Final answer:
Island arcs form at subduction zones, where an oceanic plate subducts beneath another oceanic or a continental plate. The melting of the descending plate gives rise to volcanic activity that ultimately leads to the development of an arc of islands.
Step-by-step explanation:
Island arcs are a linear belt of volcanoes that form at a specific type of plate boundary where an oceanic plate collides with either another oceanic plate or a continental plate and then subducts beneath it. These boundaries are known as subduction zones, which are responsible for some of the most dramatic geological features on Earth. For example, the Ring of Fire is a well-known area surrounding the Pacific Ocean noted for frequent earthquake activity and the presence of many volcanic arcs and ocean trenches caused by subduction.
Rift and subduction zones play a vital role in island arc formation. The process starts when an oceanic plate converges with another oceanic or continental plate. The denser plate dives underneath the less dense plate into the mantle, creating a trench. As the subducting plate sinks, it melts and forms magma that rises to create volcanic islands. Over time, these islands may form an arc shape, hence the name 'island arc'.
A good example of this process is the back arc basin, which forms near a volcanic arc on the opposite side of the oceanic trench. This is due to the extension caused by mantle convection behind a subduction zone and its associated island arc.