Supervolcano

From Wikipedia, the free encyclopedia

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.^[1] 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.

Contents

• 1 Terminology
• 2 Large igneous provinces
• 3 Massive explosive eruptions
  • 3.1 Known supereruptions
    • 3.1.1 VEI 8
    • 3.1.2 VEI 7
• 4 Ongoing studies
• 5 Media portrayal
• 6 See also
• 7 References
• 8 Further reading
• 9 External links

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.^[2] 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.^[3] In the review, Byers refers to Mount Multnomah as a supervolcano.^[4] 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.^[5][6]
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".^{[citation needed]}
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.^{[citation needed]}

Large igneous provinces

Main article: Large igneous province

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.

Massive explosive eruptions

Main article: World's largest 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)^[7] its geology and volcanic succession have recently been re-analysed in the light of new discoveries.^[8] 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 km³ (2.4 cu mi) and 25 km³ (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.

Known supereruptions

Cross-section through Long Valley Caldera

Location of Yellowstone hotspot over time (numbers indicate millions of years before the present).