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Volcanic Explosivity

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Brittany
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« Reply #15 on: April 26, 2007, 01:52:24 am »



Mt. Kazbek in Georgia, a dormant stratovolcano in the Caucasus
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Brittany
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« Reply #16 on: April 26, 2007, 01:53:47 am »



Popocatépetl, an active stratovolcano in Mexico
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Brittany
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« Reply #17 on: April 26, 2007, 01:55:51 am »

Supervolcano

A supervolcano refers to a volcano that produces the largest and most voluminous kinds of eruption on Earth. The actual explosivity of these eruptions varies, but the sheer volume of ejected tephra is enough to radically alter the landscape and severely impact global climate for years, with a cataclysmic effect on life (see also volcanic winter).

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Brittany
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« Reply #18 on: April 26, 2007, 01:59:21 am »

Word origin

The term was originally coined by the producers of the BBC popular science program, Horizon, in 2000 to refer to these types of eruption. That investigation brought the subject more into the public eye, leading to further studies of the possible effects.
•   At first, supervolcano was not a technical term used in volcanology, but more recently, in 2003 and 2004, the term has been used in articles.
•   Though there is no well-defined minimum explosive size for a "supervolcano", there are at least two types of volcanic eruption that have been identified as supervolcanoes: massive eruptions and large igneous provinces.


Large igneous provinces

A large igneous province (LIP) is an extensive region of basalts on a continental scale, resulting from flood basalt eruptions. When created, these regions often occupy several million km² and have volumes on the order of 1 million km³. In most cases, the majority of this is laid down over an extended but geologically sudden period of about several million years.

Massive eruptions

Eruptions with a Volcanic Explosivity Index of 8 (VEI-8) are mega-colossal events that eject at least 1000 km³ of pyroclastic material.
VEI-8 eruptions are so powerful that they form circular calderas rather than mountains because the downward collapse of land at the eruption site fills emptied space in the magma chamber beneath. The caldera can remain for millions of years after all volcanic activity at the site has ceased.
Known eruptions
 
VEI-8 volcanic events have included eruptions at the following locations. Estimates of the volume of erupted material are given in parentheses.
•   Lake Taupo, North Island, New Zealand - Oruanui eruption 26,500 years ago (1,170 km³)
•   Lake Toba, Sumatra, Indonesia - 75,000 years ago (2,800 km³)
•   Yellowstone Caldera, Wyoming, United States - 2.2 million years ago (2,500 km³) and 640,000 years ago (1,000 km³)
•   La Garita Caldera, Colorado, United States - Source of the truly enormous eruption of the Fish Canyon Tuff 27.8 million years ago (~5,000 km³)
The Lake Toba eruption plunged the Earth into a volcanic winter, eradicating an estimated 60%[1] [2] [3] [4] [5]of the human population, and was responsible for the formation of sulfuric acid in the atmosphere.
Many other supermassive eruptions have also occurred in the geological past. Those listed below measured 7 on the VEI scale. Most of these were larger than Tambora's eruption in 1815, which was the largest eruption in recorded history.
•   Aira Caldera, Kyūshū, Japan - 22,000 years ago (110 km³)
•   Aso, Kyūshū, Japan - four large explosive eruptions between 300,000 to 80,000 years ago (Total volume 600 km³)
•   Kikai Caldera, Ryukyu Islands, Japan - 6,300 years ago (150 km³ (bulk volume))
•   Lake Taupo, North Island, New Zealand - 181 AD (100 km³)
•   Long Valley Caldera, California, United States - 760,000 years ago (600 km³)
•   Valle Grande, New Mexico, United States - 1.12 million years ago (~600 km³)
•   Yellowstone Caldera, Wyoming, United States - 1.3 million years ago (280 km³)
•   Bruneau-Jarbidge, Idaho, United States - 10-12 million years ago (>250 km³) (responsible for the Ashfall Fossil Beds 1,600 km to the east[6])
•   Campi Flegrei, Naples, Italy - 12,000 years ago (Could be as much as 300 km³)


Media portrayal


A two-part television docudrama entitled Supervolcano was shown on BBC, the Discovery Channel, and other television networks worldwide. It looked at the events that could take place if the Yellowstone supervolcano erupted. It featured footage of volcano eruptions from around the world and computer-generated imagery depicting the event. According to the program, such an eruption would have devastating effect across the globe and would cover virtually all of the United States with at least 1 cm of volcanic ash, causing mass destruction in the nearby vicinity and killing plants and wildlife across the continent. The dramatic elements in the program were followed by Supervolcano: The Truth About Yellowstone, a documentary about the evidence behind the movie. The program had originally been scheduled to be aired in early 2005, but it was felt that this would be insensitive so soon after the 2004 Indian Ocean earthquake. The program and its accompanying documentaries were released on DVD region 2 simultaneously with its broadcast.
A National Geographic documentary called Earth Shocks portrayed the destructive impact of the rapid eruption of Lake Toba some 75,000 years ago, which caused a phenomenon known as the Millennial Ice Age that lasted for 1000 years and wiped out more than 60%[7] [8] [9] [10] [11] of the global population of the time. An eruption of the Yellowstone supervolcano was originally one of the scenarios depicted in the docu-drama End Day, but was excluded from all airings to date for unknown reasons and is only presently mentioned at the show's BBC website.
In the Stargate Atlantis episode Inferno, the main characters are caught in the eruption of a supervolcano and escape using an Ancient Warship.

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« Reply #19 on: April 26, 2007, 02:00:48 am »

Large igneous province

"Large Igneous provinces" (LIPS) were originally defined by Coffin and Eldholm (1994) as areas of Earth's surface that contain large volumes of magmatic rocks (typically basalt but including rhyolites) erupted over extremely short time intervals of a few million years or less. These provinces are not associated with normal plate tectonic magmatism, ie, mid-ocean ridges and island arcs. LIPS include continental flood basalts, oceanic plateaux, large dike swarms (the eroded roots of a volcanic province), and volcanic rifted margins, recognized by the presence of dike swarms and "seaward dipping reflectors" -- seismically imaged tabular features buried deep beneath sediment that lie parallel to a passive continental margin along the continental slope, and interpreted to represent lava flows or sills that formed during rifting of the continent). Most LIPS consist of basalt, but some contain large volumes of associated rhyolite; the rhyolite is typically very dry compared to island arc rhyolites, with much higher eruption temperatures (850º to 1000º C) than normal rhyolites.

When created, LIPS often occupy a few million km2 and have volumes on the order of 1 million km3. In most cases, the majority of a LIP's volume is emplaced in less than 1 million years. One of the conundrums of LIPS origins is to understand how enormous volumes of basaltic magma are formed and erupted over such short time scales, with effusion rates up to an order of magnitude greater than mid-ocean ridge basalts.
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« Reply #20 on: April 26, 2007, 02:02:58 am »

Submarine volcano




Pillow lava formed by a submarine volcano

Submarine volcanoes are underwater fissures in the earth's surface from which magma can erupt. They estimated to account for 75% of annual magma output. The vast majority are located near areas of tectonic plate movement, known as mid-ocean ridges. Although most are located in the depths of oceans, some also exist in shallow water, which can spew material into the air during an eruption. Hydrothermal vents, sites of abundant biological activity, are commonly found near submarine volcanoes.

The presence of water can greatly alter the characteristics of a volcanic eruption. For instance, the increased thermal conductivity of water causes magma to turn into glass much more quickly than in a terrestrial eruption. Additionally, the pressure underwater can reach over 250 times standard pressure. This greatly diminishes explosive boiling, the reaction between magma and seawater. This reduction of explosive capacity, along with the increased distance from hydrophones, makes deep-sea volcanoes difficult to detect.

The lava formed by submarine volcanoes is quite different from terrestrial lava. Upon contact with water, a solid crust forms around the lava. Advancing lava flows into this crust, forming what is known as pillow lava.

Scientists still have much to learn about the location and activity of underwater volcanoes. The Kolumbo underwater volcano in the Aegean Sea was discovered in 1650 when it burst from the sea and erupted, killing 70 people on the nearby island of Santorini. More recently, NOAA's Office of Ocean Exploration has funded missions to explore submarine volcanoes. Most notably, these have been the Ring of Fire missions to the Mariana Arc in the Pacific Ocean. Using Remote Operated Vehicles, scientists studied underwater eruptions, ponds of molten sulfur, black smoker chimneys and even marine life adapted to this deep, hot environment.

http://en.wikipedia.org/wiki/Volcanic_eruptions
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