Volcanic hazards from pyroclastic flow discharge into the sea: Examples from the 1883 eruption of Krakatau, Indonesia

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Discharge of pyroclastic flows into the sea from subaerial explosive eruptions poses some unique volcanic hazards to coastal areas adjacent to active volcanoes. Rapid transfer of flow momentum to seawater can generate devastating tsunamis that transmit the lethal effects of an eruption over large distances. Evidence from submarine volcaniclastic deposits around Krakatau volcano indicate that the great 1883 tsunamis were linked in part to pyroclastic flows entering the Sunda Straits during the August 26-27 eruption. A second hazard component of this process involves the ability of upper, dilute parts of pyroclastic flows or surges to travel over the sea surface for tens of kilometers and reach distal coastlines. During the 1883 Krakatau eruption, hot flows were able to traverse 40 km of the Sunda Straits to reach the southeast coast of Sumatra and kill approximately 2,000 people. Recognition of these hazards is important in areas where pyroclastic flows may be discharged into the sea. The 1883 eruption of Krakatau provides new insights into the nature of pyroclastic deposits that may be useful for this type of assessment.

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Special Paper of the Geological Society of America