Photographs of Obsidian Cliff, Yellowstone National Park

Obsidian Cliff exposes the interior of a thick rhyolite lava flow that erupted about 180,000 years ago. The vertical columns are cooling fractures that formed as the thick lava flow cooled and crystallized in a previously eroded valley bottom. The flow consists of obsidian, a dark rhyolitic volcanic glass.

Obsidian Cliff, Yellowstone National Park, Wyoming
 View of Obsidian Cliff. Photograph by S.R. Brantley on 20 May 2001.
Rock from Obsidian Cliff
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Close view of rocks from Obsidian Cliff showing cavities lined with microcrystals, formed by gases as the glass cooled from high temperatures. Photograph by S.R. Brantley on 23 May 2001.