A volcanic eruption occurs when -
A: extreme heat and pressure forces the melted rock in Earth's core to burst upward
B: melted rock from Earth's outer core flows into the inner core and cools into large boulders
C: centuries of chemical weathering cause Earth's mantle to break apart and reveal magma
D: tectonic plates in the Earth's crust slide past each other causing cracks in Earth's crust to widen