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Research in Geochemistry

Erosion and Weathering Processes in the Himalaya

We are pursuing a number of projects related to erosion, weathering and biogeochemical cycling in the Himalaya. Erosion rates are very high, with tremendous river fluxes during the monsoon season. Over a billion tons of sediment are transported to the ocean each year and deposited in the giant Bengal undersea fan. We study both modern processes and the records of ancient processes in sedimentary basins.
Modern sediment, water and soil chemistry combined with river fluxes give us detailed information about the active weathering and erosion cycle. River and sediment chemistry help identify weathering processes, and we are also interested in how geothermal systems and plant uptake affect chemical fluxes.
The long term geochemical and mineralogical record in Bengal Fan sediments allows us to reconstruct the erosional and weathering history of the Himalaya for the last 20+ million years. The data tell us that the Himalaya have been a major topographic feature since at least that time, but that weathering intensity has mostly been low.



Modern weathering and erosional fluxes in centeral Nepal

We are trying to understand river, sediment and soil chemistry in the watersheds of central Nepal. We are attempting to define the fluxes and sources of solutes, including radiogenic Sr, in the streams. We combine chemical and isotopic analysis to try and build mass balances for the watershed fluxes. Albert Galy, our occasional guest at Cornell, has led the work in this area. Some of our findings so far:Silicate weathering fluxes are modest in the Narayani watershed of central Nepal. Carbonate weathering is an important source of the dissolved load. However, radiogenic carbonates do not appear to dominate the flux of radiogenic Sr in the streams (Galy & France-Lanord, 1999; Galy et al., 1999).Silicate weathering rates and the release of radiogenic Sr are higher in the Siwalik foreland basin sediments and floodplain, although still poorly known.Matt Evans has shown that hot springs along the MCT are a very important source of solutes and radiogenic Sr (Evans et al., 2001, 2004).



Satellite remote sensing in the Nepal Himalaya

Alexandra Moore has been studying satellite images to try and understand the relationship between geology, climate and relief in central Nepal. The present zone of high relief is geologically located in the HHC, and the sedimentary data suggest that this must have been true for much of the last 20 Ma.The image to the left is a mosaic of two Landsat Thematic Mapper images acquired over the Himalayan Mountains in January, 1989. It extends from the High Himalayas of Nepal, south through the Siwalik hills and the Himalayan foreland of India. The Thakkola graben is the prominant N-S valley through the high part of the range; it separates the Dhaulagiri massif (west) from the Annapurna massif (east). On the eastern edge of the scene is the Manaslu Himal. This image displays TM bands 5-4-2 as red-green-blue; thus snow and ice appear blue while vegetation is green, rocks are red, and clouds are white.