RAS question
Convergent plate boundaries where an oceanic plate meets a continental plate typically form:
Correct answer: (B) Volcanic mountain ranges and deep ocean trenches.
At an oceanic-continental convergent boundary, the heavier oceanic lithosphere subducts beneath the continental plate, forming a deep ocean trench and a volcanic mountain range or volcanic arc.
Explanation
When an oceanic plate converges with a continental plate, the oceanic lithosphere is heavier, so it sinks beneath the continental plate in a process called subduction. The U.S. Geological Survey explains that this process creates a very deep trough near the line of contact, called an oceanic trench. As the subducted oceanic plate goes deeper, higher pressure and temperature cause some lightweight materials to melt and rise, forming volcanoes above the subducted plate. The typical landform pair is therefore a deep ocean trench offshore and a volcanic mountain range or volcanic arc on the continental side. The Peru-Chile Trench and the Andes are standard examples of this oceanic-continental subduction setting.
Why the other options are wrong
- (A) Rift valleys are associated with plates pulling apart at divergent boundaries, whereas oceanic-continental convergence involves plates colliding at a convergent boundary.
- (C) Transform faults mark boundaries where plates slip past one another, not where a denser oceanic plate subducts beneath a continent.
- (D) Mid-ocean ridges form where molten material rises as plates diverge and new ocean floor is made, not at oceanic-continental collision zones.
Concept
Plate tectonics separates divergent, transform and convergent boundaries by plate motion and resulting landforms. RAS often links landforms, volcanism and earthquake patterns to boundary-type identification.