Morphology and internal structure of a dormant landslide in a hilly area: The Collinabos landslide (Belgium)     

M. Van Den Eeckhaut  G. Verstraeten  J. Poesen 《Geomorphology》2007,89(3-4):258-273

This study attempts to reconstruct the history of the Collinabos landslide, a landslide with a fresh morphology that is representative for more than 150 dormant, deep-seated (> 3 m) landslides in the Flemish Ardennes (Belgium). A geomorphological map was created based on LIDAR (Light Detection and Ranging)-derived maps and detailed field surveys. The map showed that the landslide consisted of three zones with significant differences in surface topography. The northern landslide zone 1 is characterised by at least five reverse slopes, whereas zones 2 and 3, the southern landslide zones, have only two reverse slopes and a convex foot. Electric resistivity profiles measured in zones 1 and 2 revealed that the differences in surface topography were not related to differences in internal structure as both parts of the landslide were initiated as a rotational earth slide with a surface of rupture at 15 m deep, where the displaced material broke apart in two blocks. However, two shear surfaces of reactivations within landslide debris were only distinguished in the accumulation area of zone 1. The observed differences in surface morphology can be caused by a temporary conversion of a forest into cropland in zone 2. It is suggested that reverse slopes of smaller reactivations within landslide debris were obliterated during the agricultural activities. AMS radiocarbon dating of organic material found in ponds located in reverse slopes generally resulted in relatively recent dates (i.e. 1400–1950 Cal AD) suggesting that several of the small local reactivations occurred in that period. One dating at 8700–8440 Cal BP of organic matter collected in a reverse slope in zone 1 suggests that an initiation under periglacial conditions cannot be excluded for the Collinabos landslide. By combining different technologies, this study provides valuable information for a better understanding of dormant landslides.  相似文献   

Thermal surface characteristics of coal fires 1 results of in-situ measurements     

Jianzhong Zhang  Claudia Kuenzer   《Journal of Applied Geophysics》2007,63(3-4):117-134

Natural underground coal fires are fires in coal seams occurring subsurface. The fires are ignited through a process named spontaneous combustion, which occurs based on a natural reaction but is usually triggered through human interaction. Coal mining activities expose coal to the air. This leads to the exothermal oxidation of the carbon in the coal with the air's oxygen to CO₂ and – under certain circumstances – to spontaneous combustion. Coal fires occur in many countries world wide – however, currently the Chinese coal mining industry faces the biggest problems with coal fires. Coal fires destroy the valuable resource coal and furthermore lead to many environmental degradation phenomena such as the deterioration of surrounding vegetation, land subsidence and the emission of toxic gasses (CO, N₂O). They additionally contribute to the emission of green house relevant gasses such as CO₂ and CH₄ to the atmosphere.In this paper we present thermal characteristics of coal fires as measured in-situ during a field campaign to the Wuda coal fire area in south-central Inner Mongolia, China. Thermal characteristics include temperature anomaly measurements at the surface, spatial surface temperature profiles of fire areas and unaffected background areas, diurnal temperature profiles, and temperature measurements inside of coal fire induced cracks in the overlying bedrock. For all the measurements the effects of uneven solar heating through influences of slope and aspect are considered.Our findings show that coal fires result in strong or subtle thermal surface anomalies. Especially the latter can easily be influenced by heating of the surrounding background material through solar influences. Temperature variation of background rocks with different albedo, slope, aspect or vegetation cover can substantially influence the detectability of thermal anomalies. In the worst case coal fire related thermal anomalies can be completely masked by solar patterns during the daytime. Thus, night-time analysis is the most suitable for thermal anomaly mapping of underground coal fires, although this is not always feasible. The heat of underground coal fires only progresses very slowly through conduction in the rock material. Anomalies of coal fires completely covered by solid unfractured bedrock are very weak and were only measured during the night. The thermal pattern of underground coal fires manifested on the surface during the daytime is thus the pattern of cracks and vents, which occur due to the volume loss underground and which support radiation and convective energy transport of hot gasses. Inside coal fire temperatures can hardly be measured and can only be recorded if the glowing coal is exposed through a wider crack in the overlaying bedrock. Direct coal fire temperatures measured ranged between 233 °C and 854 °C. The results presented can substantially support the planning of thermal mapping campaigns, analyses of coal fire thermal anomalies in remotely sensed data, and can provide initial and boundary conditions for coal fire related numerical modeling.In a second paper named “Thermal Characteristics of Coal Fires 2: results of measurements on simulated coal fires” [Zhang J., Kuenzer C., Tetzlaff A., Oettl D., Zhukov B., Wagner W., 2007. Thermal Characteristics of Coal Fires 2: Result of measurements on simulated coal fires. Accepted for publication at Journal of Applied Geophysics. doi:10.1016/j.jappgeo.2007.08.003] we report about thermal characteristics of simulated coal fires simulated under simplified conditions. The simulated set up allowed us to measure even more parameters under undisturbed conditions — especially inside fire temperatures. Furthermore we could demonstrate the differences between open surface coal fires and covered underground coal fires. Thermal signals of coal fires in near range thermal remotely sensed imagery from an observing tower and from an airplane are presented and discussed.  相似文献   

Application of wavelet transformation to determine wavelengths and phase velocities of gravity waves observed by lidar measurements     

R. Werner  K. Stebel  G.H. Hansen  U. Blum  U.-P. Hoppe  M. Gausa  K.-H. Fricke 《Journal of Atmospheric and Solar》2007,69(17-18):2249

During the last two decades, important advances have been made in the investigation of gravity waves. However, more efforts are needed to study certain aspects of gravity waves. In the real atmosphere, gravity waves occur with different properties at different altitudes and, most often, simultaneously. In this case, when there is more than one dominant wave, the determination of gravity wave characteristics, such as the vertical wavelength and the phase velocity, is difficult. The interpretation of temperature perturbation plots versus the altitude and time as well as the application of the Fourier spectral analysis can produce errors.Exact knowledge of the wave characteristics is important both for determination of other characteristics, for example, the horizontal wave components, and for study of wave climatology. The wavelet analysis of vertical temperature profiles allows one to examine the wave's location in space. Up to now, gravity waves have been studied mainly by continuous wavelet transformation to determine dominant waves. We apply wavelet analysis to a time series of temperature profiles, observed by the ALOMAR ozone lidar at Andoya, Norway, and by the U. Bonn lidar system at ESRANGE, Sweden, both for determination of the dominant waves and for specifying the vertical wavelengths and the vertical component of the phase velocities. For this purpose, the wavelet amplitude spectra and the wavelet phase spectra are filtered and Hovmöller diagrams for dominant wavelengths are constructed. The advantage of this type of diagrams is that they give clear evidence for the localization of the dominant waves in space and time and for the development of their phase fronts.  相似文献   

Velocity and turbulence variations at the edge of saltmarshes     

U. Neumeier 《Continental Shelf Research》2007

Saltmarsh vegetation significantly influences tidal currents and sediment deposition by decelerating the water velocity in the canopy. In order to complement previous field results, detailed profiles of velocity and turbulence were measured in a laboratory flume. Natural Spartina anglica plants were installed in a 3 m length test section in a straight, recirculating flume. Different vegetation densities, water depths and surface velocities were investigated. The logarithmic velocity profile, which existed in front of the vegetation, was altered gradually to a skimming-flow profile, typical for submerged saltmarsh vegetation. The flow reduction in the denser part of the canopy also induced an upward flow (the current was partially deflected by the canopy). The skimming flow was accompanied by a zone of high turbulence co-located with the strongest velocity gradient. This gradient moved upward and the turbulence increased with distance from the edge of the vegetation. Below the skimming flow, the velocity and the turbulence were low. The structure of the flow in the canopy was relatively stable 2 m into the vegetation. The roughness length (z₀) of the vegetation depends only on the vegetation characteristics, and is not sensitive to the current velocity or the water depth. Both the reduced turbulence in the dense canopy and the high turbulence at the top of the canopy should increase sediment deposition. On the other hand, the high turbulence zone just beyond the vegetation edge and the oblique upward flow may produce reduced sedimentation; a phenomenon that was observed near the vegetation edge in the field.  相似文献   

LISPB revisited: a new look under the Caledonides of northern Britain     

P. J. Barton 《Geophysical Journal International》1992,110(2):371-391

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康普顿化的计算-推广的Kompaneets方程与Monte Carlo方法比较     

刘当波  凌家杰  陈磊  尤峻汉  HUA Xin-Min 《天文学报》2003,44(3):286-301

在X射线天文学以及辐射物理学中,当硬X射线穿过" 冷"的等离子体时所发生的Compton软化是一种重要的辐射转移过程.简要介绍推广的Kompaneets方程,该方程在hv〈mec2及kTe〈mec2较宽松的条件下广泛成立,因此不仅能处理Compton硬化过程,而且也适用于Compton软化过程,后者在目前快速发展的X射线和γ射线天文学中十分重要.基于此方程,我们对天体物理中4种常见辐射谱(Gauss型发射谱线、黑体辐射谱、幂律辐射谱和热轫致辐射谱)在Compton软化情况下的谱演化进行了数值求解,并同Monte Carlo模拟结果做比较,证实了推广的Kompaneets方程的正确性和有效性.最后指出此方程在X射线天文学和γ射线天文学中的重要意义和潜在应用.  相似文献   

Mode Identification from Line Profiles using the Direct Fitting Technique     

Luis A. Balona 《Astrophysics and Space Science》2003,284(1):121-124

The method of moments and the direct fitting method are the onlyspectroscopic methods of mode identification which allow a determination ofall pulsational parameters. The pulsation parameters are required to predictthe light amplitude and phase which can be important discriminants in modeidentification. The direct fitting method has several advantages over themethod of moments. It is not restricted to low spherical harmonic degree or form of the eigenfunction and is not sensitive to the placement of the continuum. In the last few years the method has been applied to several different types of stars. We briefly describe the method and give someexamples of its application.  相似文献   

基于电磁感应仪的表聚型土壤盐渍剖面特征解译研究   总被引：5，自引：0，他引：5  

杨劲松  姚荣江 《水文地质工程地质》2007,34(5):67-72

针对目前黄河三角洲地区存在的土壤盐渍化问题,以该地区分布最广泛的表聚型盐分剖面类型为研究对象,运用磁感大地电导率仪EM38,建立了磁感式表观电导率和土壤盐分之间的(多元)回归模型,在分析土壤盐分剖面分布特征的基础上提出了指数衰减模型,并运用该模型对盐分剖面进行了参数拟合和验证。结果表明:磁感式表观电导率EMh和EMv呈极显著的线性相关,土壤盐分在垂直方向上的变异主要表现在表层0~25cm的深度范围内。统计分析和Friedman检验结果表明,回归模型和指数衰减模型均具有较好的拟合结果和预测效果,二者的预测精度差异也不显著,表明本文提出的指数衰减模型不仅能降低待估参数的数量、提高土壤盐分剖面磁感式解译的实用性,同时还具有较高的预测精度。该研究结果为利用电磁感应仪快速、精确地进行土壤盐分预测以及盐分剖面解译提供了一定的理论参考和实践依据。  相似文献   

Nutrient dynamics in Mediterranean temporary streams: A case study in Pardiela catchment (Degebe River, Portugal)   总被引：1，自引：0，他引：1  

Ana Isabel Lilleb  Manuela Morais  Pedro Guilherme  Rita Fonseca  Antnio Serafim  Ramiro Neves 《Limnologica》2007,37(4):337-348

Most of the streams in the Mediterranean region are temporary, following predictable seasonal of flooding and drying, with a transition from lotic conditions to shallow lentic conditions. The goal of our study was to assess the nitrogen and phosphorus dynamics in channel-bed processes of temporary streams between floods. Results show that, during winter, temperatures ranged between 9.5 and 11.2 °C and oxygen concentration ranged from 8.0 to 9.5 mg L⁻¹, whereas, during summer, temperatures varied between 21.2 and 26.8 °C and oxygen between 1.2 and 5.3 mg L⁻¹, with oxygen depletion in the pools during the night. The nitrate concentrations were far more abundant during winter (February), while ammonium concentration increased after stream fragmentation into pools (especially in July when oxygen depletion conditions favoured ammonification). Results on sediment profiles showed that the most active sediment layers for NH₄-N are the top 2–3 cm, corresponding to the sediment depositional sites of the stream. Phosphate concentrations had larger variability, yet concentrations decreased from winter to spring and increased again in summer, when the shallow water pools were formed. Sediment profiles at the sediment depositional sites showed that PO₄-P was more dynamic in the first 6 cm.

In Mediterranean temporary streams, nutrient dynamics vary seasonally, as the system transits from lotic conditions to shallow lentic conditions, evidencing the regeneration of nutrients from organic and inorganic matter during the flow cessation period.  相似文献   

Evolution of the eastern margin of Korea: Constraints on the opening of the East Sea (Japan Sea)   总被引：2，自引：2，他引：2  

Han-Joon Kim  Gwang Hoon Lee  Hyeong-Tae Jou  Hyun-Moo Cho  Hai-Soo Yoo  Gun-Tae Park  Ji-Soo Kim 《Tectonophysics》2007,436(1-4):37-55

We interpreted marine seismic profiles in conjunction with swath bathymetric and magnetic data to investigate rifting to breakup processes at the eastern Korean margin that led to the separation of the southwestern Japan Arc. The eastern Korean margin is rimmed by fundamental elements of rift architecture comprising a seaward succession of a rift basin and an uplifted rift flank passing into the slope, typical of a passive continental margin. In the northern part, rifting occurred in the Korea Plateau that is a continental fragment extended and partially segmented from the Korean Peninsula. Two distinguished rift basins (Onnuri and Bandal Basins) in the Korea Plateau are bounded by major synthetic and smaller antithetic faults, creating wide and considerably symmetric profiles. The large-offset border fault zones of these basins have convex dip slopes and demonstrate a zig-zag arrangement along strike. In contrast, the southern margin is engraved along its length with a single narrow rift basin (Hupo Basin) that is an elongated asymmetric half-graben. Analysis of rift fault patterns suggests that rifting at the Korean margin was primarily controlled by normal faulting resulting from extension rather than strike-slip deformation. Two extension directions for rifting are recognized: the Onnuri and Hupo Basins were rifted in the east-west direction; the Bandal Basin in the east–west and northwest–southeast directions, suggesting two rift stages. We interpret that the east–west direction represents initial rifting at the inner margin; while the Japan Basin widened, rifting propagated southeastward repeatedly from the Japan Basin toward the Korean margin but could not penetrate the strong continental lithosphere of the Korean Shield and changed the direction to the south, resulting in east–west extension to create the rift basins at the Korean margin. The northwest–southeast direction probably represents the direction of rifting orthogonal to the inferred line of breakup along the base of the slope of the Korea Plateau; after breakup the southwestern Japan Arc separated in the southeast direction, indicating a response to tensional tectonics associated with the subduction of the Pacific Plate in the northwest direction. No significant volcanism was involved in initial rifting. In contrast, the inception of sea floor spreading documents a pronounced volcanic phase which appears to reflect asthenospheric upwelling as well as rift-induced convection particularly in the narrow southern margin. We suggest that structural and igneous evolution of the Korean margin, although it is in a back-arc setting, can be explained by the processes occurring at the passive continental margin with magmatism influenced by asthenospheric upwelling.  相似文献