There are now more than 150 recorded cases of vicious electrical storms breaking out directly above craters of erupting volcanos, dating back several centuries. The 1980 eruption of Mount St Helens in Washington state, one of the most studied eruptions in recent times, produced a lightning bolt every second. The electrical activity does not pose the same hazard as a volcano's boiling lava, choking dust clouds and drowning mud slides - though there are reports of people and animals being struck as they fled - but it sets a spectacular seal on mother nature's most awesome display of destruction.
Awesome, but not really understood. Exactly what causes volcanic lightning is still hidden in the clouds spewed from the crater. Most volcanologists seem happy with the vague notion that ash particles thrown into the air rub against each other and generate enough static charge to trigger sparks. It's the boiling lava, choking dust clouds and drowning mud slides that really concern them - particularly if they are close to the action.
There is more to the lightning than shock and awe. A better understanding of processes that cause it deep within eruption debris could help predict how the giant clouds will behave. Airlines have long feared the way volcanos can suddenly fill the sky with hazardous vertical smoke columns several miles high that rise at speeds up to 400 metres per second.
Now, an intriguing new idea that could explain volcanic lightning has emerged. Earle Williams of MIT and Stephen McNutt at the University of Alaska, say it might simply be caused by a build up of ice. Because thunder and lightning in conventional storms are down to ice and water, the two claim that large volcanic eruptions are nothing more than dirty thunderstorms.
