This unit discusses the formation of Earth's relief through internal and external forces. Internal forces such as continental drift, tectonic plates, orogeny, volcanoes and earthquakes shape relief. External forces including erosion, transport and deposition by water, wind and human activity also impact landforms. Tectonic plates consist of different blocks of the lithosphere that can move apart or collide, generating mountains, volcanoes and earthquakes. Erosion and other external forces further sculpt the landscape over time.