Generally the first phases are usually phreatomagmatic and sometimes accompanied by base surges but then usually taper to just more strombolian or hawaiian types (With exceptions, of course) that produce lava flows. But from the ocean would very likely be surtseyan or close to it The lava isn't very viscous here due to the low sillica present (Mainly mafic rocks) and so can't generate the explosive power to drive an ash column high into the air to make a plinian style eruption. That'd be more like Taranaki, ruapehu, taupo etc which are more intermediate to felsic type rocks Hope that helped clear some things up
