The processes for building new land are called constructive forces. Three of the main constructive forces are crustal deformation, volcanic eruptions, and deposition of sediment Crustal deformation occurs when the shape of land (or crust) is changed or deformed. One of the main causes is movement of the Earth's plates. When the plates collide or push toward each other, pressure builds. This can cause two things to happen. The rock can either fold or fault.