Tephra

"Pyroclasts" redirects here. For the Sunn O))) album, see Pyroclasts (album). For other uses, see Pyroclastic (disambiguation).

"Tefra" redirects here. For the Tax Equity and Fiscal Responsibility Act of 1982, see TEFRA.

See also: Volcanic ash

Volcanic tephra at Brown Bluff, Antarctica (2016)

Tephra is fragmental material produced by a volcanic eruption regardless of composition, fragment size, or emplacement mechanism.

Tephra horizons in south-central Iceland: The thick and light-coloured layer at the centre of the photo is rhyolitic tephra from Hekla.

Volcanologists also refer to airborne fragments as pyroclasts. Once clasts have fallen to the ground, they remain as tephra unless hot enough to fuse into pyroclastic rock or tuff. When a volcano explodes, it releases a variety of tephra including ash, cinders, and blocks. These layers settle on the land and, over time, sedimentation occurs incorporating these tephra layers into the geologic record.

Tephrochronology is a geochronological technique that uses discrete layers of tephra—volcanic ash from a single eruption—to create a chronological framework in which paleoenvironmental or archaeological records can be placed. Often, when a volcano explodes, biological organisms are killed and their remains are buried within the tephra layer. These fossils are later dated by scientists to determine the age of the fossil and its place within the geologic record.

Molten lava fountain at Kilauea volcano on Hawaii, with black cloud of associated tephra