What happens at tectonic plate margins
1. Constructive margin: Plates move apart, magma forces way to surface, causes mild earthquakes, results in broad flat shield volcanoes
2. Destructive margin: Plates move towards each other, dense oceanic plate subducted beneath less dense continental plate, friction causes strong earthquakes, results in steep-sided composite volcanoes
3. Conservative (transform) margin: Plates move past each other at different rates, friction builds stresses and triggers earthquakes, no volcanoes