FACTOID # 28: Austin, Texas has more people than Alaska.
 
 Home   Encyclopedia   Statistics   States A-Z   Flags   Maps   FAQ   About 
   
 
WHAT'S NEW
 

SEARCH ALL

FACTS & STATISTICS    Advanced view

Search encyclopedia, statistics and forums:

 

 

(* = Graphable)

 

 


Encyclopedia > Pyroclastic flow
Pyroclastic flows sweep down the flanks of Mayon Volcano, Philippines, in 1984
Pyroclastic flows sweep down the flanks of Mayon Volcano, Philippines, in 1984

A pyroclastic flow (also known as a pyroclastic density current) is a common and devastating result of some volcanic eruptions. The flows are fast-moving currents of hot gas, and rock (collectively known as tefra), which can travel away from the volcano at up to 700 km/h. The gas can reach temperatures of up to 1,000 degrees Celsius. The flows normally hug the ground and travel downhill, or spread laterally under gravity. Their speed depends upon the density of the current, the rate volcanic output, and the gradient of the slope. Image File history File links Pyroclastic flows at Mayon Volcano, Philippines, 1984. ... Image File history File links Pyroclastic flows at Mayon Volcano, Philippines, 1984. ... Mayon Volcano is an active volcano in the Philippines on the island of Luzon, in the province of Albay in the Bicol Region. ... Cleveland Volcano in the Aleutian Islands of Alaska photographed from the International Space Station For other uses, see Volcano (disambiguation). ... Tephra, as a generic term, refers to air-fall material produced by a volcanic eruption - regardless of composition or fragment size. ...

Contents

Naming issues

The word pyroclast is derived from the Greek πυρος, meaning fire, and κλαστός, meaning broken. An old name for small pyroclastic flows was nuée ardente (French for "burning cloud"); this was first used to describe the disastrous 1902 eruption of Mount Pelée on Martinique.[1] These pyroclastic flows glowed red in the dark. Not to be confused with the similarly named volcano on Io. ...


Pyroclastic flows that contain a much higher proportion of gas to rock are known as 'fully dilute pyroclastic density currents' or pyroclastic surges. The lower density sometimes allows them to flow over higher topographic features such as ridges and hills. They may also be "cold," containing steam, water and rock at less than 250 degrees Celsius. Cold pyroclastic surges can occur when the eruption is from a vent under a shallow lake or the sea. Fronts of some pyroclastic density currents are fully dilute, for example during the eruption of Mount Pelée in 1902 a fully dilute current overwhelmed the city of Saint-Pierre and killed nearly 30,000 people. This article does not adequately cite its references or sources. ... Not to be confused with the similarly named volcano on Io. ... Saint-Pierre was the former capital of Frances Caribbean département doutre-mer of Martinique. ...


A pyroclastic flow is a type of gravity current; in scientific literature they are sometimes abbreviated to PDC (pyroclastic density current). In fluid dynamics, a gravity current is a primarily horizontal flow in a gravitational field that is driven by a density difference. ...


Causes

There are several scenarios which can produce a pyroclastic flow:

  • Fountaining of an eruption column from a plinian eruption (e.g., Mount Vesuvius's destruction of Pompeii, see Pliny the Younger). In such an eruption, the material ejected from the vent heats the surrounding air and the turbulent mixture rises for many kilometres through convection. If the erupted jet is unable to heat the surrounding air sufficiently, there will not be enough convection to carry the plume upwards and it fountains back down the flanks of the volcano.
  • Frothing at the mouth of the vent during degassing of the erupted lava at the mouth. This can lead to the production of a type of igneous rock called ignimbrite. This occurred during the eruption of Mount Katmai in 1912 which produced the largest flows to be generated during recorded history.
  • The directional blast (or jet) when part of a volcano explodes or collapses (e.g. the May 18, 1980 eruption of Mount St. Helens) This rapidly transforms into a gravity driven current with distance from the volcano.

Eruption column over Mount Pinatubo in the Philippines An eruption column consists of hot volcanic ash emitted during an explosive volcanic eruption. ... Eruption of Vesuvius in 1822. ... This article is about the mountain in Italy. ... For other uses, see Pompeii (disambiguation). ... Gayus Plinius Colonoscopy Caecilius Secundus (63 - ca. ... Volcanic rock in North America Plutonic rock in North America Igneous rocks (etymology from Latin ignis, fire) are rocks formed by solidification of cooled magma (molten rock), with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. ... Ignimbrite is a volcanic pyroclastic rock, often of dacitic or rhyolitic composition. ... This article is about Katmai, the volcano. ... One of the Mono Craters, an example of a rhyolite dome. ... The Soufriere Hills volcano is a complex stratovolcano with many lava domes forming its summit on the Caribbean island of Montserrat. ... is the 138th day of the year (139th in leap years) in the Gregorian calendar. ... The 1980 eruption of Mount St. ...

Size and effects

Volumes range from a few hundred cubic meters to more than a thousand cubic kilometers, and the larger ones can travel for hundreds of kilometres although none on that scale have occurred for several hundred thousand years. Most pyroclastic flows are around one to ten cubic kilometres and travel for several kilometres. Flows usually consist of two parts: the basal flow hugs the ground and contains larger, coarse boulders and rock fragments, while an ash plume lofts above it because of the turbulence between the flow and the overlying air, admixes and heats cold atmospheric air causing expansion and convection.


While moving, the kinetic energy of the boulders will flatten trees and buildings in their path. The hot gases and high speed make them particularly lethal. For example, the towns of Pompeii and Herculaneum in Italy were famously engulfed by pyroclastic flows in 79 AD with heavy loss of life. A pyroclastic flow killed couple Katia and Maurice Krafft, French volcanologists on Mount Unzen, in Japan, on June 3, 1991, and in June 1997 flows killed twenty people on the Caribbean island of Montserrat. The cars of a roller coaster reach their maximum kinetic energy when at the bottom of their path. ... For other uses, see Pompeii (disambiguation). ... Herculaneum (in modern Italian Ercolano) is an ancient Roman town, located in the territory of the current commune of Ercolano. ... Katia Krafft (17 April 1942 – 3 June 1991) and her husband, Maurice Krafft ( 25 March 1946 – 3 June 1991) were French vulcanologists who died in a pyroclastic flow on Mt Unzen, in Japan, on June 3, 1991. ... Volcanology (also spelled vulcanology) is the study of volcanoes, lava, magma, and related geological phenomena. ... Mount Unzen (雲仙岳) is an active volcano near the city of Shimabara in Nagasaki Prefecture on the island of Kyushu in Japan. ... is the 154th day of the year (155th in leap years) in the Gregorian calendar. ... Year 1991 (MCMXCI) was a common year starting on Tuesday (link will display the 1991 Gregorian calendar). ... West Indies redirects here. ...


References

  1. ^ Lacroix, A. (1904) La Montagne Pelée et ses Eruptions, Paris, Masson (in French)

See also

Wikimedia Commons has media related to:
Pyroclastic flow

Image File history File links Commons-logo. ... This article does not adequately cite its references or sources. ... Pyroclastic rocks or pyroclastics (derived from the Greek πῦρ, meaning fire, and κλαστός, meaning broken) are debris thrown from volcanoes during an eruption. ... Lahar from a March 1982 eruption of Mount St. ...

External links


  Results from FactBites:
 
Pyroclastic flow - Wikipedia, the free encyclopedia (637 words)
Pyroclastic flows are a common and devastating result of some volcanic eruptions.
Flows containing a high proportion of gas to rock are known as pyroclastic surges.
A pyroclastic flow is a type of gravity current; in scientific literature they are sometimes abbreviated to PDC (pyroclastic density current).
Wikipedia: Pyroclastic flow (592 words)
Another name for a pyroclastic flow is a nuée ardente (French for "fiery cloud"), which was first used to describe the 1902 Martinique eruption.
Hot pyroclastic surges may form ahead of flows, for example during the eruption of Mount Pelee in 1902 a surge overwhelmed the city of Saint-Pierre and killed nearly 30,000 people.
A pyroclastic flow is a type of gravity current; in scientific literature they are sometimes abbreviated to PDC - pyroclastic density current.
  More results at FactBites »

 
 

COMMENTARY     


Share your thoughts, questions and commentary here
Your name
Your comments

Want to know more?
Search encyclopedia, statistics and forums:

 


Press Releases |  Feeds | Contact
The Wikipedia article included on this page is licensed under the GFDL.
Images may be subject to relevant owners' copyright.
All other elements are (c) copyright NationMaster.com 2003-5. All Rights Reserved.
Usage implies agreement with terms, 1022, m