A volcano is a rupture in the Earth's surface or crust, allowing hot, usually molten rock, ash, and gases originating profound below the surface to periodically escape. Volcanic activity connecting the extrusion of rock tends to shape mountains or mountain-like features over time.

Volcanoes are usually originated where two to three tectonic plates deviate or congregate. The mid-oceanic ridges, like the Mid-Atlantic Ridge, are typical examples of different tectonic plates where volcanoes are formed, whereas the Pacific sphere of Fire is a typical example of volcanic activity on convergent tectonic plates. Where two tectonic plates slide past one another volcanic activity is generally not found. In zones of prolonged crustal expansion and thinning within crustal plates, non-hotspot intraplate volcanism can be caused by decompression of the upper layer without either of the above processes acting.