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The Mystery of Strike and Dip


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There are things that remain somewhat mysterious to me. You can read about things like strike and dip for months, years even, but they’re words. You know dip refers to something tilting down. It’s right there in the word. Strike is more vague. I usually think of it as “striking out,” perhaps for parts unknown.

And if you’d asked me to demonstrate strike and dip in the field, I would’ve laughed in your face. The whole concept has a sort of je ne sais quois to it. I can recognize the words. I know it’s measured with a compass. I had absolutely no bloody idea how to see it.

Until now. Observe. Lockwood will show you in four photos of Sunset Bay, OR he posted on Twitter and gave me his kind permission to use, with the captions taken from his tweets.

#1: Oblique view of a single bed- rocks in sand lower middle right show up in 3 & 4 as well...

#1: Oblique view of a single bed- rocks in sand lower middle right show up in 3 & 4 as well...

Now, experienced geologists and geology students will have no problem seeing what Lockwood saw. To folks like me, this is just some bent-looking rocks. And you might, like me, be too busy wrapping your head around the idea that apparently bent rocks are actually straight to even consider strike and dip.

That’s okay. Learning this shit takes time. And that’s why inveterate teachers of geology mess about drawing things on photos for you: to help you see.

 

 

#2: Annotations on #1...

#2: Annotations on #1...

POP goes the bedding plane. Okay. So we’ve got one bed in the strata to work with. Awesome! We can begin to see WTF’s going on. Remember, we can be the plywood, and see how that bedding plane has been scooped out by erosion – it’s like we’re standing inside an up-ended layer cake with a great big slice taken out of it.

As for strike and dip, we’re still at sea. But notice that the layer cake is, while raised from the horizontal, not standing straight on end. It’s leaning.

 

#3 Looking directly into strike; rocks in sand down the lower middle same as in #1...

#3 Looking directly into strike; rocks in sand down the lower middle same as in #1...

Okay, so we’re looking into the strike. What strike? Harf?

 

#4 Annotations on #3. One can easily forget how abstract concept of strike and dip can be to beginners.

#4 Annotations on #3. One can easily forget how abstract concept of strike and dip can be to beginners.

And I still can’t claim to understand it, but at least it’s beginning to pop out now. And the dip emerges with gorgeous clarity. This abstract concept is becoming something concrete. Someday, perhaps not too far in the future, I’ll be saying, “Oh, right. That is totally abstract when you’re first starting out. Forgot about that. Whoops!”

That day still isn’t here. But I found a nifty video that helped bring some of this stuff out of Abstractland into the town of Concrete (not the one in Washington), and a series of photos that showed how to measure it, and someday, when I at last have succumbed to the temptations of a smartphone, I’ll be able to somewhat intelligently, and perhaps even nonchalantly, walk up to an outcrop and begin using its nifty geologic compass app to measure strike and dip all by me lonesome. That’s one of the things I love about geology. Ordinary folk without advanced degrees can do it.

Especially when they have friends like Lockwood helping to make the abstract concrete.

Lockwood revealing the mystery of strike and dip.

Lockwood revealing the mystery of strike and dip.

Originally published at En Tequila Es Verdad.

Dana Hunter About the Author: Dana Hunter is a science blogger, SF writer, and geology addict whose home away from SciAm is En Tequila Es Verdad. Follow her on Twitter: @dhunterauthor. Follow on Twitter @dhunterauthor.

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





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