From ashes to flashes

Volcanoes are responsible for some the most spectacular displays of lightning on the planet. However, the exact mechanisms behind volcanic lightning, and why some volcanoes generate more lightning than others, are a mystery. In a recently published scientific paper featured in the Guardian, Dr Keri Nicoll and colleagues from the University of Bristol and Oxford University, investigated the role of volcanic ash particles in generating electric charge; an important process in the production of volcanic lighting.

Using specially designed laboratory apparatus, Dr Nicoll and colleagues performed experiments with volcanic ash from the Icelandic volcanic eruptions of Eyjafjallajökull and Grímsvötn. They investigated the potential of ash particles to become charged, resulting from particles rubbing against each other (similar to the process by which charge is generated by rubbing a balloon against a woolly jumper).

The results found that the highest charge (which is likely linked to the most spectacular lightning) is created by ash with the widest range of particle sizes.  The experiments also demonstrated that ash from different volcanoes had different electrical properties, with ash from the Grímsvötn eruption charging more readily than the ash from Eyjafjallajökull. This is particularly interesting, as the Grímsvötn eruption produced much more lightning than Eyjafjallajökull. The results of this study indicate that all volcanic plumes are likely to be charged, no matter how far away from the volcano, therefore new techniques to distinguish clouds from volcanic plumes are essential to reduce potential hazards to aircraft.

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