Friday, February 12, 2016

A long time ago in an island arc not so far away...

I think this is an artifact of a 33-40 million year old earthquake that occurred in the old island-arc off Oregon that is now the Coast Range.


The lower (left in the picture) material was a coarse grained pyroclastic sand, probably deposited as an ash-flow in the shallow seas around the old island chain. At the time what is today's Oregon Coast Range was an offshore chain of volcanic islands, very like the modern Japanese home islands. These rascals huffed and puffed a lot of volcanic ash into the air and from thence into the Eocene seas off what is today the Pacific Northwest.

You can see that a layer of gray silt was deposited above it, but you can also see that the silt is broken in the middle and the orange sand has pushed right through it.

On top of the silt (to the right) the sand has flowed out onto the surface of the silt, making a layered mound; these things are called “sand blows” or “sand volcanoes” and are a typical surface feature of liquefaction during strong earthquakes.

Just my interpretation, mind you; if you have two data points and two geologists you will typically get eight working hypotheses. Still...one hopes that the Eocene building codes were being stringently enforced.

Oh, and what do you get if you have one data point and one engineer?

A regression line calculated to four significant figures.

just sayin'.

5 comments:

Ael said...

Nice.

I love puzzles and nature leaves the best ones all over the place.

All you have to do is look for them.

FDChief said...

Well...you have to be damned good or damned lucky; in our case, the latter.

But, yes.

Leon said...

Chief, you go wash your mouth out with soap for all that filthy language.

"A regression line calculated to four significant figures."

I've never heard such filthy deplorable language. And I've read Danielle Steel novels.

FDChief said...

That's engineering for you; dirty work done...well, usually for a whole shitpot of cash.

FDChief said...

And despite my reputation as a potty-mouthed sergeant, I can fuckin' talk like a fuckin' nerd when I fuckin' want to.