Origin Of Landslides Research Articles

Simulation of landslide tsunami in the Russian Far East based on 3D Navier–Stokes equations

The paper presents the results of modeling landslide tsunamis near the Kamchatka Peninsula in part of the Pacific Ocean. The paper describes the model based on the three-dimensional (3D) Navier–Stokes equations. The model is supplemented with the rheological relation based on the Bingham model to account for the rheology of landslide masses. The paper proposes a modification of the classical Bingham model with a non-zero yield strength, which implies that the medium is at rest or it moves as a solid (body) in the absence of a tension in the medium exceeding this limit. The application of the classical model is impossible within the framework of the used equation system. The paper proposes its modification, which consists in the possibility of changing the yield strength to zero value by adding a linear function to a given shear rate, until which the fluid flows as Newtonian and after reaching it, the flow conditions of the substance obeys Bingham’s law. An original algorithm is used to simulate waves in real water areas, it implements open boundary conditions. The algorithm is based on the use of a damping boundary layer that absorbs the kinetic energy of the incoming wave, which is taken into account using an additional source in the angular momentum equation. A method is proposed for determining the resistance coefficient, the value of which determines the intensity of absorption of the kinetic energy of the wave. The used mathematical model makes it possible to model in a single way the occurrence, propagation and rolling on shore of tsunami waves of landslide origin. The results of modeling of an underwater landslide in the waters of the Kamchatka Bay near the city of Ust-Kamchatsk are presented, taking into account bathymetric date. The paper includes the analysis of dependence of wave heights on the volume of landslide in the zone of its initial position and at several points of the coast, as well as sections of the coast (in particular on Bering Island), which may be most severely affected by the occurrence of landslide tsunamis in this water area.

Laboratory Simulation of Earthquake-Induced Damage in Lava Dome Rocks

Earthquakes can impart varying degrees of damage and permanent, inelastic strain on materials, potentially resulting in ruptures that may promote hazards such as landslides and other collapse events. However, the accumulation of damage in rocks under the frequency and amplitude of shaking experienced during earthquake events is rarely systematically measured due to technical limitations. Here, we characterize damage evolution during laboratory experiments on a suite of dacitic rocks from Unzen volcano, Japan, to help resolve accumulated damage and landslide susceptibility of lava domes during regional earthquake events. Damage was imparted during slow (time-dependent creep) and fast (stress-oscillation earthquake simulations) uniaxial loading in compression and tension. Damage evolution is approximated from strain during experiments; all samples accumulate strain during earthquake events, but microfracture-dominated samples tend to be more susceptible to damage than vesicle-dominated samples. The orientation of existing fabrics with respect to loading direction dictates the magnitude of strain accumulation under load oscillations. During each “earthquake” experiment of multiple dynamic stress-oscillations, samples accumulate inelastic strain. The strain imparted during each successive event is initially high and then reduces after 5-7 events, except when stressing results in failure. The strain rate during phases of intermittent stressing tends to be higher than prior to them. Understanding the accumulation of damage and the potential for brittle failure of rocks subjected to earthquakes can help define the origin and timing of certain landslides, rockfalls, lava dome collapses, and other failure events.

Potential Landslide Origin of the Seram Island Tsunami in Eastern Indonesia on 16 June 2021 Following an Mw 5.9 Earthquake

ABSTRACT A 51 cm tsunami amplitude was observed in Tehoru, Seram Island (Indonesia), following an Mw 5.9 earthquake. Such a relatively large tsunami is highly unexpected from this size earthquake. Our analyses showed that the tsunami was 15 times larger in Tehoru tide gauge station than that recorded on two other stations located nearby. These observations imply that the tsunami was most likely generated by a secondary source such as a submarine landslide that potentially occurred near Tehoru. Local people reported landslide activities around Tehoru following the earthquake. We conducted numerical modeling of the tsunami by considering the tectonic source and found that the resulting tsunami was only a few centimeters in Tehoru. Therefore, it is very likely that the earthquake was not responsible for the tsunami observed in Tehoru. By assuming that a submarine landslide was responsible for the tsunami, we applied spectral analysis and tsunami backward raytracing to gain information about the potential size and location of the landslide. Backward raytracing was also applied to identify the earthquake source of the tsunami. Numerical modeling of eight candidate landslide scenarios showed that a landslide with a length and a thickness of approximately 4 km and 50 m, respectively, was potentially responsible for the tsunami. We note that our results serve only as the first and preliminary estimates. Bathymetric surveys and high-resolution bathymetry data are essential to provide more detailed information about the landslide.

Creating a thematic geodatabase for monitoring the landslide processes of the landslide circus “Dalgia yar”

Impact on the process of landslide origin and activation is result of many factors both endogenous and exogenous. The purpose of this study is to provide possibility for analysis and assessment of the geo-processes in the “Dalgia yar” landslide located at Northern Black Sea coast of Bulgaria in order to prevent risks and disasters of natural and anthropogenic origin. An important stage was to seamlessly include data from different sources such as geodetic measurements, satellite SAR (Synthetic-aperture radar) data as well as geological and geophysical data. The established geodatabase structures the collected information on dangerous geo-processes in the mentioned area and introduces them into the GIS (Geographic information system) environment. Its purpose is to facilitate the analysis of the available geological data for this landslide and to integrate them with results of measurements from regular monitoring. Interferometric images (IFIs), data from permanent GNSS (Global Navigation Satellite Systems) stations and from local geodynamic GNSS network, geological, seismic and geophysical data, updated geological maps and maps of the risk of landslide processes are included in the database. The IFIs have been produced using well established procedure for processing large number of Sentinel-1 SAR data of the purposely created local archive. Other key element used to improve the final results of SAR data processing and important part of the geodatabase is the precise Digital Elevation Model (DEM), which is much better in terms of horizontal and vertical resolutions than the open accessed ones (SRTM). The coordinates and velocities of the GNSS points are obtained from adjustment and analysis of two epoch measurements of the geodynamic control network of landslides “Dalgia yar”. Since the area has complex geological structure, small scale maps reflecting the geological and geophysical hazards are integral part of the geodatabase. Having all this information the analysis concerning the ongoing geodynamical processes in the study area is significantly improved and more reliable information is produced for better regional planning by the local authorities and residents.

Submarine landslide origin of a tsunami at the Black Sea coast: Evidence based on swath bathymetry and 3D seismic reflection data

Tsunami waves were observed along the Bulgarian Black Sea coastline on 7 May 2007. The maximum rise and fall of the sea level were 1.2 and 2.0 m, respectively, with wave oscillations between 4 and 8 min. At first, submarine landsliding and then later on atmospheric disturbance were suggested as the cause of the tsunami. Numerical modeling, assuming a landslide displacing 30–60 million m3 material on the slope with a thickness range of more than 20–40 m, could reproduce the main characteristics of the recorded tsunami. In this early model, the landslide initiated on the shelf at a water depth of 100 m with a runout of approximately 20 km into 1000 m water depth. Subsequent and recent numerical modeling suggested that the failure may have initiated on the slope, anywhere between 200 and 1500 m seafloor depth. The runout of the transported sediments in these latest model was at 1850 m water depth. Just a few years after the tsunami, OMV and its joint venture partners, TOTAL and Repsol, acquired modern deepwater data sets in the same area where the submarine landsliding was assumed to occur. These data sets included multibeam swath bathymetry area and 3D reflection seismic data. These data sets offer a possibility to establish the presence of speculative submarine landslide responsible for the tsunami, with its geometry and nature. Our results provide direct evidence for the occurrence of large nonseismic catastrophic sediment failures along the Bulgarian coast. In this study, we illustrate Quaternary submarine landslides on 3D seismic reflection data immediately below the one responsible for the 2007 event; we also briefly point out the potential interpretation pitfall related to sediment waves and mass transport complexes.

Recent advances on geomorphology of the Gorce Mountains, the Outer Western Carpathians – state-of-the-art and future perspectives

The increase of geomorphological research during the last decades in the Gorce Mts. caused the need for state-of-art review papers. The Gorce Mountains were formed as an isolated massif with Mt Turbacz (1310 m a.s.l.) as the highest summit. River channels are remodeled by sudden and high-level floods with the critical impact of log jams. The main processes influencing hillslope relief were landsliding, run-off, and tree uprooting. The review suggests the following issues await for studies: a long-term landscape evolution, monitoring of morphogenetic processes, and origin of landslides with their contribution to denudation rates. Also, current biomorphodynamics (uprooting process) has not been sufficiently studied.

Timing and seismic origin of Nixu rock avalanche in southern Tibet and its implications on Nimu active fault

In tectonically active mountain areas, the identification, dating and determination of origin of large landslides are of special importance in recognizing the seismicity and earthquake magnitude of regional faults, reconstructing the prehistoric landscape evolution and estimating the seismic hazards. Based on field survey, high-resolution satellite image interpretation and 14C dating of substrate, this paper studied the large, long-runout Nixu rock avalanche (the NXRA) in the Angang graben of the southern Tibetan Plateau. The study revealed that: (1) the deep-seated Nixu rock avalanche straddles the Nimu active normal fault and spreads onto the Angang basin with a deposit volume of 47 Mm3 and a travelling distance of 4960 m. (2) Humus samples immediately under the deposit of rock avalanche along the natural river-erosion section suggest a 14C age of 820 ± 30 BP (1220 ± 30 CalAD) for the NXRA event. The age well matches the 1264 CE Chubushi earthquake recorded in Tibetan documents. (3) 23 adjacent landslides have been recognized with co-seismic distribution features, such as clustering and distance effect, ridge-end amplification effect and slope aspect effect. Sand liquefaction and peat deformation were discovered in the substrate beneath and at a distance of ~300 m away from the avalanche deposit. (4) This information indicate that the NXRA was triggered most likely by the 1264 Chubushi earthquake with a magnitude of Mw 7.0–7.2 estimated by empirical equations of Keefer (1994) and Wells & Coppersmith (1994). It is suggested that the Nimu fault of the Yadong-Gulu rift may be more hazardous than the northern and southern part due to its high susceptibility of large co-seismic landslides.

Tree ring evidence of slope movements preceding catastrophic landslides

Catastrophic landslides represent one of the most dangerous natural hazards. Detailed knowledge about the pre-landslide behaviour of the affected slope is crucial for effective modelling of the landslide origin in the future or even for creating an early warning system. As precise retrospective reconstruction of slope movements in the pre-landslide period is very limited, dendrogeomorphic methods can be effective tools for these purposes due to the high sensitivity of trees to slope movements and the spatial aspects of data provided by the position of affected trees. This study presents the results of tree ring-based analysis of slope movements preceding three selected catastrophic landslides of different types in the Outer Western Carpathians (Girova 2010—translational rockslide; Brodska 1997—earthflow; Hluboce 2006—rotational rockslide). Three aspects of pre-landslide slope movements were analysed in detail (frequency, intensity, spatial distribution). In total, 300 tree ring series from 150 trees disturbed by pre-landslide movements were used for these purposes. The Girova landslide was preceded by an increasing frequency and intensity of movements but without any spatial pattern. The Brodska landslide was preceded by a low frequency of low-intensity movements without any temporal trends but with significant clustering several years before the landslide. The Hluboce landslide was preceded by a decreasing frequency of movements with increasing intensity and concentration in the source zone. The character of pre-landslide movements is probably influenced by the presence of old landslide structures on the affected slope and by the mechanism of the movements themselves.

Origin, development factors and dynamics of landslides in Jurassic clay in Moscow

The article focuses on the factors and dynamics of development of large deep extrusion landslides in Jurassic clay participating in geological structure of high bank slopes of the Moscow River within the city boundaries. The history of geological development of territory in Meso-Cenozoic age is observed in briefly; the peculiarities of upper Jurassic clay structure are considered; the structure, composition, and physico-chemical properties of rocks are described both in preserved and weathered state; the morphology and zoning of landslide slope structure as well as stages and dynamics of landslide deformations are characterized. Recommendations on the engineering development of territories affected by landslides are given. The paper is based on the generalization of numerous publications and archive data devoted to this acute topic.

Interparticle Friction Leads to Nonmonotonic Flow Curves and Hysteresis in Viscous Suspensions

Hysteresis is a major feature of the solid-liquid transition in granular materials. This property, by allowing metastable states, can potentially yield catastrophic phenomena such as earthquakes or aerial landslides. The origin of hysteresis in granular flows is still debated. However, most mechanisms put forward so far rely on the presence of inertia at the particle level. In this paper, we study the avalanche dynamics of non-Brownian suspensions in slowly rotating drums and reveal large hysteresis of the avalanche angle even in the absence of inertia. By using micro-silica particles whose interparticle friction coefficient can be turned off, we show that microscopic friction, conversely to inertia, is key to triggering hysteresis in granular suspensions. To understand this link between friction and hysteresis, we use the rotating drum as a rheometer to extract the suspension rheology close to the flow onset for both frictional and frictionless suspensions. This analysis shows that the flow rule for frictionless particles is monotonous and follows a power law of exponent $\alpha \!= \! 0.37 \pm 0.05$, in close agreement with the previous theoretical prediction, $\alpha\!=\! 0.35$. By contrast, the flow rule for frictional particles suggests a velocity-weakening behavior, thereby explaining the flow instability and the emergence of hysteresis. These findings show that hysteresis can also occur in particulate media without inertia, questioning the intimate nature of this phenomenon. By highlighting the role of microscopic friction, our results may be of interest in the geophysical context to understand the failure mechanism at the origin of undersea landslides.

Computational NAMI-DANCE complex in the problem of tsunami waves

Mathematical models applicable to the simulation of generation and propagation of tsunamis of different origin - underwater earthquakes, submarine landslides, meteotsunami - are described. The basic model is based on the well-known nonlinear shallow-water theory and its dispersion generalizations in two horizontal dimensions. Long wave dispersion related to the finiteness of water depth increases the order of PDE and leads to serious computational problems. We replace the physical dispersion with the numerical one using specific conditions for spatial and temporal steps. The numerical scheme is based on a Leap-Frog method. The equations are solved in spherical coordinates fixed to the rotating Earth by taking into account dissipative effects in the near-bottom layer with the use of NAMI-DANCE code. For tsunami waves of seismic origin, the initial conditions for hydrodynamic equations are found from the Okada solution of elastic equations describing the development of an earthquake. In the case of meteotsunami, atmospheric factors are modeled by the external forces. The process of generation of tsunami waves of landslide origin is analyzed in the framework of a two-layer model with lower viscous layer modeling the motion of a submarine landslide. There are two kinds of boundary conditions: free wave passage through open boundaries (in straits, etc.) using linear shallow-water equations, and a full reflection on the coast or in near-shore area. The NAMI-DANCE code has been verified with several benchmarks. The difficulties of tsunami modelling associated with the lack of accuracy in the bottom bathymetry and land topography are mentioned. The use of the developed code for the analysis of tsunami action on the coasts and constructions is discussed.

The Numerical Technique for the Landslide Tsunami Simulations Based on Navier–Stokes Equations

The paper presents an integral technique simulating all phases of a landslide-driven tsunami. The technique is based on the numerical solution of the system of Navier–Stokes equations for multiphase flows. The numerical algorithm uses a fully implicit approximation method, in which the equations of continuity and momentum conservation are coupled through implicit summands of pressure gradient and mass flow. The method we propose removes severe restrictions on the time step and allows simulation of tsunami propagation to arbitrarily large distances. The landslide origin is simulated as an individual phase being a Newtonian fluid with its own density and viscosity and separated from the water and air phases by an interface. The basic formulas of equation discretization and expressions for coefficients are presented, and the main steps of the computation procedure are described in the paper. To enable simulations of tsunami propagation across wide water areas, we propose a parallel algorithm of the technique implementation, which employs an algebraic multigrid method. The implementation of the multigrid method is based on the global level and cascade collection algorithms that impose no limitations on the paralleling scale and make this technique applicable to petascale systems. We demonstrate the possibility of simulating all phases of a landslide-driven tsunami, including its generation, propagation and uprush. The technique has been verified against the problems supported by experimental data. The paper describes the mechanism of incorporating bathymetric data to simulate tsunamis in real water areas of the world ocean. Results of comparison with the nonlinear dispersion theory, which has demonstrated good agreement, are presented for the case of a historical tsunami of volcanic origin on the Montserrat Island in the Caribbean Sea.

Assessing the geologic evolution of Greater Thaumasia, Mars

AbstractThe Greater Thaumasia region consists of three chemical provinces that include Syria, Solis, and Thaumasia Planae, the Corprates Rise, part of the Thaumasia Highlands, and the transition zone northwest of the Argyre basin. Chemical signatures obtained from the Mars Odyssey Gamma Ray Spectrometer suggest low abundances of K and Th to the west, with low H abundances and high Si abundances to the east, relative to the bulk Martian crust at midlatitudes. These observations are confirmed and quantified with a modified box and whisker analysis that simultaneously captures the degree of deviation and significance of the regionally anomalous chemistry. Motivated by regionally unique chemistry, as well as its diverse geological history, we characterize Greater Thaumasia in terms of chemistry, mineralogy, and mapped geology to determine how such complementary data record the evolution of this region. Our observations are inconsistent with a proposed salt‐lubricated landslide origin, particularly given the lack of chemical or mineralogical signatures to support near‐surface salt deposits that should arise over geological timescales. Our observations instead support magmatic processes, such as mantle evolution over geological time, which may impart the Si‐enriched signature of the eastern portion of Greater Thaumasia as well as the K and Th depletion of the southeastern flank of Syria Planum. While the observed trend of decreasing K and Th from Noachian to Hesperian lavas is inconsistent with previous models of Martian mantle evolution, we see an increase in Ca content at the Noachian‐Hesperian boundary, consistent with predictions from thermodynamic modeling.

Climate-change versus landslide origin of fill terraces in a rapidly eroding bedrock landscape: San Gabriel River, California

Fill terraces along rivers represent the legacy of aggradation periods that are most commonly attributed to climate change. In the North Fork of the San Gabriel River, an arid bedrock landscape in the San Gabriel Mountains, California, a series of prominent fill terraces was previously related to climate-change−induced pulses of hillslope sediment supply that temporarily and repeatedly overwhelmed river transport capacity during the Quaternary. Based on field observations, digital topographic analysis, and dating of Quaternary deposits, we suggest instead that valley aggradation was spatially confined to the North Fork San Gabriel Canyon and was a consequence of the sudden supply of unconsolidated material to upstream reaches by one of the largest known landslides in the San Gabriel Mountains. New ^(10)Be-derived surface exposure ages from the landslide deposits, previously assumed to be early to middle Pleistocene in age, indicate at least three Holocene events at ca. 8−9 ka, ca. 4−5 ka, and ca. 0.5−1 ka. The oldest and presumably most extensive landslide predates the valley aggradation period, which is constrained by existing ^(14)C ages and new luminescence ages to ca. 7−8 ka. The spatial distribution, morphology, and sedimentology of the river terraces are consistent with deposition from far-traveling debris flows that originated within, and mined, the landslide deposits. Valley aggradation in the North Fork San Gabriel Canyon therefore resulted from locally enhanced sediment supply that temporarily overwhelmed river transport capacity, but the lack of similar deposits in other parts of the San Gabriel Mountains argues against a regional climatic signal. Our study highlights the potential for valley aggradation by debris flows in arid bedrock landscapes downstream of landslides that occupy headwater areas.

Numerical technology for landslide tsunami simulations based on Navier-Stokes equations

The paper presents an integral technology simulating all phases of a landslide-driven tsunami. The technology is based on the numerical solution of a set of Navier-Stokes equations for multi-phase flows. The numerical algorithm uses a fully implicit approximation method, in which the equations of continuity and momentum conservation are coupled through implicit summands of pressure gradient and mass flow. The method we propose removes strict constraints on the timestep and makes it possible to simulate tsunami propagation to arbitrarily large distances. The landslide origin is simulated as an individual phase being a Newtonian fluid with its own density and viscosity and separated from the water and air phases by an interface. The paper presents the basic equation discretization formulas and expressions for coefficients and describes the main steps of the computational procedure. To enable simulations of tsunami propagation across wide water areas, we propose a parallel technology implementation algorithm that employs an algebraic multi-grid method. The multi-grid method implementation is based on the global and cascade collection algorithms, which impose no limitations on the paralleling scale and make this technology applicable to petascale systems. We demonstrate the possibility of simulating all phases of a landslide-driven tsunami, including its generation, propagation and uprush. The technology has been verified against the problems supported by experimental data. The paper describes the mechanism of incorporating bathymetric data to simulate tsunamis in real water areas of the world ocean. Results of comparison with the non-linear dispersion theory, which demonstrated good agreement, are presented for the case of a historical tsunami of volcanic origin on the Montserrat island in the Caribbean Sea.

EXAMPLES OF LANSLIDES IN THE FEDERATION OF BOSNIA AND HERZEGOVINA WITH THE ANALYSIS OF THE CAUSES OF THEIR ACTIVATION

<p>Bosnia and Herzegovina is characterized by heterogeneous geological structure, and a high degree of tectonic and the seismic activity as well as various relief and the climatic characteristics and water flows of different gradients. All this reflected on engineering-geological characteristics of the terrain.</p><p>The main causes of landslides' activation are changes in level of underground waters, chopping down of forest, great rainfalls, snow melting, long drought periods, changes in slopes, changes in load of a slope, rock's wastage, uncontrolled diversion of surface waters, earthquakes etc. Researches on landslides are carried out in order to establish the cause of landslide's origin and to find out efficient overhaul measures. Landslide's overhaul success depends not only on established causes of landslide's origin, but also on use of technical measures for stopping that process. Overhaul measures' carrying out is important in protection of the environment.</p><p>This paper presents an analysis of co-action of natural factors and negative anthropogenic effect in a settled area, where landslides appear, by its studying and eliminating of causes we are creating the conditions for a successful stabilization of landslides. The paper shows some characteristic landslides with defining of geomorphologic, geologic, engineer geologic, hydrogeologic and geotechnical characteristics of the terrain.</p>

Evaluating landslide hazards using RCP 4.5 and 8.5 scenarios

Recently, extreme meteorological events have occurred frequently owing to climate change and its influence. Impacts of concentrated precipitation events include the damage caused by landslides. Many areas in Gangwondo (Korea) are located at high elevation and have large elevation differences; these areas are thus at high risk of landslides. The purpose of this study was to evaluate the landslide hazard of the province using representative concentration pathways (RCP) scenarios 4.5 and 8.5 and to compare results. This study produced an optimal landslide model for the province through analysis of variables and points of landslide origin. Estimates indicate that the landslide hazard area will increase to 154 km2. The RCP 8.5 scenario showed a larger (by about 59 km2) landslide hazard area than the RCP 4.5 scenario. The uncertainty of climate change scenarios was also explored using statistical values of each scenario period. An overlay analysis (overlay of landslide hazard areas and land cover map) showed that 40.6 % of farmlands would be susceptible to landslides in 2070–2099 (RCP 8.5). Additionally, damage to the alpine agriculture due to landslides was also identified as a critical area. In the RCP 8.5 scenario, the land-use types that occupy more than 20 % of the landslide hazard area are transportation, recreational facilities, and vinyl house for farming. This suggests that casualties from landslides will increase in future. It also highlights a lack of policies to manage development. Therefore, the local government of Gangwondo should consider landslide hazard areas when planning future land uses.

Morphometric characterization of a large scale rockslide, and probable seismogenic origin of landslides on the western flank of Central Precordillera, Argentina

The distribution of late Pleistocene to Holocene rockslides in the western flank of the eastern mountain ranges of Central Precordillera (30° 40′–31° S), has been analyzed to determine the triggering mechanisms. The mode of failure was determined to be translational sliding. This paper presents the results of research on one of the Holocene rockslides located in the western flank of Sierra de La Dehesa, which is composed of stratified limestones of early Paleozoic age. In order to characterize this slide, high resolution satellite imagery interpretation was carried out, along with the recognition of the landslide detachment zones and landslide bodies with the aim of reconstructing the pre-slide topography. The model proposed for this slide is a translational or planar slide, as the mode of failure was along a broadly planar surface accompanied by shear or tensile fractures and joints. The estimated rock volume involved is 1.24 Mm3. We compared rockslide occurrence patterns to slope, topography, lithology, geological structures, and seismicity records. After analysis of the spatial relationships among all the slides and the distribution of seismic epicenters, historical earthquakes and neighboring Quaternary faults as seismogenic sources, we hypothesize that these Quaternary rockslides in the Central Precordillera have been triggered by shallow seismicity associated with active faults.

Nuevas observaciones sobre el origen del Depósito Mesón Alto, Valle del Yeso, Chile central: un depósito compuesto de procesos glaciares y de remoción en masa?

The Mesón Alto chaotic deposit, located in the Main Cordillera at about 33°40’S, is an important landform with a volume of ca. 4.5 km3 unconsolidated material deposited downstream of the Yeso Dam in the Yeso Valley, Río Maipo drainage basin. Historical work related this large deposit to a glacial origin whereas later on, it was assigned to a megalandslide that originated in the Cerro Mesón Alto Massif. First results of integrated fieldwork along with petrographic and geochemical laboratory work on granitoid blocks from five different portions of the deposit, compared with the major outcropping intrusive units in the neighbourhood (La Gloria Pluton, Cerro Mesón Alto Massif and Cerro Aparejo Intrusion) point to a landslide origin of the surface blocks. The results suggest that granitoid fragments of the deposit most likely belong to the Cerro Mesón Alto Massif, the proposed source of the rock avalanche. However, morphometric parameters and field observations support the idea of a rock avalanche deposited on top of glacial material. Therefore, the Mesón Alto deposit should be assigned to a composite origin. Confirmation of a post-glacial, large volume rock avalanche in a strategic area for existent infrastructure for Santiago water supply and ongoing energy projects is fundamental for a correct hazard and risk assessment of the region.

The influences of geological and land use settings on shallow landslides triggered by an intense rainfall event in a coastal terraced environment

Several factors (including slope morphology, geological and structural settings, the mechanical properties of soils, weathering, hydrological and hydrogeological conditions and land use changes) can affect the origin and development of shallow landslides induced by rainfall. On 25 October 2011, an intense rainfall occurred in a wide area of Italy between eastern Liguria and northern Tuscany, triggering thousands of shallow landslides and causing widespread flooding. Floods and landslides caused severe damage to villages and infrastructure and caused 13 fatalities. This study was conducted to investigate the shallow landslides triggered by the rainfall in the Vernazza basin (Cinque Terre in eastern Liguria), where landslides and debris floods caused 3 fatalities and damage of approximately €130 million. The Vernazza basin, which is characterised by steep slopes, geological heterogeneity and unusual land use settings (approximately 50 % of the slopes have been terraced for centuries), was chosen as the focus of this study, conducted to assess the influences of several factors on landslide occurrence. Field surveys and engineering geological investigations, including laboratory and in situ tests, were carried out at various sites to assess the stratigraphic and geotechnical features of the soil slope covers. A basic engineering geological zoning was carried out, taking into account the bedrock lithology, the geotechnical properties of the soils and the land use settings. On the basis of a detailed inventory of the shallow landslides that occurred, the distribution of the landslides was analysed with respect to the slopes, the bedrock lithology, the land uses and the engineering geological setting. Terraced areas on impermeable bedrock were identified as the main landslide-prone areas. The results of the study also showed that the time since abandonment of terraces plays an important role in the occurrence of shallow landslides induced by rainfall.