What is it about?

A new river island called Dibru-Saikhoa has appeared very recently on the Brahmaputra valley map in Assam. More than 200 km2 in area, it is situated in the extreme upstream reach of the Brahmaputra River and represents the second biggest relict island after Majuli (a present area of about 500 km2)our study, Considering morphological changes from 1915 - to 2019 and subsurface geophysical data suggests that the anthropogenic factor, was an important ‘trigger’ of island formation, acting on a system made sensitive to change by the combination of local tectonics and rapidly changing sediment influx.

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Why is it important?

Making use of the satellite-borne Bouguer gravity data and ground survey-based seismic sections, we located some of the prominent blind faults. By plotting the braid bar/channel area (BB/CA) ratio at different segments vis-a-vis slope variability, we have proposed a criterion to assess the morpho-tectonic instability. The study has revealed the effectiveness of Second Derivative Gravity data in understanding the deep basement configuration of the basin. The integrated approach of merging gravity and seismic data is helpful for identifying blind faults influencing the surface relief of the basin.

Perspectives

The upper reach of the Brahmaputra Valley is having both flood and erosion-borne disasters. For disaster risk reduction programmes to be successful geological as well as large-scale human impacts should be brought into consideration. A simplistic civil engineering approach can incubate disasters and apparently smaller triggering factors can bring drastic changes to the riverscape.

Siddhartha Lahiri
Dibrugarh University

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This page is a summary of: Morphotectonic forcing and anthropogenic impact behind a recently emerged relict island of the Brahmaputra River, Earth Surface Processes and Landforms, July 2022, Wiley, DOI: 10.1002/esp.5443.
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