Island arcs are long chains of active volcanoes with intense seismic activity found along convergent tectonic plate boundaries (such as the Ring of Fire). Most island arcs originate on oceanic crust and have resulted from the descent of the lithosphere into the mantle along the subduction zone. They are the principal way by which continental growth is achieved.
Island arcs can either be active or inactive based on their seismicity and presence of volcanoes. Active arcs are ridges of recent volcanoes with an associated deep seismic zone. They also possess a distinct curved form, a chain of active or recently extinct volcanoes, a deep-sea trench, and a large negative Bouguer anomaly on the convex side of the volcanic arc. The small positive gravity anomaly associated with volcanic arcs has been interpreted by many authors as due to the presence of dense volcanic rocks beneath the arc. While inactive arcs are a chain of islands which contains older volcanic and volcaniclastic rocks.
The curved shape of many volcanic chains and the angle of the descending lithosphere are related. If the oceanic part of the plate is represented by the ocean floor on the convex side of the arc, and if the zone of flexing occurs beneath the submarine trench, then the deflected part of the plate coincides approximately with the Benioff zone beneath most arcs.
Most modern island arcs are near the continental margins (majorly in the northern and western margins of the Pacific Ocean). However, no direct evidence from within the arcs shows that they have always existed at their present position with respect to the continents, although evidence from some continental margins suggests that some arcs may have migrated toward the continents during the late Mesozoic or early Cenozoic.
The movement of the island arcs towards the continent could be possible if, at some point, the ancient Benioff zones dipped toward the present ocean rather than toward the continent, as in most arcs today. This will have resulted in the loss of ocean floor between the arc and the continent, and consequently, in the migration of the arc during spreading episodes.
The fracture zones in which some active island arcs terminate may be interpreted in terms of plate tectonics as resulting from movement along transform faults, which are plate margins where the crust is neither being consumed nor generated. Thus the present location of these inactive island chains is due to the present pattern of lithospheric plates. However, their volcanic history, which indicates that they are fragments of older island arcs, is not necessarily related to the present plate pattern and may be due to differences in position of plate margins in the past.
Understanding the source of heat that causes the melting of the mantle was a contentious problem. Researchers believed that the heat was produced through friction at the top of the slab. However, this is unlikely because the viscosity of the asthenosphere decreases with increasing temperature, and at the temperatures required for partial fusion, the asthenosphere would have such a low viscosity that shear melting could not occur.
It is now believed that water acts as the primary agent that drives partial melting beneath arcs. It has been shown that the amount of water present in the down-going slab is related to the melting temperature of the mantle. The greater the amount of water present, the more the melting temperature of the mantle is reduced. This water is released during the transformation of minerals as pressure increases, with the mineral carrying the most water being serpentinite.
These metamorphic mineral reactions cause the dehydration of the upper part of the slab as the hydrated slab sinks. Heat is also transferred to it from the surrounding asthenosphere. As heat is transferred to the slab, temperature gradients are established such that the asthenosphere in the vicinity of the slab becomes cooler and more viscous than surrounding areas, particularly near the upper part of the slab. This more viscous asthenosphere is then dragged down with the slab causing less viscous mantle to flow in behind it. It is the interaction of this down-welling mantle with aqueous fluids rising from the sinking slab that is thought to produce partial melting of the mantle as it crosses its wet solidus. In addition, some melts may result from the up-welling of hot mantle material within the mantle wedge. If hot material rises quickly enough so that little heat is lost, the reduction in pressure may cause pressure release or decompression partial melting.
On the subducting side of the island arc is a deep and narrow oceanic trench, which is the trace at the Earth's surface of the boundary between the down-going and overriding plates. This trench is created by the downward gravitational pull of the relatively dense subducting plate on the leading edge of the plate. Multiple earthquakes occur along this subduction boundary with the seismic hypocenters located at increasing depth under the island arc: these quakes define the Benioff zone.
Island arcs can be formed in intra-oceanic settings, or from the fragments of continental crust that have migrated away from an adjacent continental land mass or at subduction-related volcanoes active at the margins of continents.
Below are some of the generalized features present in most island arcs.
Fore-arc: This region comprises the trench, the accretionary prism, and the fore-arc basin. A bump from the trench in the oceanward side of the system is present (Barbados in the Lesser Antilles is an example). The fore-arc basin forms between the fore-arc ridge and the island arc; it is a region of undisturbed flat-bedded sedimentation.
Trenches: These are the deepest features of ocean basins; the deepest being the Mariana trench (~36,000 feet). They are formed by flexing of the oceanic lithosphere, developing on the ocean side of island arcs.
Back-arc basin: They are also referred to as marginal seas and are formed in the inner, concave side of island arcs bounded by back-arc ridges. They develop in response to tensional tectonics due to rifting of an existing island arc.
Benioff zone or Wadatti-Benioff zone: This is a plane that dips under the overriding plate where intense volcanic activity occurs, which is defined by the location of seismic events below the arc. Earthquakes occur from near surface to ~660 km depth. The dip of Benioff zones ranges from 30° to near vertical.
An ocean basin may be formed between the continental margin and the island arcs on the concave side of the arc. These basins have a crust which is either oceanic or intermediate between the normal oceanic crust and that typical of continents; heat flow in the basins is higher than in normal continental or oceanic areas.
Some arcs, such as the Aleutians, pass laterally into the continental shelf on the concave side of the arc, while most of the arcs are separated from the continental crust.
Movement between two lithospheric plates explains the major features of active island arcs. The island arc and small ocean basin are situated on the overlying plate which meets the descending plate containing normal oceanic crust along the Benioff zone. The sharp bending of the oceanic plate downward produces a trench.
This volcanic series is related to the age of the subduction zone and the depth. The tholeiitic magma series is well represented above young subduction zones formed by magma from relative shallow depth. The calc-alkaline and alkaline series are seen in mature subduction zones, and are related to magma of greater depths. Andesite and basaltic andesite are the most abundant volcanic rock in island arc which is indicative of the calc-alkaline magmas. Some Island arcs have distributed volcanic series as can be seen in the Japanese island arc system where the volcanic rocks change from tholeiite—calc-alkaline—alkaline with increasing distance from the trench.
Several processes are involved in arc magmatism which gives rise to the great spectrum of rock composition encountered. These processes are, but not limited to, magma mixing, fractionation, variations in the depth and degree of partial melting and assimilation. Therefore, the three volcanic series results in a wide range of rock composition and do not correspond to absolute magma types or source regions.
|Island arc||Country||Trench||Basin or marginal sea||Overriding Plate||Subducting plate|
|Aleutian Islands||United States||Aleutian Trench||Bering Sea||North American Plate||Pacific Plate|
|Kuril Islands||Russia||Kuril–Kamchatka Trench||Sea of Okhotsk||North American Plate||Pacific Plate|
|Japanese Archipelago||Japan||Japan Trench、Nankai Trough||Sea of Japan||North American Plate, Eurasian Plate||Pacific Plate, Philippine Sea Plate|
|Ryukyu Islands||Japan||Ryukyu Trench||East China Sea (Okinawa Trough)||Eurasian Plate||Philippine Sea Plate|
|Philippine Islands||Philippines||Philippine Trench||South China Sea, Celebes Sea||Eurasian Plate||Philippine Sea Plate|
|Sunda Arc||Indonesia||Java Trench||Java Sea, Flores Sea||Eurasian Plate||Australian Plate|
|Andaman and Nicobar Islands||India||Northern Java Trench||Andaman Sea||Eurasian Plate||Indo-Australian Plate|
|Izu Islands and Bonin Islands (Ogasawara Islands)||Japan||Izu-Ogasawara Trench||Philippine Sea Plate||Pacific Plate|
|Mariana Islands||United States||Mariana Trench||Philippine Sea Plate||Pacific Plate|
|Bismarck Archipelago||Papua New Guinea||New Britain Trench||Pacific Plate||Australian Plate|
|Solomon Islands (archipelago)||Solomon Islands||San Cristobal Trench||Pacific Plate||Australian Plate|
|New Hebrides||Vanuatu||New Hebrides Trench||Pacific Plate||Australian Plate|
|Tonga islands||Tonga||Tonga Trench||Australian Plate||Pacific Plate|
|Antilles||Puerto Rico Trench||Caribbean Sea||Caribbean Plate||North American Plate, South American Plate|
|South Sandwich Islands||British Overseas Territory||South Sandwich Trench||Scotia Sea||Scotia Plate||South American Plate|
|Aegean or Hellenic arc||Greece||Eastern Mediterranean Trench||Aegean Sea||Aegean Sea Plate or Hellenic Plate||African Plate|
|South Aegean Volcanic Arc||Greece||Eastern Mediterranean Trench||Aegean Sea||Aegean Sea Plate or Hellenic Plate||African Plate|
Remains of former island arcs have been identified at some locations. The table below mention a selection of these.
|Chaitenia||Chile, Argentina||Accreted to Patagonia in the Devonian.|
|Insular Islands||Canada, United States||Accreted to North America in the Cretaceous.|
|Intermontane Islands||Canada, United States||Accreted to North America in the Jurassic.|
The Aleutian Trench (or Aleutian Trough) is an oceanic trench along a convergent plate boundary which runs along the southern coastline of Alaska and the Aleutian islands. The trench extends for 3,400 km from a triple junction in the west with the Ulakhan Fault and the northern end of the Kuril–Kamchatka Trench, to a junction with the northern end of the Queen Charlotte Fault system in the east. It is classified as a "marginal trench" in the east as it runs along the margin of the continent. The subduction along the trench gives rise to the Aleutian arc, a volcanic island arc, where it runs through the open sea west of the Alaska Peninsula. As a convergent plate boundary, the trench forms part of the boundary between two tectonic plates. Here, the Pacific Plate is being subducted under the North American Plate at a dip angle of nearly 45°. The rate of closure is 3 inches (76 mm) per year.Burma Plate
The Burma Plate is a minor tectonic plate or microplate located in Southeast Asia, sometimes considered a part of the larger Eurasian Plate. The Andaman Islands, Nicobar Islands, and northwestern Sumatra are located on the plate. This island arc separates the Andaman Sea from the main Indian Ocean to the west.
To its east lies the Sunda Plate, from which it is separated along a transform boundary, running in a rough north-south line through the Andaman Sea. This boundary between the Burma and Sunda plates is a marginal seafloor spreading centre, which has led to the opening up of the Andaman Sea (from a southerly direction) by "pushing out" the Andaman-Nicobar-Sumatra island arc from mainland Asia, a process which began in earnest approximately 4 million years ago.
To the west is the much larger India Plate, which is subducting beneath the western facet of the Burma Plate. This extensive subduction zone has formed the Sunda Trench.Geology of Aruba
The island of Aruba formed within the past 145 million years, beginning in the Cretaceous, as part of the Lesser Antilles island arc. The island is built on a thick sequence of volcanic rock, but also has carbonate sediment deposits because it was submerged for parts of its existence.Island Arc (journal)
Island Arc (print: ISSN 1038-4871, online: ISSN 1440-1738) is a peer-reviewed quarterly scientific journal that was established in 1992, covering "Earth Sciences of Convergent Plate Margins and Related Topics". It is published by Wiley-Blackwell on behalf of the Geological Society of Japan, in association with the Japan Association for Quaternary Research, Japan Association of Mineralogical Sciences, Palaeontological Society of Japan and the Society of Resource Geology.Japanese archipelago
The Japanese archipelago (日本列島, Nihon Rettō) is a group of 6,852 islands that form the country of Japan. It extends over 3,000 km (1,900 mi) from the Sea of Okhotsk northeast to the Philippine Sea south along the northeastern coast of the Eurasia continent. It consists of islands from the Sakhalin Island Arc, the Northeastern Japan Arc to the Ryukyu Islands and the Nanpō Islands. Japan is the largest island country in East Asia and the 4th largest island country in the world with 377,973.89 km2 (145,936.53 sq mi). It has the 8th largest exclusive economic zone of 4,470,000 km2 (1,730,000 sq mi).Kermadec Islands
The Kermadec Islands (Māori: Rangitāhua) are a subtropical island arc in the South Pacific Ocean 800–1,000 km (500–620 mi) northeast of New Zealand's North Island, and a similar distance southwest of Tonga. The islands are part of New Zealand, 33.6 km2 (13.0 sq mi) in total area and uninhabited, except for the permanently manned Raoul Island Station, the northernmost outpost of New Zealand.
The islands are listed with the New Zealand Outlying Islands. The islands are an immediate part of New Zealand, but not part of any region or district., but instead Area Outside Territorial Authority.Kuril Islands
The Kuril Islands or Kurile Islands (; Russian: Кури́льские острова́, tr. Kurilskiye ostrova, IPA: [kʊˈrʲilʲskʲɪjə ɐstrɐˈva] or Russian: островá Тисима, tr. ostrova Tisima; Japanese: Kuriru rettō (クリル列島, "Kuril Islands") or Chishima rettō (千島列島, "Chishima Islands")) is a volcanic archipelago in Russia's Sakhalin Oblast that stretches approximately 1,300 km (810 mi) northeast from Hokkaido, Japan to Kamchatka, Russia, separating the Sea of Okhotsk from the north Pacific Ocean. There are 56 islands and many minor rocks. It consists of the Greater Kuril Chain and the Lesser Kuril Chain. The total land area is 10,503.2 square kilometres (4,055.3 sq mi), and the total population is 19,434.All the islands are under Russian jurisdiction. Japan claims the four southernmost islands, including two of the largest (Iturup and Kunashir), as part of its territory as well as Shikotan and the Habomai islets, which has led to the ongoing Kuril Islands dispute. The disputed islands are known in Japan as the country's "Northern Territories". In 2018, Russo-Japanese talks on reunification of islands with Japan resumed.Leeward Antilles
The Leeward Antilles (Dutch: Benedenwindse Eilanden) are a chain of islands in the Caribbean – specifically, the southerly islands of the Lesser Antilles (and, in turn, the Antilles and the West Indies) along the southeastern fringe of the Caribbean Sea, just north of the Venezuelan coast of the South American mainland. The Leeward Antilles, while among the Lesser Antilles, are not to be confused with the Leeward Islands (also of the Lesser Antilles) to the northeast.
Largely lacking in volcanic activity, the Leeward Antilles island arc occurs along the deformed southern edge of the Caribbean Plate and was formed by the plate's subduction under the South American Plate. Recent studies indicate that the Leeward Antilles are accreting to South America.Leskov Island
Leskov Island is a small uninhabited island in the Traversay Islands group of the South Sandwich Islands. It is less than 1 nautical mile (2 km) long, and lies 30 nautical miles (56 km) west of Visokoi Island. It was discovered in 1819 by a Russian expedition under Fabian Gottlieb von Bellingshausen, who named it for the third lieutenant on the expedition ship Vostok.Leskov is located to the west of the main island arc of the South Sandwich Islands, and is composed of andesitic rather than basaltic lava with its highest peak reaching 190 metres (620 ft). The subduction zone forming the South Sandwich Trench lies to the east of the island arc.The island is small and has only two named features, both named by the UK Antarctic Place-Names Committee in 1971. Bowsprit Point is the island's northeast point, named for its resemblance to a bowsprit, or prow of a ship. Rudder Point is the island's high, rocky southeast point, named in association with Bowsprit (as a rudder is at the opposite end of a ship from the bowsprit).Lesser Antilles
The Lesser Antilles is a group of islands in the Caribbean Sea. Most form a long, partly volcanic island arc between the Greater Antilles to the north-west and the continent of South America. The islands form the eastern boundary of the Caribbean Sea with the Atlantic Ocean. Together, the Lesser Antilles and the Greater Antilles compose the Antilles (or the Caribbean in its narrowest definition). When combined with the Lucayan Archipelago, all three are known as the West Indies.Lesser Antilles subduction zone
The Lesser Antilles subduction zone is a convergent plate boundary on the seafloor along the eastern margin of the Lesser Antilles island arc. In this subduction zone, oceanic crust of the South American Plate is being subducted under the Caribbean Plate.Middle America (Americas)
Middle America is a region in the mid-latitudes of the Americas. In southern North America, it usually comprises Mexico, the nations of Central America, and the Caribbean. In northern South America, it usually comprises Colombia and Venezuela. The Caribbean is occasionally excluded from the region, and the Guianas are infrequently included.Physiographically, Middle America marks the territorial transition between the rest of North America and South America, connecting yet separating the two. On the west, the Middle American mainland comprises the tapering, isthmian tract of the American landmass between the southern Rocky Mountains in the southern United States and the northern tip of the Andes in Colombia, separating the Pacific Ocean on the west and the Atlantic Ocean (viz. the Gulf of Mexico and Caribbean Sea) on the east, while the Greater and Lesser Antilles form an island arc in the east. The region developed subaerially southward from North America as a complex volcanic arc-trench system during the Early Cretaceous period, eventually forming the land bridge during the Pliocene epoch when its southern end (at Panama) collided with South America through tectonic action.
Occasionally, the term Middle America is used synonymously with Central America (compare with Middle Africa and Central Africa). In English, the term is uncommonly used as a synonym of the term Mesoamerica (or Meso-America), which generally refers to an ancient culture region situated in Middle America extending roughly from central Mexico to northern Costa Rica. In addition, some residents of the region (e.g., Costa Ricans and Nicaraguans) may be referred to as Meso-Americans or Central Americans, but not, however, as Middle Americans, which refers to a particular constituency in the United States.Northeastern Japan Arc
The Northeastern Japan Arc, also Northeastern Honshū Arc, is an island arc on the Pacific Ring of Fire. The arc runs north to south along the Tōhoku region of Honshū, Japan. It is the result of the subduction of the Pacific Plate underneath the Okhotsk Plate at the Japan Trench. The southern end of the arc converges with the Southwestern Japan Arc and the Izu-Bonin-Mariana Arc at the Fossa Magna (ja) at the east end of the Itoigawa-Shizuoka Tectonic Line (ITIL). This is the geologic border between eastern and western Honshū. Mount Fuji is at the point where these three arcs meet. To the north, the Northeastern Japan arc extends through the Oshima Peninsula of Hokkaidō. The arc converges in a collision zone with the Sakhalin Island Arc and the Kuril arc in the volcanic Ishikari Mountains of central Hokkaidō. This collision formed the Teshio and Yūbari Mountains.
The Ōu Mountains form the volcanic part of the inner arc. The volcanic front consists of Quaternary volcanoes, which extend the length of the range. It also includes the Quaternary volcanoes of southwestern Hokkaidō. The Dewa Mountains and the Iide Mountains are non-volcanic uplift ranges that run parallel to the west of the Ōu Mountains.
The outer arc ranges are the Kitakami and the Abukuma Mountains. These mountains are made from pre-tertiary rock. The mountains rose in the Cenozoic and have since been worn smooth by erosion.One Piece
One Piece (Japanese: ワンピース, Hepburn: Wan Pīsu) is a Japanese manga series written and illustrated by Eiichiro Oda. It has been serialized in Shueisha's Weekly Shōnen Jump magazine since July 22, 1997, and has been collected into 93 tankōbon volumes. The story follows the adventures of Monkey D. Luffy, a boy whose body gained the properties of rubber after unintentionally eating a Devil Fruit. With his crew of pirates, named the Straw Hat Pirates, Luffy explores the Grand Line in search of the world's ultimate treasure known as "One Piece" in order to become the next King of the Pirates.
The manga spawned a media franchise, having been adapted into a festival film produced by Production I.G, and an anime series produced by Toei Animation, which began broadcasting in Japan in 1999. Additionally, Toei has developed thirteen animated feature films, one original video animation and thirteen television specials. Several companies have developed various types of merchandising and media, such as a trading card game and numerous video games. The manga series was licensed for an English language release in North America and the United Kingdom by Viz Media and in Australia by Madman Entertainment. The anime series was licensed by 4Kids Entertainment for an English-language release in North America in 2004, before the license was dropped and subsequently acquired by Funimation in 2007.
One Piece has received praise for its storytelling, art, characterization, and humor. Several volumes of the manga have broken publishing records, including the highest initial print run of any book in Japan. The official website for Eiichiro Oda's One Piece manga announced that the manga has set the Guinness World Record for "the most copies published for the same comic book series by a single author". As of August 2019, the manga has sold 454 million copies worldwide, making it the best-selling manga series in history. It became the best-selling manga for the eleventh consecutive year in 2018. One Piece is one of the highest-grossing media franchises of all time, estimated to have generated more than $21 billion in total franchise revenue, from the manga, anime, films, games and merchandise.Ophiolite
An ophiolite is a section of the Earth's oceanic crust and the underlying upper mantle that has been uplifted and exposed above sea level and often emplaced onto continental crustal rocks.
The Greek word ὄφις, ophis (snake) is found in the name of ophiolites, because the superficial texture of some of them. Serpentinite especially evokes a snakeskin. The suffix lite from the Greek lithos means "stone". Some ophiolites have a green color. The origin of these rocks, present in many mountainous massifs, remained uncertain until the advent of plate tectonics.
Their great significance relates to their occurrence within mountain belts such as the Alps and the Himalayas, where they document the existence of former ocean basins that have now been consumed by subduction. This insight was one of the founding pillars of plate tectonics, and ophiolites have always played a central role in plate tectonic theory and the interpretation of ancient mountain belts.Sakhalin Island Arc
Sakhalin Island Arc is an ancient volcanic arc dating from the Early Miocene. The arc was a result of the Okhotsk Plate subducting beneath the Eurasian Plate in the convergence zone. The arc runs from mainland Asia through Sakhalin Island into central Hokkaido and the collision zone around the Daisetsuzan Volcanic Group, where the Kuril Island Arc and the Northeastern Japan Arc meet.Volcanic arc
A volcanic arc is a chain of volcanoes formed above a subducting plate,
positioned in an arc shape as seen from above. Offshore volcanoes form islands, resulting in a volcanic island arc. Generally, volcanic arcs result from the subduction of an oceanic tectonic plate under another tectonic plate, and often parallel an oceanic trench. The oceanic plate is saturated with water, and volatiles such as water drastically lower the melting point of the mantle. As the oceanic plate is subducted, it is subjected to greater and greater pressures with increasing depth. This pressure squeezes water out of the plate and introduces it to the mantle. Here the mantle melts and forms magma at depth under the overriding plate. The magma ascends to form an arc of volcanoes parallel to the subduction zone.
These should not be confused with hotspot volcanic chains, where volcanoes often form one after another in the middle of a tectonic plate, as the plate moves over the hotspot, and so the volcanoes progress in age from one end of the chain to the other. The Hawaiian Islands form a typical hotspot chain; the older islands (tens of millions of years old) to the northwest are smaller and more lush than the recently created (400,000 years ago) Hawaii island itself, which is more rocky. Hotspot volcanoes are also known as "intra-plate" volcanoes, and the islands they create are known as Volcanic Ocean Islands. Volcanic arcs do not generally exhibit such a simple age-pattern.
There are two types of volcanic arcs:
oceanic arcs form when oceanic crust subducts beneath other oceanic crust on an adjacent plate, creating a volcanic island arc. (Not all island arcs are volcanic island arcs.)
continental arcs form when oceanic crust subducts beneath continental crust on an adjacent plate, creating an arc-shaped mountain belt.In some situations, a single subduction zone may show both aspects along its length, as part of a plate subducts beneath a continent and part beneath adjacent oceanic crust.
Volcanoes are present in almost any mountain belt, but this does not make it a volcanic arc. Often there are isolated, but impressively huge volcanoes in a mountain belt. For instance, Vesuvius and the Etna volcanoes in Italy are part of separate but different kinds of mountainous volcanic ensembles.
The active front of a volcanic arc is the belt where volcanism develops at a given time. Active fronts may move over time (millions of years), changing their distance from the oceanic trench as well as their width.Volcanic belt
A volcanic belt is a large volcanically active region. Other terms are used for smaller areas of activity, such as volcanic fields. Volcanic belts are found above zones of unusually high temperature (700-1400 °C) where magma is created by partial melting of solid material in the Earth's crust and upper mantle. These areas usually form along tectonic plate boundaries at depths of 10–50 km. For example, volcanoes in Mexico and western North America are mostly in volcanic belts, such as the Trans-Mexican Volcanic Belt that extends 900 km from west to east across central-southern Mexico and the Northern Cordilleran Volcanic Province in western Canada.
The deeply deformed and eroded remnants of ancient volcanic belts are found in volcanically inactive regions such as the Canadian Shield. It contains over 150 volcanic belts (now deformed and eroded down to nearly flat plains) that range from 600 to 1200 million years old. These are zones of variably metamorphosed mafic to ultramafic volcanic sequences with associated sedimentary rocks that form what are known as greenstone belts. They are thought to have formed at ancient oceanic spreading centers and island arc terranes. The Abitibi greenstone belt in Ontario and Quebec, Canada is one of the world's largest greenstone belts.
Volcanic belts are similar to a mountain range, but the mountains within the mountain range are volcanoes, not mountains that are formed by faulting and folding by the collision of tectonic plates.Volcano Islands
The Volcano Islands (火山列島, Kazan Rettō) or Iwo Islands (硫黄列島, Iō-rettō) are a group of three Japanese islands south of the Ogasawara Islands that belong to the municipality of Ogasawara, Tokyo Metropolis, Japan. The islands are all active volcanoes lying atop an island arc that stretches south to the Marianas. They have an area of 32.55 square kilometres (12.57 sq mi), and a population of 380.