Well, been dealing with dense vog for almost two months now. It is survivable if the lava does not get you.
The characteristics of the eruption have to do with the composition of the lava. Composition relates to viscosity.
The lower viscosity is Basalt like you see in Hawaii and generally just blurps out and runs off in rivers.
The high viscosity Andesite/Rhyolite explodes. Pompeii is one of the better known examples.
St Helens is middle of the scale and ‘80 was a tiny burp geologically speaking.