tephra

^{ALASKA VOLCANO OBSERVATORY GLOSSARY}

Any type of rock fragment that is forcibly ejected from the volcano during an eruption.

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^{GLOSSARY OF VOLCANIC TERMS}

A general term used by volcanologists to describe all fragmental volcanic ejecta produced during explosive volcanic eruptions (Dehn and McNutt, 2000, p. 1271). This includes ash (<2mm diameter fragments), lapilli (2-64 mm diameter fragments and fragements greater than 64 mm in diameter known as bombs (semi-solid or plastic ejecta) or bombs (solid ejecta) (Tilling et al., 1987).

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^{USGS PHOTO GLOSSARY OF VOLCANIC TERMS}

Tephra is a general term for fragments of volcanic rock and lava regardless of size that are blasted into the air by explosions or carried upward by hot gases in eruption columns or lava fountains. Tephra includes large dense blocks and bombs, and small light rock debris such as scoria, pumice, reticulite, and ash.

As tephra falls to the ground with increasing distance from a volcano, the average size of the individual rock particles becomes smaller and thickness of the resulting deposit becomes thinner. Small tephra stays aloft in the eruption cloud for longer periods of time, which allows wind to blow tiny particles farther from an erupting volcano.

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Photograph by D. Wieprecht

Tephra erupted by Mount St. Helens on 18 May 1980 ranging in size from ash (left 2 piles) to lapilli (right 2 piles).

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Photograph by E. Wolfe on 24 June 1991

Volcanic ash falls to ground and creates darkness, Mount Pinatubo in the Philippines.