Giant blocks of the Earth’s crust floating in a semiplastic earth mantle and moving relative to each other at a rate of a few millimetres to centimetres per year. On the lithospheric, or tectonic plates, the Earth’s continents are located. Due to the movement of the lithospheric plates, the position of the continents on the Earth’s surface is gradually changing. Where the lithospheric plates meet, the Earth’s crust is thinner and tectonic activity, such as volcanism or earthquakes, is more frequent.