Global Volcanism Program | Image GVP-03112
The large lava flow to the lower right is the Rock Mesa lava flow on the SW flank of South Sister. The rhyodacite flow erupted about 2,300 years ago from a vent now filled by a small lava dome. Lava extrusion was preceded by explosive eruptions that produced airfall tephra and pyroclastic flows.
Photo by Willie Scott, 1981 (U.S. Geological Survey).
This image is made available as a Public Domain Work, but proper attribution is appreciated.