Global Volcanism Program | Image GVP-04572
Deep glacial valleys cut the western flanks of Mount Jefferson. The original edifice was extensively eroded by glaciers prior to formation of a younger dacite cone on top of the older edifice. Lava dome growth was associated with the younger volcano and were accompanied by major ash-producing eruptions and pyroclastic flows, before activity ceased activity during the late Pleistocene.
Photo by Lee Siebert, 1996 (Smithsonian Institution)
This image is made available under the Public Domain Dedication CC0 license, but proper attribution is appreciated.