1. Oceanic-Continental Convergence: An island arc typically forms when an oceanic plate converges with a continental plate. The oceanic plate is usually denser than the continental plate, causing it to subduct beneath the continental plate.
2. Subduction Initiation: As the oceanic plate subducts beneath the continental plate, it sinks deeper into the Earth's mantle. This process generates heat and pressure, causing partial melting of the subducting plate.
3. Magma Generation: The molten material, known as magma, rises towards the surface through the overlying continental plate. As it ascends, the magma can become trapped in the crust, leading to the formation of volcanoes.
4. Volcanic Activity: The volcanoes erupt and release lava, ash, and other volcanic materials, building volcanic islands on the surface. These islands may merge and form larger islands or island chains, known as an island arc.
5. Arc-Continent Collision: Over time, the island arc can continue to grow and move closer to the continental plate. If the convergence continues, the island arc may eventually collide with the continental plate. This collision can result in further uplift, folding, and deformation of both the island arc and the continental margin.
6. Continued Subduction: Even after the collision, subduction may continue beneath the continental plate. This ongoing subduction can lead to the formation of additional volcanoes and the growth of the island arc.
7. Accretion and Erosion: The volcanic activity and subduction processes contribute to the accretion of new material to the overriding continental plate. However, erosion and weathering can also act on the island arc, shaping its topography and influencing its long-term evolution.
It's important to note that island arcs are dynamic features, and the processes involved can vary in complexity and duration. They are influenced by factors such as the rate of convergence, the composition and properties of the tectonic plates, and the presence of other geological structures in the region.