11 October 2018

Q&A, episode 6

Posted by Callan Bentley

It’s time for a new reader-submitted question. This is part of a periodic “you ask the questions” feature here on Mountain Beltway. Anyone can ask a question, serious or spurious, and I’ll do my best to answer it here. Use the handy Google Form to to submit your questions anonymously.

This one gets personal:

8. What impassions you about Structural Geology?

Actually, someone else asked that too, a few months back:

9. What got you interested in geology? What is your story behind your passion for geology?

My answer to these questions comes now as we head toward Earth Science Week next week, an annual celebration of geoscience, facilitated by the American Geosciences Institute (AGI). This year’s theme is “the Earth as inspiration,” and I think that’s my short answer to the questions above. I think geology in general, and structural geology in particular, is inspiring.

The thing that I think first drew me into structure was the beauty of patterns.

I’ll show you what I mean, using the most general of terms: chunks, bumps, lines – before I had jargon to apply to these facts of nature, I could at least appreciate their shapes and colors…

For instance, a high-contrast pattern like this: Why are there dark chunks in light colored stuff? Why do they have those shapes?

What does that pattern mean? What does it have in common with the one we see here?

Or here’s another one, with cool colors in addition to chunks of different shapes:

Why are the chunks we sometimes see more rounded and internally massive, while others show precise internal geometries that parallel their overall shape?

Or let’s consider this gradational pattern, light to dark: What is the light-colored stuff telling us? What is the meaning of the dark stuff? Why does the light transfer crisply and utterly to dark in some places, but then they smoothly fade into one another at other transitions? …

Here is another example of that same pattern, but now the direction of the grading is reversed. We can make the observation, and we can ask “Why?”…

Or what about lines? I’ve seen some cool looking lines out there…

Sometimes lines are lines in their own right (as in the two examples above), and other times they are the intersections of planes with the face of the outcrop, as here:

Some of those planes I learned to call “beds.” Others I soon came to name as “fractures.”

The fractures appeared to have gotten soaked with stain-inducing fluids sometimes:

These stains could be quite beautiful in their own right, even once liberated from their in situ positions that spoke about the power of those fractures to conduct fluid flow:

And rusty water isn’t the only fluid that can flow through a rocky crack: sometimes a seam of totally different rock can be found there, igneous rock in a tabular mass we call a dike. Where these students in this photo now hike, was once a deep injection of thousand-degree molten rock:

Sometimes these can even cross one another, and an order of cracking, and magma injection, can be discerned:

Photo by Victor Zabielski

That is a pattern! “… X marks the spot.”

Sometimes color could draw me in. Here are a few examples, in red and green:

And what about lumps and bumps? Here are some that are more or less tongue shaped:

Here are some that are squiggly:

And here are some that appear to be circles on one view …

But viewed from a different angle, they appear to be cylinders or tubes:

These patterns that entranced me had three dimensional form; they called me in to examine them from more than one angle, to crane my neck, pull out my hand lens, crawl into caves, climb cliffs. A single glance doesn’t show the whole story, I learned.

Speaking of things that look different in different manifestations: What about this pattern, these “scalloped edges?”

The more these patterns drew me in, the more I learned about their cause, and what linked them to other varieties, like these:

Photo by Bob L’Hommedieu

All in all, my point of entry into geoscience, and one of my sustaining sources of inspiration, is this wealth of cool-looking patterns in the natural world. I could cite hundreds of other neat outcrops, beautiful hand samples, or patterns glimpsed only through a microscope, or through satellite imagery, or through LiDAR – but these photos I have shown will suffice for now. My deepest wellspring of inspiration is these observations with their distinctive geometries, textures, colors. And unlike clouds shaped like bunnies, or Rorshach blots, or grilled cheese sandwiches that show the form of the Virgin Mary, these are patterns which can be decoded – they are patterns that carry meaning. They are not fodder for pareidolia, “random noise” upon which our brain extracts a pattern that only exists in our own minds. These are the record of processes, events – actions that have transpired in the past of our planet. If you collect these patterns, and tally them up, and keep track of how they relate to one another, you can tease out a story, the story of a planet through time.

Our planet writes its autobiography in (jargon alert!) breccias and dikes, conchoidal fractures, porphryoblasts and trace fossils, flute casts and megacrysts and graded beds and slickensides, hackle fringes, amygdules and Liesegang bands. Though those words may seem alienating to the neophyte, you’ve just looked at a dozen photos of them. They are the record of the Earth’s past. They are the language that Earth uses to communicate her story; when we learn the meaning of these messages, they entice us to learn more about our home world.

What do you find inspiring about this planet? Or the science which helps us understand it better? Share your inspirations in the comments below.

If you have other questions you would like me to answer about science, the Earth system, or anything else, please ask them.