Lightning during volcano eruptions.

[Pushkin]

I've seen a few documentaries about volcanic eruptions showing lightning during CGI shots of eruptions. Ignoring storms co-inciding with the eruption, is there anything that would cause the lightning to happen?

[MikeS]

While we're waiting for a geologist to drop in, here's an article (http://www.guardian.co.uk/print/0,3858,5080955-111414,00.html) on volcanic lightning and an alternative theory as to why it occurs.