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Ash is unconsolidated tephra less than 2 mm in diameter. It can be juvenile, accessory, or accidental in origin. It can be further divided into vitric, crystal, and lithic ash, based on the abundance of glass, crystals, or rock fragments, respectively. This photo shows the ash that is abundant in the deposit from the 1790 eruption of Kilauea. Photograph by T.J. Takahashi, U.S. Geological Survey, October 28, 1984.
The above classification of tephra is based on particle size. Additional terms commonly used for volcanic products are based on texture and composition.
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