Fast-moving Landslides Research Articles

A scalable well-balanced numerical scheme for the simulation of fast landslides with efficient time stepping

We consider a single-phase depth-averaged model for the numerical simulation of fast-moving landslides with the goal of constructing a well-balanced, yet scalable and efficient, second-order time-stepping algorithm. We apply a Strang splitting approach to distinguish between parabolic and hyperbolic problems. For the parabolic contribution, we adopt a second-order Implicit-Explicit Runge-Kutta-Chebyshev scheme, while we use a two-stage Taylor discretization combined with a path-conservative strategy, to deal with the purely hyperbolic contribution. The proposed strategy allows to decouple hyperbolic from parabolic-reaction stiff contributions resulting in an overall well-balanced scheme subject just to stability restrictions of the hyperbolic term. The spatial discretization we adopt is based on a standard finite element method, associated with a hierarchically refined Cartesian grid. After providing numerical evidence of the well-balancing property, we demonstrate the capability of the proposed approach to select time steps larger than the ones adopted by a classical Taylor-Galerkin scheme. Finally, we provide some meaningful scaling results on ideal and realistic scenarios.

A Preliminary Study of the Seepage Hammer Effect and Its Impacts on the Stability of Layered Infinite Slope

A rapid change in the pore water pressure of unsaturated soil due to a wetting front is a crucial factor and may result in instabilities in layered slopes. This study presents preliminary research on such a change, which we define as the seepage hammer effect. Vertical infiltration with multiple soil layers by column test was implemented to investigate the mechanism of the seepage hammer effect and distinguish it from the well-known Lisse effect and reverse Wieringermeer effect. A two-phase flow model was utilized to understand the evolutions of pore water/air pressure and volumetric water content, and its result evolved into a layered infinite slope stability analysis. Thus, the impacts of the seepage hammer effect on slope stability can be analyzed. This study found that the seepage hammer effect was triggered when the wetting front reached the interface of multiple layers and impermeable layers, and the rising speed of pore water pressure was proportional to the air venting capacity of soil. Slope stability analysis showed that the safety factor may decline suddenly because of the seepage hammer effect. Its relationship with the factor of safety and the sliding velocity is proportional. The detection of the seepage hammer effect could be a potential application of the study of fast-moving landslides.

Experimental Analysis of the Fire-Induced Effects on the Physical, Mechanical, and Hydraulic Properties of Sloping Pyroclastic Soils

The paper investigates the changes in the physical, mechanical, and hydraulic properties of coarse-grained pyroclastic soils, considered under both wildfire-burned and laboratory heating conditions. The soil samples were collected on Mount “Le Porche” in the municipality of Siano (Campania Region, Southern Italy), hit by wildfires on 20 September 2019. The area is prone to fast-moving landslides, as testified by the disastrous events of 5–6 May 1998. The experimental results show that the analyzed surficial samples exhibited (i) grain size distribution variations due to the disaggregation of gravelly and sandy particles (mostly of pumice nature), (ii) chromatic changes ranging from black to reddish, (iii) changes in specific gravity in low-severity fire-burned soil samples different from those exposed to laboratory heating treatments; (iv) progressive reductions of shear strength, associated with a decrease in the cohesive contribution offered by the soil-root systems and, for more severe burns, even in the soil friction angle, and (v) changes in soil-water retention capacity. Although the analyses deserve further deepening, the appropriate knowledge on these issues could provide key inputs for geotechnical analyses dealing with landslide susceptibility on fire-affected slopes in unsaturated conditions.

Evaluation of Unsaturated Soil Properties for a Debris-Flow Simulation

Fast-moving landslides (i.e., debris/earth flows) are often caused by heavy rainfall occurring in small areas, and are not predictable. On the other hand, innovative methods for geomechanical characterization, numerical analysis, and modeling are required to attempt to reproduce a given debris/earth flow event. As our capability to reproduce very complex phenomena increases, we can improve our prevention approaches. In this paper, a debris flow event that occurred in the Enna area (Sicily) is described. Starting from the study of the geological framework and the historical background, this research focused on the causes that triggered the landslide. In situ and laboratory tests, including geophysical investigations and triaxial tests in unsaturated conditions, were carried out to investigate the factors affecting the dynamics of the event. This study gives us better knowledge of the mechanical and hydraulic properties that can be used to model these events, to assess the most appropriate strategies for the prevention and mitigation of related risks.

Application of GIS-Based Knowledge-Driven and Data-Driven Methods for Debris-Slide Susceptibility Mapping

Debris-slides are fast-moving landslides that occur in the Appalachian region including the Great Smoky Mountains National Park (GRSM). Various knowledge and data-driven approaches using spatial distribution of the past slides and associated factors could be used to estimate the region's debris-slide susceptibility. This study developed two debris-slide susceptibility models for GRSM using knowledge-driven and data-driven methods in GIS. Six debris-slide causing factors (slope curvature, elevation, soil texture, land cover, annual rainfall, and bedrock discontinuity), and 256 known debris-slide locations were used in the analysis. Knowledge-driven weighted overlay and data-driven bivariate frequency ratio analyses were performed. Both models are helpful; however, each come with a set of advantages and disadvantages regarding degree of complexity, time-dependency, and experience of the analyst. The susceptibility maps are useful to the planners, developers, and engineers for maintaining the park's infrastructures and delineating zones for further detailed geo-technical investigation.

Life and death of slow-moving landslides

In the most destructive and catastrophic landslide events, rocks, soil and fluids can travel at speeds approaching several tens of metres per second. However, many landslides, commonly referred to as slow-moving landslides, creep at rates ranging from millimetres to several metres per year and can persist for years to decades. Although slow-moving landslides rarely claim lives, they can cause major damage to infrastructure and sometimes fail catastrophically, transitioning into fast-moving landslides that can result in thousands of casualties. In addition, slow-moving landslides are highly erosive features that control the landscape morphology in many mountainous regions (such as the California Coast Ranges or the Apennines). The persistent and long-term motion of slow-moving landslides provides an exceptional opportunity to investigate landslide processes and mechanisms. In this Review, we examine the environmental conditions (such as geology, climate and tectonics) of slow-moving-landslide-prone regions, analyse the forcings (for example, precipitation and groundwater, earthquakes, river erosion, anthropogenic forcings and external material supply) that drive their motion and investigate the subsequent implications of the different forcings on landslide dynamics. We then discuss circumstances in which slow-moving landslides can accelerate rapidly, move large distances or even fail catastrophically. Finally, we provide new perspectives and challenges for future landslide research. Some landslides creep at low velocities of a few millimetres to metres per year, forced by external factors such as rainfall, snowmelt, earthquakes or anthropogenic forcings. This Review discusses the recent advances in understanding slow-moving landslides and examines circumstances where slow-moving landslides can accelerate and fail catastrophically.

Improved offset tracking for predisaster deformation monitoring of the 2018 Jinsha River landslide (Tibet, China)

Synthetic aperture radar (SAR) remote sensing is a potential technique for long-term monitoring of landslide-prone areas. Pixel offset tracking methods work well for fast-moving landslides (more than tens of cm/yr). However, existing methods may present some limitations, such as (i) a high dependence of estimation window design on experience, (ii) a tradeoff between the accuracy of single points and the overall efficiency, and (iii) a low confidence in the results caused by heterogeneous in-window samples. In this paper, an improved offset tracking method is proposed to address these problems. First, the workflow is optimized by a “preseparation” step added before offset estimation to distinguish between feature matching and speckle pattern matching. The optimized workflow is more efficient for natural scenes containing both feature and non-saliency regions. Second, an improved algorithm called adaptive incoherence speckle offset tracking based on homogeneous samples (AISOT-HS) is proposed for non-saliency regions. Its two key points are (i) adaptive design of the optimal estimation windows by introducing a coherence map as a guide and (ii) offset estimation without heterogeneous samples. We apply the proposed method to study the evolution of the 2018 Jinsha River landslide (Tibet, China) using SAR data from the Gaofen 3 (GF-3) satellite and the Phased Array type L-band Synthetic Aperture Radar-2 (PALSAR-2) system onboard the Advanced Land Observing Satellite (ALOS) satellite. Compared with the traditional method, the proposed method improves the efficiency and reduces the uncertainty. We also analyze the spatiotemporal displacement pattern of this landslide, which shows that the Jinsha River landslide was most likely a thrust load-caused landslide. This study demonstrates the role of SAR remote sensing in global landslide monitoring, especially where ground truth data are scarce.

SPH Simulation of High-Volume Rapid Landslides Triggered by Earthquakes Based on a Unified Constitutive Model. Part II: Solid–Liquid-Like Phase Transition and Flow-Like Landslides

High-volume fast-moving landslides undergo a solid–liquid-like phase transition. In this study we apply the smoothed particle hydrodynamics (SPH) method to simulate the solid–liquid-like phase transition in earthquake-induced landslides based on a unified constitutive model. The feasibility analysis is carried out from two aspects: the governing equations in SPH and the unified constitutive model. A sand-collapse experiment simulating the fluidization motion is performed to verify the SPH model. Strong similarities between the SPH results and the experimental results are observed, confirming that the motion of geo-materials in different states can be simulated by the unified constitutive model. The entire process of the Tangjiashan landslide is reproduced. The SPH simulation shows that during the initiation process, the sliding-mass velocity was low as the geo-materials were in solid state. As shown in Part I of this study, a continuous slip surface formed at about 15[Formula: see text]s. The sliding body gains speed as it enters the fluid state. About 50[Formula: see text]s later, the mass gradually stops moving, reaches a steady state and returns to a solid phase. Besides, the SPH simulation based on elastic–plastic model clearly shows the advantage of the proposed model.

Landslide-inventory of the Cinque Terre National Park (Italy) and quantitative interaction with the trail network

ABSTRACT The Cinque Terre National Park (38 km2) has recently recorded a remarkable increase in tourists involved in outdoor activities such as hiking. However, due to the actual slope degradation issues that affect this outstanding terraced landscape, hiking trails are increasingly threatened by the impact of landslides. This produces severe landslide-related risk scenarios for hikers. In this study, a landslide inventory map (at 1:45000 scale) has been prepared through the revision/update of previous database and the analysis of air-photos and satellite images coupled with field surveys. Furthermore, a quantitative evaluation of the interaction between landslides and hiking trails has been performed by the definition of a Footpath Landslide Index. More than 400 landslides were identified highlighting that these phenomena represent the main source of hazard. The findings of this study reveal that side-hill trails are the most hazardous since hikers can be potentially affected by flow-like or fast-moving landslides.

Submarine Landslides Induce Massive Waves in Subsea Brine Pools

Subsea hypersaline anoxic brine pools are among the most extreme habitable environments on Earth that offer clues to life on other planets. Brine is toxic to macrofauna as remotely operated vehicles commonly observe dead and preserved remains in brine pools. While brine pools are often assumed to be stable stratified systems, we show that underwater landslides can cause significant disturbances. Moreover, landslides create large-amplitude waves upon impact with the brine pool, similar to tsunami waves. We focus on the Orca Basin brine pool in the deepwater Gulf of Mexico, which contains numerous landslide deposits and blocks that originated from scarps several hundred meters above the brine pool. The impact of massive fast-moving landslides generated waves with amplitude on the order of 100 s of meters, which rival the largest known ocean waves. Brine waves can negatively affect biological communities and potentially overspill to spread hypersaline brine into surrounding basins.

Assessing debris flow activity in a changing climate

Future trends in debris flow activity are constructed based on bias-corrected climate change projections using two meteorological proxies: daily precipitation and Convective Available Potential Energy (CAPE) combined with specific humidity for two Alpine areas. Along with a comparison between proxies, future number of days with debris flows are analyzed with respect to different regional and global climate models, Representative Concentration Pathways (RCPs), and area for quantile mapping. Two different base periods are also analyzed, as debris flows were observed on only 6 (17) days between 1950 and 1979, yet on 18 (49) days between 1980 and 2009 for Fella River, NE Italy (Barcelonnette, SE French Alps). For both areas, future climate projections vary between no change up to an increase of 6.0 % per decade in days with debris flow occurrences towards the end of 21st century. In Barcelonnette, the base period and proxy have a bigger impact on the future number of debris flow days than the climate model or RCP used. In Fella River, the base period, RCP, and proxy used define the future range. Therefore the selection of proxy, base period and downscaling technique should be carefully considered for future climate change impact studies concerning debris flow activity and associated fast-moving landslides.

The RUSLE erosion index as a proxy indicator for debris flow susceptibility

Debris flows represent dangerous occurrences in many parts of the world. Several disasters are documented due to this type of fast-moving landslides; therefore, natural-hazard assessment of debris flows is crucial for safety of life and property. To this aim, much current work is being directed toward developing geotechnical-hydraulic models for the evaluation of debris flow susceptibility. A common base for such current models is parameterization of background predisposing and triggering factors such as inherent characteristics of geo-materials, topography, landscape and vegetation cover, rainfall regime, human activities, etc. which influence the occurrence of these processes on slopes. The same factors are also taken into account in soil erosion prediction models. Consequently, it seems worth investigating the effectiveness of the soil erosion index as debris flows susceptibility indicator. To this aim, a logistic regression analysis was carried out between the erosion index assessed by means of the Revised Universal Soil Loss Equation (RUSLE) model and the inventory of debris flows that have occurred in an area in Sicily (Southern Italy). Model assumptions were verified and validated by means of a series of statistical tools. Different possible scenarios were also evaluated by considering hypothetical changes in soil erosion rate under different rain erosivity conditions. Notwithstanding the rough approximations in model data collection, the outcomes appear encouraging.

토석류 유동성 평가를 위한 링 전단시험장치 개발 및 활용

산사태는 토사, 거석, 유목 등 산사태 물질의 중력사면 이동현상이다. 산사태는 수리학적, 지형학적, 지반공학적 요인에 따라 다양한 흐름 및 퇴적특성을 보인다. 흐름특성은 아주 느리게 움직이는 산사태(활동, 이류 등)에서 아주 빠르게 움직이는 산사태(토석사태, 토석류 등)까지 다양하다. 이런 점에서 산사태 발생과 확산 메커니즘의 이해를 위해 전단변형률에 따른 전단강도특성에 대한 연구가 필요하다. 본 연구는 한국형 산사태에 적합한 링 전단시험장치의 개발과 활용성에 대한 것이다. 링 전단시험장치는 산사태 유형별 피해 및 영향성 평가에 사용되는 전단강도를 측정할 수 있으며, 전단속도에 따른 산사태의 유동성을 평가하기 위한 장치이다. 비배수 전단강도 측정용 링 전단시험장치는 기존에 개발된 링 전단시험기의 수정보완형으로 '포화-압밀-배수-전단' 순으로 시험조건을 자유롭게 조절할 수 있다. 링 전단상자내 흙 시료의 전단강도의 정확한 측정을 위해 미끄럼 방지, 밀폐성 및 회전성 향상 기능을 갖춘 시험장치이다. 링 전단시험장치는 모래와 자갈 시료에 대한 예비실험을 수행하였으며 기존 시험결과와 비교하여 신뢰할 만한 결과를 확인하였다. 회전속도 100 mm/sec 로 구속할 때 배수조건에 따른 일시적 액상화 현상으로 인한 강도저하 현상이 관측되며, 전단면에 따른 입자파쇄 현상이 뚜렷하게 나타났다. 마지막으로 토석류 유변학에 기초하여 링 전단시험장치를 이용한 산사태 유동성 평가기법을 제안하였다. Landslides are known as gravitational mass movements that can carry the flow materials ranging in size from clay to boulders. The various types of landslides are differentiated by rate and depositional features. Indeed, flow characteristics are observed from very slow-moving landslides (e.g., mud slide and mud flow) to very fast-moving landslides (e.g., debris avalanches and debris flows). From a geomechanical point of view, shear-rate-dependent shear strength should be examined in landslides. This paper presents the design of advanced ring-shear apparatus to measure the undrained shear strength of debris flow materials in Korea. As updated from conventional ring-shear apparatus, this apparatus can evaluate the shear strength under different conditions of saturation, drainage and consolidation. We also briefly discussed on the ring shear apparatus for enforcing sealing and rotation control. For the materials with sands and gravels, an undrained ring-shear test was carried out simulating the undrained loading process that takes place in the pre-existing slip surface. We have observed typical evolution of shear strength that found in the literature. This paper presents the research background and expected results from the ring-shear apparatus. At high shear speed, a temporary liquefaction and grain-crushing occurred in the sliding zone may take an important role in the long-runout landslide motion. Strength in rheology can be also determined in post-failure dynamics using ring-shear apparatus and be utilized in debris flow mobility.

Evaluation of Flood and Landslide Risk to the Population of Italy

We have compiled a database of floods and landslides that occurred in Italy between AD 1279 and 2002 and caused deaths, missing persons, injuries, and homelessness. Analysis of the database indicates that more than 50,593 people died, went missing, or were injured in 2580 flood and landslide events. Harmful events were inventoried in 26.3% of the 8103 Italian municipalities. Fatal events were most frequent in the Alpine regions of northern Italy and were caused by both floods and landslides. In southern Italy, landslides were the principal agents of fatalities and were most numerous in the Campania region. Casualties were most frequent in the autumn. Fast-moving landslides, including rock falls, rockslides, rock avalanches, and debris flows, caused the largest number of deaths. In order to assess the overall risk posed by these processes, we merged the historical catalogs and identified 2682 "hydrogeomorphological" events that triggered single or multiple landslides and floods. We estimated individual risk through the calculation of mortality rates for both floods and landslides and compared these rates to the death rates for other natural, medical, and human-induced hazards in Italy. We used the frequency distribution of events with fatalities to ascertain the magnitude and frequency of the societal risks posed by floods and landslides. We quantified these risks in a Bayesian model that describes the probabilities of fatal flood and landslide events in Italy.

Small fast-moving flow-like landslides in volcanic deposits: The 2001 Las Colinas Landslide (El Salvador)

Fast-moving landslides are one of the most significant dangers deriving from slope instabilities. Landslides involving large volumes can develop in rock or debris avalanches with extreme mobility and enormous destructiveness. Nevertheless, a relevant number of casualties and damages derive from small, fast-moving landslides with flow-like behaviour. The Las Colinas landslide occurred at Santa Tecla (El Salvador, Central America) during a strong earthquake. It slid off the northern flank of the Bálsamo ridge, and resulted in almost 500 casualties and can be considered one of the most destructive landslides ever known. Earthquake shaking was amplified by the rock mass and the steep ridge topography. We collected original geological, geomorphological and geophysical data in the Cordillera del Bálsamo area. The involved materials, ranging from lapilli to tuff layers of different strength, have been mapped and characterized. Slope stability analyses have been performed both under static and dynamic conditions through limit equilibrium and finite element methods. Hazard zonation for this type of landslides requires the forecast of the movement velocity and final deposition area. We used a fully two-dimensional FEM model to simulate landslide spreading downslope. The developed code allows the use of different constitutive models and yield rules with the possibility to model and study internal deformation of the landslide mass, as well material entrainment and deposition.

Landslide fatalities and the evaluation of landslide risk in Italy

A database of landslides that occurred in Italy between 1279 and 1999 and caused deaths, missing people, injuries and homelessness was compiled from a variety of different sources. These included the archive of the National Research Council's AVI (Damaged Urban Areas) project, which compiled information on landslide events in the 20th century in Italy. The sources also included reports on historical landslide investigations for the whole of Italy, Alpine areas, the Apennines, various regions or provinces, and for single sites. Analysis of the database indicates that more than 10,000 people died in a total of 840 landslide events. Fatal landslide events were more frequent in the Alpine regions of Northern Italy and in Campania (southern Italy), and most casualties occurred in the Autumn. Fast-moving landslides caused the largest number of deaths. They included rockfalls, rockslides, rock avalanches and debris flows. The cumulative frequency of landslide events was plotted against their consequences, and the plots were compared to similar curves for the whole Alps and for Canada, Japan, China and Hong Kong. The frequency in Italy was found to be higher than in the Alps, Canada and Hong Kong, but lower than that of Japan and China. Landslide mortality rates were estimated and compared to mortality rates for other natural, medical, and human-induced hazards.