A supervolcano is any volcano capable of producing a volcanic eruption with an ejecta volume greater than 1,000 km3 (240 cu mi). This is thousands of times larger than normal volcanic eruptions. Supervolcanoes can occur when magma in the mantle rises into the crust from a hotspot but is unable to break through the crust, and pressure builds in a large and growing magma pool until the crust is unable to contain the pressure (this is the case for the Yellowstone Caldera). They can also form at convergent plate boundaries (for example, Toba).
Although there are only a handful of Quaternary supervolcanoes, supervolcanic eruptions typically cover huge areas with lava and volcanic ash and cause a long-lasting change to weather (such as the triggering of a small ice age) sufficient to threaten species with extinction.
The origin of the term "supervolcano" is linked to an early 20th-century scientific debate about the geological history and features of the Three Sisters volcanic region of Oregon, United States. In 1925, Edwin T. Hodge suggested that a very large volcano, which he named Mount Multnomah, had existed in that region. He believed that several peaks in the Three Sisters area are the remnants left after Mount Multnomah had been largely destroyed by violent volcanic explosions, similar to Mount Mazama. In 1948, the possible existence of Mount Multnomah was ignored by volcanologist Howel Williams in his book The Ancient Volcanoes of Oregon. The book was reviewed in 1949 by another volcano scientist, F. M. Byers Jr. In the review, Byers refers to Mount Multnomah as a supervolcano. Although Hodge's suggestion that Mount Multnomah is a supervolcano was rejected long ago, the term "supervolcano" was popularised by the BBC popular science television program Horizon in 2000 to refer to eruptions that produce extremely large amounts of ejecta.
Volcanologists and geologists do not refer to "supervolcanoes" in their scientific work, since this is a blanket term that can be applied to a number of different geological conditions. Since 2000, however, the term has been used by professionals when presenting to the public. The term megacaldera is sometimes used for caldera supervolcanoes, such as the Blake River Megacaldera Complex in the Abitibi greenstone belt of Ontario and Quebec, Canada. Eruptions that rate VEI 8 are termed "super eruptions".
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: large igneous provinces and massive eruptions.
Large igneous provinces
Large igneous provinces (LIP) such as Iceland, the Siberian Traps, Deccan Traps, and the Ontong Java Plateau are extensive regions of basalts on a continental scale resulting from flood basalt eruptions. When created, these regions often occupy several thousand square kilometres and have volumes on the order of millions of cubic kilometers. In most cases, the lavas are normally laid down over several million years. They release large amounts of gases. The Réunion hotspot produced the Deccan Traps about 66 million years ago, coincident with the Cretaceous–Paleogene extinction event. The scientific consensus is that a meteor impact was the cause of the extinction event, but the volcanic activity may have caused environmental stresses on extant species up to the Cretaceous–Paleogene boundary. Additionally, the largest flood basalt event (the Siberian Traps) occurred around 250 million years ago and was coincident with the largest mass extinction in history, the Permian–Triassic extinction event, although it is also unknown whether it was completely responsible for the extinction event.
Such outpourings are not explosive though fire fountains may occur. Many volcanologists consider that Iceland may be a LIP that is currently being formed. The last major outpouring occurred in 1783–84 from the Laki fissure which is approximately 40 km (25 mi) long. An estimated 14 km3 (3.4 cu mi) of basaltic lava was poured out during the eruption.
Massive explosive eruptions
Volcanic eruptions are classified using the Volcanic Explosivity Index, or VEI.
VEI – 8 eruptions are colossal events that throw out at least 1,000 km3 (240 cu mi) Dense Rock Equivalent (DRE) of ejecta.
VEI – 7 events eject at least 100 cubic kilometres (24 cu mi) DRE.
VEI – 7 or 8 eruptions are so powerful that they often form circular calderas rather than cones because the downward withdrawal of magma causes the overlying mass to collapse and fill the void magma chamber beneath.
One of the classic calderas is at Glen Coe in the Grampian Mountains of Scotland. First described by Clough et al. (1909) its geology and volcanic succession have recently been re-analysed in the light of new discoveries. There is an accompanying 1:25000 solid geology map.
By way of comparison, the 1980 Mount St. Helens eruption was a VEI-5 with 1.2 km3 of ejecta.
Both Mount Pinatubo in 1991 and Krakatoa in 1883 were VEI-6 with 10 and 25 km3 (2.4 and 6.0 cu mi) DRE, respectively. The death toll recorded by the Dutch authorities in 1883 was 36,417, although some sources put the estimate at more than 120,000 deaths.
|Name||Zone||Location||Notes||Years ago (approx.)||Ejecta volume (approx.)||Reference|
|La Garita Caldera||USA, Colorado||Source of the Fish Canyon Tuff||27,800,000||5,000 km³|
|Lake Toba||Lake Toba||Indonesia / Sumatra||The disputed Toba catastrophe theory (if true, could have eradicated 60% of human population)||74,000||2,800 km³|||
|Huckleberry Ridge eruption||Yellowstone Hotspot||USA, Idaho / Wyoming||Huckleberry Ridge Tuff||2,100,000||2,500 km³|||
|Atana Ignimbrite||Pacana Caldera||Chile, Northern||4,000,000||2,500 km³|||
|Whakamaru||Taupo Volcanic Zone,||New Zealand, North Island||Whakamaru Ignimbrite/Mount Curl Tephra||254,000||2,000 km³|||
|Heise Volcanic Field||Yellowstone Hotspot||USA, Idaho||Kilgore Tuff||4,500,000||1,800 km³.|||
|Heise Volcanic Field||Yellowstone Hotspot||USA, Idaho||Blacktail Tuff||6,000,000||1,500 km³.|||
|Lake Taupo||Taupo Volcanic Zone||New Zealand, North Island||Oruanui eruption||26,500||1,170 km³|
|Cerro Galan||Argentina, Catamarca Province||2,500,000||1,050 km³|
|Lava Creek eruption||Yellowstone Hotspot||USA, Wyoming||Lava Creek Tuff||640,000||1,000 km³|||
VEI-7 volcanic events, less colossal but still supermassive, have occurred in the geological past. The only ones in historic times are Tambora, in 1815, Lake Taupo, Hatepe, around 180 CE, and possibly Baekdu Mountain, 969 CE ± 20 years and the Minoan eruption of Santorini.
|Name||Zone||Location||Event / notes||Years Ago (Approx.)||Ejecta Volume (Approx.)|
|Mount Tambora||Sumbawa Island, West Nusa Tenggara||Indonesia||This eruption took place in 1815 CE. The following year, 1816, became known as the Year Without a Summer.||199||160 km³|
|Baekdu Mountain||China / North Korea||969 CE Baekdu Mountain. Ejecta ±19||1,030||96 km³|
|Lake Taupo||Taupo Volcanic Zone||New Zealand, North Island||Hatepe eruption 181 CE||1,800||120 km³
|Thera||South Aegean Volcanic Arc||Santorini, Greece||Minoan eruption ca. 1610 BC||3,600||60 km³|
|Kikai Caldera||Japan, Ryukyu Islands||Kikai Caldera
|Macauley Island||Kermadec Islands||New Zealand||Macauley Island 8,300 to 6,300 years ago||6,300||100 km³
|Kurile Lake||Kamchatka Peninsula||Russia||Kurile Lake
|Aira Caldera||Japan, Kyūshū||Aira Caldera||22,000||110 km³|
|Rotoiti Ignimbrite||Taupo Volcanic Zone||New Zealand, North Island||Rotoiti Ignimbrite||50,000||240 km³
|Campi Flegrei||Italy, Naples||39,280||500 km³|
|Mount Aso||Japan, Kyūshū||Four large explosive eruptions between 300,000 to 80,000 years ago.||300,000||600 km³|
|Reporoa Caldera||Taupo Volcanic Zone||New Zealand, North Island||230,000||100 km³
|Mamaku Ignimbrite||Taupo Volcanic Zone||New Zealand, North Island||Rotorua Caldera||240,000||280 km³
|Matahina Ignimbrite||Taupo Volcanic Zone||New Zealand, North Island||Haroharo Caldera||280,000||120 km³
|Long Valley Caldera||Bishop Tuff||USA, California||760,000||600 km³|
|Valles Caldera||USA, New Mexico||Two eruptions at 1.15 and 1.47 million years ago||1,150,000
|Mangakino||Taupo Volcanic Zone||New Zealand, North Island||Three eruptions from 0.97 to 1.23 million years ago||970,000||300 km³
|Henry's Fork Caldera||Yellowstone Hotspot
Mesa Falls Tuff
|USA, Idaho||Yellowstone Hotspot||1,300,000||280 km³
|Pastos Grandes Ignimbrite||Pastos Grandes Caldera||Bolivia||2,900,000||820 km³
|Heise volcanic field||Yellowstone Hotspot
|USA, Idaho||Yellowstone Hotspot||6,400,000||750 km³
|Bruneau-Jarbidge||Yellowstone Hotspot||USA, Idaho||Yellowstone Hotspot
Responsible for the Ashfall Fossil Beds 1,600 km to the east
|Bennett Lake Volcanic Complex||Skukum Group||Canada, British Columbia/Yukon||50,000,000||850 km³
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- In 2009, the apocalypse-themed film 2012 featured the super-eruption of the massive Yellowstone Caldera, a result of the Earth's core heating up. This made most of the United States uninhabitable.
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- In December 2011, author Harry Turtledove published Supervolcano: Eruption, the first of a planned four-novel series about events leading up to and following a fictional eruption of the Yellowstone Caldera. The second book in the series, Supervolcano: All Fall Down, was published in December 2012. The third book Supervolcano: Things Fall Apart, was published in December 2013. The last volume Supervolcano: Maelstrom is scheduled for 2014.
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- Overview and Transcript of the original BBC program
- Yellowstone Supervolcano and Map of Supervolcanoes Around The World
- USGS Fact Sheet – Steam Explosions, Earthquakes, and Volcanic Eruptions – What's in Yellowstone's Future?
- Scientific American's The Secrets of Supervolcanoes
- Supervolcano eruption mystery solved, BBC Science, 6 January 2014