I have never seen lightning with an erruption before
That often happens when volcanos conataining viscous rhyolite/dacite magma erupts.
Due to its high viscosity they tends to produce very explosive eruptions spewing out mostly ash instead of magma flows like Hawaiian Volcanos.
Chaiten volcano, Mt. St Helens and Mt. Pinatubo are perfect examples on that.
Static electricity makes the lightning, actually if the eruption is big enough they often makes their own weather systems.