Item 2 Explain how crustal deformation builds landforms. When sediments are laid down over vast areas the forces involved create rock over a very long period of time. When two tectonic plates start to push into each other they can rise up and build mountains, or sink under and create deep valleys. When wind and rain slowly wear away rock, they leave behind new looking land forms. When two tectonic plates slide away from each other the inner liquid layer of the mantle comes to the surface as lava and creates new islands.