AS IA
Geologic and climatic influences.
The contemporary relief of Asia was molded primarily under the influences of (1) ancient processes of planation (leveling), (2) larger vertical movements of the surface during the Cenozoic Era, and (3) severe erosive dissection of the edges of the uplifted highlands with the accompanying accumulation of alluvium in low-lying troughs, which were either settling downward or being uplifted more slowly than the adjoining heights.
The interior portions of the uplifted highlands, and the plateaus and tablelands of peninsular India, Arabia, Syria, and eastern Siberia--all of which are relatively low-lying but composed of resistant rock--largely have preserved their ancient peneplaned (i.e., leveled) surfaces. Particularly spectacular uplifting occurred in Central Asia, where the amplitude of this uplift of the mountain ranges of Tibet and of the Pamirs and the Himalayas has exceeded 13,000 feet. The eastern margin of the highlands, meanwhile, underwent subsidences of up to 2,300 feet. Uplifting as a result of fractures at great depths, of which the Kopet-Dag and Fergana ranges provide typical examples, and of folding over a large radius, examples of which may be seen in the Tien Shan and Gissar and Alay ranges, played a significant role. (see also Index: Kopet-Dag Range, Gissar Range) Erosional dissection transformed many ancient plateaus into mountainous regions. Majestic gorges were carved into the highlands of the western Pamirs and southeastern Tibet; the Himalayas, the Kunlun and Sayan mountains, the Stanovoy and Chersky ranges, and the marginal ranges of the West Asian highlands were deeply cut by the rivers, creating deep superimposed gorges and canyons. Vast areas of Middle, Central, and East Asia, particularly in the Huang Ho basin, are covered with loess (a loamy