How does a volcano erupt and what causes it to erupt?

Answer 1

When a destructive boundary of two tectonic plates occurs the oceanic crust sinks underneath the continental crust as it is more dense, the oceanic crust then melts in the subduction zone and becomes magma in the mantle, this increases the pressure in the mantle and causes the magma to shoot up the volcano shaft and burst out of the top, this is an eruption

Answer 2

A volcano erupts when pressure from molten rock beneath the surface forces magma, gases, and ash to escape through an opening in the Earth's crust. This buildup of pressure can be caused by factors such as the movement of tectonic plates, the release of gases, or the introduction of water into the magma chamber. Once the pressure becomes too great, the volcano erupts, spewing lava and volcanic ash into the air.