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Information - NH3.03 Slope movements in weathered materials: recognition, analysis, and hazard assessment (co-listed in GM)
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Event Information |
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Weathering is the process of chemical alteration and physical breakdown of rock at the Earth’s surface. Intense and/or continuous weathering may result in thick sequences of weathered materials, whose physical and geotechnical properties have been strongly altered by the action of weathering, and which thus show high complexity and heterogeneity. As a consequence, these materials are prone to slope failures, erosion and landslides. In addition, the availability of large amounts of weathered materials and loose debris in watersheds represents a significant flood and landslide hazard during intense rainfall. Landslides in weathered materials occur throughout the world, especially in areas where crystalline and sedimentary rocks have been exposed to humid and tropical climate conditions, which permit the formation of complex, thick, sequences of weathered materials. Furthermore, in many areas of the Earth, relict weathering products derived from earlier climatic regimes may be exposed. Rapid, shallow landslides (mostly soil slips evolving to debris flows) are among the most common type of slope movement in weathered materials; although large, deep-seated landslides also occur. Despite the high frequency of landslides in weathered materials and the resulting damage and casualties, the relationship between weathering and slope movements is not well studied. More work is needed to evaluate landslide hazards and mitigation in these settings. The hazard related to slope movements in weathered materials is best understood using a multi-disciplinary approach, including expertise from the fields of petrography, mineralogy, geomorphology, engineering geology, among others. In addition, geophysical surveys provide useful information to evaluate thickness and lateral continuity of weathered horizons. Recognition and mapping of materials showing different grades of weathering (and hence, different geotechnical properties) is crucial for the identification of varying susceptibility to erosion and landsliding. Different weathering grade horizons can be distinguished, and their spatial distribution on hillslopes can be mapped by means of: 1) surveying of the weathering profile on natural and excavated slopes; 2) mineralogical and petrographical analyses to determine weathering classes; and 3) characterization of the weathering grade by means of in-situ and laboratory tests. This weathering and slope movements session provides an opportunity to discuss methodologies and techniques for a better understanding of the weathering conditions of bedrock on hillslopes, of their susceptibility to slope movements (especially rapid and catastrophic landslides), and the resulting risk to life and property. Papers dealing with analysis of the relationships between slope movements and weathering at local or regional scales and in different physiographic, climatic and geological settings are solicited. Contributions presenting a multi-disciplinary approach to the problem are particularly encouraged. The objective of this symposium is to stimulate further research in the field of weathering and landslides, and to facilitate multidisciplinary cooperation among scientists.
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