Katmai National Park, Alaska. Katmai Caldera, 4 kilometers across, was formed during the giant 1912 eruption. Strangely enough, most of the ash and pyroclastic-flow deposits were erupted from a vent called Novarupta, a few kilometers away. Most of the magma chamber that was expelled, however, was apparently beneath Katmai, and that is where the major collapse occurred. The caldera now contains a lake and a small glacier.
                                  Photo copyright R.W. Decker, 1963

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