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Über dieses Buch

This volume contains peer-reviewed papers from the Fourth World Landslide Forum organized by the International Consortium on Landslides (ICL), the Global Promotion Committee of the International Programme on Landslides (IPL), University of Ljubljana (UL) and Geological Survey of Slovenia in Ljubljana, Slovenia from May 29 to June 2, 2017. The complete collection of papers from the Forum is published in five full-color volumes.

This fourth volume contains the following:

• Earthquake-Induced Landslides

• Rainfall-Induced Landslides

• Rapid Landslides: Debris Flows, Mudflows, Rapid Debris-Slides

• Landslides in Rocks and Complex Landslides: Rock Topples, Rock Falls, Rock Slides,Complex Landslides

• Landslides and Other Natural Hazards: Floods, Droughts, Wildfires, Tsunamis,

Volcanoes

Prof. Matjaž Mikoš is the Forum Chair of the Fourth World Landslide Forum. He is the Vice President of International Consortium on Landslides and President of the Slovenian NationalPlatform for Disaster Risk Reduction.

Prof. Nicola Casagli is Founding member of the International Consortium on Landslides(ICL), professor at the University of Florence and founder of the UNESCO Chair on geohydrological hazards at the same University.

Prof. Yueping Yin is the President of the International Consortium on Landslides and the Chairman of the Committee of Geo-Hazards Prevention of China, and the Chief Geologist of Geo-Hazard Emergency Technology, Ministry of Land and Resources, P.R. China”.

Prof. Kyoji Sassa is the Founding President of the International Consortium on Landslides(ICL). He is Executive Director of ICL and the Editor-in-Chief of International Journal“Landslides” since its foundation in 2004.

IPL (International Programme on Landslides) is a programme of the ICL. The programme is managed by the IPL Global Promotion Committee including ICL and ICL supportingorganizations, UNESCO, WMO, FAO, UNISDR, UNU, ICSU, WFEO, IUGS and IUGG. TheIPL contributes to the United Nations International Strategy for Disaster Reduction and the ISDR-ICL Sendai Partnerships 2015-2025.

Inhaltsverzeichnis

Frontmatter

Earthquake-Induced Landslides

Frontmatter

Session Introduction Earthquake-Induced Landslide

This session is devoted to the description of events, processes and mechanisms associated to the occurrence of landslides triggered by earthquakes. Fourteen manuscripts have been submitted to this session.

Kazuo Konagai, Gabriele Scarascia Mugnozza, Akihiko Wakai

The Role of Simultaneous Impact of Exogenous and Endogenous Forces in Landslide Process Activation

This paper reviews recent case studies completed on mass movements with probable co- seismic origin in the Uzbekistan part of Tien—Shan, Central Asia. Landslides, as any geological phenomena, formed due to simultaneous action of exogenous and endogenous forces. We consider simultaneous formation in the different areas of large landslides caused by the influence of these forces as a trigger effect. The nature of this connection, it is not only change of tectonic stress field, but at the same time the impact of climatic factors, the movement of groundwater, as well as the value of the natural frequency of oscillations in landslide-prone slopes. In this paper we consider the natural frequency of landslide-prone slopes in comparison with maximum spectral frequency of long-acting low-frequency oscillations of Hindu Kush earthquakes which caused major landslides in 2015 and spring 2016.

Rustam Niyazov, Bakhtiar Nurtaev

Local Terrain Relief: An Important Factor Influencing the Generation of Large Earthquake-Triggered Landslides

Compared with ordinary scale landslides, landslides with a large scale of volume or plane area like deep-seated landslides and rock avalanches can cause more serious damages. The study of the factors controlling large earthquake-induced landslides by the 2008 Ms8.0 Wenchuan Earthquake demonstrated that this kind of large and deep slope failures could be specifically tied to some particular geologic settings after analyzing their distribution characteristics. Also, its big earthquake magnitude was an important factor. However, observations show some exceptions. For example, the 3 August 2014 Ludian, Yinnan, China Mw6.1 (Ms6.5) earthquake, though of a moderate intensity, has caused lots of landslides. Among them, there are 18 large landslides (landslide with plane area ≥50,000 m2) and the biggest one is the Honshiyan landslide, which created a 120 m high, 1.0 × 107 m3 dam. The damage caused by this earthquake surpassed some events of M = 7 or greater due to the serious landslides disaster. Base on the distribution features of coseismic landslides caused by the Ludian earthquake, this paper analyses the statistics relationship between the local terrain relief condition and large landslides occurrences in the seismic area. It is shown that the areas with high local relief are prone to generate the large landslides. To further address this issue, 2D limit equilibrium simulation is employed. The scaling relation between the landslide amount and topographic relief has been analyzed. The results demonstrate that under the other same conditions, the scale of seismically induced landslides increases with growing local terrain relief. Thus local terrain relief or the elevation difference is an important factor influencing on the amount of coseismic landslides in mountainous regions.

Xiaoli Chen, Hongliu Ran, Qing Zhou, Bengang Zhou

Evaluation of Ground Shaking Characteristics in Residential Land Based on T/R Frequency Ratio of Microtremor

In this paper, ground shaking characteristics in residential land in Kanagawa Ward, Yokohama City, Japan are evaluated based on microtremor measurements. In particular, first, 325 measurement sites created with very high dense at not only cutting sites but also banking sites in the residential land of interest. Microtremor H/V spectra are then calculated at the created 325 sites. Based on the H/V spectral ratio, finally, ground shaking characteristics focused on not only peak frequency (Ridge frequency) but also Trough frequency were evaluated. As a result, the T/R frequency ratio of microtremor is one of effective indices to evaluate the ground shaking characteristics in a residential land.

Yoshiya Hata, Fumihiro Minato, Takaaki Ikeda, Masayuki Yamada, Masaki Yamauchi, Yutaro Okawa

Critical Displacement of Earthquake-Triggered Catastrophic Landslides

The critical displacement is referred to as a threshold for slope failure, compared with the calculated permanent displacement under seismic load using Newmark displacement analysis. The critical displacement, usually obtained from laboratory shear tests under low and constant shear rates, is defined as the coseismic displacement beyond which strength of sliding surface reach residual values. The typical value ranges a few centimeters, depending on the frictional characteristics of sheared materials. However, this definition of the critical displacement might be oversimplified since the strength of sliding surface is velocity-dependent. Therefore, we collected the shear tests results of different materials under different shear velocities to evaluate the velocity-displacement dependency. Besides, we redefine the critical displacement of catastrophic landslide (D cr ) as the accumulated permanent displacement before rapid slide occurred. The influence of the strength and seismic parameters on the newly defined critical displacement is assessed using Newmark displacement analysis incorporating velocity-displacement dependent friction law. The dip angle of sliding surface is assumed as 15°. The synthetic seismic load is simplified as sinusoidal wave with peak ground acceleration of 600 gal. Different seismic frequencies of 0.5, 1.2, 2.0 Hz are used to evaluate the influence of frequency on D cr . The results show that the range of D cr is much higher than few centimeters, and D cr is highly related to frictional characteristics of sheared materials, especially within the slip-weakening distance. Moreover, D cr is also influenced by frequency rather than peak ground motion acceleration of the sinusoidal wave. This study highlights that the initiation of landslide are extremely complex, which can be function of frictional law, seismic frequency, and geometry of sliding plane. The reasonableness of the velocity-displacement dependent friction law and the representative of the seismic wave should be considered for evaluating the initiation of catastrophic, rapid moving landslide.

Che-Ming Yang, Chang-Hsuan Hsu, Jia-Jyun Dong

Numerical Models of Unstable Slopes in Seismic Areas—Based on 3D Geomodels

This paper presents a series of new integrated 3D models of landslide sites that were investigated in very distinctive seismotectonic and climatic contexts in NW and SE Europe as well as in Central Asia (Tien Shan). First, we analyse ancient landslides with likely seismic origin marked by deep-seated failures, by a steep scarp and a massive failed body, by rock structures favouring static stability as well as by scarp initiation near the mountain top, far from river erosion processes. However, we present also one case study for a site near a major river, for which predictive slope stability models had to be developed: the right-bank slope located immediately downstream from the Rogun dam construction area. Multiple survey inputs and outputs were compiled in 3D geological-geophysical models and combined with high-resolution remote sensing data of the ground surface. Those models were used as inputs for 2D, 2.5D and 3D dynamic numerical simulations completed with the UDEC (Itasca) software. For some sites, a full back-analysis was carried out to assess the possibility of a seismic triggering of the landslide. For others, we simulated a series of possible future earthquake scenarios affecting the slopes. Simulations with discrete element codes also allowed us to model very large deformation and even dam formation. Interpretation of the complex inputs and outputs was enhanced by 3D stereo visualisation using a headset system allowing for full immersion in a virtual environment. We work now on the development of systems that allow several people to be immersed in the same virtual 3D model and to share their experience with each other.

Hans-Balder Havenith, Anne-Sophie Mreyen, Almaz Torgoev, Mihai Micu

A Characteristic-Period Based Approach for Evaluating Earthquake-Induced Displacements of the Large Büyükçekmece Landslide (Turkey)

The Büyükçekmece landslide is located in Turkey, W of Istanbul, about 15 km northward from the North Anatolian Fault Zone (NAFZ) and involves upper Oligocene to lower Miocene deposits, consisting of silty clays, tuffs and sands. No earthquake-induced re-activations are testified so far but due to the high seismicity of the area (struck by the 17th August 1999 Mw 7.4 Kocaeli and by the 12th November Mw 7.2 Düzce earthquakes) it was selected as the case-study in the framework of the European project “MARSite—Marmara Supersite: new directions in seismic hazard assessment through focused Earth observation in the Marmara Supersite”. Due to the existence of several secondary scarps, the original geological setting of the sedimentary deposits is significantly modified as many counter-slope-tilted landslide sub-masses can be identified in the landslide mass. Earthquake-induced displacements of the landslide were evaluated through a characteristic-period based (CPB) approach. To this aim, a stress-strain dynamic numerical modelling was carried out using several seismic inputs with Arias intensity (AI) values ranging from 1 and 0.01 m/s and characteristic periods, Tm, ranging from 0.3 to 16.5 s. Depending on the landslide dimensions (thickness and length), characteristic periods for thicknesses (Ts) and lengths (Tl), were computed to define the corresponding ratios over Tm. The obtained results indicate that the effective characteristic period of the landslide (Tl*) corresponds to the length of a single sub-mass, and not to the total length of the landslide. Moreover, for the lowest AI values the maximum earthquake-induced displacements correspond to Tm values close to resonance period of the landslide while for higher AI values, such a 2D interaction between landslide mass and seismic waves is much more evident.

Salvatore Martino, Luca Lenti, Celine Bourdeau

Finite Element Simulation for Seismic Ground Response in Mountainous Areas in Nepal

In this study, dynamic elasto-plastic finite element method is applied to simulate seismic ground response in mountainous districts in Nepal, which aims to reevaluate the earthquake-induced landslides occurred at the time of The 2015 Nepal Gorkha Earthquake. In the analysis, nonlinear material properties of the ground as well as 3D topography, geological conditions and input motion are taken into account appropriately. Those factors strongly influence the dynamic amplification effects relevant to slope failures. Throughout the comparisons of the results between the calculated one and observed facts in local areas, it can be concluded that the proposed numerical method has a sufficient ability to predict the phenomena and can be possibly utilized for predicting overall distribution of earthquake-induced landslide which would be helpful for developing landslide susceptibility maps in mountainous areas in Nepal.

Akihiko Wakai, Daisuke Higaki, Hiroshi Yagi, Go Sato, Masahiro Chigira

Geophysical Investigation of the Landslide-Prone Slope Downstream from the Rogun Dam Construction Site (Tajikistan)

The ongoing construction and further operation of the Rogun HPP in one of the most seismically active regions of Central Asia can cause activation of dangerous processes along the slopes adjacent to the dam and reservoir. Among the gravitational mass displacements recorded near the major hydroelectric facilities, the old right-bank landslide located downstream the hydrosystem is worth of special consideration. Possible landslide activation triggered by earthquakes and/or flooding may cause collapse of unstable masses with adverse consequences for the major HPP facilities. The complex geological and tectonic conditions of the construction area, the great height of the earth-fill Rogun dam, as well as large-scale man-made impacts on the slopes surrounding major HPP facilities, including the filling of the reservoir, require a profound analysis of slope stability downstream from the dam with assessment of possible landslide risk scenarios. This report describes the main results of the comprehensive studies, calculations and dynamic modeling of stability of the right-bank landslide-prone slope, which suggest that the potentially unstable mass of strongly weathered rocks with the volume from 2 to 5 × 106 m3 on a steep part of the slope may fully or partially collapse in case of combination of strong seismic action (PGA > 0.3 g) and of precipitation. In case of synchronous collapse of about five-million m3 of unstable rocks, the blockage of the Vakhsh River by a landslide dam is inevitable, with risk of flooding of the tunnels and consequential disturbance of normal functioning of the HPP.

Torgoev Isakbek, Havenith Hans-Balder, Torgoev Almaz, Cerfontaine Philippe, Ischuk Anatoly

Spatial Relations of Earthquake Induced Landslides Triggered by 2015 Gorkha Earthquake Mw = 7.8

This paper presents the results of an extensive mapping of co-seismic landslides triggered by the 2015 Gorkha earthquake in central Nepal. More than 19,332 landslides have been identified covering 61.5 km2 of land in about 20,500 km2 area of investigation using Google Earth imagery. Their spatial distribution characteristics and relation to the triggering mechanism is studied. Interesting regional localization and angular distribution characteristics, more controlled by the rupture directivity is observed. Seismic, geomorphic and lithological parameters that induce susceptibility to their occurrence is studied using two indices of landslide concentration: Landslide Area Percentage (LAP) and Landslide Number Percentage (LNP) in comparison with % area of each parameter classes. Positive correlation with the chosen triggering parameters are observed but there are some significant differences in the parameter values and distribution plots to co-seismic landslides in other parts of world. These results provide valuable information about the slope response characteristics in case of seismic activation in thrust faulting Himalayan landscapes, and this is important in further researches on co-seismic landslide prediction models for mountainous settlements, sediment yield studies and cascading landslide disasters after major earthquakes.

Kaushal R. Gnyawali, Basanta R. Adhikari

Distribution Characteristics of Geohazards Induced by the Ludian Earthquake on 3 August, 2014 and a Comparison to the Jinggu and Yingjiang Earthquakes

On 3 August 2014, a M s 6.5 earthquake occurred near the city of Zhaotong in Ludian County, China. The earthquake caused 617 deaths and triggered more than 1700 geohazards, most notably the large Hongshiyan, Wangjiapo, and Ganjiazhai landslides. In 2014, the Jinggu (M s 6.6) and Yingjiang (M s 6.1) earthquakes also occurred in the same region. In this study, the authors compared the relationships between geohazards and earthquake magnitude, fault activity, geomorphology, slope angle, seismic intensity, and population density in the three earthquakes areas. In addition, the concept of “dry” landslides is proposed. Some of the conclusions are as follows: (1) The number of geohazards significantly increased after the Ludian earthquake; (2) Large-scale landslides are controlled by active faults; (3) There is a strong correlation between topographic elevation at which geohazards occur and microtopography; (4) Slope angles in the Ludian earthquake area are significantly steeper than in the Jinggu and Yingjiang earthquake areas, with slope angles being a key factor for landslide development; (5) Mountains, canyons, rivers, river terraces, and towns are interdependent in southwestern China, which means that post-earthquake reconstruction must pay attention not only to seismic issues, but also consider geohazard prevention and geological environmental safety.

Zhiqiang Yin, Wuji Zhao, Yongqiang Xu, Lanpeng Sa

Seismic-Induced Landslides: Lessons Learned from Recent Earthquakes in Spain

On February 23, 2015, an earthquake of magnitude Mw 4.7 (Imax = V, scale EMS) struck the center of the Spain, triggering dozens of instabilities in taluses and natural slopes of an area characterized by low relief. These instabilities were characterized by: (1) very small size, most of them with volumes lower than 1 m3, and (2) to occur in rock masses affected by multiple discontinuities, which pre-defined blocks that fell down during the shaking. The inventory of instabilities of this earthquake has shown that most of the instabilities occurred on the slopes of the road network, although the larger instabilities were observed in natural slopes. The comparative analysis of this inventory with those made for other recent earthquakes occurred in the SE of Spain (1999, 2002, 2005 and 2011), all of them of similar magnitude Mw (between 4.7 and 5.1), allow to recognize that the vast majority of instabilities induced by these earthquakes were rock/soil falls, being other typologies of landslides very rare. In all cases, the size of instabilities triggered were small, usually with volumes of 1 m3 or less, reaching the larger volumes up to 500–1000 m3. Data available from these events point out that large landslides, as known in relation with historical earthquakes in Spain, cannot be induced by moderate to low magnitude earthquakes. Besides, slope morphology seems to control the location of induced instabilities. Thus, when the terrain is steep, as in the area affected by the earthquake in Lorca (2011, Mw 5.1), most of instabilities occur in natural slopes and affect the upper part of slopes. As the relief is less rugged, natural slopes instabilities are progressively less frequent until the extreme case of the 2015 event, when instabilities were located mostly on slopes of the road network.

José Delgado, Martín J. Rodríguez-Peces, Francisco J. García-Tortosa, Jesús Garrido, Iván Martín, Pedro Alfaro

Landslides Triggered by the Ms6.5 Ludian, China Earthquake of August 3, 2014

Ludian Earthquake (Ms6.5, Mw6.1) on August 3, 2014 has induced many new slope failures, and resulted in more than 600 deaths and significant property losses. The seismogenic fault is a left-lateral strike-slip hidden fault, an extension of NW–SE Baogunao-Xiaohe Fault. 235 landslides induced by the earthquake have been interpreted by field investigation and remote sensing. The high-susceptibility ranges of different effective factors to the landslides are examined by the index of the ratio of occurrence probabilities. Unlike other earthquake events such as the Wenchuan earthquake in 2008, most of the landslides are located in the footwall, and their spatial arrangement is controlled by the NE oriented main fault of Zhaotong-Ludian, not by the NW seismogenic fault. Four large-scale landslides very closed to the seismogenic fault are described in details. The sliding direction of the four landslides is influenced strongly by the fault properties and the aspect of free face, and there are two principal directions for the large landslides.

Kai-heng Hu, Xing-zhang Chen, Yong-gang Ge, Xing-yuan Jiang, Yang-chun Wang

Earthquake-Induced Rockfalls Caused by 1998 Mw5.6 Earthquake in Krn Mountains (NW Slovenia) and ESI 2007 Intensity Scale

The 12 April 1998 Mw5.6 Krn Mountains earthquake with a maximum intensity of VII-VIII on the EMS-98 scale caused extensive environmental effects in the Julian Alps. The application of intensity scales based mainly on damage to buildings was limited in the epicentral area, because it is a high mountain area and thus very sparsely populated. On the other hand the effects on the natural environment were prominent and widespread. These facts and the introduction of a new Environmental Seismic Intensity scale (ESI 2007) motivated a research aimed to evaluate the applicability of ESI 2007 to this event. All environmental effects were described, classified and evaluated by a field survey, analysis of aerial images and analysis of macroseismic questionnaires. These effects include rockfalls, landslides, secondary ground cracks and hydrogeological effects. It was realized that only rockfalls (78 were registered) are widespread enough to be used for intensity assessment, together with the total size of affected area, which is around 180 km2. Rockfalls were classified into five categories according to their volume. The volumes of the two largest rockfalls were quantitatively assessed by comparison of Digital Elevation Models to be 15 × 106 and 3 × 106 m3. Distribution of very large, large and medium size rockfalls has clearly defined an elliptical zone, elongated parallel to the strike of the seismogenic fault, for which the intensity VII-VIII was assessed. This isoseismal line was compared to the tentative EMS-98 isoseism derived from damage-related macroseismic data. The VII-VIII EMS-98 isoseism was defined by four points alone, but a similar elongated shape was obtained. This isoseism is larger than the corresponding ESI 2007 isoseism, but its size is strongly controlled by a single intensity point lying quite far from others, at the location where local amplification is likely. The ESI 2007 scale has proved to be an effective tool for intensity assessment in sparsely populated mountain regions not only for very strong, but for moderate earthquakes as well.

Andrej Gosar

Earthquake Induced Landslides in Russian Altai: Absolute Dating Applying Tree-Ring and Radiocarbon Analysis

In order to properly understand the seismic potential of a region, and to assess the associated seismic hazard, extensive studies are necessary to take full advantage from the geological evidence of past earthquakes including seismically triggered landslides. As a period of instrumental observations is insignificant in comparison with the recurrence interval of strong earthquakes the historical data are being involved as well as paleoseismogeological investigations, which are focused on studying ground effects from past earthquakes preserved in the geologic and geomorphic environment. In this context absolute age determination of such ground effects, including seismically triggered landslides, is one of the key problems. By now radiocarbon method is the most exploitable and widely applicable dating technique in numerical age estimations of seismically induced landslides. In case of spreading the forest vegetation in seismically active areas tree-ring analysis can be used as an additional or alternative approach. It has a great potential due to utmost precision of dating. In this study we report new radiocarbon dates of previously unknown evidences of strong prehistoric earthquakes within the highest and most seismically active southeastern part of Russian Altai (SE Altai) during the last 4 ka. In addition to estimating the germination ages of trees growing on the bare surfaces of seismically-triggered landslides, utilizing dendrochronological analysis of wood penetrating injuries of trees (both dead and living ones) caused by seismically induced rock-falls allowed establishing the date of strong medieval earthquake—AD 1532. Obtained results argue for the high regional seismicity in the second half of the Holocene and clarify the chronology of seismic events within the SE Altai. The specified recurrence interval of strong earthquakes is about 400 years during the last 4000 years.

R. K. Nepop, A. R. Agatova

Rainfall-Induced Landslides

Frontmatter

Analysis of the Predisposing Factors for Different Landslide Types Using the Generalized Additive Model

In this paper, a semi-parametric nonlinear regression technique, known as Generalized Additive Model (GAM), was implemented for the landslide susceptibility assessment in the Gravegnola catchment (Northern Apennines, Eastern Liguria, Italy), which was affected by more than 500 shallow landslides on the 25 October 2011 intense rainfall event. Twelve explanatory variables derived from DEM with 5-m resolution, river network, land use and geological maps were considered to investigate their influence on landslide type occurrence. The predictive performance of different combinations of explanatory variables has been evaluated through a cross-validation technique and ROC curve analysis. Different susceptibility maps for each landslide type were finally produced and the results were compared. The preliminary results show the higher ability of GAM than a single regression technique in selecting the most influent predisposing factors on the basis of the type of movement involved in landsliding.

Carlotta Bartelletti, Roberto Giannecchini, Giacomo D’Amato Avanzi, Yuri Galanti, Michele Barsanti, Maria Giuseppina Persichillo, Massimiliano Bordoni, Claudia Meisina, Andrea Cevasco, Jorge Pedro Galve Arnedo

Large-Scale Synoptic Weather Types and Precipitation Responsible for Landslides in Southern Norway

The contribution of large-scale synoptic weather types to the occurrence of weather-induced landslides was investigated for southern Norway. Landslides from the period 2000–2014 were analyzed on a regional scale, using existing climatic and landslide regionalizations. The classification provides a time series of landslide classes and Kruskal-Wallis tests and chi-tests were conducted to analyze how well the classification performs for each landslide region. The synoptic classification (SynopVis Grosswetterlagen, SVG) of daily weather types was later compared with the precipitation classification. In order to predict the occurrence of landslides within a region, a logistic regression analysis was used where the independent variables were the SVG classes, mean daily rainfall and snowmelt. The results showed that in seven of the twelve landslide regions in southern Norway the SVGs have the highest predictive power in terms of landslide occurrence. In these regions, with the exception of one, the models are significantly better than a null model, and the models are good in predicting weather-induced landslide occurrence. The highest predictive probability of weather-induced landslide occurrence is given by the weather type Zonal Ridge across Central Europe (BM), which yields a 90% probability of weather-induced landslides on the west coast.

Graziella Devoli, Lisa Jørandli, Kolbjørn Engeland, Lena M. Tallaksen

Deterministic and Probabilistic Rainfall Thresholds for Landslide Forecasting

In this paper, authors focus attention on different threshold schemes, which can be adopted when a model is used for landslide forecasting. In some cases they represent the occurrence probability of a landslide, in other cases the exceedance probability of a critical value for an assigned mobility function Y (a function of rainfall heights), indicated as Y cr , and in further cases they only indicate the exceeding of Y cr or its prefixed percentages. Clearly, the discussion here reported can be easily extended to the case of flood forecasting models. The empirical model named FLaIR (Forecasting of Landslides Induced by Rainfall, Capparelli and Versace 2011) is used for the study area of Gimigliano municipality (located in Calabria region, southern Italy), characterized by a database with 27 historical landslide events in the period 1940–2011.

Pasquale Versace, Davide L. De Luca

Definition of Rainfall Thresholds Triggering Landslides in Slovenia

In this paper the definition of rainfall thresholds for rainfall-induced landslides in Slovenia is presented. The thresholds have been calculated by collecting approximately 900 landslide data and the relative rainfall amounts, which have been collected from 41 rain gauges all over the country. The thresholds have been defined by the use of an existing procedure, developed for a test site with very different geological and climatic characteristics (Tuscany, central Italy). A single national threshold has been firstly defined, subsequently the country was divided into four zones, on the basis of major the river basins and a single threshold has been calculated for each of them. The effectiveness of the thresholds has been verified by the use of several statistical parameters and it resulted in quite good performances, even if with some uncertainties, probably due to the quality of the available data. Beside the setting of a threshold system, usable for civil protection purposes at national scale, an additional outcome of this work was the possibility of applying, with good results, a methodology defined for another region, therefore testing its degree of exportability in different settings.

Ascanio Rosi, Tina Peternel, Mateja Jemec-Auflič, Marko Komac, Nicola Casagli

Regional Rainfall Thresholds for Shallow and Deep-Seated Mass Movements Triggering in the South Eastern French Alps

The main objective of this work is to propose hydro-meteorological thresholds for the triggering of shallow (slides, debris/mud flows) and deep-seated mass movements within a vast area of the South-East French Alps (Queyras, Ubaye, Tinée) characterized by various rainfall patterns. For this purpose, we exploit a landslide catalogue (containing more than 600 events) for the period 1928–2014 describing the date (and sometimes the hours) of occurrence, the type of mass movement, the geographical location and the nearest meteorological station. Rainfall data are available for 36 stations. A statistical analysis of rainfall conditions associated to triggering of shallow mass movements at various time scales (yearly, monthly, daily and hourly) reveals that rainfall thresholds are spatially highly variable.

Alexandre Remaître, Jean-Philippe Malet

Explore on Hydro-Mechanical Threshold for Early Warning of Rainfall Induced Shallow Landslides

After the Wenchuan earthquake on May 12th, co-seismic landslides and fractured slopes were more susceptible to rainfall-induced shallow mass re-mobilization and post-earthquake disasters were gained widespread significance for the disaster mitigation. However, despite the rainfall thresholds, the hydrological parameters of rainfall induced mass re-mobilization in natural environment of Wenchuan earthquake regions is not well understood and widely used for disaster early warning. In this study, shallow rainfall triggered slope failures under partially saturated conditions in the hollows of the gully was proved by instrumental evidence of in situ experimental tests in a natural co-seismic landslide for simulating the rainfall triggered erosion process of shallow failures in debris flow catchment. In addition, the results revealed the transient process and unsaturated condition for mass movement in response to rainfall, and demonstrated the importance of hydrological parameters includes soil matrix suction and moisture content for shallow slope failure in the hollows, and the stability analysis suggested a hydro-mechanical thresholds including water contents and matrix suction based on the mechanism of slope failure for early warning of the mass-remobilization in hollows of debris flows. These findings were expecting for contribution effectively on improvement of early warning accuracy for rainfall induced shallow landslides and debris flows in earthquake hit region.

Zong-ji Yang, Jian-ping Qiao, Taro Uchimura, Lin Wang, Dong Huang, Xiao-qin Lei, Li-li Shi

Influences of Rainfall on Shallow Slope Failures

Assessment of rainfall-induced shallow slope failures is very important to reduce damages of infrastructures and lives of people living close to hazardous areas. Although the rainfall intensity-duration thresholds for initiation of slope failure (ID thresholds) based on the historical slope failure data is commonly used to assess slope failure, critical influence factors triggering shallow slope failures are often disregarded. Three sets of parametric study were therefore performed through finite element model to investigate the effect of saturated permeability of soil, slope angle and antecedent rainfall on instability of shallow slope. It is found that the hydrological mechanisms involving the rainfall induced shallow slope failure are either (1) the rising of water table mode or (2) the rainfall infiltration mode. The hydrological mode during the failure depends on the magnitude of rainfall intensity comparing with the infiltration capacity at soil saturation state. The rate of reduction in safety factor increases with an increasing the intensity of rainfall, only in a range of lower than the infiltration capacity at soil saturated state. As such the saturated permeability of the soil, which is equal to the infiltration capacity at soil saturated state, plays an important role in the shallow slope failure. The saturated permeability was found also to govern a range of applicability of the ID thresholds. If the rainfall intensity is not greater than the infiltration capacity at soil saturated state, the rainfall duration to failure (Trf) can be read from the ID thresholds. Slope angle and antecedent rainfall were found to play role on instability of the shallow slope. They control the initial stability of slope, which results in the different linear relationship of ID thresholds. In addition, the slope angle might accelerate the rate of rain water infiltration, and hence it reflects the slope of the ID thresholds

Taworn Teerametatiparat, Avirut Chinkulkijniwat, Somjai Yubonchit

Modelling Shallow Landslides Triggered by Rainfall in Tropical and Mountainous Basins

Shallow landslides triggered by rainfall in tropical environments are controlled by the weathering tropical profile and its water storage capacity. Although landslides triggered by rainfall are common in tropical and mountainous basins, few studies have been applied to the case of tropical regions, which are characterized by intense rainfall and deep weathering profiles. Thus, it is necessary to implement over these areas physical models and methodologies to determine the spatial location of landslides and their susceptibility level. In this work, a conceptual and physically based model called SHIA_Landslide (Simulación HIdrológica Abierta, or SHIA, in Spanish) that is supported by geotechnical and hydrological features occurring on a basin-wide scale in tropical and mountainous terrains is described. This model incorporates a comprehensive distributed hydrological tank model that includes water storage in the soil coupled with a classical infinite-slope stability analysis under saturated conditions. Additionally, this work presents the analyses and results of the implementation of the SHIA_Landslide model to estimate the landslides caused by a rainfall occurred on September 21st, 1990, in a basin of tropical and mountainous terrains of Colombian Andes. In less than 3 h, a precipitation of 208 mm fell within the study area, triggering more than 800 landslides. The results obtained by the model are compared with a landslide inventory presented during the event. Finally, the efficiency of SHIA_Landslide is evaluated in terms of landslide density and susceptibility classes (degree of fit and success-rate curve), and the prediction capacity by ROC (Receiver Operating Characteristics) analysis. It is possible to show a good performance of the model suggesting that SHIA_Landslide is able to simulate the physics involved on landslides triggered by rainfall in tropical and mountainous terrains.

Edier Aristizábal, Hernán Martínez-Carvajal, Edwin García-Aristizábal

High Mobility of Large-Scale Shallow Landslide Triggered by Heavy Rainfall in Izu Oshima

On Oct. 16, 2013, catastrophic shallow landslides were triggered on the west-side hillslopes in Izu-Oshima Island, Japan, by the heavy rainfall accompanying Typhoon Wipha. The displaced landslide materials were characterized by rapid and long runout movement. These landslides resulted in 36 dead, 3 missing, and 46 buildings being completely destroyed on the downstream area of Motomachi area. To understand the initiation and movement mechanisms of these shallow landslides, we surveyed the field and found that besides heavy rainfall, strong wind might also have play a key role in triggering of slope instability on the deep slopes. We took sample from the source areas and examined the shear behavior of these samples under partially drained or undrained condition. We also triggered landslides within soil layers made up of these samples by rainfall in a flume, and examined the variation of soil moisture, pore-water pressure and landslide movement with the introduction of rainwater. Test results showed that high pore-water pressure can be built up and maintained within the displaced landslide material and then elevate the landslide mobility, even though the thickness of displaced landslide materials is 0.7–1.2 m.

Gonghui Wang, Yao Jiang

Probabilistic Analysis of Shallow Landslide Susceptibility Using Physically Based Model and Fuzzy Point Estimate Method

The geomechanical parameters of soils used in physically based model for landslide susceptibility analyses are uncertain due to the inherent uncertainty and variability. In addition, limited sampling is another source of the uncertainty since the input parameters were obtained from very wide study area. Therefore, the analysis of rainfall-induced shallow landslides susceptibility using physically based model requires accounting for the uncertainty. Subsequently, the probability theory has been used to quantify the uncertainty. However, some uncertainties, caused by incomplete information, cannot be managed satisfactorily by probability theory, so fuzzy set theory is more appropriate in the case. In this study, the uncertain parameters in landslide susceptibility analysis were expressed as fuzzy numbers and fuzzy set theory was employed. In order to take into account the fuzzy uncertainties in the evaluation of the probability of failure, point estimate method was applied with fuzzy set theory. This proposed process was performed in GIS based environments since GIS has strong spatial data processing capacity. In order to check the feasibility of the proposed approaches, the proposed methods were applied to a practical example. To evaluate the performance of the model, the results of the landslide susceptibility assessment were compared with the landslide inventories using ROC graph. Based on the results of the practical application, it was concluded that the application of fuzzy set theory shows consistent analysis results and can obtain reasonable results.

Jung-Hyun Lee, Hyuck-Jin Park, Jung-Yoon Jang

Assessing Potential Effects of Climate Change on Rainfall-Induced Shallow Landslides in the Peloritani Mountains Area, Sicily

Climate change due to atmospheric greenhouse gas emissions may cause significant modifications to precipitation and other meteorological processes, with potential consequences on the frequency of occurrence of shallow landslides. This study aims at investigating the potential effects of climate-change induced rainfall modifications on the future occurrence of rainfall-induced shallow landslides, based on the analysis of RCM projections and hydrologic and slope stability simulations. Changes in precipitation are assessed by comparing future RCM-simulated rainfall series with hindcasts valid for the historical baseline (assumed as 1961–1990), and by considering the two emission scenarios RCP4.5 (intermediate) and RCP8.5 (high-emissions). The estimated changes enable to adjust the parameters of a stochastic rainfall model, used as input to carry out Monte Carlo simulations allowing to estimate the probability of landslide triggering for future periods. The method is applied to the Peloritani mountains area in Sicily (Italy), which has been hit several times by diffused shallow landslides in the past decade. The obtained results prevalently indicate a future decrease of the probability of landslide triggering, directly connected with climate-change induced increase of the inter-arrival times of rainfall events. Outcomes of the study also evidence the importance of assessing RCM data uncertainty, given that different climate-projection data may provide opposite indications.

David J. Peres, Antonino Cancelliere

Variations in Landslide Frequency Due to Climate Changes Through High Resolution Euro-CORDEX Ensemble

The paper presents the main findings of a research aimed to provide probabilistic projections about the variation of local weather patterns recognized as relevant for triggering of rainfall-induced landslide events affecting pyroclastic covers in Campania Region (Southern Italy). The study focuses on the municipality of Nocera Inferiore affected by several events (1960, 1972, 1997 and 2005). Euro-CORDEX multimodel ensemble at high resolution (about 12 km on the area of interest) provides daily precipitation data weighted on the basis of the performances and scenario consistency through the REA (Reliability Ensemble Averaging) method proposed by Giorgi and Mearns (2002). The results indicate a general worsening of the slope stability conditions in the investigated area up 2100 under the two different concentration scenarios. The developed approach is easily deployable for all impact studies and then it could represent a valuable tool in developing effective adaptation strategies and proper prioritizations of interventions to cope with Climate Changes.

Guido Rianna, Alfredo Reder, Veronica Villani, Paola Mercogliano

Potential Effects of Climate Changes on Landslide Activity in Different Geomorphological Contexts

The anthropogenic global warming could significantly affect weather patterns, with variable impacts at the regional scale. Geo-hydrological hazards represent an interesting example of the possible impacts. We present a study of the effects of potential climate change on slope stability conditions in two different contexts in the Italian Apennines. Although the two examined sites are 400 km apart, climate simulations return similar variations in weather patterns, which are characterized by a strong increase in air temperature, a reduction in seasonal cumulative precipitation, and an increase in daily precipitation. In spite of the similar input, the response of the two sites, lying respectively on saturated clays and on unsaturated non-plastic silts, might be completely different. Although these studies do not currently provide quantitative estimates, they represent a valuable support to policy makers and communities for the definition and prioritization of adaptation actions and for investments to cope with the expected climate changes.

Guido Rianna, Luca Comegna, Stefano Luigi Gariano, Fausto Guzzetti, Paola Mercogliano, Luciano Picarelli, Paolo Tommasi

Historical Patterns of Heavy Rainfall Event and Deep-Seated Rapid Landslide Occurrence in Japan: Insight for Effects of Climate Change on Landslide Occurrence

To clarify effects of climate change on deep-seated rapid landslide frequency, we compiled about 300 landslides information through a literature search since 1600 and the frequency of heavy rainfall event since 1901 in Japan. In the last 120 years, the deep-seated rapid landslide frequency was relatively large. However, the frequency of deep-seated rapid landslide did not increase monotonically with time. The frequency of deep-seated rapid landslide temporary varied and showed decadal-scale patterns. In the last 120 years, three periods of high frequency of deep-seated rapid landslide were existed. Since 1901, the decadal-scale deep-seated rapid landslide frequency well agreed with the decadal-scale heavy rainfall frequency. Mean annual number of deep-seated rapid landslides in the period of high frequency of heavy rainfall events were around 6–8 times larger than those of the low frequency periods. So, the past temporal change of heavy rainfall event frequency already induced temporal change of deep-seated rapid landslide frequency, suggesting that if in future, the heavy rainfall event frequency will increase due to the climate change, the deep-seated rapid landslide frequency might be larger than that in the past.

Taro Uchida, Wataru Sakurai, Atsushi Okamoto

Geomorphologic and Structural Controls on Landslide Types in Nigeria

Complex rock-debris avalanches, debris flow, soils slip and earth slumps in Nigeria lead to the destruction of lives and resources worth several millions of dollars annually. While long travel landslides, which are almost always catastrophic, mostly occur on igneous and metamorphic terrains at the boundary of Nigeria and Cameroon, the south east sedimentary terrains are subject to deep and wide gullies resulting from aggressive erosion and slumping movements. Slope failures in the two regions are therefore distinctively different with research revealing that the differences are in geology, structural geometry, style of deformation, slope gradient and the volumes involved. At the Nigeria-Cameroon border, complex, rock-debris avalanches are found on steep dipping slopes, where slope parallel, basal sliding planes along foliation and lineation surfaces control failure and mobility of materials downslope.

Ogbonnaya Igwe

Geomorphology and Susceptibility to Rainfall Triggered Landslides in Gudbrandsdalen Valley, Norway

During the last decade, several high-intensity landslide events have changed the image of the Gudbrandsdalen valley in Central Eastern Norway from a region with moderate landslide activity to being considered one of the most active landslide areas in Norway. Succeeding a localized, but intense, landslide event in the Northern part of the valley in year 2008, two larger regional events occurred in the years 2011 and 2013. Many landslides were triggered in each of these events, including flash floods and debris flows/debris slides in small and steep tributary rivers along the valley slopes, as well as translational and rotational slides on open slopes. In the first phase of the 2008 landslide event, landslides were triggered in dry weather, by ground-water flow from infiltration of snowmelt in areas far away from the landslide zone. In the 2011 and 2013 events, most landslides were triggered by intense rainfall, sometimes with daily rainfall of 30–50 mm and more. For this region, with annual rainfall as low as 300 mm, such daily rainfall values are unusual, and the landscape is sensitive to extreme rainfall. Although high susceptibility to extreme rainfall events has been clearly demonstrated through these events, the effect on landslide activity of an expected climate change towards a generally more humid regional climate needs further research. In the Centre for Research-based Innovation (CRI) “Klima 2050”, financed by the Research Council of Norway and other public, private and scientific partners in the period 2015–2022, work is underway in order to improve the understanding of landslide processes and triggering mechanisms in this environment.

Håkon Heyerdahl, Øyvind A. Høydal

Overview of Rainfall Induced Landslide Events and Importance of Geotechnical Investigations in Nilgiris District of Tamil Nadu, India

Landslide is a major natural hazard, which possesses serious threat to human population and various other infrastructures such as road, rail routes and other structures in the hilly terrain. Nilgiris district, located in southern state of Tamil Nadu in India, is basically a hilly region, lying at an elevation of 1000–2600 m above Mean Sea Level (MSL). The district regularly receives rainfall during both the southwest and the northeast monsoons. The average rainfall in this region is between 1500 and 3000 mm. Due to the steep slopes and heavy rainfall during monsoons, the district is highly prone to landslides. In recent times, occurrence of landslides in Nilgiris is increased due to sudden burst of development activities in the region. The present study gives an overview of landslide events and remedial options practiced so far in Nilgiris and emphasises the importance of geotechnical investigation in that region. The history of landslide events has been collected and soil samples have been taken from the places where, major landslides have occurred in the past to characterise them. The rainfall data have been collected to understand the influence of rainfall on landslide occurrence. From this study, it is observed that the main triggering factor for landslide in Nilgiris is heavy intense rainfall. Though the rainfall is main triggering factor, many causal factors are also involved in triggering of landslides. It is also observed that, the remedial measures practiced in this area was not site specific and mainly concentrated on construction of retaining walls and small gabion walls. To understand the failure mechanism of landslides, various effects of pore water pressure and to suggest suitable site specific remedial measure to prevent the recurrence of such failures in the future, detailed geotechnical investigations are required.

V. Senthilkumar, S. S. Chandrasekaran, V. B. Maji

Physically-Based Models for Estimating Rainfall Triggering Debris Flows in Campania (Southern Italy)

The societal risk related to rainfall-triggered rapid debris flows is commonly managed in urbanized areas by means of early warning systems based on monitoring of hydrological parameters (such as rainfall or soil moisture) and analysis of thresholds values. This paper deals with physically-based modelling of ash-fall pyroclastic soil coverings involved in debris flows along mountain slopes nearby the Somma-Vesuvius volcano (Campania, southern Italy), which represent one of the major geohazards of Italy. The methods adopted combine deterministic approaches at the site-specific and distributed scales to estimate Intensity-Duration rainfall thresholds triggering debris flows. The first approach is based on the reconstruction of detailed physical models of ash-fall pyroclastic soil coverings in representative source areas of debris flows and on the related hydrological and slope stability modelling. The second is focused on a regional distribution model of ash-fall pyroclastic soils over mountain slopes surrounding the Somma-Vesuvius volcano, which takes into account total thicknesses of pyroclastic coverings and variable stratigraphic settings. For both, effects of different initial antecedent hydrological conditions, associated with summer and winter, are considered.

Pantaleone De Vita, Francesco Fusco, Elisabetta Napolitano, Rita Tufano

Physical Modelling of the Rainfall Infiltration Processes in Pyroclastic Soil Responsible of Landslide Trigger

Landslides cause many damages to people, structures and infrastructure. The prediction of these natural processes is important. A good predictive model can allow the implementation of an equally good warning system, reducing the risk caused by such phenomenons (Capparelli et al. in “Ingredienti essenziali” di un sistema Early Warning per l’innesco di colate di fango in coltri di natura pirocalstica: resistenza a taglio in condizioni di parziale saturazione e curve di ritenzione idrica, 2014). There are many researches to understand the underlying processes trigger a landslide. Rainfall is the most common cause of landslides, so it is important to know the infiltration processes responsible for a failure. In our research, we study the infiltration processes, using an integrated approach, comparing data station in situ with the results and interpretations of physical models, trying to simulate with mathematical models. The aim is to observe and interpret laboratory tests to reproduce and simulate the phenomenon with mathematical models. The following we propose two tests carried out in laboratory scale using a physical model for the simulation of landslides induced by rainfall. The soil used for the tests was taken from the site Sarno (Southern Italy), near the volcano Vesuvius. This area had a mudflow in May 1998.

Giovanna Capparelli, Pasquale Versace, Gennaro Spolverino

The Role of the Precipitation History on Landslide Triggering in Unsaturated Pyroclastic Soils

A wide area around the town of Naples is mantled by shallow unsaturated volcanoclastic soils that are highly susceptible to fast rainfall-induced flow-like landslides. Some casualties and huge damage recorded in the last twenty years testify the serious threat posed by such events. Due to the impact of these phenomena, the local research community is strongly committed in studies whose results have allowed to understand some key aspects of the triggering and propagation mechanisms. However, the way to run for risk mitigation is still long: given the density of population and of infrastructure, the setting up of reliable early warning systems would be a fundamental tool to this aim. Based on a rich data-base about the features of the rainfall-induced landslides in unsaturated volcanoclastic soils occurred on January, 10th, 1997, in a small area located in the Sorrento peninsula, and the history of precipitations occurred in the same area in the last fifty years, the paper examines the relation between rainstorms and landslides, showing the fundamental role of the recent precipitation history.

Luca Comegna, Melania De Falco, Fatemeh Jalayer, Luciano Picarelli, Antonio Santo

Role of Land Use in Landslide Initiation on Terraced Slopes: Inferences from Numerical Modelling

Land use/land cover is widely considered as a relevant factor for shallow landslide occurrence; therefore, in this work we used a physically-based model, whose input parameters have been evaluated taking into account the land use setting. In detail, assuming that vegetation affects the surface runoff and infiltration rate, as well as increases the shear strength of soil due to the root reinforcement effect, we calibrated several specific model parameters (such as friction angle, cohesion and hydraulic conductivity) by varying their values within a reasonable range, on the basis of a detailed land use map specifically prepared for some small coastal basins located in the Cinque Terre area (eastern Liguria, Italy). Since this area is characterized by the widespread presence of agricultural terraces, mainly abandoned, their degree of abandonment has also been considered. Different numerical simulations have been performed with TRIGRS (transient rainfall infiltration and grid-based slope stability), a well-known regional, physically-based stability model, with the aim of reproducing the landslide event occurred in the study area on October 25th, 2011. The safety factor (FS) maps obtained by using TRIGRS have been compared with the inventory map of the landslides triggered during the event. Then, a ROC (receiver operating characteristic) curve analysis has been carried out in order to quantify the performance of the model. The obtained results emphasize the influence of land use in shallow landslide occurrence.

Luca Schilirò, Andrea Cevasco, Carlo Esposito, Gabriele Scarascia Mugnozza

Analysis of the Impact of Precipitation on Landslide Activity Within the Erosive Slopes of River Valleys of the South of Ukraine

In the article the results of many years of observations of landslide activity on the slopes of the river valleys in the south of Ukraine (Northern Black Sea region) are presented. Northern Black Sea region includes the territory of the Odessa, Nikolaev and Kherson region. Characteristics of the main factors in the formation of landslides and their variability over time are shown. The degree of influence of precipitation on landslide process mode detected. The periodic component in the precipitation regime is established, which allows to predict periods of activation of landslide process.

Galina Pedan, Olena Dragomyretska, Oleksandr Dragomyretskyy

Heavy Rains and Flash Floods at Rocky Coast. The Costiera Amalfitana (Southern Italy)

Bedrock rivers are commonly affected by debris torrents during periods of heavy rain. This is particularly true in steep rocky coastal areas characterized by headwater catchments and alluvial fan at stream mouths. In these settings sudden torrents of water (flash floods) are caused by high-intensity and very localized cloudbursts of short duration, inducing slope erosion and sediment delivery from slope to stream. The elevated bed load transport produces fast-moving hyperconcentrated flows ranging from debris flood to coarse-grained flow with significant catastrophic implications. At Amalfi Coast alluvial fan flooding has been the most frequent and destructive geologic hazard since historical times. The steep coastal slopes are deeply dissected by a complex fluvial system with small catchments that are very high relative to the base sea level. These rivers show a distinct seasonality and torrential behavior with main delivery areas into the adjacent marine shelf. The reported rainfall events last from about 1 h to few hours with maximum rainfall intensity ranging from 100 to 200 mm h−1, and are strongly conditioned by the orographic features and the thermic anomalies of the coastal waters. The analysis of historical data indicate that more than 100 events have occurred in the last five centuries on the Amalfi coast, confirming the severe impact produced by flash floods in this area.

Crescenzo Violante, Eliana Esposito, Giuseppe Tranfaglia, Giovanni Braca

Drainage and Shear Velocity Dependent Shear Characteristics of Abandoned Imgi Mine Waste Materials in Ring Shear Tests

This paper presents the ring shear characteristics of abandoned Imgi mine waste materials (Busan Metropolitan City, Republic of Korea) as a function of drainage and shear velocity with the help of ring shear tests. The soil samples are mainly composed of gravelly sands with little percentage of fines. Normal stress, drainage (drained/undrained condition) and shear velocity (0.01–100 mm/s) were applied under the unlimited shear deformation. The test results show that the peak and residual shear strength were influenced as a function of shear velocity. The shear stresses increase with increasing shear velocity. The shear stresses measured from drained condition is much larger than those from undrained condition at the same shear velocity. It is due to the fact that a progressive grain crushing and sedimentation may occur strongly in the drained condition. Grain crushing is also significant with shear velocity: the higher the shear speed, the larger the crushed fines. Thus, high mobile characteristics of failed masses should be examined in terms of grain crushing and pore water generation.

Sueng-Won Jeong, Sung-Sik Park, Hiroshi Fukuoka, Sang-Woo Ji, Choon-Oh Lee

Landslide Monitoring and Management Challenge in Remote Papua New Guinea

Landslide monitoring and management is a challenging task in the remote, rugged and sparsely-populated Ok Tedi Mine area of Papua New Guinea (PNG). Ground elevations are 500–2200 m above sea level. Annual rainfall is 8000–13000 mm. Earthquakes may exceed magnitude 7 on the Richter scale; but are commonly 3–6. Avalanche debris from an ancient landslide dating back to 6700 BC underlies much of the existing terrain. Recent landslides often involve reactivation of old debris materials. The stability situation is compounded by local inhabitants’ deforestation of rugged hillsides to establish gardens. Limitations of various monitoring systems are discussed and case studies presented.

Norbert Baczynski, Neil Bar

Rapid Landslides: Debris Flows, Mudflows, Rapid Debris Slides

Frontmatter

Session Introduction—Rapid Landslides: Debris Flows, Mudflows, Rapid Debris Slides

This session is devoted to the description of events, processes and mechanisms associated to the occurrence of rapid landslides and mass movements. Fifteen manuscripts have been submitted to this session. Experimental tests and in situ measurements are fundamental for a better understanding of these phenomena and the design of possible efficient countermeasures.

Giovanni Crosta

Characterization and Modeling of a Debris Flow in a Dolomitic Basin: Results and Issues

Debris flows are rapid gravity-induced flows of high-concentration granular-liquid mixtures, consisting of clay, silt, sand and boulders with a variable quantity of water. Due their high speed and energy, they represent a severe hazard in mountain regions. In this study, we investigate the properties and the dynamic of a debris flow occurred on 29th August 2003 in Valcanale valley (Friuli Venezia Giulia, Italy). Among the many watersheds affected by debris flow during the catastrophic alluvial event, we have chosen a dolomitic one, called “Solari” stream. Grain size, mineralogy and rheological behavior were characterized through laboratory analysis; later two-dimensional simulations, using the Flo-2D software, were performed on a 5 × 5 m grid obtained by the extrapolation of elevation values of the Regional Technical Map (CTRN), surveyed in 2003, in order to replicate the event, and on a 5 × 5 m grid obtained by the resampling of a LiDAR DTM, surveyed in 2008, to test the efficiency of the mitigation works. This work points out the safety of the infrastructures downstream, protected by an adequate deposition basin. At the same time, it underlines some issues during the rheological analysis and the overestimation of the depositional extent of the debris flow, when the laboratory data were used to run the simulations.

Chiara Boccali, Romano Lapasin, Luca Zini, Chiara Calligaris, Franco Cucchi

Debris Flow Hazard Assessment (Cave del Predil—NE Italy)

Debris flows are one of the most frequent mass movement processes which develop on the mountain river network. With high flow velocity, long run-out, and high impacts, they are one of the most hazardous types of landslide. The material involved is heterometric debris with an extremely heterogeneous grain size distribution. The present research is focused on the interaction between the potential debris flow deposits from Rio Conzen and Canalone Andrea rivers with one of the four settling slag basins created during mining operations in the Cave del Predil mine (Tarvisio, Friuli Venezia Giulia, NE Italy). The mine is historical, the first written record of its existence dates back to 800BC. It remained active for a long period, and was the cause of dispute between the Italians and Austrians during WWI when the Austrians used a tunnel to transport troops and war material. After 1991 when the mine was closed, some levels were partially flooded in order to grant stability to the mine. The latter was later converted into a touristic area that along with the whole Val Canale valley was hit by an extremely intense alluvial event in August 2003 when more than 100 debris flows occurred. The valley is orthogonal to Val Canale where more intense damages occurred, but the possibility of the occurrence of new events (return period of 300y) is still high. The aim of this study was to create a possible scenario of the event, using FLO-2D software. The scenario obtained allow to study the interactions between debris flow deposits and the slag basins, and provide an understanding of the possibility of a river interruption. Scenarios can be considered extremely useful data to assist in informed future territorial planning of the area providing a good indication for hazard definition.

Chiara Calligaris, Glenda Nicola, Giacomo Casagrande, Luca Zini, Franco Cucchi

Stony Debris Flow Debouching in a River Reach: Energy Dissipative Mechanisms and Deposit Morphology

Stony debris flows are investigated at the laboratory scale. A set of 11 experiments are carried out, to simulate the stony debris flow propagation in a typical mountain confluence with a downstream water channel. The dynamic of the tributary flow just upstream of the junction with the river, surrogated through the volumetric mixture discharge, is assessed through the analysis of velocity profiles, while observations on deposit morphology provide insight into the condition which cause the blockage of the main stream. Energy dissipation within the solid–liquid mixture is mainly controlled by collisions between grains, and a dilatant fluid model is found to approximately reproduce the velocity profile. The degree of river blockage caused by the delivered material is classified according to three configurations: (i) full blockage, whereby the entire transversal river section is dammed (100% river obstruction); (ii) no blockage when less than 60% of the transversal river section is interested by the deposit; (iii) partial blockage for intermediate damming configurations (>60% and <100% of the river obstruction).

Antonio Fichera, Laura Maria Stancanelli, Stefano Lanzoni, Enrico Foti

Velocity Attenuation of Granular Debris Flows During Impact on Rigid Barriers

Effective design of rigid debris-resisting barriers remains a challenging problem for practitioners. At present, a pseudo-static approach is commonly used for the estimation of debris impact loads acting on barriers. In this approach, the dynamic impact pressure is estimated using the hydrodynamic equation and an assumed value of the dynamic pressure coefficient. The bulk density and travel velocity of the landslide debris are also required for the calculations. To this end, the debris velocity under free-field conditions can be obtained from a conventional debris mobility assessment. A limitation of this approach is that it ignores the attenuation of the debris’ velocity during the deposition process behind the barrier. To provide a scientific basis for assessing the velocity of granular debris flows during impact on rigid barriers, this paper presents results of debris velocity from a laboratory study of debris-barrier interaction using physical flume modelling. High-speed cameras were used to capture the dynamic motion of the flowing debris. The images obtained were analysed using the particle image velocimetry (PIV) technique to estimate the velocity of the debris. The results show that, following the first stage of impact, the accumulated debris behind the model barrier formed a stationary zone and caused the remaining debris to slow down in a run-up process. As a result, the peak debris momentum was 30% lower compared to that observed under free-field conditions. The findings of this study will allow practitioners to optimise the design of debris-resisting barriers in the future.

C. H. Raymond Koo, S. H. Julian Kwan, Carlos Lam, Wai-Keung Pun, W. W. Charles Ng, E. Clarence Choi

Impact Forces of a Supercritical Flow of a Shear Thinning Slurry Against an Obstacle

In mountainous areas after long or intense rains, landslides may evolve into debris- or mud-flows. Their impact against obstacles may produce huge damages, sometimes with loss of lives. Prediction of the impact forces is required for a proper design of the flow barriers protecting risk prone areas. To this aim, both the effective characterization of the mud rheology and a suitable mathematical model of the flow propagation are needed. The present paper proposes a modeling framework in which the mudflow is idealized as the flow of a power-law fluid over an incline with a rigid impervious wall at the downhill end. The flow model employs the von Kármán depth-integration of the one-dimensional mass and momentum conservation equations, in the long-wave approximation. The governing equations have been solved through a space/time second-order accurate numerical method. This modeling framework is applied to a test-case, based on the soil collected from Cervinara site (Avellino, South Italy), affected by a catastrophic landslide in 1999. The investigated soil is both the raw one and a washed one, the latter introduced to mimic the effect of an intense rain in terms of removal of the dissolved soil organic carbon. The rheology of both the shear-thinning mixtures has been deeply characterized in the form of a power-law function, and the dynamics of a dam-break wave ad its impact on an obstacle, has been numerically analyzed. It is shown that the removal of the soil organic carbon affects the propagation of the mudflow and at a minor extent the maximum forces and torques acting on the downstream wall. Remarkably, in the investigated conditions, the mudflow action consists of a strong impact occurring few seconds after the landslide triggering, and a subsequent cyclic loading of about three minutes.

Michele Iervolino, Claudia Carotenuto, Corrado Gisonni, Mario Minale, Andrea Vacca

Observation and Numerical Simulation of Debris Flow Induced by Deep-Seated Rapid Landslide

Deep-seated landslide sometimes lead to large-scale debris flow and triggered serious damages. To predict hazard area and magnitude of damage due to deep-seated rapid-moving landslide, several numerical simulation methods have been proposed. However, since adequate information about flow depth and velocity of debris flow was generally lacking, the applicability of these simulation methods for describing flow velocity and depth has not been fully examined. We focused a debris flow triggered by deep-seated rapid-moving landslide occurred on July 28th in 2015 at Fukaminato River in Kagoshima prefecture, Japan. We interpreted temporal variation of velocity and flow depth of debris flow at around 1 km downstream from the landslide using video camera images. We applied numerical simulation which describe the phase-shift for of fine sediment in debris flow. As a result, if we considered effects of phase-shift of fine particles on mobility of debris flow, simulated result of the front velocity and depth of the debris flow agreed well with observed data.

Taro Uchida, Yuki Nishiguchi, Naoki Matsumoto, Wataru Sakurai

Analysis on Debris Flow Non-rectilinear Motion—From Case Study to Hazard Zone Delimitation Discussion

This study aims to discuss the possibility of debris flow non-rectilinear motion and the current debris flow torrent delimitation method. The recent debris flow disaster in Taiwan triggered by torrential rainfall caused turning curve at alluvial fan and damaged community which was thought out of disaster potential. In order to clarify the factors causing this phenomenon and recognize torrents with similar susceptibility, numerical simulations were carried out by Flo-2D. In the previous study, simulations were given to the disaster case during Typhoon Soula and verified with investigation data. The result shows possible factors may trigger debris flow non-rectilinear motion, including slope gradient difference, geologic materials, and sediment material at the flooding part. In order to clarify the similar potential of non-rectilinear motion of the other torrents, this study selected five torrents in Kao-Ping basin for further analysis. Three accumulation types will occur by comparing the last and the first of accumulation areas. The type of entirely different accumulation areas after three times of debris flow occurrence was the one with non-rectilinear motion susceptibility, and the other types include extended accumulation area by more debris flow occurs and the same accumulation area but increasing depth. These types caused completely different risks to the communities inside or nearby the alluvial fan of the torrent. The qualitative analysis of flowing and accumulation parts of each torrent was given. Torrents with debris slide potential distributing along the flowing part, gradient difference between flowing and accumulation parts, and obvious gully terrain, have higher susceptibility of non-rectilinear motion. The geologic material that easily generates large border is also a significant factor, but it relies on detailed onsite investigation. This study successfully built an analysis process to clarify the possibility of non-rectilinear motion of debris flow torrents and some conclusions were therefore summarized.

Tingyeh Wu, Su-Chin Chen

Frequency Difference of Debris Flows in Moxi Basin, Southwestern China

Debris flow is one type of remarkable geomorphological hazards in mountain area. The primary objective of this study is to investigate the relationship between active fault and debris flow frequency (including high-frequency debris flow (HDF) and low-frequency debris flow (LDF)) in Moxi basin. The study area is a typical high mountain environment dominated by tectonic uplifting and glacier movement, where debris flow frequency shows a distinct difference and many debris flow fans occupy the valley bottom. Based on the field survey, literatures study and the interview with residents, this paper uses geographic information systems (GIS) techniques to outline their relation with fault, and analyse possible effects on their frequency differences. Results show that the spatial distribution, topographic characteristics of debris flow gully, return period and numbers of debris flow are mainly controlled by the Xianshuihe fault because of the tectonic uplift. The frequency difference between HDFs and LDFs is mainly controlled by the glacier distribution, because the glacier deposits act as the available loose debris in source area of debris flow.

Yongbo Tie, Jintao Jiang, Zhi Song, Alena V. Kadetova, Artem A. Rybchenko

Debris Flow Activity in Permafrost Regions in Austria During the 20th Century

Debris flows typically result from a critical combination of relief energy, water, and sediment. Hence, besides water-related trigger conditions, the availability of abundant sediment is a major control on debris flows activity in alpine regions. Increasing temperatures due to global warming are expected to affect the periglacial environment and by that the distribution of alpine permafrost and the depth of the active layer. This might lead to increased debris flow activity and increased interference with human interests. Here we assess the importance of permafrost on documented debris flows in the past by connecting the modeled permafrost distribution with a large database of historic debris flows in Austria. The permafrost distribution is estimated based on the model PERMAKART 3.0, which mainly depends on altitude, relief, and exposition. The database of debris flows includes more than 4500 debris flow events in around 1900 watersheds in the Austrian Alps. We find that around 10% of documented debris flows occurred in watersheds having a permafrost fraction larger than 5% in their headwaters. Only around 50% of historic debris flow events were documented in watersheds where permafrost is clearly absent. Our results indicate that watersheds without permafrost experience less, but more intense debris flow events than watersheds with modeled permafrost occurrence. We find no trend of increased debris flow occurrence rate from permafrost regions in recent years. Our study aims to contribute to a better understanding of geomorphic activity and the impact of climate change in alpine environments.

Roland Kaitna, Thomas Huber

Statistical Methods for the Assessment of Rainfall Thresholds for Triggering Shallow Landslides: A Case Study

La Spezia Province (880 km2; Liguria, northwestern Italy) is frequently hit by intense rainfalls, which often cause shallow landslides and damage to population and environment. In this regard, the Provincial Administration of La Spezia and the Earth Sciences Department, University of Pisa, promoted a study to define the rainfall thresholds for shallow landslides occurrence. In fact, on 25 October 2011 a very intense rainfall hit two parts of the provincial territory (Cinque Terre-Riviera area and Vara Valley) causing at least 3500 shallow landslides. This event was analyzed together with other 134 shallow landslide events occurred from 2008 to 2014. The rainfall conditions of these events were determined using an algorithm implemented by the CNR-IRPI of Perugia. The rainfall thresholds at different exceedance probability levels of landslide were defined using two statistical techniques: least-squares linear fit (LSF) and Quantile Regression (QR). The results highlight that the LSF thresholds seems to be the best performing from a statistical point of view and, consequently, the “best” for the study area.

Yuri Galanti, Michele Barsanti, Roberto Giannecchini, Giacomo D’Amato Avanzi, Gianni Benvenuto

Using Weather Radar Data (Rainfall and Lightning Flashes) for the Analysis of Debris Flows Occurrence in Emilia-Romagna Apennines (Italy)

During the last years, the Emilia-Romagna Apennines have been severely affected by debris flows, a type of landslide that is relatively uncommon in this area. These phenomena occur as a result of intense rainfall. The two most significant events are the one that affected the Province of Parma in October 2014 and the one that affected the Province of Piacenza in September 2015, in the night between the 13th and 14th. The objective of this work is to identify relationships between rainfall and debris flows occurrence for the Piacenza 2015 event, through the analysis of the distribution of debris flows with respect to rainfall data from weather radar and rain gauges recorded by ARPAE. The analysis of the relationships between spatial occurrence of debris flows and rainfall peaks has been based on the definition of the % of debris flow triggering points that can be contoured inside isohyets and on the ROC curve method. Moreover, we analyzed possible correlations between rainfall intensity and density or number of lighting flashes. The rainfall intensity vs duration plot showed that the September 2015 event largely exceeded debris-flows triggering thresholds proposed in literature. Analysis of debris flows occurrence with respect to hourly precipitation peaks retrieved by weather radar data, evidenced that 100% of the debris flows points occurred above the 30 mm/h isohyet, 97%, above the 50 mm/h isohyet and 82.5% above the 60 mm/h isohyet. Using ROC curves, the spatial distribution of debris flows triggering points can be more precisely predicted by considering, rainfall peaks at 1 h and 30 min over the event or by considering hourly rainfall between 02:00 and 03:00 of 15/09/2015. Rainfall classes of the best cut-off points in these ROC curves, i.e. most significant classifiers of the location debris flows points, are 75–90 mm/1 h and 45–60 mm/30 min. The analysis of lightning data shows that rainfall intensity was directly correlated to the lightning density but, also, that in some sub-areas a better correlation is obtained by considering rainfall intensity versus the lightning density recorded in the previous 30 min.

Giuseppe Ciccarese, Alessandro Corsini, Pier Paolo Alberoni, Miria Celano, Anna Fornasiero

Monitoring of Debris Flows with an Improved System Setup at the Lattenbach Catchment, Austria

The Lattenbach creek, District of Landeck, Tyrol is a very active torrent located in a geologic fault zone in the western part of Austria with a catchment area of 5.3 km2. The channel separates the Northern Limestone Alps in the North from the Crystalline Alps in the South. The highest elevation in the watershed is around 2900 m above sea level (asl), the confluence with the river Sanna at 840 m asl. Aside from the regular flood events with bedload transport, the torrent produced five debris flows and three debris floods within recent years. Due to the frequent debris flows and debris floods events the torrent is monitored by the Institute of Mountain Risk Engineering since several years. The parameters that are currently measured during an event include meteorological data (rainfall, temperature, etc.) in the upper part of the catchment (station Dawinalpe) and run-off data from the middle and lower reach of the torrent at the villages Grins and Pians. In the last years the monitoring equipment has been constantly improved. Additional to the standard sensors like radar for water level measurements, seismic sensors for ground motion detection and infrasound sensors for acoustic wave identification a high frequency Pulse Doppler Radar has been installed, which provides the opportunity to measure the surface velocity of a debris flow in different range gates. Together with a recently installed 2D-Laser scanner this setup provides the possibility to determine a very precise approximation of the discharge with a high temporal resolution. In August 2015 this setup worked properly for three debris flows, which occurred within eight days. These torrential events proved the applied concept to record data of debris flows in a high temporal resolution.

Johannes Hübl, Andreas Schimmel, Richard Koschuch

Natural Hazard Analysis for a Small Alpine Catchment in the Nepalese Himalayas

Owing to the disastrous damages due to the earthquakes in spring 2015 and the following monsoon period, numerous debris flows, land- and rockslides occurred in the Nepalese mountains. Within this study, the complex natural hazard system of the Gongar Khola (GK) catchment area consisting of large rockslides and rockfall areas in the uppermost part to slope processes such as landslides and channel processes including high water, debris- and mudflows that deliver material to the fan, respectively into the Tamakoshi River was investigated. Magnitudes of rockslides up to approx. 1.3 million m3 in the upper part as well landslide areas between 10,000 m3 and several 100,000 m3 in the lower regions were estimated. Torrential process such as debris- and mudflows endangered the Gongar Khola village as well as operations buildings and infrastructure of the 456 MW Upper Tamakoshi Hydroelectric Project (UTKHEP) that are situated in the lower GK catchment. Debris flow modeling for the lower GK catchment was performed using the numerical simulation tool RAMMS-DF. In a final step, a protection concept was designed for the affected areas consisting of structural measures such as gabion walls (partially with reinforced soil) in combination with armour stone rows taken resources available on-site into account.

Klaus Schraml, Christian Uhlir, Johannes Hübl

Small-Scale Factors Controlling Onset of the Debris Avalanche of 4 March 2005 at Nocera Inferiore (Southern Italy)

The debris avalanche occurred on 4 March 2005 in Nocera Inferiore (SA) was a further case of deadly landslides in pyroclastic soil mantled slopes of Campania (southern Italy), which caused the loss of three human lives. The landslide was triggered by a heavy rainstorm occurred in the preceding hours and hydrologically predisposed by snowfall of the antecedent days. The landslide took place on a slope with approximately linear longitudinal and transversal profiles, with a slope angle varying between 30° and 40°. It involved ash-fall pyroclastic soils, mainly derived from the eruptive activity of the Somma-Vesuvius volcano, deposited on bedrock constituted of Mesozoic fractured limestone. As typical of this type of shallow landslides, the mass movement initiated with a small debris slide (about 400 m3) that activated a subsequent debris avalanche. Owing to the apparently equivalent influence of recognizable landslide susceptibility factors such as slope angle, slope shape and man-made morphological alterations, specific field surveys were carried out to understand features controlling landslide initiation and its precise localization. A total thickness of the pyroclastic mantle, generally varying from 1.5 to 3.5 m, and a spatially variable stratigraphic setting were found. The matching between the landslide initiation zone and the local increase of pyroclastic soil thickness is the most important outcome. This finding extends the understanding of the landslide susceptibility in pyroclastic soil mantled slopes of the Campania region (southern Italy), also associating it to the spatially inhomogeneous distribution of pyroclastic soils along slopes.

Pantaleone De Vita, Durante Aquino, Pietro Bruno Celico

Experimental Study of Fluidized Landslide

Fluidized landslides that travel long distances at high speed are one of the most dangerous types of landslides. A fluidized slope movement can occur in both artificially designed slopes and natural slopes and generally results in extensive property damage and significant loss of life. However, the initiation mechanisms triggering this type of landslide are still not clearly known. This study attempts to assess the initiation of fluidized landslides through data from flume tests. The samples were collected from the rock avalanches deposits in Wenchuan earthquake area of China, where many huge debris flows which were transformed from fluidized landslide were triggered after earthquake. With the installation of ultra-high sensitivity seismic accelerometers at the bottom of the flume, it was possible to record the vibrations induced by the movement of soil particles during the fluidization of the slope. It was found that just before the liquefaction of the slope, indicated by a sudden rise of pore water pressure, a vibration signal appeared which was weaker than the vibration signal caused by the subsequent movement of the slope. This signal was related to the instability of the soil assembly. Furthermore, the flume tests showed evidence of internal erosion, a phenomenon responsible for the instability of soil structures which can also play a key role in triggering fluidized landslides.

Hu Wei, Hicher Pierre-Yves, Qiang Xu, van Asch Theo, Wang Gonghui

Landslides in Rocks and Complex Landslides

Frontmatter

A New Calculation Method to Flexural Toppling Failure of Anti-dipped Rock Slope

By using Aydan’s idea in this paper, the basal failure plane of anti-dipped rock slope will be regarded as a linear type plane. However, we consider that there is an angle (also called failure angle) between the basal failure plane and plane normal to the discontinuities, and the value of the failure angle is determined by the stress state of the rock stratums. Based on the principle of the minimum factor of safety, we suppose that the best failure angle is the one with the minimum factor of safety, and a new method to search for the best failure angle is introduced in this paper. The scope of slope failure angle will be in zero to θ0 (the difference between face slope angle and plane normal to the discontinuities). By changing the failure angle constantly, a series of slope safety factors can be obtained through the limit equilibrium method. The minimum one is defined as the final safety factor and the failure angle corresponding to the final safety factor is the final failure angle. The linear type failure plane corresponding to the final safety factor is the basal failure plane of slope. Taking Galandrood highway slope as a numerical example, the result shows that the obtained safety factor is smaller than that obtained by Aydan’s method.

Su Lijun, Qu Xin, Zhang Chonglei

Rock Slope Stability Assessment Using Stereographic Projection Method and Limit Equilibrium Analysis

Stability of rock slopes significantly influence by the structural geology of the rock in which the slope is excavated. Therefore, the structural and the engineering geological studies are necessary in assessment and identification of potential slope instability. Instability identification is essential to follow-up stabilization measures needed to ensure the long-term stability and integrity of the rock slope. The study was focused to identify the possible modes of failures occur during the widening of Thennekumbura—Ragala road of Sri Lanka. Hence, the study was focus to propose suitable remedial measures to stabilize the rock slope. Detailed field mapping was carried out to identify the lithological variations and to measure the orientations, intensity of discontinuities of the rock slope. Discontinuity orientation data were analyzed by stereographic projection method to identify the possible modes of failures along the road trace. In between each chainage, limit equilibrium analysis was performed to obtain the factor of safety for each mode of failure. Stability predictions were made based on the factor of safety achieved by the limit equilibrium analysis. According to the study, the predominant types of instability along the road trace were planar and wedge failures. As remedial measures, reduction of slope angle, rock benches with safe slope angle and rock bolting were proposed by analyzing the conditions of each site. In this study expected factor of safety of was 1.5. Furthermore, structural geological analysis can be used to predict the possible mode of failures in rock slope stability analysis; hence, remedial measures can be applied accordingly.

P. H. E. Dulanjalee, Jagath Gunathilake

Insights into Deep-Seated Rockslides in Metamorphic Rock Masses: Lessons Learned from Field Surveys, In Situ Investigations and Numerical Modelling

Lessons learned from several case studies of deep-seated rockslides in foliated metamorphic rocks in Tyrol (Austria) are presented. Based on surface and subsurface investigations as well as monitoring and modelling campaigns the main topics are the geometry, structure, kinematics, hydrogeology and geomechanics of deep-seated rockslides. Experience was gained from geological field surveys, monitoring campaigns based on remote sensing and classical geodetic methods, sub-surface investigations by core drillings and drifts, geophysical methods and numerical modelling studies. These insights may help to understand the processes and mechanisms of case studies in similar geological situations where comprehensive investigations are not feasible or new investigation campaigns should be planned.

Christian Zangerl, Thomas Strauhal, Christine Fey, Michael Holzmann, Sebastian Perzlmaier

Structural and Climatic Control of Mass Movements Along the Karakoram Highway

The Karakoram Highway (KKH) connects Pakistan and China by traversing through rapidly rising mountainous Karakoram area, which is the junction between the Indian and Eurasian plates including the Kohistan Island Arc. Being a plate boundary, the area is highly prone to active tectonics. The Main Mental Thrust, Main Karakorum Thrust, Main Continental Thrust and Panjal Thrust are the major fault systems operating in the region. The area is seismically active and various major earthquakes (Muzaffarabad Oct, 2005: M = 7.6, Afghanistan Oct, 2015: M = 7.5) have occurred. The geology of the area primarily consists of rocks including sedimentary, metamorphic and plutonic rocks. Granite and ultramafic rocks, slates and quartzites are the dominant lithologies of the area. Alterations of these rocks result in a large amount of incompetent and weak lithologies. The KKH passes through some of the world’s deepest gorges with high relief. The floor of these gorges is filled by glacial deposits (moraines). Since its construction in 1979, it has been damaged at various locations by a number of mass movements. In our study, data of mass movement events was acquired from Frontier Works Organisation. Then a spatial distribution map was prepared along KKH using ArcGIS. Furthermore, this mass movement distribution data was correlated with active faults, seismic information and rainfall data aiming to quantify the regression of mass movements and individual distance to active faults in the study area. Moreover, the impact of rainfalls on slope stabilities in the region is investigated. The active faults in this area have caused brittle deformation of crystalline rocks. This has resulted into poor to fair rockmass close to faults with densely populated joints having low shear strength. As a result, distances from active faults have inverse effects on mass movement events. Furthermore, rockmass quality close to the active faults is very poor having multiple joint sets. In addition, during heavy rainfall water seeps down into these joint which results in further decrease of shear strength and increase of pore water pressure, ultimately resulting in mass movements. Mass movements in Hassan Abdal-Gilgit Section showed dependence on rainfall intensity, whereas, mass movements in Gilgit-Khunjrab Pass section are function of temperature and rainfall intensity.

Sajid Ali, Sascha Schneiderwind, Klaus Reicherter

The Influence of the Geological Model in the Stress-Strain Analysis of the 1963 Vajont Landslide

The catastrophic nature of the Vajont landslide (volume of about 300 million m3) that occurred on 9 October 1963 in northeastern Italy emphasises the decisive role of a good geological model on the understanding of the mechanical behaviour of a large unstable rock slope. This large rockslide is a reference case study that is very useful for understanding the decisive role of the assumed geological model on the analysis criteria adopted in the slope stability evaluation. A recent (2006–present) survey performed on the failed mass and on the detachment surface allowed us to acquire considerable new geological data on the landslide structure and on the materials involved in the 1963 slope failure. The catastrophic en-masse sliding that occurred in 1963 was effectively a reactivation of a prehistoric large rockslide, as already hypothesised by previous studies dealing with the Vajont slide, but the structure of the prehistoric landslide was different from what was previously thought. The main result of the recent geological re-examination of the 1963 Vajont landslide is the identification of a thick shear zone (40–50 m) located at the base of an overlying unstable block. The occurrence of the basal shear zone, made up of limestone angular gravel, clay lenses and displaced rock masses, permitted a rapid seepage inflow triggered by the reservoir filling and also favoured the unusual en-masse movement of the upper unstable block. In particular, two specific unfavourable geologic conditions played an important role in the 1963 catastrophic event: the high permeability of the thick shear zone and the considerably low shear strength of some very thin clay lenses. Without considering this recently acquired geological data, it is very difficult to perform hydromechanical analyses or more sophisticated numerical models capable of reproducing the catastrophic Vajont slope failure and its unexpected final en-masse movement.

Paolo Paronuzzi, Alberto Bolla

True 3D Kinematic Analysis for Slope Instability Assessment in the Siq of Petra (Jordan), from High Resolution TLS

The present paper describes a specific research performed in the framework of the project “Sustainable monitoring techniques for assessing instability of slopes in the Siq of Petra, Jordan” carried out by ISPRA from July 2012 to May 2015. Focus is given to true 3D kinematic analysis for slope stability assessment in the Siq from high resolution terrestrial laser scanning (TLS). The effectiveness of the model and its algorithm implemented for the analysis has been verified and tested after the May 2015 rockfall. The sudden rock collapse, affecting a portion of the Siq cliff, was previously identified by the model as potentially unstable. This knowledge, associated to the outcome of the stability analyses, also through a numerical model, will help in identifying the most sustainable actions to be realized to mitigate the risk of collapse in such a vulnerable and complex context.

Claudio Margottini, Daniele Spizzichino, Giovanni Gigli, Heinz Ruther, Nicola Casagli

Susceptibility to Sea Cliff Failures at Cala Rossa Bay in Favignana Island (Italy)

Since the Roman Age and until the last century, an intense quarry activity took place at Favignana Island (Sicily, Italy) that significantly changed the morphology of the eastern part of the Island that is characterized by sea cliffs. This mining activity produced an extensive network of open air quarries, underground quarries and tunnels, locally named “Pirrere”, that are hosted into Pleistocene calcarenites. The sea cliffs of the eastern coast of Favignana Island were also influenced by the past mining activity and they are currently affected by diffused instabilities as proved by the wide block-size talus distributed all along the coast. A more detailed slope stability analysis was performed on a sea cliff located in the western sector of Cala Rossa Bay. To constrain such an analysis, engineering-geological field and remote surveys were carried out to reconstruct the geological setting as well as to characterize the mechanical properties of the rock mass. Finally a 3D model of the joints net was obtained. Based on geometrical and geomechanical joints features, a kinematic-compatibility analysis for rock landslide mechanisms (i.e. planar sliding, wedge sliding and toppling) allowed to identify 78 rock blocks particularly prone to failure. Considering hydrostatic pressure related to joints saturation condition as well as pseudostatic forces due to earthquake, 12 hazard scenarios were considered as reliable for the sea cliff area. The obtained results demonstrate that: (i) planar and wedge sliding are more suitable landslide mechanisms respect to toppling; (ii) the SE part shows higher susceptibility to failures; (iii) water pressures within joints play a more destabilizing action respect to earthquakes. Such an analysis represents a preliminary contribution to manage protection strategies for reducing the landslide risk in the touristic site of Cala Rossa bay and to preserve the unique heritage of the “Pirrere” quarries.

Roberto Iannucci, Salvatore Martino, Fabio Martorelli, Luca Falconi, Vladimiro Verrubbi

Complex Rainfall-Driven Kinematics of the Slow-Moving Pisciotta Rock-Slide (Cilento, Southern Italy)

The Pisciotta landslide is a slow-moving deep-seated rock slide in the Cilento region (southern Italy), which involves in the middle of its body a provincial road causing continuous interruptions of vehicular traffic. It also represents a danger for two railway tunnels crossing its foot. The landslide affects a complexly folded and tectonized turbidite series composed of intercalated calcarenites, marls and mudrocks. The principal objective of this study was the kinematic analysis of the landslide and its relationship with rainfall patterns. The analysis was based on monitoring of ground deformations carried out on 50 optical targets by topographical techniques. The latters were distributed in the middle-upper part of the landslide body, in order to set an early warning system for the provincial road. The monitoring activity was performed in the periods August 2005–March 2010 (1699 days) and May 2011–September 2013 (721 days). Besides the analysis of basic kinematic parameters, such as displacement, direction of movement and velocity, also the strain field was modelled and analyzed through the SSPX numerical code. Among principal results, spatial distribution of displacements, velocities and deformation patterns revealed a strong coherence with the detected surficial structures of the landslide. Moreover, the coupled spatial and temporal variability of deformation patterns allowed understanding a complex kinematics of the landslide body whose movements were related to a series of interacting blocks of flysch rock-masses. The analysis of the temporal variability of the landslide kinematics revealed uncommon findings such as that the landslide was always in motion (active) in the observation periods, with velocities ranging from the very low to low classes. Maximum velocities were observed unexpectedly in summer, during the dry period. Cross-correlation analyses performed between mean landslide velocity and rainfall time series showed a delay of about six months.

Pantaleone De Vita, Delia Cusano, Giovanni La Barbera

Numerical Simulation on Gentle Dip Slope Deformation Caused by River Erosion

This study investigated the creep deformation of a gentle dip slope induced by river erosion. In the Ai Liao River (Southern Taiwan), more than 20 rainfall events have induced massive landslides in the dip slope terrain as a result of lateral erosion of the river channel. Numerical simulations revealed that when the riverbank cutting angle is less than 30°, only circular slip and creep folds occur in the slope, with multiple small folds occurring from the toe to the top of riverbank (but no rapid damage occurs). When the river cutting angle is between 30° and 45°, drag bending folds are likely to occur on the contact surface between the surface and bottom layer, and a sliding surface appears along the contact surface. Finally, when the river cutting angle is more than 45°, slope movements occur, leading to significant, rapid block damage.

Tien-Chien Chen, Feng-Long Chou, Cheng Meng Hsieh

Mass Movement Processes of Quaternary Deposits in the Vipava Valley, SW Slovenia

Slope sediments of the Vipava Valley represent a complex sedimentary system deposited by very different mechanisms of transport and sedimentary processes that are controlled by a specific lithological and tectonic structure as well as climate conditions of the valley. Varying intensities and dynamics of mass movement processes in this area during the recent geological history (late Pleistocene and early Holocene) influenced the spatial distribution of slope sediments.

Tomislav Popit, Jernej Jež, Timotej Verbovšek

Characteristics, Causes and Hazards of Large-Scale Debris Flows on June 23 at Haitong Watershed, Tibet, China

Debris flows seriously endanger the highway from Chengdu to Lhasa (G318)and often interrupt traffic in rain seasons, especially at the southeast of Tibet. A large-scale debris flow, occurred on June 23, 2012 at Haitong Watershed, blocked the Xiqu River and formed a dammed lake with the average width of 60 m, the length of 300 m and the reservoir volume of 90,000–100,000 m3. The traffic of G318 Highway was interrupted until June 30th as the result that the highway base was buried about 230 m by debris flow deposits and inundated over 160 m by dammed lake. The investigation and the analysis of debris flow deposit samples showed that the debris flow delivered about 100,000 m3 sediment out of watershed, deposited along Xiqu River and formed a dam with the length of 230 m, the width of 100 m and the average thickness of 7–8 m. The clay content and density of debris flow deposits was 0.41–0.86% and 1.89–2.01 t/m3, respectively. Using the parameters of cross sections obtained by field measuring,the velocities and peak discharge for debris flow were estimated,and the velocities of flow reached 10.9–12.1 m/s by virtue of steep channel as well as the peak discharge at the mouth, the right gully and the left gully was 924, 642 and 336 m3/s, respectively. The debris flow on June 23 formed a hazard chain which was composed of flash flood, debris flow, dammed lake and outburst flood, and the threshold of debris flow blocking river was that the discharge, the magnitude and the deposits at river channel of debris flow was 230–850 m3/s, 11,709 and 9233 m3. The active tectonic movement, abundant erosion deposits and steep geomorphology are responsible for debris flow formation, the rainstorm after long-period drought triggered debris flows and the sediments induced by channel deposits initiation at the lower of the watershed further supplied and enlarged debris flow. The highway risk were assessed using the model which was established based on dynamic mechanism, and the high-dangerous zone and middle-dangerous zone occupied 86.5%, which agreed with the actual, where were buried by debris flow deposits or submerged by the following dammed lake. Based on the hazards and risk of debris flows on June 23, the protection measures, including dangerous debris flow identification, risk assessment, rational route, integrated control and emergency plans, were recommended.

Ge Yonggang, Zou Qiang, Zhang Jianqiang, Guo Xiaojun

Joint Modelling and Monitoring on Case Pennetta and Case Costa Active Landslides System Using Electrical Resistivity Tomography and Geotechnical Data

The aim of this paper is to study the Case Costa and Case Pennetta active landslides complex in the Northern Apennines (Parma, Italy). A ground model of an active and complex landslide system in instability prone rocks, made mainly by sandstones and claystones (Scabiazza Sandstones, Ligurian Unit), is developed through an integrated approach, utilizing different monitoring tools. Some of the tools are traditional (i.e. piezometers and inclinometers) and others are innovative, such as the acquisition of electrical tomographic data in time-lapse mode (TL-ERT). The latter has many practical applications to the study of subsurface properties and processes. This approach will allow to create a model of the physical state of the complex landslides, to observe the groundwater circulation and its variation with time, by relating it to the kinematics of the landslide bodies. Results of the landslide investigation revealed that an integrated approach, centred on volumetric geophysical imaging, successfully achieves a detailed understanding of structure and lithology of a complex landslide system, which cannot be attained through the use of remotely sensed data or discrete intrusive sampling alone. This paper describes this multi-technique approach for landslide hazard assessment reporting the preliminary monitoring results; such approach seems to be applicable to other hazardous earthworks and natural slopes.

Andrea Quagliarini, Andrea Segalini, Alessandro Chelli, Roberto Francese, Massimo Giorgi, Laura Spaggiari

Large-Scale Rockslope Deformations in Sogn Og Fjordane County (Norway)

Large rockslope deformations are characterized by distinctive geomorphic signatures such as up-facing ridges, grabens, open cracks, etc. which extend along large sections of valley flanks. They often present relatively low displacement rates (up to tens of mm/y). Among the different factors that condition their development, local relief, structural conditions, rock mechanic behavior, and time are the key factors. In Norway, large scale rockslope deformation are widely represented. In this work we give an overview of the conditioning factors of four unstable slopes in the Sogn og Fjordane county, and their current degree of activity by using field mapping, remote sensing and different monitoring techniques such as dGPS and InSAR.

Ivanna M. Penna, Martina Böhme, Reginald Hermanns, Trond Eiken, John Dehls

Landslide Zoning Using the Principal Component Analysis on Monitoring Data: The Sauna Earth Slide—Earth Flow (Parma, Italy)

In this contribute, we present the morphodynamic zoning of the Sauna complex earth slide—earth flow (Corniglio municipality, Northern Apennines) obtained by integrating results of field surveys and of Principal Component Analysis (PCA) of continuous displacement monitoring data. Since January 2014, the area is surveyed by an Automated Total Station (ATS) monitoring 30 prisms with duty cycles of 2 h. An evacuation plan has been adopted by the local authorities, which is based on pre-defined movement thresholds. However, during more than 2 years of monitoring, the results have evidenced that in different zones of the slope, differentiate displacement rates and timings of response to precipitations take place. Therefore, in order to fine tune evacuation plans, movement thresholds should be more appropriately tailored on the basis of morphodynamic zones rather than being left spatially generic. The final result is a morphodynamic zonation of the slope that represents a useful document to identify areas in which differentiated movement thresholds can be assessed for alert and alarm.

Marco Mulas, Francesco Bonacini, Marcello Petitta, Francesco Ronchetti, Giovanni Truffelli, Michela Diena, Alessandro Corsini

Landslides and Other Natural Hazards

Frontmatter

Experimental Study on Impact Behavior of Submarine Landslides on Communication Cables

Submarine landslides, which are characterized by large scale and long run-out, could destroy submarine tunnels, gas pipelines and communication cables, thus resulting in a great number of economic losses. Due to the harsh and extreme undersea environment, field work for landslide mechanics is nearly impossible. Therefore, a physical model test apparatus was developed in this work to simulate the motion of a submarine landslide and investigate its impact behavior acting on an underwater cable. The main part of the apparatus is an annular flume which can rotate in a vertical plane at a certain velocity. Water and soil material are placed at the bottom of the flume to simulate the submarine landslide. During the rotation of the annular flume, water and soil remain at the bottom of the apparatus under the action of gravity, and their motion relative to the apparatus bottom and cable responses similarly to a real submarine landslide. A simulant cable is set paralleling to the axel of the flume, and two load cells are fixed at both sides of the cable to measure the impact force. The relationship between the distributed load exerting on the cable with the rotation velocity and sand volume are investigated, and some promising results are obtained. Though the test results are qualitative, they still can provide a certain scientific basis for disaster evaluation of the submarine landslides and the design of underwater cables.

Zili Dai, Fawu Wang, Yasutaka Nakahara

RFID-Aided Sediment Transport Monitoring—Laboratory and Preliminary Field Test Results

Although often disregarded during natural hazard evaluation, sediment transport phenomena could represent a matter of major significance when dealing with hydro-geological instabilities with possible adverse impacts on river basin management, structural integrity of hydraulic structures, and public safety. Under conditions of high precipitation and consequent propagation of flood waves, the phenomenon is severely intensified, especially in Alpine and pre-Alpine areas, characterized by relatively high slopes and intense sediment supply from the upstream valleys. This study investigates the application of RFID (Radio-Frequency IDentification) transponders (also referred to as tags) as a qualitative and quantitative sediment transport monitoring tool. Preliminary laboratory and field tests have been carried out on both transponders and transponder-equipped pebbles under various conditions of the surrounding environment such as burial and water depth in order to evaluate the performance of the technology. Results of the laboratory experiments indicate that the detection distance depends on the orientation of the tag itself and therefore insertion of two or even 3 tags in a single pebble according to its axes is necessary in order to ensure higher recovery rates. Further, characteristic grain size curves have been used to identify 90 RFID-equipped and painted grains divided in several size classes and used in a first field experiment. The groups have been deployed at predefined locations characterized by similar granulometry and flow conditions. Two recovery campaigns have been since carried out, with the former some 15 h after a relatively intensified rainfall event and the latter two days later. A relatively high recovery rate has been recorded (72% during the first and 78% during the second campaign) to a distance of up to 50 m downstream of the initial deployment point. Despite some limitations, the technology appears to yield promising insights in the more detailed understanding of sediment transport.

Vladislav Ivov Ivanov, Davide Brambilla, Laura Longoni, Diego Arosio, Monica Papini

Flash Floods in the Rwenzori Mountains—Focus on the May 2013 Multi-Hazard Kilembe Event

Over the past 50 years, at least seven major flash floods have affected catchments of the Rwenzori Mountains. The Rwenzori Mountains are not only subject to flash floods; forest fires, earthquakes and landslides occur as well. Many of the flash floods therefore co-occurred with other hazards. One of the most devastating of these events occurred on May 1st 2013, in the Nyamwamba catchment. Here we reconstruct the circumstances under which this flash flood event was triggered and its effects in this multi-hazard region. This includes the identification and characterization of different processes acting upon the catchment dynamics, their controlling and triggering factors and the estimation of the damaging effects of the flash flood within the catchment. The combined occurrence of intense rainfall, a forest fire having burned 18% of the catchment area and the occurrence of 29 landslides providing debris to the river system, induced a debris-rich and very destructive flash flood which caused several fatalities, the destruction of 70 buildings, several bridges, a hospital and a school, a tarmac road and several life lines. Peak flow discharge is estimated between 850 and 1300 m3/s. This case-study demonstrates that flash floods in the region should not be considered as self-determined phenomena but as a result of several cascading and interacting hazard processes including wildfires and landslides, occurring within a short time period.

Liesbet Jacobs, Jan Maes, Kewan Mertens, John Sekajugo, Wim Thiery, Nicole van Lipzig, Jean Poesen, Matthieu Kervyn, Olivier Dewitte

Debris Flow Generation in Burned Catchments

Wildfires affect large forested areas in many countries worldwide, producing damage and economic losses, both as direct effect of the fires and as consequent events, including erosion and sedimentation in the recently burned areas. In addition to destruction of the vegetation, and direct losses to the built-up environment, further effects may be registered as a consequence of the fire, even weeks or months after its occurrence. Wildfire can have, in fact, profound effects on the hydrologic response of watersheds, and debris-flow activity is among the most destructive consequences of these effects. The two primary processes that have been identified for the initiation of fire-related debris flows are (i) erosion and entrainment of material by surface runoff, and (ii) infiltration-triggered failure and mobilization of a discrete, shallow landslide mass. The first process is reported by far as the most frequent. Field evidence indicates that unlike landslide-triggered debris flows, those produced in recently burned catchments have no identifiable initiation source and can occur with little or no antecedent moisture. Runoff-initiated debris flows have been produced in response to storms that occur typically from a few months to three years after the fire, often in response to the first significant rainfall of the storm season. After a wildfire, and in consequence of the following rainstorms, rills typically develop on hillslopes, initiated as miniature soil slips, and involving a few mm-thin saturated layer of soil. The persistence of such features downslope, until producing a true debris flow, depends upon a series of factors, including slope steepness, presence of loose materials, and availability of stream flow water. Typically, a discreet landslide mass of significant size is lacking at the head of the flow, whilst erosion and entrainment of significant amounts of surficial material is observed within hollows and in low-order channels. It therefore seems that the main process acting consists of surface runoff from a rainfall event, eroding sediments from hillslope and channels until a position within the drainage network where sufficient material has been entrained, relative to runoff volume, for a debris flow to be generated. The present paper analyzes, with some examples, the generation of debris flows in burned catchments, with the aim to describe the processes at the origin of these dangerous phenomena.

Mario Parise, Susan H. Cannon

Residual Slope Stability in Low Order Streams of Angangueo Mining Area (Michoacán, Mexico) After the 2010 Debris Flows

Mexico, largely a tropical mountainous region, is continually subjected to natural hazards like landslides induced by heavy rainfalls. At the end of January 2010, two cold fronts and low-pressure storms moved over the State of Michoacán (central Mexico) and in February the town of Angangueo, in the eastern sector of the Monarch Butterfly Biosphere Reserve, was devastated by a huge muddy debris flow. The in situ observations after the event showed that considerable material was removed from the countryside surrounding the urban area. In this framework two low order streams were indicated as the main suppliers of granular material to the Angangueo River: Melon and Catingón creeks. To evaluate the residual risk and slope stability along these two torrential watercourses, specific investigations were carried out. A GIS-based map of the most relevant hazardous features was performed at high level of detail by means of targeted field surveys that distinguished natural and anthropogenic elements like: (i) riverbanks and slopes with new signs of instability and already collapsed areas; (ii) large accumulations of debris and plant remains in channels and slopes; (iii) deposits of mining waste and abandoned mining areas; (iv) hydraulic works along the riverbeds and (v) cultural elements potentially at risk. In both circumstances, a generalized criticality emerged; moreover, all the riverbanks along the Catingón creek are almost still under unstable conditions, whereas Melon creek has precarious riverbanks only for about 1/3 of the considered slopes. In both cases, the depth of their rupture surfaces seems directly related to the different geotechnical properties of existing materials with some influence from gradients.

Stefano Morelli, Veronica Pazzi, Victor Hugo Garduño Monroy, Nicola Casagli

Landslides Risk Assessment Along Roads: The Transportation Corridors of the “Dolomiti Lucane” (Basilicata)

This paper deals with mass movement risk assessment along roads using a modified qualitative method. In fact, one of the most important problems for transportation corridors is linked to the risk caused by natural phenomena like mass movements and landslides. These events could cause serious damage to people and properties. In particular the roads and motorways, more so than the other communication lines, assume an important role especially in the emergency conditions because their inefficiency could cause substantial damages connected to delays in rescue operations, creating other inconveniences such as social and economic problems. The applied method regards the use of exponential scoring functions allowing the assessment of landslide risk along roads. It has been applied to the three main transportation corridors of the Dolomiti Lucane, in Basilicata (Southern Italy). This method represents an important tool for the preliminary mapping of the landslides risk along roads, allowing researcher to identify the most dangerous slopes and the roads sections that need more detailed investigations and, later, urgent remedial works.

Lucia Losasso, Stefania Pascale, Francesco Sdao

Monitoring Eruption-Induced Mass-Wasting at Active Volcanoes: The Stromboli Case

With the aim of understanding the relationship between eruptive activity and slope instability at active volcanoes, in this work displacement data from a permanent-sited, Ground Based Interferometric Synthetic Aperture Radar (GBInSAR) installed at Stromboli (Italy), were compared with the evolution of reflectivity (amplitude) of SAR images collected by means of X-band, space-borne, COSMO-SkyMed satellites (CSK-SAR). The analysis of the dataset (May-December 2014) cover a period characterized by “normal” Strombolian activity, punctuated by episodes of “high-intensity activity”, with the occurrence of overflows from the crater terrace toward the Sciara del Fuoco (SdF), and by the occurrence of the August 7th 2014–November 13th 2014 flank eruption. The integration of GBInSAR displacement data and the analysis of CSK-SAR amplitude images, allowed us to identify the evolution of the slope instability phenomena and geomorphological process affecting the SdF slope. GBInSAR data recorded the inflation of the summit plumbing system two months before the onset of the 2014 flank eruption. Moreover, evidence of mass-wasting recorded by the GBInSAR preceded the fracture opening by ~11 h, the fracture propagation and North East Crater (NEC) collapse by ~15 h, suggesting that 11–15 h before the onset of the effusive eruption, magma was intruding below the NEC area, inducing the slope instability observed on the NEC. SAR images were used with the aim of understanding the relationship between eruptive activity, geomorphologic evolution and slope instability. CKS-SAR data results highlights phases of erosion of the volcanoclastic deposits of the SdF during the “normal” Strombolian activity, whereas in periods characterized by higher-intensity volcanic activity, amplitude images revealed lava flow emplacement, as well as the deposition of dry gravel/debris flows.

Federico Di Traglia, Teresa Nolesini, Nicola Casagli

Development of a Rockfall Risk Mitigation Plan in the Montserrat Massif (Central Catalonia, Spain)

Within the last years, several rockfall events have affected different roads and facilities of the Montserrat Massif, located about 50 km North-West of Barcelona (central Catalonia, Spain). It shows a high number of exposed buildings, such as the monastery area, funiculars and a rack railway. Furthermore, the increasing number of annual visitors has highlighted the risk derived from rockfalls. To face this challenge, a geological risk Mitigation Plan in Montserrat has been launched by the Catalan government. The Plan aims at reducing the rockfall risk, progressively, taking into account the particularities of the site, considered as a natural and cultural heritage. Thus, a risk management strategy is required according to sustainability principles; the monitoring of the rock walls is a key factor that contributes to a continuous enhanced understanding of the hazard and risk factors for the consequent application of countermeasures. A first test and implementation phase was established for the period 2014–2016 followed by a second phase, which is expected to start from 2017, for the complete development of the plan. Then, a permanent third phase is also foreseen in order to guarantee the continuity and operability of the reached safety. The plan responds to a cyclical conception of risk management, where mitigation is a preventive stage providing preparedness and resilience for the emergency response stage. Furthermore, for the mitigation goal, four stages are designed in cyclic sequence of tasks involved in the plan.

Pere Buxó, Marc Janeras, Guillem Domènech, Judit Pons, Elisabet Prat, Ferran López

Assessment of Rockslide Dam Scenarios at Catchment Scale in the Context of Cascading Hazards

In rivers, temporary dams formed by landslides, rock falls or debris flows pose a severe threat to human life, public infrastructure and private assets. Besides the on-site impacts from the mass movement itself, these phenomena can cause disastrous off-site impacts by backwater inundation or catastrophic outburst floods. These secondary fluvial hazards can affect areas at substantial distances both up- and downstream of the site where the blockage occurred. In the present case study, the formation of rockslide dams and their subsequent impacts are viewed as a cascade of linked geomorphological and hydrological phenomena and assessed accordingly. The case study area extends over the two municipalities of Stilfs/Stelvio and Prad am Stilsferjoch/Prato allo Stelvio in the Autonomous Province of Bozen/Bolzano (South Tyrol) in Northern Italy, where the upper part of the slope above the village of Trafoi is at risk of a sudden failure. The present work builds on previous modelling attempts that predicted deposition heights up to 75 m in the channel of the Trafoi River. In this paper, we qualitatively identify all involved processes and create scenarios of various dam heights and dam breach processes. Modelling results show that the river downstream of the temporary dam features a channel conveyance sufficient for the peak discharge associated to a dam height of 4 m whereas dam heights of 16 m and 75 m would lead to severe flood events within the downstream municipality of Prad am Stilfser Joch. The modelled peak discharge values range from 35 m3 s−1 to 2554 m3 s−1, which fits well with values reported from other dam breach occurrences.

Christian Kofler, Francesco Comiti, Bernhard Gems, Benni Thiebes, Stefan Schneiderbauer, Romy Schlögel

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