Convection occurs because: Question 11 options: Small earthquakes occur within the Earth's crust causing rocks to shake and change temperature. Oceanic crust is being destroyed at deep ocean trenches. Molten rock comes close to the Earth's core it heats up, becomes less dense and rises and the molten rock near the Earth's crust cools down, becomes more dense, and sinks causing the cycle of convection. Convection does not occur within the Earth.