Earth movements generate tensional forces that pull the crust apart. Tensional forces are generated when two plates move away from each other, creating a gap or a rift. As the plates move apart, the tension between them causes the crust to stretch and thin, forming a basin or a depression. This can lead to the formation of a rift valley or a mid-ocean ridge. The tensional forces can also cause earthquakes and volcanic eruptions as the magma rises to the surface through the cracks in the crust.