Assessing physical vulnerability in large cities exposed to flash floods and debris flows: the case of Arequipa (Peru)     

Jean-Claude Thouret  Susanne Ettinger  Mathieu Guitton  Olivier Santoni  Christina Magill  Kim Martelli  Giulio Zuccaro  Victor Revilla  Juan Antonio Charca  Anita Arguedas 《Natural Hazards》2014,73(3):1771-1815

Understanding the physical vulnerability of buildings and infrastructure to natural hazards is an essential step in risk assessment for large cities. We have interpreted high spatial resolution images, conducted field surveys, and utilized numerical simulations, in order to assess vulnerability across Arequipa, south Peru, close to the active El Misti volcano. The emphasis of this study was on flash floods and volcanic or non-volcanic hyperconcentrated flows, which recur on average every 3.5 years across the city. We utilized a geographic information system to embed vulnerability and hazard maps as a step to calculate risk for buildings and bridges along the Río Chili valley and two tributaries. A survey of ~1,000 buildings from 46 city blocks, different in age, construction materials, and land usage, provided architectural and structural characteristics. A similar survey of twenty bridges across the three valleys was based on structural, hydraulic, and strategic parameters. Interpretation of high spatial resolution (HSR) satellite images, which allows for quick identification of approximately 69 % of the structural building types, effectively supplemented field data collection. Mapping vulnerability has led us to pinpoint strategic areas in case of future destructive floods or flows. Calculated vulnerability is high if we examine structural criteria alone. We further consider physical setting with the most vulnerable city blocks located on the lowermost terraces, perpendicular or oblique to the flow path. Statistical analysis conducted on 3,015 city blocks, considering nine criteria identified from HSR images, indicated that building-type heterogeneity and the shape of the city blocks, along with building and street network density, are the most discriminant parameters for assessing vulnerability.  相似文献   

Erosion calderas: origins, processes, structural and climatic control   总被引：1，自引：0，他引：1  

Dávid Karátson  Jean-Claude Thouret  Ichio Moriya  Alejandro Lomoschitz 《Bulletin of Volcanology》1999,61(3):174-193

 The origin and development of erosion-modified, erosion-transformed, and erosion-induced depressions in volcanic terrains are reviewed and systematized. A proposed classification, addressing terminology issues, considers structural, geomorphic, and climatic factors that contribute to the topographic modification of summit or flank depressions on volcanoes. Breaching of a closed crater or caldera generated by volcanic or non-volcanic processes results in an outlet valley. Under climates with up to ∼2000–2500 mm annual rainfall, craters, and calderas are commonly drained by a single outlet. The outlet valley can maintain its dominant downcutting position because it quickly enlarges its drainage basin by capturing the area of the primary depression. Multi-drained volcanic depressions can form if special factors, e.g., high-rate geological processes, such as faulting or glaciation, suppress fluvial erosion. Normal (fluvial) erosion-modified volcanic depressions the circular rim of which is derived from the original rim are termed erosion craters or erosion calderas, depending on the pre-existing depression. The resulting landform should be classed as an erosion-induced volcanic depression if the degradation of a cluster of craters produces a single-drained, irregular-shaped basin, or if flank erosion results in a quasi-closed depression. Under humid climates, craters and calderas degrade at a faster rate. Mostly at subtropical and tropical ocean-island and island-arc volcanoes, their erosion results in so-called amphitheater valleys that develop under heavy rainfall (>∼2500 mm/year), rainstorms, and high-elevation differences. Structural and lithological control, and groundwater in ocean islands, may in turn preform and guide development of high-energy valleys through rockfalls, landsliding, mudflows, and mass wasting. Given the intense erosion, amphitheater valleys are able to breach a primary depression from several directions and degrade the summit region at a high rate. Occasionally, amphitheater valleys may create summit depressions without a pre-existing crater or caldera. The resulting, negative landforms, which may drain in several directions and the primary origin of which is commonly unrecognizable, should be included in erosion-transformed volcanic depressions. Received: 4 January 1998 / Accepted: 18 January 1999  相似文献   

Electrical imaging of lateritic weathering mantles over granitic and metamorphic basement of eastern Senegal, West Africa     

Michel Ritz  Jean-Claude Parisot  S. Diouf  A. Beauvais  F. Dione  M. Niang 《Journal of Applied Geophysics》1999,41(4):105

The electrical properties of several tens of metres of lateritic weathering mantle were investigated by using electrical resistivity tomography (ERT) in two basement areas of eastern Senegal. The field survey was conducted along two profiles providing continuous coverage. Colour-modulated pseudosections of apparent resistivity vs. pseudo-depth were plotted for all survey lines, giving an approximate image of the subsurface structure. In the area underlain by granitic basement, the pseudosection suggests a very inhomogeneous weathered layer in which the apparent resistivity changes more rapidly than thickness. In the second area, underlain by schists, the lateral changes in electrical properties are less pronounced than those of the granitic area. Interpretation of 2D Wenner resistivity data yielded considerable detail about the regolith, even without pit information. In both areas, the near-surface topsoil comprising undersaturated lateritic material is highly resistive. The intermediate layer with low resistivities (e.g., 20–100 Ωm) contains clays including small quantities of water. The third, highly resistive layer reflects the granitic basement. Comparison of ERT survey results with pit information shows general agreement and suggests that ERT can be used as a fast and efficient exploration tool to map the thick lateritic weathering mantle in tropical basement areas with hard rock geology.  相似文献   

Facies and geometry of tidal channel-fill deposits (Arcachon Lagoon, SW France)     

Hugues Fenies  Jean-Claude Faugres 《Marine Geology》1998,150(1-4):131-148

The Arcachon Lagoon has an important network of tidal channels and well developed tidal flats covered by the marine grass Zostera marina. Based on 66 piston cores taken from the Graveyron tidal channel, and observations on the neighbouring channels, this paper documents the facies and geometry of the channel-fill deposits. In the inner lagoon (studied area) the tidal channels are 80 to 150 m wide and have a meandering morphology with sandy point bars 2 to 5 m thick. The channel-fill does not consist of the classic inclined heterolithic bedding typical of many channel-fills (Reineck, 1958), but of cross-stratified sandy deposits characterized by the absence of slack-water clay-drapes. These unusual facies characteristics are due to the low turbidity of the lagoonal waters which is caused by the lack of significant river inflow and the dense coverage of Zostera marina on the tidal flats. The overall geometry of the channel-fill deposits is characterized by a narrow sand-ribbon shape, a few kilometres long, 80 to 150 m wide and 1 to 5 m thick. This sand ribbon is made of elliptical sand bodies, deposited as point bars, that coalesce longitudinally along the channel axis. This narrow shape is due to the fact that the lateral migration of the channel is virtually nil (reduced to a few metres). In spite of their characteristic meandering morphology, these channels do not deposit extensive tabular sand sheets of amalgamated point bars like the tidal creeks on the North Sea tidal flats. Two factors are thought to control this lack of channel migration. (1) The tidal flats adjacent to the tidal channels are made of 3- to 5-m-thick cohesive muddy sediments covered by Zostera marina that prevents the erosion of the channel banks. This first mechanism is supported by the observation that the tidal creeks that drain the muddy tidal flats covered by Zostera marina do not migrate laterally, whereas those that drain the sandy tidal flats devoid of a dense coverage of marine grass do have active lateral migration. (2) The tidal channels are not fed by any river and therefore do not receive any fluvial sand influx during the winter floods. Their morphology is in equilibrium with the tidal discharge and represents a stable stage in the development of the channel. This second mechanism is supported by the fact that the only tidal channels that actively migrate laterally in the lagoon receive sandy fluvial influx from the River Leyre located in the southeastern corner of the lagoon.  相似文献   

Reconstructing fluvial incision rates based on palaeo-water tables in chalk karst networks along the Seine valley (Normandy,France)     

Carole Nehme  Andrew Farrant  Daniel Ballesteros  Dominique Todisco  Joel Rodet  Diana Sahy  J. Michael Grappone  Jean-Claude Staigre  Damase Mouralis 《地球表面变化过程与地形》2020,45(8):1860-1876

Quantifying rates of river incision and continental uplift over Quaternary timescales offer the potential for modelling landscape change due to tectonic and climatic forcing. In many areas, river terraces form datable archives that help constrain the timing and rate of valley incision. However, old river terraces, with high-level deposits, are prone to weathering and often lack datable material. Where valleys are incised through karst areas, caves and sediments can be used to reconstruct the landscape evolution because they can record the elevation of palaeo-water tables and contain preserved datable material. In Normandy (N. France), the Seine River is entrenched into an extensive karstic chalk plateau. Previous estimates of valley incision were hampered by the lack of preserved datable fluvial terraces. A stack of abandoned phreatic cave passages preserved in the sides of the Seine valley can be used to reconstruct the landscape evolution of the region. Combining geomorphological observations, palaeomagnetic and U/Th dating of speleothem and sediments in eight caves along the Lower Seine valley, we have constructed a new age model for cave development and valley incision. Six identified cave levels up to ∼100 m a.s.l. were formed during the last ~1 Ma, coeval with the incision of the Seine River. Passage morphologies indicate that the caves formed in a shallow phreatic/epiphreatic setting, modified by sediment influxes. The valley's maximum age is constrained by the occurrence of late Pliocene marine sand. Palaeomagnetic dating of cave infills indicates that the highest-level caves were being infilled prior to 1.1 Ma. The evidence from the studied caves, complemented by fluvial terrace sequences, indicates that rapid river incision occurred during marine isotope stage (MIS) 28 to 20 (0.8–1 Ma), with maximal rates of ~0.30 m ka⁻¹, dropping to ~0.08 m ka⁻¹ between MIS 20–11 (0.8–0.4 Ma) and 0.05 m ka⁻¹ from MIS 5 to the present time. © 2020 John Wiley & Sons, Ltd.  相似文献   

Effect of water content on permanent deformation of fine/coarse soil mixtures with varying coarse grain contents and subjected to multi-stage cyclic loading     

Su  Yu  Cui  Yu-Jun  Dupla  Jean-Claude  Canou  Jean 《Acta Geotechnica》2022,17(8):3259-3268

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Modeling the suction- and deviator stress-dependent resilient modulus of unsaturated fine/coarse soil mixture by considering soil–water retention curve     

Su  Yu  Cui  Yu-Jun  Dupla  Jean-Claude  Canou  Jean 《Acta Geotechnica》2022,17(9):3747-3763

Experimental observations have shown that the resilient modulus M_r of fine/coarse soil mixture can be significantly affected by the coarse grain content f_v, deviator stress σ_d and suction \(\psi\). In this study, a constitutive model incorporating the soil–water retention curve (SWRC) was proposed to describe the effects of \(\psi\) and \(\sigma_{{\text{d}}}\) on M_r. This model was then extended to the effect of f_v. The proposed model implied the resilient modulus at saturation condition (M_r-sat), the resilient modulus at optimum moisture content (OMC) condition (M_r-opt), the suction at OMC (\(\psi_{{{\text{opt}}}}\)) and the parameters related to SWRC. The model was validated using experimental data from five studies reported in the literature. Comparisons with three representative existing models showed that the proposed model was capable to well describe the suction-dependent effect of deviator stress in the full range of suction, while the existing models gave satisfactory simulation results only in the low suction range. Indeed, experimental studies revealed that there was a threshold suction \(\psi_{{{\text{th}}}}\), and with increasing \(\sigma_{{\text{d}}}\), the M_r decreased when \(\psi < \psi_{{{\text{th}}}}\), but increased when \(\psi > \psi_{{{\text{th}}}}\). When \(\psi < \psi_{{{\text{th}}}}\), all models gave good simulations. On the contrary, when \(\psi > \psi_{{{\text{th}}}}\), only the proposed model gave good simulations, in particular when \(\psi_{{{\text{th}}}} > \psi_{{{\text{opt}}}}\). This showed the performance of the proposed model in describing the variation in resilient modulus of unsaturated fine/coarse soil mixtures with changes in coarse grain content, deviator stress and suction.

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