Anak Krakatoa is just one of many volcanoes in the Indonesian portion of the ‘ring of fire’. But it’s been putting on a rare show of volcanic lightning. Picture: Photovolcanica
Anak Krakatoa is just one of many volcanoes in the Indonesian portion of the ‘ring of fire’. But it’s been putting on a rare show of volcanic lightning. Picture: Photovolcanica

Krakatoa unleashes its demon sprites

KRAKATOA. It's a name you've probably heard before. It's a volcano. And when it blew in 1883, it sent shockwaves around the globe. Now, it's erupting again.

It's not the beast it once was. But it is producing some rare effects.

A new mound of ash and lava has been steadily growing in the caldera left behind by the enormous explosion which killed some 36,000 people through its thermal flash and ensuing tsunamis.

It was so loud it was heard for thousands of kilometres. The effects of the gas and dust it pumped high into the atmosphere caused temperatures to drop around the world for years to come.

Anak Krakatoa junior has a lot of growing to do before it reaches that scale again. But, judging from the show it has been putting on, it has ambitions …

Vulcanologist Dr Richard Roscoe has captured some extraordinary footage of the volcano hurling glowing rocks high into the sky.

But he also captured another, extraordinary volcanic act: creating its own lightning.

Bolts of electricity arc out from its ash clouds, throwing a brief blue flash over the red and black landscape.

It's a phenomenon that has not been understood until recently.

It only happens when the right mix of ash, gas and super-hot lava bubble up from below the Earth's surface.

 

Volcanic lightning is seen flickering through the ash plume in this timelapse picture of the Puyehue volcano in 2011. Picture: AP
Volcanic lightning is seen flickering through the ash plume in this timelapse picture of the Puyehue volcano in 2011. Picture: AP

 

Flowing lava rapidly cools, creating a significant difference in temperatures over a small area. Thick clouds of ash billow in the volcano's plume - with the soot particles regularly thumbing into each other.

Putting the two together is an explosive mix.

The atoms that make up the ash cloud, in the violent heat, start bouncing electrons around. Eventually, it builds up enough of a charge that it must find a way to escape.

And cooler, low-charged air is conveniently nearby.

 

Lighting seen amid the lava and ash erupting from the vent of the Eyjafjallajokull volcano in central Iceland
Lighting seen amid the lava and ash erupting from the vent of the Eyjafjallajokull volcano in central Iceland

 

So the air itself spontaneously turns into a conductor. Then, in a flash, that charge expends itself - as a lightning strike.

Volcanologists say the particular chemistry that produces volcanic lightning has been observed some 150 times over the past few centuries.