Animation of the Earth showing the tectonic plates and the boundaries between them. The ocean has been removed to show the bathymetry of the seabed. The Earth's crust is made up of seven or eight main tectonic plates, with smaller ones between them. The plates comprise a lower, denser layer of oceanic crust, partly overlain with lighter continental crust. Boundaries between plates can either be divergent, convergent or transform. Divergent boundaries, such as Mid-Atlantic Ridge, are the sites of the creation of new crust, which rises from the mantle and moves away from the boundary. Transform boundaries, such as the San Andreas Fault in California, USA, occur where plates slide past one another. At a convergent boundary, either the denser plate slides beneath the lighter, forming a subduction zone, as at the Great Sumatran Fault, or continental crust collides and is lifted into mountains, such as the Himalayas.