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VOLCANIC HAZARDS Hawaiian volcanoes can erupt either at their summits or on their flanks. Young Hawaiian volcanoes, such as Kilauea and Mauna Loa, have summit calderas. A caldera is a crater several miles in diameter that forms as the result of collapse when magma drains from beneath the summit. (Magma is the term used for molten rock that is still beneath the earth's surface; it is called lava when it reaches the surface.) Summit eruptions of Kilauea and Mauna Loa occur within or ne ...