The impact of wave loads and pore-water pressure generation on initiation of sediment transport

The build-up of pore-water pressure by waves can lead to sediment liquefaction and subsequent transport by traction currents. This process was investigated by measuring pore-water pressures both in a field experiment and laboratory wave tank tests. Liquefaction was observed in the wave tank tests. The results suggest that sand is less susceptible than silts to wave-induced liquefaction because of the tendency to partially dissipate pore-water pressures. However, previous studies have determined that pore-water pressures must approach liquefaction before current velocities necessary to initiate transport are reduced. Once liquefaction has occurred more sediment can be transported.     

Launching and joining of a product carrier of 30,500 DWT built in two sections

This paper describes the process of launching and joining of two sections of a product carrier of 30,500 DWT built at Dianca shipyard at Puerto Cabello, Venezuela. The specifications and characteristics of this ship are in line with the market requirements. This paper deals with the problems encountered during the decision of dividing the ship in two halves, use of syncrolift for launching and subsequent joining of two halves in the dry dock.     

Hydrothermal Metalliferous Sediments and Waters Off the Lesser Antilles

Considerable metal enrichments have been found in hydrothermal fluids and metalliferous sediments off the central Lesser Antilles Volcanic Arc. The elements variably enriched in the fluids as a result of the hydrothermal activity are Fe, Mn, As, Si, B, Li and in the sediments, Fe, P, Mo, As, Sb, Hg, Cu and Pb. Variations in the concentrations of these elements in both fluids and sediments along the arc result from a number of factors, the most important of which is the stage that each island's volcano has reached in its eruptive cycle. Although hydrothermal mineralization on the sea floor off the islands is only low grade, phase separation in the hydrothermal fluids at depth could be leading to higher grade stockwork mineralization below the vent fields or the discharge of metal rich brines on the lower flanks of the volcanic islands.     

Growth Aspects and Magnesium Carbonate Concentrations of the Reef Building Octocoral Heliopora coerulea (Pallas) after Transplantation

Abstract. An experiment to test C have's hypothesis on temperature dependent MgCO₃ concentrations in marine calcareous skeletons was undertaken by transplanting colonies of Heliopora coerulea. The corals were transferred from a shallow lagoon with high average temperatures to the outer bottom of a fringing reef, 16 m depth, with low average temperatures. Against expectation, a statistically significant increase of average mol % concentrations from 0.48 to 0.54 % for upper growth regions and from 0.49 to 0.62% for lower growth regions was obtained. Temperature records during the experimentation period and the above data indicate that the mol% MgCO₃ concentration in the skeleton of living Heliopora colonies increases when transplanted to an environment with a lower temperature average than that of their original growth site, and with seasonal temperature fluctuations which are smaller in the experimental site than in the control site. Temperature fluctuations at the control site were up to 2.5 times greater than at the experimental site for most of the observation months. This supports the conclusion that the parameters a) minimum temperature and b) temperature stability of the environment are essential for the incorporation of Mg into the carbonate skeleton matrix of marine organisms. Within this study the results of a quantitative chemical analysis of the carbonate skeleton of H. coerulea are presented and growth data of transplanted colonies compared with those from the control site.     

Beginning integrated coastal management efforts in Madagascar

Integrated coastal management (ICM) is an emerging approach in East Africa for the solution of various coastal issues. This paper is intended to provide an update on the current practical aspects concerning the ICM process and related policies and strategies in Madagascar. Efforts are being made in Madagascar for the mutual integration of numerous coastal projects and activities within the Environment Program of the National Environmental Action Plan. The foundations for an ICM program, built during an ICM workshop, which took place at the end of 1996 upon existing activities, are being expanded presently. These developments concern, above all, the institutional aspects related to the formulation of an ICM program. Therefore, the actual situation sees an overgrowing collaboration of the national and international agencies involved in the implementation of coastal projects, in an expandingly integrating way, within an institutional framework that grows progressively stronger. The case of Madagascar suggests reflections on how ICM can mitigate potential sectoral conflicts as well as on, how the sometimes complex nature of the social and cultural issues may influence the development of an ICM program. The need for monitoring ICM is stressed and the role of outside partners clarified.     

Magnetic anomalies in the canary basin and the Mesozoic evolution of the central North Atlantic

The data from a recent magnetic compilation by Verhoefet al. (1991) off west Africa were used in combination with data in the western Atlantic to review the Mesozoic plate kinematic evolution of the central North Atlantic. The magnetic profile data were analyzed to identify the M-series sea floor spreading anomalies on the African plate. Oceanic fracture zones were identified from magnetic anomalies and seismic and gravity measurements. The identified sea floor spreading anomalies on the African plate were combined with those on the North American plate to calculate reconstruction poles for this part of the central Atlantic. The total separation poles derived in this paper describe a smooth curve, suggesting that the motion of the pole through time was continuous. Although the new sea floor spreading history differs only slightly from the one presented by Klitgord and Schouten (1986), it predicts smoother flowlines. On the other hand, the sea floor spreading history as depicted by the flowlines for the eastern central Atlantic deviates substantially from that of Sundvik and Larson (1988). A revised spreading history is also presented for the Cretaceous Magnetic Quiet Zone, where large changes in spreading direction occurred, that can not be resolved when fitting magnetic isochrons only, but which are evident from fracture zone traces and directions of sea floor spreading topography.Deceased 11 November 1991