It is believed that the crust, beneath the oceans as well as the continents, together with the upper part of the mantle is divided into huge slabs called plates. The movement of the plates is explained by the earlier theory of Continental Drift.

     There are eight identified major plates plus an assortment of smaller ones. The major plates include the Eurasian plate, the African plate, the North American plate, the South American plate, the Antarctic plate, the Indoaustralian plate, the Pacific plate and the Nazca plate.

(Fig 1.10) Major plates of the world.

     Figure 1.10 shows the different plates on the world map, which shows that the plates are capped by both the oceanic and continental crust. Most volcanoes are found along and around the plate edges.