Volcanic ash

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Diamond Head, a well-known backdrop to Waikiki in Hawaii, is an ash cone that solidified into tuff

Volcanic ash is rock particles less than 0.25 inch across ejected from a volcanic vent. 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. Also, 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 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.

Volcanic ash sample

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").

de:Vulkanische Asche