Puu Oo eruption, Kilauea Volcano, Hawaii. Most aa lava flows move only a few meters per hour, but sometimes they surge, as seen in this photo. Before the aa surge occurred, the flow front thickened from about 1 meter to 3 meters, and then the flow began to move downslope at speeds up to 100 meters per minute. U.S. Geological Survey Photo by R.W. Decker
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