and or dunes. Over time, more and more sand is deposited on top as the beach builds out into the ocean. Due to the pressure of the overlying sediments and minerals deposited by groundwater percolating through the sand, the grains adhere to one another and form sandstone.

When the beach goes through a period of erosion, this sandstone is exposed and the action of the waves weather it (break it apart) and erode it (carry it away). Different layers of the sandstone are more or less resistant to weathering due to their make up (different grain size, different sand composition, different amounts and types of minerals that hold the grain together). So in some places the lower layers are less resistant to the elements and you end up with odd shapes. Notice how the layers with red color, indicating iron rich deposits by groundwater, tend to be more resistant than those without.

Tim’s comments are particularly interesting since they jibe with recent events on the Oregon Coast. First, take a look at the satellite photo at left. It shows the house we stayed in and the beach where these structures can be found. Notice the size and composition of the beach. Now, compare that with the first photo in this post (which was taken closer to low tide than high tide). The beach appears to have gone through a radical transformation. First, the sandstone formations are nowhere to be seen in the satellite photo. And second, the beach was much wider when the satellite photo was taken. Both observations probably indicate that a lot of sand was recently washed away.

In fact, up and down the Oregon Coast, storms from the winter of 2007 caused massive erosion and exposed all kinds of interesting things, including shipwrecks, cannons, stumps, and even stone formations similar to the ones we saw in Yachats.

These formations certainly added an element of interest to the time we spent exploring the beach. But unfortunately, the beach is now so narrow at that location that for multiple hours around high tide, it basically becomes impassable. In addition, significant bank erosion also appears to be happening in this area. As beautiful and dramatic as the area is, it certainly makes me glad I am not a homeowner there!

(More information on the cannons recovered on the beach near Arch Cape is available from the Oregon Parks and Recreation Department. Additional information about the shipwreck of the George L. Olson can be found on here and on the Bureau of Land Management website.)

Here are links to each of the posts in this series: Oregon Coast Trip, Coastal Scenery, Yaquina Head Lighthouse, Sandstone Formations, Oregon Coast Aquarium, Evan & Erin, and Sunsets.

This entry was posted by Steve on Tuesday, April 15th, 2008 at 10:13 pm and is filed under Local/Regional, Photo, Travel. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.