The largest tectonic plate is the Pacific plate, measuring over 100 million square kilometres. It is known as an oceanic plate as most of its crust is below sea level. At its centre, the Pacific plate has a hot spot which is responsible for forming the Hawaiian Islands.
Tectonic plates can be up to 200 kilometres deep and are composed of the entire crust layer, most of the moho layer and a fraction of the upper mantle. Collectively these layers are known as the lithosphere. The crust layer is continually moving, like a conveyor belt, with new material pushing older material towards the plate boundary.