Flood hazard assessment and mapping of River Swat using HEC-RAS 2D model and high-resolution 12-m TanDEM-X DEM (WorldDEM)

Natural Hazards - Floods are among the most devastating and recurring natural hazards and have caused extensive economic losses to human lives and infrastructures around the world. Swat valley in...     

利用ASTER卫星立体像对提取喀斯特数字地形模型——以广西大化高峰丛深洼地喀斯特地貌为例

ASTER卫星立体像对已经被成功地用于提取全球数字地形模型（DEM）,其有效性已经在不同类型的非喀斯特地貌区域得到验证。和一般地貌相比,喀斯特地形,特别是中国南方喀斯特,具有自己独特的形态特征。能否从ASTER影像中精确地提取喀斯特地貌DEM目前尚未见到有任何报道。本文利用ASTER影像成功地提取了广西大化地区高峰丛深洼地的喀斯特地貌DEM,并且将提取结果与同一地区1∶5万地形图控制点的高程和4个剖面的高程变化进行了对比。研究区内绝大部分区域是喀斯特地貌,但在其西北部有一舌状砂岩地貌分布,从而提供了一个很好的喀斯特和非喀斯特地貌DEM精度对比的机会。本文的研究结果表明,从ASTER影像提取出来的砂岩地貌的DEM均方根误差要小于喀斯特地区,表明从ASTER影像中能更有效地提取非喀斯特地貌的DEM。相比之下,提取得到的喀斯特DEM精确度则稍差。究其原因主要是因为研究区内独特的高峰丛深洼地地形形态。由于峰丛地形的阴影在构成立体像对的两幅影像（nadir-looking和aft-loo-king）上的大小和形态差异很大,导致了DEM生产过程中两幅影像不能精确配准,从而产生比较大的误差。相比之下,砂岩地区地貌相对比较平坦,地形阴影大小和形态在两幅影像上差别不大,故而能得到精度比较高的数字地形模型。本文研究结果同时还表明适当增加地面控制点能在一定程度上改善提取出来的喀斯特地貌DEM的精度。尽管提取的数字地形模型精度稍低,其均方根误差仍然远远小于该地区峰丛和洼地个体体量。因此本研究认为从ASTER立体像对提取的数字地形模型可广泛用于喀斯特地貌形态特征研究。     

Crustal structure under the central High Atlas Mountains (Morocco) from geological and gravity data

Seismic wide angle and receiver function results together with geological data have been used as constraints to build a gravity-based crustal model of the central High Atlas of Morocco. Integration of a newly acquired set of gravity values with public data allowed us to undertake 2–2.5D gravity modelling along two profiles that cross the entire mountain chain. Modelling suggests moderate crustal thickening, and a general state of Airy isostatic undercompensation. Localized thickening appears restricted to the vicinity of a north-dipping crustal-scale thrust fault, that offsets the Moho discontinuity and defines a small crustal root which accounts for the minimum Bouguer gravity anomaly values. Gravity modelling indicates that this root has a northeasterly strike, slightly oblique to the ENE general orientation of the High Atlas belt. A consequence of the obliquity between the High Atlas borders and its internal and deep structure is the lack of correlation between Bouguer gravity anomaly values and topography. Active buckling affecting the crust, a highly elevated asthenosphere, or a combination of both are addressed as side mechanisms that help to maintain the high elevations of the Atlas mountains.     

Correction to: Flood hazard assessment and mapping of River Swat using HEC-RAS 2D model and high-resolution 12-m TanDEM-X DEM (WorldDEM)

Natural Hazards - The original article was updated and corrected due to numbering errors in Figure 8’s subfigures and the placement of some of the article’s other figures. Additional...     

Late Cretaceous (Cenomanian-Turonian) ammonites from southern Morocco and south western Algeria

On the basis of nine lithostratigraphical profiles, 23 cephalopods taxa (nautilus and ammonites) are described from the Preafrican Trough and the Kem Kem region. Among them, a new species is proposed: Spathites (Jeanrogericeras) asflaensis nov. sp. This fauna is placed in its biostratigraphical framework and correlated with the standard zonation of the late Cenomanian–early Turonian. Moreover, stratigraphic correlations are proposed for the whole Maghreb from the Tarfaya Basin in the west to central Tunisia in the east. Selected taxa reveal the paleogeographical context of the western Tethys; a complex distribution of emerged areas and epicontinental seas impacted by an important marine trangression that constantly modified the costaline.     

Trend of total column ozone over Mexico from TOMS and OMI data (1978-2013)

Using satellite measurements from the Total Ozone Mapping Spectrometer (TOMS) and Ozone Monitoring Instrument (OMI) version 8, this work presents the total column ozone (TCO) trends over Mexico and, in particular, over the state of Zacatecas. Interannual variations and their statistical dispersion show a surprisingly systematic behavior. Yearly low values occur during December and January, while high values between April and May. A significant depletion of about 2.5% in TCO between 1978 and 1994 is derived from their statistical analysis, which also shows stabilization from 1996 to 2013. Although the depletion is merely significant, it is a sign that the studied regions, crossed by the Tropic of Cancer, have not escaped to the depletion of the ozone layer. The characterization described herein is important in terms of the correlation of TCO and ultraviolet radiation levels.     

Urban social vulnerability assessment with physical proxies and spatial metrics derived from air- and spaceborne imagery and GIS data

Risk management in urban planning is of increasing importance to mitigate the growing amount of damage and the increasing number of casualties caused by natural disasters. Risk assessment to support management requires knowledge about present and future hazards, elements at risk and different types of vulnerability. This article deals with the assessment of social vulnerability (SV). In the past this has frequently been neglected due to lack of data and assessment difficulties. Existing approaches for SV assessment, primarily based on community-based methods or on census data, have limited efficiency and transferability. In this article a new method based on contextual analysis of image and GIS data is presented. An approach based on proxy variables that were derived from high-resolution optical and laser scanning data was applied, in combination with elevation information and existing hazard data. Object-oriented image analysis was applied for the definition and estimation of those variables, focusing on SV indicators with physical characteristics. A reference Social Vulnerability Index (SVI) was created from census data available for the study area on a neighbourhood level and tested for parts of Tegucigalpa, Honduras. For the evaluation of the proxy-variables, a stepwise regression model to select the best explanatory variables for changes in the SVI was applied. Eight out of 47 variables explained almost 60% of the variance, whereby the slope position and the proportion of built-up area in a neighbourhood were found to be the most valuable proxies. This work shows that contextual segmentation-based analysis of geospatial data can substantially aid in SV assessment and, when combined with field-based information, leads to optimization in terms of assessment frequency and cost.     

Crustal density structure in the Spanish Central System derived from gravity data analysis (Central Spain)

Shallow and deep sources generate a gravity low in the central Iberian Peninsula. Long-wavelength shallow sources are two continental sedimentary basins, the Duero and the Tajo Basins, separated by a narrow mountainous chain called the Spanish Central System. To investigate the crustal density structure, a multitaper spectral analysis of gravity data was applied. To minimise biases due to misleading shallow and deep anomaly sources of similar wavelength, first an estimation of gravity anomaly due to Cenozoic sedimentary infill was made. Power spectral analysis indicates two crustal discontinuities at mean depths of 31.1 ± 3.6 and 11.6 ± 0.2 km, respectively. Comparisons with seismic data reveal that the shallow density discontinuity is related to the upper crust lower limit and the deeper source corresponds to the Moho discontinuity. A 3D-depth model for the Moho was obtained by inverse modelling of regional gravity anomalies in the Fourier domain. The Moho depth varies between a mean depth of 31 km and 34 km. Maximum depth is located in a NW–SE trough. Gravity modelling points to lateral density variations in the upper crust. The Central System structure is described as a crustal block uplifted by NE–SW reverse faults. The formation of the system involves displacement along an intracrustal detachment in the middle crust. This detachment would split into several high-angle reverse faults verging both NW and SE. The direction of transport is northwards, the detachment probably being rooted at the Moho.     

Rotation of the Hyades derived from Hipparcos data

Data from the Hipparcos catalog are used to study the internal kinematics of the Hyades cluster. Cluster members whose proper motions and parallaxes are known with precisions not less than 5 mas/yr and 3 mas were used. The proper motions were reduced to the cluster center. A correlation between a component of the tangential velocity and the parallax provides evidence for possible rotation of the cluster. The total velocity gradient is 0.04±0.03 km s^?1 pc^?1. The rotation axis is located perpendicular to the direction to the Hyades apex on the celestial sphere.     

Comprehensive physicochemical study of dioctahedral palygorskite-rich clay from Marrakech High Atlas (Morocco)

This study is devoted to the physicochemical and mineralogical characterizations of palygorskite from Marrakech High Atlas, Morocco. The raw clay and its Na⁺-saturated <2 μm fraction were characterized using chemical, structural, and thermal analytical techniques. Measurements of specific surface area and porous volume are reported. The clay fraction was found to be made up of 95 % of palygorskite and 5 % of sepiolite. An original feature of this palygorskite is its deficiency in zeolitic H₂O. The half-cell structural formula of its dehydrated form was determined on the basis of 21 oxygens to be (Si_7.92Al_0.08)(Mg_2.15Al_1.4Fe_0.4Ti_0.05 $ \square_{1} $ )(Ca_0.03Na_0.08K_0.04)O₂₁, while the hydrated form could be formulated as (Si_7.97Al_0.03)(Mg_2.17Al_1.46Fe_0.40Ti_0.05)(Ca_0.03Na_0.07K_0,03)O_20.18(OH)_1.94(OH₂)_3.88·2.43 H₂O. These formulas show that the (Al³⁺+Fe³⁺)/Mg²⁺ ratio is around 0.84, revealing a pronounced dioctahedral character. Further, inside its octahedral sheet, it was determined that the inner M₁ sites are occupied by vacancies, whereas the M₂ sites are shared between 90 % of trivalent cations (78 % for Al³⁺ and 22 % for Fe³⁺), 7.5 % of Mg²⁺, and 2.5 % of Ti⁴⁺, all of them linked to 1.94 of structural hydroxyls. The two remaining Mg²⁺ by half-cell occupy edge M₃ sites and are coordinated to 3.88 molecules of OH₂. Channels of this palygorskite are deficient in zeolitic H₂O since they contain only 2.43 H₂O molecules. A correlation was found between these results and the observation of very intense and well-resolved FTIR bands arising from dioctahedral domains (mainly Al₂OH, Fe₂OH, and AlFeOH) along with very small responses from a trioctahedral domain (Mg₃OH). Accordingly, a schematic representation of the composition of the octahedral sheet was proposed. The cation exchange capacity, specific surface area, and total pore volume were also assessed to be ca. 21.2 meq/100 g, 116 m²/g, and 0.458 cm³/g, respectively.     

Cooling history of nested plutons from the Variscan Tichka plutonic complex (Morocco)

International Journal of Earth Sciences - Four imbricated mafic to felsic plutons of Variscan age from Morocco have been investigated for their cooling history and geochemical interactions with...     

Extraction and analysis of geological lineaments by combining ASTER-GDEM and Landsat 8 image data in the central high atlas of Morocco

Natural Hazards - The present work focuses on using remote sensing techniques and geographical information system (GIS) to automatically extract lineaments in the southeast of Morocco, which is one...     

Melting and undercooled crystallisation of felsic xenoliths from minor intrusions (Jebilet massif, Morocco)

Granitic and gneissic xenoliths within microdiorite dykes from the Palaeozoic Jebilet massif (Morocco) contain up to 40% of granophyric intergrowths that occur as films along quartz-feldspar contacts and form an interconnected grain boundary network. The composition of the feldspar megacrysts — i.e. large embayed crystals surrounded by the granophyric intergrowths — implies high-temperature crystallisation (T >900 °C) and the sievetexture (or finger-print texture) indicates that these crystals underwent incipient melting. Moreover, the microstructural position and bulk composition of the granophyre are similar to that of glass in partly molten felsic xenoliths from lavas or pyroclastics. It is argued that the granophyre originated after partial melting of the xenoliths when incorporated into the dioritic magma. Crystallisation of that melt resulted in most cases in the formation of vermicular and/or cuneiform granophyre, which testifies to moderate degrees of undercooling. A few occurrences of plumose granophyre i.e. very thin intergrowths that are close to quartz-bearing spherulites, indicate that some xenoliths crystallised at higher degrees of undercooling.

Together with granophyric xenoliths, a number of microgranular inclusions also occur. These are characterized by phenocrysts of quartz and feldspar in a microgranular groundmass. Finger-print texture in feldspar suggests that these inclusions, like the granophyric xenoliths, underwent ultra-metamorphism and melting. The microgranular groundmass is most probably indicative of crystallisation at lower degrees of undercooling, but the relationships between the two types of xenoliths still remain to be explored in detail.     

Evaluation of morphometric parameters of drainage networks derived from topographic maps and DEM in point of floods

An evaluation of morphometric parameters of two drainage networks derived from different sources was done to determine the influence of sub-basins to flooding on the main channel in the Havran River basin (Balıkesir-Turkey). Drainage networks for the sub-basins were derived from both topographic maps scaled 1:25.000 and a 10-m resolution digital elevation model (DEM) using geographic information systems (GIS). Blue lines, representing fluvial channels on the topographic maps were accepted as a drainage network, which does not depict all exterior links in the basin. The second drainage network was extracted from the DEM using minimum accumulation area threshold to include all exterior links. Morphometric parameters were applied to the two types of drainage networks at sub-basin levels. These parameters were used to assess the influence of the sub-basins on the main channel with respect to flooding. The results show that the drainage network of sub-basin 4—where a dam was constructed on its outlet to mitigate potential floods—has a lower influence morphometrically to produce probable floods on the main channel than that of sub-basins 1, 3, and 5. The construction of the dam will help reduce flooding on the main channel from sub-basin 4 but it will not prevent potential flooding from sub-basin 1, 3 and 5, which join the main channel downstream of sub-basin 4. Therefore, flood mitigation efforts should be considered in order to protect the settlement and agricultural lands on the floodplain downstream of the dam. In order to increase our understanding of flood hazards, and to determine appropriate mitigation solutions, drainage morphometry research should be included as an essential component to hydrologic studies.     

An abelisaurid from the latest Cretaceous (late Maastrichtian) of Morocco,North Africa

During the latest Cretaceous, distinct dinosaur faunas were found in Laurasia and Gondwana. Tyrannosaurids, hadrosaurids, and ceratopsians dominated in North America and Asia, while abelisaurids and titanosaurians dominated in South America, India, and Madagascar. Little is known about dinosaur faunas from the latest Cretaceous of Africa, however. Here, a new abelisaurid theropod, Chenanisaurus barbaricus, is described from the upper Maastrichtian phosphates of the Ouled Abdoun Basin in Morocco, North Africa on the basis of a partial dentary and isolated teeth. Chenanisaurus is both one of the largest abelisaurids, and one of the youngest known African dinosaurs. Along with previously reported titanosaurian remains, Chenanisaurus documents the persistence of a classic Gondwanan abelisaurid-titanosaurian fauna in mainland Africa until just prior to the end-Cretaceous mass extinction. The animal is unusual both in terms of its large size and the unusually short and robust jaw. Although it resembles South American carnotaurines in having a deep, bowed mandible, phylogenetic analysis suggests that Chenanisaurus may represent a lineage of abelisaurids that is distinct from those previously described from the latest Cretaceous of South America, Indo-Madagascar, and Europe, consistent with the hypothesis that the fragmentation of Gondwana led to the evolution of endemic dinosaur faunas during the Late Cretaceous.     

Early Cretaceous (Valanginian – Hauterivian) belemnites from western Morocco: stratigraphy and palaeoecology

Recent field work in Lower Cretaceous successions of the Agadir-Essaouira region, western High Atlas, Morocco, have resulted in 489 belemnite guards collected bed-by-bed from the lower Valanginian – upper Hauterivian interval. These findings are described and discussed in their biostratigraphic, taxonomic, palaeoecologic and palaeobiogeographic context. The most common belemnite genera, Hibolithes, Vaunagites?, and Duvalia, are of Meditteranean affinities and closely related to Spanish, French, and Bulgarian faunas. Less common taxa include Pseudoduvalia and Berriasibelus. The genus Pseudobelus, however, common in southeastern France and southern Spain, is rare in the Moroccan sections. The palaeoecological interpretation of these observations result in the recognition of three belemnite assemblages, characterizing different marine settings: 1) A Hibolithes - Duvalia assemblage which is typical for inner to middle shelf settings. These are relatively shallow marine environments with a high input of siliciclastics. 2) A Duvalia - Hibolithes assemblage of the outer shelf setting. Duvalia spp. is the most common genus, Hibolithes spp. is less common, while Berriasibelus spp. and Pseudobelus spp. are rare. 3) A Duvalia - Pseudobelus assemblage of hemi-pelagic preference. Duvalia is most common, next is Pseudobelus.     

Crustal structure of Japan as derived from explosion seismic data

Crustal structures of Japan were investigated under the Upper Mantle Project in three profiles, Kurayosi-Hanabusa, western Japan; Atumi-Noto, central Japan; Kesennuma-Oga, northeastern Japan. These investigations have revealed that the crust of Japan is of continental type. The variation of the crustal structure reflects the topography, especially the water depth; so the thinning of the crust occurs near the shore where the water depth increases rapidly. The velocity below the Mohorovi?i? discontinuity is smaller than 8.0 km/sec, but it is possible that a deeper layer with a velocity of over 8.0 km/sec may exist. The basaltic layer in central Japan, if existing at all, must be thin.     

Sedimentary evolution of Lake Van (Eastern Turkey) reconstructed from high-resolution seismic investigations

This paper presents results of a multi-channel seismic reflection survey at Lake Van and provides constraints on the sedimentary evolution of the lake. The geophysical data of the lake confirm the existence of three physiographic provinces: a shelf, a slope, and a deep, relatively flat basin. The most prominent features identified on the shelf and slope are clinoforms, submerged channels, as well as closely spaced lake floor depressions, reflecting a highly variable lake-level history. The morphological depressions are interpreted as resulting from subaquatic erosion by channelized, sediment-laden currents into horizontally bedded fan sediments. Submerged channels on the eastern shelf are interpreted as meandering-slope channels, probably as a consequence of a lake-level fall that exposed the shelf area. Clinoforms on the Eastern fan may represent relict deltas formed during stationary or slightly rising lake-level intervals. Merging subsurface imaging interpretation with morphological studies of exposed sediments reveals lake-level fluctuations of several hundreds of meters during the past ca. ~550 ka. The lake has three prominent basins (Tatvan, Deveboynu, and the Northern basin) separated by basement ridges (e.g., the Northern ridge). The seismic units in the Tatvan and Northern basins are dominated by alternations of well-stratified and chaotic reflections, while the Deveboynu basin subsurface consists mainly of chaotic units. The chaotic seismic facies are interpreted as mass-flow deposits, probably triggered by earthquakes and/or rapid lake-level fluctuations. The moderate-to-high-amplitude, well-stratified facies seen in the deeper parts of the basins are interpreted as lacustrine deposits intercalated with tephra layers. The occurrence of a clinoform in the deepest part of the lake suggests a major flooding stage of Lake Van more than ~400 ka ago. Seismic profiles from the deepest part of the lake basin show remarkably uniform and continuous stratigraphic units without any major erosional feature following the flooding event, indicating that the lake was never completely dry afterward and therefore significantly older than previously suggested.