Which term describes damage caused by an unexpected and violent eruption?

The correct term that describes damage caused by an unexpected and violent eruption is "Explosion." In insurance contexts, an explosion is typically characterized by a sudden and forceful release of energy, which can lead to considerable destruction and damage, often across a wide area. This aligns with the idea of an eruption being unexpected and violent, such as a gas explosion or an industrial accident.

The other terms listed describe different types of occurrences: hail refers to precipitation in the form of ice, which can cause damage but is a natural weather event; a riot pertains to a public disturbance involving a group of people acting violently, typically in a social or political context; and vandalism involves the intentional destruction of property. While each of these terms describes a type of damage, none captures the essence of a sudden and forceful eruption like the term "explosion."