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1.
Despite threats emanating from the influence of climate and non-climate forcing on the barrier island coastal region of southwestern Nigeria, the extent of the coastal erosion is poorly understood. We report evidence of coastal erosion and sediment accumulation in the region over a 34-year period (1973–2017), using Landsat imagery at intervals of approximately six years. Landsat image corrections and various water-extraction algorithms were used to systematically delineate coastal erosion and accumulation in the area. The region was subdivided into western and eastern subregions separated by Lagos Harbour. In the west, erosion took place during the periods 1973–1979, 1979–1984, 1990–1999 and 2005–2011, whereas in the east, erosion occurred during 1973–1979, 1990–1999 and 1999–2005. Coastal sediment accumulation occurred in the east during 1979–1984, 1984–1990, 2005–2011 and 2011–2017, whereas gains in the west occurred during 1984–1990, 1999–2005 and 2011–2017. The study revealed substantial net erosion of 1 228.1 ha in the region as a whole, over the full period. Sediment accumulation accompanying the coastal erosion appears to be linked to longshore drift. Erosion between 1973 and 2011 was probably attributable to climate change (storms and tidal conditions), longshore drift, the inflow and outflow of water at Lagos Harbour, coastal morphology and, possibly, human impacts. However, the coastal changes between 2011 and 2017 were more obviously associated with human activities, such as development of the Eko Atlantic construction project. Coastal surveillance, together with the use of environmentally sensitive protective measures, could possibly help to reduce coastal erosion in the region. Careful coastal management practices, including artificial nourishing and the installation of resilient structures (e.g. seawalls), should be undertaken to protect human settlements that are already at risk from sea-level rise. 相似文献
2.
M. S. Kapdaşli 《Geo-Marine Letters》1990,10(1):45-49
Flume experiments were carried out to determine the threshold of movement of sand on rippled surface and flat beds under the
codirectional combined flows due to waves and currents. The results indicate that Shields's curve can be used to determine
the threshold condition under combined flows, provided that the maximum bed shear stress is used. 相似文献
3.
Erdal Dolu Erkan Gökaşan Engin Meriç Mustafa Ergin Tolga Görüm Hüseyin Tur Berkan Ecevitoğlu Niyazi Avşar Muhittin Görmüş Fatmagül Batuk Buğser Tok Oktay Çetin 《Geo-Marine Letters》2007,27(6):355-381
The Quaternary evolution of the Gulf of İzmit, situated on the tectonically active North Anatolian Fault Zone (NAFZ), was
investigated using seismic reflection, paleontologic, and sediment textural data. On the basis of seismic stratigraphic and
sedimentologic-paleontologic interpretations, four depositional units were distinguished within the Plio-Quaternary sequence
of the Gulf of İzmit. According to these data, Plio-Quaternary deposits supplied from the northern terrestrial area started
to accumulate during a progradational phase, in a south-facing half-graben. A coarse-grained sedimentary unit prograding into
the gulf from the south since 200 ka b.p. indicates a dramatic variation in the evolution of the gulf, with the initiation of a new strike-slip fault of the NAFZ
and a corresponding uplift of the Armutlu Peninsula in the south of the gulf. During the evolution of this fault from a wide
shear zone consisting of right-stepped strike-slip faults and pull-apart basins to a localized principal fault zone, sediments
were deposited under the influence of northerly prograding terrestrial and shallow-marine conditions due to relative sea-level
fluctuations in the Marmara Sea. During this period, the Gulf of İzmit was invaded mainly by Mediterranean and partly by Black
Sea waters. In the latest glacial period, shallow areas in the gulf became subaerially exposed, whereas the central and western
sub-basins of the gulf turned into lakes. The present evolution of the Gulf of İzmit is controlled by the after effects of
the new rupture of the NAFZ and the estuarine nature of the gulf environment. 相似文献
4.
O. Algan N. Çağatay A. Tchepalyga D. Ongan C. Eastoe E. Gökaşan 《Geo-Marine Letters》2001,20(4):209-218
The sediment infill over the Paleozoic bedrock in the Bosphorus Strait consists of four sedimentary units which were deposited in the last 26,000 14C years B.P. The stratigraphy of these units suggests that this part of the Bosphorus was a freshwater lake between 26,000 and 5,300 14C years B.P., depositing sands with a freshwater mollusc fauna of Black Sea neo-euxinian affinity (Dreissena rostriformis, Dreissena polymorpha, and Monodacna pontica). The first appearance of euryhaline Mediterranean molluscs (e.g., Ostrea edulis, Mytilus edulis) was observed at 5,300 14C years B.P. in this part of the Bosphorus. Deposition of coarse Mytilus-bank and Ostrea-bank units suggests that the establishment of the present dual-flow regime in the Bosphorus took place at about 4,400 14C years B.P. 相似文献
5.
The Karalar galena-barite deposits are typical examples of the carbonate-hosted barite-galena deposits widely occurring in
the Central Tauride Belt. These deposits are located in Permian limestones as ore veins along fault zones that are discordant
to the bedding planes and as thin veinlets within hardly brecciated bottom zones of Permian limestones. The ore deposits contain
mainly barite and galena and small amounts of sphalerite, pyrite, fahlore, limonite, quartz, and calcite. Barites occur during
the earlier episode of mineralization and were mylonitized before the formation of galena. Galena and other minerals occur
epigenetically with barite along porous zones between brecciated barite crystals and are especially abundant in the hardly
mylonitized zones. Fluid inclusion studies indicate that the ore deposits of the area were developed by hydrothermal fluids
with following characteristics: they contained NaCl, CaCl2, and MgCl2; the salinity of the fluids was relatively high and their temperature was low during the crystallization of barites in the
earlier episode of mineralization; and the salinity of the fluids decreased and their temperature increased during the crystallization
of sulfide minerals through the later episode of mineralization. δ18O and the δD results indicate that the water in the mineralizing fluid was of meteoric origin. The deposits were formed by
deep meteoric water circulating through marine sediments. Shallow circulating and slightly warmed fluids dissolved Ba and
sulfate from marine sediments of the basement and transported them to the mineralization environment during the early episode,
while deep circulating and more heated fluids dissolved Pb, Zn, and other elements from the basement and reached the environment
during the later episode of mineralization.
The text was submitted by the authors in English. 相似文献
6.
Turkey was struck by two major events on 17 August and 12 November 1999, named Izmit (M w = 7.4) and Düzce (M w = 7.2) earthquakes, respectively. Rubble mound breakwaters in Izmit Bay experienced little damage, as forecasted by the new risk assessment model in which tsunami occurrence risk was included in the damage estimations. In order to determine the occurrence probability of structural damage under design conditions, including the environmental loading parameters of tsunami and storm waves, tidal range and storm surge, the Conditional Expections Monte Carlo simulation was applied in the risk assessment model developed in this study for the Esenköy Fishery Harbour, Turkey. A tsunami was not the key design parameter when compared to storm waves for the main breakwater of the harbour, however, in places with great seismic activity, the tsunami risk should be important depending on the occurrence probability and magnitude of the tsunami. 相似文献
7.
The devastating 1999 Marmara and Düzce earthquakes led to a significant increase in the earthquake studies in Turkey in geological,
engineering and financial aspects. Extreme Value Theory (EVT) has a range of applications from stock market changes to natural
disasters like floods and hurricanes. Here EVT is fitted to the ordinary and earthquake reinsurance claims of Turkey. 相似文献
8.
An earthquake of magnitude 7.2 on the Richter scale occurred on 12 November 1999 in the Düzce-Bolu region of Turkey. The region was also hit approximately 3 months before during the devastating Kocaeli earthquake of 17 August 1999. Besides high casualties and damage to various engineering structures and buildings, slope and embankment failures on the highway and the country roads occurred. In this study, the authors are concerned with the back-analysis of an embankment failure that occurred on the four lanes E-5 highway connecting Ankara to Gstanbul at Bakacak in the Bolu Province during the 1999 Düzce earthquake. Both pseudo-dynamic and dynamic limiting equilibrium methods are used to back analyse the conditions for the initiation of failure and also displacement responses of the embankment during the earthquake shaking. After having given a brief summary of the investigations on the post-failure state, the geology and geotechnical characteristics of the site, and the dynamic limiting equilibrium method developed and used for analyses are described. The results of the back-analysis based on a pseudo-dynamic approach, revealed that the maximum ground acceleration to initiate the failure of the embankment was probably about 0.125 g. On the other hand, the application of a method for computing the displacement and velocity responses of the failed embankment showed that the failure was possible when the embankment was subjected to ground accelerations similar to that recorded at the Düzce station. In addition, the computations also revealed that the time history of accelerations could be very important for the failure of slopes and embankments. 相似文献
9.
10.