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Explosive eruption

Mount St. Helens explosive eruption on July 22, 1980 Eruption of Mount Pinatubo in the Philippines on June 12, 1991 (PST). Its ash would spread as far west as mainland South Eas...

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Mount St. Helens explosive eruption on July 22, 1980
Eruption of Mount Pinatubo in the Philippines on June 12, 1991 (PST). Its ash would spread as far west as mainland South East Asia.

In volcanology, an explosive eruption is a volcanic eruption of the most violent type. A notable example is the 1980 eruption of Mount St. Helens. Such eruptions result when sufficient gas has dissolved under pressure within a viscousmagma such that expelled lava violently froths into volcanic ash when pressure is suddenly lowered at the vent. Sometimes a lava plug will block the conduit to the summit, and when this occurs, eruptions are more violent. Explosive eruptions can expel as much as 1,000 kg (2,200 lb) per second[1] of rocks, dust, gas and pyroclastic material, averaged over the duration of eruption, that travels at several hundred meters per second as high as 20 km (12 mi) into the atmosphere. This cloud may subsequently collapse, creating a fast-moving pyroclastic flow of hot volcanic matter.

Physics

An early stage of the July 12, 2009, eruption of Sarychev volcano, seen from space

Viscous magmas cool beneath the surface before they erupt. As they do this, bubbles exsolve from the magma. Because the magma is viscous, the bubbles remain trapped in the magma.[2] As the magma nears the surface, the bubbles and thus the magma increase in volume. The pressure of the magma builds until the blockage is blasted out in an explosive eruption through the weakest point in the cone, usually the crater. (However, in the case of the eruption of Mount St. Helens, the pressure was released on the side of the volcano, rather than the crater.[3]). The release of pressure causes more gas to exsolve, doing so explosively. The gas may expand at hundreds of metres per second, expanding upward and outward. As the eruption progresses, a chain reaction causes the magma to be ejected at higher and higher speeds.[2]

Volcanic ash formation

The violently expanding gas disperses and breaks up magma, forming an mixture of gas and magma called volcanic ash. The cooling of the gas in the ash as it expands chills the magma fragments, often forming tiny glass shards recognisable as portions of the walls of former liquid bubbles. In more fluid magmas the bubble walls may have time to reform into spherical liquid droplets. The final state of the emulsions depends strongly on the ratio of liquid to gas. Gas-poor magmas end up cooling into rocks with small cavities, becoming vesicular lava. Gas-rich magmas cool to form rocks with cavities that nearly touch, with an average density less than that of water, forming pumice. Meanwhile, other material can be accelerated with the gas, becoming volcanic bombs. These can travel with so much energy that large ones can create craters when they hit the ground.[2]

Pyroclastic flows

Kanlaon erupted on December 9, 2024, releasing a plume of volcanic ash and pyroclastic flow that reached 4,000 metres (13,000 feet)

When an emulsion of volcanic gas and magma falls back to the ground, it can create a density current called a pyroclastic flow. The emulsion is somewhat fluidised by the gas, allowing it to spread. These can often climb over obstacles, and devastate human life.[2] Earthly pyroclastic flows can travel at up to 80 km (50 mi) per hour and reach temperatures of 200 to 700 °C (392 to 1,292 °F). The high temperatures can burn flammable materials in the flow's path, including wood, vegetation, and buildings. Alternately, when an eruption has contact with snow, crater lakes, or wet soil in large amounts, water mixing into the flow can create lahars,[4] which pose significant known risks worldwide.

Types

  1. Vulcanian eruption
  2. Peléan eruption
  3. Plinian eruption

Other mechanisms

An explosive eruption is usually triggered by exsolution of volatiles but there are other ways to create an explosive eruption.

Phreatic eruption

Una erupción freática puede ocurrir cuando se despresuriza agua caliente a presión. La despresurización reduce el punto de ebullición del agua, por lo que al despresurizarse, el agua hierve repentinamente. [ 5 ] También puede ocurrir cuando el agua subterránea se calienta repentinamente, convirtiéndose en vapor de forma repentina. [ 6 ] Cuando el agua se convierte en vapor, se expande a velocidades supersónicas, hasta 1700 veces su volumen original. Esto puede ser suficiente para fracturar roca sólida y lanzar fragmentos de roca a cientos de metros. [ 7 ]

Una erupción freatomagmática contiene material magmático, a diferencia de una erupción freática que no lo contiene. [ 8 ]

Hidratos de clatrato

Un mecanismo para el criovolcanismo explosivo es el contacto del criomagma con hidratos de clatrato . Los hidratos de clatrato, si se exponen a temperaturas cálidas, se descomponen fácilmente. Un artículo de 1982 señaló la posibilidad de que la producción de gas a presión tras la desestabilización de los hidratos de clatrato al entrar en contacto con magma caliente ascendente pudiera producir una explosión que rompiera la superficie, dando lugar a criovolcanismo explosivo. [ 9 ]

Vapor de agua en el vacío

Si una fractura alcanza la superficie de un cuerpo helado y la columna de agua ascendente queda expuesta al casi vacío de la superficie de la mayoría de los cuerpos helados, comenzará a hervir inmediatamente, ya que su presión de vapor es mucho mayor que la presión ambiente. Además, cualquier sustancia volátil presente en el agua se disolverá. La combinación de estos procesos liberará gotas y vapor, que pueden ascender por la fractura, creando una columna de agua. Se cree que esto es parcialmente responsable de las columnas de hielo de Encélado . [ 9 ]

Véase también

Referencias

  1. ↑ Mason, Ben G.; Pyle, David M.; Oppenheimer, Clive (1 de diciembre de 2004). "El tamaño y la frecuencia de las erupciones explosivas más grandes de la Tierra" . Boletín de Vulcanología . 66 (8): 735– 748. Bibcode : 2004BVol...66..735M . doi : 10.1007/s00445-004-0355-9 . ISSN 1432-0819 . S2CID 129680497 .  
  2. 1 2 3 4 "Volcanes" (PDF) .
  3. ↑ Skinner, Brian J. (2004). Dynamic Earth: An Introduction to Physical Geology . John Wiley & Sons. Inc. Hoboken, NJ. ISBN 978-0-471-15228-6.
  4. ↑ "Los flujos piroclásticos se mueven rápidamente y destruyen todo a su paso" .
  5. ↑"Dangerous water vapor: phreatic eruptions".
  6. ↑"VHP Photo Glossary: Phreatic eruption". Volcano Hazards Program. U.S. Geological Survey. Retrieved 13 November 2010.
  7. ↑Cronin, Shane (December 9, 2019). "Steam-driven volcanic eruptions difficult to predict, still poorly understood".
  8. ↑"Phreatomagmatic Eruption as Explained to Kids". January 14, 2020.
  9. 12Fagent, Sarah A.; Lopes, Rosaly M.C.; Quick, Lynnae C.; Gregg, Tracy K.P. "Chapter 5 Cryovolcanism"(PDF).
  • "Recent Developments in Explosive Volcanism". Commission on Explosive Volcanism (CEV). Archived from the original on 21 July 2011. Retrieved 17 May 2010.
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