The sedimentary dynamics of active fluvial channels on the Okavango fan, Botswana

The 1800-km² Okavango alluvial fan of northern Botswana represents an unusual depositional setting in which peat-forming perennial swamps (6000 km²) occur in a region of aeolian and semi-arid sedimentation within an incipient graben of the East African Rift. A channel system distributes water and sediment on the fan surface but cannot contain seasonal flood water, which spreads laterally from the channels through permeable channel margins, sustaining the flanking swamps. All sediment introduced is deposited on the fan. A detailed study of sediment movement and associated hydrological conditions in the channels was undertaken to examine sediment dispersal. Bedload greatly exceeds suspended load (at least by a factor of four). Vegetation and peat form permeable levees which confine the channels. In the upper reaches, two-way exchange of water occurs between channel and swamp depending on the season, but on the fan itself, channels lose water to the swamp. Bedload measurements reveal that the channel system is in a state of grade disequilibrium, with interspersed depositional and erosional reaches. Deposition of most of the incoming bedload occurs on the upper portion of the fan in a meandering and anastomosed channel system, but on the midfan, deposition of bedload occurs by channel-bed aggradation, at a rate of up to 5 cm yr^–1. Further down slope, the channel enters a large lake where all remaining bedload is deposited. The presently observed sedimentation patterns may be due to a recent disturbance of the fluvial system, either by avulsion or neotectonics.     

Intra-urban patterns of domestic solid waste recycling in sub-Saharan Africa: towards an exploratory search for insights in Gaborone,Botswana

Botswana is among those developing countries that are rapidly transitioning from predominantly rural to urban societies. Gaborone, its capital city, is seriously confronted by formidable challenges of sustainable metropolitan management, including the proper handling of solid domestic waste. Although the international convention of the 3-Rs, namely, Recycle, Reduce, Reuse is generally accepted; its implementation remains elusive. It is therefore of utmost importance to unravel significant determinants of the gap between nominal acceptance and praxis in order to influence policy. This preliminary case study, consequently, sought to identify the underlying factors that differentiate waste recycling practices from high, medium, and low socio-economic areas Gaborone. Key informants, including municipal officials and company representatives, in charge of city solid waste management, were interviewed. A probit model was used to analyze those factors that could influence recycling and waste separation practices. Results showed that tenure, gender, income, affluence, location of house increase the likelihood of recycling while age, education level, household size and source of waste management information did not influence the likelihood of recycling. Stakeholders should place greater emphasis on positive environmental awareness, and appropriate reward systems for recycling domestic solid waste and recycling should be tailored according to the locational needs.     

Characteristics of tropical cyclones in China and their impacts analysis

This paper discusses the characteristics of tropical cyclones (TCs) based on available data from 1951 to 2008, including the frequency of TC generation in the Western North Pacific (WNP) and those which make landfall in China. The impacts of TCs on both human and economic losses for the period 1983–2008 are also discussed. Examination of the frequency indicates a decreasing trend in the generation of TCs in the WNP since the 1980s, but the number of TCs making landfall has remained constant or shown only a slight decreasing trend. The number of casualties caused by TCs in China appears to show a slight decreasing trend while the value of economic loss is increasing significantly. These results can be attributed to increased natural disaster prevention and mitigation efforts by the Chinese government in recent years, and also reflect the rapid economic development in China particularly in TC-prone areas.     

Spatiotemporal dynamics of land cover and their impacts on potential dust source regions in the Tarim Basin,NW China

Human-driven dynamics of land cover types in the Tarim Basin are able to affect potential dust source regions and provide particles for dust storms. Analyses about dynamics of potential dust source regions are useful for understanding the effects of human activities on the fragile ecosystem in the extremely arid zone and also provide scientific evidence for the rational land development in the future. This paper therefore selected the Tarim Basin, NW China, as a representative study area to reveal spatiotemporal dynamics of land cover and their impacts on potential dust source regions. The results showed that farmland, desert and forest increased by 28.63, 0.64 and 29.27%, while grassland decreased by 10.29% during 1990–2010. The largest reclamation, grassland loss and desertification were 639.17 × 10³, 2350.42 × 10³ and 1605.86 × 10³ ha during 1995–2000. The relationship between reclamation and grassland loss was a positive correlation, while a highly positive correlation was 0.993 between the desertification and grassland loss at different stages. The most serious dust source region was the desertification during 1990–2010 (1614.58 thousand ha), and the serious region was stable desert (40,631.21 thousand ha). The area of the medium and low dust source region was 499.08 × 10³ and 2667.27 × 10³ ha. Dramatic reclamation resulted in the desertification by destroying natural vegetation and breaking the balance of water allocation in various regions.     

Spatiotemporal analysis of dust patterns over Mesopotamia and their impact on Khuzestan province,Iran

Dust storms are yet quite frequent in various parts of the world, particularly ancient Mesopotamia (approximately corresponding to most parts of Iraq as well as certain surrounding regions toward its north). To add to the ongoing difficulty, monitoring dust patterns has been proven to be a rather difficult endeavor given the absence of reliable ground-based monitoring stations in the corresponding area. Additionally, western provinces of Iran, especially Khuzestan in the southwest of Iran, have been severely affected by dust storms carried by the westerly winds, blown through neighboring countries in ancient Mesopotamia. This study proceeds to employ aerosol optical depth (AOD), extracted from the MODerate-resolution Imaging Spectroradiometer onboard the Terra spacecraft, to assess spatial dust variations between 2001 and 2017 over the Khuzestan province and ancient Mesopotamia. The variations were also correlated with the temporal dust changes in the Khuzestan province. Frequency of occurrence for AOD?>?1 was used to identify and categorize major dust sources in the aforementioned regions. The findings were indicative of an increasing trend in the annual AODs of the Khuzestan province, which eventually led to a significant increase from 2008 toward the end of 2012, but decreased again in the following years. Correspondingly, the entire time period (2001–2017) was further divided into three sub-periods: the first time period spanning from 2001 to 2007, followed by the second from 2008 to 2012 and finally a third time period from 2013 to 2017. Dust source identification was speculative of numerous dust spots in Iraq, Syria, Kuwait and also the southern parts of Khuzestan province which have become more active in recent years. Additionally, a large active dust spot was pinpointed between the northwest Iraq and eastern Syria border which has become extremely active during the second time period, possibly due to a severe drought in the Fertile Crescent.

     

The deformation patterns of two Archaean greenstone belts in Rhodesia and Botswana

Variations in intensity of deformation have been examined in the Fort Victoria greenstone belt in southern Rhodesia and in the Tati belt in northeast Botswana, both of which are on the diffuse northern border of the Limpopo mobile belt. Much of the deformation is related to widespread Limpopo events, and not to diapiric granite intrusions previously considered of major importance in the development of the Early Precambrian crust.Variations in intensity of deformation are due to the form of the major structures and to localised major ductile shear zones which cut both granites and greenstone belts. The pattern of deformation within the belts depends partly on how the granites behaved. Whether the schist belts deformed homogeneously or were part rotated and cut by shear zones depended on whether the granites deformed homogenously with the schist belt matrix or whether they were deformed by block sliding.     

Groundwater-related thallium transfer processes and their impacts on the ecosystem: southwest Guizhou Province,China

The small karstic watershed of Lanmuchang, in a Hg–Tl mineralized area in SW Guizhou Province, China, exhibits an enrichment of toxic Tl in groundwater and related stream water. This affords an excellent demonstration of the natural processes of Tl dispersion, and the resultant impact on the local ecosystem. The distribution of Tl in the water system follows a decreasing concentration pattern from deep groundwater to stream water to shallow groundwater. Tl shows high levels (13–1100 μg/L) in deep groundwater within the Tl-mineralized area, decreasing with distance away from the mineralized area to background levels (0.005 μg/L). The distribution of Tl in the water system is constrained by Tl mineralization, water–rock interactions and hydrogeological conditions. Tl concentrations in waters generally correlate with concentrations of total dissolved solids, sulphate, Ca and pH values, suggesting the contribution of water-rock interactions to water geochemistry. Water–rock interactions are driven by weathering of Tl-bearing sulfides which decreases pH values in groundwater, and by dissolution of limestone enhanced by acid fluids. Tl in stream water in both the base-flow and flood-flow regimes shows higher concentrations than it does in shallow groundwater that serves as the stream's source (mainly springs, dug-well flows and karstic cave waters). Concentrations of Tl in stream water in the flood-flow regime are generally lower than in the base-flow regime due to dilution effects, but those in the waters of mid-stream are almost the same as in the base-flow regime, probably due to contribution from Tl-rich soil water seepage or from acid mine drainage (AMD). Unexpectedly, Tl concentrations in stream water in both regimes are remarkably higher (2–30 fold) downstream than up- and mid-stream. These pronounced increases of Tl concentration are likely caused by unidentified discharges of deep groundwater through fractured zones to the downstream trace. The groundwater-related Tl transfer processes affect the ecosystem through contamination of water supply and arable soil and ultimately the food chain with undoubted risks to human health. Therefore, the results of this study are important for environmental planning and regulations, and will also serve as baseline data for future research on Tl natural dispersion processes.     

Morphological,structural and lithological records of terrestrial impacts: an overview

Impact cratering produces not only craterform topographic features, but also structural disturbances at the site of impact, and a spectrum of transformed and newly formed rocks. The term ‘coptogenesis’ (from the Greek χoπτo, to destroy by shock) may be used collectively to describe the impact process—a process fundamental to all cosmic bodies. Principal coptogenic topographic features of terrestrial impact craters may be subdivided into excavational, structural and accumulative landforms, most of which subsequently experience various processes of degradation. Nevertheless, the original shape of craters may in some cases be reconstructed and compared with fresh craters on other planets. An immediate conformity between the pre-erosional topographic features of complex terrestrial craters, and the morphostructural elements of their erosional remnants, is not a standing rule. Geological observations show that the inner structure of the proximal crater fill and distal ejecta are characterised by pseudo-stratification and that these materials represent a group of facies of impact-derived and impact-related, or coptogenic, lithologies. The study of these facies allows us to distinguish various facies settings of rock-forming processes. Impact lithologies, or coptogenic rocks, may be systematised and classified using the principles adopted by igneous petrology and volcanology. Appropriate geological methods and approaches should be applied to the investigation of terrestrial impact craters, including their identification, mapping, and study of their various physiographic, structural, and lithological features.     

Magma dynamics at the base of an evolving mafic magma chamber: Incompatible element evidence from the Partridge River intrusion, Duluth Complex, Minnesota, USA

A characteristic feature of the Partridge River intrusion of the Keweenawan Duluth Complex is the approximately fivefold to ninefold increase in the concentrations of incompatible elements in the lower zone compared with cumulates stratigraphically higher. The concentrations of incompatible elements decrease from the lower zone upward to steady state values, which is ascribed to variations in the proportions of trapped liquid rather than variable degrees of fractional crystallization of a single parental magma. The calculated average composition of trapped liquid using our algorithm is similar to typical Keweenawan low-alumina, high Ti---P basalts associated with the Duluth Complex but is different from the leading edge ferrodioritic liquid quenched in the chilled margin of the intrusion. This difference suggests that the chilled margin does not represent the original (parental) magma composition from which the whole intrusion solidified, and that the enrichment of incompatible elements may be related to the local flotation of magmatic suspensions. To test the latter hypothesis numerically, we have used heat-mass transfer models, assuming a sheet-like magma chamber, to calculate the parameters of the model that best reproduce the observed distribution of incompatible elements in a mush zone at the base of the Partridge River intrusion. The results indicate that a mush zone enriched in the incompatible elements is produced if the velocity of movement of the lower solidification front into the magma body was less than the floating velocity of the bulk crystal mush. The dynamic parameters that best reproduce the observed distribution of incompatible elements include a magma emplacement pressure of 2 kbar, critical crystallinities of 50–68% in the mush zone from which the liquid is being expelled, and an emplacement temperature of 1160°C for the initial magma.     

Human impacts on Laguna de Bay, Philippines and management strategies for their mitigation

Laguna de Bay is the largest lake in the Philippines bordering metropolitan Manila, the nation's capital and the industrial hub of the country. As a multiple-use resource the lake is of prime importance for its fisheries, as a transport route and as a water source for the cooling of industrial plants and for irrigation. The lake is also envisaged to supply the domestic water needs of the basin in the year 2000. With rapid urbanization, industrial development and deforestation of its watershed, Laguna de Bay has been stressed with sedimentation, overexploitation of its fisheries and pollution. Various management strategies have been adopted by government to address such human impacts. Among the major programs are the installation of a hydraulic control structure, implementation of a zoning and management plan and the formulation of a master plan. There is need for an integrated approach for the management of the Laguna de Bay basin for its sustainable development.     

Sea level rise and impacts on nearshore sedimentation: an overview

 Impacts on nearshore sedimentation arising from potential sea level change of the magnitude predicted in Intergovernmental Panel on Climatic Change scenarios associated with global warming are reviewed. For sandy duned coasts, the obvious sedimentation impacts include potential erosion of coastal dunes with implied deposition of the eroded material in the nearshore, possible deepening of embayments, and flooding of wetlands. For the sandy coasts a number of two-dimensional models are available for predicting shoreline change, but there are significant difficulties in applying Bruun-type models for dune erosion and assessment of sediment redistribution over the inner shelf, and for predicting the amount of shoreline retreat for a given rate of sea level rise. If the beach profile contains excessive sand relative to its equilibrium profile, sensu Dean (1991), then shoreline retreat may not occur upon sea level rise. From the evidence of Kiel Bay, at least in these semi-enclosed basin types, it is during major transgressions that maximum deposition in adjacent basins occurs, due to the sea eroding weakly consolidated and weathered surface regolith. But at the same time climatic patterns were re-adjusting and probably contributed to maximum deposition in adjacent shelf and basins below wave base. Received: 16 June 1995 / Accepted: 29 January 1996     

Variable temperature and moisture conditions in Yungang Grottoes,China, and their impacts on ancient sculptures

Deterioration of grottoes induced by the negative impacts of the variable temperature and moisture conditions has been an important issue in the conservation of heritage sites in China. In this case study, the spatial distributions and varying patterns of moisture and temperature in the caves of Yungang Grottoes, China, were investigated. The relative air humidity was approximately 100 % in the deep zone of the unsaturated surrounding rocks of the grottoes where the temperature remained almost steady at around 9.4 °C. However, the indoor air temperature, relative humidity, and rock surface temperature in the caves varied significantly because of the active exchange of the air with the outside atmosphere. The condensation water appeared on cave walls in the summer when the dew point in the air was higher than the rock surface temperature. Preliminary assessments with a special collection device indicated that the thickness of the transient condensation water could reach 0.03–0.10 mm on the back wall of a cave. The occurrence of this condensation water is expected to worsen salt deterioration of the sculptures in the grottoes. As revealed by long-term observations, a wooden building in front of a cave can weaken the indoor air temperature fluctuation and reduce the condensation water, and consequently, prevent the negative effects of the microclimate for the sculptures.     

Mid-Holocene lateral collapse of Antuco volcano (Chile): debris avalanche deposit features,emplacement dynamics,and impacts

Antuco (37.4°S, 71.4°W; Chile) is a dominantly basaltic stratovolcano whose original?~?3300 m altitude main cone experienced a catastrophic sector collapse at?~?7.1 cal ka BP, producing a volcanic debris avalanche deposit (VDAD) with hummocky surface and?~?6.4 km³ of volume. We carried out geological studies of its debris avalanche deposit, which was distributed to the W and displays a longitudinal facies transformation from edifice’s megablocks and block to mixed facies in distal areas (up to 25 km from the scar). Our observations support the behavior of the avalanche beginning as a translational slide, and then as plug flow when confined within the Laja River valley. Clay abundance and high content of hydrothermally altered material may suggest active participation of water; flow velocities are estimated to?~100 m s^?1. We primarily identify the steep-sided flanks of the cone, and hydrothermal alteration promoted the edifice instability, while basement seismogenic structures may have ultimately triggered the landslide. Subsequent landslide-led events include the transformation of the volcanic activity with explosive eruptions producing a sequence of dilute pyroclastic density currents (PDCs) ending?~3.4 ky BP, and extensive lava effusion rapidly reconstructing the collapsed edifice. Moreover, the Antuco VDAD also blocked the natural output of the Laja Lake, increasing its level by?~200 m and then triggering cataclysmic outburst floods by dam rupture, preserved as high-energy alluvial beds with ages between 2.8 and 1.7 ky BP. The Antuco constitutes an excellent example of a critical chain of events initiated by a stratovolcano lateral collapse and warns for detailed hazard investigations to better comprehend its related impacts.

     

Effect of geology and geomorphology on landuse/landcover in Himalayan foothill, Dehradun

A detailed geological, geomorphological and landuse/landcover study has been carried in a small watershed of Himalaya by visual interpretation of FCC prepared from band 123 of ASTER satellite imagery. On the basis of interpretation and field check, major litounits identified in the study area include Lesser Himalaya conglomerate consisting of quartzite, granite, phyllite boulder and pebble, Middle Siwalik sandstone and Upper Siwalik boulder beds and valley fill with Doon gravel of Holocene age. Geomorphologically the study area is characterized by typical Himalayan topography with rugged terrain. Various landforms identified and recognized include, Doon Fan Gravel Terrace, Doon Fan Gravel Dissected hill, Sub Recent Fan Terrace, Moderately Dissected Structural Hill, Piedmont Dissected Slope, River Terrace, Channel Bar and River channel. Supervised classification of ASTER False Colour Composite (FCC) (123) shows that the major landuse category in the study area is agriculture while major landcover class is forest covered land. The study shows the effect of geology and geomorphology on the type of landuse and landcover in an active tectonic zone of the study area.     

Groundwater evolution, chemical sedimentation and carbonate brine formation on an island in the Okavango Delta swamp, Botswana

The Okavango Delta of semi-arid northern Botswana is a large alluvial fan (22,000 km²) covered by permanent and seasonal swamps from which 96% of the annual discharge is lost by evapotranspiration. Many small islands (1ha) within the permanent swamps are the sites of accumulation of sodium carbonate salts and many contain saline pans. The associated alkaline soils are toxic to vegetation. An understanding of the processes involved in alkalinization could be of potential benefit to long-term conservation planning in this unique ecosystem. The relation between soil chemistry and mineralogy, and swamp and groundwater chemistry were investigated on an island in the swamps. The study revealed that the water table beneath the island is depressed and swamp water enters the groundwater regime of the island from the margins and below, and flows toward the centre. The water becomes progressively more saline, initially owing to transpiration by trees and ultimately by evaporation in the central parts of the island. As a result of increasing salinity, amorphous SiO₂ and magnesium calcite precipitate in the soils beneath the marginal zone of the island, raising the land surface, while the more soluble alkali carbonates are concentrated in the centre of the island as surface crusts and brine ponds. Leaching of these salts into the soil during the rainy season and gravity-driven flow of saline brines in the dry season causes the downward movement of Al and Fe in the central zone of the island. K-feldspar and possibly amorphous allophane develop in the deeper soils under the central zone of the island.     

Land degradation impacts on tropical agricultural basins and their management: the Nigerian example

This study uses the fault-tree technique to identify the major effects of land degradation caused by the adoption of a malfunctioning shifting cultivation technology for food production in tropical basins. Through reference to existing empirical research, the sequence of events in the process of degradation of the Nigerian agricultural basins and the adjoining river systems was identified and related to the appropriate causal agent. A complete picture of the cost of land degradation goes beyond the degraded terrain and includes damage in areas where there is an unloading of large quantities of run-off and sediments. The causal pathway showed that existing land degradation management policies have focused on the symptoms rather than on the cause of the degradation process. Through a thorough examination of those malfunctioning components of the traditional farming technology, appropriate management strategies are proferred. An institutional organization for land degradation management in Nigeria which includes the federal, state and local governments is strongly recommended.     

Landslide hazard and risk assessment and their application in risk management and landuse planning in eastern flank of Menoreh Mountains,Yogyakarta Province,Indonesia

The Menoreh Mountains in Yogyakarta are severely affected by landslides. Due to the high population densities, mass movements are generally damaging and fatal. More than other Javanese mountains, the Menoreh Mountains cumulate several factors causing landslides. Therefore, it is necessary to evaluate the ways to map landslide risk in order to improve the risk mitigation. The objectives of this paper are to provide landslide hazard and risk assessment that will be useful for risk prevention and landuse planning in the Menoreh Mountains. So far, risk management has been developed by the Research Centre for Disasters Gadjah Mada University in collaboration with the Regional Development Planner (BAPPEDA), which carries out fundamental and applied researches. The results of the studies have been integrated in the risk prevention and landuse planning in order to improve the integrated landslide mitigation programme.     

Structural and metamorphic controls on the distribution of zircon in an evolving quartzofeldspathic migmatite: an example from the Reynolds Range, central Australia

Three types of zircon occur in a complexly deformed and variably migmatized quartzofeldspathic gneiss from the Reynolds Range, central Australia. The oldest type is inherited from the granitic precursor of the gneiss, and is overgrown by a second group of zircon grains that formed during prograde, granulite facies metamorphism. Partial melting of the gneiss resulted in solution of both the inherited and metamorphic zircon. No new zircon growth accompanied crystallization of the partial melt, suggesting loss of zirconium–rich residual fluids. Hydrous, amphibolite facies retrogression of the gneiss and its migmatized variants during late shearing produced new, idiomorphic zircon in both the shear zone and its wall rocks.
Important implications of this study are that (i) zircon has a tendency to dissolve if it comes into direct contact with a melt produced from anhydrous biotite breakdown in a quartzofeldspathic granulite, (ii) melt crystallization is not necessarily accompanied by zircon growth, and (iii) euhedral zircon can grow from a hydrous fluid phase under subsolidus, amphibolite facies conditions, e.g. within shear zones.     

Migration of hydrothermal systems in an evolving collisional orogen, New Zealand

The Pacific–Australian tectonic plate boundary through the South Island of New Zealand consists of the transpressional Southern Alps mountain belt and the transcurrent Marlborough Fault System, both of which have active tectonically driven hydrothermal systems, with topographically driven meteoric incursion and warm springs. The Southern Alps hydrothermal system is relatively diffuse, with little or no fault control, and is channelled through scattered extensional sites beneath the mountains, where gold mineralisation is occurring locally. The hydrothermal activity along the Marlborough Fault System is controlled by the principal faults in well-defined valleys separated by narrow high ridges. Lateral evolution of Marlborough fault strands southwestwards into the Southern Alps has caused diversion of diffuse Southern Alps hydrothermal activity into the structural superimposition zone, where fluid flow is increasingly being controlled by faults. This hydrothermal diversion was accompanied by major topographic reorientation and river drainage reversal in the late Quaternary. Vein swarms now exposed in the remnants of the Southern Alps north of the superimposition zone formed at shallow levels, with some evidence for fluid boiling, from a mixture of meteoric and deep-sourced fluid. These veins, some of which contain gold, are part of an abandoned <1 million-year-old hydrothermal zone beneath the fossil topographic divide of the Southern Alps that has now been dismembered by lateral incursion of the Marlborough fault strands. Observations on this active plate boundary provide some insights into processes that controlled orogenic gold mineralisation in ancient belts, particularly with respect to relationships between hydrothermal fluid flow, structure and topography.     

Reservoir operation using system dynamics under climate change impacts: a case study of Yamchi reservoir,Iran

This paper proposes a decision support system for Yamchi reservoir operation in semi-arid region of Iran. The paper consists of the following steps: Firstly, the potential impacts of climate change on the streamflow are predicted. The study then presents the projections of future changes in temperature and precipitation under A2 scenario using the LARS-WG downscaling model and under RCP2.6, RCP4.5, and RCP8.5 using the statistical downscaling model (SDSM) in the northwestern of Iran. To do so, a general circulation model of HadCM3 is downscaled by using the LARS-WG model. As a result, the average temperature, for the horizon 2030 (2011–2030), will increase by 0.77 °C and precipitation will decrease by 11 mm. Secondly, the downscaled variables are used as input to the artificial neural network to investigate the possible impact of climate change on the runoffs. Thirdly, the system dynamics model is employed to model different scenarios for reservoir operation using the Vensim software. System dynamics is an effective approach for understanding the behavior of complex systems. Simulation results demonstrate that the water shortage in different sectors (including agriculture, domestic, industry, and environmental users) will be enormously increased in the case of business-as-usual strategy. In this research, by providing innovative management strategies, including deficit irrigation, the vulnerability of reservoir operation is reduced. The methodology is evaluated by using different modeling tests which then motivates using the methodology for other arid/semi-arid regions.