Explosive eruption

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Mount Saint Helens explosive eruption on July 22, 1980 MSH80 st helens eruption plume 07-22-80.jpg
Mount Saint Helens explosive eruption on July 22, 1980

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 viscous magma 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 send rocks, dust, gas and pyroclastic material up to 20 km (12 mi) into the atmosphere at a rate of up to 100,000 tonnes per second,[ citation needed ] traveling at several hundred meters per second. This cloud may then collapse, creating a fast-moving pyroclastic flow of hot volcanic matter.

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Stages of an explosive eruption

An early stage of the July 12, 2009, eruption of Sarychev volcano, seen from space Sarychev Volcano edit.jpg
An early stage of the July 12, 2009, eruption of Sarychev volcano, seen from space

An explosive eruption always begins with some form of blockage in the crater of a volcano that prevents the release of gases trapped in highly viscous andesitic or rhyolitic magma. The high viscosity of these forms of magma prevents the release of trapped gases. The pressure of the flowing magma builds until eventually the blockage is blasted out in an explosive eruption. The pressure from the magma and gases are released through the weakest point in the cone, usually the crater. However, in the case of the eruption of Mount St. Helens, pressure was released on the side of the volcano, rather than the crater. [1]

The sudden release of pressure causes the gases in the magma to suddenly froth and create volcanic ash and pumice, which is then ejected through the volcanic vent to create the signature eruption column commonly associated with explosive eruptions. The size and duration of the column depends on the volume of magma being released and how much pressure the magma was under.

Types of explosive eruptions

  1. Vulcanian eruption
  2. Peléan eruption
  3. Plinian eruption
  4. Phreatic eruption
  5. Phreatomagmatic eruption
    1. Surtseyan eruption

Pyroclastic flows

Pyroclastic flows occur towards the end of an explosive eruption, as pressure begins to decline. The eruption column of ash is supported by pressure from the gases being released, and as the gases are depleted, pressure falls and the eruption column begins to collapse. When the column collapses in on itself, ash and rock fall back down to the ground and begin to flow down the slopes of the volcano. These flows can travel at up to 80 km per hour, and reach temperatures of 200° to 700° Celsius. The high temperatures can cause combustion of any flammable materials in its path, including wood, vegetation, and buildings. When snow and ice melt as a part of an eruption, large amounts of water mixed in with the flow can create lahars. The risk of lahars is particularly high on volcanoes such as Mount Rainier near Seattle and Tacoma, Washington. [2]

Supervolcanoes

The eruptions of supervolcanoes are the rarest of volcanic eruptions but also the most destructive. The timescale between these eruptions is generally marked by hundreds or thousands of years. This type of eruption generally causes destruction on a continental scale, and can also result in the lowering of temperatures worldwide. [3]

See also

Related Research Articles

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Mount Unzen mountain in Nagasaki Prefecture, Japan

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Ejecta particles that came out of a volcanic vent

Ejecta are particles ejected from an area. In volcanology, in particular, the term refers to particles including pyroclastic materials (Tephra) that came out of a volcanic explosion and magma eruption volcanic vent, or crater, has traveled through the air or under water, and fell back on the ground surface or on the ocean floor.

Santa María (volcano) mountain

Santa María Volcano is a large active volcano in the western highlands of Guatemala, in the Quetzaltenango Department near the city of Quetzaltenango.

Soufrière Hills Volcano on Montserrat in the Caribbean

The Soufrière Hills are an active, complex stratovolcano with many lava domes forming its summit on the Caribbean island of Montserrat. Many volcanoes in the Caribbean are named Soufrière. These include La Soufrière or Soufrière Saint Vincent on the island of Saint Vincent, and La Grande Soufrière on Guadeloupe. After a long period of dormancy, the Soufrière Hills volcano became active in 1995 and has continued to erupt ever since. Its eruptions have rendered more than half of Montserrat uninhabitable, destroying the capital city, Plymouth, and causing widespread evacuations: about two thirds of the population have left the island.

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Eruption column

An eruption column or eruption plume is a cloud of super-heated ash and tephra suspended in gases emitted during an explosive volcanic eruption. The volcanic materials form a vertical column or plume that may rise many kilometers into the air above the vent of the volcano. In the most explosive eruptions, the eruption column may rise over 40 km (25 mi), penetrating the stratosphere. Stratospheric injection of aerosols by volcanoes is a major cause of short-term climate change.

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Vulcanian eruption type of volcanic eruption

A Vulcanian eruption is a type of volcanic eruption characterized by a dense cloud of ash-laden gas exploding from the crater and rising high above the peak. They usually commence with phreatomagmatic eruptions which can be extremely noisy due the rising magma heating water in the ground. This is usually followed by the explosive clearing of the vent and the eruption column is dirty grey to black as old weathered rocks are blasted out of the vent. As the vent clears, further ash clouds become grey-white and creamy in colour, with convolutions of the ash similar to those of Plinian eruptions.

Villarrica (volcano) Chilean volcano

Villarrica is one of Chile's most active volcanoes, rising above the lake and town of the same name, 750 km (470 mi) south of Santiago. It is also known as Rucapillán, a Mapuche word meaning "devil's house". It is the westernmost of three large stratovolcanoes that trend NW-SW obliquely perpendicular to the Andean chain along the Mocha-Villarrica Fault Zone, along with Quetrupillán and the Chilean portion of Lanín, are protected within Villarrica National Park. Guided ascents are popular during summer months.

Volcanic gas

Volcanic gases are gases given off by active volcanoes. These include gases trapped in cavities (vesicles) in volcanic rocks, dissolved or dissociated gases in magma and lava, or gases emanating directly from lava or indirectly through ground water heated by volcanic action.

Lascar (volcano) volcano (stratovolcano)

Lascar is a stratovolcano within the Central Volcanic Zone of the Andes, a volcanic arc that spans the countries of Peru, Bolivia, Argentina and Chile. It is the most active volcano in the region, with records of eruptions going back to 1848. It is composed of two separate cones with several summit craters. The westernmost crater of the eastern cone is presently active. Volcanic activity is characterized by constant release of volcanic gas and occasional vulcanian eruptions.

Prediction of volcanic activity

Prediction of volcanic eruption, or volcanic eruption forecasting, is an interdisciplinary monitoring and research effort to predict the time and severity of a volcano's eruption. Of particular importance is the prediction of hazardous eruptions that could lead to catastrophic loss of life, property, and disruption of human activities.

Types of volcanic eruptions Basic mechanisms of eruption and variations

Several types of volcanic eruptions—during which lava, tephra, and assorted gases are expelled from a volcanic vent or fissure—have been distinguished by volcanologists. These are often named after famous volcanoes where that type of behavior has been observed. Some volcanoes may exhibit only one characteristic type of eruption during a period of activity, while others may display an entire sequence of types all in one eruptive series.

Lava Molten rock expelled by a volcano during an eruption

Lava is molten rock generated by geothermal energy and expelled through fractures in planetary crust or in an eruption, usually at temperatures from 700 to 1,200 °C. The structures resulting from subsequent solidification and cooling are also sometimes described as lava. The molten rock is formed in the interior of some planets, including Earth, and some of their satellites, though such material located below the crust is referred to by other terms.

Taupo Volcano Caldera Volcano in New Zealand

Lake Taupo, in the centre of New Zealand’s North Island, is the caldera of a large rhyolitic supervolcano called the Taupo Volcano. This huge volcano has produced two of the world’s most violent eruptions in geologically recent times.

Ubinas volcano in Peru

Ubinas is a stratovolcano in the Moquegua Region of southern Peru, 60 kilometres (37 mi) east of the city of Arequipa. Part of the Central Volcanic Zone of the Andes, it is 5,672 metres (18,609 ft) above sea level. The volcano's summit is cut by a 1.4-kilometre (0.87 mi) wide and 150-metre (490 ft) deep caldera, which itself contains a smaller crater. Below the summit, Ubinas has the shape of an upwards-steepening cone with a prominent notch on the southern side. The gently sloping lower part of the volcano is also known as Ubinas I and the steeper upper part as Ubinas II; they represent different stages in the geologic history of Ubinas.

References

  1. Skinner, Brian J. (2004). Dynamic Earth: An Introduction to Physical Geology. John Wiley & Sons. Inc. Hoboken, NJ. ISBN   978-0-471-15228-6.
  2. http://volcanoes.usgs.gov/hazards/pyroclasticflow/index.php
  3. Oppenheimer, C. (2011): Eruptions that shook the world. Cambridge University Press. ISBN   978-0-521-64112-8