Dike emplacement and flank instability at Mount Etna: Constraints from a poro-elastic-model of flank collapse |
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| Authors: | M Battaglia M Di Bari V Acocella M Neri |
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| Institution: | 1. CNR-ISAC, Bologna, Italy;2. NASA-GSFC and Earth System Science Interdisciplinary Center, University of Maryland, College Park, MD, USA;1. Key Laboratory of Arable Land Conservation (Middle and Lower Reaches of Yangtze River), Ministry of Agriculture, College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, China;2. Key Laboratory of Poyang Lake Basin Agricultural Resource and Ecology of Jiangxi Province, College of Land Resource and Environment, Jiangxi Agricultural University, Nanchang 330045, China;3. Physical Chemistry and Soft Matter, Wageningen University, Dreijenplein 6, 6703 HB Wageningen, The Netherlands;4. Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100039, China;1. Department of Civil Engineering, The University of Hong Kong, Hong Kong, PR China;2. College of Civil Engineering and Architecture, Shandong University of Science and Technology, Qingdao, PR China;1. Simmons Comprehensive Cancer Center, UT Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, TX 75390, USA;2. Department of Clinical Sciences, UT Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, TX 75390, USA;3. Veterans Affairs San Diego Healthcare System, Division of Gastroenterology, Department of Medicine, 3350 La Jolla Village Dr, San Diego, CA 92161, USA;4. Moores Cancer Center, UC San Diego, 3350 La Jolla Village Dr, San Diego, CA 92161, USA;5. Department of Internal Medicine, UT Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, TX 75390, USA;6. People Designs, 1304 Broad St, Durham, NC 27705, USA;7. Department of Family & Community Medicine, UT Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, TX 75390, USA;8. Indiana University School of Nursing, 1111 Middle Drive, Indianapolis, IN 46202, USA;9. Indiana University Simon Cancer Center, 1030 W. Michigan Street, Indianapolis, IN 46202, USA |
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| Abstract: | Many volcanic edifices are subject to flank failure, usually produced by a combination of events, rather than any single process. From a dynamic point of view, the cause of collapse can be divided into factors that contribute to an increase in shear stress, and factors that contribute to the reduction in the friction coefficient μ of a potential basal failure plane. We study the potential for flank failure at Mount Etna considering a schematic section of the eastern flank, approximated by a wedge-like block. For such geometry, we perform a (steady state) limit equilibrium analysis: the resolution of the forces parallel to the possible basal failure plane allows us to determine the total force acting on the potentially unstable wedge. An estimate of the relative strength of these forces suggests that, in first approximation, the stability is controlled primarily by the balance between block weight, lithostatic load and magmatic forces. Any other force (sea load, hydrostatic uplift, and the uplift due to mechanical and thermal pore-fluid pressure) may be considered of second order. To study the model sensitivity, we let the inferred slope α of the basal surface failure vary between ?10° and 10°, and consider three possible scenarios: no magma loading, magmastatic load, and magmastatic load with magma overpressure. We use error propagation to include in our analysis the uncertainties in the estimates of the mechanics and geometrical parameters controlling the block equilibrium. When there is no magma loading, the ratio between destabilizing and stabilizing forces is usually smaller than the coefficient of friction of the basal failure plane. In the absence of an initiating mechanism, and with the nominal values of the coefficient of friction μ = 0.7 ± 0.1 proposed, the representative wedge will remain stable or continue to move at constant speed. In presence of magmastatic forces, the influence of the lateral restraint decreases. If we consider the magmastatic load only, the block will remain stable (or continue to move at constant speed), unless the transient mechanical and thermal pressurization significantly decrease the friction coefficient, increasing the instability of the flank wedge for α > 5° (seaward dipping decollement). When the magma overpressure contribution is included in the equilibrium analysis, the ratio between destabilizing and stabilizing forces is of the same order or larger than the coefficient of friction of the basal failure plane, and the block will become unstable (or accelerate), especially in the case of the reduction in friction coefficient. Finally, our work suggests that the major challenge in studying flank instability at Mount Etna is not the lack of an appropriate physical model, but the limited knowledge of the mechanical and geometrical parameters describing the block equilibrium. |
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