South Asia

South Asia, corresponding to the Indian sub-continent, has three major physiographic components based on geologic structure and terrain. These are: (1) the Himalayan and associated fold mountains, (2) the ancient crystalline block of Peninsular India, and (3) the alluvial Indo-Gangetic lowland in between the two. The last component is an extensive plain and lies outside the mountain realm. Nevertheless, its genesis owes much to the deposition of materials from the adjoining highlands. The vast thickness of its sediments, up to 6,500 metres along the foothills, is indicative of the dynamic processes operating in the Himalayan Mountains. The mountain ranges of the first two physiographic components are grouped into five units: the Karakoram, the Himalaya, north-east ranges, peninsular ranges, and north-western ranges (Figure 1 and Annex A). They are described in a clock-wise sequence starting from the Karakoram in the extreme north.

Figure 1: South Asia