Slow-moving Landslides Research Articles

Empirical fragility and vulnerability curves for buildings exposed to slow-moving landslides at medium and large scales

Slow-moving landslides yearly induce huge economic losses worldwide in terms of damage to facilities and interruption of human activities. Within the landslide risk management framework, the consequence analysis is a key step entailing procedures mainly based on identifying and quantifying the exposed elements, defining an intensity criterion and assessing the expected losses. This paper presents a two-scale (medium and large) procedure for vulnerability assessment of buildings located in areas affected by slow-moving landslides. Their intensity derives from Differential Interferometric Synthetic Aperture Radar (DInSAR) satellite data analysis, which in the last decade proved to be capable of providing cost-effective long-term displacement archives. The analyses carried out on two study areas of southern Italy (one per each of the addressed scales) lead to the generation, as an absolute novelty, of both empirical fragility and vulnerability curves for buildings in slow-moving landslide-affected areas. These curves, once further validated, can be valuably used as tools for consequence forecasting purposes and, more in general, for planning the most suitable slow-moving landslide risk mitigation strategies.

Controls and feedbacks in the coupling of mountain channels and hillslopes

Abstract Mountain channels can be strongly coupled with adjacent hillslopes, exchanging both mass and energy. However, hypotheses of the underlying cause and effect relations are based on indirect observations that do not resolve the mechanics of channel-hillslope coupling at the process scale. Here we present direct observational data of a coupled channel-hillslope system in the catchment area of the Erlenbach, a mountain stream in Switzerland. A slow-moving landslide flanking this alpine stream failed after a flood had eroded an alluvial step in the channel at its base, representing evidence for an upsystem link in channel-hillslope coupling. Progressive accumulation of landslide debris in the channel resulted in a renewed step, stabilizing the hillslope and restoring the channel step in a downsystem link. Thus, upsystem and downsystem coupling mechanisms are joined in a negative feedback cycle. In this cycle, debuttressing and rebuttressing due to channel bed erosion and alluviation are the dominant controls on hillslope stability. Based on an order of magnitude estimate it is plausible that the observed feedback mechanism is a relevant process in the production of coarse (>2 mm) sediment in the Erlenbach.

Spaceborne, UAV and ground-based remote sensing techniques for landslide mapping, monitoring and early warning

BackgroundThe current availability of advanced remote sensing technologies in the field of landslide analysis allows for rapid and easily updatable data acquisitions, improving the traditional capabilities of detection, mapping and monitoring, as well as optimizing fieldwork and investigating hazardous or inaccessible areas, while granting at the same time the safety of the operators. Among Earth Observation (EO) techniques in the last decades optical Very High Resolution (VHR) and Synthetic Aperture Radar (SAR) imagery represent very effective tools for these implementations, since very high spatial resolution can be obtained by means of optical systems, and by the new generations of sensors designed for interferometric applications. Although these spaceborne platforms have revisiting times of few days they still cannot match the spatial detail or time resolution achievable by means of Unmanned Aerial Vehicles (UAV) Digital Photogrammetry (DP), and ground-based devices, such as Ground-Based Interferometric SAR (GB-InSAR), Terrestrial Laser Scanning (TLS) and InfraRed Thermography (IRT), which in the recent years have undergone a significant increase of usage, thanks to their technological development and data quality improvement, fast measurement and processing times, portability and cost-effectiveness. In this paper the potential of the abovementioned techniques and the effectiveness of their synergic use is explored in the field of landslide analysis by analyzing various case studies, characterized by different slope instability processes, spatial scales and risk management phases.ResultsSpaceborne optical Very High Resolution (VHR) and SAR data were applied at a basin scale for analysing shallow rapid-moving and slow-moving landslides in the emergency management and post- disaster phases, demonstrating their effectiveness for post-disaster damage assessment, landslide detection and rapid mapping, the definition of states of activity and updating of landslide inventory maps. The potential of UAV-DP for very high resolution periodical checks of instability phenomena was explored at a slope-scale in a selected test site; two shallow landslides were detected and characterized, in terms of areal extension, volume and temporal evolution. The combined use of GB-InSAR, TLS and IRT ground based methods, was applied for the surveying, monitoring and characterization of rock slides, unstable cliffs and translational slides. These applications were evaluated in the framework of successful rapid risk scenario evaluation, long term monitoring and emergency management activities. All of the results were validated by means of field surveying activities.ConclusionThe attempt of this work is to give a contribution to the current state of the art of advanced spaceborne and ground based techniques applied to landslide studies, with the aim of improving and extending their investigative capacity in the framework of a growing demand for effective Civil Protection procedures in pre- and post-disaster initiatives. Advantages and limitations of the proposed methods, as well as further fields of applications are evaluated for landslide-prone areas.

Seasonal change in permeability of surface soils on a slow-moving landslide in a heavy snow region

This study demonstrated seasonal changes in the topsoil permeability due to vegetation growth in summer and snow loading in winter of a landslide in a temperate snowy area of northern Japan, which is underlain by soft Neogene sedimentary rocks. The decrease in saturated hydraulic conductivity due to loading was also examined for undisturbed and remolded specimens of surface soils from the landslide, using a newly developed apparatus for the consolidation permeability test. Infiltration capacity measured in the field increased gradually after snowmelt to a peak in midsummer and decreased exponentially with increasing snow load in winter. In the laboratory experiment, saturated hydraulic conductivity declined as an exponential function of loading. The topsoil was permeable enough to infiltrate rainwater into the ground, even for intense rain storms in summer, but became less permeable under heavy snow load during winter and was not capable of full infiltration of meltwater during the snowmelt period. This suggested that Hortonian overland flow should occur in late winter, at least patchily, under the melting snowpack.

Correlation of satellite image time-series for the detection and monitoring of slow-moving landslides

Slow-moving landslides are widespread in many landscapes with significant impacts on the topographic relief, sediment transfer and human settlements. Their area-wide mapping and monitoring in mountainous terrain, however, is still challenging. The growing archives of optical remote sensing images offer great potential for the operational detection and monitoring of surface motion in such areas. This study proposes a multiple pairwise image correlation (MPIC) technique to obtain a series of redundant horizontal displacement fields, and different multi-temporal indicators for a more accurate detection and quantification of surface displacement. The technique is developed and tested on a series of monoscopic and stereoscopic Pléiades satellite images at a test site in the South French Alps. Empirical tests confirm that MPIC significantly increased detection accuracy (F−measure=0.85) and that the measurement error can be reduced by averaging velocities from all pair combinations covering a given time-step (i.e. when stereo-pairs are available for at least one date). The derived inventory and displacement fields of 169 slow-moving landslides show a positive relationship between the landslide size and velocities, as well as a seasonal acceleration of the largest landslides in response to an increase in effective precipitation. The processing technique can be adapted to better exploit increasingly available time-series from a variety of optical satellites for the detection and monitoring of landslide displacement.

Post-failure evolution analysis of a rainfall-triggered landslide by multi-temporal interferometry SAR approaches integrated with geotechnical analysis

Persistent Scatterers Interferometry (PSI) represents one of the most powerful techniques for Earth's surface deformation processes' monitoring, especially for long-term evolution phenomena. In this work, a dataset of 34 TerraSAR-X StripMap images (October 2013–October 2014) has been processed by two PSI techniques - Coherent Pixel Technique-Temporal Sublook Coherence (CPT-TSC) and Small Baseline Subset (SBAS) - in order to study the evolution of a slow-moving landslide which occurred on February 23, 2012 in the Papanice hamlet (Crotone municipality, southern Italy) and induced by a significant rainfall event (185mm in three days). The mass movement caused structural damage (buildings' collapse), and destruction of utility lines (gas, water and electricity) and roads. The results showed analogous displacement rates (30–40mm/yr along the Line of Sight – LOS-of the satellite) with respect to the pre-failure phase (2008–2010) analyzed in previous works. Both approaches allowed detect the landslide-affected area, however the higher density of targets identified by means of CPT-TSC enabled to analyze in detail the slope behavior in order to design possible mitigation interventions. For this aim, a slope stability analysis has been carried out, considering the comparison between groundwater oscillations and time-series of displacement. Hence, the crucial role of the interaction between rainfall and groundwater level has been inferred for the landslide triggering. In conclusion, we showed that the integration of geotechnical and remote sensing approaches can be seen as the best practice to support stakeholders to design remedial works.

Towards Slow-Moving Landslide Monitoring by Integrating Multi-Sensor InSAR Time Series Datasets: The Zhouqu Case Study, China

Although the past few decades have witnessed the great development of Synthetic Aperture Radar Interferometry (InSAR) technology in the monitoring of landslides, such applications are limited by geometric distortions and ambiguity of 1D Line-Of-Sight (LOS) measurements, both of which are the fundamental weakness of InSAR. Integration of multi-sensor InSAR datasets has recently shown its great potential in breaking through the two limits. In this study, 16 ascending images from the Advanced Land Observing Satellite (ALOS) and 18 descending images from the Environmental Satellite (ENVISAT) have been integrated to characterize and to detect the slow-moving landslides in Zhouqu, China between 2008 and 2010. Geometric distortions are first mapped by using the imaging geometric parameters of the used SAR data and public Digital Elevation Model (DEM) data of Zhouqu, which allow the determination of the most appropriate data assembly for a particular slope. Subsequently, deformation rates along respective LOS directions of ALOS ascending and ENVISAT descending tracks are estimated by conducting InSAR time series analysis with a Temporarily Coherent Point (TCP)-InSAR algorithm. As indicated by the geometric distortion results, 3D deformation rates of the Xieliupo slope at the east bank of the Pai-lung River are finally reconstructed by joint exploiting of the LOS deformation rates from cross-heading datasets based on the surface–parallel flow assumption. It is revealed that the synergistic results of ALOS and ENVISAT datasets provide a more comprehensive understanding and monitoring of the slow-moving landslides in Zhouqu.

Rate-weakening friction characterizes both slow sliding and catastrophic failure of landslides

Catastrophic landslides cause billions of dollars in damages and claim thousands of lives annually, whereas slow-moving landslides with negligible inertia dominate sediment transport on many weathered hillslopes. Surprisingly, both failure modes are displayed by nearby landslides (and individual landslides in different years) subjected to almost identical environmental conditions. Such observations have motivated the search for mechanisms that can cause slow-moving landslides to transition via runaway acceleration to catastrophic failure. A similarly diverse range of sliding behavior, including earthquakes and slow-slip events, occurs along tectonic faults. Our understanding of these phenomena has benefitted from mechanical treatments that rely upon key ingredients that are notably absent from previous landslide descriptions. Here, we describe landslide motion using a rate- and state-dependent frictional model that incorporates a nonlocal stress balance to account for the elastic response to gradients in slip. Our idealized, one-dimensional model reproduces both the displacement patterns observed in slow-moving landslides and the acceleration toward failure exhibited by catastrophic events. Catastrophic failure occurs only when the slip surface is characterized by rate-weakening friction and its lateral dimensions exceed a critical nucleation length [Formula: see text] that is shorter for higher effective stresses. However, landslides that are extensive enough to fall within this regime can nevertheless slide slowly for months or years before catastrophic failure. Our results suggest that the diversity of slip behavior observed during landslides can be described with a single model adapted from standard fault mechanics treatments.

Cold Temperatures Set Off Slow-Moving Landslides

Falling ground temperatures in the cold season are found to trigger shallow, slow-moving landslides on slopes with clayey soil.

Seismic noise monitoring of the water table in a deep-seated, slow-moving landslide

Daily correlations of ambient seismic noise on a large landslide at Utiku, New Zealand, reveal seismic velocity changes up to [Formula: see text] that follow a summer/winter cycle consistent with the pore-water pressures monitored at the basal slip surface in the landslide. The annual pattern of velocity changes is borne by a limited frequency band (6–8 Hz typically) that suggests a localized change in the medium. The Rayleigh waves that form the seismic signal within this frequency band have a maximum sensitivity at a depth of 2–3 m below the ground surface, consistent with the water table level. Fluid saturation changes in the landslide modeled using the Biot-Gassmann theory explain the limited frequency band and the amplitude of the seismic velocity change. This set of arguments suggests that seismic noise correlations are sensitive to water table oscillations through saturation changes and could be used as a nondestructive hydrologic monitoring tool.

Combined use of statistical and DInSAR data analyses to define the state of activity of slow-moving landslides

Statistical analyses have been often used for landslide susceptibility zoning at small to medium scale when relevant base and thematic maps are available. Since the beginning of the last decade, images remotely acquired by spaceborne Synthetic Aperture Radar (SAR) and processed via Differential SAR Interferometry (DInSAR) proved extremely useful for non-invasive and non-destructive monitoring of displacements of the topographic surface. The present paper proposes an original procedure for the definition of the state of activity of slow-moving landslides via the combined use of multivariate statistical analyses and DInSAR data. The procedure is based on the following essential elements: distinction between terrain units used for computational purposes and the final zoning units; independent statistical and DInSAR analyses and activity models leading to first-level state of activity zoning maps; a consistency model between statistical and DInSAR analyses; two confidence and combination models leading, respectively, to second- or third-level state of activity zoning maps. The application in a test area including 19 municipalities in southern Italy, where slow-moving landslides are widespread and accurately mapped by using geomorphological criteria, allowed the generation of the three above-mentioned levels of zoning maps. The results were successfully crosschecked by exploiting a different DInSAR dataset and the results of previous works based on the use of slow-moving landslide-induced damage to facilities surveys.

Advanced SAR Interferometric Analysis to Support Geomorphological Interpretation of Slow-Moving Coastal Landslides (Malta, Mediterranean Sea)

An advanced SAR interferometric analysis has been combined with a methodology for the automatic classification of radar reflectors phase histories to interpret slope-failure kinematics and trend of displacements of slow-moving landslides. To accomplish this goal, the large dataset of radar images, acquired in more than 20 years by the two European Space Agency (ESA) missions ERS-1/2 and ENVISAT, was exploited. The analysis was performed over the northern sector of Island of Malta (central Mediterranean Sea), where extensive landslides occur. The study was assisted by field surveys and with the analysis of existing thematic maps and landslide inventories. The outcomes allowed definition of a model capable of describing the geomorphological evolution of slow-moving landslides, providing a key for interpreting such phenomena that, due to their slowness, are usually scarcely investigated.

Effect of gravel content on creep behavior of clayey soil at residual state: implication for its role in slow-moving landslides

Soil creep is mostly manifested in slow-moving landslides. It is often the case for active slow-moving landslide with slip zone comprising clayey soil where creep would develop in the residual condition. If gravel is presented in clayey soil, this will have considerable impact on creep behavior of clayey soil. However, knowledge about creep behavior of the clayey soil containing gravel particles is scarce. This paper discusses creep behavior of natural clayey soil with gravel at residual state through a series of creep shear tests. Soil samples for this testing program were collected from the slip zones of two large slow-moving landslides in China. The collected soil samples consisted of clayey soil containing various amounts of gravel particles. The test results show that the soil specimens underwent two different creep patterns. An attenuating creep pattern was observed when the soil specimens were subjected to creep stress less than the residual strength, and a creep with increasing strain rate, or a nonattenuating creep pattern, with no evident secondary creep was noted when creep stress was intestinally increased to a level slightly greater than the residual strength. The creep patterns of clayey soil with gravel at the residual state observed in this study were noted to be very consistent with those of the gravel-free clayey soil reported in Bhat et al. (Int J Geomater 1(1):39–43, 2011, Nat Hazards 69(3):2161–2178, 2013) and Di Miao et al. (Eng Geol 162:53–66, 2013). This gives an indication that creep patterns of clayey soils with and without gravel at the residual state are essentially the same, or in other words, that the presence of gravel does not change the creep pattern of clayey soil. However, the test results in this study illustrate that the presence of gravel does have a notable effect on creep behavior of clayey soil. Specifically, the creep stress leading to creep failure of clayey soil and the minimum ratio of the creep stress to residual strength (RCSR) increased with gravel content, and the displacement until the tertiary creep was also larger in samples containing more gravel particles. It is postulated that creep behavior of clayey soil at the residual state in this study and its relationship with gravel content may be related to strength recovery and crushing of gravel-sized particles during creep.

Activity of Slow-Moving Landslides Recorded in Eccentric Tree Rings of Norway Spruce Trees (<i>Picea Abies</i> Karst.) — An Example from the Kamienne MTS. (Sudetes MTS., Central Europe)

We found ubiquitous evidence of ongoing slope instability by analysing the variability of tree-ring eccentricity index in trees growing on three apparently relict landslide slopes in the Sudetes (Poland, Central Europe). Slow movement of these landslide bodies occurs in the present-day conditions and is recorded almost every year, although with variable intensity. Correlation of dendrochronological record with the rainfall record from a nearby station in Mieroszów for the 1977–2007 period is very poor for two deep-seated rotational slides at Mt Suchawa and Mt Turzyna but considerably better for a shallow flowslide at Mt Garbatka. While this may reflect higher permeability of heavily jointed rocks involved in deep-seated sliding this could be linked with imperfections in the rainfall record. Dendrochronology proved capable of detecting minor displacements within landslides which otherwise show no geomorphic evidence of recent activity. Therefore, claims for the entirely relict nature of the landslides are not substantiated.

Kinematics of a giant slow-moving landslide in Northwest China: Constraints from high resolution remote sensing imagery and GPS monitoring

Slow-moving landslides generally are long-lived and characterized by continuous movement with some fluctuation in sliding rate following changes of environmental factors, such as rainfall and earthquake. Analysis on kinematics of this type of landslide is essential for understanding its mechanism and identifying causal factors controlling its movement behavior. This paper presents a study on kinematics of a giant slow-moving landslide in northwest China, called the Xieliupo landslide, which is about 72×106m3 in volume and has been slowly moving for more than 100years. This study is conducted using archival high resolution remote sensing images from multi-sources over a period about 43years and the data from 15-month GPS monitoring. Six sets of multi-source remote sensing images in 1969, 1971, 2004, 2008, 2010 and 2012 with spatial resolution higher than 2.5m were used, and GPS monitoring data were recorded from September 2012 to December 2013. Obvious geomorphologic changes identified from the images in 1971 and 2004 confirm that this landslide did move slowly in the past. Quantitative analysis reveals that movement of the landslide was persistent and behaved in a block by block mode with the greatest and the least velocities in its middle and lower parts, respectively. Distance measurement between the homologous point pairs on the orthorectified images in 2005, 2010 and 2012 indicates that annual ground displacement of the landslide ranged from 0.52m to 6.54m in the seven years. GPS monitoring data shows that the landslide ground displacement in the 15months varied from 0.49m to 2.91m, and annually between 0.39m and 2.33m, with a rather uniform movement pattern as identified using the remote sensing images. GPS monitoring results also reveal that the landslide movement is intermittent inter-annually. It is further discussed that movement behavior of the landslide is largely controlled by its topography with great influence of the active fault along its left hand flank and river erosion at its toe. Rainfall may affect inter-annual movement behavior of the landslide.

A-Differential Synthetic Aperture Radar Interferometry analysis of a Deep Seated Gravitational Slope Deformation occurring at Bisaccia (Italy)

This paper presents the results of an investigation on a Deep Seated Gravitational Slope Deformation (DSGSD), previously only hypothesized by some authors, affecting Bisaccia, a small town located in Campania region, Italy. The study was conducted through the integration of conventional methods (geological-geomorphological field survey, air-photo interpretation) and an Advanced-Differential Interferometry Synthetic Aperture Radar (A-DInSAR) technique. The DSGSD involves a brittle lithotype (conglomerates of the Ariano Irpino Supersynthem) resting over a Structurally Complex Formation (Varycoloured Clays of Calaggio Formation). At Bisaccia, probably as a consequence of post-cyclic recompression phenomena triggered by reiterated seismic actions, the rigid plate made up of conglomeratic sediments resulted to be split in five portions, showing different rates of displacements, whose deformations are in the order of some centimeter/year, thus inducing severe damage to the urban settlement.A-DInSAR techniques confirmed to be a reliable tool in monitoring slow-moving landslides. In this case 96 ENVIronmental SATellite-Advanced Synthetic Aperture Radar (ENVISAT-ASAR) images, in ascending and descending orbits, have been processed using SUBSOFT software, developed by the Remote Sensing Laboratory (RSLab) group from the Universitat Politècnica de Catalunya (UPC). The DInSAR results, coupled with field survey, supported the analysis of the instability mechanism and confirmed the historical record of the movements already available for the town.

An Exponential Matrix Method for the Buckling Analysis of Underground Pipelines Subjected to Landslide Loads

Due to their dimensions, long pipelines often cross areas that are highly susceptible to landslides. In Italy, this problem requires special attention, as many slow-moving landslides interact with buried pipelines. The paper analyzes such interaction problem with particular reference to buckling analysis, tackling the solution of the governing equations by an exponential matrix method. In the paper the basic equation, its computational aspects and numerical analysis options are outlined. Representative results of the proposed methodology and potential applications on buckling analysis of buried pipes are presented.

Ground-penetrating radar observations for estimating the vertical displacement of rotational landslides

Abstract. The objective of this paper is to demonstrate the applicability of ground-penetrating radar (GPR) for monitoring the displacement of slow-moving landslides. GPR data are used to estimate the vertical movement of rotational slides in combination with other surveying techniques. The study area is located along the Normandy coast (northeast France) where several rotational landslides are continuously affected by a seasonal kinematic regime (low displacement rates of 0.01 to 0.10 m yr−1) and periodically by major acceleration events (high displacement rates of 1.0 to 7.0 m per event).

Kinematics of earthflows in the Northern California Coast Ranges using satellite interferometry

Slow-moving landslides exhibit persistent downslope motion with variations in velocity driven by transient stress perturbations along the sliding surface. Here, we use satellite InSAR and high-resolution topographic data to identify 50 slow-moving landslides in the Northern California Coast Ranges, and monitor their seasonal kinematics over 4years. These landslides have similar mechanical properties and are subject to the same external forcings, which allows us to explore geometrical controls on kinematics. To overcome errors associated with large deformation gradients we incorporate a deformation model in the InSAR processing that enables us to generate deformation time series. We test our novel methodology using a synthetic deformation time series, confirming our ability to resolve seasonal velocity patterns. Time series analysis of four representative landslides reveals that seasonal velocity changes are characterized by comparatively rapid acceleration and gradual deceleration. Each slide displays distinct kinematic zones with different mean velocities, although velocity changes appear to occur synchronously along the landslide body over seasonal timescales. Because these deformation patterns are sensitive to subsurface geometry, we employ a commonly used non-Newtonian viscous flow law to infer slide thickness and find that these slides likely exhibit a highly variable thickness and an irregular (i.e. rough and non-planar) basal sliding surface. Our results suggest that slide geometry controls long-term motion, but does not strongly regulate their response to seasonal stress perturbations.

Earthquake-driven acceleration of slow-moving landslides in the Colca valley, Peru, detected from Pléiades images

Major earthquakes in mountainous areas often trigger rapid landslides. Some observations also suggest that earthquakes can damage landslide prone areas or cause slow-moving landslides to accelerate, with a risk of evolution to rapid landslides in the following months after the earthquake. Here, we use optical images from the Pléiades satellites to detect slow-moving landslides and quantify the effect of earthquakes on the landslide motion. We process multi-temporal Pléiades images acquired in March, April, and July 2013 over an area of 210km2 in the Colca valley (South Peru), to obtain two Digital Elevation Models (DEM) and three displacement fields of the area. The processed DEMs have an uncertainty of 0.6m (1σ), an order of magnitude better than two global and freely available DEMs (GDEM-v2 and SRTM), whereas the displacement fields have an uncertainty of between 0.11 and 0.18m (1σ) in both horizontal directions. Using these data, we detect 9 slow-moving landslides and compare their velocities during the March–April and April–July periods. We find that landslide velocities are highest during the wet season, which suggests a strong groundwater control, and we also highlight a landslide acceleration caused by a regional Mw 6.0 earthquake. The major parameters controlling the acceleration of the slow-moving landslides are the rock type and the distance to the source, suggesting that friction at the basal interface in the weeks after the earthquake is dependent on the shaking intensity.