Global Volcanism Program | Image GVP-03106
The Rock Mesa obsidian lava flow is seen here in an aerial view from the north above South Sister volcano. It is the largest of a series of lava flows which erupted about 2,300 to 2,000 years ago from vents on the SW and SE flanks.
Photo by Dan Miller, 1977 (U.S. Geological Survey).
This image is made available as a Public Domain Work, but proper attribution is appreciated.