Global Volcanism Program | Image GVP-03234
A vertical aerial photo shows the lobate form of the Glass Mountain obsidian flow, erupted less than 1000 years ago from a series of vents near the buried east rim of Medicine Lake caldera. The Glass Mountain eruption originated from a series of NW-SE-trending vents, seen here cutting across the photo from the upper left. Initial dacitic lavas were transitional into rhyolitic obsidian flows. The smoother-textured, partially vegetated lava flow at the lower left is the dacitic Hoffman flow, erupted only a few hundred years prior to the Glass Mountain flow.
Photo by U.S. Geological Survey (published in Green and Short, 1971).