The landslide hazard and human vulnerability in La Paz City, Bolivia

Landslides in the city of La Paz, Bolivia are complex in space and time. Their distribution within the city is differentiated by geographical variations in slope gradient, the nature of overlying surface deposits, and drainage density patterns. When mapped, the distribution of the most landslide-prone locations in the city coincides with the most mobile surface deposits on the higher and steeper slopes of the city. The timing of landslides is triggered when slope materials become saturated with moisture by rainfall, stream water, water seepage from high surrounding water tables, and from domestic sources. Landslide frequencies over the last 40 years show the role of inter-annual variations in summer rainfalls, especially the late summer period (Jan–Mar), and rising water tables connected to Lake Titicaca. Associations with ENSO events, both warm (El Nino) and cold (La Nina), prove negative, pointing to the importance of moisture sources from the north, south and east (Amazon) but not from the west (Pacific). The most vulnerable group exposed to the landslide hazard comprise the inhabitants of the self-built informal housing areas who occupy the more elevated steeper slopes of the northern part of the city. But societal vulnerability to earth movement in the city is widespread and interconnected. Higher income groups in the southern part of the city are affected by slower, if less dramatic, forms of land failure, and rich housing in downstream areas of the city are impacted by flash flooding encouraged by deforestation on the northern hill slopes where the poor live. Two case studies highlight the vulnerability and plight of the inhabitants of the self-built settlements in the aftermath of a major landslide, and a brief discussion of hazard mitigation and the importance of building hazard resilient communities concludes the paper.     

Mapping landslide susceptibility in Travis County, Texas, USA

A geographic information system (GIS) was used to construct a landslide hazard map for Travis County, Texas. The County is experiencing rapid growth, and development has encroached into unstable terrain that is vulnerable to landslides. Four layers of data were superimposed to create the landslide hazard map. Slope was given the most emphasis, followed by geology, vegetation, and proximity to faults. The final map shows areas of low, medium, and high landslide susceptibility. Areas of high susceptibility occupy stream and reservoir banks, rock escarpments, and agricultural land. The landslide hazard map can be a useful geologic criterion for land use planning. Planners can use the map to allocate appropriate land uses to unstable terrain, and to identify existing structures at risk from landslide activity. The methods presented in this paper can be adapted to other counties in the U.S. and elsewhere. Results of this study suggest that geographic information systems can effectively compile and overlay several data layers relevant to landslide hazards.     

Using earthquakes to assess lichen growth rates

Botanists make yearly measurements of lichen sizes that describe highly variable radial expansion of young, and old, Rhizocarpon subgenus Rhizocarpon that is a function of thallus size and age. Such non‐uniform growth would negate use of lichens to date geomorphic events, such as landslides and moraines, of the past 1000 years. Fortunately, many crustose lichens tend toward circular shapes, which can be achieved only when overall uniform radial growth prevails. Largest lichen measurements on rockfall blocks that accumulate incrementally as hillslope talus in earthquake‐prone California plot as distinct peaks in frequency distributions. Rockfall surface‐exposure times are known to the day for historical earthquakes and to the year where mass movements damage trees. Lichenometry consistently dates regionally synchronous rockfall events with an accuracy and precision of ±5 years. Only historical records and tree‐ring dating of earthquakes are better. The four crustose lichens used here have constant long‐term growth rates, ranging from 9.5 to 23.1 mm per century. Growth rates do not vary with altitude or climate in a 900 km long mountainous study region in California, USA. Linear growth regressions, when projected to the present, constrain estimates of colonization time and possible styles of initial lichen growth.     

Mapping areas of potential slope failures in cohesive soils using a shadow-casting algorithm – A case study from SW Sweden

When performing landslide susceptibility mapping of rotational slides in fine grained soils, slope algorithms found in common GIS software have two major shortcomings. Firstly, these types of terrain algorithms only consider the slope angle at the surface. Secondly, the algorithm is local by its design i.e. it only considers neighbouring pixels. Due to the behaviour of a retrogressive rotational landslide, it would be more preferable to consider slope information as a predetermined cross-section angle from the base of the slope. This paper presents a new method using shadow casting algorithms for preliminary landslide susceptibility mapping in cohesive soils. A case study from western Sweden is also presented.     

Investigation and Assessment of Landslides and Debris Flows in Sichuan Province of China by Remote Sensing Technique

Taking TM images, ETM images, SPOT images, aerial photos and other remote sensing data as fundamental sources, this research makes a thorough investigation on landslides and debris flows in Sichuan Province, China, using the method of manual interpretation and taking topography maps as references after the processes of terrain correction, spectral matching, and image mosaic. And then, the spatial characteristics of landslides and debris flows in the year of 2005 are assessed and made into figures. The environmental factors which induce landslides and debris flows such as slope, vegetation coverage, lithology, rainfall and so on are obtained by GIS spatial analysis method. Finally, the relationships of landslides or debris flows with some environmental factors are analyzed based on the grade of each environmental factor. The results indicate： 1） The landslides and debris flows are mainly in the eastern and southern area of Sichuan Province, however, there are few landslides and debris flows in the western particularly the northwestern Sichuan. 2） The landslides and debris flows of Sichuan Province are mostly located in the regions with small slope degree. The occurring rate of debris flow reduces with the increase of the vegetation coverage degree, but the vegetation coverage degree has little to do with the occurrence of landslide. The more rainfall a place has, the easier the landslides and debris flows take place.     

基于升降轨Sentinel-1A SBAS InSAR的西南山区滑坡隐患早期识别研究

以贵州省水城县为研究区,使用SBAS InSAR分别对2018-07~2019-07鸡场镇滑坡发生前31期升轨和30期降轨Sentinel-1A数据进行处理,提取地表形变场。结果表明：1）鸡场镇滑坡发生前SBAS InSAR形变场并未出现明显形变,已超出12 d重访周期SAR的形变监测能力;2）研究区存在5个明显形变区,推断与斜坡失稳、地下/露天采矿和矿物加工的抽排水有关;3）升降轨数据的SBAS InSAR形变场相互补充、验证,可显著提升卫星雷达对山区滑坡隐患早期识别和形变监测能力。研究方法可为贵州省以及中国西南山区滑坡隐患调查与早期识别提供技术参考。     

基于公里网格单元的地震滑坡人员死亡率评估模型——以2014年鲁甸MS6.5地震为例

为提高地震人员伤亡预评估的准确性,完善地震灾害损失评估模型,科学评估地震地质灾害可能造成的人员伤亡数量,以2014年鲁甸MS6.5地震滑坡人员死亡数据为样本,建立了一种基于公里网格单元的地震滑坡人员死亡率logistic回归模型。采用F检验法对所建模型的合理性进行检验,计算得到的F值无限接近于1,表明模型无限接近于完全模型,具有极好的数学统计意义。根据模型评估的死亡率反演得到鲁甸地震灾区滑坡致死人数为233人,比实际少17人,总精确度为93.20%,实际死亡人数与模型识别人数在空间上也有很好的一致性,说明计算得到的地震滑坡人员死亡率是实际死亡人数的良好指标。     

Slope control on the frequency distribution of shallow landslides and associated soil properties,North Island,New Zealand

The extrapolation of results from field trials to larger areas of land for purposes of regional impact assessment is an important issue in geomorphology, particularly for landform properties that show high stochastic variability in space and time, such as shallow landslide erosion. It is shown in this study, that by identifying the main driver for spatial variability in shallow landslide erosion at field scales, namely slope angle, it is possible to develop a set of generic functions for assessing the impact of landslides on selected soil properties at larger spatial scales and over longer time periods. Research was conducted within an area of pastoral soft‐rock Tertiary hill country in the North Island of New Zealand that is subject to infrequent high intensity rainfall events, producing numerous landslides, most of which are smaller than several hundred square metres in size and remove soil to shallow depths. All landslides were mapped within a 0·6 km² area and registered to a high resolution (2 m) slope map to show that few landslides occur on slopes < 20° and 95% were on slopes > 24°. The areal density of landslides from all historical events showed an approximately linear increase with slope above 24°. Integrating landslide densities with soil recovery data demonstrates that the average value of a soil property fluctuates in a ‘saw‐tooth’ fashion through time with the overall shape of the curve controlled by the frequency of landslide inducing storm events and recovery rate of the soil property between events. Despite such fluctuations, there are gradual declines of 7·5% in average total carbon content of topsoil and 9·5% in average soil depth to bedrock, since the time of forest clearance. Results have application to large‐scale sediment budget and water quality models and to the New Zealand Soil Carbon Monitoring System (CMS). Copyright © 2012 John Wiley & Sons, Ltd.     

地质构造对三明市羊口仔后山滑坡的控制研究

在勘察、施工开挖及物探的基础上,揭示断层控制滑坡的诸多现象和特征,为研究福建省地质构造与滑坡的相关性问题提供案例。     

四川汶川地震-滑坡-泥石流灾害链形成演化过程

2008年“5·12”汶川Ms 8.0级地震之后,地震灾区表现出显著的强震地质灾害后效应。地震造成山体分水岭及山脊部位产生大量的崩塌和滑坡,崩滑体大多散落在山体的中上部,在强降雨作用下大量松散堆积物沿陡峻的沟道汇聚、加速,形成破坏性极大的高位泥石流,从而构成典型的地震-滑坡-泥石流灾害链。在回顾汶川地震灾区同震地质灾害的基础上,调查分析了震后汛期地质灾害的主要类型及其6种表现形式,将地震-滑坡-泥石流灾害链形成、演化过程划分为4个阶段：孕育阶段、地震同震滑坡阶段、震后滑坡-泥石流发育阶段、高位泥石流的动态演化阶段,提出高位泥石流的判识指标,并探讨其分布特征、动态变化趋势及其防治对策。