Global Volcanism Program | Image GVP-02703
The tree trunk next to the geologist was buried by ash deposits from the Bridge River eruption of the Meager volcanic complex about 2,350 years ago, which was then covered by a pyroclastic flow. The deposit has an unwelded base and a darker, more massive welded layer at the top of this photo.
Photo by Willie Scott, 1990 (U.S. Geological Survey).
This image is made available as a Public Domain Work, but proper attribution is appreciated.