Geo 365: April 6, Day 96: Lord of the Ring Dike

Looking a bit more southerly from Elephant Rock, you can see the general ring-like outline of the invasive dikes at Seal Rock State Park. The "classic" example of a ring dike on the Oregon Coast is at Otter Rock. I've only visited that spot once- it's one I should get back to- and the only thing I remember is that even as a wet-behind-the-ears newbie, the explanation offered sounded more like arm-waving than a reasonable idea. Something about a piston intrusion at depth, creating a circular fault, then injection of basalt into that ring. The fact is, even with years of geology behind me, that sounds almost more reasonable than what is apparently now believed- CRB flows onto unconsolidated sediments, then owing to their greater density, intuding down into them. Sort of a ball-and-pillow structure with lava.

When I was doing volunteer teaching for my "Geology of the Corvallis Area" class, I had some jokey additional "principles of geology," which I felt were both funny, and contained important elements of truth. One of them was the "Don't Tell" principle: "Don't tell the rocks what they can and can't do. They've already done it. Your job is to figure out how they've done what they've done."

All these years later, I still like that one; I can't say how many times I've peered at an outcrop, and felt tempted to say "But, but, but... you can't DO that!" But they did. Rocks do weird things, and I guess that's a big part of why I love them.

Photo unmodified. March 8, 2012. FlashEarth Location.