A rift valley is related to plate tectonics, and the term refers to an extensive belt-like structure in the lithosphere with high-angle normal faults forming boundaries on both sides. Rift valleys are formed by extensional tectonics, which causes the lithosphere to rupture and become thinner. Rift valleys are the initial stage of continental disintegration and oceanic basin formation. Based on their activity, rift valleys can be classified into active rift valleys (such as the East African Rift Valley) and passive rift valleys (such as the Rhine Rift). Based on the type of crust, rift valleys can also be divided into continental rift valleys (rift valleys with continents on both sides, such as the East African Rift, the Rhine Rift and the Baikal Rift) and oceanic rift valleys (such as the Mid-Atlantic Ridge, the Indian Ocean Ridge and the Mid-Pacific Oceanic Ridge).