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An island arc is a type of archipelago 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.

Most of these island arcs are formed as one oceanic tectonic plate subducts another one and, in most cases, produces magma 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 arcs, 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 in the Mediterranean Area, composed of numerous islands such as Crete, is an island arc, but is not volcanic. Parallel to it is the South Aegean Volcanic Arc, which is the volcanic island arc of the same tectonic system.^{[citation needed]}

Classification[link]

There is some debate about the usefulness of the distinction between island arcs and volcanic arcs.^{[citation needed]} 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[link]

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):

In the subduction zone, loss of volatiles from the subducted slab induces partial melting of the overriding mantle. This process, called flux melting, generates low-density calc-alkaline magma that buoyantly rises to intrude and be extruded through the lithosphere of the overriding plate. The resulting volcano 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.^{[citation needed]}

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 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 earthquakes occur along this subduction boundary with the seismic hypocenters located at increasing depth under the island arc: these quakes define the Wadati-Benioff zones.^{[citation needed]}

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 collision. This process has happened repeatedly in the geologic history of the Earth.^{[citation needed]}

Examples[link]

Ancient Island arcs[link]

• Insular Islands
• Intermontane Islands

See also[link]

• Back-arc basin
• Volcanic arc

References[link]

Drum Island
Origin	Tromsø, Norway
Genres	Electronic Ambient
Years active	1997
Labels	Sony Apollo
Associated acts	Röyksopp Alanïa Aedena Cycle Biosphere Those Norwegians
Past members
Torbjørn Brundtland Svein Berge Rune Lindbæk Ole Johan Mjøs

Drum Island is a former Norwegian electronic music group from Tromsø, composed of Torbjørn Brundtland (from Röyksopp), Rune Lindbæk and Ole Johan Mjøs. Svein Berge and Gaute Barlindhaug are contributors. Their only release is a self-titled album released in 1997, along with two singles. The album was released on Apollo and Sony. Drum Island - Drum Island was rated 4,5/5 stars by Allmusic.^[1]

The album has been mentioned as the "test album" for Röyksopp's Melody A.M. by Beatservice Records founder Vidar Hanssen.^[2]

See also[link]

• Röyksopp
• Svein Berge
• Torbjørn Brundtland
• Alanïa
• Aedena Cycle

External links[link]

• Drum Island at Last.fm
• Drum Island discography at Discogs

References[link]