22 April 2010

Eyjafjallajökull could be worse

According to an Australian scientist, the Eyjafjallajökull volcano eruption is not as 'big' as Mount Pinatubo (1991). From ABC (Australia)

In fact, the eruption of Eyjafjallajokull (which means 'island mountain glacier') is small compared to other recent eruptions such as Pinatubo and Mount St Helens, says Professor Ray Cas from Melbourne's Monash University.

Scientists use a scale called the Volcanic Explosivity Index or VEI to provide a relative measurement of the explosiveness of a volcanic eruption. The largest eruptions to date have a VEI of 8.

At 7 on the VEI scale, the eruption of the Tambora volcano in Indonesia in 1815 is "probably the largest historic eruption that we know of," says Cas.

Mount Pinatubo, on the Philippine island of Luzon erupted in 1991, killing hundreds. Considered to be the second largest volcanic eruption of the twentieth century it had a VEI of 6 — that's the equivalent to 200 megatons of TNT, or about 13 thousand times more powerful than the atomic bomb dropped on Hiroshima in Japan.

Pinatubo was the same size as the 1883 eruption of Krakatoa in the Sunda Strait between the Indonesian islands of Java and Sumatra. That eruption culminated in a series of massive explosions and tsunamis, which destroyed most of the island leaving a giant caldera and killed at least 36,417 people.

"People often talk about Krakatoa. The eruption blast was so loud it was heard thousands of kilometres away in central Australia and is said to be the loudest noise ever heard by humans," says Cas.

In 1980, Mount St Helens in the US state of Washington erupted sending a column of gas and ash over 24 kilometres into the air, melted glaciers creating volcanic mudslides (lahar) and gouged a crater in the left side of the peak. The eruption rated 4 on the VEI scale.

Rated a 2 on the VEI scale, Eyjafjallajokull's eruption caused glacial flooding and created a 10 kilometre-high column of ash that shut down air travel over Europe. But, unlike the Pinatubo, Krakatoa or Mt St Helens eruptions, it is not expected to have any effect on global temperatures.

One of the biggest concerns surrounding Eyjafjallajokull is the fear that it could spark its much larger neighbour, Mount Katla, to erupt.

Cas says the two could share the same magma source and the subsurface plumbing between the pair may be connected.

"There's some history that when one erupts the other also erupts for a short time. But as I understand it there's no signs of activity under Katla at the moment."

An eruption by Katla could be far more explosive than Eyjafjallajokull. Past history has seen eruptions from Katla with an VEI of 4 or 5.

There should also be economic impact assessments made as a basis of comparison.

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