The Ring of Fire
Map of the "Ring of Fire" showing volcanoes, seismicity and plate boundaries around the Pacific Ocean.
The “Ring of Fire” refers to the chains of volcanoes skirting the Pacific Ocean. These numerous volcanoes sit on top of subduction zones, which are convergent plate boundaries. There, the dense oceanic crust dives under the light continental crust. Around the Pacific Ocean this kind of tectonic configuration is very common (South America, Alaska, Aleutian Islands, Japan, Philippines, Indonesia and New Zealand).
The sinking oceanic plate is full of water. When it reaches a certain depth, this water lowers the melting point of the surrounding solid mantle, which creates molten magma. This molten magma, hotter and less dense than the surrounding rocks, rises up towards the surface, where it creates an intense and lasting volcanism. This is the reason why the map of volcanoes around the Pacific Ocean matches so well the map of subduction zones.