The Volcanic Explosive Index: A Way to Measure an Eruption's Strength

Humanity and all other life on the planet may not exist were it not for volcanic activity, but being close to some of the more violent ones, one like the ones that make up the Hawaiian islands where the lava simply oozes out have caused some of the greatest disasters in human history. The Minoan civilization, which some scholars believe to be the mythical Atlantis described by Plato was likely sent under the sea by the eruption of the volcano that dominated its home island.

Scientist have come up with a way to measure the the size or magnitude of the eruptions. The volcanic explosive index is a scale that ranges from 0 to 8, with the eruptions increasing in power as the scale increases. Like the Richter scale used to measure the power of earthquakes, the Volcanic Explosive index of VEI is exponential. (An eruption measuring five on the scale will be ten times as powerful than one that got rated as a four.)

The scale goes up to eight and no known volcanic eruptions in the history of the earth rated higher. The event that destroyed the Roman cities of Pompeii and Herculaneum managed to obtain a five on the scale, as did the eruption of Mount Saint Helens in Washington State in 1980.

The blast from Kratatoa which could be heard from 300 miles away and caused the destruction of the island the mountain was one achieved a six on the scale and of course gave the world beautiful sunsets for a year afterward and probably lowered the global temperature by one degree Celsius. The same could be said of the sunsets after the eruption of Mount Pinatubo in the 1990s.

As devastating as Krakatoa was, it is not the most powerful volcanic eruption in recorded history. It rated an eight on the Volcanic Explosive Index scale That occurred in 1815 at the Tombora volcano in Indonesia. The result of the eruption caused several newspaper editors in the United States to refer to 1816 as "the year without a summer." While Krakatoa and Pinatubo's eruptions lowered the temperature by about a degree Celsius, the blast from Tombora caused a three degrees Celsius plummet worldwide. (The death toll from the event was increased by crop followers because of the ash ejected from the mountain.)

Fortunately, no volcanic events that ranked eight on the scale are known to have happened in recorded history, although geologist believe such an event occurred seventy thousand years ago in Sumatra. Ash left in the atmosphere after the explosion might have caused a six year "nuclear winter."

Sources:

http://pubs.usgs.gov/gip/volc/eruptions.html

http://volcanoes.usgs.gov/Products/Pglossary/vei.html

http://www.mediasmm.org/pompeii/pompeii_faqs.pdf

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