The horseshoe-shaped Collier Cone on the NNW flank of North Sister, partially covered by the Collier Glacier in this 1984 photo, was the source about 1,600 years ago of the youngest dated eruption in the North Sister volcanic field. Lava flows traveled 5 km NW and 13.5 km W down the White Branch Creek. The foreground portion of the cone in this view looking NE has been partially eroded by Collier Glacier when it was at the level of the gray glacial moraine in the foreground on the left margin of the glacier.

Photo by Lee Siebert, 1984 (Smithsonian Institution).

This image is made available under the Public Domain Dedication CC0 license, but proper attribution is appreciated.

Keywords: scoria cone | crater

Three Sisters