Published on Jan 12, 2014. The largest volcanic eruption of the past two million years occurred on the Indonesian island of Sumatra some 75,000 years ago. The impact from the supervolcano Lake Toba decimated the local habitat, but gas, ash and debris from Toba made their way around the planet and formed a shield in the atmosphere that deflected the suns warming rays. Temperatures plummeted and the planet was thrown into a volcanic winter and may have even pushed the planet into an ice age. 3-D computer animation will recreate the storm and unveil how this one volcano could have brought humanity to the edge of extinction. 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 either when magma in the mantle rises into the crust from a hotspot but is unable to break through the crust, thus 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), but 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. Terminology 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, U.S.A. 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 Hodges 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.[citation needed] 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. The Ontong Java Plateau now 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.
Posted on: Sat, 01 Nov 2014 17:30:43 +0000
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