Question

Boundary between sub-himalaya and indo-gangetic plain

Answer 1

The Himalayan Frontal Fault (HFF) defines the southern limit of the Himalaya against the Indo-Gangetic Plains, and the steeply inclined Main Boundary Thrust (MBT) has brought the Lesser Himalayan rocks upon the Cenozoic sedimentary terrain of the Outer Himalaya. Subrecent to recent geomorphic surfaces in the Bhutan-Darjiling foothills have been upwarped and elevated along E-W faults related to the HFF. In the foothills of the Kumaun Himalaya, the Siwalik front abruptly rises 60-90 m above the Indo-Gangetic plains, the steep ungullied escarpment demarcating the HFF. Fluvial fans at the mouths of entrenched streams breaking through the raised hill front are uplifted and deformed into pressure ridges and depressions adjacent to the HFF. Movements on the intra-Siwalik faults resulting in uplift of the footwalls have given rise to the formation of lakes and the developments of "duns' - synclinal valleys filled with thick coarse gravels. Holocene reactivation of the faults have raised and deformed the lacustrine deposits and Dun fans throughout the Siwalik area. In the Kumaun Himialay, the MBT has registered rotational as well as strike-slip movements in Holocene time. -

Answer 2

Indo-Gangetic Plain, also called North Indian Plain, extensive north-central section of the Indian subcontinent, stretching westward from (and including) the combined delta of the Brahmaputra River valley and the Ganges (Ganga) River to the Indus River valley. The region contains the subcontinent’s richest and most densely populated areas. The greater part of the plain is made up of alluvial soil, deposited by the three main rivers and their tributaries. The eastern part of the plain has light rains or drought in the winter, but in summer rainfall is so heavy that vast areas become swamps or shallow lakes. The plain becomes progressively drier toward the west where it incorporates the Thar (Great Indian) Desert.