RAS question
Fold mountains are formed by:
Correct answer: (C) Compression of tectonic plates (convergent boundary).
Fold mountains are formed when converging tectonic plates compress rock layers, causing them to fold and rise at a convergent boundary.
Explanation
Fold mountains form at convergent plate boundaries, where plates move towards each other and compress the crust. The USGS explains that convergence can occur between oceanic and continental plates, two oceanic plates, or two continental plates. In a continental-continental collision, such as India meeting Asia, neither continent is readily subducted; instead, the crust buckles, crumples and is pushed upward or sideways. That process explains the Himalayas, where the Indian and Eurasian plates converged over millions of years. The Andes, Himalayas and Alps are mountain belts linked to plate convergence and compression, not to erosion or simple fault displacement.
Why the other options are wrong
- (A) Volcanic activity may build volcanic mountains, but fold mountains form through compression at convergent plate boundaries.
- (B) Faulting breaks and displaces rock blocks, whereas fold mountains require rock layers to buckle and fold under compression.
- (D) Erosion wears down and reshapes landforms; it does not create fold mountains by compressing crustal layers.
Concept
Plate tectonics links convergent boundaries with mountain building. RAS often returns to convergent-boundary mountain building because physical geography requires candidates to connect landforms with their governing geomorphic process.