- a curved chain of islands, as the Aleutians or Antilles, usually convex toward the ocean and enclosing a deep-sea basin.[1905-10]
* * *Long, curved chain of oceanic islands associated with intense volcanic and seismic activity and mountain-building processes.Examples include the Aleutian-Alaska Arc and the Kuril-Kamchatka Arc. Most island arcs consist of two parallel rows of islands. The inner row is a string of volcanoes, and the outer row is made up of nonvolcanic islands. In the case of single arcs, many of the islands are volcanically active. An island arc typically has a landmass or a partially enclosed, unusually shallow sea on its concave side. Along the convex side there usually exists a long, narrow deep-sea trench.
* * *long, curved chain of oceanic islands associated with intense volcanic and seismic activity and orogenic (mountain-building) processes. Prime examples of this form of geologic feature include the Aleutian (Aleutian Islands)-Alaska Arc and the Kuril (Kuril Islands)-Kamchatka (Kamchatka Peninsula) Arc.Most island arcs consist of two parallel, arcuate rows of islands. The inner row of such a double arc is composed of a string of explosive volcanoes, while the outer row is made up of nonvolcanic islands. In the case of single arcs, many of the constituent islands are volcanically active.An island arc typically has a land mass or a partially enclosed, unusually shallow sea on its concave side. Along the convex side there almost invariably exists a long, narrow deep-sea trench. The greatest ocean depths are found in these depressions of the seafloor, as in the case of the Mariana and Tonga trenches.Destructive earthquakes occur frequently at the site of island arcs. Unlike the shallow earthquakes that are recorded in other areas of the world, these are deep-focus seismic events emanating from as much as 370 miles (600 km) below the base of an arc. The quakes tend to have foci of progressively greater depth toward the arc's concave side.The majority of island arcs occur along the western margin of the Pacific Basin. The few exceptions are the East Indian and the West Indian arcs and the Scotia Arc in the South Atlantic. According to prevailing theory, island arcs are formed where two lithospheric plates (enormous rigid slabs that constitute segments of the Earth's surface) converge. Upon colliding, one of the plates—that bearing heavy, oceanic crust—buckles downward and is forced into the partially molten lower mantle beneath the second plate with lighter, continental crust. An island arc is built up from the surface of the overriding plate by the extrusion of basalts and andesites. The basalts are thought to be derived from the semimolten mantle, whereas the andesites are probably generated by the partial melting of the descending plate and the sediments that have accumulated on its surface.
* * *
Look at other dictionaries:
island arc — a chain, often arc shaped, of volcanic islands. These are undersea volcanoes which have grown through repeated eruptions to break the surface. They are the product of a subduction zone where either the continental plate is so low lying that its … Geography glossary
island arc — GLOSSARY OF VOLCANIC TERMS A curved chain of islands, generally convex towards the open ocean, which is bounded on its convex side by a deep oceanic trench (typically a subduction zone) and generally a deep sea basin (AGI, 1976, p. 234) … Glossary of volcanic terms
island arc — noun : an arcuate chain of islands … Useful english dictionary
Sakhalin island arc — is an ancient volcanic arc dating from the Early Miocene.cite book|last=Ivanov|first=Andrey |title=The Physical Geography of Northern Eurasia|editor=Shahgedanova, Maria|publisher=Oxford University Press|location=Google Books|date=March 27,… … Wikipedia
Bronson Hill Island Arc — The Bronson Hill Island Arc is a bimodal volcanic terrane and associated sediments that are thought to have docked with Laurentia (North American) during Ordovician Time, (ca 450 Ma) to create the Taconic Orogeny. These rocks are presently well… … Wikipedia
Arc Drum Island — L Arc Drum Island est une section du manga One Piece. Sommaire 1 Résumé 2 Personnages 2.1 Tony Tony Chopper 2.2 Dalton … Wikipédia en Français
Arc — may refer to: Computing and gaming*Arc (programming language), a Lisp dialect in development by Paul Graham *.arc, a file extension for archive files *arc, the command line interface for ArcInfo *Arc System Works, a video game… … Wikipedia
Arc Enies Lobby — L Arc Enies Lobby est une section du manga One Piece. Sommaire 1 Résumé 2 Personnages 2.1 Jyabura 2.2 Fukurou … Wikipédia en Français
Arc Thriller Bark — L Arc Thriller Bark est une section du manga One Piece. Sommaire 1 Résumé 2 Personnages 2.1 Brook 2.2 Dr. Hogback … Wikipédia en Français
Arc Alabasta — L Arc Alabasta est une section du manga One Piece. Sommaire 1 Résumé 2 Personnages 2.1 Roi Cobra 2.2 Chaka … Wikipédia en Français