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رؤية مستقبلية لتطوير تطبيقات الاستشعار عن بعد ونظم المعلومات الجغرافية فى جيومورفولوجية الأراضى الجافة
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Landslides triggered by meteorological phenomena occur worldwide and cause extensive and severe damages to properties, and life loss. Detailed maps of event landslides can sensibly shorten emergency response time, possibly resulting in reduced death tolls. In most cases, however, optical post-event images are not always available right after the event, due to dense cloud cover. Since Synthetic Aperture Radar (SAR) sensors overcome the limitation of cloud cover, in this work we explore the use of C-band Sentinel-1 SAR amplitude images to map event landslides. A team of four expert photo-interpreters first defined interpretation criteria of SAR amplitude post-event images of the backscatter coefficient (β₀) and of the derived images of change. The same team mapped two large event landslides occurred in Villa Santa Lucia (Chile) and Tonzang (Myanmar). Maps were prepared on a total of 72 images for the Chile test case and 54 for the Myanmar test case. Images included VV (vertical transmit, vertical receive) and VH (vertical transmit, horizontal receive) polarisation, ascending and descending orbits, multilook processing, adaptive and moving window filters, post-event images and images of change. In the first case, interpreters were asked to map the event landslide on an optical post-event image before mapping on SAR images, whereas in Myanmar it was done in the end. Results were quantitatively compared to the maps prepared on post-event optical images, assumed as benchmark. Results revealed a good agreement between the SAR-derived maps and the benchmark. Locally, errors can be due to geometrical distortions, and speckling-like effects. Also polarisation plays an important role, as opposed to filtering. Despite the preliminary nature of this study, it proved that SAR amplitude derived products are suitable to prepare accurate maps of large event landslides, and that they should be further tested to prepare event inventories.
Landslide is a natural phenomenon that can turn into a natural disaster. The main goal of this research was to spatial prediction of a high-risk region located in the Zagros mountains, Iran, using hybrid machine learning and metaheuristic algorithms, namely the adaptive neuro-fuzzy inference system (ANFIS), support vector regression (SVR), the Harris hawks optimisation (HHO), and the bat algorithm (BA). The landslide occurrences were first divided into training and testing datasets with a 70/30 ratio. Fourteen landslide-related factors were considered, and the stepwise weight assessment ratio analysis (SWARA) were employed to determine the correlation between landslides and factors. After that, the hybrid models of ANFIS-HHO, ANFIS-BA, SVR-HHO and SVR-BA were applied to generate landslide susceptibility maps (LSMs). Finally, in order to validation and comparison of the applied models, two indexes, namely mean square error (MSE) and area under the ROC curve (AUROC), were used. According to the validation results, the AUROC values for the ANFIS-HHO, ANFIS-BA, SVR-HHO and SVR-BA were 0.849, 0.82, 0.895, and 0.865, respectively. The SVR-HHO showed the highest accuracy, with AUROC of 0.895 and lowest MSE of 0.147, and ANFIS-BA showed the least accuracy with an AUROC value of 0.82 and MSE value of 0.218. Based on the results, although four hybrid models with more than 80% accuracy can generate very good results, the SVR is superior to the ANFIS model, whereas the HHO algorithm outperformed the bat algorithm. The map generated in this study can be employed by land use planners in more efficient management.
Cenozoic tectono-geomorphic growth processes of the Yabrai Fault (YBF) along Yabrai Mountain (YM) and their impacts on the landscape formation of Badain Jaran Desert (BJD) during the late Quaternary are still unsolved, and yet are crucial to exploring the tectonic evolution of the boundary between the northeastern Tibetan Plateau and southern Gobi Alxa block. This study addresses these issues using information extraction-based interpretations of multiple satellite images coupled with field observations. The 138 km-long NE-NEE striking YBF can be divided into 3 segments: southwestern, central, and northeastern segments all characterized by left-lateral faulting with normal faulting components. Apatite (UTh)/He thermochronology and calcite (UTh) dating integrated with regional tectonic evolution history provides new geochronological evidence for understanding the multi-stage evolution of the YM and YBF. (1) Before the late Cretaceous (135–72 Ma), the mountain experienced rapid cooling and uplift. (2) During the late Cretaceous to Eocene (ca. 70–33.9), the YM is likely to have experienced denudation and flattening. (3) From the Oligocene to early Pliocene (33.9–5 Ma), the YBF underwent ~47 km of left-lateral displacement that accommodated the slip of Altyn Tagh Fault (ATF). (4) Since the Pliocene (5 ± 1 Ma), the YBF is characterized by left-lateral strike-slip faulting with a normal faulting component. The normal faulting resulted in uplift and the creation of topography along the central segment of the YBF. This has impeded the southeastward migration of sand dunes, building the world's highest megadune within the BJD. The tectono-geomorphic growth of the YM and YBF plays a key role in formation of the unique megadune-lake pattern and in preventing the merging of the BJD and Tengger Desert (TD).
Geomatics engineering (GIS, GPS, Remote sensing, and photogrammetry) offers a lower cost and faster prediction of the threat of landslides to road traffic safety. They reduce the cost and the time needed for the monitoring of the active sliding land areas around the highways. The objective is to assess the potential of geomatics engineering in deciding slope failure occurrence after landslide to insure traffic safety. Several types of geomatics data (GPS, Photogrammetry, high resolution satellite images) will be used to predict the threat of landslides on the highway.
Landslides around the highways lead to dangerous accidents, significant economic loss and disruption of traffic flow. As a case study, we considered unstable area with continuous landslides where a major highway is traversing and suffers from yearly disruption and accidents due to landslides. An area around the North Highway (Amman-Jerash highway) which connects the capital Amman to three important governorates Irbid, Jerash and Ajloun was studied and analysed using Geomatics engineering techniques to predict its stability after land slide. This highway traverses a mountainous area with repeated unpredicted dangerous landslides after the rainy season. Landslides cause tremendous problems to this artery highway and sometimes corrupt traffic for months. The late landslides occurred in 2017 and 2019 caused massive destruction and disruption of the traffic flow.
For the sake of comparison with the used classical methods, the results of land stability detection obtained from geomatics processing were compared with those obtained by the classical methods (based on field and laboratory works). The results (obtained from the use of geomatics techniques) completely agreed with the geo-technique, geologic and water studies using data obtained from the Ministry of Public Works and Housing (MPWH). As a result, Geomatics techniques provided the same detection results faster and at lower cost.
The High Plateaus Basin is an important region to understand landscape evolution and human occupation in North Africa during the Quaternary. We focused on the Gara Soultana area, applying Unmanned Aerial Vehicles, photogrammetry and a submeter Global Navigation Satellite System, for large scale geomorphological mapping. This work in the upper Moulouya catchment has allowed us to define the landform sequence. Conglomerate platforms previously considered to be fluvial terraces, are interpreted here as exhumed bedrock layers of the Plio-Pleistocene stacked series. The El Haï river incision consists of a first phase, represented only by the exhumation of Gara Soultana butte, and a second phase when five strath terraces developed from +20-22 m to the thalweg, formed since the Middle Pleistocene. Holocene terraces could be associated with brief aggradation phases in the lower Moulouya catchment due to rapid climate changes. Fluvial incision led to the formation of mantled pediments and talus flatirons.
Karst landforms cover a considerable area of the Earth's surface. With increasing population and demand for further land exploitation, the prospect of being affected by karsts has increased dramatically over the past decades. Among karst landforms, salt karsts show higher vulnerability and faster evolution in the human life-span. In Iran, most of salt karst studies have been carried out in the south (mainly Zagros). Contrariwise, the northern and central parts of the country have been rarely studied. This study investigates a salt karst system in the northeastern part of the Central Iran. Field investigation and satellite image analysis of the area revealed a salt karst in the Upper Red Formation (URF) comprising elements of a mature karstic system including dolines, ponors, caves, shafts, valleys, poljes, springs, and streams. Tectonics by creating open fractures in impermeable salts provided conduits for fluid transport and development of the karst. Since salts are highly soluble and disappear very soon, arid climate in the studied area led to the preservation of the salt karst. Although the area is a cold desert with small amounts of precipitation, it is hydrologically active. This is ascribed to the increased water efficiency by the karst system that immediately funnels the runoffs into the ground and prevents from evaporation. Water efficiency is amplified by an impermeable substrate of the karst and timing of the precipitation. The studied karst partly underlies the Tehran–Mashhad railway which endangers the infrastructure, and can cause failure and casualties. Since the salt bearing URF extends throughout large parts of Central Iran, this study suggests comprehensive morphological, hydrogeological, and geophysical studies of this formation for providing hazard maps.
The morphology of collapse dolines varies according to their maturity and effectiveness of the removal of collapsed
material. In addition, the variable balance between various geomorphic processes due to local geologic,
hydrologic and climatic settings results in a diverse morphology of collapse dolines and dynamics of their morphogenesis.
A single generalised proposed sequence of collapse dolines morphogenesis has therefore limited
value and more detailed study is needed in terrains which differ in terms of geology, hydrology and/or climate.
There is a particularly well exposed karst in Stockyard Gully National Park in the southwestern coastal part of
Western Australia, formed in Quaternary aeolianites, consisting of a dense field of collapse dolines up to 100 m
in diameter and on average 10 m deep. Extensive field work combined with available data of local rock stratigraphy
and a comparison to collapse dolines worldwide revealed that the principal processes of collapse doline
formation in Stockyard Gully National Park are similar to processes responsible for collapse doline formation
worldwide (i.e., collapses above underground chambers and removal of the collapsed material). However, rock
characteristics in the area influence their morphometry due to the mechanical weakness of aeolianite compared
to well-cemented limestones, and a surface calcrete layer with stronger mechanical resistance than underlying
aeolianite. Consequently,we propose a new4-stage multiphase breakdown sequence of collapse doline morphogenesis
in aeolianites, divided into cave dome, calcrete caprock dome, young collapse doline, and mature collapse
doline. Calcrete caprock dome is stabilised by the uppermost well cemented calcrete and represents a distinctive
phase just before the final breakdown to form an actual collapse doline.
The Paria Plateau is a potentially important but relatively unstudied aeolian sand source area in the Grand Canyon region of Arizona, USA. This study used unmanned aerial vehicle (UAV) - based LiDAR and structure-from-motion (SfM) photogrammetry to produce high-resolution topographic models of aeolian dunes on the plateau. We combined the dune topography data with a high-resolution satellite image maximum likelihood classification (producer's accuracy = 87.2%) to quantify potential aeolian sand source areas across the 958 km² plateau. We mapped all the unvegetated active aeolian dunes on the plateau and estimate they contain 24 Tg of sand, and could, therefore, be a proportionately important regional sand source considering the annual sand loads of the downwind Paria River at its confluence with the Colorado River are generally <1 Tg. The results and data from this study could be useful for future investigations that wish to explicitly link aeolian sand on the Paria Plateau to downwind sediment dynamics in the region. The methodology for UAV and satellite remote sensing that we demonstrate could be applied to quantify sand at large geographic extents in other aeolian environments around the world.
The Earth’s surface comprises minerals diagnostic of weathering, deposition and erosion. The first continental-scale mineral maps generated from an imaging satellite with spectral bands designed to measure clays, quartz and other minerals were released in 2012 for Australia. Here we show how these satellite mineral maps improve our understanding of weathering, erosional and depositional processes in the context of changing weather, climate and tectonics. The clay composition map shows how kaolinite has developed over tectonically stable continental crust in response to deep weathering during northwardly migrating tropical conditions from 45 to 10 Ma. The same clay composition map, in combination with one sensitive to water content, enables the discrimination of illite from montmorillonite clays that typically develop in large depositional environments over thin (sinking) continental crust such as the Lake Eyre Basin. Cutting across these clay patterns are sandy deserts that developed <10 Ma and are well mapped using another satellite product sensitive to the particle size of silicate minerals. This product can also be used to measure temporal gains/losses of surface clay caused by periodic wind erosion (dust) and rainfall inundation (flood) events. The accuracy and information content of these satellite mineral maps are validated using published data.
Medieval fortified granaries known as “agadirs” are very common in southern Morocco, being catalogued as world cultural heritage by United Nations. These Berber buildings (made of stones and tree trunks) usually located on rocky promontories, constitute historical testimonials related to the origin of Morocco, and, as tourist attractions, have a positive impact on the local economy. The sustainability of these ancient monuments requires geological-risk evaluations of the massif stability under the agadir with the proposal of stabilization measures, and an architectonic analysis with appropriate maintenance of the structural elements. An interdisciplinary study including climate, seismicity, hydrology, geology, geomorphology, geotechnical surveys of the massif, and diagnosis of the degradation of structural elements have been performed on the Amtoudi Agadir, selected as a case study. The main findings from this study are that the prevalent rocks used for construction (coming from the underlying substratum) are good-quality arkosic sandstones; the SW cliffs under the agadir are unstable under water saturation; some masonry walls are too thin and lack interlocking stones and mortar; and failures in the beams (due to flexure, fracture, and exhaustion in the resistance due to insect attacks or plant roots) are common. The basic risk assessment of ancient buildings of cultural heritage and their geologic substratum are needed especially in undeveloped areas with limited capacity to implement durable conservation policies. Therefore, recommendations have been provided to ensure the stability and maintenance of this important archaeological site.
This paper examines the use of optical visible and infrared (IR) data, Synthetic Aperture Radar data (SAR), and Ground Penetrating Radar (GPR) for detection, identification and mapping of exposed and buried channels under sands in the western Negev, Israel and northern Sinai, Egypt. Field observations and shallow geophysical methods corroborated the observations.The Halutza, Agur and Shunra sand dunes are the continuation of the northern Sinai dunes. Playa-type sediments from the late Quaternary are found in upper reaches of dry river channels between the dunes of the Northwest Negev and represent a deterioration of the drainage system, caused by shifting sand dunes.A dual-polarimetric radar SIR-C image from SRL-1, having two frequencies and two polarizations, exhibits meaningful differences in reflectance between the buried and abandoned channels and their surroundings. The buried continuation of Wadi Mobra and the larger Nahal Nizzana channels, under the western Shunra sand dunes, can be observed in L-band radar data. These channels are not clearly observed either in the Landsat thematic mapper TM Visible, nor in the near-infrared (NIR) images. The radar wavelengths and polarizations that improve the contrast between the buried river beds and the surrounding sand mantle are (in descending order): L(HV), L(HH) and C(HH). However, in places where the sand mantle is very thick, or where channels cut through bedrock, the visible and near infrared data (from Landsat TM) are easier to interpret, and tend to be more useful for mapping fluvial patterns.
Please click here to download the map associated with this article.The Messak is a central Saharan massif cut into Cretaceous sandstone and delimited to the north and the west by a high scarp. It is a relict of a peneplain, dissected by dendritic wadis, and has originated since the late Tertiary under a rich water supply. Geomorphological mapping of the area was carried out by means of field survey and satellite imagery analysis. Due to the almost complete absence of vegetation (related to arid environmental conditions), the analysis of multispectral data permitted the identification of the main geomorphological units, while a band ratio allowed characterization of the properties of the exposed land surface. The main physiographic units correspond to residual surfaces (hamada and serir, resulting from etchplanation and linear erosion), solutional depressions, slope deposits, and a composite escarpment. Most of the geomorphological features are fossil, originating during warm and rainy phases dated to the Tertiary, the Pleistocene interglacials, and the Early Holocene.
Laser measurements have been used in a fluvial context since 1984, but the change detection possibilities of mobile laser scanning (MLS) for riverine topography have been lacking. This paper demonstrates the capability of MLS in erosion change mapping on a test site located in a 58 km-long tributary of the River Tenojoki (Tana) in the sub-arctic. We used point bars and river banks as example cases, which were measured with the mobile laser scanner ROAMER mounted on a boat and on a cart. Static terrestrial laser scanner data were used as reference and we exploited a difference elevation model technique for describing erosion and deposition areas. The measurements were based on data acquisitions during the late summer in 2008 and 2009. The coefficient of determination (R2) of 0.93 and a standard deviation of error 3.4 cm were obtained as metrics for change mapping based on MLS. The root mean square error (RMSE) of MLS‑based digital elevation models (DEM) for non-vegetated point bars ranged between 2.3 and 7.6 cm after correction of the systematic error. For densely vegetated bank areas, the ground point determination was more difficult resulting in an RMSE between 15.7 and 28.4 cm.
The study of dune morphology represents a valuable tool in the investigation of planetary wind systems--the primary factor controlling the dune shape is the wind directionality. However, our understanding of dune formation is still limited to the simplest situation of unidirectional winds: There is no model that solves the equations of sand transport under the most common situation of seasonally varying wind directions. Here we present the calculation of sand transport under bimodal winds using a dune model that is extended to account for more than one wind direction. Our calculations show that dunes align longitudinally to the resultant wind trend if the angle(w) between the wind directions is larger than 90 degrees. Under high sand availability, linear seif dunes are obtained, the intriguing meandering shape of which is found to be controlled by the dune height and by the time the wind lasts at each one of the two wind directions. Unusual dune shapes including the "wedge dunes" observed on Mars appear within a wide spectrum of bimodal dune morphologies under low sand availability.
The Sanlongsha dune field, on the northern edge of China’s Kumtagh Desert, is a large area with strong winds, causing rapid dune migration and evolution of dune morphology. By combining remote sensing images with field monitoring, we analyzed seasonal and annual migration of the barchan dunes and the factors that influence this migration. Dunes moved fastest in late spring and summer, and slowest in winter and early spring. The annual migration rates ranged between 7 and 95.2 m/yr, and averaged 35.6 m/yr. The migration directions ranged between 186.6° and 210.8°, and averaged 200.8°.Based on the influence of wind intensity and sand dune size, we found: (1) There is a robust linear relationship between the wind intensity (RDP) and dune migration; (2) In the absence of barchan volume, the basal area as indicators of dune scale can better measure the relationship between dune size and dune migration; (3) Barchan migration distance can be predicted based on the basal area covered by the dune, the resultant drift potential during the prediction period, and the regional annual average resultant drift potential (Di = (RDPi/ RDPmean) × α BAβ). The migration of barchan dunes is also affected by the dune shape, dune density (dune number per unit area), properties of the underlying surface, and topography. This research enhances our understanding of the dynamic mechanisms of sand dune evolution and migration, and provides theoretical guidance for windbreak and sand fixation projects and dynamic monitoring of desertification.
Unconsolidated gravel surfaces, alluvial terraces, and yardangs are widespread in the Turpan-Hami topographical depression of NW China. These landscape features provide an opportunity to investigate the wind erosion history and landscape evolution of the Hami Basin. Along with anomalously high near-surface wind speeds, these features suggest that the Hami Basin was an important source of mineral dust during the Pleistocene. We present the results of an integrated geomorphologic, stratigraphic, and chronologic study on the genesis of unconsolidated gravel surfaces and yardang fields in the Hami Basin. Mobilization of silt- to sand-sized fractions from the surfaces of the Quaternary alluvial sediments occurred under generally dry conditions, leaving unconsolidated gravels to organize into inflationary-type desert pavement surfaces (Type-1) and deflationary-type desert pavements surfaces (Type-2). We propose that the Pleistocene alluvial terraces of the Hami Basin formed principally during wetter intervals, which are assumed to correspond with interglacial periods. The coarse-grained alluvium atop terraces protected underlying strata from wind erosion. The bedrock then began to be sculpted into yardangs after the removal of the coarse-grained armoring surfaces. With mostly sub-horizontal bedding, the geometries of yardangs was controlled by lithology, wind and water erosion. Based on UAV-3D models, optically-stimulated luminescence (OSL) and electron spin resonance (ESR) ages, we find an erosion rate of ~0.23 mm/yr since ~200 ka, This, combined with widespread uneroded strata armored by unconsolidated gravel surfaces, indicates that the Hami Basin had considerable dust emission potential in the past.
The relationship between morphological characteristics (e.g. gravel size, coverage, angularity and orientation) and local geomorphic features (e.g. slope gradient and aspect) of desert has been used to explore the evolution process of Gobi desert. Conventional quantification methods are time-consuming, inefficient and even prove impossible to determine the characteristics of large numbers of gravels. We propose a rapid image-based method to obtain the morphological characteristics of gravels on the Gobi desert surface, which is called the “morphological characteristics gained effectively technique” (McGET). The image of the Gobi desert surface was classified into gravel clusters and background by a machine-learning “classification and regression tree” (CART) algorithm. Then gravel clusters were segmented into individual gravel clasts by separating objects in images using a “watershed segmentation” algorithm. Thirdly, gravel coverage, diameter, aspect ratio and orientation were calculated based on the basic principles of 2D computer graphics. We validated this method with two independent datasets in which the gravel morphological characteristics were obtained from 2728 gravels measured in the field and 7422 gravels measured by manual digitization. Finally, we applied McGET to derive the spatial variation of gravel morphology on the Gobi desert along an alluvial-proluvial fan located in Hami, Xinjiang, China. The validated results show that the mean gravel diameter measured in the field agreed well with that calculated by McGET for large gravels (R² = 0.89, P < 0.001). Compared to manual digitization, the McGET accuracies for gravel coverage, gravel diameter and aspect ratio were 97%, 83% and 96%, respectively. The orientation distributions calculated were consistent across two different methods. More importantly, McGET significantly shortens the time cost in obtaining gravel morphological characteristics in the field and laboratory. The spatial variation results show that the gravel coverage ranged from 88% to 65%, the gravel diameter was unimodally distributed and ranged from 19 mm to 13 mm. Most gravels were bladed or rod-like, with a mean aspect ratio of 1.57, and had no preferred orientation on the surveyed Gobi desert. From the center to the edge of the fan, gravel coverage decreased 2.2% per 100 m elevation decrease (R² = 0.69, P < 0.001), mean gravel diameter decreased 0.5 mm per 100 m elevation decrease (R² = 0.52, P < 0.001), and mean aspect ratio slightly increased 0.004 per 100 m elevation decrease (R² = 0.26, P < 0.05). These results imply that surface washing was the main process on the investigated Gobi desert. This study demonstrates that the new method can quickly and accurately calculate the gravel coverage, diameter, aspect ratio and orientation from the images of Gobi desert.
Ground subsidence and sinkhole collapse are phenomena affecting regions of karst geology worldwide. The rapid development of such phenomena around the Dead Sea in the last four decades poses a major geological hazard to the local population, agriculture and industry. Nonetheless many aspects of this hazard are still incompletely described and understood, especially on the eastern Dead Sea shore. In this work, we present a first low altitude (¡150 m above ground) aerial photogrammetric survey with a Helikite Balloon at the sinkhole area of Ghor Al-Haditha, Jordan. We provide a detailed qualitative and quantitative analysis of a new, high resolution digital surface model (5 cm px −1) and orthophoto of this area (2.1 km²). We also outline the factors affecting the quality and accuracy of this approach.
Based on four decades of research by Professor Andrew Goudie, this volume provides a state-of-the-art synthesis of our understanding of desert geomorphology. It presents a truly international perspective, with examples from all over the world. Extensively referenced and illustrated, it covers such topics as the importance of past climatic changes, the variability of different desert environments, rock breakdown, wind erosion and dust storm generation, sand dunes, fluvial and slope forms and processes, the role of the applied geomorphologist in desert development and conservation, and the Earth as an analogue for other planetary bodies. This book is destined to become the classic volume on arid and semi-arid geomorphology for advanced students and researchers in physical geography, geomorphology, Earth science, sedimentology, environmental science, and archaeology.
In the mountainous region north of Amman, Jordan, Cenomanian calcareous rocks are being monitored constantly for their mass wasting processes which occasionally cause severe damage to the Amman-Irbid Highway. Satellite remote sensing data (Landsat TM, ASTER, and SRTM) and ground measurements are applied to investigate the anatomy of landslides along the Dead Sea Transform Fault System (DSTFS), a prominent strike-slip fault. The joints and faults pertinent to the DSTFS match the architectural elements identified in landslides of different size. This similarity attests to a close genetic relation between the tectonic setting of one of the most prominent fault zones on the earth and modern geomorphologic processes. Six indicators stand out in particular:
The percentage hypsometric curve (area-altitude curve) relates horizontal cross-sectional area of a drainage basin to relative elevation above basin mouth. By use of dimensionless parameters, curves can be described and compared irrespective of true scale. Curves show distinctive differences both in sinuosity of form and in proportionate area below the curve, here termed the hypsometric integral. A simple three-variable function provides a satisfactory series of model curves to which most natural hypsometric curves can be fitted. The hypsometric curve can be equated to a mean ground-slope curve if length of contour belt is taken into account. Stages of youth, maturity, and old age in regions of homogeneous rock give a distinctive series of hypsometric forms, but mature and old stages give identical curves unless monadnock masses are present. It is therefore proposed that this terminology be replaced by one consisting of an inequilibrium stage, an equilibrium stage, and a monadnock phase. Detailed morphometric analysis of basins in five sample areas in the equilibrium stage show distinctive, though small, differences in hypsometric integrals and curve forms. In general, drainage basin height, slope steepness, stream channel gradient, and drainage density show a good negative correlation with mean integrals. Lithologic and structural differences between areas or recent minor uplifts may account for certain curve differences. Regions of strong horizontal structural benching give a modified series of hypsometric curves. Practical applications of hypsometric analysis are foreseen in hydrology, soil erosion and sedimentation studies, and military science.
The recently available Shuttle Radar Topography Mission (SRTM) data, with ∼90 m horizontal resolution, are used to delineate the entire Tushka mega-watershed. It is calculated that the watershed covers an area of 150 000 km2 and composed of four subwatersheds. This study indicates that the Tushka basin is a closed hydrological system independent of the Nile hydro-system, the Qena Valley system, and the Chad basin as well. More importantly, the study demonstrates that this basin drains northeasterly toward the westernmost of the recently flooded lakes in the Tushka depression, west of Lake Nasser. The hydrological activities within the basin resulted in the formation of the largest paleo-lake deposit in Egypt at Bir-Tarfawi. The vast sand sheets that cover the Tushka basin accentuate the theory of El-Baz [1982. Genesis of the Great Sand Sea, Western Desert of Egypt. International Association of Sediment, 11th International Conference, Hamilton, Ontario, Canada, p. 68], which relates sand accumulations within basins in today's deserts to previous fluvial activities. The present study illustrates the capability of the SRTM in penetrating desert sand surfaces and mapping the ancient drainage networks, which remarkably correlate with subsurface channels detected in Radarsat-1 images.
A detailed study of a small hill in NE Mojave Desert in eastern California was conducted to elucidate the effect of climate on the variations in soil erosion rates through Holocene. Field surveys and sampling were carried out to obtain information on topography, geomorphology, soil and vegetation conditions, seismic refraction, sediment deposition, and hillslope processes. Integration of this information allowed reconstruction of the hill topography at the end of the Pleistocene, deduction of the evolution of the hill from the end of the Pleistocene to the present, and estimation of total soil losses resulting from various hillslope processes. The estimates are consistent with the premise that early Holocene climate change resulted in vegetation change, soil destabilization, and topographic roughening. Current, very slow, hillslope transport rates (e.g., 5 mm ky−1 by rodent burrowing, a presently important transport form) appear inconsistent with the inferred total soil loss rate (31 mm ky−1). Packrat midden studies imply that the NE Mojave Desert experienced enhanced monsoonal precipitation in the early Holocene, presumably accentuating soil loss. Water erosion on one slope of the hill was simulated using Water Erosion Prediction Project (WEPP), a process-based erosion model, using 4 and 6 ky of precipitation input compatible with an appropriate monsoonal climate and the present climate, respectively. The WEPP-predicted soil losses for the chosen slope were compatible with inferred soil losses. Identification of two time periods within the Holocene with distinct erosion characteristics may provide new insight into the current state of Mojave Desert landform evolution.
Geomorphic mapping of Egypt's Western Desert from LANDSAT-MSS images reveals oriented aeolian landforms that record, in part, Holocene winds. Wind directions reconstructed from these landforms indicate the dominance of N–S airflow from 30°N to 20°N, turning clockwise southward to NE–SW, conformable with modern circulation. A second direction appears over western Egypt, W between 30°N and 26°N, NW between 26°N and 20°N. Cross-cutting aeolian landforms show that W/NW winds are older than the N/NE winds. Geomorphic evidence, abundant south to 26°N and less abundant to 20°N, also indicates that W and NW winds were early Holocene ‘palaeowesterlies’. Some evidence also indicates that they extended eastward to at least 30°E, perhaps to the Red Sea. These winds steered moist Atlantic/Mediterranean air masses to Egypt, sustaining early Holocene lakes and playas north of the limit of tropical monsoonal rainfall at 20°N. Upon aridification, beginning after 5 kyr BP, yardangs oriented west to east were eroded in early Holocene basinal sediments in western Egypt, indicating that these winds continued there for 1–2 kyr, until 3–4 kyr BP. Optically stimulated luminescence (OSL) ages of surface sand sheet in southern Egypt indicate that the present north–south winds were established ca. 3–4 kyr BP, at the same time as the northern savanna boundary was stabilized at its present position.
Incluye bibliografía e índice
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Map of the world distribution of arid regions: Map at scale 1:25,000,000 with explanatory note
United Nations Educational, Scientific and Cultural Organization (UNESCO). (1979): Map of the world distribution of
arid regions: Map at scale 1:25,000,000 with explanatory note. MAB Technical Notes 7, UNESCO, Paris, 53p.