Definitions

Supervolcano

Supervolcano

A supervolcano or super volcanic eruption is a volcanic eruption which is orders of magnitude greater than any volcano in historic times (generally accepted to be greater than 200 cubic kilometres). This kind of eruption is typically sufficient to cause a long-lasting change to weather (such as the triggering of an ice age) sufficient to threaten the extinction of species, and cover huge areas with lava and ash.

Word origin

The term was originally used in the BBC popular science program Horizon in 2000 to refer to these types of eruptions. That programme introduced the subject of large scale eruptions to the general public.

Volcanologists and geologists do not refer to "super volcanoes" or "megacalderas" in their scientific work, but sometimes do in public presentations. However, they do describe eruptions that rate VEI 7 or 8 as "super eruptions".

  • Until 2003, supervolcano was not a technical term used in volcanology. 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.
  • 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.
  • Supervolcanoes were seen on other planets via the Voyager program craft on the moons of Jupiter and Saturn. However, this kind of volcano on earth was not discovered until long after the Voyager had gone on to their interstellar missions. The outer Solar System volcanoes were mostly cryovolcanoes, not magma volcanoes. Theoretically a supervolcano could be a cryovolcano, but none has been found within the solar system.

Large Igneous Provinces

Large igneous provinces (LIP) e.g. Iceland, the Siberian Traps, Deccan Traps, 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 km2 and have volumes on the order of millions km3. In most cases, the lavas are normally laid down over several million years. They do release massive amounts of gases. The Réunion hotspot produced the Deccan Traps about 65 Mya. Research continues into the effect of the outpourings and whether they impacted upon the extinction of the dinosaurs at the end of the Cretaceous.

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 1783-1784 from the Laki fissure which is ~40 km long. An estimated 14 km3 of basaltic lava was poured out during the eruption.

The Ontong Java Plateau has an area of about 2 million km2 .

Massive eruptions

Eruptions with a Volcanic Explosivity Index of 8 (VEI-8) are colossal events that throw out at least 1,000 km³ Dense Rock Equivalent (DRE) of ejecta; VEI-7 events eject at least 100 km³ (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 has 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 at the lower end of VEI-5 with 1.2 km³, and both Mount Pinatubo in 1991 and Krakatoa in 1883 were VEI-6 with 25 km³.

Known super eruptions

Estimates of the volume of ejected material are given in parentheses.

VEI–9 volcanic events are only known to have happened once since the end of the Precambrian.

VEI-8 volcanic events have included eruptions at the following locations.

The Lake Toba eruption plunged the Earth into a volcanic winter, eradicating an estimated 60% of the human population (although humans managed to survive, even in the vicinity of the volcano), and was responsible for the formation of sulfuric acid in the atmosphere.

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, and Lake Taupo (Hatepe), around 180 AD

For large flood basalt eruptions, see large igneous province.

Media portrayal

A National Geographic documentary called Earth Shocks portrayed the destructive impact of the rapid eruption at Lake Toba approximately 75,000 years ago, which caused a phenomenon known as the Millennial Ice Age that lasted for ~1000 years and killed an estimated 60 to 75% of the human 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 transmissions to date for unknown reasons and is only presently mentioned at the show's BBC website (dead as of May 18, 2007; Internet Archive version).

In 2005 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 transmitted in early 2005, but it was felt that this would be insensitive so soon after the 2004 Indian Ocean tsunami. The program and its accompanying documentaries were released on DVD region 2 simultaneously with its broadcast. Nova featured an episode Mystery of the Megavolcano, examining such eruptions in the last 100,000 years.

In 2006 the Sci Fi Channel aired the documentary Countdown to Doomsday which featured a segment called "Supervolcano".

In 2006 ABC News aired the documentary Last Days on Earth which featured a segment called "Supervolcano".

In the Stargate Atlantis episode Inferno, the main characters are caught in the eruption of a supervolcano and escape using an Ancient warship.

In 2008 the Yellowstone supervolcano was featured in the BBC program 10 things you didn't know about Volcanoes, presented by Dr Iain Stewart, a volcanologist.

See also

References

Sources

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