CRPG-Recherche

Himalayan erosion

Through its unique topography and orographic control on the Asian monsoon, the Himalayan system constitute the largest erosion system of the planet. It annually carries more than a billion tons of sediment and dissolved materials to the oceans, which corresponds to an erosion of of few millimeters per year. This transfer continental affects the environment at very different time scales. At geological timescales, Himalayan erosion contributes to the control of the long term carbon cycle through organic matter transport and burial. It can also act on the tectonic evolution of the range by isostatic rebound of eroded areas. At shorter term, the environment of the Himalayan basin depends on the erosion processes that control some of the risk in the Himalayas (landslides, glaciers), also controlling soilstability and fertility.

Scientific objectives

The broad objective is to understand the interactions between geological processes and Earth’s environment. Plate tectonic shapes the topography of the planet and thus generates a complex network of interactions at the center of which are erosion and climate. The Himalayan system considered from top of Everest to the bottom of the Bengal basin is a unique place to understand the fundamental processes of erosion because of it’s global impact and of the intensity of process . The challenge of research on the Himalayan erosion is to estimate the strength of its effect on the global environment and to test the existence of interactions between climate and tectonics:

- Erosion and the carbon cycle - Erosion plays a crucial role in the carbon cycle as it mobilizes the CO2 from the atmosphere and transfer it to the sedimentary reservoirs. Erosion uses atmospheric CO2 to alter silicates which generates a flux of dissolved cations and alkalinity to the oceans. They supply precipitation of biogenic carbonates that sequesters C on a geological time scale. Meanwhile, erosion drains organic fragments with particle flow of rivers. The sedimentary burial of these fragments is also a C sink in the long term. This later process dominates in Himalaya. The "orogenic forcing of climate" hypothesis proposes that the development of mountain ranges amplifies the process leading to a decrease in atmospheric PCO2 and subsequent global cooling. This coupling could have played a role in the Cenozoic glaciation.

Uplift, erosion and climate - Plate tectonic acts strongly on climate when it generates a mountain ranges as it changes the continental distribution and creates orographic barriers. The development of the Himalayan uplift and the aridification of Central Asia during the Cenozoic initiated the Asian monsson climate. Climate also plays a role on uplift as erosion tends to increase the elevation by isostatic rebound effect.

Field work

Népal, Inde (Bihar, Assam, Arunachal Pradesh), Bangladesh, Océan Indien

Approaches

The approach is based primarily on the quantitative and descriptive study of modern processes of erosion across the Himalayan basin, from the mountain sources rocks down to the sediments of the Bengal fan in the Indian Ocean. Sedimentary deposits of the Himalayan erosion are used in parallel to reconstruct past changes in environmental conditions and erosion. The goal is to combine these informations to reconstruct the erosion fluxes, which are then used to model the tectonic-climate-erosion interactions at different scales of time and space. This "source to sink" approach is based on field observations and sampling (specific studies, mid term observations, oceanographic exploration), experimental approaches, developments of geochemical tracers and the development of appropriate modelling.

Example of erosion tracing using cosmogenic 10Be in quartz from river sediments to derive Himalayan denudation rates and sediment fluxes (Lupker et al. 2012). (Fc): Floodplain corrected denudation rates, calculated using production rates from upstream sediment-contributing areas 4300 m. (Sc): Floodplain corrected denudation rates for the Himalayan range only, i.e. corrected for southern tributary contributions.

French collaborations

Chatherine Chauvel, Pascale Huyghes LGCA Grenoble, François Chabaux, LHYGES Strasbourg, Jérôme Gaillardet, François Métivier, Frédéric Perrier IPG Paris, Olivier Beyssac IMPMC Paris, Yves Goddéris LMTG Toulouse

International collaborations

Tribhuvan University, Kathmandou Nepal (Prof. Upreti, Dr Gajurel)
Indian Institute of Technology Kanpur, India (Prof. Rajiv Sinha)
Physical Research Laboratory, Ahmadabad India (Dr Sunil K. Singh)
Dhaka University, Bangladesh (prof. Mustafizur Rahman)
Marum, Bremen Universitaet, Germany, (Prof. H. Kudrass, Prof. V. Spiess)
Cornell University, Ithaca NY USA (prof. Lou Derry)