Influence of harbour constructions on morphosedimentary changes in the Tinto-Odiel estuary mouth (south-west Spain)

The Odiel-Tinto estuary is one of the most significant estuarine systems along the mesotidal Huelva Coast. The dynamics of this coastal sector are controlled by the interaction of ebb-tidal currents and the prevailing southwesterly waves. The main sediment supply is provided by an intensive west-to-east longshore current, transporting sand from Portuguese cliffs and discharge from the River Guadiana. The tidal range is mesotidal (2.0 m) and the mean significant wave height is 0.6 m with an average period of 3.6 s. This estuary mouth comprises three different barriers separated by the main estuary channel, and another marginal one that drains a significant part of the system. Saltés Island can be found between these two channels, which is composed of sandy barriers separated by muddy salt marshes that form a protected natural park. East of the main channel is Mazagón Beach, one of the most important tourist resorts on this coast. Recent papers have demonstrated that Saltés Island evolved as a chenier plain over the last 3000 years. The cause of this evolution was a special wave refraction scheme caused by two ebb-tidal delta systems located at the end of the two tidal channels. Three important harbour infrastructures have been constructed at the estuary mouth: a) a jetty at the end of Saltés Island, finished in 1977; b) a second and shorter jetty bordering the marginal channel constructed in 1984, and; c) a dock for sailing activities built on Mazagón Beach. These three structures have modified the natural dynamic scheme. The first consequence was to inhibit the functioning of the chenier plain, affecting the natural environment; the second was to intensively erode Mazagón Beach, endangering this tourist site.This paper analyses the causal relationships that exist between the harbour infrastructures and the resultant modifications.     

Bedding-controlled coastal landslides in Southeast Britain between Axmouth and the Thames Estuary

The coastline of Southeast Britain is formed in sedimentary rocks of Jurassic, Cretaceous and Tertiary age, the majority of these deposits containing thick strata of mudrocks, which have very low angles of dip. Where these strata are appropriately exposed, particularly at the foot of a coastal slope, they give rise to landslides where all or part of the sliding surface follows a single bed of mudrock. Where the dip of the bedding is steep, such landslides are referred to as dip-slope failures. However, landslides where the basal sliding surface is controlled by the location and orientation of a single argillaceous bed in the sequence are better termed bedding-controlled landslides. In addition, where coastal slopes contain several layers of mudrocks, geometrically similar landslides may occur with perched slide surfaces breaking out at a higher level within the slopes. Landslides with strong bedding-controlled basal shear surfaces are the predominant form of instability along the southeast coastline of Britain. Many of the individual landslide cases used in this paper have been studied separately over many years. The general similarity of the different records is discussed, drawing important inferences on a number of aspects of these landslides with a variety of basal sliding surface geometries.     

石河子垦区一次低压大风天气的成因分析

通过对石河子一次低压大风天气的成因分析，发现“降压增温”是其前兆。前期降水，有利的垂直风场．不稳定能量释放是低压产生持续大风的关键，并提出今后的预报着眼点。     

Stratigraphical and palynological appraisal of the Late Quaternary mangrove deposits of the west coast of India

The organic deposits derived from the mangrove swamps form reliable stratigraphic markers within the Late Quaternary sequence of Kerala–Konkan Basin. Three generations of such deposits have been identified. The older one is dated to around 43,000–40,000 ¹⁴C yr B.P., with a few dates beyond the range of radiocarbon. The younger ones date from the Middle Holocene to latest Pleistocene (10,760–4540 ¹⁴C yr B.P.) and the Late Holocene (<4000 ¹⁴C yr B.P.). Pollen analyses confirm that the deposits are mostly derived from the mangrove vegetation. Peat accumulation during the period 40,000–28,000 ¹⁴C yr B.P. can be correlated with the excess rainfall, 40–100% greater than modern values, of the Asian summer monsoon. The low occurrence of mangrove between 22,000 and 18,000 ¹⁴C yr B.P. can be attributed to the prevailing aridity and/or reduced precipitation associated worldwide with Last Glacial Maximum, because exposure surfaces and ferruginous layers are commonly found in intervals representing this period. The high rainfall of 11,000–4000 ¹⁴C yr B.P. is found to be the most significant as the mangrove reached an optimum growth around 11,000 ¹⁴C yr B.P. but with periods of punctuated weaker monsoons. From the present and previous studies, it has been observed that after about 5000 or 4000 ¹⁴C yr B.P., the monsoons became gradually reduced leading to drying up of many of the marginal marine mangrove ecosystems. A case study of Hadi profile provided an insight to the relevance of magnetic susceptibility (χ) to record the ecological shift in Late Holocene.     

The negative effect of environmental geological conditions of some geo-archaeological sites of North Coast and Alexandria

Three geo-archaeological sites at the North Coast and Alexandria, namely, the Alexandria wall (El Shalalat Park site), Abu Soir temple, and Marina excavations, were investigated to determine the negative impact of a salty environmental condition. The monuments suffer from rock decay of different rates. The geo-archaeological sites were built mainly from oolitic limestone blocks (i.e., the Alexandria wall at the El Shalalat Park site and Abu Soir temple) or excavated on them (i.e., Marina excavations). Field inspection and a lab analysis were carried out to understand the weathering mechanism. Salt weathering criteria such as disintegration, pitting, scaling, exfoliation, and honeycomb are observed on the Alexandria wall and upper parts of the Abu Soir temple, while dangerous cracks are detected on the Marina excavation tombs. The petrographic study of the oolitic limestone samples shows that they consist mainly of oolities and drusy sparite as a cement (oolitic grainstone). Some oolities have quartz grains as nuclei. Hydrochemical analysis shows that the total dissolved salts of extracted solutions of the North Coast quarry samples range from 539 to 686 ppm and dramatically increase (i.e., ten times) for extracted solutions from monument samples, ranging from 5395 to 6880 ppm. The dominant cation is sodium while the dominant anion is chlorine. Acid insoluble residue analysis shows that the carbonate content ranges from 89.2% to 96.4% for fresh samples from quarries and from 9.2% to 94.8% for weathered monument samples. The weight loss of the quarry oolitic limestone samples range from 30.7% to 32.7% and its physical and mechanical properties become worse after being subjected to 15 cycles of a durability simulation soundness test (using a sodium sulphate solution). Our main recommendations are to use suitable grouting for binding the cracks, high durability reconstruction rocks, and suitable cleaning methods to remove salts from the monuments.     

窄带回波在大风超短时预报中的应用

利用新一代天气雷达回波资料,结合地面实况资料,对2004年8月22日发生在新疆准噶尔盆地南缘的一次雷雨大风天气过程进行了分析,认为窄带回波的形态特征及其演变可为大风超短时预报提供较可靠的信息。     

舟山群岛一次低压大风过程的诊断分析

通过对舟山群岛一次低压大风过程的天气形势及各种物理量的诊断分析认为：地面的倒槽波动，加上高空的涡度平流、低层南北两支气流相遇形成的强烈的切变是地面低压能够形成并发展的关键。中低层的温度平流、降水凝结释放潜热维持上升运动，是低压进一步发展的有利条件。高空动量下传最终形成了地面的强风。     

华南沿海海平面的变化速率

应用回归分析和切比雪夫拟合二种方法，根据验潮资料研究了华南沿海海平面的变化速率，进而结合区域研究近２０年来华南海平面的变化特征，并讨论了将其用于地震趋势分析的可能性。     

Extensive deformations of rock slopes in southern Coast Mountains, southwest British Columbia, Canada

Extensive deformations of mountain slopes occur in crystalline intrusive rocks in the southern Coast Mountains of British Columbia. Typical morphological evidence of slope movement includes extensive systems of tension cracks, grabens, and antislope scarps (collectively referred to here as linears). These landforms involve displacements along penetrative joints observed in surface exposures. Kinematic tests on rock-structural data indicate that the observed patterns of linears are generally consistent with the feasible gravitational movements along the dominant discontinuities. Most sites indicate sliding as the most likely initial mode of movement, followed by or accompanied by toppling and toppling-induced sliding movements, and do not support the view that linears are the traces of active faults.