Impact of landsliding on chemical weathering in the volcanic island of Reunion
Abstract
Tropical precipitation regimes allow for strong erosion that creates dramatic landscapes. Understanding and quantifying erosion processes in tropical volcanic islands is important for both scientific challenges (e.g. regarding their implications for global biogeochemical cycles and their links with climate) and societal matters (e.g. socio-economic and ecosystem damages in highly populated areas). Despite the fact that the link between chemical weathering and physical erosion has long been studied, most research has focused on active mountain ranges. Here we use Reunion Island as a natural laboratory to explore this link in a tectonically inactive environment.In Reunion, estimates show that intense erosion rates are mainly due to stochastic bedrock landsliding. Although landslides affect only a small portion of the landscape they supply rivers with huge amounts of fresh broken rocks and organic matter, which are then available for chemical alteration and for transport. In this study, we measured water chemistry of several streams in Reunion and of landslide seepage water sampled on 2 majors landslides ("Grand Éboulis" and "Mahavel", both > 50 yrs old). Seepage samples from Grand Éboulis show high Total Dissolved Solids (TDS) compared to local streams, in agreement with previous observations showing that landslides promote chemical weathering [1]. However, the low TDS of the Mahavel seep water samples compared to local streams, suggest that the impact of landslides on weathering fluxes may strongly depend on the rate at which landslide debris are transferred downstream and their subsequent residence time in the catchment. In order to calculate such sediment transfer rates in Mahavel, we developed an automated photogrammetric workflow allowing for deriving Digital Elevation Models from historical aerial photos. Using the 30 years of images archived at the Institut Geographique National (5 campaigns), we will be able to delineate the extent of landslide debris, to estimate volumes of the released mass, and to calculate rates of displacement downstream the Mahavel landslide. This tool will allow us to address the potential kinetic limitation of landslide-promoted weathering. [1] Emberson et al. Chemical weathering in active mountain belts controlled by stochastic bedrock landsliding, Nat. Geo. 2015
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2017
- Bibcode:
- 2017AGUFMEP53B1705G
- Keywords:
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- 1824 Geomorphology: general;
- HYDROLOGY;
- 1826 Geomorphology: hillslope;
- HYDROLOGY;
- 1862 Sediment transport;
- HYDROLOGY;
- 5419 Hydrology and fluvial processes;
- PLANETARY SCIENCES: SOLID SURFACE PLANETS