Why are there both earthquakes and volcanoes at convergent plate boundaries?

Convergent plate boundaries, also known as destructive plate boundaries, occur when 2 plate boundaries move towards one another due to convection currents in the mantle. The oceanic crust is subducted (forced beneath) the continental crust as the oceanic crust is more dense.  Due to intense, friction, heat and the oceanic crust melts which increases the pressure in the mantle. This means viscous (thick) magma is forced out under pressure through the Earth's crust, resulting in a violent volcanic eruption from a composite cone volcano. When the plates move together, there is plenty of friction meaning there are powerful earhquakes at these plate margins too.