Volcanic ash

Volcanic ash is the term for very fine rock and mineral particles less than 2 mm in diameter that are ejected from a volcanic vent. Ash is created when solid rock shatters and magma separates into minute particles during explosive volcanic activity. The usually violent nature of an eruption involving steam (phreatic eruption) results in the magma and perhaps solid rock surrounding the vent, being torn into particles of silt to sand size. The plume that is often seen above an erupting volcano is composed primarily of ash and steam. The ejection of large quantities of ash will produce an ash cone. A layer of volcanic ash tends to become cemented together (see pozzulana) to form a firm rock called tuff (pronounced "toof"). The very fine particles may be carried for many miles, settling out as a dust-like layer across the landscape. This is known as an "ash fall." The term for any material explosively thrown out from a vent is ejecta or pyroclastic debris. If liquid magma is ejected as a spray, the particles will solidify in the air to small fragments of volcanic glass. The very fine particles may be carried many miles, settling out as a dust-like layer across the landscape. Ejecta particles of gravel size are termed cinder.

Related Topics:
Rock - Mineral - Mm - Volcanic - Magma - Silt - Sand - Ash cone - Pozzulana - Tuff - Gravel - Cinder

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