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Pyroclastic Surge Hazards at Crater Lake

Building remnant in Francisco Leon destroyed by pyroclastic surges and flows during eruption of El Chichon volcano in Mexico 1982. Reinforcement rods in concrete bend in direction of flow. (Credit: Tilling, Robert.) (Public domain.)

The most serious hazard posed by a magma/water eruption would produce a mixture of air, volcanic gas, steam, and tephra that would move along the ground surface at velocities up to a hundred or more meters per second near the eruption source (many hundreds of miles per hour) – a pyroclastic surge. Surges behave differently than pyroclastic flows because the amount of tephra in them is lower, which means they can travel over topographic barriers. With temperatures that range from the boiling point of water to the temperature of magma, they can destroy or incinerate most structures and living things in their path. If a surge-producing eruption were to occur in the lake, the hazards would likely be limited to the lake area, the rim and areas near the rim.