Mysterious lightning flashes that appear to predict earthquakes could be sparked by movements in the ground below, US scientists say.
Unidentified glowing objects were spotted moments before major quakes in China and Italy recently.
These flickers could be triggered by shifting soil layers which generate huge electrical charge, say scientists.
Using a tub of plain kitchen flour, they discovered an entirely new physical phenomenon.
They announced their findings at the American Physical Society meeting in Denver.
"Our first suspicion was this has got to be a mistake. There must be something stupid we are doing," said Professor Troy Shinbrot, of Rutgers University, New Jersey.
"We took a tupperware container filled with flour, tipped it back and forth until cracks appeared, and it produced 200 volts of charge.
"There isn't a mechanism I know that can explain this. It seems to be new physics. "
Repeat experiments with other granular materials produced the same voltage phenomenon.
If it occurs along geological faultlines, sliding and cracking of soil grains could be generating millions of volts of electrostatic charge.
This in turn could seed lightning in the air above - creating a natural "early-warning system" for impending earthquakes.