Molten lava is contained by a shell called the Tectonic Plates. The plates are constantly shifting and forcing against each other. Gaps between them allow magma to seep between the plates and bulge in the crust.
There is a specific geographical area around the Pacific Ocean where those plates supporting the sea-bed beneath the Pacific Ocean meet head-on with the lighter plates of the surrounding Continental land mass.
The resulting action has forced the Pacific plates to move beneath the Continental plates and become ‘subduction plates’ (moving below). Magma finds gaps and, fissures, between the plates and rise towards the Earth’s crust as larva; the beginning of a volcanic formation.
All land masses (and ocean floors), continents and islands, their soil, sand, rock, mud, and oceans ride atop tectonic plates. The tectonic plates are constantly shifting although we may not notice; occasionally there is a more powerful movement and we experience an earthquake.
Earthquakes sometimes lead to Tsunamis in the oceans. Tsunamis are another powerful, destructive force in Natures arsenal
Realizing the potential for danger associated with a volcano, there are organizations locally and internationally that constantly monitor their moods.