volcanic ash

Volcanic ash consists of rock, mineral, and volcanic glass fragments smaller than 2 mm (0.1 inch) in diameter, which is slightly larger than the size of a pinhead. Volcanic ash is not the same as 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 0.025 mm (1/1,000th of an inch) in diameter are common.
Ash is 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 violent separation of magma (molten rock) into tiny pieces. Explosive eruptions are generated when ground water is heated by magma and abruptly converted to steam and also when magma reaches the surface so that volcanic gases dissolved in the molten rock expand and escape (explode) into the air extremely rapidly. After being blasted into the air by expanding steam and other volcanic gases, the hot ash and gas rise quickly to form a towering eruption column directly above the volcano.
Photo 1
Photograph by D.E. Wieprecht.
Volcanic ash collected in Randle, Washington, located about 40 km NNE of Mount St. Helens. The north edge of the eruption cloud of May 18, 1980, passed over Randle and deposited between 1 and 2 cm of ash on the community. At the same distance along the axis of the eruption cloud, however, about 7 cm of ash and larger-sized tepra fell to the ground.
Photo 2
SEM image provided by A.M. Sarna-Wojcicki.
Close view of a single ash particle from the eruption of Mount St. Helens; image is from a scanning electron microscope (SEM). The tiny voids or "holes" are called vesicles and were created by expanding gas bubbles during the eruption of magma.

Glossary of volcanic terms. - University of Wisconsin Oshkosh. . 2001.

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  • Volcanic ash — consists of small tephra, which are bits of pulverized rock and glass created by volcanic eruptions,United States Geological Survey. [http://volcanoes.usgs.gov/Hazards/What/Tephra/tephra.html Tephra: Volcanic Rock and Glass Fragments.] Retrieved… …   Wikipedia

  • Volcanic ash — Ash Ash, n., sing. of {Ashes}. [1913 Webster] Note: Ash is rarely used in the singular except in connection with chemical or geological products; as, soda ash, coal which yields a red ash, etc., or as a qualifying or combining word; as, ash bin,… …   The Collaborative International Dictionary of English

  • volcanic ash — noun or volcanic ashes : ash 1c * * * Geol. ash (def. 2). [1790 1800] * * * volcanic ash or volcanic ashes see under ↑ash1 • • • Main Entry: ↑ …   Useful english dictionary

  • Volcanic ash — Ashes Ash es, n. pl. [OE. asche, aske, AS. asce, [ae]sce, axe; akin to OHG. asca, G. asche, D. asch, Icel. & Sw. aska, Dan. aske, Goth. azgo.] 1. The earthy or mineral particles of combustible substances remaining after combustion, as of wood or… …   The Collaborative International Dictionary of English

  • volcanic ash — vulkaniniai pelenai statusas T sritis chemija apibrėžtis Vulkano išsiveržimo metu į atmosferą išmestos smulkios (iki 1 mm) uolienų nuolaužos. atitikmenys: angl. volcanic ash rus. вулканический пепел …   Chemijos terminų aiškinamasis žodynas

  • volcanic ash — vulkaniniai pelenai statusas T sritis ekologija ir aplinkotyra apibrėžtis Ugnikalnio išsiveržimo metu į atmosferą išmestos smulkios (iki 1 mm) uolienų nuolaužos. atitikmenys: angl. cinder; volcanic ash vok. Vulkanasche, f; vulkanische Asche, f… …   Ekologijos terminų aiškinamasis žodynas

  • volcanic ash — /vɒlkænɪk ˈæʃ/ (say volkanik ash) noun fine particles of mineral matter from a volcanic eruption …   Australian English dictionary

  • volcanic ash — Geol. ash (def. 2). [1790 1800] * * * …   Universalium

  • Volcanic Ash Advisory Center — Carte de la couverture des neuf Volcanic Ash Advisory Center. Un Volcanic Ash Advisory Center, ou VAAC, est un observatoire météorologique organisant la collecte et la diffusion des informations relatives aux cendres volcani …   Wikipédia en Français

  • volcanic ash advisory center — A meteorological center designated by regional air navigation agreement to provide advisory information to meteorological watch offices, area control centers, flight information centers, world area forecast centers, relevant regional area… …   Aviation dictionary

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