A Short Earth Science Week Photo Post: Splort!

Last summer, August 20, 2011, to be exact, Dana, Intrepid Companion, and I visited Table Rock, at the south side of the Fort Rock/Christmas Lake Basin (FlashEarth location; crosshairs very close to photo location- zoom in to see details.) Table Rock is very much like Fort Rock, but much larger, filled with lava late in its eruption, and not as well known. It also has a slew of primary sedimentary structures along with secondary soft-sediment deformation and tectonic structures. While I don't know the details of its history, I love ogling its little tidbits.

I found the spot below especially fun, and was at a loss making sense of what had happened, because I was focused on what had gone where, and not paying attention to the faults that had allowed those motions...

So I sent it off to Callan, the geoblogosphere's structural go-to guy, with some comment about "the rarely seen splort structure."

 The larger context- the splort structure is in the middle of the lower left quadrant of this photo.

And here it's on the middle right edge.

Callan responded later with this terrific annotation, which instantly cleared up my confusion as to just what the heck had happened here- at least in terms of structure, if not in terms of exactly what caused it. Regarding that latter, the environment would have been the distal edge of a very violent phreatic eruption, and sedimentation of debris would have been very rapid, at the same time that the pile was being shaken by blasts from the central vent- roughly 3 miles from here- and frequent earthquakes. So stress fields would have been changing rapidly in a deep pile of unconsolidated sediment. It seems to me that in such an environment, nearly contemporaneous normal and reverse faulting might not be that surprising. And while I like "splort," Callan tells me this is more properly called a pop-up.