Monday, June 6, 2011

accretionary wedge - varves

Accretionary Wedge #35 is up at Georneys - the question is, what's your favorite Geology word?

I thought of a bunch of stupid ones right off the bat - the kind that ends up on t-shirts, like "gneiss schist" or "gneiss cleavage". And then the ones that just sound funny, like 'a'a.

But I wanted to pick a term that's cool and actually relevant to something I do. So my favorite geology word is varve. "Varve" sounds funny to my ear, because they only come in multiples.

Varves are very, very fine bands of sediment that usually represent seasonal variations in deposition in still water bodies that ice over in winter. In the warm months, sediment can fall down normally, leaving light colored, wider bands. Once the lake freezes over, nothing can enter the water and the very fine sediment is allowed to slowly filter down, leaving a dark layer. Cores can represent thousands of years.

Why Varves? Well, I don't work in an area of the world with terribly exciting geology. I'm dealing with contamination and dirt. I don't get to work in places with cool morphology because the geology is generally buried. But varves are cool because they're formed in quiet lakes - the perfect quiet location to hang out and just be. And they're just about the coolest non-anthropogenic material that I run into on a regular basis.

Varves are a lot cooler in person - the bands of color are generally so fine, they're hard to see. My examples didn't photograph well. So here's one from a paper...



And here's another - somewhat local!

1 comment:

reynardo said...

So the more water {with sediment} that comes in, the thicker the carves? I take it that means 3874 was one hell of a dry year, and 3877 made up for it.

Fascinating - thank you for that one.