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Volcanic tephra at Brown Bluff, Antarctica (2016) Brown Bluff-2016-Tabarin Peninsula-Volcanic tephra.jpg
Volcanic tephra at Brown Bluff, Antarctica (2016)

Tephra is fragmental material produced by a volcanic eruption regardless of composition, fragment size, or emplacement mechanism. [1]


Tephra horizons in south-central Iceland: The thick and light-coloured layer at the centre of the photo is rhyolitic tephra from Hekla. Icelandic tephra.JPG
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 together into pyroclastic rock or tuff.

A 2007 eruptive plume at Mount Etna produced volcanic ash, pumice, and lava bombs. 04Sep2007 Etna from SE Crater.jpg
A 2007 eruptive plume at Mount Etna produced volcanic ash, pumice, and lava bombs.


Rocks from the Bishop tuff, uncompressed with pumice on left; compressed with fiamme on right BishopTuff.jpg
Rocks from the Bishop tuff, uncompressed with pumice on left; compressed with fiamme on right

The distribution of tephra following an eruption usually involves the largest boulders falling to the ground quickest, therefore closest to the vent, while smaller fragments travel further – ash can often travel for thousands of miles, even circumglobal, as it can stay in the stratosphere for days to weeks following an eruption. When large amounts of tephra accumulate in the atmosphere from massive volcanic eruptions (or from a multitude of smaller eruptions occurring simultaneously), they can reflect light and heat from the sun back through the atmosphere, in some cases causing the temperature to drop, resulting in a temporary "volcanic winter". The effects of acidic rain and snow, the precipitation caused by tephra discharges into the atmosphere, can be seen for years after the eruptions have stopped. Tephra eruptions can affect ecosystems from miles to kilometers depending on the size of the eruption. [2]


Tephra fragments are classified by size:

Volcanic breccia in Jackson Hole. Volcanic breccia in Jackson Hole.JPG
Volcanic breccia in Jackson Hole.

The use of tephra layers, which bear their own unique chemistry and character, as temporal marker horizons in archaeological and geological sites, is known as tephrochronology.


The word "tephra" and "pyroclast" both derive from Greek: τέφρα tephra means "ash", while the word pyroclast is derived from the Greek πῦρ (pyr), meaning "fire", and κλαστός (klastos), meaning "broken in pieces".

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Bridge River Vent mountain in Canada

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Volcanic ash volcanic material formed during explosive eruptions with the diameter of the grains less than 2 mm

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  1. This is the broad definition of tephra (Greek tephra, "ash") proposed by the Icelandic volcanologist Sigurður Þórarinsson (Sigurdur Thorarinsson) in 1954, in connection with the eruption of Hekla (Thorarinsson, "The eruption of Hekla, 1947-48II, 3, The tephra-fall from Hekla, March 29th, 1947", Visindafélag Íslendinga (1954:1-3).
  2. Ayris, Paul Martin; Delmelle, Pierre (2012-11-01). "The immediate environmental effects of tephra emission". Bulletin of Volcanology. 74 (9): 1905–1936. doi:10.1007/s00445-012-0654-5. ISSN   1432-0819.