ACTIVE HIMALAYAN FRONTAL FAULT, MAIN BOUNDARY THRUST AND RAMGARH THRUST IN SOUTHERN KUMAUN

The Siwalik front has been lifted up 60-90 m against the Holocene IndoGangetic plains. The movements on the Himalayan Frontal Fault are evident from 6-15-degrees northward tilting of Late Pleistocene Dun Gravel, and spectacular incised meanders in streams breaking through the hill barrier, and uplift in three episodic phases of the fluvial terraces resting on the tilted Dun Gravel. In southeastern Kumaun, dextral strike-slip movement on an active fault has caused 6 km westward deflection of the Kali (Sharada) River from its consistently southerly course. Movements of fault blocks in the Siwalik domain have given rise to minor horsts and grabens, and caused blocking of streams and rivers, leading to formation of lakes now represented by intramontane fluviolacustrine terraces. The Main Boundary Thrust registers variable neotectonic movements. While the Lesser Himalaya rides over the Lower Siwalik, lifting (by 70 m) the recent fluvial deposits of the Ladhiya River in the east, it is the Siwalik that has risen up relative to the Lesser Himalaya in the central and western sectors. The amount of displacement of the fluvial terraces and colluvial cones is of the order of 40 to 30 m in the Nainital area and 30 to 10 m in the Mandal valley. Quaternary episodic movements have rejuvenated the old mature topography of the Lesser Himalaya. Movements on faults and thrusts in the southern belt are evident from abrupt narrowing in the fault zones into deep gorges of wide meandering streams, development of cascades and knickpoints and triggering of huge debris avalanches on steepened slopes. Damming of streams by colluvial cones and fans have resulted in the formation of lakes in the Bhawali-Shyamkhet area, east of Nainital.