The aerodynamic behaviour of volcanic aggregates

A large proportion of solid material transported within the atmosphere during volcanic eruptions consists of particles less than 500 m in diameter. The majority of these particles become incorporated into a wide range of aggregate types, the aerodynamic behaviour of which has not been determined by either direct observation or in the laboratory. In the absence of such data, theoretical models of fallout from volcanic plumes make necessarily crude assumptions about aggregate densities and fall velocities. Larger volcanic ejecta often consists of pumice of lower than bulk density. Experimental data are presented for the fall velocities of porous aggregates and single particles, determined in systems analogous to that of ejecta falling from a volcanic plume. It is demonstrated that the fall of aggregates may be modelled in identical fashion to single particles by using a reduced aggregate density dependent on the porosity, and a size corresponding to an enclosing sphere. Particles incorporated into aggregates attain a substantially higher fall velocity than single particles. This is due to the larger physical dimensions of the aggregate, which overcomes the effect of lower aggregate density. Additionally, the internal porosity of the aggregate allows some flow of fluid through the aggregate and this results in a small increase in fall velocity. The increase in fall velocity of particles incorporated into aggregates, rather than falling individually, results in the enhanced removal of fine material from volcanic plumes.     

Potentials of monitoring rock fall hazards by GPR: considering as example the results of Salzburg

A part of the IUGS-UNESCO research project "Landslide Hazard Assessment and Cultural Heritage" (IGCP-Project No. 425) includes testing the application of geophysical methods for assessing hazard risks to people and cultural assets. In this work, Austria contributed with a study on the assessment of rock-fall hazards. As the Old Town of Salzburg is a prime example of such hazards, systematic GPR-measurements were made on major rock surfaces. The aim of the exploration with GPR was to assess the potential of the method for monitoring rock walls. That is, whether structures in the rock mass which could become important when considering the risk of a rock fall, can be imaged. To manage this problem successfully, moving the antenna over the rough rock surface was made as regular as possible. The effects of vegetation lifting the antenna from the rock surface and of overhanging regions could not be avoided. Due to the loss of coupling of the antenna and the change of radiation pattern, some interference of the records occurred. Thus, only after processing could it become clear which reflections came from within the rock. A three-dimensional survey of discontinuities in the rock requires accurate mapping of the rock surface by photogrammetric methods, to get a digital terrain model for the analysis of the GPR records. The results of repeated measurements have proved to be of essential relevance. They have shown that it is possible to reveal changes with time. For the interpretation of such observations, modeling is a very useful tool.     

利用三架飞机联合探测资料分析层积混合云催化物理效应

利用2009年4月18日三架飞机联合探测层积混合云资料,结合MICAPS再分析资料、雷达、卫星及地面台站资料等,在准确区分自然云区与催化响应区的基础上,对这次降水性层积混合云的微结构和催化物理响应进行了深入研究。结果表明:云上部(4 800 m层,距云顶1 700 m,距云底3 000 m)累积了云中大部分的过冷水,是云内发展强盛区;云上部嵌入式积云区温度低于周围层云区2℃,积云区含水量分布不均,最大值为1.5 g/m~3,标准差为0.4 g/m~3,而层云区含水量最大值和标准差分别为0.6 g/m~3和0.15 g/m~3,积云区和层云区的云滴谱峰值直径分别为25μm和15μm,云滴数浓度的量级分别为102cm-3和101cm-3。对催化云而言,此次联合探测在4 800 m层捕捉到嵌入式积云区的催化响应,人工播撒Ag I会促进该层云的消散过程,催化后1 h内云区占比由71%降至13%,云中液态含水量持续减少且趋于均匀分布,催化后10 min与20 min云中含水量的最大值分别为1.0 g/m~3和1.5 g/m~3,标准差为0.3 g/m~3和0.15 g/m~3,凇附与聚合增长为主要冰相微物理过程,云滴谱先变窄,后因H-M冰晶凇附繁生而拓宽;在云的中下层则受上层催化影响而产生旺盛云区,10 min内该层云区范围显著扩大,云滴及冰相粒子尺度均增加一倍,同时旺盛云区自上而下扩展。     

Paleoearthquake Investigation along the Chenghai Fault Zone since ~500 ka, Southeast Margin of the Tibetan Plateau

The Chenghai fault zone is located in the Sichuan–Yunnan rhombus block, which is surrounded by the Honghe River, Xianshuihe–Xiaojiang, and Jinsha River fault zones. As a mid-continental active fault, it is one of the most important seismogenic fractures in the southeast margin of the Tibetan Plateau. Geological seismic study is an important supplement to the historical seismic record; therefore, identification of paleoearthquake events in this region is of great significance to reveal the pattern and mechanism of earthquake development. In this study, detailed investigation has been carried out on the earthquake traces that formed in the Quaternary sediments in the Jinsha River section of the Chenghai fault zone, and samples for dating chronology testing were also collected. Many paleoearthquake traces were discovered in the field, including earthquake fissions, dammed lake sediments and landslides, earthquake-generated rock falls, seismic faults, and sand liquefaction veins. The collected samples were tested using optically stimulated luminescence, electron-spin resonance, and U-series methods. A total of 68 chronological samples were dated, combined with the results of field investigations, and 10 large paleoearthquake events were discovered in this region since 500 ka, which are at approximately 450, 400, 345, 300, 250, 190, 155, 105, 75, and 25 ka. Ten tectonic activity periods that produced multiple paleoearthquake events were identified since 500 ka. This study identifies paleoearthquake events in longer scales, larger spaces, and more extensive sediments, which provides new perspectives and new ideas for paleoearthquake research.     

南四湖清障工程行洪分析

根据1999年竣工的南四湖清障工程实施前后的水文观测资料,从湖区水面比降、洪水落平时间等要素的变化,进行了湖区行洪分析。通过分析发现:工程的实施,降低了卡口段的水位,减小了工程位置以下的湖区水面比降,缩短了湖区行洪时间,加快了洪水宣泄,使入湖河道洪水尽快下泄,提高了湖区行洪能力,分析成果对南四湖防洪调度以及进一步做好湖内清障工程,具有重要的参考价值。     

Computer simulation-based evaluation of rock fall roll-out distances for catchment ditch design in Ohio,USA

Catchment ditches along highways are designed to contain hazardous rock falls from cut slopes. RocFall, a rock fall simulation software, was used to evaluate the maximum roll-out distances of rock falls in order to determine rock fall catchment ditch dimensions for Ohio's cut slopes. Based on stratigraphy, cut slopes in Ohio were classified into five types. The parameters required for simulation process included friction angle between rock fall and slope face, coefficient of normal and tangential restitution, slope roughness and average weight of rock falls. A total of 400 simulations were performed for various slope heights, slope angles and catchment ditch slopes. The results are useful in designing catchment ditch for Ohio and neighbouring states where the stratigraphy consists of sub-horizontal, inter-layered hard and soft rock units. The widely used guidelines developed by the Oregon Department of Transportation do not work well for Ohio's stratigraphy.     

鄂尔多斯沙区飞播杨柴固沙技术的研究

通过对鄂尔多斯沙区飞播杨柴固沙技术的研究与实践,总结了一套行之有效的飞播技术以及飞播植被管理和利用的措施。结果是：①鄂尔多斯沙区飞播杨柴固沙技术是选择适宜的沙地类型;确定适宜与杨柴混播植物及播量是,杨柴６．７５ｋｇ／ｈｍ２＋籽蒿３．０ｋｇ／ｈｍ２＋沙打旺（草木栖）１．５ｋｇ／ｈｍ２,适宜播期是５月下旬至６月上中旬。②播后管理措施是及时防治鼠、兔、虫、病害,播区围封管护,对杨柴幼苗设置防蚀沙障,幼苗、根蘖苗移稠补稀,适时平茬更新。③飞播杨柴植被合理利用是选择缓起伏沙地建立采种地,作为打草场一年刈割１次为宜,杨柴枝叶加工后是舍饲家畜的饲料,播区植被盖度６０％时,可在冬春季放牧利用。     

福建建瓯万木林柑橘与锥栗凋落物数量、组成及动态

2010年1-12月,对福建省建瓯市万木林保护区内的柑橘（CitrusreticulataBlanco）和锥栗（Castaneahenryi）凋落物的组成及动态进行观测研究,结果表明：柑橘和锥栗的年凋落物量分别为2315．47±149．02kg·hm^-2·a^-1和2414．62±211．05kg·hm^-2·a^-1,凋落物均以落叶为主,分别占到年总凋落物量的57．6％和50．7％,落花和落果在凋落物中所占比例较大;经方差分析检验,柑橘和锥栗的落枝、落花和杂物差异显著（P〈0．05）,其他组分差异不显著;柑橘与锥栗凋落物量季节变化曲线均呈双峰型,柑橘凋落物量在3月和7月出现2次较大峰值,而锥栗凋落物量峰值则出现在6月和11月．     

播种期对栽培甘草越冬性及根系生长特征的影响

甘草不同播种期的试验研究表明：甘草的适宜播种期较长,4月下旬至8月初播种都能较安全地越冬,但4月下旬至5月中旬播种完全安全,越冬率达100%,6月上旬至8月初播种的甘草抗寒能力有所下降,有一部分植株在越冬时死亡,但越冬率仍在90%以上。不同播种期播种的甘草越冬后植株的地上茎和根系都能正常生长发育,而且播种期晚的甘草在根长和根粗生长特征上表现出“追长”和“追粗”效应,光合产物也有明显向根系转移的特征。