Tectonics shape the stream junction angles in the Himalaya

Mahaur, Sarthak (2025) Tectonics shape the stream junction angles in the Himalaya. Masters thesis, Indian Institute of Science Education and Research Kolkata.

Text (MS Dissertation of Sarthak Mahaur (20MS045)) 20MS045_Thesis_file.pdf - Submitted Version Restricted to Repository staff only Download (25MB)

Abstract

Stream networks are present on the face of the Earth and record climate and tectonic forcings in their longitudinal and planform geometry. While the impact of these forcings on the river longitudinal profile has been well studied, their impact on the planform geometry of the network has been overlooked. One attribute of the fluvial network’s planform geometry is the junction angles at which the streams meet. Previous research has explored the individual role of climate (aridity index) and tectonics (channel slope) in shaping the stream junction angles. However, the interplay between the two that controls the junction angles in a region of climate-tectonics interaction is a nascent research field that has just started to get attention. Here, we analyse the junction angles formed by low-order streams in the Himalaya, a region of known climatetectonics coupling, to decipher the relative role of each in shaping the fluvial planformgeometry. Our results suggest that while climate does control the junction angles, with higher angles observed in more humid climates, tectonics takes the upper hand in controlling the junction angles in regions of high uplift rates, with a diminished role of climate. The stronger tectonic signal overprints the climate signal in such regions. We also explore the dynamic nature of the junction angles, where new tectonic perturbations force the junction geometry to adjust to the new tectonic conditions. We see that this adjustment takes place by fluvial processes of erosion and deposition at the junction, an unexplored idea that Howard put forth more than fifty years ago.

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