An archipelago is a group of islands closely scattered in a body of water. Usually, this body of water is the ocean, but it can also be a lake or river. For example, the Malay archipelago, the largest group of islands in the world, consists of more than 17,000 islands in Indonesia and approximately 7,000 islands in the Philippines. Types of archipelagos: Depending on the geological origin, the islands of the archipelagos can be oceanic or continental islands.

• Oceanic archipelagos: These are the group of islands that do not belong to a particular continental tectonic plate, but are of volcanic origin. These forms at a greater speed. For example, the Hawaiian archipelago.
• Continental archipelago: These islands are formed by continental fragments that have been separated from the continent by the movement of tectonic plates and other geological processes. For example, the British Isles and Balearic Islands.

Processes involved in the formation of archipelagos include:

• Volcanic activity: Volcanic activity that can form archipelagos includes a hotspot, where an area within the oceanic crust is heated and has a constant supply of magma spewing out from within and cooling off to form land. The relatively stationary hotspot acting on the shifting crust is what creates a chain of islands or archipelagos. For example, the Hawaiian archipelago is formed by a series of volcanoes.
• Erosion and sediment deposit formation: The movement of erosional agents like water can break down rock into sediments. These small sediments can be carried away to a new location and settle to form island-like structures. For example, the coral clay archipelago of Florida Keys formed out of sediments transported by ocean currents and gradually built up on the reef structure.
• Tectonic movements: Continental fragments are archipelagos that have separated from a continental landmass due to the Earth’s tectonic movements. For example, Farallon Islands off the coast of California.
  • Apart from this, archipelagos also form at a convergent plate boundary where oceanic plate gets subducted into the mantle and melt to raise convection currents. Such a group of islands is called an Island arc volcano. For example, Fiji, and Alaska’s Aleutian Islands.
• Glacial retreat: This phenomenon leads to the flooding of valleys and a rise in sea level leaving coastal mountain ranges standing tall. The coastal mountain ranges eventually become archipelagos. For example, the Malay archipelago, the largest on the Earth, was formed by a glacial retreat.
• Post-glacial rebound: In this process, land that was squashed by the weight of heavy glaciers during the Ice Age slowly regains its shape, like a sponge, and islands are formed out of this land. For example, the Finnish archipelago (the archipelago in Finland).

Apart from these major processes, archipelagos also form due to changes in the course of rivers, the drying up of lakes, etc. Archipelagos, as a geological structure, are not only important in terms of human settlement but are also pertinent for ecological preservation.