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

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.     

Spatial and temporal changes in estuarine water quality during a post-flood hypoxic event

A major fish kill occurred in the Richmond River estuary in January 2008 due to oxygen depletion following extensive overbank flooding. This paper examines spatial and temporal changes in the chemistry of main channel waters, thereby identifying the primary sources of deoxygenating water. Over 40 km of the mid- to lower estuary main channel was deoxygenated within seven days of the flood peak. Hypoxia was confined to downstream of the confluences with mid-estuary backswamp basins and occurred during the later phase of the flood recession. Water chemistry at key locations in the estuary indicated elevated concentrations of redox sensitive species associated with acid sulfate soils (ASS) during the hypoxic period. Peak concentrations of Fe²⁺ up to 18.2 μmol L⁻¹, dissolved Mn up to 4.3 μmol L⁻¹, chemical oxygen demand (COD) up to 2052 μmol L⁻¹, dissolved organic carbon (DOC) up to 960 μmol L⁻¹ and elemental S⁰ up to 4.7 μmol L⁻¹ were found in the backswamp discharge confluences and mid-estuary main channel locations. The geochemical signature of main channel floodwaters identifies anaerobic decomposition of floodplain vegetation in ASS backswamps as a primary process leading to generation of hypoxic waters. The transport of these hypoxic floodwaters to the estuary has been accelerated and prolonged by extensive floodplain drainage, thereby enhancing the magnitude and duration of estuarine deoxygenation.     

Water and carbon fluxes of European ecosystems: an evaluation of the ecohydrological model RHESSys

This study investigated whether the regional hydro-ecological simulation system RHESSys is a suitable tool for long-term global change impact studies under selected climatic conditions of Europe, taking advantage of the strongly varying climate along elevational gradients in mountain regions. We performed a validation of RHESSys using daily, monthly and yearly data on (1) streamflow and snow cover in five Alpine catchments and (2) water and carbon fluxes at 15 EUROFLUX sites. The simulation results generally agreed well with observations. RHESSys reasonably reproduced daily and monthly streamflow, as well as the seasonal cycle and amplitude of typical Alpine discharge regimes. Furthermore, RHESSys was capable of capturing the key features of the carbon cycle of various forested ecosystems, including significant differences between managed and close-to-natural forests, and more subtle distinctions between coniferous and deciduous systems. Our analyses confirmed that RHESSys is a suitable tool for studying global change impacts on mountain hydrology. Regarding the simulation of the carbon cycle, this investigation detected some data and model limitations that are discussed in detail. Finally, suggestions for model improvements are made, mainly concerning the formulations of decomposition and respiration rates in biogeochemical models. Copyright © 2006 John Wiley & Sons, Ltd.     

A brief review of ophiolites in China

Ophiolites are widely distributed in western, southwestern and northern China, where they fall into four principal age groups; Neoproterozoic, Early Paleozoic, Late Paleozoic and Mesozoic–Cenozoic. Neoproterozoic ophiolites are known only in the North Qinling orogenic belt, in NE Jiangxi Province and in western Sichuan Province. Phanerozoic ophiolites are grouped into the Paleo-Asian, Tethyan and Circum-Pacific series. The Paleo-Asian ophiolites crop out in the western and northern parts of China between the Siberian and North China Blocks, and range in age from early to late Paleozoic. All of these ophiolites are of the Franciscan (formerly Cordilleran) type and many are superimposed on one another, suggesting repeated accretion of arc assemblages in an environment similar to the present-day western Pacific Ocean. Mediterranean-type (formerly Tethyan-type) ophiolites are confined to SW China, particularly Tibet and Yunnan Province. Paleo-Tethyan ophiolites are characterized by MORB-type lavas and are typically bounded by old continental lithosphere, suggesting that they formed in small, intercontinental ocean basins. Neo-Tethyan ophiolites contain a range of lava types including MORB, IAT and boninite, indicating formation in a variety of suprasubduction zone (SSZ) environments. Circum-Pacific ophiolites occur sporadically in Taiwan and NE China, where they form tectonic mélanges composed mainly of metaperidotite, gabbro and basalt.     

Cenomanian-Turonian high-resolution biostratigraphy of north-eastern Mexico and its correlation with the GSSP and Europe

Thin-bedded and millimetrically laminated platy marly limestone quarried near Vallecillo, north-eastern Mexico, contains abundant excellently preserved marine fossils. Planktic foraminifers, inoceramids, and ammonites occur throughout the 7.7-m-thick section of this plattenkalk and provide a precise and detailed biostratigraphic zonation from the uppermost Cenomanian to early Turonian, with a mixed assemblage of Tethyan and Western Interior Seaway faunal elements. Five species of inoceramids are present and described herein: Inoceramus pictus pictus, Mytiloides hattini, M. puebloensis, M. goppelnensis, and M. kossmati. The faunal characteristics of the Vallecillo fossil assemblage combined with the monotonous lithology are favourable attributes for correlation with the GSSP at Pueblo, Colorado, and the Eastbourne section in southern England. The first appearances (FAs) of Watinoceras and Mammites nodosoides are considered approximately isochronous and thus suited for long-distance correlation. In contrast, the FAs of Pseudaspidoceras flexuosum, Fagesia catinus, and Helvetoglobotruncana helvetica are clearly diachronous. The range of M. kossmati needs further evaluation.     

Avalanche Hazard Mitigation Strategies Assessed by Cost Effectiveness Analyses and Cost Benefit Analyses—evidence from Davos,Switzerland

This paper demonstrates the application of cost effectiveness analysis and cost benefit analysis to alternative avalanche risk reduction strategies in Davos, Switzerland. The advantages as well as limitations of such analysis for natural hazards planning are discussed with respect to 16 avalanche risk reduction strategies. Scenarios include risk reduction measures that represent the main approaches to natural hazards planning in Switzerland, such as technical, organisational, and land use planning measures. The methodologies used outline how concepts and techniques from risk analysis, hazard mapping, Geographic Information System, and economics can be interdisciplinary combined. The results suggest important considerations, such as possible sources of uncertainty due to different choices in the calculation of cost effectiveness ratio and net present value. Given the parameters and assumptions, it seems as if the current approach to avalanche risk reduction in the study area approximates to economic and cost efficiency and serves the aim of reducing risk to human fatalities.     

Structural and geochronological constraints on the tectonic evolution of the Dulong-Song Chay tectonic dome in Yunnan province, SW China

The Dulong-Song Chay tectonic dome lies on the border of China (SE Yunnan Province) and northern Vietnam, and consists of two tectonic and lithologic units: a core complex and a cover sequence, separated by an extensional detachment fault. These two units are overlain unconformably by Late Triassic strata. The core complex is composed of gneiss, schist and amphibolite. SHRIMP zircon U–Pb dating results for the orthogneiss yield an age of 799±10 Ma, which is considered to be the crystallization age of its igneous protolith formed in an arc-related environment. A granitic intrusion within the core complex occurred with an age of 436–402 Ma, which probably formed during partial closure of Paleotethys. Within the core complex, metamorphic grades change sharply from upper greenschist-low amphibolite facies in the core to low greenschist facies in the cover sequence. There are two arrays of foliation within the core complex, detachment fault and the cover sequence: S₁ and S₂. The pervasive S₁ is the axial plane of intrafolial S₀ folds. D₁ deformation related to this foliation is characterized by extensional structures. The strata were structurally thinned or selectively removed along the detachment faults, indicating exhumation of the Dulong-Song Chay tectonic dome. The major extension occurred at 237 Ma, determined by SHRIMP zircon U–Pb and ³⁹Ar/⁴⁰Ar isotopic dating techniques. Regionally, simultaneous tectonic extension was associated with pre-Indosinian collision between the South China and Indochina Blocks. The S₂ foliation appears as the axial plane of NW-striking S₁ buckling folds formed during a compressional regime of D₂. D₂ is associated with collision between the South China and Indochina Blocks along the Jinshajiang-Ailao Shan suture zone, and represents the Indosinian deformation. The Dulong granites intruded the Dulong-Song Chay dome at 144±2, 140±2 and 116±10 Ma based on ³⁹Ar/⁴⁰Ar measurement on muscovite and biotite. The dome was later overprinted by a conjugate strike-slip fault and related thrust fault, which formed a vortex structure, contemporaneously with late Cenozoic sinistral movement on the Ailao Shan-Red River fault.     

The silicon isotopic composition of surface waters in the Atlantic and Indian sectors of the Southern Ocean

We report here the silicon isotopic composition (δ³⁰Si) of dissolved silicon (DSi) from 42 surface water samples from the Drake Passage, the Weddell Gyre, other areas south of the Southern Boundary of the Antarctic Circumpolar Current (ACC), and the ACC near the Kerguelen Plateau, taken between the beginning of February and the end of March 2007. From the beginning to end of the cruise (ANTXXIII/9), DSi diminished in the Antarctic by 50 μmol L⁻¹ while concentrations of nitrate + nitrite and phosphate showed no net decline, indicating that the high seasonal Si/N removal ratios well known for the Southern Ocean may be more related to the strength of the silicate pump in the Southern Ocean than to the instantaneous Si/N uptake ratio of diatoms. The δ³⁰Si of DSi in samples containing more than 20 μM DSi were strongly negatively correlated to DSi concentrations, supporting the use of δ³⁰Si as a proxy for DSi removal. The “open system” fractionation observed, ε = −1.2 ± 0.11‰, agrees well with results from previous work in other areas, and the estimate of the initial δ³⁰Si of DSi of +1.4‰ is not far off observations of the δ³⁰Si of DSi in Winter Water (WW) in this area. Results were used to model DSi draw down in the past from the δ³⁰Si of sediment cores, although isotopic fractionation during silica dissolution appeared to influence the δ³⁰Si of some surface water samples, inviting further study of this phenomenon.