How are island archipelagos also called island arcs formed.

When two oceanic plates converge, one of the plates sinks underneath the other and forms a deep depression called ocean trench. The plate sinks further down into the mantle and begins to melt. The molten rock (magma) rises toward the surface from the melting plate forming a chain of volcanic islands (island arcs) behind the ocean trench.

Explanation:

The Earth's crust is divided into several hard and rigid tectonic plates that slide over the mantle. Tectonic plates can interact in three different ways: converge (move toward one another), diverge (move away from one another) or transform (slide past one another). The plate margins are the boundaries where plates meet and they are of three kinds: oceanic-oceanic, continental-continental, and continental-oceanic.

When two oceanic plates converge, one of the plates sinks underneath the other and forms a deep depression called ocean trench. The plate sinks further down into the mantle and begins to melt. The molten rock (magma) rises toward the surface from the melting plate forming a chain of volcanic islands (island arcs) behind the ocean trench.

An island arc comprises a curving series or group of volcanic islands that form near the convergent boundary of two tectonic plates. They are formed from the volcanic activity along a subduction zone, where one oceanic tectonic plate subducts (one plate sinks under another plate into the mantle of the Earth) another oceanic plate. This movement pushes the lower plate further deeper to a point where the temperature is sufficient to melt the subducted plate and results in the production of magma directly below the top tectonic plate. This magma then rises through fractures and reaches the upper crust and forms volcanoes which eventually rise high enough to become islands. The islands of Japan, the Aleutian Islands, etc are examples of island arcs.

When two continental plates converge, they collide and compress to create complex mountain ranges having great height. The Himalayas formed by the collision of the Indian-Australian plate and the Eurasian plate is an example.

During the convergence of continental and oceanic plates, the denser oceanic plate sinks below the continental plate and a chain of volcanoes known as a volcanic arc are formed. The examples of volcanic arcs are the Cascade Mountains of North America and the Andes Mountains of South America.