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A volcanic arc (also known as a magmatic arc [1]: 6.2 ) is a belt of volcanoes formed above a subducting oceanic tectonic plate, [2] with the belt arranged in an arc shape as seen from above. Volcanic arcs typically parallel an oceanic trench, with the arc located further from the
There are generally three volcanic series from which the types of volcanic rock that occur in island arcs are formed: [15] [16] The tholeiitic series – basaltic andesites and andesites. The calc-alkaline series – andesites. The alkaline series – subgroups of alkaline basalts and the rare, very high potassium-bearing (i.e. shoshonitic) lavas.
The concepts "island arc", "volcanic arc", "oceanic arc" and "continental arc" may be confused: Volcanic arcs are made of an arc-shaped chain of volcanoes, the position of which could be continental or mid-ocean. Island arcs must be offshore, but they do not necessarily have to be volcanic (e.g. the non-volcanic Hellenic arc).
Hotspot volcanoes are considered to have a fundamentally different origin from island arc volcanoes. The latter form over subduction zones, at converging plate boundaries. When one oceanic plate meets another, the denser plate is forced downward into a deep ocean trench.
The Aleutian Arc is a large volcanic arc of islands extending from the Southwest tip of the U.S. state of Alaska to the Kamchatka Peninsula of the Russian Federation. It consists of a number of active and dormant volcanoes that have formed as a result of the subduction of the Pacific plate beneath the North American plate along the Aleutian ...
The volcanic belt also contains three large shield volcanoes that were formed between 8 and 1 million years ago, called the Ilgachuz Range, Rainbow Range and the Itcha Range. The Chilcotin Group in southern British Columbia is a north–south range of volcanoes, thought to have formed as a result of back-arc extension behind the Cascadia ...
Geologically, a volcanic island is an island of volcanic origin. The term high island can be used to distinguish such islands from low islands, which are formed from sedimentation or the uplifting of coral reefs (which have often formed on sunken volcanoes). [1]
The Kermadec Islands are an active volcanic island arc stretching north-northeast from New Zealand's North Island towards Tonga. While only a few volcanoes in the arc are tall enough to form islands, it includes about 30 sizeable submarine volcanoes with many in the South Kermadec Ridge Seamounts at the New Zealand end of the chain.