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9. Lassen Peak, California. The steep summit area is a large lava dome that extruded about 27,000 years ago. The most recent eruption of Lassen Volcano occurred in 1914-1921. Explosive activity in 1915 created the "devastated area" in the center-left that apparently resulted from a combination of pyroclastic flows and snow-melt mudflows. Photo by R. W. Decker, 1970. |