The Earth’s crust is composed of enormous sections of rock called tectonic plates. Tectonic plates resemble puzzle pieces which move constantly against each other. Volcanoes often form in the areas where tectonic plates make contact. The friction created between two plates by the constant movement melts the Earth’s crust, causing the rock underneath the crust to turn into magma due to the great temperatures created by friction.
The now molten hot rock or magma creates great pressure, and over time, it finds its way through the fractures in the plates. Once magma reaches the surface of the Earth, it is called lava. Approximately 1500 volcanoes around the world are considered active, and from these, nearly 90% lie in the Ring of Fire, which is a ring of oceanic volcanoes circling the Pacific Ocean.
Most divergent plate boundaries lie in the bottom of the oceans. That is why most volcanic activity occurs in the oceans. Volcanoes may be formed at subduction zones. A subduction zone is a place where two plates, one oceanic plate and one continental plate, collide. At a subduction zone, an oceanic plate submerges under a continental plate. The friction creates magma. When magma reaches the surface, then, a volcano is formed. A typical example of this type of volcano is Mount Etna on the east coast of Italy.