火山碎屑流 Pyroclastic flow
（重定向自Ash flow）
火山碎屑流是某些火山爆发的一个平常但极具毁灭性的现象。为快速流动的炽热的气体、灰和岩石（被称为火山灰或火山碎屑），可能从火山以700公里每小时的速度向外喷出。气体通常是在温度100-800 摄氏度。火山碎屑流通常顺火山斜坡向下运动，速度取决于其密度、喷发速度与山坡的倾斜度。
Ash flow
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Pyroclastic flow 火山碎屑流
（重定向自Ash flow）
A pyroclastic flow (also known scientifically as a pyroclastic density current) is a fast-moving current of hot gas and rock (collectively known as tephra), which reaches speeds moving away from a volcano of up to 700 km/h (450 mph). The gas can reach temperatures of about 1,000 °C (1,830 °F). Pyroclastic flows normally hug the ground and travel downhill, or spread laterally under gravity. Their speed depends upon the density of the current, the volcanic output rate, and the gradient of the slope. They are a common and devastating result of certain explosive volcanic eruptions.