South-East Asia

South-East Asia is the least compact among the regions of the Asian continent. Out of its total land surface, estimated at four million sq.km., the mainland mass has a share of only 40 per cent. The rest is accounted for by several thousand islands of the Indonesian and Philippine archipelagoes. Thus, it is composed basically of insular and continental components. Nevertheless the orographic features on both these landforms are interrelated. This is due to the focal location of the region where the two great axes, one of latitudinal Cretaceo-Tertiary folding and the other of the longitudinal circum-Pacific series, converge. This interface has given a distinctive alignment to the major relief of the region as a whole. In brief, the basic geological structures that determine the trend of the mountains are (a) north-south and north-east in the mainland interior, (b) east-west along the Indonesian islands, and (c) north-south across the Philippines. The mountain ranges of the region are described in three geographic divisions: the continental interior, peninsular, and insular (Figure 7 and Annex E).

Figure 7: South-East Asia