An Indian research team has discovered how geological activities coupled with climatic changes have sculpted the landscape lying southwest of Itanagar, the capital of Arunachal Pradesh. The region where its two streams Senkhi and Dokhoso flow, show unpaired terraces consisting of very poorly sorted riverbed materials lacking stratification1. This indicates tectonic activity that might have played a role during the deposition of materials.
Between 40 and 50 million years ago, the Indian plate collided with the Eurasian plate, thrusting the earth's crust skyward and forming the jagged Himalayan peaks. The studied region lies between the Main Boundary Thrust (MBT) and the Himalayan Front Fault (HFF) within the Sub-Himalaya of the Eastern Himalaya. The region shows five levels of terraces on the eastern part and four levels of terraces on the western part. Studying the deposits on terraces, the research team found clear signs of climatic flip-flop during Pleistocene-Holocene times.
The Pleistocene (between 1.8 million and 10,000 years before present) and Holocene (between 10,000 years before present) epochs saw ice sheets and glaciers encroach and retreat with rise and fall of sea levels. The movement of glaciers altered the shape and nature of terraces. "In the study area, the older terraces show a well-oxidized and semi-consolidated nature compared to the unoxidized nature of the younger terraces, marking the Pleistocene-Holocene boundary," says lead researcher R. K. Mrinalinee Devi of Wadia Institute of Himalayan Geology, Itanagar.
