what causes a volcano to erupt

Volcanic eruptions are caused by the movement of tectonic plates. When a thin, heavy oceanic plate moves under a thicker continental plate, the ocean plate sinks into the mantle, causing some of the rocks to melt and form magma. This magma is lighter than the surrounding rock and rises up, collecting in magma chambers miles below the surface. When enough magma builds up in the chamber, it forces its way up to the surface and erupts, often causing volcanic eruptions. The buoyancy of the magma, the pressure from the exsolved gases in the magma, and the injection of a new batch of magma into an existing magma chamber are the three main factors that trigger a volcanic eruption. Scientists have made significant advances in forecasting volcanic eruptions, but they cannot yet predict them with certainty