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Volcano's Deadly Warning

Anatomy of a Volcano

 

Intro |  Ash  | Lava flow | Lava dome | Lava | Vent | Tephra | Caldera | Lahar | Fissure | Dike | Magma

Volcano's Deadly Warning homepage

Ash
Diagram of a volcano

Ash
Volcanic ash consists of rock, mineral, and volcanic glass fragments smaller than a tenth of an inch in diameter—or slightly larger than a pinhead. Volcanic ash is quite different from the soft, fluffy ash that results from burning wood, leaves, or paper. It is hard, does not dissolve in water, and can be extremely small—ash particles less than 1/1,000th of an inch in diameter are common. It is also extremely abrasive (similar to finely crushed window glass), mildly corrosive, and electrically conductive, especially when wet.

Volcanic ash is created during explosive eruptions by the shattering of solid rocks and the violent separation of magma into tiny pieces. Explosive eruptions result when groundwater heated by magma abruptly converts to steam and also when magma reaches the surface so that volcanic gases dissolved in the molten rock expand and escape into the air extremely rapidly. Hot ash and gas rise quickly to form a towering eruption column directly above the volcano.

Above left: Ash from the 1993 eruption of Unzen volcano in Kyushu, Japan rises halfway up the walls of a house.

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