How were the major mountain belts of the world produced?

The major mountain belts of the world, such as the Himalayas, the Alps, the Andes, and the Rockies, were produced by folding. These are known as fold mountains.

Folding occurs when tectonic plates converge (move toward each other). The immense compressional forces squeeze layers of sedimentary rock that have accumulated in geosynclines (deep troughs on the ocean floor) between the plates. These rock layers are crumpled and pushed upward into a series of folds, forming mountain ranges. The upward arches are called anticlines and the downward troughs are called synclines.

The other processes do not create mountain belts:

• Wind erosion wears down existing landforms; it does not build mountains.
• Glacial erosion carves and reshapes existing mountains (creating features like cirques, aretes, and U-shaped valleys) but does not produce them in the first place.
• Weathering is the breakdown of rocks in place by physical, chemical, or biological processes. It destroys rather than builds mountains.

All the world's young fold mountain systems were formed by plate convergence and the folding of sedimentary strata, making folding the correct process.