This may occur as a result of the recycling of surface deposits of sulfur dioxide. The lava forms a cap over the sulfur dioxide deposits, and subsequent lava flows bury the deposits even deeper. After many repeated flows, the sulfur dioxide reaches a depth at which it becomes liquefied due to the high pressure of overlying material. When an underground intrusion of magma comes in contact with the deeply buried sulfur dioxide deposit, some of it becomes superheated and converts to vapor. The pressure from this vapor increases until a path to the surface is opened, resulting in a plume eruption.
Material ejected during the eruption returns to the surface and the recycling process is repeated.