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Volcanic ash is a volcanic rock which is exploded from a vent.  Volcanic ash is like small glass particles so if anything comes across it damages it very bad.  During heavy ash rains houses and buildings may fall over and animals and people could get hurt.  When the ash first erupts it may be solid or molten.  Volcanic ash comes from the fragmentation of lava.  Volcanic ash beds are known to be tuffs.  They are known to be in central North Dakota.  These tuffs are to range to 70 to 20 million years old.  Including clouds of ash that rise above a volcano some explosive eruptions produce avalanches of hot ash, rock and gas that move high speeds down a slope of a volcano.  Ash flows are the worst part of volcanic activity.