An island arc is a type of archipelago

Archipelago

An archipelago , sometimes called an island group, is a chain or cluster of islands. The word archipelago is derived from the Greek ἄρχι- – arkhi- and πέλαγος – pélagos through the Italian arcipelago...

 composed of a chain of volcanoes which alignment is arc-shaped, and which are situated parallel and close to a boundary between two converging tectonic plates

Tectonic Plates

Tectonic Plates is a 1992 independent Canadian film directed by Peter Mettler. Mettler also wrote the screenplay based on the play by Robert Lepage. The film stars Marie Gignac, Céline Bonnier and Robert Lepage.-Plot summary:...

.

Most of these island arcs are formed as one oceanic tectonic plate subducts

Subduction

In geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge. These 3D regions of mantle downwellings are known as "Subduction Zones"...

 another one and, in most cases, produces magma

Magma

Magma is a mixture of molten rock, volatiles and solids that is found beneath the surface of the Earth, and is expected to exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and dissolved gas and sometimes also gas bubbles. Magma often collects in...

 at depth below the over-riding plate. However, this is only true for those island arcs that are part of the group of mountain belts which are called volcanic arc

Volcanic arc

A volcanic arc is a chain of volcanoes positioned in an arc shape as seen from above. Offshore volcanoes form islands, resulting in a volcanic island arc. Generally they result from the subduction of an oceanic tectonic plate under another tectonic plate, and often parallel an oceanic trench...

s, a term which is used when all the elements of the arc-shaped mountain belt are composed of volcanoes. For example, large parts of the Andes/Central American/Canadian mountain chain may be known as a volcanic arc, but they are not islands (being situated upon and along a continental area) and are thus not classified as an island arc. On the other hand, the Aegean or Hellenic arc

Hellenic arc

The Hellenic arc or Aegean arc is an arcuate tectonic feature of the eastern Mediterranean Sea related to the subduction of the African Plate beneath the Aegean Sea Plate...

 in the Mediterranean Area, composed of numerous islands such as Crete

Crete

Crete is the largest and most populous of the Greek islands, the fifth largest island in the Mediterranean Sea, and one of the thirteen administrative regions of Greece. It forms a significant part of the economy and cultural heritage of Greece while retaining its own local cultural traits...

, is an island arc, but is not volcanic. Parallel to it is the South Aegean Volcanic Arc

South Aegean Volcanic Arc

The South Aegean Volcanic Arc is a chain of volcanic islands in the South Aegean Sea formed by plate tectonics as a consequence of the subduction of the African tectonic plate beneath the Eurasian plate...

, which is the volcanic island arc of the same tectonic system.

Classification

There is some debate about the usefulness of the distinction between island arcs and volcanic arcs. The term "volcanic island arc" is merely a sub-classification of "island arc." Island arcs are tectonically created arc-shaped mountain belts that are partly below sea level. Essentially, they represent a specific geographic-topographic situation in which a mountain belt is partly submerged in ocean. Many of these are composed of volcanoes, and can thus be further classified as volcanic island arcs.

Tectonic formation

Following is a brief description of a subduction zone and its relation with volcanism, one of the more common causes of (volcanic) island arcs (for more information, see the Page covering subduction

Subduction

In geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge. These 3D regions of mantle downwellings are known as "Subduction Zones"...

):

In the subduction zone, loss of volatiles from the subducted slab

Slab (geology)

In geology, a slab is the portion of a tectonic plate that is being subducted.Slabs constitute an important part of the global plate tectonic system. They drive plate tectonics both by pulling along the lithosphere to which they are attached in a processes known as slab pull and by inciting...

 induces partial melting of the overriding mantle. This process, called flux melting

Flux melting

In igneous petrology flux melting occurs when water and other volatile components are added to a hot solid rock. The ultramafic rock of the upper mantle can be melted by the addition of volatiles from below. The source of the water and volatiles is the subducting slab of oceanic crust which...

, generates low-density calc-alkaline

Calc-alkaline

The calc-alkaline magma series is one of two main magma series in igneous rocks, the other magma series being the tholeiitic. A magma series is a series of compositions that describes the evolution of a mafic magma, which is high in magnesium and iron and produces basalt or gabbro, as it...

 magma

Magma

Magma is a mixture of molten rock, volatiles and solids that is found beneath the surface of the Earth, and is expected to exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and dissolved gas and sometimes also gas bubbles. Magma often collects in...

 that buoyantly rises to intrude and be extruded through the lithosphere of the overriding plate. The resulting volcano

Volcano

2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...

 chain has the shape of an arc parallel to the convergent plate boundary and convex toward the subducting plate. One of the theories to explain the arc shape views this as a consequence of the geometry of the spherical plate crumpling along a line on a spherical surface, but only the more broadly shaped arcs can be explained in this way.

On the subducting side of the island arc is a deep and narrow oceanic trench

Oceanic trench

The oceanic trenches are hemispheric-scale long but narrow topographic depressions of the sea floor. They are also the deepest parts of the ocean floor....

, which is the trace at the Earth’s surface of the boundary between the downgoing and overriding plates. This trench is created by the gravitational pull of the relatively dense subducting plate pulling the leading edge of the plate downward. Multiple earthquake

Earthquake

An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...

s occur along this subduction boundary with the seismic hypocenter

Hypocenter

The hypocenter refers to the site of an earthquake or a nuclear explosion...

s located at increasing depth under the island arc: these quakes define the Wadati-Benioff zones.

Ocean basins that are being reduced by subduction are called 'remnant oceans' as they will slowly be shrunken out of existence and crushed in the subsequent orogenic

Orogeny

Orogeny refers to forces and events leading to a severe structural deformation of the Earth's crust due to the engagement of tectonic plates. Response to such engagement results in the formation of long tracts of highly deformed rock called orogens or orogenic belts...

 collision. This process has happened repeatedly in the geologic history of the Earth.

Examples

Island arc	Country	Trench	Basin Oceanic basin Hydrologically, an oceanic basin may be anywhere on Earth that is covered by seawater, but geologically ocean basins are large geologic basins that are below sea level...  or marginal sea Marginal sea The term marginal sea has differing meanings. In one sense the term is equivalent to territorial waters. In another sense the term indicates a partially enclosed sea adjacent to or widely open to the open ocean, but bounded by submarine ridges...	Plate	Subducting plate Subduction In geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge. These 3D regions of mantle downwellings are known as "Subduction Zones"...
Aleutian Islands	United States United States The United States of America is a federal constitutional republic comprising fifty states and a federal district...	Aleutian Trench Aleutian Trench The Aleutian Trench is a subduction zone and oceanic trench which runs along the southern coastline of Alaska and the adjacent waters of northeastern Siberia off the coast of Kamchatka Peninsula. It is classified as a "marginal trench" in the east as it runs along the margin of the continent, and...	Bering Sea Bering Sea The Bering Sea is a marginal sea of the Pacific Ocean. It comprises a deep water basin, which then rises through a narrow slope into the shallower water above the continental shelves....	North American Plate North American Plate The North American Plate is a tectonic plate covering most of North America, Greenland, Cuba, Bahamas, and parts of Siberia, Japan and Iceland. It extends eastward to the Mid-Atlantic Ridge and westward to the Chersky Range in eastern Siberia. The plate includes both continental and oceanic crust...	Pacific Plate Pacific Plate The Pacific Plate is an oceanic tectonic plate that lies beneath the Pacific Ocean. At 103 million square kilometres, it is the largest tectonic plate....
Kuril Islands Kuril Islands The Kuril Islands , in Russia's Sakhalin Oblast region, form a volcanic archipelago that stretches approximately northeast from Hokkaidō, Japan, to Kamchatka, Russia, separating the Sea of Okhotsk from the North Pacific Ocean. There are 56 islands and many more minor rocks. It consists of Greater...	Russia Russia Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...	Kuril-Kamchatka Trench Kuril-Kamchatka Trench The Kuril–Kamchatka Trench or Kuril Trench is an oceanic trench in the northwest Pacific Ocean. It lies off the southeast coast of Kamchatka and parallels the Kuril Island chain to meet the Japan Trench east of Hokkaido...	Sea of Okhotsk Sea of Okhotsk The Sea of Okhotsk is a marginal sea of the western Pacific Ocean, lying between the Kamchatka Peninsula on the east, the Kuril Islands on the southeast, the island of Hokkaidō to the far south, the island of Sakhalin along the west, and a long stretch of eastern Siberian coast along the west and...	North American Plate	Pacific Plate
Japanese Archipelago Japanese Archipelago The , which forms the country of Japan, extends roughly from northeast to southwest along the northeastern coast of the Eurasia mainland, washing upon the northwestern shores of the Pacific Ocean...	Japan Japan Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...	Japan Trench Japan Trench __notoc__The Japan Trench is an oceanic trench, a part of the Pacific Ring of Fire, in the floor of the northern Pacific Ocean off northeast Japan. It extends from the Kuril Islands to the Bonin Islands and is at its deepest. It is an extension of the Kuril-Kamchatka Trench to the north and the... 、Nankai Trough Nankai Trough The Nankai Trough is a submarine trough located south of Japan's island of Honshū, extending approximately 900 km offshore. In plate tectonics, the Nankai Trough marks a subduction zone that is caused by subduction of the Philippine Sea Plate beneath Japan, part of the Eurasian plate...	Sea of Japan Sea of Japan The Sea of Japan is a marginal sea of the western Pacific Ocean, between the Asian mainland, the Japanese archipelago and Sakhalin. It is bordered by Japan, North Korea, Russia and South Korea. Like the Mediterranean Sea, it has almost no tides due to its nearly complete enclosure from the Pacific...	North American Plate, Eurasian Plate Eurasian Plate The Eurasian Plate is a tectonic plate which includes most of the continent of Eurasia , with the notable exceptions of the Indian subcontinent, the Arabian subcontinent, and the area east of the Chersky Range in East Siberia...	Pacific Plate, Philippine Sea Plate
Ryukyu Islands Ryukyu Islands The , also known as the , is a chain of islands in the western Pacific, on the eastern limit of the East China Sea and to the southwest of the island of Kyushu in Japan. From about 1829 until the mid 20th century, they were alternately called Luchu, Loochoo, or Lewchew, akin to the Mandarin...	Japan	Ryukyu Trench Ryukyu Trench The Ryukyu Trench is a 2,250 kilometer long oceanic trench along the southeastern edge of Japan's Ryukyu Islands in the Philippine Sea in the Pacific Ocean. It is located between northeastern Taiwan and southern Japan...	East China Sea East China Sea The East China Sea is a marginal sea east of China. It is a part of the Pacific Ocean and covers an area of 1,249,000 km² or 750,000 square miles.-Geography:...  (Okinawa Trough Okinawa Trough The is a seabed feature of the East China Sea. It is an active, initial back-arc rifting basin which has formed behind the Ryukyu arc-trench system in the West Pacific. It developed where the Philippine Sea Plate is subducting under the Eurasia Plate.... )	Eurasian Plate	Philippine Sea Plate
Philippine Islands Philippines The Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...	Philippines Philippines The Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...	Philippine Trench Philippine Trench The Philippine Trench is a submarine trench to the east of the Philippines. It has a length of approximately 1,320 km and a width of about 30 km from the centre of the Philippine island of Luzon trending southeast to the northern Maluku island of Halmahera in Indonesia...	South China Sea South China Sea The South China Sea is a marginal sea that is part of the Pacific Ocean, encompassing an area from the Singapore and Malacca Straits to the Strait of Taiwan of around... , Celebes Sea Celebes Sea The Celebes Sea of the western Pacific Ocean is bordered on the north by the Sulu Archipelago and Sulu Sea and Mindanao Island of the Philippines, on the east by the Sangihe Islands chain, on the south by Sulawesi, and on the west by Kalimantan in Indonesia...	Eurasian Plate	Philippine Sea Plate
Sunda Islands Sunda Islands The Sunda Islands are a group of islands that form part of the Malay archipelago.They are further divided into the Greater Sunda Islands and the Lesser Sunda Islands.-Administration:...	Indonesia Indonesia Indonesia , officially the Republic of Indonesia , is a country in Southeast Asia and Oceania. Indonesia is an archipelago comprising approximately 13,000 islands. It has 33 provinces with over 238 million people, and is the world's fourth most populous country. Indonesia is a republic, with an...	Java Trench Java Trench The Sunda Trench, earlier known as, and sometimes still indicated as the Java Trench, located in the northeastern Indian Ocean, with a length of and a maximum depth of , is the second-deepest point in the Indian Ocean after Diamantina Trench, which is 8,047 metres deep...	Java Sea Java Sea The Java Sea is a large shallow sea on the Sunda Shelf. It was formed as sea levels rose at the end of the last ice age. The Java Sea lies between the Indonesian islands of Borneo to the north, Java to the south; Sumatra to the west, and Sulawesi to the east... , Flores Sea Flores Sea The Flores Sea covers 93,000 square miles of water in Indonesia.- Geography :The seas that border the Flores Sea are the Bali Sea , Java Sea , and the Banda Sea ....	Eurasian Plate	Australian Plate Indo-Australian Plate The Indo-Australian Plate is a major tectonic plate that includes the continent of Australia and surrounding ocean, and extends northwest to include the Indian subcontinent and adjacent waters...
Andaman and Nicobar Islands	India India India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...	Northern Java Trench	Andaman Sea Andaman Sea The Andaman Sea or Burma Sea is a body of water to the southeast of the Bay of Bengal, south of Burma, west of Thailand and east of the Andaman Islands, India; it is part of the Indian Ocean....	Eurasian Plate	Indo-Australian Plate Indo-Australian Plate The Indo-Australian Plate is a major tectonic plate that includes the continent of Australia and surrounding ocean, and extends northwest to include the Indian subcontinent and adjacent waters...
Izu Islands Izu Islands The are a group of volcanic islands stretching south and east from the Izu Peninsula of Honshū, Japan. Administratively, they form two towns and six villages; all part of Tokyo. The largest is Izu Ōshima, usually called simply Ōshima....  and Bonin Islands (Ogasawara Islands)	Japan	Izu-Ogasawara Trench Izu-Ogasawara Trench The , also known as Izu-Bonin Trench is an oceanic trench in the western Pacific Ocean. It stretches from Japan to the northernmost section of Mariana Trench. The Izu-Ogasawara Trench is an extension of the Japan Trench...		Philippine Sea Plate	Pacific Plate
Mariana Islands Mariana Islands The Mariana Islands are an arc-shaped archipelago made up by the summits of 15 volcanic mountains in the north-western Pacific Ocean between the 12th and 21st parallels north and along the 145th meridian east...	United States	Mariana Trench Mariana Trench The Mariana Trench or Marianas Trench is the deepest part of the world's oceans. It is located in the western Pacific Ocean, to the east of the Mariana Islands. The trench is about long but has a mean width of only...		Philippine Sea Plate	Pacific Plate
Bismarck Archipelago Bismarck Archipelago The Bismarck Archipelago is a group of islands off the northeastern coast of New Guinea in the western Pacific Ocean and is part of the Islands Region of Papua New Guinea.-History:...	Papua New Guinea Papua New Guinea Papua New Guinea , officially the Independent State of Papua New Guinea, is a country in Oceania, occupying the eastern half of the island of New Guinea and numerous offshore islands...	New Britain Trench		Pacific Plate	Australian Plate
Solomon Islands (archipelago) Solomon Islands (archipelago) The Solomon Islands are an archipelago in the South-Western Pacific Ocean, northeast of Australia, in the region known as Melanesia. The archipelago is currently divided between two countries; Papua New Guinea, in which they make up the autonomous province of Bougainville; and the Solomon Islands,...	Solomon Islands Solomon Islands Solomon Islands is a sovereign state in Oceania, east of Papua New Guinea, consisting of nearly one thousand islands. It covers a land mass of . The capital, Honiara, is located on the island of Guadalcanal...	San Cristobal Trench		Pacific Plate	Australian Plate
New Hebrides New Hebrides New Hebrides was the colonial name for an island group in the South Pacific that now forms the nation of Vanuatu. The New Hebrides were colonized by both the British and French in the 18th century shortly after Captain James Cook visited the islands...	Vanuatu Vanuatu Vanuatu , officially the Republic of Vanuatu , is an island nation located in the South Pacific Ocean. The archipelago, which is of volcanic origin, is some east of northern Australia, northeast of New Caledonia, west of Fiji, and southeast of the Solomon Islands, near New Guinea.Vanuatu was...	New Hebrides Trench		Pacific Plate	Australian Plate
Tonga islands Geography of Tonga -Geology:Though administratively divided into the three main island groups of Tongatapu, Ha'apai, and Vava'u , the Tonga archipelago is actually made of two geologically different parallel chains of islands....	Tonga Tonga Tonga, officially the Kingdom of Tonga , is a state and an archipelago in the South Pacific Ocean, comprising 176 islands scattered over of ocean in the South Pacific...	Tonga Trench Tonga Trench The Tonga Trench is located in the South Pacific Ocean and is deep at its deepest point, known as the Horizon Deep.The Tonga Trench is a convergent plate boundary. The trench lies at the northern end of the Kermadec-Tonga Subduction Zone, an active subduction zone where the Pacific Plate is being...		Australian Plate	Pacific Plate
Antilles Antilles The Antilles islands form the greater part of the West Indies in the Caribbean Sea. The Antilles are divided into two major groups: the "Greater Antilles" to the north and west, including the larger islands of Cuba, Jamaica, Hispaniola , and Puerto Rico; and the smaller "Lesser Antilles" on the...		Puerto Rico Trench Puerto Rico Trench The Puerto Rico Trench is an oceanic trench located on the boundary between the Caribbean Sea and the Atlantic Ocean. The trench is associated with a complex transition between the subduction zone to the south along the Lesser Antilles island arc and the major transform fault zone or plate boundary...	Caribbean Sea Caribbean Sea The Caribbean Sea is a sea of the Atlantic Ocean located in the tropics of the Western hemisphere. It is bounded by Mexico and Central America to the west and southwest, to the north by the Greater Antilles, and to the east by the Lesser Antilles....	Caribbean Plate Caribbean Plate The Caribbean Plate is a mostly oceanic tectonic plate underlying Central America and the Caribbean Sea off the north coast of South America....	North American Plate, South American Plate South American Plate The South American Plate is a continental tectonic plate which includes the continent of South America and also a sizeable region of the Atlantic Ocean seabed extending eastward to the Mid-Atlantic Ridge....
South Sandwich Islands	United Kingdom United Kingdom The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...	South Sandwich Trench South Sandwich Trench The South Sandwich Trench is a deep arcuate trench in the South Atlantic Ocean lying 100 km to the east of the South Sandwich Islands. The trench is produced by the subduction of the southernmost portion of the South American Plate beneath the small South Sandwich Plate. The South Sandwich...	Scotia Sea Scotia Sea The Scotia Sea is partly in the Southern Ocean and mostly in the South Atlantic Ocean.-Location and description:Habitually stormy and cold, the Scotia Sea is the area of water between Tierra del Fuego, South Georgia, South Sandwich Islands, South Orkney Islands and the Antarctic Peninsula, and...	Scotia Plate Scotia Plate The Scotia Plate is an oceanic tectonic plate bordering the South American Plate on the north, the South Sandwich Plate to the east, and the Antarctic Plate on the south and west....	South American Plate
Egean, or Hellenic arc Hellenic arc The Hellenic arc or Aegean arc is an arcuate tectonic feature of the eastern Mediterranean Sea related to the subduction of the African Plate beneath the Aegean Sea Plate...	Greece Greece Greece , officially the Hellenic Republic , and historically Hellas or the Republic of Greece in English, is a country in southeastern Europe....	Eastern Mediterranean Trench	Aegean Sea Aegean Sea The Aegean Sea[p] is an elongated embayment of the Mediterranean Sea located between the southern Balkan and Anatolian peninsulas, i.e., between the mainlands of Greece and Turkey. In the north, it is connected to the Marmara Sea and Black Sea by the Dardanelles and Bosporus...	Aegean Sea Plate Aegean Sea Plate The Aegean Sea Plate is a small tectonic plate located in the eastern Mediterranean Sea under southern Greece and far western Turkey. Its southern edge is a subduction zone south of Crete, where the African Plate is being swept under the Aegean Sea Plate...  or Hellenic Plate	African Plate African Plate The African Plate is a tectonic plate which includes the continent of Africa, as well as oceanic crust which lies between the continent and various surrounding ocean ridges.-Boundaries:...
South Aegean Volcanic Arc South Aegean Volcanic Arc The South Aegean Volcanic Arc is a chain of volcanic islands in the South Aegean Sea formed by plate tectonics as a consequence of the subduction of the African tectonic plate beneath the Eurasian plate...	Greece Greece Greece , officially the Hellenic Republic , and historically Hellas or the Republic of Greece in English, is a country in southeastern Europe....	Eastern Mediterranean Trench	Aegean Sea Aegean Sea The Aegean Sea[p] is an elongated embayment of the Mediterranean Sea located between the southern Balkan and Anatolian peninsulas, i.e., between the mainlands of Greece and Turkey. In the north, it is connected to the Marmara Sea and Black Sea by the Dardanelles and Bosporus...	Aegean Sea Plate Aegean Sea Plate The Aegean Sea Plate is a small tectonic plate located in the eastern Mediterranean Sea under southern Greece and far western Turkey. Its southern edge is a subduction zone south of Crete, where the African Plate is being swept under the Aegean Sea Plate...  or Hellenic Plate	African Plate African Plate The African Plate is a tectonic plate which includes the continent of Africa, as well as oceanic crust which lies between the continent and various surrounding ocean ridges.-Boundaries:...