The formation and evolution of the barrier islands of Inhaca and Bazaruto, Mozambique

The barrier islands of Inhaca and Bazaruto are related to the extensive coastal dune system of the Mozambican coastal plain, south-east Africa. Optically stimulated luminescence (OSL) dating of key stratigraphic units indicates that accretion of sediment within these systems is episodic. Both islands appear to have been initiated as spits extending from structural offsets in the coastline. Superposition of significant quantities of sediment upon these spits during subsequent sea-level highstands formed the core of the islands, which were anchored and protected by beachrock and aeolianite formation. At least two distinct dune-building phases occurred during Marine Oxygen Isotope Stage (MIS) 5, tentatively attributed to marine transgressions during sub-stages 5e and 5c. Although some localized reactivation of dune surfaces occurred prior to the Holocene, large quantities of sediment were not deposited on either island during the low sea-levels associated with MIS 2. Significant dune-building and sediment reworking occurred immediately prior to and during the Holocene, though it is not clear whether these processes were continuous or episodic. Significant erosion of the eastern shoreline of Bazaruto suggests that it is far less stable than Inhaca and may suffer further large-scale erosion. A model is presented for the formation of barrier islands along the Mozambican coastal plain.     

Lake-Level Fluctuations and Small-Scale Vegetation Patterns During the Late Glacial in The Netherlands

Late glacial changes in the vegetation were studied in and around a former lake on the southeastern side of a coversand ridge near Milheeze (southern Netherlands). Analyses of microfossils and macroremains and AMS ¹⁴C dating were performed on four sediment cores along a transect from sand ridge to the lake centre. Small-scale vegetation patterns and lake-level fluctuations were reconstructed in detail based on the information provided by the transect. For the first time in The Netherlands, cores along a transect within one lake were used to reconstruct the amplitude of late glacial lake-level fluctuations. Near Milheeze, a small and shallow lake was formed during the Bølling. The large increase in the water level during the Bølling and early Allerød, and the transition to more eutrophic conditions at the start of the Allerød, were probably related to the disappearance of permafrost. During the Allerød, open birch and pine woodlands developed in the area. In the lake, organic deposits accumulated, and the lake size and depth fluctuated. At the start of the Younger Dryas, higher lake water levels were recorded and woodlands became more open as a result of both a drop in the temperature and an increase in the effective precipitation. During the late Younger Dryas the lake water level dropped as the climate became drier and temperatures slightly increased. Accumulation of organic deposits in the lake ceased at the end of the Younger Dryas, which was caused by a drop in the water level in combination with the hydroseral succession process within the lake itself. The climatic signal reflected in the late glacial flora and lake-level fluctuations agree well with other published data from The Netherlands.     

Ecological and functional roles of mycorrhizas in semi-arid ecosystems of Southeast Spain

Mycorrhizas are worldwide symbiotic associations established between certain soil fungi and most vascular plants and are fundamental in optimizing plant fitness and soil quality. Mycorrhizal symbioses improve the resilience of plant communities against environment stresses, including nutrient deficiency, drought and soil disturbance. Since these stresses are paramount in the degradation of semi-arid ecosystems in the SE Spain, a series of basic, strategic and applied studies have been made to ascertain how the activity and diversity of mycorrhizal fungi affect plant community composition, structure and dynamics in this region. These investigations are reviewed here in terms of: (i) analysing the diversity of mycorrhizal fungi; (ii) assessing the ecological and functional interactions among plant communities and their associated mycorrhizal fungal populations; and (iii) using mycorrhizal inoculation technology for the restoration of degraded semi-arid areas in Southeast Spain. Disturbance of the target semi-arid ecosystems decreases the density and diversity of mycorrhizal fungust populations. Nevertheless, the mycorrhizal propagules do not disappear completely suggesting a certain degree of stress adaptation, and these remaining, resilient ecotypes are being used as plant inoculants. Numerous field experiments, using plant species from the natural succession inoculated with a community of indigenous mycorrhizal fungi, have been carried out in revegetation projects in the semi-arid Iberian Southeast. This management strategy improved both plant development and soil quality, and is a successful biotechnological tool to aid the restoration of self-sustaining ecosystems. However, despite a 20-year history of this work, we lack a comprehensive view of the mycorrhizal potential to improve the composition, diversity, structure and functionality of drought-adapted plant communities in the Region.     

Comparative analysis of cladoceran microfossils in the Don and Scarborough Formations,Toronto, Canada

Pleistocene deposits at Toronto, consisting of Don Formation (considered to be of Sangamonian interglacial age) and Scarborough Formation (interpreted to be Early Wisconsinan, >50 000 years B.P.) were examined at three sites: Don Valley Brickyard, Leaside, and at the south end of Brimley Road at the foot of the Scarborough Bluffs. Comparison of the cladoceran microfossil assemblages described from these sites has enabled reconstruction of the lacustrine environment of the region.Cladoceran microfossil evidence from each site confirmed the disparity in community composition and structure, and in environmental conditions that existed during deposition of the Don and Scarborough Formations. Cladocera community composition averaged 40–45% remains of littoral species in the warmer Don interval at all three sites. The Scarborough Formation contained a more homogeneous cladoceran assemblage, with higher community similarity across sites than observed in the Don Formation. However, there was greater variation in the littoral: planktonic ratio among sites, ranging from >0.90 at Leaside to <0.10 at Brimley Road.Stratigraphically constrained cluster analysis of cladoceran microfossil assemblages clearly separated the communities in the Don Formation from those in the Scarborough Formation at each site. During the interglacial, the Don Brickyard site appears to have been a shallow, protected embayment on the lake shore, whereas the other sites are more distinctly lacustrine. The Scarborough assemblage at each site is representative of deeper, oligotrophic, subarctic lakes.     

Historical Changes in the Flood Hazard at Khartoum, Sudan: Lessons and Warnings for the Future

The 1988 floods at Khartoum were frequently described as "unprecedented". However, an examination of evidence for floods caused by the Nile and rain storms during the nineteenth and twentieth centuries leads to the conclusion that neither the Nile flood nor the rain storms nor their coincidence in one season were unprecedented and that similar situations will recur.We argue that most problems were created by complacency, lack of planning and mismanagement. We conclude with some simple suggestions for flood amelioration in the future and warn that complacency is the single most important phenomenon likely to recur to the detriment of Greater Khartoum in the future.     

Revaluation of the natural-resource potential of Ukraine

We provide a rationale for the technique of revaluating the natural-resource potential which is built upon the natural crop yield of Ukrainian lands obtained, with the observance of rotation cropping and by implementing the complex of mechanical tillage operations without fertilizer application. An assessment is made of Ukraine’s natural-resource potential within the context of three physical-geographical countries, four zones, three subzones, and 14 krais.     

VLF radiation from lightning

Summary. Electrical and magnetic fields due to arbitrarily oriented lightning over an imperfectly conducting ground have been obtained. The theory has been applied to K -changes, return strokes and horizontal lightning. The results are in good agreement with the experimental observations previously reported by many workers.     

Use of Kirchhoff s formula for body wave calculations in the Earth

Summary. Kirchhoff's time-dependent surface integral representation of a scalar wavefield is applied to the problem of computing synthetic seismograms for P -waves in the Earth. By means of an appropriate parameterization, the Kirchhoff integral is transformed into a convolution of a weight function with the derivative of the source function in the time domain. The weight function is calculated using simple ray theory. The method extends the applicability of simple ray theory to caustics and other diffraction phenomena and allows certain kinds of departures from spherical symmetry to be taken into account. The method is illustrated in detail by application to the PKP -wavefield in the Earth.     

Fan beheading and drainage diversion as evidence of a 3200-2800 BP earthquake event in the Esmeraldas-Tumaco seismic zone: A case study for the effects of great subduction earthquakes

The San Lorenzo area belongs to the Esmeraldas–Tumaco seismic zone where some of the strongest earthquakes of South America occurred during the 20th century. This paper provides evidence for a succession of geomorphic changes characterized by the disruption of the Quaternary drainage network and the reshaping of the Cayapas–Santiago estuary. The rise of the La Boca uplift bordered by the La Boca and San Lorenzo faults is responsible for the southward diversion of the Palabi, Tululbi, Bogotá and Carolina rivers toward the Santiago and Cayapas rivers. The increase of the discharge directed to the Cayapas River generated the change of the channel pattern downstream from the confluence, and the avulsion of a new estuary through the coastal plain. According to the dating of beach ridges the avulsion occurred in the period 3200–2800 BP. This period corresponds also to a faster accretion of the beach ridge margin, interpreted as a response to a small uplift of the shore. The coherency of the three morphologic evidences—diversion of drainage network, avulsion and increase of coastal accretion—suggest a unique morphotectonic event, in relation with the activity of the Esmaraldas–Tumaco seismic zone. The opening of a direct communication through the mangrove margin may have brought favorable conditions for the development of the La Tolita archaeological site after 3000 BP.