Tectonic anabranching of Brahmaputra River system: implications on survival of world’s largest inhabited river island Majuli

Abstract

Abstract Brahmaputra is a large, tropical, trans-boundary river with high sediment load and has the unique distinction of possessing both largest and smallest inhabited river islands. Majuli is the largest inhabited river island situated in the Indian state of Assam and bounded by Brahmaputra on the south, Subansiri River on the northwest, and the Kherkatia River (anabranch of Brahmaputra) on the northeast. The island was formed during a flooding event in 1750 with a sudden change in the course of the Brahmaputra from a low energy meandering to a high energy braided river and subsequent capture of one of its tributaries. The island is a part of the Brahmaputra alluvium squeezed between active Himalayan and Indo-Burmese orogenic belts in an intricate tectonic regime. The dominant flow path of Brahmaputra is controlled by the crustal scale reorganization in this part of the world. The tectonic factors that controlled the anabranching process and created the island, is at present acting as the destroyer of the same by the means of unabated erosion. The erosion pattern of the two rivers viz. Brahmaputra and Subansiri were studied and areas with marked selective erosion have been found. From a combined study of satellite imaging, bathymetric survey and mapping, it is found that the lobate shaped erosions in the study areas are restricted to traces of the tectonic elements related to the Himalayan thrust system through which the rivers are trying to anabranch.

Keywords

• River erosion
• Anabranching
• Tectonics
• Brahmaputra
• Majuli