Settling-velocity distributions and sorting processes on a longitudinal dune: A case study     

Daniel Hartmann  Christian Christiansen 《地球表面变化过程与地形》1988,13(7):649-656

The processes acting on a longitudinal dune are inferred from the response in the area size-sorting characteristics of the sediment of the active layer. The sediment size distributions are determined by settling and are best described by a log-hyperbolic model which provides the most information on size-sorting processes. Size-sorting characteristics are markedly different across the low round-crested part of the dune from cross-sections of the high more sharp-crested part. This results in changes in textural parameters along the lee-side consistent with changes in the lee-side separation vortex. This is the first time that the effect of wind speed up on the lee-side is observed to be reflected in the sediment; it can only be detected with the very sensitive log-hyperbolic parameters.  相似文献   

On some problems about testing stochastic models of the earthquake time series     

Gerassimos A. Papadopoulos 《Natural Hazards》1993,7(2):99-108

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Dynamics of fluvial and slope processes in the changing geomorphic environment of singapore     

Kalyani Chatterjea 《地球表面变化过程与地形》1994,19(7):585-607

The nature and rates of fluvial and slope processes change over time and space as urbanized areas replace forested land in Singapore. Storm-based and time-based data, from undisturbed rainforests, heavily disturbed construction sites, urban grass-covered slopes and an experimental plot, are collected to observe the impact of rainwater on the soil moisture conditions, surface microtopography, runoff generation, sediment movement, and ground lowering in the three different categories of land use. The undisturbed forested environment is characterized by high throughfall (58% of total rainfall) and frequent negative soil moisture suctions. The slow and unconcentrated overland flow during heavy storms is restricted by the forest floor microtopography. No rills develop. Ground lowering is recorded as 3·2–3·4 mm a^?1. But sediment movement is episodic and suspended sediment concentrations in overland flow are 172–222 mg l^?1. During urban construction, gully development is rapid on the bare slopes, runoff generation, voluminous, and sediment-laden discharges (5200–75498 mg l^?1) lead to sediment plumes at channel mouths. Ground lowering rates are measured at 132·4 mm a^?1. Once grass-covered, runoff carries less suspended sediment (800 mg l^?1) and ground lowering rates are reduced, but depend on the condition of the cover, ranging from 0·2 to 8·2 mm a^?1. As urban development continues, environments are altered both in time as well as spatially.  相似文献   

The Evolutionary History of Ore-forming Processes of Metallic Ore Deposits in Northern Guangxi1     

Chen Yuchuan  Mao Jinwen  Wang Ping'an 《《地质学报》英文版》1995,8(2):155-170

Abstract The northern Guangxi region is an important rare metal, rare earth metal and polymetallic metallogenic province. In the region there exist five metallogenic series and two metallogenic subseries, whose metallogenesis shows features of polycyclic spiral evolution throughout the geological history. As far as various cycles are concerned, mantle-derived ore substances were reduced while crust-derived ore substances increased from early to late times; in the whole geological evolutionary history, mantle-derived substances decreased gradually while crust-derived ones increased. Meanwhile ore element associations became more and more varied. In terms of space, mineralization migrated from the old basement outwards, i.e. from west to east during the Precambrian, and from north to south during the Phanerozoic, and again from east to west during the Yanshanian.  相似文献   

Numerical Modelling of Melting Processes and Induced Diapirism In the Lower Crust   总被引：5，自引：0，他引：5  

D. Bittner  H. Schmeling 《Geophysical Journal International》1995,123(1):59-70

The processes of partial melting and magmatic diapirism within the lower crust are evaluated using a numerical underplating model. Fully molten basalt ( T = 1200°C) is emplaced at the Moho beneath a solid granite ( T = 750°C) in order that a melt front grows into the granite. If diapirism does not occur, this melt front in the granite reaches a minimal depth in the crust before (like in the molten basalt) crystallization takes place. the density contrast between the partially molten granite layer and the overlying solid granite can lead to a Rayleigh-Taylor instability (RTI) which results in diapiric rise of the partially molten granite. Assuming a binary eutectic system for both the granite and the underplating basalt and a temperature- and stress-dependent rheology for the granite, we numerically solve the governing equations and find (a) that diapirism occurs only within a certain but possibly realistic range of parameters, and (b) that if diapirs occur, they do not rise to levels shallower than 15 or perhaps 12km. the growth rate depends on the degree of melting and the thickness of the partially molten layer, as well as the viscosity of the solid and the partially molten granite. From a comparison of the growth rate with the velocity of a Stefan front it is possible to predict whether a melt front will become unstable and result in diapiric ascent or whether a partially molten layer is created, which remains at depth. We carry out such a comparison using our thermodynamically and thermomechanically consistent model of melting and diapirism.  相似文献   

CHARACTERISTICS OF TURBULENCE SPECTRA IN DIFFERENT WEATHER PROCESSES UNDER UNSTABLE CONDITIONS^*          下载免费PDF全文

Zhu Wenqin  Zhu Cuijuan  Li Xingsheng 《Acta Meteorologica Sinica》1994,8(3):296-304

In this paper,the data chosen from measurements by supersonic anemometers in Tongxian County of Beijing in 1990 are used to study characteristics of turbulence spectra in precipitation weather.Some turbulence parameters such as turbulence intensity,heat and momentum fluxes,friction velocity,M-O length and stability parameter are calculated and their dependence on turbulence spectra in different stability conditions are analyzed.Some encouraging results are obtained and compared with others' results.  相似文献   

热液成矿作用的一般动力学方程   总被引：3，自引：1，他引：3       下载免费PDF全文

鲍征宇  唐促华 《地球科学》1994,19(3):313-319

分析了热液成矿作用的基本特点和研究现状，推导出热液成矿作用动力学体系的一般方程，并着重讨论了方程中表征热液与围岩之间化学反应的速率项，除目前一般采用动力学实验实测反应速率常数外，作者根据局域平衡原理，认为成矿作用可视为体系内各点随着温度和压力的变化不断重建平衡的过程，可用温度和压力变化时成矿反应的平衡常数的变化速度表征成矿反应的动力学行为，成矿化学反应的速率还可用主要成矿物质的溶解的变化率来表征。  相似文献   

Winds and sand movements in the Namib Sand Sea     

N. Lancaster 《地球表面变化过程与地形》1985,10(6):607-619

Wind regimes in the vicinity of the Namib Sand Sea are high energy unimodal near the coast, becoming bimodal or complex inland. There is an overall decrease in wind energy and sand transport rates from south to north and west to east, such that sand moves from coastal and southern source areas to accumulate in the northern and central parts of the sand sea. Such a pattern can explain much of the observed spatial variability in dune types, sizes, and sediment characteristics and lends support to a climatic model of sand sea formation in this region. Seasonal and daily cycles of wind velocity and direction give rise to episodic sand transport, most of which is generated by winds of moderate velocity and frequency.  相似文献   

Eolian processes in alpine belts of the high Tatra mountains,Poland     

Bogdana Izmailow 《地球表面变化过程与地形》1984,9(2):143-151

Eolian processes were the subject of detailed studies in the high-mountain area of the Tatra Mts. The field investigations in 1975–80 attempted to determine the amount of deflation and eolian deposition and to improve understanding of their mechanism. The net rates of these processes were determined from repeated survey of deflational forms and of eolian deposits. Observations of the mechanism of material displacement were based on field experiments carried out during strong winds. All the investigations were conducted using simple methods and traps. Relationships between the course and intensity of processes and wind conditions and soil properties were obtained.  相似文献   

Slope process change and colluvium deposition in Swaziland: An SEM analysis     

Andrew Goudie  Peter A. Bull 《地球表面变化过程与地形》1984,9(3):289-299

Electron microscope analysis of sixty samples taken from six colluvium sites in Swaziland has shown that the quartz grains exhibit marked edge abrasion in the uppermost beds of exposures. This edge abrasion is lacking in the lower beds in all sections examined and indicates slope process change during colluvium deposition. A model of slope evolution is provided, in which slope erosion progressively brings about more channelling and causes greater surface roughness because of the exhumation of more core stones and differentially weathered rock. This roughness causes increased edge abrasion.  相似文献