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volcanic ash[väl′kan·ik ′ash]
an incorrect but widespread name for a product of the natural pulverization of magma; it consists of a mixture of dust and sand, with a particle size less than 2 mm. Admixtures of foreign rocks are characteristic. It occurs as a result of the atomization of liquid or solid lavas of various compositions.
Depending on the size of the particles, the force of the eruption, and the wind, volcanic ash can settle at significant distances from the place of the eruption. Thus, for example, during the explosion of Bezymiannyi Volcano (on Kamchatka) in 1956, ash floated as far as Great Britain, and during the explosion of Krakatoa (Indonesia) in 1883, the smallest volcanic dust particles floated almost twice around the world.
Volcanic ash is used to make light concretes, glass for containers, cement, thermal-insulation material, and filtration material. It is also used as a medium for growing plants.