Ocean-ocean convergence
Topic: Continental Drift, Sea-floor Spreading and Plate Tectonics · NCERT: Class 11, Ch 4 "Distribution of Oceans and Continents"
Meaning
Ocean-ocean convergence happens when two ocean plates move towards each other. One plate, usually the older and heavier one, sinks under the other. This sinking is called subduction. A very deep trench forms where the plate goes down. The sinking plate melts at depth, and the magma rises to build a curved chain of volcanic islands parallel to the trench. This chain is called an island arc. Deep earthquakes are common here.
Example
In the western Pacific, the Pacific plate sinks under the Philippine plate. This formed the Mariana Trench and the Mariana Islands arc. The Challenger Deep in the Mariana Trench is about 11 km deep, the deepest point in the oceans. Japan, the Aleutians, Indonesia and India's Andaman-Nicobar arc formed in the same way.
Don't confuse with
- Ocean-continent convergence: there, the ocean plate sinks under a continent, so volcanoes and fold mountains rise on land (e.g. the Andes), not as islands at sea.
Related concepts
- Convergent boundary
- Subduction zone
- Ocean-continent convergence
- Island arc
- Continent-continent convergence
- Fold mountain
- Wadati-Benioff zone