Saturday, May 8, 2010

Volcanology

After the eruption at Eyjafjallajokull, the volcano in Iceland that few of us had heard of before and none of us can pronounce, there has been some good media coverage of our chances of meeting magma. The chances are higher than we would like, really. Especially if you live in Iceland, but also here in New Zealand.

The excellent Paul Gorman, one of the few New Zealand journalists to have a science background, writes about the likelihood of Taupo erupting again in today’s Your Weekend magazine which comes with the Waikato Times and, I assume, the Press and Dom-Post. (It is not online but it is well worth buying a Fairfax Saturday paper for. Excellent graphics, too.)

As he says, the Taupo eruption in about 180 AD, which ejected 120 cu km of material, was the fifth biggest eruption of the last million years. The Oruanui eruption in about 24,500 BC, which created the lake, was the second biggest and ejected 1170 cu km of material. (To put this in perspective, the famous Krakatoa eruption of 1883 ejected 25 cu km of material; Mount St Helens in 1980 ejected 1.2 cu km; Ruapehu in 2007 ejected 0.001 cu km.) The third biggest eruption, says Gorman, was Whakamaru in 252,000 BC which ejected 1100 cu km, but I can’t find much online about it apart from this and this.

Anyway, the money quote in today’s story is from volcanologist Gill Jolly:
If we had something the size of the [180 AD] Taupo or the Oruanui eruption [24,500 BC, and the world’s second-largest in the last million years], I wouldn’t want to be this side of Auckland really.
I am so glad we have friends in Ngunguru we can flee to.

Last week in the Guardian, Simon Winchester, author of Krakatoa, had this to say:
There is perhaps no better recent example of the havoc that a big eruption can cause than that which followed the explosive destruction of Mt Toba, in northern Sumatra, some 72,000 years ago (which, in geological time, is very recent indeed). [. . .] On the widely used volcanic explosivity index (VEI), Toba is thought to have been an eight Рmeaning that in the unusually flamboyant official language of vulcanology it was a super-plinian type eruption with mega-colossal characteristics (Eyjafjallajökull is by contrast listed as a strombolian type, with its characteristic regarded as merely gentle, and having a probable VEI rating of just two). [. . .]

But others of the 47 known VEI-8 volcanoes are more alarmingly recent. Taupo in New Zealand erupted with mega-colossal force some 22,500 years ago. The newer of the great eruptions that helped form the mountains of today’s Yellowstone national park in Wyoming took place just 640,000 years ago, and all the current signs – from such phenomena as the rhythmic slow rising and falling of the bed of the Yellowstone river, as if some giant creature is breathing far below – suggest another eruption is coming soon. When it does, it will be an American Armageddon: all of the north and west of the continent, from Vancouver to Oklahoma City, will be rendered uninhabitable, buried under scores of feet of ash. (I mentioned this once in a talk to a group of lunching ladies in Kansas City, soothing their apparent disquiet by adding that by “soon” I was speaking in geologic time, and that meant about 250,000 years, by which time all humankind would be extinct. A woman in the front row exploded with a choleric and incredulous rage: “What?” she said. “Even Americans will be extinct?”)

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