Depositional processes on oceanic island shelves – Evidence from storm‐generated Neogene deposits from the mid‐North Atlantic

Oceanic islands – such as the Azores in the mid‐North Atlantic – are periodically exposed to large storms that often remobilize and transport marine sediments along coastlines, and into deeper environments. Such disruptive events create deposits – denominated tempestites – whose characteristics reflect the highly dynamic environment in which they were formed. Tempestites from oceanic islands, however, are seldom described in the literature and little is known about storm‐related sediment dynamics affecting oceanic island shelves. Therefore, the geological record of tempestite deposits at oceanic islands can provide invaluable information on the processes of sediment remobilization, transport and deposition taking place on insular shelves during and after major storms. In Santa Maria Island (Azores), a sequence of Neogene tempestite deposits was incorporated in the island edifice by the ongoing volcanic activity (thus preserved) and later exposed through uplift and erosion. Because it was overlain by a contemporary coastal lava delta, the water depth at the time of deposition could be inferred, constituting an excellent case‐study to gain insight on the still enigmatic processes of insular shelf deposition. Sedimentological, palaeontological, petrographic and palaeo‐water depth information allowed the reconstruction of the depositional environment of these sediments. The sequence typifies the characteristics of a tempestite (or successive tempestites) formed at ca 50 m depth, in a steep, energetic open insular shelf, and with evidence for massive sediment remobilization from the nearshore to the middle or outer shelf. The authors claim that cross‐shelf transport induced by storm events is the main process of sediment deposition acting on steep and narrow shelves subjected to high‐energetic environments, such as the insular shelves of open‐sea volcanic islands.     

Fundamental aspects of prolonged electrokinetic flows in kaolinites

Electrokinetic flows include the migration of fluid, chemicals, fine particles, bacteria, and electrons through a soil–fluid–chemical system driven by an externally applied direct-current (d.c.) electric field. The promising potential of electrokinetic remediation of contaminated fine-grained soils has stimulated recent interest in the study of electrokinetic flow processes, in particular the impact of a prolonged application of a d.c. electric field on fine-grained soils. The results of a bench-scale laboratory experimental investigation on some of the fundamental aspects of prolonged electrokinetic flows in kaolinites, including gas generation rates at power electrodes, electrochemical behaviour of the soil–fluid–chemical system, time variation of electric current intensity flowing through the soil, pH gradient development in the soil, effects of reservoir chemistry on electro-osmotic fluid volume flow rate and flow direction through the soil, time variation of electro-osmotic volume flow rate, and energy requirements per unit volume of fluid transported, are presented in this paper. Effects of soil type and pore fluid chemistry on these aspects were also studied.     

地球磁尾中重联产生的磁流通管的运动

本文通过MHD理论研究了细磁流通管在二维静止平衡介质中的运动.用地球磁尾中的一维细丝来表示流通管,通过数值模拟可以得到细丝随时间变化的一些性质.重联产生的细丝磁场比周围磁场偶极性更强,运动时表现出了很强的地向流.结果还显示了阿尔芬波、慢激波等MHD波从磁层的赤道面传播到地球电离层上并部分地反射回来.细丝在电离层上的足点的赤道向运动滞后于赤道面上的地向运动.虽然在模拟中细丝的初始等离子体压强低于周围压强,但是当它开始迅速向地球方向运动时,它的等离子体压强很快上升到与周围压强相当,甚至有时候大于周围压强的值.     

Depth–energy and depth–force relationships in open channel flows. II: Analytical findings for power-law cross-sections

In a recent work [Valiani A, Caleffi V. Depth–energy and depth–force relationships in open channel flows: analytical findings. Adv Water Resour 2008;31(3):447–54], the authors analytically inverted the depth–specific energy and depth–total force relationships for flows in open channels with wide rectangular cross-sections.     

稀性泥石流的平均运动速度研究

泥石流的运动速度是泥石流动力学研究中最重要的参数。稀性泥石流是常见也是危害较大的泥石流类型,准确而简洁地计算稀性泥石流的运动速度非常重要。现有的稀性泥石流平均速度经验公式,在使用上和适用地区上还存在一些问题。本文通过分析一系列稀性泥石流观测资料中的体积浓度与稀性泥石流的运动速度和阻力特征的关系,得出了一个新的计算稀性泥石流平均运动速度的经验公式,该公式能适应各种类型的泥石流沟,适用于一般急流的稀性泥石流;对于缓流稀性泥石流,计算值与观测值相比偏大,但很接近;不适用于缓慢稀性泥石流。本文提出的经验公式,使用简洁,计算稳定,与其他方法计算的稀性泥石流平均运动速度很接近。该速度计算经验公式也适用于稀性泥石流堆积扇上游沟道,但对于堆积扇上的速度,计算值偏大,且越往堆积扇的下游,偏差越大。     

Heat transfer between a thermochemical plume channel and the surrounding mantle in the presence of horizontal mantle flow

Heat and mass transfer processes in the conduit of a thermochemical plume located beneath an oceanic plate far from a mid-ocean ridge (MOR) proceed under conditions of horizontal convective flows penetrating the plume conduit. In the region of a mantle flow approaching the plume conduit (in the frontal part of the conduit), the mantle material heats and melts. The melt moves through the plume conduit at the average velocity of flow v and is crystallized on the opposite side of the conduit (in the frontal part of the conduit). The heat and the chemical dope transferred by the conduit to the mantle flow are carried away by crystallized mantle material at the velocity v.The local coefficients of heat transfer at the boundary of the plume conduit are theoretically determined and the balance of heat fluxes through the side of the plume conduit per linear meter of the conduit height. The total heat generation rate, transmitted by the Hawaiian plume into the upper and lower mantle, is evaluated. With the use of regular patterns of heat transfer in the lower mantle, which is modeled on the horizontal layer, heated from below and cooled from above, the diameter of the plume source, the kinematic viscosity of the melt in the plume conduit, and the velocity of horizontal lower-mantle flows are evaluated and the dependences of the temperature drop, viscosity and Rayleigh number for the lower mantle on the diameter of the plume source are presented.     

泥石流颗粒组成的分形特征

1 IntroductionD ebris flow s in certain sense are a process of m ass interchanges through erosion and depositionbetw een the fluid and the sedim ent; and the interchange of m aterial caused change in thestructure of the flow s that can be ultim ately redu…     

The Kwinana Coastal Fumigation Study: III – Meteorological and Turbulence Modelling on Selected Days

The Kwinana Coastal Fumigation Study took place inearly 1995 at Kwinana near Perth in Western Australia.The study involved surface and elevated meteorologicaland plume fumigation measurements in sea-breeze flowsnear the coast, and has yielded a comprehensive dataset that is suitable for assessing meteorological andplume dispersion models. In this paper, wesimulate the meteorology and turbulence on four casestudy days, and compare model results with thedetailed surface and aircraft measurements takenduring the study. These days had surface synopticwinds ranging from southerly to northeasterly, witheither stable or near-neutral temperature profilesover the sea.The model used was based on that developed by Hurley(Boundary-Layer Meteorol. 83, 43–73, 1997), but extended here to allow domain nesting,optional non-hydrostatic simulations, and a vegetativecanopy at the surface. The model was forced bystandard weather service synoptic data, and thesimulations have captured the essential features ofthe strong sea-breeze circulation observed on thesedays. The boundary-layer structure over the sea waspredicted to be near-neutral or stable in agreementwith the observations on the particular day. The windspeed and direction in the sea-breeze flow weregenerally predicted well, although the predictedmaximum inflow speed over the land was a little toohigh. The potential temperature was generallyover-predicted, but temperature gradients agreed well.Predicted turbulence levels in the bottom-half of thethermal internal boundary layer compared well to theobservations, but under-estimated the observations inthe in the upper half of this layer. Near-surfacemeasurements of meteorological variables werepredicted well over the entire diurnal cycle, althoughthe predicted sea-breeze onset was generally tooearly. A quantitative model evaluation for thenear-surface sites showed the model performance to bebetter than that from other studies, with Index ofAgreement (IOA) values of 0.8 (wind speed) and 0.96(temperature), compared with values of 0.5–0.6 (windspeed) and 0.33 (temperature) obtained from otherstudies.The availability of new higher resolution synopticanalyses should obviate the lack of spatial andtemporal resolution in synoptic inputs. Theincorporation of these higher resolution synopticinputs and new parameterisation schemes should improvefuture model performance.     

Pyroclast/snow interactions and thermally driven slurry formation. Part 1: Theory for monodisperse grain beds

Received: 15 March 1999 / Accepted: 9 December 1999     

Circulation and boundary layers in differentially heated rotating stratified fluid

Recent laboratory experiments with rotating stratified water in a cylinder have revealed many of the predictions of linearized, analytic theory. Earlier measurements of the velocity field generated in a cylinder by top heating compared well with theory. Large stratification clearly suppressed Ekman pumping so that the interior velocity field (primarily azimuthal) responded by satisfying no-slip top and bottom boundary conditions without the need for Ekman layers. This interior flow also occupied a boundary layer of greater thickness than the Ekman layer under some conditions. Theory and experiments have now been conducted for sidewall heating. As before, experiment and theory agree well over some parameter ranges. But for some parameters, the flow is unstable. The exact nature of the instability remains poorly understood. The size of one combination of both vertical and horizontal boundary layers is governed by the Rossby radius of deformation multiplied by the square root of the Prandtl number. Sidewall boundary layers and their scales will be reviewed with the present results in mind.