Fault zone hydrogeology in arid environments: The origin of cold springs in the Wadi Araba Basin,Egypt

The role of faults in controlling groundwater flow in the Sahara and most of the hyper-arid deserts is poorly understood due to scarcity of hydrological data. The Wadi Araba Basin (WAB), in the Eastern Sahara, is highly affected by folds and faults associated with Senonian tectonics and Paleogene rifting. Using the WAB as a test site, satellite imagery, aeromagnetic maps, field observations, isotopic and geochemical data were examined to unravel the structural control on groundwater flow dynamics in the Sahara. Analysis of satellite imagery indicated that springs occur along structurally controlled scarps. Isotopic data suggested that cold springs in the WAB showed a striking similarity with the Sinai Nubian aquifer system (NAS) water and the thermal springs along the Gulf of Suez (e.g., δ¹⁸O = −8.01‰ to −5.24‰ and δD = −53.09‰ to −31.12‰) demonstrating similar recharge sources. The findings advocated that cold springs in the WAB represent a natural discharge from a previously undefined aquifer in the Eastern Desert of Egypt rather than infiltrated precipitation over the plateaus surrounding the WAB or through hydrologic windows from deep crystalline basement flow. A complex role of the geological structures was inferred including: (1) channelling of the groundwater flow along low-angle faults, (2) compartmentalization of the groundwater flow upslope from high-angle faults, and (3) reduction of the depth to the main aquifer in a breached anticline setting, which resulted in cold spring discharge temperatures (13–22°C). Our findings emphasize on the complex role of faults and folds in controlling groundwater flow, which should be taken into consideration in future examination of aquifer response to climate variability in the Sahara and similar deserts worldwide.     

Modeling of the radial and transverse components of the albedo function

In this work, we shall confine ourselves to solve analytically the integrals called , for the two components of albedo radiation pressure on an Earth’s satellite. When the Earth’s albedo is variable, as far as we know, this case has not been dealt with analytically. We shall solve these two integrals when the satellite’ horizon is illuminated and when the sun lies on the equator. This approach will facilitate the evaluation of the mentioned two equations. We will also compare our results with previous works obtained numerically.     

Alteration Patterns Related to Hydrothermal Gold Mineralizaition in Meta-andesites at Dungash Area, Eastern Desert, Egypt

Abstract: The hydrothermal alteration patterns associating with the gold prospect hosted by metavolcanics in the Dungash area, Eastern Desert of Egypt, were investigated in order to assign their relationship to mineralization. The metavolcanics of andesitic composition are generated by regional metamorphism of greenschist facies superimposed by hydrothermal activity. Epidote and chlorite are metamorphic minerals, whereas sericite, carbonates, and chlorite are hydrothermal alteration minerals. The auriferous quartz vein is of NEE‐SWW trend and cuts mainly the andesitic metavolcanics, but sometimes extends to the neighbouring metapyroclastics and metasediments. Quartz‐sericite, sericite, carbonate‐sericite, and chlorite‐sericite constitute four distinctive alteration zones which extend outwards from the mineralized quartz vein. The quartz‐sericite and sericite zones are characterized by high contents of SiO₂, K₂O, Rb, and As, the carbonate‐sericite zone is by high contents of CaO, Au, Cu, Cr, Ni, and Y, and the chlorite‐sericite zone is by high contents of MgO, Na₂O, Zn, Ba, and Co. Gold and sulphide minerals are relatively more abundant in the carbonate‐sericite zone followed by the sericite one. The geochemistry of the alteration system was investigated using volume‐composition and mass balance calculations. The volume factors obtained for the different alteration zones, mentioned above (being 1.64, 1.19, 1.17, and 1.07, respectively), indicate that replacement had taken place with a volume gain. The mass balance calculations revealed addition of SiO₂, K₂O, As, Cu, Rb, Ba, Ni, and Y to the system as a whole and subtraction of Fe2O3 from the system. Initial high aK+ and aH+ for the invading fluids is suggested. As the fluids migrated into wallrocks, they became more concentrated in Mg, Ca, and Na with increasing activities of CO₂ and S. The calculated loss‐gain data are in agreement with the microscopic observations. Breakdown of ferromagnesian minerals and feldspars in the quartz‐sericite, sericite, and chlorite‐sericite zones accompanied by loss in Mg, Fe, Ca, and Na under acidic conditions and low CO2/H2O ratio may obstruct the formation of carbonates and sulphides, and the precipitation of gold in these zones. The role of metamorphic fluids in the area is expected to be restricted to the liberation of Au and some associated elements from their hosts.     

Determining the spatial scale of variation in soil radon concentration

Increasing concern about possible links between emissions of radon and certain types of malignant disease has led to local and regional surveys to measure radon concentrations in the soil and in dwellings. The spatial scale at which radon varies is largely unknown, and so efficient sampling schemes and methods of mapping cannot be selected. To determine the spatial scale of radon variation in the English Midlands we measured radon in the soil using solid-state nuclear track detection in three areas of different geological complexity. In two of them we used an unbalanced multistage sampling scheme with seven stages of nesting: the Hereford survey covered distances from 10 m to 7.5 km, and the Buxton survey distances from 1 m to 3.75 km. The results from the nested surveys suggested that geology exerts a strong control on the variation. Finally radon was measured every 20 m along a 2-km long transect which crossed several lithologies close to Nottingham. The soil radon values changed in an erratic way along the transect. The sample variogram of radon has a substantial nugget variance, suggesting that much of the variation occurred for distances less than the sampling interval. The structure at the longer scale seems to be controlled by the underlying geology. These results have implications for designing further surveys and for selecting a method of mapping. Stratification based on lithology might be the only feasible solution to sampling, estimating and mapping radon concentrations over large areas. Where the locally erratic component of variation is large, estimation by kriging, for example, would confer little additional benefit compared with that by classification.     

The catastrophic cyclone of April 1991: Its Impact on the economy of Bangladesh

A very severe cyclonic storm with wind speeds of over 240 km/h struck the coastal areas of Bangladesh in the full moon night of 29 April 1991. The path of the eye, close to the shore, raised a storm surge of unusual height, reportedly more than 9 m above the mean sea level, which devastated the offshore islands and the mainland coast. The damage to the physical infrastructure of the port of Chittagong and adjoining industrial area has been colossal, and recovery will take years. Death tolls from the cyclone, storm surge and its aftermath exceeded 145 000 making it one of the world's major natural disasters of this century.This paper is concerned with examining the magnitude and intensity of the disaster. It analyses how the people of Bangladesh, and the environment in which they live, were affected by the cyclone. A brief account is presented of loss of life and of the damage suffered in various sectors, including agriculture, industry, and physical infrastructure.The paper lays emphasis on the need of building a sufficient number of multipurpose cyclone shelters in the disaster-prone coastal areas of Bangladesh. Adequate measures should be taken for evacuating people from vulnerable areas and putting them into these shelters in the event of a cyclonic storm. Simplification of the current cyclone warning system is recommended.The difficulties of providing relief to the survivors are discussed. And finally, the need for improvement of the communication infrastructure in the coastal areas is highlighted.     

Structures and microstructures related to steady-state mantle flow in the Neyriz ophiolite, Iran

Structural analysis in the well-exposed and well-preserved Neyriz ophiolite suggests that it is a relatively undisturbed piece of oceanic lithosphere. Detailed structural mapping of high-T deformation mantle flow revealed the presence of three elliptical shaped diapirs trending NW–SE. These diapirs are characterized by vertical mantle foliations associated with vertical plunging stretching lineations, which progressively incline toward parallelism with the gently NE-dipping Moho. The NW–SE direction of asthenospheric upwelling of diapirs is parallel with the orientations of the vertical sheeted dike complex. This suggests that the Neyriz ophiolite was created by two NW–SE palaeo-ridge axes. These palaeo-ridges are classified as fast-spreading ridges. These ridges are segmented by a dextral palaeo-transform fracture zone. This is consistent with fast-spreading ridges. Comparison between the Neyriz and Oman ophiolites reveals that they show similar characteristics. Most of the Oman palaeo-ridge systems are oriented NW–SE and NNW–SE. They also display similar sheeted dike complex orientations and crustal thickness variations. These two ophiolites originally were part of the Neo-Tethyan oceanic lithosphere and afterwards were separated by the Oman line during continental collision of the Iranian micro-continent and Afro-Arabian continent.     

Changes in the mullet fishery of Lake Manzala,Egypt

Growth rates of the main mullet species (Liza ramada andMugil cephalus) in Lake Manzala are low compared to those in other Egyptian lakes. But average growth rates during the period 1989–1993 were relatively faster than in the 1960's. Spawning and migration seasons have been determined for every species, and their distribution in the lake, in terms of certain ecological parameters (salinity, turbidity and dissolved oxygen) have been investigated. Changes in the mullet fishery in the lake during the past 70 years have been studied. Due to an increase in nutrient loading and a decrease in salinity, mullet declined from 65 per cent of the total catch during the 1920's to only 2.2 per cent during the early 1980's. As a result of fisheries management and development programmes from 1989 to 1993, mullet production increased to 9.2 per cent of the total catch.     

Methane,carbon monoxide and methylchloroform in the southern hemisphere

New observational data on CH₄, CO and CH₃CCl₃ in the southern hemisphere are reported. The data are analysed for long term trends and seasonal cycles. CH₃CCl₃ data are used to scale the OH fields incorporated in a two dimensional model, which in turn, is used to constrain the magnitude of a global CH₄ source function. The possible causes of observed seasonality of CH₃CCl₃, CH₄ and CO are identified, and several other aspects of observed CH₄ variability are discussed.Possible future research directions are also given.     

Simulation of groundwater level in a coastal aquifer

Abstract

The groundwater levels can have a significant impact on structures and infrastructures of coastal areas. The simulation of the hydraulic behavior of coastal aquifers is very important due to its specific boundary conditions. In this study, the groundwater level in the Bandar-e-Gaz coastal aquifer in the Gorgan Gulf region located in northern Iran is simulated using the MODFLOW mathematical model. The modeling of the coastal aquifer behavior carried out in two calibrations (steady and unsteady states). The validation periods (unsteady state), the mean absolute error (MAE) and mean bias error (MBE) were used to evaluate the results. The values of MAE and MBE criteria for the steady state were 0.31 (m) and –0.08 (m), while the average of these criteria in the unsteady state in calibration period were 0.46 and –0.39, and in the validation period were 0.42 (m) and –0.31 (m), respectively. The mentioned results confirm the precision of the model for the entire simulation period, they also indicate that the simulation has a limited underestimation behavior. Moreover, it shows that the precision of the results has a negligible variability, which means the simulation also has considerable reliability. The highest and lowest amount of error in the winter and summer seasons are in accordance with the lowest and highest seawater levels, and it shows the significant sea effect on the hydraulic behavior of the coastal aquifer.     

The use of numerical modeling to optimize the construction of lined sections for a regionally-significant irrigation canal in Egypt

Environmental Earth Sciences - Water balance is considered as an important tool to assess the amount of water and its availability in a region. The Small Aral Sea is a salt lake in the territory of...