Here's why:

* Subduction: One plate, typically the denser one, will subduct (slide) beneath the other.

* Magma Formation: As the subducting plate descends, the high pressure and temperature melt the surrounding mantle. This molten rock, or magma, rises towards the surface.

* Volcanoes: The magma erupts through the overriding plate, forming volcanoes. Over time, these volcanoes can grow above sea level, forming islands.

* Island Arcs: A chain of these volcanic islands, often curved, is called an island arc.

Examples of Island Arcs:

* The Aleutian Islands (Alaska)

* The Mariana Islands (Pacific Ocean)

* The Lesser Antilles (Caribbean Sea)

Let me know if you'd like more detail on any of these processes!