River Response to Continuing Movements and the Scarp Development in Central Sahyadri and Adjoining Coastal Belt

Fieldwork coupled with interpretation of topographic maps resulted in the identification and delineation of a number of long, discontinuous strike-slip faults trending in the NNW-SSE and N-S directions that post-date ESE-WNW to E-W oriented reverse faults and shear zones in the western part of the Dharwar Craton in the Southern Indian Shield. The northerly-trending faults have caused not only pronounced deflection of rivers and streams and development in some places of loops and hairpin geometry of drainage, but also present-day stream ponding. The modification of Holocene landforms including (i) the deep incisions across ridges in the undulating terrain, (ii) the descent of old winding rivers as waterfalls and cascades through deep gorges across fault-delimited ridges, (iii) the occurrence of planar scarps and triangular facets devoid of gullies or with a few straight furrows, (iv) the repeated blockage of streams as they cross or follow the NNW-SSE trending faults, and (v) the higher-than-normal seismicity indicates geologically recent and continuing tectonic movements in the fault-riven Sahyadri and coastal domains.

In the western margin of the Dharwar Craton, the Central Sahyadri mountain emerged from the erosion surface, that lay a little above the sea-level, as a consequence of pronounced vertical movements accompanying northward strike-slip displacement along the NNW-SSE faults. The northerly push of the fault-delimited blocks caused breaking up at their edges on the ESE-WNW oriented reverse faults and shear zones, giving rise to peculiar rightside-overstepping arrangement of the high mountain ranges and en echelon configuration of the more than 700 m high Western Ghat escarpment. While a part of the Dharwar Craton margin became a rising 700 to >1800 m high horst mountain (the Sahyadri), the coastal belt failed to rise beyond 40 to 120 m above sea level and thus became an undulating terrain of low ridges and very shallow depressions. The original escarpment has been considerably reshaped through headward erosion by the rivers that flow west.