华南沿海地质灾害类型、发育规律和防治对策

本文系统和全面地论述华南沿海地质灾害的类型和发育规律。从宏观控制因素划分出岩石圈、大气圈、水圈及生物圈控制的四大地质灾害类型,阐明各类型发灾特点,论述主要地质灾害类型的分布和发育规律,提出灾害的总体防治对策。     

Remote Sensing of Mangrove Change Along the Tanzania Coast

This article contributes to the understanding of the changes in distribution and total area of mangrove forests along the mainland Tanzania coast over the past decade. Mangroves are recognized as critical coastal habitat requiring protection and special attention. The Tanzania coastline forms a suitable habitat for establishment of mangrove forests. Mangrove forests are distributed from Tanga in the north to Mtwara in the south covering approximately 109,593 hectares from 1988-1990 and about 108,138 hectares in 2000. The largest continuous mangrove stands are found in the districts of Rufiji, Kilwa, Tanga-Muheza, and Mtwara. Comparison of data between these two time periods shows that the geographic coverage of mangroves has no dramatic change in the past decade. The Tanzania Mangrove Management Project and other closely related programs and efforts pertaining to mangrove conservation contribute to direct restoration and natural regeneration of mangroves. This study documents the changes of mangroves and demonstrates that remote sensing and GIS offer important data and tools in the advancement of coastal resource management and ecosystem monitoring. Application of geographic information technologies is critical for improved coastal resources management and decision making for sustainable development in Tanzania.     

Subsurface geology of Louisiana hazardous waste landfills: A case study

Many hazardous waste sites in the south Louisiana Gulf Coast have been emplaced in sediments of Plio-Pleistocene to Recent age. Because of the fining upward nature of these regressive-transgressive fluvial-deltaic sequences and the purported confining capabilities of the shallow clay layers within them, this area would seem to be ideal for the location of surface waste landfills. However, detailed geologic mapping at a site in southeastern Louisiana documents how the three-dimensional distribution of sediment types and early diagenetic features, both of which were ultimately controlled by depositional history, can increase effective vertical permeability of finegrained sequences. Many bodies of sand that appear to be isolated in standard geotechnical cross sections can be shown to be part of spatially complex three-dimensional distributary networks, with fine-grained sediments representing overbank and backswamp deposits. Some clay layers are actually a composite of thinner clay beds, each subjected to subaerial exposure and the development of secondary porosity related to soil formation. There has been documented leakage of wastes down through the clays, and a recent study indicates that the effective vertical hydraulic conductivity of the clay layers exceeds 10^–5 cm s^–1, or from one to four orders of magnitude higher than values measured on samples from cores of the same sediment. An understanding of the depositional framework, facies architecture, and diagenetic history of geologic materials underlying waste disposal sites in Louisiana is required for rational development of monitoring and remediation plans.     

中国潮汐汉道研究的进展

潮汐汊道（ｔｉｄａｌｉｎｌｅｔ）是一种重要的海岸类型。本世纪７０年代，在欧美等国成为研究热点。８０年代，我国不少海岸学家加入这一研究行列。分析了潮汐汊道及其与其它潮汐海岸类型如潮汐河口、潮流冲刷槽等在学术概念上的差异与重合，评述了中国潮汐汊道研究的进展，重点介绍有代表性的研究成果，提出了今后我国应优先研究的主要课题。     

Possible geothermal resources in the Coast Plutonic Complex of southern British Columbia,Canada

In southern British Columbia the terrestrial heat flow is low (44 mW m^–2) to the west of the Coast Plutonic Complex (CPC), average in CPC (50–60 mW m^–2),and high to the east(80–90 mW m^–2). The average heat flow in CPC and the low heat generation (less than 1 W m^–3) indicate that a relatively large amount of heat flows upwards into the crust which is generally quite cool. Until two million years ago the Explorer plate underthrust this part of the American plate, carrying crustal material into the mantle. Melted crustal rocks have produced the inland Pemberton and Garibaldi volcanic belts in the CPC.Meager Mountain, a volcanic complex in the CPC 150 km north of Vancouver, is a possible geothermal energy resource. It is the product of intermittent activity over a period of 4 My, the most recent eruption being the Bridge River Ash 2440 y B.P. The original explosive eruption produced extensive fracturing in the granitic basement, and a basal explosion breccia from the surface of a cold brittle crust. This breccia may be a geothermal reservoir. Other volcanic complexes in the CPC have a similar potential for geothermal energy.Earth Physics Contribution No. 704.     

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.     

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.