Friday, April 9, 2010

Hot Rocks

Mary at Geographile found an amazing videoclip of time-lapse basalt flows in Hawaii.

This is actually a series of clips, some of which are quite short, and it's a little jarring sometimes in the way it flicks from one scene to another. There were a number of things that held my attention, though; the silvery sheen on the freshly cooled surface is striking. I've looked at an awful lot of basalt in my time, but none this fresh. I'm guessing it's a glassy surface thing, a very thin patina that weathers off quickly, exposing the dull black that I associate with that rock. Another thing that had me thinking was trying to picture how these forms would look in later outcrop, or conversely, how I could look at a pile of older basalt in cross section and puzzle out the progression and form of the flow that created it. And finally, the inflation of flows followed by fresh break-outs reminds me that "rivers of fire" are the exceptions, and not really typical. In pahoehoe-type flows, most of the flow is in the interior under a cooled and hardened crust. Fresh lava regularly breaks out around the snout, but exposed incandescent fluid is actually only a small portion of an active flow.


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