8 Different Types of Archipelagos

This is an aerial view of the Indonesian archipelago Wayang of Raja Ampat.

Archipelagos are a scattering of islands formed closely together in a body of water. Generally, archipelagos are oceanic islands. These islands are the results of volcanic eruptions. A collection of oceanic islands is called an island arc.

The formation of archipelagos affects the way they are characterized, for example, by volcanoes, erosion, sediment deposition, ocean currents, tectonic plates, global warming, post-glacial uplift, and glacial retreat. There are island arcs and archipelagic aprons. UNESCO protects many archipelagos.

Archipelagos’ beauty extends beyond their fantastical fauna and flora. The different formations of the various Archipelagos are evidence of the earth’s complexity and elegant machinery.

Table of Contents

What are Archipelagos- Definition

This is an aerial view of one of the Aegian Islands.

The word archipelago is a geographical term derived from Ancient Greek, (arkhi) – chief and (pelagos) – sea. In the ancient past, it was the name for the Aegean Sea. The term changed to describe the Aegean Islands. Island chains or island clusters are also known as Archipelagos. The islands in an archipelago form close together.

This collection of islands is mainly created in oceanic saltwater but does exist in rivers, freshwater. The islands vary in area size; they are single islands situated distinctly from each other. Archipelagos are characteristically beautiful and pleasing to the senses, with lush plantations and exotic flora. The species of the archipelagos are endemic.

Endemism and micro-endemism are the existence of a species and all its intrinsic attributes resulting from its heritage and nativity, belonging to a single isolated part, location of the world. Fauna and flora that are indigenous to a region are not endemic if they exist elsewhere.

There are many ways that Archipelagos form, which influences their traits. Different examples include island arcs or archipelagic aprons.

The Different Formations of Archipelagos

Archipelagos are the consequence of several distinct geographical activities; this includes volcanic eruptions, erosion and sediment deposit, flooding, evaporation, ocean currents, tectonic plate shift, glacial ice retreat, post-glacial uplift, and global warming.  

Archipelagos are a result of Volcanic Eruptions

This is an aerial view of the Banda Islands with lava flowing from the volcano.

Predominately archipelagos are formed due to volcanic eruptions on the surface of the ocean’s floor. These begin forming as volcanoes erupt, emitting hot lava into the sea. As the lava loses heat, it transforms into solid rock. It’s a process that continues over time, as eventually, the solidified lava breaks through the ocean surface.

The lava increasingly amasses covering the surface of the ocean floor. The island will, in due course, gain substantially in size, enough to encourage and maintain the development of living organisms.

The formation of the volcanic archipelagos is an interconnection of several volcanoes. They are either a series of individual islands or one island; tectonic plate activities shift over the volcano on the ocean floor, forming the islands as it moves.

These island arcs result from hotspots. When each plate shifts its crust layer, the areas where there are hot spots of volcanic activity remain stationary. That is, they don’t move with the crust. It builds islands in a sequence of arcs that also outline the direction of the tectonic movement.    

The Hawaiian archipelagos began growing from volcanic eruptions 80 million years ago. They are the consequence of the Pacific tectonic plate, northwest movement over a volcanic hotspot. Magma continually rises through the earth’s mantle and erupts through the surface of the ocean floor.

Tectonic Plate Convergence and Archipelagos

This is an aerial view of Kujuku Islands in Japan.

Plate tectonic movement shifts land to rupture and form islands. Tectonic plates or lithospheric plates strike against each other along a convergent boundary. Lithospheric plates are gigantic, unbending segments that make up the earth’s surface.

If both lithospheric plates are ocean plates, it’s an ocean-ocean convergence. Ocean-ocean convergence is responsible for the formation of archipelagos or volcanic island arcs. In ocean-ocean convergence, the atmospheric plate that is thicker and heavier subducts beneath the lighter oceanic crust into the asthenosphere.

The asthenosphere is the uppermost level belonging to the earth’s mantle. It has minimum resistance to plastic flow and is the area where convection occurs. Convection is the tendency of the fluid to heat up through movement, thereby permitting regions in the mantle that contain less material to rise.

Due to the convergence, a trench develops along the convergent boundary. As the ocean floor crust, which is full of sediments, subducts into the asthenosphere, the rocks in the subduction area become metamorphosed. Metamorphosed is defined as the changing structure of the stone as a result of high pressure and temperatures.

After sinking to depths of about 65 miles, the lower crust transforms into magma. Magma possesses less density at higher temperatures. It then rises upwards due to the buoyant force. The buoyant force arrives as thicker material that surrounds the magma pushes or displaces the magma upward.

The magma then pours out and over onto the seafloor. The continued upward flow of magma creates an area of constant volcanism; that eventually forms islands.

The area beneath the convergence zone is the zone of subduction. There is volcanism above the subduction zone, and this develops successive layers of rocks. Volcanic landforms along the convergent boundary create archipelago island arcs.

Orogenesis is the process of building mountains. It builds continental crust by replacing oceanic crust. Replacing oceanic crust with continental crust occurs at a much later time, over millions of years. Japan is an example of continental crust replacing oceanic crust; new islands arrive around Japan every few years.

Ocean-ocean convergence is responsible for the Indonesian archipelagos, the Japanese Archipelago, Philippine Island Arc, and Caribbean islands. 

Archipelagos formed as a Result of Ocean Currents

This is an aerial view of the Florida Keys in America.

Currents are the engine of the ocean. It is a force responsible for the dynamic systems on the planet. Currents navigate varied water movements within the tide, from regular water motion to streams of fast-flowing water and against other sea tides.   

The constant, eternal rhythm of the tide carries sediments away from the giant landmass. The recurring waves will force smaller landmass areas to fracture and assume their island shape; however, this is an infrequent occurrence that doesn’t happen regularly.

Ocean currents play a role in the erosion, transportation, and depositing of sediments that contribute to the formation of archipelagos. Archipelagos are formed laterally through the force of ocean currents.

Archipelagos Formation from Erosion and Sediment Buildup

Erosion is the process whereby the earth’s solid rock breaks into millions of minute fragments of rock. High-speed windstorms, running water, ocean currents, and acid rain are examples of the force driving the process of erosion.

The fragments or pieces of rock are sometimes transported to different locations and accumulate in one area, referred to as sediment deposition. Contingent to the environmental surroundings, the sediment could solidify into rock and form a large landmass, including islands.

Erosion creates an archipelago island chain by constantly wearing away at a giant landmass; this constant motion over time fashions small islands. Akin to this is when deposits of eroded sediments gather in a specific area. Over a considerable duration of time, this forms an island.

The Florida Keys is an example of how erosion and sedimentary deposit create archipelagos. They are called coral cay archipelagos that arrive after successive oceanic tides transport sediments that progressively develop the island on the reef surface.

The Role Global Warming Plays in Creating Archipelagos

This is an aerial view of the Antartica region.

As temperatures rise through a phenomenon known as global warming, glaciers begin to melt into the oceans and cause the level to rise. Glaciers are enormous bodies of freshwater ice that shift steadily above land. There are two common types of glaciers: alpine glaciers and ice sheets.

Alpine glaciers exist on mountainsides and follow the force of gravity downwards into valleys, usually at a slow pace. They can also be responsible for valley formation by exerting pressure on soil and an array of different materials as they move. Alpine glaciers reside on every continent except Australia. 

In contrast, ice sheets can exist independently without relying on land to develop. Ice sheets grow vast domes that span out from their midpoints in all directions. As ice sheets expand, they envelop absolutely everything, including plains, valleys, and whole mountains.

Continental glaciers are enormous ice sheets. They encapsulate immense regions like the continent of Antarctica and Greenland. When temperatures rise, the ice melts, the topography of the surface of the earth changes; this includes archipelagos formation.

Archipelagos Created from Continental Glacial Retreat

This is the archipelago aerial view of Hanko, Finland.

Over the past 600 000 years, the earth has experienced three ice ages. The Last Glacial Maximum (LGM) was the most recent glacial period that ice sheets were at their total volume. The ice sheets grew to 1,86 miles in size.

Many archipelagos exist today, formed during the last ice age because of glacial retreat. As the massive ice sheets covering North America, Canada, Eurasia began to retreat or rapidly melt, the level of the oceans increased, and low-lying valleys flooded. The characteristic scattering of the Archipelago recognizes the remaining surfaced land.

The largest Archipelago in the world is the Malay Archipelago, formed by a glacial retreat. The Malay Archipelago is found between the Pacific and Indian oceans and encompasses 25,000 islands in Southeast Asia.

The myriad of islands belonging to Indonesia and Malaysia are a feature of the Malay Archipelago. A portion of these islands and their partitioning straits belonged to mainland Asia during the last ice age.

Finland’s archipelagos inhabit the Baltic Sea and surface after the end of the last ice age. There are over 50 000 islands in Finland’s Archipelago Sea, many of which are small and closely clustered.

Archipelagos and Post Glacial Rebound

This is a view of the large glacier in Antartica.

Post-glacial rebound describes the reformation of a landmass to its original shape after being weighed down by the ice sheet or continental glacier. The continent has its elasticity and reacts like a sponge, regaining its form. Isostatic rebound or crustal rebound are other terms to describe post-glacial rebound.

During the LGM approximately 20 000 years ago, the stupendous weight of the glaciers forced the mantle beneath the crust to displace. This viscoelastic mantle material very slowly gravitates back to the area where it transferred. The process is still occurring.  

As post-glacial rebound is presently happening, islands are still rising from the Archipelago Sea in the Baltic at a rate of 0,393 inches a year. The rise covers an area of 4,34 square miles per year.

The Categories of Archipelagos

Island Arcs

This is an aerial view of the Siargao islands and lagoons in the Philippines.

Island arcs are a long chain of oceanic islands characterized by intense seismic and volcanic activity and orogenic (mountain building) features. Chief examples of island arcs are Aleutian-Alaska Arc and the Kuril-Kamchatka Arc.

Generally, island arcs comprise two parallel strings of islands. The inner row of the double stretch of islands contains a chain of explosive volcanos, and the outer row is composed of non-volcanic islands. Regarding single arcs, numerous constituent islands are volcanically active.

Generally, an island arc possesses an abnormally shallow sea on the concave side; however, there is an elongated, tapered deep-sea trench on the convex side at every instance of this Archipelago formation.

The most extensive deep-sea trenches are in the depressions of the ocean floor, as is the example of the Marianna Trench and the Tonga Trenches. These island arcs form when to lithospheric plates collide. One plate is forced downward into the lower mantle beneath the second plate with the lighter earth’s crust.  

Devastating earthquakes happen regularly at the location of the island arc. In contrast to shallow earthquakes on continents, these are deep-focus earthquakes, the seismic occurrences arising from as much as 370 miles from the base of an arc.

The bulk of island arcs reside within the western margin of the Pacific Basin, with exceptions of the East Indian and West Indian arcs and the Scotia arc in the South Atlantic.  

Japan is a formation of 6,852 islands that make up the nation, and it is three island arcs. It covers 1,900 miles, from the Sea of Okhotsk in the northwest to East China and Philippine Seas.  

Japan has four large islands: Hokkaido, Honshu, Shikoku, Kyushu, and approximately 3000 smaller islands. In several locations in the Japanese Archipelago, volcanoes are continuously active.

Archipelagic Apron

This is an aerial view of the Marshall Islands.

Archipelagic aprons result from successive layers of volcanic rock that create a fan-like shape around clusters of ancient or recent islands. They occur mainly in the Pacific Ocean and feature gentle slopes or veneers.

Aprons generally possess a slope of 1/2-degree, then decrease toward the shore. Although the topography is coarse, the constant current of the turbid tide depositing sediment over the past 10 000 years makes it smooth.

Archipelago aprons exist in Hawaii, Samoa, Marquesas Islands, Marshall Islands, and the Gilbert Islands. Aprons result from a layer of rock, referred to as the second layer, that transmits seismic surges (at a velocity of 2,5 and 4 miles per second).

Pyroclastic flows cause the formation of the second layer- fluid lava emits out of crevices close to the base of the volcanic island. Aprons comprise around 8% of the Pacific area.      

Archipelagos and UNESCO- Outstanding Universal Value

Today many archipelagos are protected as United Nations Educational Scientific and Culture Organization (UNESCO) world heritage sites that possess outstanding value.

UNESCO world heritage sites possess qualities that contribute positively to the human experience. These locations are universally appreciated. They preserve an irreplaceable legacy through the protection of the international community.

Outstanding value is the essence of the World Heritage Convention. The World Heritage Operational Guidelines define value; these qualities must be unsurpassed, remarkable, and acknowledged by all nations worldwide.      

UNESCO- Galapagos Island

This is a view of Batolome Island in the Galapagos archipelago.

The Galapagos Island is in the Pacific Ocean, approximately 563 miles from the South American Continent off Ecuador; it is an Ecuadorian province. The Galapagos are volcanic archipelagos that are composed of 19 islands and an enclosing marine reservation. The marine reserve is an organic, biological museum and evolutionary showcase; Charles Darwin originated his theory of evolution through observation of the Galapagos.  

The Galapagos Islands are at the confluence of three separate ocean currents: the Humboldt Current, the Panama Flow, and the Cromwell Current. The nautical conditions that arrive at Galapagos are exceptional.

The Humboldt Current is a surface ocean current, and the Cromwell current arrives from dark depths of the ocean; both streams contain an abundance of nutrients. These nutrients are the decaying matter that sinks below the ocean’s surface from dead flora and fauna. They come from the Antarctic.

Deep below the ocean surface, the moving current hits the volcanic formations of the Archipelago; these nutrients move up, called upwelling. These incidents give the coasts and their proximate islands nutrient-rich waters on which the biodiversity and ecosystem rely.

The foundation of marine ecosystems is plankton. The Cromwell Current rushes at 300 feet below the surface currents. As it hits the Galapagos, it deflects towards the surface with its chill nutrient tide. The enriched plankton tide provides a base feed for the marine ecosystem.

The Panama Current is a warmer current that flows down from Central America. It doesn’t contain as many nutrients but assists with the biodiversity in numerous other ways, like supporting lush vegetation.  

UNESCO- The Quirimbas Archipelago

This is an aerial view of the Vilankulo island in Mozambique.

The Quirimbas are a cluster of islands located in northern Mozambique. This Archipelago comprises 31 islands strewn across 200 miles from Cape Delgado. These islands lie parallel to the coast; they connect to the shore of the continent’s coast through coral reefs, sand bars, and mangroves.

The water between these two landmasses is abundant with marine life, which includes: dugongs, dolphins, whales, and turtles thrive around the coral reef; it’s been a world heritage site since 2008.

The islands of Ibo hold particular significance; the islands Quisiva and Matembo to a lesser degree.  The Quirimbas contains vast cultural value as it represents a melting pot of Portuguese, Arabian, and African influences.

There are landmarks with immense historical significance., such as the old fort on the Ibo island. These relay events in history that detail slavery, pirates, and the infamous ivory trade.

On Ibo Island is the historic Stone Town; it combines numerous cultural influences over centuries. This historic landmark is heterogeneous; centuries have seen the synchronization of Europe, Arabia, Swahili, and India. The town is quintessentially Swahili, especially in its architecture, with colonial additions.

UNESCO- High Coast/ Kvarken Archipelago

This is an aerial panorama view of the Kvarken archipelago.

The Kvarken Archipelago belongs to Finland, and the High Coast belongs to Sweden. These are in the Gulf of Bothnia. Corrugated washboard moraines characterize the 5,600 islands that compose the Archipelago.

Washboard moraines are a geomorphic attribute fashioned from thawing continent ice sheets about 10 000- 24 000 years ago. They only stand a few feet high and are consistently spaced parallel crests.   

The Archipelago is constantly elevating due to post-glacial rebound, or glacial-isostatic uplift. This site allows scientists to investigate the earth’s tectonic movements; this includes post-glacial uplift and isostatic processes.

UNESCO- Socotra Archipelago

This is an aerial view of the Socotra Island in the Indian Ocean in Yemen.

Socotra Archipelago resides in the northwest Indian Ocean close to the Gulf of Aden and is about 155 miles long. The Socotra Archipelago comprises four islands and two rock-strewn islands; these appear as an elongated extension of the Horn of Africa.

This location is universally relevant as it retains a wealth of biodiversity; 37% of 825 plant species, 90% of its reptile species, and 95% of its snail species don’t exist anywhere else in the world.  

UNESCO- Vegaøyan- The Vega Archipelago

This is an aerial view of the Vega Archipelago.

Vegaøyan is located immediately south of the Arctic circle in Norway; as of 2004, UNESCO protects its cultural landscape.  The fisherman of Vegaøyan has preserved the means to survive on an inhospitable terrain for over 1500 years. Women have collected eiderdown for centuries and contributed to a unique method for harvesting.

The eider duck has made Vegaøyan their home and breed in large numbers on the island. The feathers are gathered by the residents on the islands and contribute to their sustained livelihoods.

UNESCO- Archipiélago de Revillagigedo

This is an aerial view of the Benedicto volcano island in the Revillagigedo Archipelago.

The Archipiélago de Revillagigedo is situated in East Pacific, 448-603 miles from the coast of Mexico, and is a Mexican province. This archipelago is comprised of four islands: Isla San Benedicto, Isla Socorro, Isla Roca Partida and Isla Clarión. Each island possesses a marine-protected enclosure that expands 12 nautical miles surrounding each.

Volcanos create the islands; therefore, the ocean depths surrounding each island increase suddenly at 6-8 miles off their shoreline. The Archipiélago de Revillagigedo belongs to a submarine mountain range. The four islands are the tips of volcanoes that penetrate the surface of the ocean.

This Archipelago is an invaluable area that two marine biogeographic regions converge: the Northeastern Pacific and the Eastern Pacific. This location is a confluence of the Equatorial current and the Californian current. This confluence precipitates a highly productive, intricate nexus.

These Islands are viewed as a crucial area for extensive wildlife species to rest, recuperate and then relocate. In the area resides a wealth of humpback whales, turtles, sharks, and manta rays. Each island reveals the characteristic endemic species that arise from isolated regions.

The Archipiélago de Revillagigedo possesses many endangered species and is vital to ensuring the species’ sustained longevity. This Archipelago is the singular place that breeds the seriously endangered Townsend Shearwater bird.

UNESCO- Archipelago Sea Area Bioreserve Finland

This is an aerial view of the islands and wind turbines of Pori, Finland.

Located in Pori and Turku’s provinces in Southwest Finland, it is a coastal environment that comprises numerous smaller islands in the Baltic Sea. The inhabitants have engaged with the island for generations. The fishing and agricultural lifestyle began to diminish at the beginning of the 20th century; populations have since decreased.

The archipelagos are described as mosaics and contain 6,500 unique islands. The post-glacial land rise creates identifying features that illustrate how this process of the planet evolves.

The bedrock of the archipelagos is the remains of an ancient mountain range called the Svecofennides. It is a peneplain, a geomorphological feature characterized by constant erosion over an extensive period and undisturbed by plate tectonics.

Conclusion

Archipelagos are stunning and wondrous features of the earth.  They are remarkable for their processes. The clusters of islands are renowned for their rich biodiversity and complex marine ecosystems. Numerous procedures create archipelagos; these include volcanoes, erosion, sediment deposition, ocean currents, glacial retreat, post-glacial retreat, and global warming. There are two categories of archipelagos; these are island arcs and archipelagic aprons.

UNESCO world heritage sites preserve many archipelagos around the world for their unsurpassed worth. Areas include the Galapagos Islands, the Quirimbas Archipelagos, Archipelago Sea Area Bioreserve Finland, Archipiélago de Revillagigedo, Vegaøyan- The Vega Archipelago, Socotra Archipelago and the Kvarken Archipelago. These regions offer worth in their biodiversity, ecosystems, protection of endangered species, and scientific inquiry.

References:

National Geographic: Archipelago

Australian Government Department of Agriculture, Water and Environment: Understanding World Heritage: what is outstanding universal value?

UNESCO WHC: Galápagos Islands

UNESCO WHC: The Quirimbas Archipelago

UNESCO WHC: High Coast / Kvarken Archipelago

UNESCO WHC: Socotra Archipelago

UNESCO WHC: Vegaøyan – The Vega Archipelago

UNESCO WHC: Archipiélago de Revillagigedo

UNESCO: Archipelago Sea Area Biosphere Reserve, Finland

Britannica: Island Arc

Living Oceans Foundation: Galapagos Currents

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Wonderopolis: What is an Archipelago

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The Royal Society Publishing: The age and origin of the Pacific islands: a geological overview

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U.S. Forest Service: What is the Importance of Islands to Environmental Conservation

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National Geographic: Ice Sheet

The Guardian: Melting glaciers reveal five new islands in the Arctic

CNN World: Melting glaciers in the Russian Arctic reveal five new islands

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