how do island arcs form?

Answer 1

I think your talking about coral reef atolls? Usually a volcano raises up, builds up a little island, and the heat attracts coral to build around it. When the volcano subsides, arcs, rings etc. are formed.

Answer 2

Island Arcs are formed on the opposing edge of a subducted slab by a series of volcanos which pour out enough material to form substantial amounts of land. Examples of island arcs are the Japanese islands, the Kuril Islands, and the Aleutian Islands of Alaska, shown here. In each case, there is an associated subducting slab and a trench. The trenches for these island arcs can barely be made out in this map. The second way in which islands are formed is via plumes or hot spots in the lithosphere. The Hawaiian Islands are an example of this type of island formation. In this case, there is no associated subducting slab nor trench.

Answer 3

If you are talking about a chain of islands in an arc shape, they can be created when there is a 'hot spot' under the earths crust or a shifting tectonic plate. In this case there is volcanic activity which forms an island, as the plate shifts the hot spot remains in the same place... further volcanic activity creates another island. Depending on how quickly the plates are shifting and how much volcanic activity you have, you get a string of islands which can be arc shaped depending on the direction the plate is shifting.

Answer 4

You start with a roughly conical undersea mountain, usually a volcano. Coral starts to grow in a circle at the right depth so you get a circular coral atoll, and the next time the sea level rises, some parts are submerged. So instead of getting a circle of coral, you've got an arc of islands.

Answer 5

At subduction boundaries, the crust goes down into the lithosphere. The crust melts into magma and rises, forming volcanic activity, which sometimes creates islands. Picture here: http://www.geol.ucsb.edu/faculty/hacker/geo102C/lectures/thumbnails/islandArc_t.jpg

Answer 6

A giant inactive volcano eroding partly into the ocean....this is what happened on the Waianae and Windwardside of Oahu. (2 Koolau Mountain ranges- former active volcanoes.)

Answer 7

I think for emerged lands