Thursday, September 30, 2010

Mmmm, Basalt

Politics has been a thoroughly depressing subject of late. Here are some pictures of some rocks...

These are pictures of some bits of columnar basalt surrounded by breccia basalt that I saw while at Cape Perpetua a couple of weeks ago. This first one shows the contrast pretty nicely:
Image credit: All photos by Cujo359
[click on the images to enlarge]

Believe it or not, that's all the same basic kind of rock, made out of the same basic materials. The only difference is that the columnar basalt, the stuff that's more obviously crystallized, cooled more slowly than the breccia that surrounds it.

As Lockwood DeWitt, who was our geological spirit guide on this journey, put it yesterday:
Others have also pointed out that columns are not necessarily "columns," i.e. up and down. Here are some horizonal columns in a basaltic dike cutting through basaltic breccia. Again, the consistent theme is that the fractures form perpendicular to the surface of cooling. This was from Cape Perpetua[.]

Columns: Variations on a Meme
[I added that embedded link to the picture Lockwood is referring to in the text.]

Here's a picture of more columnar basalt from that beach, which shows a little better how differently the two types of rock have weathered:

[I should note that both of these pictures are panoramas stitched together from two or more pictures. If you notice a discontinuity that doesn't make sense, it's possible that's the reason.]

This stuff was all over the place at Cape Perpetua. At first, I assumed that the rocks with the different colors and structures must be layers of different kinds of rocks. My companions set me straight on this, and I soon noted that these dikes were everywhere, going in many different directions, so it was most unlikely they were different layers of rock. But then, as I've mentioned before, I'm not a geologist.

I don't feel bad. There were more than a few times when Lockwood and Dana, my traveling companions who are both enthusiastic rock hounds, weren't sure what the heck they were looking at.

One of the things that amazes me about such geology is how much small differences in the rate of cooling can affect the appearance and the properties of rocks. I took physics and materials science courses in college, yet the more I learn about geology the more I'm reminded that understanding how something happened is often a matter of figuring out which physical and chemical processes are the predominate ones in a situation.

This is something I've written in the past regarding various 9/11 conspiracy theories. You can be very knowledgeable about basic physical sciences, and yet look at a pile of rocks or a pile of broken construction materials and still have no idea what it all means. There's considerable context to learn before assuming that there's no other rational explanation to what you're looking at than the first one that pops into your head.

Thanks to Lockwood and Dana Hunter for trying to educate me about this stuff. It may not have looked it, but every once in a while that effort had an effect.


karen marie said...

Great rocks. I love rocks. I'm not a geologist, and you couldn't even consider me a rock hound, I just love rocks.

Especially ringed rocks. I have a nice little collection, though I have culled out the larger ones as the moving men tend to complain about 200 pound boxes of rocks.

Cujo359 said...

I have so much junk already that I doubt I could find room for 200 lbs. of rocks. Still, a few on desks and mantelpieces can make a place more interesting, no?

Dana Hunter said...

Yup. It's happening. We're turning him into a geologist. ;-)

I'm glad you got something out of this trip. I was afraid Lockwood and I were boring you to tears.

Karen Marie, I think after you've hit 100lbs of rocks, you're dabbling your toes in rock hound territory. Not that any of us are hardcore - f'r instance, I've yet to start doing the gem trails looking for perfect mineral specimens. Having too much fun with ordinary rocks at the moment.

Can't wait to see the looks on the boys' faces when next I move. They already groan over the hundreds and hundreds of books... hee. Hey, that's what we pay 'em the big bucks for, tho.

Cujo, darling, believe me - I could find room in your place to insert a few hundred pounds' worth o' rocks. You just let me know if it comes to that!

Expat said...!

much easier than trying to stand on water.