A supervolcano is a large volcano that has had an eruption with a Volcanic Explosivity Index (VEI) of 8, the largest recorded value on the index. This means the volume of deposits for that eruption is greater than 1,000 cubic kilometers (240 cubic miles).
Supervolcanoes occur when magma in the mantle rises into the crust but is unable to break through it and pressure builds in a large and growing magma pool until the crust is unable to contain the pressure. This can occur at hotspots (for example, Yellowstone Caldera) or at subduction zones (for example, Toba).
Large-volume supervolcanic eruptions are also often associated with large igneous provinces, which can cover huge areas with lava and volcanic ash. These can cause long-lasting climate change (such as the triggering of a small ice age) and threaten species with extinction. The Oruanui eruption of New Zealand's Taupo Volcano (about 26,500 years ago) was the world's most recent VEI-8 eruption.
The term "supervolcano" was first used in a volcanic context in 1949.[note 1]
Its origins lie in an early 20th-century scientific debate about the geological history and features of the Three Sisters volcanic region of Oregon in the United States. In 1925, Edwin T. Hodge suggested that a very large volcano, which he named Mount Multnomah, had existed in that region.[note 2] He believed that several peaks in the Three Sisters area were the remnants of Mount Multnomah after it 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. This book was reviewed in 1949 by another volcanologist, F. M. Byers Jr. In the review, Byers refers to Mount Multnomah as a supervolcano.
More than fifty years after Byers' review was published, the term supervolcano was popularised by the BBC popular science television program Horizon in 2000, referring to eruptions that produce extremely large amounts of ejecta.
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 eruptions that have been identified as supervolcanoes: large igneous provinces and massive eruptions.
Main article: Large igneous province
Large igneous provinces, 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 unknown whether it was solely responsible for the extinction event.
Such outpourings are not explosive, though lava fountains may occur. Many volcanologists consider Iceland to be a large igneous province 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 (VEI 4).
The Ontong Java Plateau has an area of about 2,000,000 km2 (770,000 sq mi), and the province was at least 50% larger before the Manihiki and Hikurangi Plateaus broke away.
See also: List of largest volcanic eruptions
Volcanic eruptions are classified using the Volcanic Explosivity Index, or VEI. It is a logarithmic scale, which means that an increase of one in VEI number is equivalent to a tenfold increase in volume of erupted material. VEI 7 or VEI 8 eruptions are so powerful that they often form circular calderas rather than cones because the downward withdrawal of magma causes the overlying rock mass to collapse into the empty magma chamber beneath it.
Based on incomplete statistics, at least 60 VEI 8 eruptions have been identified. Below is a list of well-known super-eruptions.
|Name||Zone||Location||Notes||Years ago (approx.)||Ejecta bulk volume (approx.)||Reference|
|Youngest Toba eruption||Toba Caldera Complex, North Sumatra||Sumatra, Indonesia||Produced 2200–4400 million tons of H2SO4||75,000||2,000–13,200 km3|||
|Flat Landing Brook Formation||Tetagouche Group||New Brunswick, Canada||Possibly the largest known supereruption. Existence as a single eruption is controversial, and it could have been a multiple 2,000+ km³ event that spanned less than a million years.||466,000,000||2,000–12,000 km3|||
|Wah Wah Springs||Indian Peak–Caliente Caldera Complex||Utah, United States||The largest of the Indian Peak-Caliente Caldera Complex eruptions, preserved as the Wah Wah Springs Tuff; includes pyroclastic flows more than 4,000 meters (13,000 ft) thick.||30,600,000||5,500–5,900 km3|||
|La Garita Caldera||San Juan volcanic field||Colorado, United States||Fish Canyon eruption||27,800,000||5,000 km3|||
|Grey's landing Supereruption||Yellowstone hotspot||United States of America||Deposited the Grey's landing Ignimbite||8,720,000||2,800 km3|||
|La Pacana||Andes Central Volcanic Zone||Chile||Responsible for the Antana Ignimbrite||4,000,000||2,500 km3|||
|Huckleberry Ridge eruption||Yellowstone hotspot||Idaho, United States||Huckleberry Ridge Tuff; consisted of three distinct eruptions separated by years to decades||2,100,000||2,450–2,500 km3|||
|Taupo Nui a tia||Taupo Volcanic Zone||North Island, New Zealand||Whakamaru Ignimbrite/Mount Curl Tephra||340,000||2,000 km3|||
|Heise Volcanic Field||Yellowstone hotspot||Idaho, United States||Kilgore Tuff||4,500,000||1,800 km3|||
|McMullen Supereruption||Yellowstone hotspot||Southern Idaho, United States||McMullen Ignimbrite||8,990,000||1,700;km3|||
|Heise Volcanic Field||Yellowstone hotspot||Idaho, United States||Blacktail Tuff||6,000,000||1,500 km3|||
|Cerro Guacha||Altiplano-Puna volcanic complex||Sur Lípez, Bolivia||Guacha ignimbrite, two smaller eruptions identified||5,700,000||1,300 km3|||
|Mangakino Caldera||Taupo Volcanic Zone||North Island, New Zealand||Kidnappers eruption||1,080,000||1,200 km3|||
|Oruanui eruption||Taupo Volcanic Zone||North Island, New Zealand||Taupo Volcano (Lake Taupo)||26,500||1,170 km3|||
|Cerro Galán||Andes Central Volcanic Zone||Catamarca, Argentina||Consisted of three distinct eruptions, separated by 30-40 thousands of years||2,500,000||1,050 km3|||
|Lava Creek eruption||Yellowstone hotspot||Idaho, Montana, and Wyoming, United States||Lava Creek Tuff; consisted of two distinct eruptions separated by years||640,000||1,000 km3|||
|Bishop Tuff||Long Valley Caldera||California, United States||A single eruption completed within 6 days; volume in dense rock equivalent||760,000||600 km3|||
The minimum total volume of tephra is 1,200 km3 but probably nearer 2,000 km3, ...