Effect of disturbed zone thickness on rock slope stability

Natural Hazards - Cut slope surfaces are affected by excavation activities and weathering agents. Disturbances on the surface can penetrate down to a certain depth. Slope stability analyses made on...     

Über die Beziehung zwischen äquatorialen Konvektionsregen und der Meereshöhe auf Ceylon

Zusammenfassung Die Beziehung zwischen äquatorialen Konvektionsregen und der Meereshöhe wird am Beispiel der Südabdachung der Haputale Range auf Ceylon (etwa 7° nördl. Br. und rund 1400 m Höhenunterschied) untersucht. Auf der Grundlage unveröffentlichter Niederschlagsmessungen von 21 Stationen, vorwiegend Teeplantagen, für die Periode von 1951–1965 wird die Änderung der Niederschlagsmenge mit der Höhe an Hand der mittleren jährlichen und mittleren monatlichen Niederschlagsmengen diskutiert. Hierbei ergibt sich im Jahresmittel und in den Monaten mit vorwiegend konvektiver Niederschlagsbildung — das sind die Intermonsunmonate März, April und Mai sowie Oktober und November —, daß nach anfänglicher Zunahme des Niederschlags mit wachsender Höhe oberhalb einer kritischen Höhenlage zwischen 900–1400 m NN eine stetige Abnahme des Niederschlags eintritt.

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Summary The relationship between equatorial convective rain and altitude above sea-level is investigated taking the southern slope of the Haputale Range in Ceylon (7° N, about 1400 m range of altitude) as an example. On the basis of unpublished precipitation observations of 21 stations, most of them on tea-estates, from the period 1951 to 1965 the variation of the amount of precipitation with altitude is discussed using mean annual and mean monthly precipitation totals. It appears that in the annual mean and during the months with prevailing convective rain — these are the intermonsoonal months March, April, May and October, November — the precipitation totals increase with altitude up to a critical level between 900 and 1400 m a.s.l. and then decrease again monotonically.

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Résumé On examine ici la relation existant entre les précipitations équatoriales de convection d'une part et l'altitude d'autre part. Pour ce faire, on se sert de l'exemple offert par le versant sud de l'Haputale Range de Ceylan (situé à environ 7° de latitude N et présentant une différence d'altitude de 1400 m environ). Sur la base de mesures non publiées des précipitations — mesures effectuées de 1951 à 1965 à 21 stations, en majeure partie des plantations de thé — on discute les modifications que subissent les sommes de précipitations avec l'altitude. Dans ce but, on utilise les moyennes annuelles et mensuelles de cet élément. Il en résulte que les précipitations augmentent tout d'abord avec l'altitude et cela jusqu'à une zone critique située entre 900 et 1400 m. Au-dessus, les précipitations diminuent de nouveau régulièrement. Cette constatation est valable aussi bien pour la moyenne annuelle que pour les mois caractérisés avant tout par des précipitations d'origine convective c'est à dire ceux qui se situent entre les périodes de mousson (mars, avril, mai, octobre et novembre).

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High-resolution seismic studies of gas hydrates west of Svalbard

 A strong bottom-simulating reflection (BSR) with high-amplitude variations is detectable in high- resolution reflection seismic profiles west of Svalbard. Above the BSR, anomalously high velocities up to 1840 m/s, calculated from high-frequency ocean-bottom hydrophone (HF-OBH) data, indicate the existence of gas-hydrated sediments. Below the BSR, a low-velocity layer, interpreted as gas-bearing sediments, shows thickness variations from 12 to 25 m. In addition, two other low-velocity layers clearly containing free gas are detected within the classic hydrate stability zone (HSZ) where, a theoretical viewpoint, free gas cannot exist. Received: 6 August 1997 / Revision received: 26 January 1998     

Tidal Effects on Determining a Point at the Bottom of the Sea by Combining GPS and Sonar Observations

This paper discusses tidal effects on an observation scheme to determine a point at the bottom of the sea by combining GPS and Sonar observations. For the purpose, three kinds of Earth tides are introduced (i.e., the crust tide, the equipotential surface point (ocean depth) tide, and the geoid tide). The corresponding mathematical expressions are derived to demonstrate the tidal effects on GPS and Sonar observations. The relations between the Earth tides are also discussed. Theoretical results imply a very interesting conclusion, namely that, for a local area, the static position of a point at the bottom of sea can be obtained by the dynamic observations without any tidal correction. Actually, the tidal effects cancel each other in the mentioned observation scheme. It therefore indicates that the observation scheme is free of tidal effects. Furthermore, we learned that the divergence caused by any error source on ocean surface is canceled and does not affect the final results. Therefore, to determine the position of a point at the bottom of sea, we need not consider any tidal effects.     

Implementation of Tidal Constituent Interpolation Method for the Israeli Coastline

Many ship-borne geodetic surveys at sea, such as Global Navigation Satellite System (GNSS)-based sea surface height (SSH) observation, acoustic profiling of the bottom, and others, deal with a dynamic topography which undergoes several changes during the survey campaign (e.g., changes in tide, salinity and currents). Those changes affect the measurements and may causes for some variations in the results. There are several methods for tidal variations correction, being the most dominant phenomena, such as tidal zoning, tidal constituent interpolation or ocean tidal models. In this study, we have implemented the tidal constituent interpolation method for the Israeli coastline in order to assess its quality and determine whether it is suitable for use in this particular region. This paper depicts the interpolation method, discusses some difficulties in the implementation for the Israeli coast and presents results from exemplary processing. In addition, we compare the results to those obtained using global and regional tidal models.     

The curse of physiology—challenges and opportunities in the interpretation of geochemical data from mollusk shells

Physiology corrupts geochemical records of mollusk shells in many ways, e.g., by actively controlling the incorporation of trace elements in the skeleton. However, the effects of variable biomineralization rates and growth cessation have largely remained unconsidered. Mediated by endogenous timekeeping mechanisms, mollusks stop growing skeletal material on a regular basis ranging from ultradian to annual timescales. During growth cessation, the shells do not record environmental conditions. Shell growth also stops when environmental conditions are beyond the physiological tolerance of the organism, e.g., above and below genetically determined, species-specific thermal extremes where shell growth slows and eventually ceases. Such growth disruptions can occur at non-periodic time intervals. Due to growth retardations and halts, proxy records of mollusk shells are thus incomplete, and reconstructed environmental amplitudes prone to truncation. Furthermore, environmental records are biased toward the physiological optimum of the animal. Favorable environmental conditions increase shell growth, whereas adverse environmental conditions result in reduced shell production and lowered overall metabolism. Not least, the duration of the growing season and overall growth rate decrease as the mollusk grows older. Mathematical modeling approaches can significantly improve proxy records obtained from mollusk shells. For example, if the duration of growth cessation is known, it may be possible to model the missing environmental record. It is also fairly easy to account for age-related growth trends, or variable time-averaging in different portions of the shell. However, a major premise for a reliable interpretation of proxy records from a mollusk shell or other organisms secreting biogenic hard parts is a proper understanding of the physiology, and of course, a high-resolution record of the many different environmental factors that may influence physiology and shell growth. The present paper reviews examples from the literature, and unpublished data on how physiology influences geochemical proxy records from mollusk shells, and presents methods how to eliminate such adverse effects.     

Protein carbonyls and antioxidant defenses in corkwing wrasse (Symphodus melops) from a heavy metal polluted and a PAH polluted site

The use of fish in environmental monitoring has become increasingly important in recent years as anthropogenic substances, many of which function as prooxidants, are accumulating in aquatic environments. We have measured a battery of antioxidant defenses as a measure of oxidative status, as well as protein carbonylation as a measure of oxidative damage, in corkwing wrasse (Symphodus melops) captured near a disused copper mine, where water and sediment are contaminated with heavy metals, and an aluminum smelter, a site contaminated with PAHs. Results were compared to two different reference sites. Fish at the heavy metal site had lower glucose-6-phosphate dehydrogenase activity and elevated protein carbonyls (1.8 times) compared to fish from the reference site. At the PAH site, EROD was increased 2-fold, while total glutathione and methemoglobin reductase concentration, were decreased. No differences were seen in protein carbonyl levels at the PAH site. Measures of both antioxidant defenses and oxidative damage should be used when assessing effects of xenobiotics on oxidative stress in fish species.     

A note on ocean surface drift with application to surface velocities measured with HF Radar

The ocean drift current consists of a (local) pure drift current generated by the interaction of wind and waves at the sea surface, to which the surface geostrophic current is added vectorially. We present (a) a similarity solution for the wave boundary layer (which has been validated through the prediction of the 10-m drag law), from which the component of pure drift current along the direction of the wind (and hence the speed factor) can be evaluated from the 10-m wind speed and the peak wave period, and (b) a similarity solution for the Ekman layers of the two fluids, which shows that under steady-state neutral conditions the pure drift current lies along the direction of the geostrophic wind, and has a magnitude 0.034 that of the geostrophic wind speed. The co-existence of these two similarity solutions indicates that the frictional properties of the coupled air-sea system are easily evaluated functions of the 10-m wind speed and the peak wave period, and also leads to a simple expression for the angle of deflection of the pure drift current to the 10 m wind. The analysis provides a dynamical model for global ocean drift on monthly and annual time scales for which the steady-state neutral model is a good approximation. In particular, the theoretical results appear to be able to successfully predict the mean surface drift measured by HF Radar, which at present is the best technique for studying the near surface velocity profile.