I've never seen it, but I did just see a show on the Discovery Channel (and slept in a Holiday Inn Express). The way some of the volcanoes erupt is very similar to the convection we are after when we chase. Super heated air/ash mixture gets launched 70,000 feet into the air, and finally fans out into an anvil. With that kind of updraft you can imagine there is going to be A LOT of lightning.
Now, since the updraft is so strong, and we know that things other than supercells can produce vorticies, such as forrest fires, and Tcu... have there ever been any documented Volcanonados. You don't want to core punch on one of those chases. :wink:
Happens quite often with ash eruptions--anything from anvil-zit short bolts to really large honkers. Just like with a lot of regular lightning photography, most of the volcano lightning shots you see are time exposures, whish skews your perspective on how often it happens. It's not generally 10 bolts/sec like you see in a supercell.