After that a quiet eruption produces a lava flow covering the rock particles. After many eruptions a cone shaped mountain forms. . . . . . . . . Dust is the smallest particle. It is less than one quarter of a millimeter wide. . Ashes are from one quarter to five mm in diameter.
Volcanic ash can affect people hundreds of miles away from the volcano.
Several of the deaths from the Mount St. Helens volcano in 1980 were caused by inhalation of volcanic ash. Volcanic ash can contaminate water supplies, cause electrical storms, and collapse roofs. . Cinders are about the size of a golf ball. . Bombs can be several meters large.