Avalanche Run-Out on Counter-Slopes

Counter-slopes in avalanche paths influence avalanche flow in similarways as defence structures. Measurements and calculations of run-outon such slopes will improve our understanding of retaining damdesign. We have studied three different, well described avalancheevents; for each case we have calculated the run-out distance usingthe Noren, Irgens and Schieldrops continuum model (NIS), adjustingthe parameters to fit the simulated avalancheto the observed one. Using the same parameters, the run-out onidentical terrain, but without counter-slope, is computed. Comparisonbetween the energy dissipation in these different cases tells us whichtopography most efficiently retards an avalanche. With a smoothly curved valley bottom, the energy dissipation at agiven point on the opposite slope is less than on a flatrun-out. The explanation to this is that, when gravity retards anavalanche, a smaller portion of the energy loss is due to dissipationfrom viscous (velocity dependent) friction. When the avalanche travelsover a retaining dam, with much smaller curvature radii, a significantportion of the energy is dissipated. The consequence of this is that defence structures are not sodependent on the counter-slope inclination as on the curvature radiusin the transition to up-gradient. Further, introduction of acounter-slope in an avalanche path may conserve energy rather thancausing dissipation – if the inclination is not altered abruptlyenough. If the counter-slope is smooth, and not large enough tocompletely stop the avalanche, it will not reduce destructive energyon the downstream side. In fact, the destructive energy may bepartially conserved until the run-out.     

The marine 14C age of the Vedde Ash Bed along the west coast of Norway

Articulated molluscs, sea urchins and barnacle fragments close to the Vedde Ash Bed in a shallow marine deposit on the west coast of Norway have been ¹⁴C dated. The weighted mean of four dates from a sediment slice 8 cm thick centred on the Vedde Ash Bed is 10920 ± 24 ¹⁴C yr BP. The most accurate ¹⁴C age of the Vedde Ash from terrestrial plant macrofossils is 10310 ± 50 yr BP. The difference is the ¹⁴C reservoir age for coastal water at the west coast of Norway during the mid‐Younger Dryas and equals 610 ± 55 yr. This is 230 yr older than the reservoir age for the Bølling/Allerød and for the present day in this area. The result supports earlier conclusions of a higher reservoir age for the Younger Dryas in the North Atlantic and Nordic Seas, although our reservoir age of 610 ± 55 yr is a few hundred years younger. This suggests that the ¹⁴C reservoir age at Vedde Ash time may increase from coastal water towards the open North Atlantic and Nordic Seas. Copyright © 2001 John Wiley & Sons, Ltd.     

Water column monitoring near oil installations in the North Sea 2001-2004

Fisheries have been vital to coastal communities around the North Sea for centuries, but this semi-enclosed sea also receives large amounts of waste. It is therefore important to monitor and control inputs of contaminants into the North Sea. Inputs of effluents from offshore oil and gas production platforms (produced water) in the Norwegian sector have been monitored through an integrated chemical and biological effects programme since 2001. The programme has used caged Atlantic cod and blue mussels. PAH tissue residues in blue mussels and PAH bile metabolites in cod have confirmed exposure to effluents, but there was variation between years. Results for a range of biological effects methods reflected exposure gradients and indicated that exposure levels were low and caused minor environmental impact at the deployment locations. There is a need to develop methods that are sufficiently sensitive to components in produced water at levels found in marine ecosystems.     

Dynamic instability of clays: an energy approach

The dynamic instability of any soil is based on the ability to accumulate from cycle to cycle a part of the energy to be dissipated. Using the general thermodynamic approach in combination with high resolution experiments it is possible to analyze the transformations of energy in soil under dynamic loading. Undisturbed specimens of two Norwegian clays, sufficiently different in their engineering properties, were used in a number of undrained cyclic triaxial tests to study the influence of confining stress, coefficient of earth pressure at rest (K₀), dynamic stress amplitude and frequency of loading in the development of instability in the clays. This paper discusses the unit dissipated energy and the unit activation energy as possible energy criteria for evaluation of dynamic instability in soils.     

Assessing and monitoring local and long-range-transported hydrocarbons as potential stressors to fish stocks

The Arctic is poorly described and understood compared to the North Sea and other boreal areas. We need to learn how knowledge obtained at boreal conditions may be applied at Arctic conditions. Increasing activity of the hydrocarbon industry may cause exposure stress from discharges. Within a joint industry research programme (Biosea) we studied how responses in fish from oil exposure may differ at North Sea boreal and Barents Sea Arctic conditions. Hydrocarbon uptake, metabolites, and enzymatic and genotoxic biomarker type of effect responses were measured in cod (Gadus morhua L.). Hydrocarbon metabolites remain longer in fish bile than original hydrocarbons, which are eliminated fast from tissues. The metabolites may be measured to background concentrations. They describe exposure and they constitute a link to other effects. Body burden, biliary polyaromatic hydrocarbon (PAH) metabolite concentration, and quantities of Cytochrome P-450 1A (CYP1A) and DNA adducts increased with oil in water concentration. The extent of biomarker expression was lower for some biomarkers and elimination was slower at the lowest temperature. The results show that several factors have to be accounted for if warm-water biomarker data are to be applied in cold water.     

Diagnosing ocean tracer transport from Sellafield and Dounreay by equivalent diffusion and age

A simple approach for estimating the equivalent diffusion for diagnosing tracer transport is proposed. Two different expressions are derived; one is based directly on an analytical solution of the two-dimensional advection-diffusion equation, the other uses the variance of the tracer distribution. To illustrate some features of the equivalent diffusion and possible applications thereof, idealized releases of passive tracers from the nuclear fuel reprocessing plants at Sellafield in the Irish Sea and Dounreay on the northern coast of Scotland have been simulated with a regional isopycnic co-ordinate Ocean General Circulation Model. Both continuous and pulse releases are considered; the former being representative of the actual historical discharges from the reprocessing plants, the latter resembling an accidental scenario. Age tracers are included to calculate the mean time elapsed since the tracers left their source regions. It is found that in the Nordic Seas the age of tracers from Dounreay is approximately 2 years younger than the age from Sellafield. Although tracers from both sources eventually end up along the same transport routes, significant qualitative differences regarding the dispersion properties are found. It is argued that one single parameter, the equivalent horizontal diffusion, which is estimated to be in the range of 20 56 m^2 s^-1 from Sellafield and 170-485 m^2 s^-1 from Dounreay, determines these differences.     

Effects of chronic exposure to dispersed oil on selected reproductive processes in adult blue mussels (Mytilus edulis) and the consequences for the early life stages of their larvae

Mussels (Mytilus edulis) were continuously exposed to dispersed crude oil (0.015-0.25 mg/l) for 7 months covering the whole gamete development cycle. After 1 month exposure to 0.25 mg oil/l, the level of alkali-labile phosphates (ALP) and the volume density of atretic oocytes in female gonads were higher than those in the gonads of control females, indicating that oil affected the level of vitellogenin-like proteins and gamete development. Spawning of mussels was induced after 7 months oil exposure. Parental oil exposure did not affect subsequent fertilization success in clean seawater but this was reduced in 0.25 mg oil/l. Parental exposure to 0.25 mg oil/l caused both slow development and a higher percentage of abnormalities in D-shell larvae 2 days post-fertilization; reduced growth 7 days post-fertilization. These effects were greatly enhanced when larval stages were maintained at 0.25 mg oil/l. Similar studies are warranted for risk assessment prognosis.     

Phenomenological issues related to strain localization in sensitive clays

A negative second order work, strain softening, is often noticed in contractant material like sensitive clays. Failure in such clays will lead to the formation of localized deformation zone of intense inelastic strain, known as shear band. Conditions, emergence and inclination of shear band has been very well demonstrated in past decades in different manners, however a definite thickness of shear band is still an open question due to several reasons. Mesh dependency, loss of ellipticity is another challenge associated with finite element analyses for strain softening clays. This paper covers a comprehensive review of classical theories of strain localization and associated limitation. Mesh dependency, ill-possed boundary value problem is addressed using finite element simulation examples and experimental results.     

Application of Soft Data in Nodule Resource Estimation

Natural Resources Research - Minerals and metals are of uttermost importance in our society, and mineral resources on and beneath the deep ocean floor represent a huge potential. Deciding whether...