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Pyroclastic rocks or pyroclastics (derived from the Greek πῦρ, meaning fire, and κλαστός, meaning broken) are debris thrown from volcanoes during an eruption. It consists of fresh lava that has risen to the surface or older volcanic material that has remelted and has been expelled into the air by the explosion. Image File history File links Broom_icon. ... For other uses, see Volcano (disambiguation). ... Look up lava, Aa, pahoehoe in Wiktionary, the free dictionary. ...

Three modes of transport can be distinguished: pyroclastic flow, pyroclastic surge, and pyroclastic fall. During Plinian eruptions, pumice and ash are formed when silicic magma is fragmented in the volcanic conduit, because of decompression and the growth of bubbles. Pyroclasts are then entrained in a buoyant eruption plume which can rise several kilometers into the air and cause aviation hazards. Particles falling from the eruption clouds form layers on the ground (this is pyroclastic fall or tephra). Pyroclastic density currents, which are referred to as 'flows' or 'surges' depending on particle concentration and the level turbulence, are sometimes called glowing avalanches. The deposits of pumice-rich pyroclastic flows can be called ignimbrites. Pyroclastic flows sweep down the flanks of Mayon Volcano, Philippines, in 1984 Pyroclastic flows are a common and devastating result of some volcanic eruptions. ... A pyroclastic surge is a fluidized mass of turbulent gas and rock fragments which is ejected during some volcanic eruptions. ... A pyroclastic fall is a uniform deposit of material which has been ejected from an eruption or plume such as an ash fall or tuff. ... Eruption of Vesuvius in 1822. ... Specimen of highly porous pumice from Teide volcano on Tenerife, Canary Islands. ... Ash plume from Mt Cleveland, a stratovolcano Diamond Head, a well-known backdrop to Waikiki in Hawaii, is an ash cone that solidified into tuff Volcanic ash consists of very fine rock and mineral particles less than 2 mm in diameter that are ejected from a volcanic vent. ... The chemical compound silicon dioxide, also known as silica, is the oxide of silicon, chemical formula SiO2. ... Magma is molten rock located beneath the surface of the Earth (or any other terrestrial planet), and which often collects in a magma chamber. ... Tephra refers to air-fall material produced by a volcanic eruption regardless of composition or fragment size. ... Ignimbrite is a volcanic pyroclastic rock, often of dacitic or rhyolitic composition. ...

A pyroclastic eruption entails spitting or "fountaining" lava, where the lava will be thrown into the air along with ash, pyroclastic materials, and other volcanic byproducts. Hawaiian eruptions such as those at Kilauea can eject clots of magma suspended into gas; this is called a 'fire fountain'. The magma clots, if hot enough may coalesce upon landing to form a lava flow. KÄ«lauea is an active volcano in the Hawaiian Islands, one of five shield volcanoes that together form the Island of Hawaii. ... In computer programming jargon, lava flow is a problem in which computer code, usually written under less than optimal conditions, is put into production and then built on when still in a developmental state. ...

The term "pyroclastics" can be applied to anything resulting from a volcanic eruption (ash, lava, cinder, and other volcanic debris). Pyroclasts of different sizes are classified as volcanic bombs, lapilli and volcanic ash. Ash is considered to be a "pyroclastics" because it is a fine dust made up of volcanic rock. A volcanic bomb is a globule of molten rock (tephra) larger than 2. ... Lapilli are small particles of solidified lava (tephra) thrown into the air by volcanic eruptions. ... Ash plume from Mt Cleveland, a stratovolcano Diamond Head, a well-known backdrop to Waikiki in Hawaii, is an ash cone that solidified into tuff Volcanic ash consists of very fine rock and mineral particles less than 2 mm in diameter that are ejected from a volcanic vent. ...

Pyroclastic deposits consist of pyroclasts which are not cemented together. Pyroclastic rocks (tuff) are pyroclastic deposits which have been lithified. Welded tuff at Golden Gate in Yellowstone National Park Tuff (from the Italian tufo) is a type of rock consisting of consolidated volcanic ash ejected from vents during a volcanic eruption. ... Lithification (from the Greek word lithos meaning rock and the Latin-derived suffix -ific) is the process whereby sediments compact under pressure, expel connate fluids, and gradually become solid rock. ...

References

• Blatt, Harvey and Robert J. Tracy (1996) Petrology: Igneous, Sedimentary, and Metamorphic, W.H. Freeman & Company; 2nd ed., pp. 26-29; ISBN 0-7167-2438-3