Mount Washington, reflected here in Big Lake on its NW side, is a Pleistocene shield volcano deeply dissected by glaciers. Erosion has exposed many dikes in the summit cone, which has not erupted since the late Pleistocene. Vents on the NE flank, behind the ridge on the left, erupted about 1300 years ago, probably as part of a a fissure-fed eruption at Blue Lake Crater.

Photo by Lee Siebert, 1995 (Smithsonian Institution).

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

Washington