High-magnitude landslide events on a limestone-scarp in central Germany: morphometric characteristics and climatic controls

There are both internal and external controlling factors leading to slope instability and susceptibility to mass movement processes. This paper explores which external climatic variables of different temporal scales influence the occurrence of high-magnitude landslide events. The investigations were focused on the Wellenkalk-cuesta scarp in the Thuringia Basin (Thüringer Becken) in central Germany. The cuesta scarp is composed of a densely jointed limestone caprock (Wellenkalk), and impermeable mudstones and marls of the Upper Bunter Sandstone (Röt) in the lower part of the slope. Mass movements are a typical feature of the Wellenkalk-scarp. The entire scarp slope length (1000 km) has been systematically mapped and investigated in a comprehensive research project in order to provide reliable information on the spatial distribution and control of the mass movements. More than 20% of the scarp slope has been influenced by various types of Holocene mass movements with strong differences in spatial frequencies. Sixteen high-magnitude landslides (Sturzfließungen) were identified by field inspection and mapping of slope geomorphology. Information on locations, morphometric characteristics, stratigraphic positions and rainfall-related attributes of the scarp slopes affected by the large landslides is presented.Mean annual rainfall amounts decrease from more than 800 mm in the western part of the basin to less than 550 mm in the east. Meteorological statistics on the spatial distribution of heavy rainfall intensities of different durations and return periods show that greatest precipitation intensities in short events (1 h) are reached at the western margin. Differences in rainfall intensities between the western and eastern parts decrease with increasing duration of the events. Where available, event-related meteorological information was collected. The spatial distribution of the landslides is most closely mirrored in the pattern of mean annual precipitation, though this variable is generally not thought to be a satisfactory or reliable climatic controlling factor. No landslides occur below a threshold value of 700 mm. The empirical data show that some general level of average perennial water input into the slope system seems to be of decisive importance for the occurrence of high-magnitude mass movements. Only when the precondition of a more general hydrological disposition is fulfilled, a direct triggering of high-magnitude mass movements by a short-time intensive rainfall period or event can become effective.     

Geomorphological research of large-scale slope instability at Machu Picchu, Peru

A multidisciplinary approach has been adopted to study the slope movements and landscape evolution at the archaeological site of Machu Picchu and its immediate surroundings. The basic event in the paleogeomorphological evolution of the area was the large-scale slope movement, which destroyed the originally higher ridge between Mt. Machupicchu and Mt. Huaynapicchu. Within remnants of that primary deformation, several younger generations of slope movements occurred. The laboratory analyses of granitoids revealed highly-strained zones on the slopes of Mt. Machupicchu, which strongly affect the largest slope deformation. The borders of the largest slope deformation are structurally predisposed by the existence of fault zones. The majority of various types of slope movements on the so-called Front Slope (E facing) and Back Slope (W facing) are influenced by the alignment between topography and joints. Along with slope movements, fluvial erosion and tectonic disturbance of the rocks have been affecting the evolution of the landscape. A monitoring network for dilatometric and extensometric measurements was used to detect the present-day activity of rock displacements within the archaeological site. In addition to standard mapping of surface hydrogeological phenomena, eleven express slug tests were conducted to verify the infiltration potential of precipitation. The results of these surveys indicate that recent large-scale slope movement as suggested by some previous studies is doubtful, and the detected movements can be explained by individual movements of rock blocks or several other mechanisms including sinking of archaeological structures, subsurface erosion and annual changes in the water content of the soils.     

The Barranco de Tirajana basin,Gran Canaria (Spain). A major erosive landform caused by large landslides

The Barranco de Tirajana (BdT), located on the island of Gran Canaria (Spain), has some specific features that differentiate it from the ravines of other volcanic islands in the Atlantic Ocean. The origin of this unusually wide upper basin (35 km²) has been under discussion over the last century although its erosional origin is nowadays widely accepted. The purpose of this paper is to describe the landslide deposits that appear at the bottom of the basin and to assess their role in the geomorphological evolution of the basin. We suggest that the BdT basin is a major erosional landform initiated by important ravine incision and widened by a large number of landslides.There are 28 large landslides within the BdT basin. The main movements were of rock-slide and debris-slide types, affecting 70% and 25% of the total area, respectively. In addition, modes of displacement were predominantly translational (rock-, debris-, and earth-slides) consisting of 89% of the total, compared to rotations and flows that constitute only 11%.Three main periods of landslide activity have been established in the development of the BdT basin, using geomorphological criteria. Period I includes ancient movements that could have started at about 0.6 Ma or even 2.7 Ma ago and are considered as abandoned landslides. Period II corresponds to old landslides considered as dormant, which occurred within the Middle–Upper Pleistocene. Finally, period III includes recent Upper Pleistocene landslides and Holocene landslides that are still active. We suggest that interglacials in the Canary Islands and NW Africa included humid and wet episodes that could account for the occurrence of periods of landslide activity in the BdT basin.     

Landslides in blanket peat on Cuilcagh Mountain, northwest Ireland

The northern and eastern sides of the Cuilcagh Mountain upland, in northwest Ireland, are mantled with over 50 km² of blanket bog that has experienced an unusually high spatial and temporal frequency of peat mass movements. In all, 29 peaty-debris slides, nine bog slides, two peat slides and five more peat landslides of uncertain type have been recorded within this study area. More than 27 km² of this peatland has been afforded several levels of statutory protection as well as international recognition of its geo-environmental importance. Field and laboratory investigations of the peat at several of the more recent failure sites showed it to be typical of Irish and Pennine (northern England) blanket bogs in most physical and hydrological respects. Field geomorphological evidence and modelling of stability thresholds indicate that the particular susceptibility of the Cuilcagh Mountain blanket bog to failure arises from two local factors: (i) the attainment of threshold maximum peat depths on the East Cuilcagh plateau, and (ii) the unconformable deposition of thin layers of glacial till (in places) and blanket peat over the pre-existing topographic surface formed from the major shale formations that underlie the northern slopes. With two exceptions, there is no conclusive evidence that human activities and management strategies for the area have had any significant influence on the occurrence of the peat landslides. The high frequency of large rainfall events since 1961 that did not trigger landslides suggests that failures are unlikely to become more frequent in response to climate change effects because they are controlled by slowly changing internal thresholds.     

Predictive landslide susceptibility assessment using the weight-of-evidence method in north-central Garhwal Himalaya,India

Landslides are frequent natural disasters in mountainous regions, particularly in the Himalayas in India during the southwest monsoon season. Although scientific study of landslides has been in progress for years, no significant achievement has been made to preclude landsliding and allay disasters. This research was undertaken to understand the areal distribution of landslides based on geological formations and geomorphological processes, and to provide more precise information regarding slope instability and mechanisms of failure. After completing a landslide inventory, prepared through field investigation and satellite image analysis, 493 landslides, comprising 131 investigated in the field and 362 identified from satellite imagery, were identified and mapped. The areal distribution of these landslides shows that sites more prone to landsliding have moderate to steep slopes, the lithology of the Lesser Himalayan formations, and excavations for road corridors. Landslide susceptibility zones were delineated for the area using the weight-of-evidence method on the basis of the frequency and distribution of landslides. Weights of selected variables were computed on the basis of severity of triggering factors. The accuracy of landslide susceptibility zones, calculated statistically (R² = .93), suggests high accuracy of the model for predicting landsliding in the area.     

四川地区地震崩塌滑坡的基本特征及危险性分区

四川地区地震崩塌及滑坡非常发育，时常造成严重灾害，本文在现场调查资料及已有研究的基础上，对四川地区地震崩塌，滑坡的分布规律，类型，特征及其灾害性进行了更深入的分析，并就其特征进行了分区。     

Landslides in the Central Coalfield (Cantabrian Mountains, NW Spain): Geomorphological features, conditioning factors and methodological implications in susceptibility assessment

A geomorphological study focussing on slope instability and landslide susceptibility modelling was performed on a 278 km² area in the Nalón River Basin (Central Coalfield, NW Spain). The methodology of the study includes: 1) geomorphological mapping at both 1:5000 and 1:25,000 scales based on air-photo interpretation and field work; 2) Digital Terrain Model (DTM) creation and overlay of geomorphological and DTM layers in a Geographical Information System (GIS); and 3) statistical treatment of variables using SPSS and development of a logistic regression model. A total of 603 mass movements including earth flow and debris flow were inventoried and were classified into two groups according to their size. This study focuses on the first group with small mass movements (10⁰ to 10¹ m in size), which often cause damage to infrastructures and even victims. The detected conditioning factors of these landslides are lithology (soils and colluviums), vegetation (pasture) and topography. DTM analyses show that high instabilities are linked to slopes with NE and SW orientations, curvature values between − 6 and − 0.7, and slope values from 16° to 30°. Bedrock lithology (Carboniferous sandstone and siltstone), presence of Quaternary soils and sediments, vegetation, and the topographical factors were used to develop a landslide susceptibility model using the logistic regression method. Application of “zoom method” allows us to accurately detect small mass movements using a 5-m grid cell data even if geomorphological mapping is done at a 1:25,000 scale.     

Geomorphological characteristics and slope processes associated with different basins: Mallorca (Western Mediterranean)

We compare the different geomorphological processes which occurred in Pliocene–Quaternary times on two very similar slopes in Mallorca, one located at the Tramuntana Range and the other in the Llevant Ranges. Both slopes have the same geological structure, the same stratigraphic and lithological levels, and the same altitude and orientation. The different slope processes are due to the relationship between the accommodation space and the sedimentation rate in the adjacent basins: In the Valencia Trough (located N of the Tramuntana Range), the sedimentation rate has not been sufficient to fill the accommodation space, whereas in the Alcudia Basin (adjacent to the Llevant Ranges), the sedimentation rate has been sufficient to fill the accommodation space. This difference has resulted in major landslides on the Tramuntana slope, whereas the Llevant slope is characterized mainly by alluvial fans and debris screes.     

The environmental significance of the remobilisation of ancient mass movements in the Atbara–Tekeze headwaters, Northern Ethiopia

Old landslides are prominent features in the landscape around Hagere Selam, Tigray Highlands, Ethiopia. The available evidence suggests their Late Pleistocene to Middle Holocene age and conditions of soil humidity. The affected geological layers, often silicified lacustrine deposits prone to sliding, rest upon or above the water holding Amba Aradam sandstone aquifer.Three examples of present-day (remobilisation of old) mass movements are illustrated and discussed. The aims of the study were to unravel the environmental conditions of the present-day remobilisation of ancient flows, as well as those of first-time landslides. The first two mass movements discussed are slumps, located in areas with vigorous regeneration of (grassy) vegetation. Their activation is thought to be the consequence of an increase in infiltration capacity of the soils under regenerating vegetation. One of these slumps had a horizontal movement of the order of 10–20 m in 1 day.The other case is the remobilisation of the May Ntebteb debris flow below the Amba Aradam sandstone cliff. The debris flow presently creeps downslope at a rate of 3–6 cm year⁻¹. Palynological evidence from tufa shows that the reactivation of the flow started 70 years ago. Shear resistance measurements indicate the danger for continuous or prefailure creep. From the soil mechanics point of view, the reactivation of the debris flow is due to the combination of two factors: (1) the reduction of flow confining pressures as a result of gully incision over the last hundred years, and (2) the increase of seepage pressure as a consequence of the cumulative effect of this incision and the increase in infiltration rates on the lobe since grazing and woodcutting have been prohibited 8 years ago. The role of such exclosures as possible landslide triggers is discussed.From the geomorphological point of view, the ancient movements and their present-day reactivation cannot be compared: the ancient movements led to the development of debris flows, whereas the reactivations relate to the dissection of these mass movement deposits.     

澜沧江―湄公河地区地形地貌划分

地形地貌反映了地质构造运动特征,是影响和制约区域经济社会发展的基础。本研究以澜沧江-湄公河地区1:250 000TM遥感影像图为基础,考虑到本区新构造运动异常活跃以及微地貌的特殊性,结合其坡度形态及海拔高度,采用成因类型-成因形态-物质形态-坡度形态-微地貌形态的方法进行地貌类型划分研究。采用地势起伏度分级、野外查证等方法进一步验证了地貌划分成果,结果表明本次地形地貌划分研究较好地反映了客观实际。     

Geomorphological study of the Fadalto landslide, Venetian Prealps, Italy

This research deals with the Fadalto landslide (Lapisina Valley, Venetian Prealps), which took place in the Lateglacial and has continued its activity until today. Our aim is to recognize how the landslide failed, the causes of such failure and the activity of this landslide. The study of this landslide is important not only to understand the geomorphological history of this alpine area, and why the Piave River modified its course in the Late Pleistocene, but also the links with human activities, and specifically with the road and rail network.The geomorphological study, carried out by the interpretation of aerial photos and by a detailed field survey, has been integrated with a geological survey, geophysical investigations and a morphometric analysis (DTM). The Fadalto landslide is considered to be a rockslide reactivated in various phases, with different dimensions and with different characters (slides, slumps and flows). The landslides have been provoked by natural causes, both external and internal; the fundamental external causes are the retreat of the Würmian glacier and tectonic activity; the internal factors that decrease the shear resistance are the bedding planes and joints of the bedrock, the attitude of the rocks dipping towards the valley bottom and, as regards more recent failures, the presence of glacial deposits underlying the landslide debris. Besides, in recent times, we must also consider human activity as a cause of slope instability.As to the activity, the Fadalto landslide is defined “dormant”. This means that in this area there is a geomorphological risk connected with the important road and rail network of the Lapisina Valley.     

试论地貌学的新进展和趋势

地貌变化有内在的规律,对环境保育、资源利用和自然灾害防治有重要影响。作为交叉学科和地理学的重要分支学科,地貌学具有重要理论价值和实际意义。过去10多年来,随着遥感、地理信息技术和沉积物定年、地球物理和地球化学探测以及数值模拟等新技术和新方法的应用,地貌学家的研究视野和深度不断扩大与加深,在构造地貌、气候地貌和人类活动与地貌过程等传统领域有很多新进展,揭示了不同地貌单元的变化规律和机理,极大地推动了地貌学的发展。在新时代,除了继续加强传统地貌单元的深入研究外,地貌学的发展应与全球环境变化和未来地球等重大科学问题(计划)紧密结合;地貌学家要关心人类活动对地貌过程的影响及适应,并利用新技术开展地貌过程的定量重建和数值模拟。同时加强地理学专业学生的地质学基础学习、发展定量地貌学和行星地貌学、系统开展人类活动对地貌过程的影响和适应研究,是提升中国地貌学水平的途径,也可为推动国际地貌学发展做出贡献。     

Landslide susceptibility analysis with a heuristic approach in the Eastern Alps (Vorarlberg, Austria)

The aim of the study is landslide hazard assessment carried out on a working scale of 1:25 000. The study area within the Northern Calcareous Alps was geologically and geotechnically mapped in order to identify causes and mechanisms of active mass movements. The field surveys were digitised by a Geographical Information System and divided into data layers. The geological units were classified according to their geotechnical properties. All layers were converted into grids and spatially analysed together with a Digital Elevation Model. Comparing the layers with the inventory of active landslides, the prevailing factors leading to sliding movements were identified. Because of the complex tectonic setting and the small number of active landslides, a statistical method of hazard assessment was not applicable. Using the heuristic approach of an index method, the data layers of geotechnical class, bedding conditions, tectonic layouts, slope angles, slope orientations, vegetation and erosion were analysed. The susceptibility of each layer has been evaluated with help of bivariate statistics. The layers have been weighted with indices due to their importance iteratively and were combined into a landslide susceptibility map.     

Two treatments of the origin of ridge topography in the Kuraiskaya depression of Gornyi Altai

On the basis of the regularities of channel flow dynamics and the propagation of the emptying wave, it is shown that the value of the mean flow velocity above the field of giant ripples necessary for the ridge movement cannot be attained under given hydraulic and geomorphological conditions. Presented are the erosional dissection mechanisms for the surface of fluvioglacial deposits which contribute to the subparallel occurrence of ephemeral streams.     

Factors affecting landslides occurrence in agro-ecological zones in the Merek catchment, Iran

Part of the mountainous semi-arid areas of Iran is geologically and topographically susceptible to landslides. A study was conducted at the Merek catchment, Iran which is geologically characterized by limestone, sandstone, shale and marls so as to determine the factors responsible for the occurrence of landslides. In this study, geomorphological units within the catchment were mapped by overlapping geological, topographical, land use and erosion data, using satellite image and GIS. Rocks and soils were sampled within each unit to determine their physico-chemical and mineralogical properties. It was found that landslides have affected about 15% of the Merek catchment and that their occurrence were promoted by unstable soils, being eroded at the rate of 18.57 t ha⁻¹ yr⁻¹. These landslides were initiated by crack formation in areas having smectite, a mineral which can swell and contract, depending on the availability of water. Smectite is the dominant mineral in about 80% of the area affected by landslides. Low aggregate stability in the topsoil further promotes the occurrence of landslides. Field verification showed that landslides occur mainly in the forest where the canopy cover is less than 15% with slope of 10-40%. Deforestation, overgrazing and improper tillage practices were found to accelerate landslides in this catchment.     

长江三峡库区梯田稳定性分析与对策*──以鄂西秭归县为例

三峡库区历史上就是滑坡、崩塌作用强烈的地带,在调查分析秭归县滑坡、崩塌对梯田稳定性的影响的基础上,探讨了四种不稳定梯田培坎的特征、性质和现状,提出了利用优势植物固土护坎等相应的对策。     

Sequence of instability processes triggered by heavy rainfall in the northern Italy

Northern Italy is a geomorphologically heterogeneous region: high mountains, wide valleys, gentle hills and a large plain form a very varied landscape and influence the temperate climate of the area. The Alps region has harsh winters and moderately warm summers with abundant rainfall. The Po Plain has harsh winters with long periods of subfreezing temperatures and warm sultry summers, with rainfall more common in winter.Geomorphic instability processes are very common. Almost every year, landslides, mud flows and debris flows in the Alpine areas and flooding in the Po flood plain cause severe damage to structures and infrastructure and often claim human lives. Analyses of major events that have struck northern Italy over the last 35 years have provided numerous useful data for the recognition of various rainfall-triggering processes and their sequence of development in relation to the intensity and duration of rainfall. Findings acquired during and after these events emphasise that the quantity and typology of instability processes triggered by rainfall are related not only to an area's morphological and geological characteristics but also to intense rainfall distribution during meteorological disturbances. Moreover, critical rainfall thresholds can vary from place to place in relation to the climatic and geomorphological conditions of the area. Once the threshold has been exceeded, which is about 10% of the local mean annual rainfall (MAR), the instability processes on the slopes and along the hydrographic networks follow a sequence that can be reconstructed in three different phases.In the first phase, the initial instability processes that can usually be observed are soil slips on steep slopes, mud–debris flows in small basins of less than 20 km² in area, while discharge increases substantially in larger stream basins of up to 500 km². In continuous precipitation, in the second phase, first mud–debris flows can be triggered also in basins larger than 20 km² in area. Tributaries swell the main stream, which is already in a critical condition. The violent flow causes severe problems mainly along valley bottoms of rivers with basins up to 2000 km² in area. First bedrock landslides can occur, reaching a considerable area density, with volumes from a few hundred up to about one to two million cubic meters. In continuous precipitation, in the third phase, basins of more than 2000 km² in area reach their first critical stage. River-bed morphology is extensively modified, with erosional and depositional processes which can locally undermine the stability of structures and infrastructures. Waters overflow levees, flooding villages and towns to various widths and depths and sometimes claiming casualties. Some days after an intense rainfall period, large landslides involving the bedrock can still take place. These processes usually cause the movement of very large rock masses. The total duration of rainfall usually has a greater effect on these landslides than does the number of short periods of very intensive precipitation. This sequence cannot be divided into separate phases when the events occur simultaneously because of the presence of intense rainfall pulses and the generation of very diffuse surface runoff. Such situations usually happen during short-lasting heavy summer rainstorms or in late spring, when snow melt combines with intense rainfall. The three-phase sequence has been identified in three severe events that are analysed in this paper: Valtellina (Lombardy) in 1987, Tanaro Valley (Piedmont) in 1994 and Aosta Valley in 2000; but this sequence has also been observed during other events that occurred in northern Italy: in Piedmont in 1968, 1977, 1978, 1993 and 2000; in Lombardy in 1983 and 1992; in the Aosta Valley in 1993.     

海岸横向沙脊的移动与形态变化——以河北昌黎黄金海岸横向沙脊为例

采用RTKGPS测量技术与方法,2006～2008年连续三年共9次对我国海岸沙丘主要分布区域之一的河北昌黎黄金海岸翡翠岛的一个典型海岸横向沙脊进行了三个横剖面的高精度观测。海岸横向沙脊高程、断面及其典型位置的观测结果表明,观测期间海岸横向沙脊脊顶和背风坡坡脚夏秋季东移、冬春季节西移,脊顶总体向西移动,年均最大移距1．8...     

Empirical models of rain-spells characteristics – A case study of a Mediterranean-arid climatic transect

Environmental (geomorphological, hydrological and ecological) processes are controlled by rainfall, particularly in the Mediterranean, semi-arid and arid regions. Rainfall was analyzed using the concept of rain-spells, i.e., a period of successive rain days preceded and followed by at least one day without rainfall. Daily data from 13 stations along a climatic transect extending from the Judean Mountains with a Mediterranean climate to the Dead Sea arid region in Israel were studied. Rain-spell characteristics (number, yield and duration), based on these data, are presented for different rainfall thresholds, which might be used for different environmental processes such as rock weathering, soil organic matter dynamics, landslides, overland flow and floods and soil erosion. Three estimation models have been developed in order to predict the mean annual Number of Rain-Spells (NRS), mean Rain-Spell Yield (RSY), and mean Rain-Spell Duration (RSD) for the mean annual rainfall and for any given rainfall threshold. These models can be used for current climatic conditions and for scenarios in which the rainfall total changes.