Tephra is air-fall material produced by a volcanic eruption regardless of composition or fragment size. Plate tectonics and hotspots Divergent plate boundaries At the [1] Tephra is typically rhyolitic in composition, as most explosive volcanoes are the product of the more viscous felsic or high silica magmas. This page is about a volcanic rock For the ghost town see Rhyolite Nevada, and for the satellite system see Rhyolite/Aquacade. Viscosity is a measure of the resistance of a Fluid which is being deformed by either Shear stress or Extensional stress. Felsic is a term used in Geology to refer to Silicate minerals, Magma, and rocks which are enriched in the lighter elements such as Silicon The Chemical compound silicon dioxide, also known as silica or silox (from the Latin " Silex " is an Oxide Magma (Plurals magmas and magmata) is molten rock that sometimes forms beneath the surface of the Earth (or any other Terrestrial planet
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 or tuff. Pyroclastic rocks or pyroclastics (derived from the Greek πῦρ, meaning fire and κλαστός, meaning broken are Clastic rocks Tuff (from the Italian "tufo" is a type of rock consisting of consolidated volcanic ash ejected from vents during a volcanic eruption 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 for several weeks. The stratosphere is the second major layer of Earth's atmosphere, just above the Troposphere, and below the Mesosphere. 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". A volcanic winter is the reduction in temperature caused by Volcanic ash and droplets of Sulfuric acid obscuring the Sun and lowering the Albedo Tephra mixed in with precipitation can also be acidic and cause acid rain and snowfall. Acid rain is Rain or any other form of precipitation that is unusually Acidic It has harmful effects on plants aquatic animals and infastructure
Tephra fragments are classified by size:
- Ash - particles less than 2 mm in diameter
- Lapilli or volcanic cinders - between 2 and 64 mm in diameter
- Volcanic bombs or volcanic blocks - greater than 64 mm in diameter
The words "tephra" and "pyroclast" both derive from Greek. Volcanic ash consists of small Tephra, which are bits of pulverized rock and glass created by volcanic eruptions less than in diameter Lapilli is a size classification term for Tephra, which is material that falls out of the air during a volcanic eruption. A volcanic bomb is a globe of molten rock ( Tephra) larger than 65 mm (2 Volcanic blocks are fragments of rock which measure more than 64mm in size and are erupted in a solid condition Greek (el ελληνική γλώσσα or simply el ελληνικά — "Hellenic" is an Indo-European language, spoken today by 15-22 million people mainly 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 is a geochronological technique that utilises discrete layers of Tephra &mdashvolcanic ash from a single eruption&mdashto create a chronological
Notes
- ^ This is the broad definition of tephra (Greek tephra, "ash") proposed by the Icelandic volcanologist 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 ĺslendinga (1954:1-3). Hekla is a Stratovolcano located in the south of Iceland with a height of.
External links
Dapyx Software network: MP3 Explorer | Ebook Manager | Zenithic