Fuente: Science News
Expuesto el: jueves, 14 de junio de 2012 20:50
Autor: Science News
Asunto: 13th century volcano mystery may be solved
| Indonesia implicated as location of biggest eruption in last seven millennia Web edition : 5:50 pm
SELFOSS, Iceland — One of the biggest mysteries in volcanology may finally have a solution. An eruption long thought to have gone off in the year 1258, spreading cooling sulfur particles around the globe, happened the year before in Indonesia, scientists report. Until now, researchers have known a big volcano went off somewhere in the world around that time, but they didn’t know exactly where or when. The new report still remains something of a mystery. Franck Lavigne, a geoscientist at Panthéon-Sorbonne University's Laboratory of Physical Geography in Meudon, France, showed data and close-up photographs of the remains of the perpetrator volcano on June 14 at an American Geophysical Union conference on volcanism and the atmosphere. But he declined to name the specific volcano, saying he had agreed with his international colleagues not to identify it until the work is published in a peer-reviewed journal. “We have new and solid evidence for the biggest volcanic eruption in 7,000 years,” Lavigne said. Consensus in the meeting hallways was that he showed pictures of Indonesia. Lavigne would say only that Indonesia has more than 130 active volcanoes. Scientists know a big eruption must have happened in the mid-13th century because ice cores from Greenland and Antarctica dating to that time contain huge amounts of sulfur. Tree rings, historical records and other evidence also show that the planet cooled soon thereafter. Big volcanic eruptions can spew sulfur particles into the upper atmosphere, where they spread around the globe and reflect sunlight, temporarily chilling the planet. Leading candidates for the 1258 eruption have included Mexico’s El Chichón, which also erupted in 1982, and Quilotoa in the Ecuadorean Andes. But the chemical composition of rocks from those volcanoes, among other factors, don’t really match the 1258 sulfur from ice cores. At the meeting, Lavigne showed geochemical analyses of rocks from his mystery volcano. They matched the chemistry of the polar sulfur almost perfectly. The rocks come from a caldera, the collapsed remains left behind after a large volcanic eruption drains an underground magma chamber. Newly unearthed historical records and other evidence show that climate changes were already happening in the region by the winter of 1257-1258, Lavigne said. “We think the eruption may have been in the late spring or summer of 1257,” he said. That’s nearly a year earlier than previously thought. Computer simulations suggest the eruption sent pumice flying into the air more than 40 kilometers high, showering debris for tens of kilometers around. The eruption would have ranked a 7 on the volcanic explosivity scale that measures an eruption’s magnitude. That scale tops out at 8. Still, volcanologists have spent decades looking for the source of the 1257/1258 eruption. It’s not yet clear whether Lavigne will be able to marshal enough evidence to convince everyone else.
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