Thursday, February 28, 2013

Geo 365: Feb. 28, Day 59: Table Rock Ball-and-Pillow

We drove up the little dirt road- it's a bit rutted, but in good shape overall- parked near the base of Table Rock, then followed the base north a hundred yards or so. There are a multitude of sedimentary and volcanic structures nicely highlighted by contrasty beds. Actual lava flows didn't make it to this area- or or if they did, they were later, higher in the pile, and have subsequently been removed by erosion- so this is strictly a volcanoclastic sedimentary environment. I suspect it's highly influenced by very rapid deposition, with surges of water and sediment triggered by explosive volcanism a mile or two away, and further modified by frequent quakes and shocks associated with the eruption.

Above, we see a pair of ball-and-pillow structures. It looks as if the material overlying the structures was planed off, then filled in again later- a disconformity. These are quite common in Table Rock.

Photo unmodified. August 20, 2011. FlashEarth Location. Just to the west of the crosshairs, you can see a flat area that's good for parking, so you don't obstruct the dirt road, and aren't sitting over dry grass (fire hazard!) but to be honest, I have never seen anyone else off the paved road here.

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