黄土滑坡的基本类型与活动特征

高位黄土滑坡具有高势能、突发性、隐蔽性、滑动速度迅速、威胁范围广、破坏冲击能力强等特点,破坏形式多为摧毁和压埋为主,是黄土地区防灾减灾、工程治理棘手难题。不同的地形地貌类型、地层岩性、水文地质条件、地质构造等对滑坡形成都具有本质上的差异。结合平凉市静宁县仁大镇和天水市麦积区大沟高位黄土滑坡典型实例,通过工程地质测绘、工程地质勘查、无人机高精度航测等技术手段,从空间分布、滑坡特征、成因、运动机理、成灾特点等方面进行了系统研究。结果表明,根据地形地貌归属可分为坡面型和沟谷型高位黄土滑坡,其中平凉市静宁县仁大镇滑坡属于坡面型,以 “土浪” 的形式运动,在运动时间上与滑坡启动具有同周期性和连续性,运动速度迅速,运动顺序为滑体脱离母体→土体滑动→土体堆积;天水市麦积区大沟属于沟谷型,以泥流的形式进行运动,滑坡滑动与堆积体启动在时间上具有一定的滞后性,速度相对前者较缓慢,运动顺序为滑体脱离母体→土体堆积→土体滑动→淤积,其运动、堆积特点和黏性泥石流基本相似。     

Landform‐oriented flow‐routing algorithm for the dual‐structure loess terrain based on digital elevation models

The loess landform in the Loess Plateau of China is with typical dual structure, namely, the upper smooth positive terrain and the lower cliffy negative terrain (P–N terrain for short). Obvious differences in their morphological feature, geomorphological mechanism, and hydrological process could be found in the both areas. Based on the differences, a flow‐routing algorithm that separately addresses the dual‐structure terrain would be necessary to encompass this spatial variation in their hydrological behaviour. This paper proposes a mixed flow‐routing algorithm to address aforementioned problems. First, the loess landform surface is divided into P–N terrains based on digital elevation models. Then, specific catchment area is calculated with the new algorithm to simulate the water flows in both positive and negative terrain areas. The mixed algorithm consists of the multiple flow‐routing algorithm (multiple‐flow direction) for positive areas and the D8 algorithm for negative areas, respectively. The approach is validated in two typical geomorphologic areas with low hills and dense gullies in the northern Shaanxi Loess Plateau. Four indices are used to examine the results, which show that the new algorithm is more suitable for loess terrain in simulating the spatial distribution of water accumulation, as well as in modeling the flow characteristics of the true surface by considering the morphological structures of the terrain. Copyright © 2013 John Wiley & Sons, Ltd.     

Size and spatial distribution of loess slides on the Chinese Loess Plateau

ABSTRACT

The size and spatial distribution of loess slides are important for estimating the yield of eroded materials and determining the landslide risk. While previous studies have investigated landslide size distributions, the spatial distribution pattern of landslides at different spatial scales is poorly understood. The results indicate that the loess slide distribution exhibits a power-law scaling across a range of the size distribution. The mean landslide size and size distribution in the different geomorphic types are different. The double Pareto and inverse gamma functions can coincide well with the empirical probability distribution of the loess slide areas and can quantitatively reveal the rollover location, maximum probability, and scaling exponents. The frequency of loess slides increases with mean monthly precipitation. Moreover, point distance analysis showed that > 80% of landslides are located < 3 km from other loess slides. We found that the loess slides at the two study sites (Zhidan and Luochuan County) in northern Shaanxi Province, China show a significant clustered distribution. Furthermore, analysis results of the correlated fractal dimension show that the landslides exhibit a dispersed distribution at smaller spatial scales and a clustered distribution at larger spatial scales.     

Intra-interstadial environmental changes in Last Glacial loess revealed by molluscan assemblages from the Upper Palaeolithic site of Amiens-Renancourt 1 (Somme,France)

The Amiens-Renancourt 1 site recently yielded one of the most important Upper Palaeolithic human occupations of northern France by the number of flint artefacts and especially by the presence of Venus figurines. All the material comes from a single archaeological layer located in a tundra gley bracketed by loess units. A multi-proxy study combining a detailed stratigraphy, luminescence and radiocarbon datings and high-resolution (5 cm per sample) grain size and molluscan analyses was therefore carried out to reconstruct and date the associated environmental changes and to determine the exact context of the human occupation. The chronological frame thus established supports the correlations of the archaeology-bearing tundra gley and of an underlying arctic brown soil with Greenland interstadials GI-4 and GI-3. Composition changes in the molluscan population enabled the identification of transitional and optimum phases and sub-phases within these two pedogenetic horizons. A conceptual correlation model linking molluscan phases with millennial-scale variations of Greenland ice-core and Sieben Hengste speleothem climate records is proposed. The Human occupation appears contemporaneous to the end of the stadial–interstadial transition of GI-3. Synchronous in Amiens-Renancourt 1 and Nussloch, subsequent micro-gleys may also result from a regional/global forcing. Such a level of detail is unprecedented in a loess sequence.     

The variation of crustal stretching and different modes of rifting along the Australian southern continental margin

The southern margin of Australia is a passive continental margin, formed during a Late Jurassic–Cretaceous rifting phase. The development of this passive margin is mainly associated with extensional processes that caused crustal thinning. In this work, we have measured the amount of extension and the stretching factor (β factor) across seven transect profiles approximately evenly distributed across the margin. The obtained results show that the amount of extension and the β factor along the margin vary from west to east. The lowest amount of extension, low–intermediate β factors and a very narrow margin are observed in the western part with 80 km of extension and is underlain mostly by the Archean Yilgarn Craton and the Albany–Fraser Orogen. The Gawler Craton in the centre of the south Australian margin is another region of low extension and low–intermediate β factor. The largest amount of extension (384 km) and the largest β factor (β = 1.88) are found in the eastern part of the passive margin in an area underlain by Phanerozoic Tasman Orogen units. Our results imply that there is a strong control of the age and thickness of the continental lithosphere on the style of rifting along the Australian passive margin. Rifting of old and cold lithosphere results in a narrow passive margin, with the formation of relatively few faults with relatively wide spacing, while rifting of younger, warmer lithosphere leads to wide rifting that is accommodated by a large number of faults with small spacing.     

甘肃永靖黑方台4·29罗家坡黄土滑坡的特征

2015年4月29日上午,甘肃省永靖县盐锅峡镇黑方台滑坡高频发区的党川村罗家坡同一斜坡处连续发生了2次大规模黄土滑坡,总体积约65×10~4m~3,最大滑距630 m,摧毁14户居民房屋和3家工厂.通过现场详细调查、取样试验、1∶500地形测量、滑坡影像、视频等资料分析,对灌溉引发的罗家坡黄土滑坡的特征、滑动过程、形成机理进行了探讨.结果表明:第1次滑坡经过近2 a变形过程,整体突然失稳,高速远程滑动;第2次滑坡变形时间仅3 h,分块逐步滑动,滑动历时长而过程复杂,总体为低速远程滑动.高陡的地形和强度低、水敏感性强的土体是滑坡发生的基础,黄土台塬区长期农业灌溉是引发因素,大量水体入渗形成了20余米厚的饱和软弱基座,使抗剪强度降低,导致斜坡失稳滑动.黄土滑坡高速远程滑动的主要原因是滑坡剪出口位置高,滑动势能大,释放条件好,剪出口下部陡坡段为主要加速段;前方有开阔的滑动空间且有一定坡度、平缓的滑道;滑体底部饱和软弱黏性土在滑道上持续产生超孔隙水压力、液化等低摩阻效应,是远程滑动的润滑剂.同时,两次滑体间还存在冲击加速和能量传递作用.     

Visualising 30 Years of Population Density Change in Australia’s Major Capital Cities

ABSTRACT

This study uses a novel spatial approach to compare population density change across cities and over time. It examines spatio-temporal change in Australia’s five most populated capital cities from 1981 to 2011, and documents the established and emerging patterns of population distribution. The settlement patterns of Australian cities have changed substantially in the last 30 years. From the doughnut cities of the 1980s, programs of consolidation, renewal and densification have changed and concentrated population in our cities. Australian cities in the 1980s were characterised by sparsely populated, low density centres with growth concentrated to the suburban fringes. ‘Smart Growth’ and the ‘New Urbanism’ movements in the 1990s advocated higher dwelling density living and the inner cities re-emerged, inner areas were redeveloped, and the population distribution shifted towards increased inner city population densities. Policies aimed at re-populating the inner city dominated and the resultant changes are now visible in Australia’s five most populated capital cities. While this pattern has been reported in a number of studies, questions remain regarding the extent of these changes and how to analyse and visualise them across urban space. This paper reports on a spatial method which addresses the limitations of changing statistical boundaries to identify the changing patterns in Australian cities over time and space.     

The past in dust: current trends and future directions in Pleistocene geoarcheology of European loess

Loess is a main archive of Pleistocene landscapes and environments and therefore has an important connection to the preservation and interpretation of Paleolithic sites. In Europe, anthropogenic sites have been found in loess because of past local occupation. At one extreme, sites are well preserved with minimal disturbance often accompanied by embedded proxies to estimate ecological parameters. On the other hand, loess deposits have undergone post-depositional alterations such as weathering, pedogenesis or bioturbation due to changing environmental conditions or other disturbances that obscure anthropogenic sites. We outline the current state of research and connections between Paleolithic archeology and loess research while introducing a series of subsequent regional case studies as part of a special issue. We also make recommendations for future work to incorporate a wider variety of methods to create more robust inferences on hominin and environmental evolution and their connections.