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Pyroclastic Flows at Mount Shasta

Some pyroclastic flows originating at the summit vent and at the Shastina vent extended more than 20 km (12.4 mi). Ones from the Black Butte vent extended about 10 km (6.2 mi) southwestward. If pyroclastic flows occur in the future, they may affect low- and flat-lying areas almost anywhere within about 20 km (12.4 mi) of the source vent for the eruption. If they originate at the summit, the flows could sweep down almost any side of the mountain, although the area west of Shastina would probably be protected by the barrier formed by the Shastina cone. If future eruptions were to occur at new vents or domes located on a flank of the volcano, pyroclastic flows would primarily affect only those areas of the mountain downslope from the vents.