1. Plate Movement - Constructive margins
Also called Divergent margins.
Occur where two plates are diverging (moving apart). the space between the diverging plates is filled with basaltic lava upwelling from below. New crust is constantly being created at constrictive margins, and are therefore some of the youngest parts of the earth's surface.
Features:
Mid-oceanic ridges are created when a constrictive boundary occurs in an oceanic area - for example the mid-Atlantic ridge
Rift valleys are created when a constructive boundary occurs in continental crust - for example the East African rift valley, and the rift valley visible at Thingvellir national park, Iceland
^Thingvellir, iceland. rifting in the rock is clearly visible, caused by the steady pulling apart of the Eurasian and North American plates