http://www.newscientist.com/article/dn24792
It’s a “build your own volcano” kit like no other. A team of geologists in Germany has built a model volcano that crackles with lightning as it erupts. But this is no toy science kit for kids – it could offer insights into the disruption risk to aircraft in the aftermath of an eruption.
Volcanic lightning was first documented by Pliny the Younger following an eruption of Mount Vesuvius in AD 79. The exact cause of the lightning remains unclear. Previous work suggests that ash particles slam into each other as they are ejected from the vent, generating a frictional charge. So Corrado Cimarelli at Ludwig Maximilian University in Munich, Germany, built a model volcano to mimic this charging process.
They took ash from recent eruptions, including the infamous 2010 eruption of Iceland’s Eyjafjallajökull, the ash cloud from which grounded European flights for weeks. They put the ash in a tube and held it there at 100 times atmospheric pressure before venting it through a nozzle into a large tank filled with air at normal pressure, mimicking the sudden release of pressurised material from a volcanic vent.
Lo and behold, their tiny volcanic eruptions generated lightning sparks, which they recorded with high-speed video. The finer the ash particles, the more lightning the team recorded.
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http://www.youtube.com/watch?v=PaLNrA9vYgc