This is an image of a pyroclastic flow going down the slopes of a volcano.
Click on image for full size
Image from: U.S. Geological Survey, photo by B. Yount
Sometimes a cloud of ash and lava fragments can be carried through the air by hot vapors from the volcano. Such a flow is usually *very* hot, and moves *rapidly* down the slopes of a volcano. Surges of flowing ash may start fires and kill or burn people and animals. The most destructive ash flow occured during the eruption of Mt. Pelee in 1902.
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