GEOLOGY

Detailed explanation-1: -According to the theory of plate tectonics, the asthenosphere is the repository for older and denser parts of the lithosphere that are dragged downward in subduction zones.

Detailed explanation-2: -Thick layers of sediment may accumulate in the trench, and these and the subducting plate rocks contain water that subduction transports to depth, which at higher temperatures and pressures enables melting to occur and ‘magmas’ to form. The hot buoyant magma rises up to the surface, forming chains of volcanoes.

Detailed explanation-3: -Recall that there are three types of plate boundaries: convergent, divergent, and transform. Volcanism occurs at convergent boundaries (subduction zones) and at divergent boundaries (mid-ocean ridges, continental rifts), but not commonly at transform boundaries.

Detailed explanation-4: -Volcanoes are mostly found at plate boundaries Some are the result of areas of thin asthenosphere. This thin area allows for the formation of hot plumes of magma. Island chains are the formed as the lithosphere moves over the asthenosphere.