Archipelago
An archipelago is defined as a group of islands that are closely clustered together, typically found in oceans, lakes, or rivers. This geographical formation can be found in various parts of the world, with notable examples including the British Isles, the Galápagos Islands, and the Malay Archipelago, which is the largest in terms of area, comprising over 25,000 islands. The term originates from the Aegean Islands, derived from Greek words meaning "leader" and "sea."
Archipelagos can form through several geological processes, including changes in sea levels due to climate fluctuations, glacial activity, volcanic eruptions, and plate tectonics. For instance, the Malay Archipelago was created when rising sea levels separated islands from the mainland during the last ice age. In contrast, volcanic activity forms oceanic islands, such as those in Hawaii and Japan, which continue to grow through ongoing eruptions.
Additionally, archipelagos are not limited to saltwater environments; they can also be found in freshwater settings. The Great Lakes in North America and Lake Victoria in Africa host several islands, with the Georgian Bay in Canada recognized as the largest freshwater archipelago. Overall, archipelagos are significant both ecologically and culturally, representing diverse ecosystems and human histories.
Archipelago
An archipelago, pronounced "ar-kih-PEL-lih-goh," is a group of islands that are tightly clustered together in an ocean, lake, or river, with most being found in the ocean. Some examples of archipelagos include the British Isles, the Galápagos Islands, Bermuda, Japan, New Zealand, the Philippines, and the Hawaiian Islands.
The term archipelago originated with the Aegean Islands in the Aegean Sea and is derived from the Greek words arkhi (leader) and pelagos (sea). Archipelagos are most likely to be found in open waters, but some, including the largest archipelago on Earth, are relatively geographically close to larger landmasses.
The Largest Archipelagos
The levels of Earth's seas change over time because of changes in the average temperature. Colder periods result in more water turning to ice near the poles; this reduces sea level and exposes more land. Warmer periods melt polar ice, causing lowland and coastal areas to flood. When this occurs, higher areas can become separated from the main body of land by the water that floods the lowlands.
This is how the Malay Archipelago, the largest archipelago in the world by geographic area, was formed. The Malay Archipelago is a massive cluster of more than 25,000 islands in Southeast Asia, in the area between the Pacific and Indian Oceans. It includes the many islands of Indonesia and Malaysia.
The Malay Archipelago was originally part of the larger landmass of Asia but became separated during the last ice age, between 21,000 and 11,500 years ago. At this time, the glaciers began to retreat, and rising sea levels flooded lower land areas near the coast. Mountainous ranges at higher locations formed continental islands. Geologists believe this is how the Malay Archipelago formed.
Glaciers can also form archipelagos in another way. As the extremely heavy masses of ice move over land, the land is compressed and flattened. When the weight of the ice is removed, the land can slowly resume its previous shape, much like a foam pillow or mattress does when pressure is applied and released. As the land rebounds, it sometimes pushes above the water level, creating an island. Scientists have determined that post-glacial rebound is responsible for the Archipelago Sea. This includes more than 50,000 Finnish islands in a section of the Baltic Sea and is the largest number of islands of any known archipelago. Some of these islands are less than half a hectare (about one acre) in size. Post-glacial rebound can occur over thousands of years; islands continue to appear in the Archipelago Sea into the twenty-first century.
Other Sources of Archipelagos
While glaciers played a role in the creation of many archipelagos around the world, other archipelagos can credit their development to fire rather than ice. Some archipelagos are formed over hot spots on the ocean floor. These very hot sections of Earth just under the surface of the ocean floor are created through a process known as convection, where heat from Earth's core rises up to the planet's crust. The heated material, known as magma, can break through the crust to form volcanoes, or it can cause the crust to shift over it, which forms a ridge of islands that correspond to the direction of the movement.
The Hawaiian Islands were formed in this way and continue to grow through volcanoes fed by hot spots. Material from an erupting volcano will build up on the ocean floor; over time, the eruptions create a mass large enough to rise above the ocean level and become an island. These are known as oceanic islands; an archipelago that is formed of this type of island is known as an island arc. Before a volcanic mass reaches the surface, the underwater volcano is also known as a seamount. In the Hawaiian Island chain, the seamount Kama'ehuakanaloa (formerly known as Lō'ihi) is an example that will eventually become an island in its own right. Erupting volcanoes can also add to existing islands, as happens in Hawaii, the so-called "Big Island" of the chain, where two active volcanoes continue to build up the land area.
Japan is another example of a volcanic island arc. The country is made up of more than 3,000 small islands and four larger islands, some of which continue to grow through volcanic activity. But the island chain was also formed through plate tectonics, or the shifting of the large landmasses that make up the Earth's surface both above and beneath the water. Researchers say this accounts for the fact that many islands in the Japanese archipelago have large amounts of geological material that is more in line with continental landmasses than volcanic activity; portions of the islands were formed when parts of the mainland rippled and were pushed out to sea.
Freshwater Archipelagos
While many archipelagos form in large seas, they can also be found in lakes and rivers. The Great Lakes in North America host several archipelagos, as does Lake Victoria in Africa. The 30,000 islands in Georgian Bay in Ontario, Canada, are generally considered the largest freshwater lake archipelago in the world and were created by glacial activity. The Anavilhanas Archipelago in Brazil's Rio Negro, a tributary of the Amazon River, boasts more than 400 islands during the dry season and claims the title of largest freshwater river archipelago. These islands, like many river islands and archipelagos, were formed by collections of sediment deposited by the river itself.
Bibliography
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"Georgian Bay Islands National Park." Parks Canada, 16 Oct. 2023, www.pc.gc.ca/eng/pn-np/on/georg/index.aspx. Accessed 7 Dec. 2024.
Roza, Greg. The Creation of Islands. Rosen Publishing Group, Inc., 2010.
"Volcano Watch - Kamaʻehuakanaloa - The Volcano Formerly Known as Lōʻihi Seamount." U.S. Geological Survey, 27 Jan. 2022, www.usgs.gov/observatories/hvo/news/volcano-watch-kamaehuakanaloa-volcano-formerly-known-loihi-seamount. Accessed 7 Dec. 2024.
“What Is an Archipelago?” NOAA's National Ocean Service, 16 June 2024, oceanservice.noaa.gov/facts/archipelago.html. Accessed 7 Dec. 2024.