The factors that affect the force of a volcanic eruption are How fast or slow the magma moves The temperature The amount of dissolved gas The amount of pressure
If the magma has a high water content, then the volcano will most likely have an explosive eruption. Also, vocanoes can have explosive eruptions if the magma contains a large percentage of silica....
High silica magmas are higher in viscosity and produce violent eruptions. Basaltic magmas are much less viscous and tend to flow when erupted, not explode.