Topic: Supervolcanos and Massive eruptions

[Astronuc]

From Wikipeida - http://en.wikipedia.org/wiki/Supervolcano

Eruptions with a Volcanic Explosivity Index of 8 (VEI-8) are mega-colossal events that extrude at least 1000 km³ of magma and pyroclastic material. Such an eruption would erase virtually all life within a radius of hundreds of kilometers from the site, and entire continental regions further out can be buried meters deep in ash. VEI-8 eruptions are so powerful that they form circular calderas rather than mountains because the downward collapse of land at the eruption site fills emptied space in the magma chamber beneath. The caldera can remain for millions of years after all volcanic activity at the site has ceased.

VEI-8 volcanic events have included eruptions at the following locations (with estimates of the volume of erupted material at the event):

Aira Caldera, Kyushu, Japan
Aso, Kyushu, Japan
Campi Flegrei, Campania, Italy
Kikai Caldera, Ryukyu Islands, Japan
Long Valley Caldera, California, United States
Lake Taupo, North Island, New Zealand
Lake Toba, Sumatra, Indonesia (2,800 km³)
Valle Grande, New Mexico, United States
Yellowstone Caldera, Wyoming, United States
La Garita Caldera, Colorado, United States (over 5,000 km³)
The most recent VEI-8 eruption was at Lake Toba, Sumatra (the Toba event), and occurred around 74,000 years ago, plunging the Earth into a volcanic winter.

The largest known eruption on Earth occurred at the La Garita caldera in the San Juan Mountains approximately 28 million years ago.

http://en.wikipedia.org/wiki/Toba_eruption
http://en.wikipedia.org/wiki/Lake_Toba

The San Juan Mountains are a rugged mountain range in southwestern Colorado.
http://en.wikipedia.org/wiki/San_Juan_Mountains

[Astronuc]

An explorer identified the massive caldera in 1871. But satellite-based global positioning systems (GPS), gravity mapping and a seismic network are all helping scientists isolate more details of the area. And other new information is being uncovered all the time.
 
In fact, the Yellowstone caldera is the place where Smith and other geophysicists are beginning to finally pull aside the curtain that's been hiding one of geology's most stubborn secrets: the strange workings of Earth's "hot spots."
 
These "hot spots" are areas of volcanic activity not found in the usual location, at the edges of Earth's tectonic plates. Why they exist is a subject of scientific debate. And there are many around the world, not just Yellowstone.
 
But at this hot spot's current position under Yellowstone there have been three massive eruptions: 2.1 million, 1.3 million and 640,000 years ago. While those eruptions have been spaced roughly 800,000 and 660,000 years apart, three events are not enough statistically to declare this an eruption pattern, explains Smith.

 

Yellowstone Caldera on the Discovery Channel