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Encyclopedia > Volcanic ash
Ash plume from Mt Cleveland, a stratovolcano
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
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. Ash is created when solid rock shatters and magma separates into minute particles during explosive volcanic activity. The usually violent nature of an eruption involving steam (phreatic eruption) results in the magma and perhaps solid rock surrounding the vent, being torn into particles of clay to sand size. Image File history File links Download high-resolution version (1000x662, 186 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Volcanic ash Mount Cleveland (Alaska) ... Image File history File links Download high-resolution version (1000x662, 186 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Volcanic ash Mount Cleveland (Alaska) ... Mount Cleveland is a mountain that forms the western half of Chuginadak Island in the central Aleutian Islands of Alaska. ... Stratovolcano Mount St. ... Photograph of Diamond Head taken from Kapiolani Park in Waikiki, Hawaiian Islands. ... Photograph of Diamond Head taken from Kapiolani Park in Waikiki, Hawaiian Islands. ... Welded tuff at Golden Gate in Yellowstone National Park Tuff (from the Italian tufo and pronounced tuf) is a type of rock consisting of consolidated volcanic ash ejected from vents during a volcanic eruption. ... The rocky side of a mountain creek near Orosí, Costa Rica. ... Minerals are natural compounds formed through geological processes. ... A millimetre (American spelling: millimeter), symbol mm is an SI unit of length that is equal to one thousandth of a metre. ... Volcano 1. ... Magma is molten rock located beneath the surface of the Earth (or any other rocky planet), and which often collects in a magma chamber. ... Magma is molten rock located beneath the surface of the Earth (or any other rocky planet), and which often collects in a magma chamber. ... The Gay Head cliffs in Marthas Vineyard are made almost entirely of clay. ... For other uses, see Sand (disambiguation). ...


The plume that is often seen above an erupting volcano is composed primarily of ash and steam. The very fine particles may be carried for many miles, settling out as a dust-like layer across the landscape. This is known as an "ash fall". The term for any material explosively thrown out from a vent is tephra or pyroclastic debris. If liquid magma is ejected as a spray, the particles will solidify in the air to small fragments of volcanic glass. Tephra particles of gravel size are termed cinders. Tephra refers to air-fall material produced by a volcanic eruption regardless of composition or fragment size. ... Pyroclastic rocks are formed from lavas which are ejected into the air, as occur in pyroclastic flows or Plinian eruptions. ... Magma is molten rock located beneath the surface of the Earth (or any other rocky planet), and which often collects in a magma chamber. ... Gravel being unloaded from a barge Gravel is rock that is of a certain grain size range. ... Cinders are nut-sized pieces of red or black rock fragments resulting from the ejection of liquid lava that are uncemented vitric, vesicular, pyroclastic material, more than 2. ...


The ejection of large quantities of ash will produce an ash cone. A layer of volcanic ash tends to become cemented together to form a solid rock called "tuff". Puu Oo, a cinder-and-spatter cone on Kilauea, Hawaii Volcanic cones are among the simplest volcano formations. ... Welded tuff at Golden Gate in Yellowstone National Park Tuff (from the Italian tufo and pronounced tuf) is a type of rock consisting of consolidated volcanic ash ejected from vents during a volcanic eruption. ...

Contents

Characteristics

Volcanic ash sample
Volcanic ash sample

Unlike the ash that forms from burning wood or other combustible materials, volcanic ash is hard and abrasive, rather than soft and fluffy. It does not dissolve in water, and it conducts electricity, especially when it is wet. During a severe ash fall, the sky may seem hazy or yellow, and light may fade altogether. The approaching ash cloud may appear to be a weather cloud: lightning and thunder are often present. The air often smells of sulfur. Volcanic ash Source: US Government File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Volcanic ash Source: US Government File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Combustion or burning is a complex sequence of chemical reactions between a fuel and an oxidant accompanied by the production of heat or both heat and light in the form of either a glow or flames. ... General Name, Symbol, Number sulfur, S, 16 Chemical series nonmetals Group, Period, Block 16, 3, p Appearance lemon yellow Atomic mass 32. ...


Dangers

Volcanic ash is not poisonous, but inhaling it may cause problems for people whose respiratory system is already compromised by disorders such as asthma or emphysema. The abrasive texture can cause irritation and scratching of the surface of the eyes. People who wear contact lenses should wear glasses if they are experiencing an ash event. Furthermore, the combination of volcanic ash with the moisture in the lungs may create a substance akin to liquid cement. People should also take caution to filter the air they breathe with a damp cloth or a face mask when facing an ash event. A pair of contact lenses when not inserted in the eye. ... This article does not cite its references or sources. ...


The most devastating effect of volcanic ash comes from pyroclastic flows. These occur when a volcanic eruption creates an "avalanche" of hot ash, gases, and rocks that flow at high speed down the flanks of the volcano. These flows can be impossible to outrun. In 1902, the city of St. Pierre in Martinique was destroyed by a pyroclastic flow which killed over 29,000 people. Pyroclastic flows sweep down the flanks of Mayon Volcano, Philippines, in 1984 Pyroclastic flows are a common and devastating result of some volcanic eruptions. ... 1902 (MCMII) was a common year starting on Wednesday (see link for calendar). ...


Ash and aviation

Tephra or Volcanic ash jams machinery. This poses a great danger to aircraft flying near ash clouds. There are many instances of damage to jet aircraft as a result of an ash encounter. Engines may quit, and fuel and water systems may become fouled, requiring repair. After the Galunggung, Indonesia volcanic event in 1982, a British Airways Boeing 747 flew through an ash cloud that fouled all 4 engines, stopping them. The plane descended from 11,000 metres to only 3,500 metres before the crew could manage to restart the engines. An Airbus A380, currently the worlds largest airliner An aircraft is any vehicle or craft capable of atmospheric flight. ... Galunggung (Galoen-gong, Gunung Galunggung) is a stratovolcano on Java, Indonesia. ... 1982 (MCMLXXXII) was a common year starting on Friday of the Gregorian calendar. ... British Airways Flight 009, sometimes referred to as the Jakarta incident, was a scheduled flight from London Heathrow to Auckland, with stops in Bombay, Madras, Kuala Lumpur, Perth and Melbourne. ...


Increasing numbers of events like that prompted the aviation industry to meet in 1991 to decide how to best distribute information about ash events. One solution was the creation of Volcanic Ash Advisory Centers. There is one VAAC for each of 9 regions of the world. VAACs can issue advisories and serve as liaisons between meteorologists, volcanologists, and the aviation industry.


Atmospheric effects

Very fine ash particles may remain high in the atmosphere for many years, spread around the world by high-altitude winds. This suspended material contributes to often spectacular sunsets, as well as an optical phenomenon known as "Bishop's Ring". This refers to a corona or halo effect around the sun. A Bishops Ring is a diffuse brown or bluish halo observed around the sun in the presence of large amounts of dust in the stratosphere. ...


See also

Pozzolana is a fine sandy volcanic ash, originally discovered and dug at Pozzuoli in the region around Vesuvius, but later at a number of other sites. ...

External links

  • A map of the 9 VAAC regions
  • What to do during an ash fall event

 
 

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