Thursday, May 2, 2013

Geo 365: May 2, Day 122: Breadcrust #1

A breadcrust bomb, along the stairs from the parking area to the fire watchtower, at the summit of Lava Butte. "Bomb" indicates a blob of lava tossed in a still-fluid form from an active vent, and "breadcrust" texture forms when the exterior of the bomb cools and solidifies, but the interior is still somewhat fluid and degassing. As the sticky interior expands, it "crackles" the exterior shell in a manner very similar to the crusts of some artisanal breads. In the area where the exterior shell has broken off, above and to the left of the lens cap, you can see the foamy interior of the bomb. Foamy basalt is called scoria, just as foamy rhyolite is called pumice.

Photo unmodified. August 21, 2011. FlashEarth Location.

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