Biogenic silicate accumulation in sediments, Jiaozhou Bay

1 INTRODUCTION Silicate, or silicic acid (H4SiO4), is a very im- portant nutrient in the ocean. Unlike other major nu- trients such as phosphate and nitrate or ammonium, which are needed by almost all marine plankton, silicate is an essential chemical req…     

鱼卡煤田大煤沟组高分辨率层序地层特征及聚煤规律

利用高分辨率层序地层学理论和技术方法,综合地震、测井、岩芯和煤质资料对柴达木盆地北缘鱼卡煤田中下侏罗统大煤沟组地层河湖三角洲沉积体系进行高分辨率层序地层学分析,从中识别出短期、中期、长期3个级别的基准面旋回层序,划分出向上"变深"非对称型、向上"变浅"非对称型及对称型3种短期基准面旋回基本结构类型。依据等时地层对比法则进行不同级次基准面旋回层序的联井对比,建立了大煤沟组的等时地层格架,在等时地层格架内进行了煤层对比,并在等时地层格架内分析了聚煤规律。     

Evaluation of approaches to calculate debris-flow parameters for hazard assessment

Many different runout prediction methods can be applied to estimate the mobility of future debris flows during hazard assessment. The present article reviews the empirical, analytical, simple flow routing and numerical techniques. All these techniques were applied to back-calculate a debris flow, which occurred in 1982 at La Guingueta catchment, in the Eastern Pyrenees. A sensitivity analysis of input parameters was carried out, while special attention was paid to the influence of rheological parameters. We used the Voellmy fluid rheology for our analytical and numerical modelling, since this flow resistance law coincided best with field observations. The simulation results indicated that the “basal” friction coefficients rather affect the runout distance, while the “turbulence” terms mainly influence flow velocity. A comparison of the velocity computed on the fan showed that the analytical model calculated values similar to the numerical ones. The values of our rheological parameters calibrated at La Guingueta agree with data back-calculated for other debris flows. Empirical relationships represent another method to estimate total runout distance. The results confirmed that they contain an important uncertainty and they are strictly valid only for the conditions, which were the basis for their development. With regards to the simple flow routing algorithm, this methods could satisfactorily simulate the total area affected by the 1982 debris flow, but it was not able to directly calculate total runout distance and velocity. Finally, a suggestion on how different runout prediction methods can be applied to generate debris-flow hazard maps is presented. Taking into account the definition of hazard and intensity, the best choice would be to divide the resulting hazard maps into two types: “final hazard maps” and “preliminary hazard maps”. Only the use of numerical models provided final hazard maps, because they could incorporate different event magnitudes and they supplied output-values for intensity calculation. In contrast, empirical relationships and flow routing algorithms, or a combination of both, could be applied to create preliminary hazard maps. The present study only focussed on runout prediction methods. Other necessary tasks to complete the hazard assessment can be looked up in the “Guidelines for landslide susceptibility, hazard and risk zoning” included in this Special Issue.     

Assessment of disaster resilience capacity of hillslope communities with high risk for geological hazards

This study presents a novel preparedness assessment method for assessing hazard mitigation and environmental planning of hillslope communities. A professional questionnaire was utilized to weight each indicator. Communities in Hsinchu, Taichung and Nantou counties with debris flow hazards were taken as study samples. Debris flow risk and landslide susceptibility for each community were determined using Geographic Information System (GIS) technology and logistic regression analysis. Thus, a novel risk assessment method for evaluating disaster resilience capacity of hillslope communities was established. This method was then applied to assess casualties caused by Typhoon Herb in 1996 and Typhoon Mindulle in 2004. Additionally, the analytical results generated by this assessment method were discussed with the aim of developing references for implementation of risk analysis, increasing the effectiveness of disaster mitigation, and reducing future loss of life and property.     

Deep-seated gravitational slope deformations and their influence on consequent mass movements (case studies from the highest part of the Czech Carpathians)

Gravitational spreading of mountain ridges displays primary disequilibrium of flysch mountain areas of the Czech Carpathians. The progression of various types of mass movements is a product of long-term ridge disintegration and is predisposed by the geological structure of the area and the upper Tertiary-Quaternary morphogenesis of the mountain area. Deep-seated slope deformations are spatially interconnected by the occurrence of some other types of slope deformations (e.g. debris flows, debris slides, slumps, rock avalanches, etc.), which pose a considerable risk for the existence of human society. An important causative factor in these dynamically developing hazardous processes is, among other factors, the way in which land has been used in the last three centuries. Therefore, the occurrence of various types of slope deformations is studied in terms of their relation to deep-seated gravitational deformations and in terms of other limiting factors (structural geological, morphological and climatic factors, manmade impacts, etc.). The paper presents several case studies of slope deformations (Velká Čantoryje Mt, Lysá hora Mt, Ropice Mt and Smrk Mt) in the area of the Outer Carpathians within the territory of the Czech Republic and also adverts to some consequences in terms of the socioeconomic structure of the landscape.     

Rain-induced debris and mudflow triggering factors assessment in the Santiago cordilleran foothills,Central Chile

Debris and mudflows are some of the main geological hazards in the mountain foothills of the Chilean capital city of Santiago. There, the risk of flows triggered in the basins of ravines that drain the range into the city increases with time due to the city growth. A multivariate statistical study based on the logistic regression method is presented. The model provides equations that allow the computation of combined meteorological triggering factors associated with a probability of rain-induced flow occurrence. Daily rainfall, accumulated rainfall and the snowfall level, traditionally considered as the relevant factors, are analysed for a 25-year period. The results show a strong relevance of the rainfall on the day of the flow event over the other factors. However, the relatively low probabilities returned for some real flow events suggest that the model does not capture all the significant variables and the problem is more complex than as it has been traditionally assumed, and further investigations are needed to develop predictive models of flow triggering.     

GPS卫星反射信号增强技术研究

本文根据GPS卫星反射信号在海洋参数测量、无源雷达目标探测以及大地测绘中的应用,从天线接收、信号处理运算和多路径信号抵消角度,详细地研究了GPS卫星反射信号增强技术,给出了相应天线和电路结构及信号处理方法,并进行了计算机仿真,结果表明所提出的技术能增强GPS卫星反射信号。     

长江河口洪水造床作用

据多年实测资料统计 ,长江口年径流总量 92 4 0亿m3,年输沙量 4 .86亿t,洪季的径流量和输沙量分别占全年总量的71.7%和 87.2 %。如遇洪水年 ,当洪峰流量超过 6 0 0 0 0m3 s时 ,中、下游河道水位明显抬高而进入防汛警戒状态 ,河床有明显冲淤变化 ;洪峰流量超过 70 0 0 0m3 s时 ,新生汊道及切滩串沟频频出现 ,给河口治理及深水航道开发带来重要的影响。从长江河口河槽演变基本特征及南港、北槽底沙输移强度引证长江洪水在河口地区的造床作用     

Response of the barrier island coastal region of southwestern Nigeria to climate and non-climate forcing

Despite threats emanating from the influence of climate and non-climate forcing on the barrier island coastal region of southwestern Nigeria, the extent of the coastal erosion is poorly understood. We report evidence of coastal erosion and sediment accumulation in the region over a 34-year period (1973–2017), using Landsat imagery at intervals of approximately six years. Landsat image corrections and various water-extraction algorithms were used to systematically delineate coastal erosion and accumulation in the area. The region was subdivided into western and eastern subregions separated by Lagos Harbour. In the west, erosion took place during the periods 1973–1979, 1979–1984, 1990–1999 and 2005–2011, whereas in the east, erosion occurred during 1973–1979, 1990–1999 and 1999–2005. Coastal sediment accumulation occurred in the east during 1979–1984, 1984–1990, 2005–2011 and 2011–2017, whereas gains in the west occurred during 1984–1990, 1999–2005 and 2011–2017. The study revealed substantial net erosion of 1 228.1 ha in the region as a whole, over the full period. Sediment accumulation accompanying the coastal erosion appears to be linked to longshore drift. Erosion between 1973 and 2011 was probably attributable to climate change (storms and tidal conditions), longshore drift, the inflow and outflow of water at Lagos Harbour, coastal morphology and, possibly, human impacts. However, the coastal changes between 2011 and 2017 were more obviously associated with human activities, such as development of the Eko Atlantic construction project. Coastal surveillance, together with the use of environmentally sensitive protective measures, could possibly help to reduce coastal erosion in the region. Careful coastal management practices, including artificial nourishing and the installation of resilient structures (e.g. seawalls), should be undertaken to protect human settlements that are already at risk from sea-level rise.