Island arc
Topic: Continental Drift, Sea-floor Spreading and Plate Tectonics · NCERT: Class 11, Ch 12 "Water (Oceans)"
Meaning
An island arc is a curved chain of volcanic islands. It forms where one ocean plate sinks under another ocean plate at a subduction zone. The sinking plate melts deep down, and the magma rises to build volcanoes on the sea floor. These volcanoes grow into islands in a line parallel to a deep ocean trench. Island arcs have frequent strong earthquakes, and some also have tsunamis.
Example
The Andaman-Nicobar Islands in the Bay of Bengal form an island arc. Barren Island, India's only active volcano, lies on this arc. Other examples are Japan, the Aleutians, the Mariana Islands and Indonesia.
Don't confuse with
- Hotspot island chain: a chain like Hawaii forms in the middle of a plate as it moves over a mantle plume. It is a straight line of islands that get older in one direction, not a curved arc beside a trench.
- Fold mountain range: the Andes also have volcanoes over a subduction zone, but they rise on a continent, not as islands in the sea.
Related concepts
- Convergent boundary
- Subduction zone
- Ocean-continent convergence
- Ocean-ocean convergence
- Continent-continent convergence
- Fold mountain
- Wadati-Benioff zone