Scientists have discovered tiny, perfectly round spheres of glass in the ash left over from volcanic explosions, and say they could be the key to understanding how and why lightning forms in these crazy-volatile events.

The team, led by volcanologist Kimberly Genareau from the University of Alabama in the US, examined the ash from two massive eruptions - the 2009 Mount Redoubt eruption in Alaska, and the 2010 Eyjafjallajökull eruption in Iceland - to find glass balls measuring just 50 microns across (a micron equals 0.001 millimetres). 

Researchers have known for years that volcanic eruptions produce tiny, jagged fragments of glass, but the consistent shape and smooth surface of these spheres came as something of a surprise. It's thought that the glass fragments are caused when massive ash clouds are spewed forth from the mouth of a volcano, and as the individual ash particles make contact and rub against each other, they produce enough static electricity to convert into bursts of lightning. 

This lightning could be the key to creating the spheres, says Becky Oskin at Live Science, because they heat the air within the ash clouds to temperatures of around 30,000 degrees Celsius (54,000 degrees Fahrenheit), within mere millionths of a second. This melts the glass particles into a molten liquid, and as these liquid droplets are plummeting through the air, they cool into a little orb shapes.

"You don't need volcanic lightning to make glass [in ash], just to get that unusual shape," Genareau told Oskin. 

To test this theory, Genareau worked with researchers from the University of Canterbury in New Zealand to replicate the conditions of a volcanic eruption in the lab and see what glass shapes they could produce. Publishing in the journal Geology, the team describes how they placed artificial ash in a high-voltage insulator experiment to produce super-smooth glass spheres, plus other imperfect balls that had been dented, pocked, and skewed, likely due to boiling too quickly before cooling and setting.

Now that they suspect volcanic lightning has to be present to create these pretty little orbs, Genareau and her team are going to use them to learn more about this curious phenomenon. "Not much is known about how often volcanic lightning occurs, and this provides physical evidence that may be preserved in the geologic record," she told Live Science. 

German filmmaker Marc Szeglat recently captured some rare footage on the Japanese island of Kyushu of the Sakurajima volcano spewing lightning from its fiery spout. It's pretty spectacular:

Source: Live Science