Explain the formation of thousands of islands in Indonesian and Philippines archipelagos.

Indonesia and Philippines constitute two of the five main archipelagos in the world, with Indonesia being the largest archipelagic state in the world, in terms of area and population. Archipelago refers to a cluster or group of relatively small islands. Archipelagos tend to be predominantly volcanic, with their island arcs (chain of volcanoes forming an arc shape) being created either due to subduction or erosion, deposition and land elevation.

Both Indonesian and Philippines archipelagos are a result of a combination of volcanic activity and tectonic plate movement. Both islands have been hotbeds of volcanic and seismic activity due to the convergence of continental plates. The islands are initially cause by the volcanoes, and later the shifting of tectonic plates results in their consolidation as a grouping of small islands in a relatively small area. Underwater volcanoes lead to seepage of magma onto the sea, thereby creating rock formation. Continual release of magma causes these rock formations to emerge onto the surface of the sea, thus creating an island. The shifting tectonic plates and existence of subduction zone in the area where the Indonesian and Philippines Islands are located causes the formation of an island arc or archipelago.