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Tephra is air-fall material produced by a volcanic eruption
Volcano

A volcano is an opening, or rupture, in a planet's surface or Crust , which allows hot, molten rock, ash, and gases to escape from below the surface....
 regardless of composition or fragment size. Tephra is typically rhyolitic
Rhyolite

This page is about a volcanic rock. For the ghost town see Rhyolite, Nevada, and for the satellite system, see Rhyolite/Aquacade.Rhyolite is an igneous rock, volcanic rock , of felsic composition ....
 in composition, as most explosive volcanoes are the product of the more viscous
Viscosity

Viscosity is a measure of the Drag of a fluid which is being deformed by either shear stress or extensional stress. In everyday terms , viscosity is "thickness"....
 felsic
Felsic

Felsic is a term used in geology to refer to silicate minerals, magma, and rock which are enriched in the lighter elements such as silicon, oxygen, aluminium, sodium, and potassium....
 or high silica magma
Magma

Magma is molten Rock that is found beneath the surface of the Earth, and may also exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and gas bubbles....
s.

Volcanologists also refer to airborne fragments as pyroclasts or sometimes just clasts. Once clasts have fallen to the ground they remain as tephra unless hot enough to fuse together into pyroclastic rock
Pyroclastic rock

Pyroclastic rocks or pyroclastics are clastic rocks composed solely or primarily of volcanic materials. Where the volcanic material has been transported and reworked through mechanical action, such as by wind or water, these rocks are termed volcaniclastic....
 or tuff
Tuff

Tuff is a type of Rock consisting of consolidated volcanic ash ejected from vents during a volcanic eruption. Tuff is also sometimes called tufa, particularly when used as construction material....
.






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Tephra is air-fall material produced by a volcanic eruption
Volcano

A volcano is an opening, or rupture, in a planet's surface or Crust , which allows hot, molten rock, ash, and gases to escape from below the surface....
 regardless of composition or fragment size. Tephra is typically rhyolitic
Rhyolite

This page is about a volcanic rock. For the ghost town see Rhyolite, Nevada, and for the satellite system, see Rhyolite/Aquacade.Rhyolite is an igneous rock, volcanic rock , of felsic composition ....
 in composition, as most explosive volcanoes are the product of the more viscous
Viscosity

Viscosity is a measure of the Drag of a fluid which is being deformed by either shear stress or extensional stress. In everyday terms , viscosity is "thickness"....
 felsic
Felsic

Felsic is a term used in geology to refer to silicate minerals, magma, and rock which are enriched in the lighter elements such as silicon, oxygen, aluminium, sodium, and potassium....
 or high silica magma
Magma

Magma is molten Rock that is found beneath the surface of the Earth, and may also exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and gas bubbles....
s.

Volcanologists also refer to airborne fragments as pyroclasts or sometimes just clasts. Once clasts have fallen to the ground they remain as tephra unless hot enough to fuse together into pyroclastic rock
Pyroclastic rock

Pyroclastic rocks or pyroclastics are clastic rocks composed solely or primarily of volcanic materials. Where the volcanic material has been transported and reworked through mechanical action, such as by wind or water, these rocks are termed volcaniclastic....
 or tuff
Tuff

Tuff is a type of Rock consisting of consolidated volcanic ash ejected from vents during a volcanic eruption. Tuff is also sometimes called tufa, particularly when used as construction material....
. The distribution of tephra following an eruption usually involves the largest boulders falling to the ground quickest and 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
Stratosphere

The stratosphere is the second major layer of Earth's atmosphere, just above the troposphere, and below the mesosphere. It is stratified in temperature, with warmer layers higher up and cooler layers farther down....
 for several weeks. 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 climate change: "volcanic winter
Volcanic winter

A volcanic winter is the reduction in temperature caused by volcanic ash and droplets of sulfuric acid obscuring the sun and lowering the albedo , during a large particularly explosive type of volcano....
". Tephra mixed in with precipitation can also be acidic and cause acid rain
Acid rain

Acid rain is rain or any other form of Precipitation that is unusually acidic. It has harmful effects on plants, aquatic animals, and infrastructure....
 and snowfall.

Tephra fragments are classified by size:

  • Ash
    Volcanic ash

    Volcanic ash consists of small tephra, which are bits of pulverized rock and glass created by volcano eruptions, less than in diameter. There are three mechanisms of volcanic ash formation: gas release under decompression causing magmatic eruptions; thermal contraction from chilling on contact with water causing phreatomagmatic eruptions...
     - particles less than 2 mm in diameter
  • Lapilli
    Lapilli

    Lapilli is a size classification term for tephra, which is material that falls out of the air during a volcano. Lapilli means "little stones" in Latin....
     or volcanic cinders - between 2 and 64 mm in diameter
  • Volcanic bomb
    Volcanic bomb

    A volcanic bomb is a mass of molten rock larger than 65 mm in diameter, formed when a volcano ejects viscosity fragments of lava during an eruption....
    s or volcanic blocks
    Volcanic blocks

    Volcanic blocks are fragments of rock which measure more than 64mm in size and are erupted in a solid condition.Blocks are formed from material from previous eruptions or from Country rock and are therefore mostly accessory or accidental in origin....
     - greater than 64 mm in diameter


The words "tephra" and "pyroclast" both derive from Greek
Greek language

Greek is an Indo-European languages native to the southern Balkan peninsula, the language of the Greek people. It forms an independent branch within Indo-European....
. Tephra means "ash". Pyro means "fire" and klastos means "broken"; thus pyroclasts carry the connotation of "broken by fire".

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
Tephrochronology

Tephrochronology is a Geochronology technique that utilises discrete layers of tephra—volcanic ash from a single eruption—to create a chronological framework in which Paleoenviroment or Archaeology records can be placed....
.

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