The Chaiten Volcano in southern Chile erupted almost two years ago. It's a large volcano that is quite active. It erupted for over a month. The large plume of ash and debris it spewed is seen in the picture below. Check out the lightning that accompanied it. Click on it for a super large picture.
A recent study in the scientific journal Nature found that volcanic plumes can spin like tornadoes in large thunderstorms.
Credit for the image goes to UPI photographer Carlos Gutierrez.
Then there is this shot video of lightning in action. Ssss-lllll-oooo-wwww motion.
The search for a path proceeds through the treelike process [early in the video]. Finding the the thin trails that are somewhat lower resistance than clear air. Basically, a slightly higher density dust particle or raindrop allows enough electrical current to flow as it seeks out more path (most lightning never reaches the ground). These tendrils of ionization last a little while--long enough to present a temptingly lower resistance for the main strike. It is a race to which one completes the circuit first. The path of current downward seems to last a long time. Remember though, it's slow motion and it only takes a 1/10 of a second.
Once the path between the sky and ground has been found and established a surge of current (~56 x 10^19 electrons or so), flows through the slightly lower resistance pathway blasting the outer electrons from the atoms of atmosphere in its path to from a plasma arc. the dramatically lower resistance causes it to continue passing the surge current. The electrons stripped from the atoms of the atmosphere (oxygen, nitrogen, carbon dioxide, and argon) are free electrons that carry the current until the lightning strike dissipates the electrical charge that started the process in the first place. This upward blast is calculated to travel at very near the speed of light. It's the mixture of gasses that provide the color of the lightning that you see.
Two other short notes on lightning. First, we now know that lightning strikes are such high energy that they produce x-rays. The process of stripping electrons away from the atoms of the atmosphere and they recovery of the electrons as they fall back towards the nucleus would produce electromagnetic radiation at energy levels all the way to x-rays. Secondly, the air that was super-heated as the lightning passed through would cool just as fast as it left, and the rush of that air back and it's slamming together with the rest of the air makes a loud sound. A lot of it.