Lightning bolts that flash and clash high above erupting volcanoes can forge flying ash into glass, new research finds. The mechanism could explain the origins of odd microscopic glass beads found embedded in ash deposits, the researchers report online February 27 in Geology.
A volcanic eruption can kick up electrically charged material into the atmosphere, sparking lightning bolts that heat the surrounding air to more than 3,000° Celsius — more than hot enough to melt any nearby airborne debris. When rocky material heats up and quickly cools off, it can transform into glass.
Volcanologist Kimberly Genareau of the University of Alabama in Tuscaloosa and colleagues sifted through ash deposits from the 2009 eruption of Mount Redoubt in Alaska and the 2010 eruption of Eyjafjallajökull in Iceland. The researchers also mimicked the conditions above erupting volcanoes by shocking artificial ash with strong electric discharges. In both cases, the researchers spotted microscopic glass balls. The artificial glass spheres averaged 17 micrometers wide while the naturally occurring ones averaged 48 micrometers wide. As much as 5 percent of the volcanic ash was reformed into glass, the researchers estimate. The transformation from ragged rocks to smooth, aerodynamic glass would cause the volcanic debris to fall faster and be less apt to clump together, the researchers note.