* They are all formed by the eruption of magma (molten rock) from the Earth's interior. This magma, when it reaches the surface, is called lava.

* They all have a vent or opening through which the magma erupts. This vent can be a single opening or a series of fissures.

* They all are a result of tectonic activity, particularly plate boundaries.

* They all pose potential hazards to humans and the environment. This includes lava flows, ash falls, pyroclastic flows, and volcanic gases.

While they share these similarities, they also have significant differences in their shape, size, composition, and eruptive style.