Quantifying the effects of an extreme earthquake on a large river system

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This project will assemble the first integrated picture of how key chemical and physical characteristics of a major river system are affected by extreme disturbance from a large earthquake, using as a basis for study the response of the Min Jiang, or Yangtze River, to the 2008 8.0 Mw earthquake in Wenchuan, China. This earthquake triggered widespread landslides in the Min Jiang catchment area, and our preliminary data indicate that these landslides significantly changed the amount and composition of sediment carried by the river, and the chemistry of the river water. In our research, which seizes the opportunity presented by this rare natural experiment, we will collaborate with colleagues from the UK, Germany, and China to combine (i) compilation and interpretation of hydrometric data from the Chinese Hydrologic Bureau, (ii) fieldwork to collect representative samples, and (iii) new analyses targeted to explore key geochemical signatures in material carried by the river. The results of our measurements will be compared to data collected before the earthquake. In particular, we will explore differences before and after the earthquake in (i) the amount of suspended sediment carried by the river; (ii) the 10Be concentration in riverbed sediments; (iii) the dissolved major element composition of river waters; and (iv) the concentration and flux of particulate organic carbon transported as part of river sediment. In rivers around the world, measurements of sediment concentrations, and of the chemical properties of sediment and river water, have been routinely used to understand some of the most important processes at the Earth?s surface such as 1) physical erosion and sediment mobilization that pose widespread engineering hazards and 2) mineral weathering and organic carbon transport that play central roles in the global carbon cycle. It is commonly assumed that measurements made at any one point in time on a river reflect what is going on over much longer periods of time. If very large disturbances that happen only very rarely ? such as an extreme earthquake ? have significant effects on these measured parameters, then our quantitative understanding of important processes like erosion, sediment mobilization, and the global carbon cycle may be incomplete. The 2008 Wenchuan earthquake in Sichuan, China, provides an ideal and rare opportunity to explore whether this is the case, because the large-magnitude earthquake had such a significant effect in triggering landslides in the headwaters of the Yangtze River, and because we can take advantage of extensive data that were collected on the Yangtze prior to the earthquake. Our research will seize this opportunity by building an international collaboration that will apply a range of approaches to studying this river system.