Morphotectonic setting of the Ganga Lake, Itanagar capital complex, Arunachal Himalaya

The Ganga Lake is situated on the western part of the Itanagar capital complex in Arunachal Pradesh, India. It represents a unique topography with an ovuculate-triangular shape amongst the highly dissected rugged hills in the outer Himalayan ranges. The lake has an areal coverage of about 67,500 m2 and is located very close to the boundary of the Pachin and Pam watersheds. The drainage around the lake shows a subdendritic to subparallel pattern. Of these, the higher order streams show more or less trellis drainage pattern, indicating structural control of the drainage. neaments and the channel segments of the surrounding area have been studied. It is concluded that most of the streams are structurally controlled and others are carving out their own path. The Ganga Lake seems to have been formed from ponding of a tributary of the Budhibeta stream during neotectonic activity. Its peculiar triangular shape signifies its structural trauma in the Quaternary period. Abrupt deflection in the course of the Chimpu and Senkhi streams, presence of faults and vertical faults, triangular facets, fault scarps, uplifted river terraces, and active landslides in the Itanagar Capital complex confirm neotectonism and indicate that the area has remained tectonically unstable.