Original paper

River response to continuing movements along the active faults in the Siang Valley, North-Eastern Himalaya, India

Misra, D.K. Srivastava

Abstract

The Siang River section in the NE India cuts through the Proterozoic to Cenozoic rocks, which occur in the form of eight distinct thrust bound litho-tectonic units. From SW to NE, in ascending structural order they are: 1. the Siwalik Group, 2. the Gondwana Group, 3. the Yinkiong Group, 4. the Miri Group, 5. the Bomdila Group, 6. the Sela Group, 7. the Tidding Formation and 8. the Lohit Plutonic Complex. Extensive field studies in the last one decade coupled with interpretation of topographic maps resulted in the identification and delineation of a large number of NNW to WNW-SSE to ESE, N-S, NNE to NE-SSW to SW and E-W trending active faults which post-date the boundary thrusts and shear zones. Recent movements on the faults have caused not only pronounced deflection of rivers and streams but also formed loops and present-day ponding. Movements along faults are also responsible for the abrupt rise of mountain front, occurrence of a planar scarp and triangular facets devoid of gullies or with a few straight furrows, huge landslides, debris fan, abrupt narrowing down of wide meandering rivers and uplifted fluvial terraces. The geomorphic configuration of the terraces coupled with Optically Stimulated Luminescence dating indicated that the bedrock incision rates of Siyom River at Along in the Lesser Himalayan Zone of NE Himalaya is ∼ 7.5 mm/year which is higher than those reported from similar lithotectonic zone in NW Himalaya.