Lightning bolts are born from friction, ice and ash
My kids’ first concept of lightning was an ancient one. As depicted in Fantasia, lighting was the result of a bored Zeus, asking the mythical blacksmith Hephaestus for forged bolts of electricity to throw at terrified, reveling satyrs and unicorns. The takeaway was that lighting was something to be feared, because not only was it capable of blowing a tree to cinders, but it likely being targeted right at you. It’s certainly more dramatic than the bits of ice bumping into each other you find in real clouds, but maybe those don’t match Beethoven too well.
The ice in question is a mix of tiny crystals and slightly larger pellets. These particles get tossed around in the wind at speeds up to 100 miles-per-hour, with positively-charged crystals moving up, rubbing past ice pellets with negative charges on their way down. Like rubbing socks on a carpet, this contact can build up an electrical charge, leading to a spark, but you would only notice it if enough ice is discharging at once. That’s not a big problem for a good storm cloud though, as even a modest storm might have around 11,000 tons of ice to toss around, which is good to produce mega-volt discharges three times as hot as the surface of the sun.
Ice particles aren’t the only way to get lightning though. When a volcano erupts, it spews tons of debris and ash into the sky, sometimes reaching as high as 12 miles up into the stratosphere. This is actually high enough to get ice crystals and the associated lightning, but the ash lower to the ground can also do the job. Just like the ice crystals, bits of ash being blown against each other can build up an electrical charge. The resulting lighting is more likely to hit the ground, as well as look completely awesome over spewing magma. Maybe even enough to warrant some Beethoven.
Source: Electric Ice by Dr. Tony Phillips, NASA Science News