SOFTWARE REVIEWS

Electromap World Atlas , Version 1.1. Interactive Population Statistical System , Version 1.0. Jerry W. Wicks and Jose Luiz Pereira de Almeida MATHCAD , Version 2.5. Memory Mate. Micro DEM +, Version 5.21. Peter Guth NCSS – Number Cruncher Statistical System , Version 5.02. Dr. Jerry L. Hintze     

Annual variation of sea surface height,dynamic topography and circulation in the South China Sea

TOPEX/Poseidon satellite altimetry data from 1993 to 1999 were used to study mean annual variation of sea surface height anomaly (SSHA) in the South China Sea (SCS) and to reproduce its climatological monthly surface dynamic topography in conjunction with historical hydrographic data. The characters and rules of seasonal evolution of the SCS dynamic topography and its upper circulation were then discussed. Analyses indicate that annual variation of the SCS large-scale circulation could be divided into four major phases. In winter (from November to February), the SCS circulation is mainly controlled by double cyclonic gyres with domination of the northern gyre. Other corresponding features include the Kuroshio intrusion from the Luzon Strait and the northeastward off-shelf current in the area northwest off Kalimantan Island. The double gyre structure disassembled in spring (from March to April) when the northern gyre remains cyclonic, the southern gyre becomes anticyclonic, and the general circulation pattern shows a dipole. There is no obvious large-scale closed gyre inside the SCS basin in both summer (from May to July) and autumn (from August to October) when the SCS Monsoon Jet dominates the circulation, which flows northeastward across the SCS. Even so, circulation patterns of these two phases diverse significantly. From May to July, the SCS monsoon jet flows northward near the Vietnam coast and bends eastward along the topography southeast off Hainan Island at about 18°N forming an anticyclonic turn. It then turns northeastward after crossing the SCS. From August to October, however, the monsoon Jet leaves the coast of Vietnam and enters interior of the basin at about 13°N, and the general circulation pattern becomes cyclonic. The Kuroshio intrusion was not obvious in spring, summer and autumn. It is suggested from these observations that dynamic adjustment of the SCS circulation starts right after the peak period of the prevailing monsoon.     

Large-scale failures on domes and stratocones situated on caldera ring faults: sand-box modeling of natural examples from Kamchatka, Russia

Edifices of stratocones and domes are often situated eccentrically above shallow silicic magma reservoirs. Evacuation of such reservoirs forms collapse calderas commonly surrounded by remnants of one or several volcanic cones that appear variously affected and destabilized. We studied morphologies of six calderas in Kamchatka, Russia, with diameters of 4 to 12 km. Edifices affected by caldera subsidence have residual heights of 250–800 m, and typical amphitheater-like depressions opening toward the calderas. The amphitheaters closely resemble horseshoe-shaped craters formed by large-scale flank failures of volcanoes with development of debris avalanches. Where caldera boundaries intersect such cones, the caldera margins have notable outward embayments. We therefore hypothesize that in the process of caldera formation, these eccentrically situated edifices were partly displaced and destabilized, causing large-scale landslides. The landslide masses are then transformed into debris avalanches and emplaced inside the developing caldera basins. To test this hypothesis, we carried out sand-box analogue experiments, in which caldera formation (modeled by evacuation of a rubber balloon) was simulated. The deformation of volcanic cones was studied by placing sand-cones in the vicinity of the expected caldera rim. At the initial stage of the modeled subsidence, the propagating ring fault of the caldera bifurcates within the affected cone into two faults, the outermost of which is notably curved outward off the caldera center. The two faults dissect the cone into three parts: (1) a stable outer part, (2) a highly unstable and subsiding intracaldera part, and (3) a subsiding graben structure between parts (1) and (2). Further progression of the caldera subsidence is likely to cause failure of parts (2) and (3) with failed material sliding into the caldera basin and with formation of an amphitheater-like depression oriented toward the developing caldera. The mass of material which is liable to slide into the caldera basin, and the shape of the resulted amphitheater are a function of the relative position of the caldera ring fault and the base of the cone. A cone situated mostly outside the ring fault is affected to a minor degree by caldera subsidence and collapses with formation of a narrow amphitheater deeply incised into the cone, having a small opening angle. Accordingly, the caldera exhibits a prominent outward embayment. By contrast, collapse of a cone initially situated mostly inside the caldera results in a broad amphitheater with a large opening angle, i.e. the embayment of the caldera rim is negligible. The relationships between the relative position of an edifice above the caldera fault and the opening angle of the formed amphitheater are similar for the modeled and the natural cases of caldera/cone interactions. Thus, our experiments support the hypothesis that volcanic edifices affected by caldera subsidence can experience large-scale failures with formation of indicative amphitheaters oriented toward the caldera basins. More generally, the scalloped appearance of boundaries of calderas in contact with pre-caldera topographic highs can be explained by the gravitational influence of topography on the process of caldera formation.Editorial responsibility: J. Stix     

Interpretation from large-scale shake table tests on piles undergoing lateral spreading in liquefied soils

Results from a benchmark test on full-scale piles are used to investigate the response of piles to lateral spreading. In the experiment, two single piles, a relatively flexible pile that moves together with the surrounding soil and a relatively stiff pile that does not follow the ground movement have been subjected to large post-liquefaction ground displacement simulating piles in laterally spreading soils. The observed response of the piles is first presented and then the results are used to examine the lateral loads on the pile from a non-liquefied soil at the ground surface and to evaluate the stiffness characteristics of the spreading soils. The measured ultimate lateral pressure from the crust soil on the stiff pile was about 4.5 times the Rankine passive pressure. The back-calculated stiffness of the liquefied soil was found to be in the range between 1/30 and 1/80 of the initial stiffness of the soil showing gradual decrease in the course of lateral spreading.     

Three-dimensional non-cohesive earthen dam breach model. Part 2: Validation and applications

Our proposed three-dimensional dam breach model is tested using one field test from the European Community funded IMPACT project. Results show that this three-dimensional model accurately predicts the peak breach discharge and final breach width for this case. It is shown that the three-dimensional model is capable of simulating the breaches that develop in different locations along a hypothetical long non-cohesive dam while accounting for variations in the natural valley topography, including symmetrical and asymmetrical settings. Our results show that both the breach location and reservoir shape have a significant effect on the peak breach discharge and the outflow hydrograph shape. Different inflow hydrographs were found not to significantly change the peak breach discharge rate for the hypothetical reservoir and spillway. Comparisons with laboratory and field dam breach tests and one historically breached dam show that the real shape of the breach channel during the breach process is successfully modeled.     

地形对山地森林景观格局多尺度效应

以TM影像和野外调查为数据源,3S技术为研究手段,分析了泰山的森林景观结构、景观异质性动态变化以及景观格局高程的分异。选择相对高差较大的区域设计了8个地形方位,采用3种由连续样方组成的辐射状样带,在遥感影像上进行信息采集,研究地形对森林景观格局的多尺度效应。分析了10个地形因子对森林景观分异的影响。结果表明:1.在景观尺度上,地形方位、海拔、山地类型是影响森林景观镶嵌格局的控制因素,坡向、坡度是重要因素,坡形、坡位是不明显因素;2.以TM影像为信息源,从森林景观分异和梯度分析上,首先要考虑海拔坡向指数、坡形坡位指数和海拔,并立足于地形方位;3.地形主要因子间存在着稳定的显著正相关,明显地对森林分异多尺度格局具有较强的综合解释能力,不论尺度大小对森林景观分异贡献率可稳定地达到70%左右,其解释量随尺度增大而增加,但可解释性减弱。