Animation of the rotating planet Earth, first removing the oceans to reveal the seafloor topography, and then highlighting the boundaries (red) between the tectonic plates. Earth's tectonic plates are irregular subdivisions of its surface rock, around 100 kilometres thick, which form the rigid lithosphere. These plates float on top of the more fluid asthenosphere, and move towards, away from or adjacent to neighbouring plates. These boundaries are known as faults, and are highly active geologically. Most of the world's volcanoes and earthquakes are attributed to these faults.