Wednesday, August 12, 2009

Yes. There is a sediment lens trapped between two flows in the West Crater Lava

It is at Dogleg Bar. You can see it as a squinty-eyes shaped discontinuity in the lava stack to the right/east of the terrace sequence. I got out there today to find out that the lens is comprised of weakly cross-stratified, moderately sorted, pea to pebble gravel composed entirely of cinders and fragmented vesicular basalt with a glassy outer rind. Fairly clear evidence for the river dealing directly with hot lava. I suspect that there are more examples of this. I tried to get to the big face in Qbw where the prominent fracture is located between Bogus Falls and Dogleg. Too steep and dangerous to peer over the edge far enough. The photo I have of that area from last May, however, is suggestive of a sediment lens akin to the one I visited today.

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Posted via email from Fresh Geologic Froth

1 comment:

  1. Good find Dr. Jerque. Playing the Devil's advocate here: how do we know the lava under the sediment lens is WC--can it be Saddle Butte or Clarks Butte? (You probably have considered this already but these contact relations have fooled me in the past.) I am pretty sure that the p-mag at the base of Bogus Falls shows that lava is WC--so can we trace those flow units downstream?


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