Major Mountain Belts Of The World
Most mountains and mountain ranges are parts of mountain belts that have formed where two lithospheric plates have converged and where, in most cases, they continue to converge. In effect, many mountain belts mark the boundaries of lithospheric plates, and these boundaries in turn intersect other such boundaries. Consequently, there exist very long mountain systems where a series of convergent plate boundaries continue from one to the next. A nearly continuous chain of volcanoes and mountain ranges surrounds most of the Pacific basin—the so-called Circum-Pacific System. A second nearly continuous chain of mountains can be traced from Morocco in North Africa through Europe, then across Turkey and Iran through the Himalayas to Southeast Asia; this chain, the Alpine-Himalayan (or Tethyan) System, has formed where the African, Arabian, and Indian plates have collided with the Eurasian Plate. Nearly all mountain ranges on the Earth can be included in one of these two major systems and most that cannot are residual mountains, which originated from ancient continental collisions that occurred hundreds of millions of years ago.
The Circum-Pacific System
A nearly continuous chain of volcanoes surrounds the Pacific Ocean. The chain passes along the west coast of North and South America, from the Aleutian Islands to the south of Japan, from Indonesia to the Tonga Islands, and to New Zealand. The Pacific basin is underlain by separate lithospheric plates that diverge from one another and that are being subducted beneath the margins of the basin at different rates. This Circum-Pacific chain of volcanoes (often called the Ring of Fire) and the mountain ranges associated with it owe their formation to the repeated subduction of oceanic lithosphere beneath the continents and the islands that surround the Pacific Ocean. Differences among the various segments of the Circum-Pacific chain arise from differences in the histories of subduction of the different plates.