Supervolcano


A supervolcano is a volcano that produces the largest kinds of eruption on Earth. T he volume of ejected tephra (airfall material) is enough to radically change the landscape and severely affect global climate for years and the "volcanic winter" supervolcanoes produce can have a dramatic effect on life.
The term was originally coined by the producers of the BBC program, "Horizon", in 2000 to refer to these types of eruption. That investigation brought the subject more into the public eye, leading to further studies of the possible effects.
  • Until 2003, supervolcano was not a technical term used in the study of volcanoes.
  • There is no well-defined minimum explosive size for a "supervolcano".
  • Volcanologists do not use the term "super volcano or mega caldera," except when dealing with the media as it seems it is the only way the media and hence some non-scientific people understand the scale of the phenomena.


Massive Eruptions:
Eruptions with a Volcanic Explosivity Index of 7 or 8 (VEI-7 or 8) are colossal events that eject at least 1,000 km³ Dense Rock Equivalent (DRE) of pyroclastic material.
VEI-7 or 8 eruptions are so powerful that they often form circular calderas rather than cones because the magma chamber that produces uplift becomes drained and the land above the chamber collapses into it. One of the closes calderas to our location is the Yellowstone caldera located north and west of (and including part of) Yellowstone Lake.

VEI-8 volcanic events have included eruptions at the following locations. Estimates of the volume of erupted material are given in parentheses.
  • Lake Taupo, North Island, New Zealand - Oruanui eruption 26,500 years ago (1,170 km³)
  • Lake Toba, Sumatra, Indonesia - 75,000 years ago (2,800 km³)
  • Yellowstone Caldera, Wyoming, United States - 2.2 million years ago (2,500 km³) and 640,000 years ago (1,000 km³)
  • La Garita Caldera, Colorado, United States - Source of the truly enormous eruption of the Fish Canyon Tuff 27.8 million years ago (~5,000 km³)

The Lake Toba eruption plunged the Earth into a volcanic winter, eliminating 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.

The Yellowstone Caldera:
The Yellowstone Caldera is a volcanic caldera in Yellowstone National Park and measuresYNP_Caldera.jpg about 55 kilometers (34 mi) by 72 kilometers (45 mi). The caldera was discovered based on geological field work conducted by Bob Christiansen of the United States Geological Survey in the 1960s and 1970s. After a BBC television science program coined the term supervolcano in 2000, it has often been referred to as the "Yellowstone supervolcano."

Yellowstone, like the Hawaiian Islands, is believed to lie on top of one of the planet's few dozen hotspots where light, hot, molten mantle rock rises towards the surface. The Yellowstone hotspot has a long history. It is thought that over the past 17 million years or so, successive eruptions have flooded lava over wide stretches of Washington, Oregon, California, Nevada, and Idaho, forming a string of comparatively flat calderas linked like beads, as the North American plate moves across the stationary hotspot. The oldest identified caldera remnant is straddling the border near McDermitt, Nevada-Oregon. The calderas' apparent motion to the east-northeast forms the Snake River Plain. However, what is actually happening is the result of the North American plate moving west-southwest over the stationary hotspot deep underneath.

Yellowstone sits on top of three overlapping calderas. Currently, volcanic activity is exhibited only via numerous geothermal vents scattered throughout the region, including the famous Old Faithful Geyser, but within the past two million years, it has undergone three extremely large explosive eruptions, up to 2,500 times the size of the 1980 Mount St. Helens eruption. The three eruptions happened 2.1 million years ago, 1.3 million years ago, and the most recent such eruption produced the Lava Creek Tuff 640,000 years ago and spread a layer of volcanic ash over most of the North American continent. Between major eruptions and in the time since then, several small volcanic episodes have occurred along with continuing geothermal activity (see "Thermal features") as a result of a large chamber of magma located below the caldera's surface. The magma in this chamber contains gases that are kept dissolved only by the immense pressure that the magma is under. If the pressure is released to a sufficient degree by some geological shift, then some of the gases bubble out and cause the magma to expand. This can cause a runaway reaction. If the expansion results in further relief of pressure, for example, by blowing crust material off the top of the chamber, the result is a very large gas explosion.Yellowstone_Caldera_map.jpg

Geologists are closely monitoring the rise and fall of the Yellowstone Plateau, which averages +/- 1.5 cm yearly, as an indication of changes in magma chamber pressure.


Sources:
1. Wikipedia - http://en.wikipedia.org/wiki/Supervolcano
2. Wikipedia -
3. Northwest Volcano image: www.anthonares.net/ Yellowstone_Caldera_map.gif
4. Yellowstone Caldera image:http://volcanoes.usgs.gov/yvo/LvlMap.html