Rivers in the Himalayas: investigating links between tectonics, climate and topography

Overview

The shape of Earth’s topography reflects the interplay between tectonics, climate, and sediment transport processes. Analysing and quantifying landscape morphology therefore provides the potential for extracting tectonic information, such as rates of fault motion and regions of high seismicity, from topographic data alone. In the past few decades, the amount of high-resolution topographic data available throughout the globe has increased exponentially, providing a revolution in our ability to identify geomorphic processes across the scale of whole landscapes and orogens.

One of the most striking examples of the impact of tectonics on topography is the Himalayan mountain range, which has fascinated geoscientists for centuries. Many studies have suggested that topography in the Himalayas is responding to active tectonics, shown by analysis of river networks (e.g. Seeber and Gornitz, 1983) and exhumation patterns (e.g. King et al., 2016, van der Beek et al., 2016). In contrast, other workers argue that climate, by causing focused erosion, can instead control the pattern of deformation and tectonic processes (e.g. Finlayson et al., 2002, Thiede et al., 2004). Recent work has suggested that rainfall-induced erosion in the Himalayas may control topographic form and obscure signatures of tectonics (Adams et al., 2020). Links and feedbacks between climate, tectonics and surface processes have yet to be fully understood.

One potential way to explore these feedbacks is through the examination of fluvial terraces, a rich sedimentary archive of climate and tectonics through geological time. For example, Lav and Avouac (2000) showed that terraces in the Siwalik foothills recorded active folding along the Himalayan Main Frontal thrust. Sinclair et al. (2017) combined structural mapping with dating of terrace sediments to measure tectonic shortening across the Indus River Valley in the NW Himalayas, demonstrating the potential that terraces hold for reconstructing tectonics. However, previous studies have been limited by our ability to map fluvial terraces and quantify their geometry over large spatial scales.

This project will explore the links between tectonics and topography across the Himalayan mountain front. The student will use new techniques for mapping terraces automatically from topography to conduct a compilation of terrace surfaces across the entire Himalayan mountain front and explore controls on terrace elevations and geometry. The distribution of terraces will be used to constrain the motion of major faults across the mountain front, while terrace sedimentology will be used to explore catchment-scale processes such as the past records of fluvial discharge, landsliding and glaciation. Targeted field work will allow the characterisation of terrace deposits and surface dating, to validate the results of the topographic analysis. These data will be integrated with modern observations of tectonics such as InSAR-derived strain rates, seismic datasets, and satellite-derived climate observations.

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Image Captions

Terraces in the Kali-Gandaki river valley, Nepal. Credit: Arne kelheim, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=17388677

Methodology

The student will build on and further develop techniques for mapping fluvial terraces implemented in LSDTopoTools, an open-source software package for topographic analysis (Clubb et al., 2017). This will involve working with researchers at the University of Glasgow, University of Edinburgh, and Queen Mary University of London as part of a collaborative development effort. The student will primarily be based at Durham University, but funding will be provided for travel to Glasgow and Edinburgh to discuss and brainstorm with the other project supervisors. Experience in one or more programming languages (preferably Python/C++) is desirable, although training will be provided as part of this PhD project. The student will work primarily with large scale digital elevation models (DEMs) available for the Himalayan region, such as the Shuttle Radar Topography Mission (SRTM) 30 m dataset, as well as DEMs derived from ALOS-PALSAR. They will learn how to efficiently analyse digital topography to understand geomorphic process.

The student will combine topographic analysis with field work to constrain the evolution and age of the fluvial terraces derived from the automated mapping. This field work will involve detailed sedimentology of terrace deposits, as well as radiocarbon age dating of terrace sediments. This will involve two field seasons to the Nepal Himalayas over the course of the project.

The location and geometry of terraces surfaces across the Himalayan front will be compared to large scale remote sensing datasets characterising both climate and tectonics. The student will gain experience in working with strain rate datasets derived from InSAR, satellite-derived climate observations, and remotely sensed vegetation indices such as NDVI.

Project Timeline

Year 1

Literature review, training in programming and topographic analysis, software development, first field season for terrace analysis.

Year 2

Extraction of terrace surfaces across the Himalayas, quantification of terrace geometries, processing of radiocarbon samples, second field season to collect additional datasets or to expand the analysis region, presentation of initial results at national/international conferences.

Year 3

Comparison of terrace geometries with remotely sensed tectonic and climate datasets, analysis and interpretation of terrace age dates, presentation of results at conferences, writing up of main results, preparation of papers for publication.

Year 3.5

Finalising results, writing up and presentation of final thesis, preparation of papers for publication.

Training
& Skills

During this project the student will receive training in programming with Python and potentially C++, as well as the analysis of large environmental datasets. They will learn how to move beyond traditional desktop-based GIS software in the analysis of topography and become comfortable with performing analyses in a Linux environment on supercomputing clusters.

The student will also conduct two field seasons during which they will learn how to perform sedimentological analysis of terrace deposits and radiocarbon age dating. They will also be trained in the analysis of remote sensing datasets to characterise climatic and tectonic regimes.

As part of this project the student will also present their results at both international and national conferences, where they will further develop their skills in presenting and communicating scientific research. The student is also encouraged to apply for small grants from the Royal Geographic Society, British Society for Geomorphology, and Durham Institute of Hazard, Risk and Resilience which will allow them to gain experience with writing funding proposals.

References & further reading

Adams, B.A., Whipple, K.X., Forte, A.M., Heimsath, A.M. and Hodges, K.V., 2020. Climate controls on erosion in tectonically active landscapes. Science Advances, 6(42).

Clubb, F.J., Mudd, S.M., Milodowski, D.T., Valters, D.A., Slater, L.J., Hurst, M.D. and Limaye, A.B., 2017. Geomorphometric delineation of floodplains and terraces from objectively defined topographic thresholds. Earth Surface Dynamics, 5(3).

Finlayson, D.P., Montgomery, D.R. and Hallet, B., 2002. Spatial coincidence of rapid inferred erosion with young metamorphic massifs in the Himalayas. Geology, 30(3), pp.219-222.

King, G.E., Herman, F. and Guralnik, B., 2016. Northward migration of the eastern Himalayan syntaxis revealed by OSL thermochronometry. Science, 353(6301), pp.800-804.

Lavé, J. and Avouac, J.P., 2000. Active folding of fluvial terraces across the Siwaliks Hills, Himalayas of central Nepal. Journal of Geophysical Research: Solid Earth, 105(B3), pp.5735-5770.

Seeber, L. and Gornitz, V., 1983. River profiles along the Himalayan arc as indicators of active tectonics. Tectonophysics, 92(4), pp.335-367.

Sinclair, H.D., Mudd, S.M., Dingle, E., Hobley, D.E.J., Robinson, R. and Walcott, R., 2017. Squeezing river catchments through tectonics: Shortening and erosion across the Indus Valley, NW Himalaya. GSA Bulletin, 129(1-2), pp.203-217.

Thiede, R.C., Bookhagen, B., Arrowsmith, J.R., Sobel, E.R. and Strecker, M.R., 2004. Climatic control on rapid exhumation along the Southern Himalayan Front. Earth and Planetary Science Letters, 222(3-4), pp.791-806.

van der Beek, P., Litty, C., Baudin, M., Mercier, J., Robert, X. and Hardwick, E., 2016. Contrasting tectonically driven exhumation and incision patterns, western versus central Nepal Himalaya. Geology, 44(4), pp.327-330.

Further Information

Dr. Fiona Clubb -fiona.j.clubb@durham.ac.uk, 0191 334 1852
Dr. Martin Hurst – martin.hurst@glasgow.ac.uk, 0141 330 2326
Prof. Simon Mudd -simon.m.mudd@ed.ac.uk

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