Landslide Mobility Research Articles

Runout Number: A New Metric for Landslide Runout Characterization

ABSTRACT Landslide runout has traditionally been quantified by the height-to-length ratio, H/L, which, in many cases, is strongly influenced by the slope of the runout path. In this study, we propose an alternative mobility measure, the unitless Runout Number, measured as the landslide length divided by the square root of the landslide area, which characterizes landslide shape in terms of elongation. We used a database of 158 landslides of varying runout distances from locations in northern California, Oregon, and Washington state to compare the two runout measurement methods and explore their predictability using parameters that can be measured or estimated using geographic information systems. The Runout Number better describes the overall runout for several landslide and slope geometries. The two mobility measures show very little correlation to each other, indicating that the two parameters describe different landslide mobility mechanisms. When compared to predictive parameters shown by prior research to relate to landslide runout, the two runout measurement methods show different correlations. H/L correlates more strongly to initial slope angle, upslope contributing area, landslide area, and grain size distribution (percent clay, silt, total fines, and sand). The Runout Number correlates more strongly to planimetric curvature, upslope contributing area normalized by landslide area, and percent sand. Although these correlations are not necessarily strong enough for prediction, they indicate the validity of both runout measurement methods and the benefit of including both numbers when characterizing landslide mobility.

Modelling of mobility of Rissa landslide and following tsunami

Landslides in sensitive clays pose a major threat to life, property and the environment. The lack of warning signs and the extreme mobility of quick clays increase the risk. When occurring along fjords, lakes or large rivers, the landslides can generate destructive tsunamis. Historical records show that 45% of the shoreline landslides in marine sediments in Norway triggered tsunamis with run-up height of 1 to 15 m. To improve the management of the hazard and risk due to landslides in sensitive materials, the profession needs to develop tools for modelling the mobility of landslides and their tsunamigenic potential. The paper back-calculates the 1978 Rissa landslide, one of the largest quick clay landslides in Norway. Because of the quantity of data available, the Rissa landslide provides a unique benchmark to study the mobility of the quick clay, and the tsunami following the landslide. The paper describes a new approach to model landslide mobility and tsunami run-up, and presents the results of the analyses and a comparison of the results with the observations. The back-calculated mobility (runout distance, flow velocity and debris thickness) and wave run-up on the lakeshore agreed well with the measurements.

Insights into the mobility characteristics of seismic earthflows related to the Palu and Eastern Iburi earthquakes

As an important indicator for landslide hazard and risk assessments, landslide mobility has attracted considerable attention in the literature, yet few studies have investigated seismic earthflows. Therefore, the earthflows induced by the 2018 Mw 7.5 Palu earthquake (Indonesia) and the 2018 Mw 6.5 Eastern Iburi earthquake (Japan) and their mobility characteristics were analyzed. Long-term irrigation for cultivation of wet rice and heavy rainfall produced by Typhoon Jebi introduced substantial moisture into alluvial fans (Palu earthquake) and pyroclastic fall deposits (Eastern Iburi earthquake), respectively, and seismic shaking liquefied these moist deposits, which consequently traveled long distances. Four earthflows that were triggered on very gentle slopes of 1–3° by the Palu event exhibited very high mobility levels (H/L) of 0.0129, 0.01125, 0.0209 and 0.0271 (average H/L = 0.018), whereas 7058 earthflows triggered by the Eastern Iburi event exhibited an average mobility of 0.33. Different liquefied layers were located below or above the low permeability layer, and movement restrictions and complex final flow disturbances could be responsible for obvious mobility differences triggered by the two seismic events. However, the earthflow mobility induced by the Eastern Iburi earthquake was obviously higher than that of coseismic rock landslides worldwide and is described by the following relationship: H/L = 1.46–0.24 × log10 (earthflow_area). Furthermore, the earthflow area, peak ground acceleration (PGA) and slope angle all have increase influences on mobility.

Prediction of Slow-Moving Landslide Mobility Due to Rainfall Using a Two-Wedges Model

In the present study, the landslides cyclically reactivated by water-table oscillations due to rainfall are dealt with. The principal kind of motion that usually characterizes such landslides is a slide with rather small velocity. As another feature, soil deformations are substantially accumulated inside a narrow shear zone situated below the landslide body so that the latter approximately slides rigidly. Within this framework, a new approach is developed in this paper to predict the mobility of this type of landslides due to rainfall. To this end, a two-wedges model is used to schematize the moving soil mass. Some analytical solutions are derived to link rain recordings with water-table fluctuations and in turn to landslide displacements. A well-documented landslide frequently activated by rainfall is studied to check the forecasting capacity of the proposed method.

A catastrophic flowslide that overrides a liquefied substrate: the 1983 Saleshan landslide in China

AbstractFlowslides that override a liquefied substrate can vastly enhance a disaster after failure initiation. These effects may result from the rapid velocity and long runout distance from slides mobilized into flows. It is thus crucial to provide an improved understanding of the transformation mechanisms of catastrophic flowslides for hazard evaluation. This study examines the Saleshan landslide in Gansu, China, which occurred in 1983 and killed more than 200 people. The Saleshan landslide travelled for approximately 1 km due to pore water pressure generation resulting from overrunning and liquefication of the alluvial sands in the river valley below. We used geomorphologic and topographic maps to determine its dynamic features and mobilization behaviors on the landslide body, and placemarks and seismic signals to identify its approximate velocity at different sites. Electrical resistivity tomography (ERT) surveys also revealed the hydrogeological conditions post‐landslide, showing a clear groundwater table along with the liquefied alluvial sand and gravel layers. Particle size distributions and triaxial shear behaviors confirmed more ready liquefaction of superficial loess and underlying alluvial sand in comparison with the red soil above and below them. Novel loading impact triaxial testing was also performed on the alluvial sand to elucidate its liquefaction potential in undrained and drained conditions. The alluvial sand was found to be markedly prone to liquefaction in undrained conditions due to impact‐induced increased pore water pressure. The results further demonstrated that the Saleshan landslide underwent a transformation from a slowing slide on a steep slope, where it originated, to flow on a nearly flat terrace with abundant groundwater that it overrode. The transformation mechanism involved the liquefied alluvium sand substrate, which greatly enhanced the landslide mobility. Along with recent, similar findings from landslides globally, substrate liquefaction may result in a widespread, significant increase in landslide mobility and thus hazard, and the present study identifies the requisite conditions for this phenomenon to occur.

Effects of the attitude of dominant joints on the mobility of translational landslides

Geological structures and ground undulation affect the mobility of translational landslides. Combining field investigation, back-analysis, and numerical simulation, we explore the role of dominant joint dip angle in controlling the mobility of translational landslides. First, the attitudes of the geological structures are revealed by aerial photography measurements. The pre-failure slope surface of the Wolong landslide, Southeastern Tibetan Plateau, is estimated from the contours of the adjacent stable hillslopes and the deposit bottom boundary. Then, to back-analyze cohesion and internal fraction angle of the landslide, we fit a maximum stable relief limit based on Culmann’s model to the upper envelope of 96 rock scars and 37 previously published landslides. Next, we design eight scenarios (S1–S8) for the simulation of landslide mobility, respectively, corresponding to the eight joint dip angles between 20° and 60°. The mobility index H/L increases with the dip angle β, as confirmed by the best-fit line H/L = 0.288 ln(β) − 0.698. The numerical results of the runout characteristics, velocity, and energy consumption of the simulated landslides in the eight scenarios indicate that (1) the momentum losses at slope break are closely related to the joint dip, apparent friction angle, and height of the mass center; (2) local undulations in substrate have an inapparent effect on mobility of large and long runout landslides; and (3) conventional mobility indexes need to be improved or modified when high mobile landslides encounter high obstacles at slope bottom, opposite hills, or mountains. This study will be useful for hazard evaluations of translational landslides in mountainous regions.

Prediction of rainfall-induced landslide movements in the presence of stabilizing piles

Among the different techniques usually employed to stabilize landslide bodies, the use of one or more rows of piles firmly embedded in the stable portion of the slope is commonly considered a reliable and effective measure. Nevertheless, a landslide may still be reactivated by an increase in the groundwater level due to rainfall. In this context, a novel method is proposed in the present study for a preliminary evaluation of the rainfall-induced movements of landslides in the presence of stabilizing piles. This method uses a water balance equation to evaluate the groundwater level changes due to rainfall, and the motion equation to relate these changes to landslide displacements. The piles contrast the landslide movements by a passive resistance force the value of which depends on the pile–soil failure mode and pile arrangement. The proposed method appears attractive from an engineering viewpoint, since it can be readily implemented in a common electronic sheet and requires few parameters as input data. Most of these parameters can be obtained from conventional geotechnical tests, whereas the remaining ones should be calibrated on the basis of available measurements of rainfall, groundwater level and soil displacement. After performing this parameter calibration, the method may be employed for predictive purposes to relate future landslide movements to expected rainfall scenarios. The predictive capability of the present approach is assessed by comparing the results with those observed in a published case study concerning a landslide body periodically reactivated by rainfall, in which a row of stabilizing piles was installed. • The paper deals with landslides reactivated by rainfall. • A method is proposed for predicting landslide movements in the presence of piles. • The method directly relates rain recordings to landslide movements. • The method is simple and can be readily implemented in a common electronic sheet. • One or more rows of piles are able to reduce the landslide mobility of about 70%.

Coupling InSAR and numerical modeling for characterizing landslide movements under complex loads in urbanized hillslopes

Landslides, as a representative geohazard in fault zones, threaten the safety of buildings and infrastructure. Landslide movements are often subject to multiple loads in urbanized hillslopes from both natural and human activity. Synthetic aperture radar interferometry (InSAR) has been used to measure landslide movements. Used independently, InSAR can measure only surface deformation, and the points are sparse. Numerical modeling can simulate the full-scale movements, but it requires a prior knowledge of soil properties that are often not available in practice. To address these limitations, we proposed to couple InSAR and numerical modeling for characterizing landslide movements under multiple loads. We used 60 ascending and 56 descending Sentinel-1 images to measure surface movements in urbanized Daguan County Town. Of 31 landslides in the inventory map, 24 were successfully identified. The InSAR results assisted in determining the optimal soil properties through back-analysis. We used geological, geotechnical, and meteorological data to set three boundary conditions, that is, body loads, precipitation-induced hydraulic conditions, and construction-induced forces. Landslide mobility was demonstrated more distinctly using the coupled analysis. The numerical results revealed that body loads dominated the cumulative downslope movements by squeezing water and air from voids, and precipitation caused seasonal movements with the direction perpendicular to the slope surface. Construction works caused permanent changes (accelerating and decelerating) in time-series trends. Coupling InSAR and numerical modeling can facilitate analysis of the effects of complex loads and potentially predict future deformation. The method developed can be extended to study other urbanized landslide areas for early warning and risk mitigation.

An Event-Based Inventory Approach in Landslide Hazard Assessment: The Case of the Skolis Mountain, Northwest Peloponnese, Greece

Assessment of landslide hazard across mountains is imperative for public safety. Pre- and post-earthquake landslide mapping envisage that landslides show significant size changes during earthquake activity. One of the purposes of earthquake-induced landslide investigation is to determine the landslide state and geometry and draw conclusions on their mobility. This study was based on remote sensing data that covered 72 years, and focused on the west slopes of the Skolis Mountains, in the northwest Peloponnese. On 8 June 2008, during the strong Movri Mountain earthquake (Mw = 6.4), we mapped the extremely abundant landslide occurrence. Historical seismicity and remote sensing data indicate that the Skolis Mountain west slope is repeatedly affected by landslides. The impact of the earthquakes was based on the estimation of Arias intensity in the study area. We recognized that 89 landslides developed over the last 72 years. These landslides increased their width (W), called herein as inflation or their length (L), termed as enlargement. Length and width changes were used to describe their aspect ratio (L/W). Based on the aspect ratio, the 89 landslides were classified into three types: I, J, and Δ. Taluses, developed at the base of the slope and belonging to the J- and Δ-landslide types, are supplied by narrow or irregular channels. During the earthquakes, the landslide channels migrated upward and downward, outlining the mobility of the earthquake-induced landslides. Landslide mobility was defined by the reach angle. The reach angle is the arctangent of the landslide’s height to length ratio. Furthermore, we analyzed the present slope stability across the Skolis Mountain by using the landslide density (LD), landslide area percentage (LAP), and landslide frequency (LF). All these parameters were used to evaluate the spatial and temporal landslide distribution and evolution with the earthquake activity. These results can be considered as a powerful tool for earthquake-induced landslide disaster mitigation

Mobility characteristics of debris slides and flows triggered by Hurricane Maria in Puerto Rico

Mobility is an important element of landslide hazard and risk assessments yet has been seldom studied for shallow landslides and debris flows in tropical environments. In September 2017, Hurricane Maria triggered > 70,000 landslides across Puerto Rico. Using aerial imagery and a lidar digital elevation model (DEM), we mapped and characterized the mobility of debris slides and flows in four different geologic materials: (1) mudstone, siltstone, and sandstone; (2) submarine basalt and chert; (3) marine volcaniclastics; and (4) granodiorite. We used the ratio of landslide-fall height (H) to travel length (L), H/L, to assess the mobility of landslides in each material. Additionally, we differentiated between landslides with single and multiple source areas and landslides that either did or did not enter drainages. Overall, extreme rainfall contributed to the mobility of landslides during Hurricane Maria, and our results showed that the mobility of debris slides and flows in Puerto Rico increased linearly as a function of the number of source areas that coalesced. Additionally, landslides that entered drainages were more mobile than those that did not. We found that landslides in soils developed on marine volcaniclastics were the most mobile and landslides in soils on submarine basalt and chert were the least mobile. While landslides were generally small (< 100 m2) and displayed a wide range of H/L values (0.1–2), coalescence increased the mobility of landslides that transitioned to debris flows. The high but variable mobility of landslides that occurred during Hurricane Maria and the associated hazards highlight the importance of characterizing and understanding the factors influencing landslide mobility in Puerto Rico and other tropical environments.

An Empirical Power Density‐Based Friction Law and Its Implications for Coherent Landslide Mobility

AbstractThe evolution of the shear resistance at the base of a coherent landslide body can effectively control its dynamic behavior. High‐velocity rotary shear experiments have allowed scientists to explore stress‐strain conditions close to those found in large landslides and faults. These experiments have led to two alternative models being proposed, which describe the evolution of the shear resistance through friction laws that depend either on normal stress or on velocity. Here, we discuss an integrated approach, first proposed to study seismic fault behavior, that reconciles these two models under a single parameter—the power density—which we utilize for the first time to investigate landslide dynamics. Using thermodynamic and process‐based considerations, different soil and rock types can be related to different weakening mechanisms, which in turn can determine different landslide behaviors.

Spatiotemporal evolution, mineralogical composition, and transport mechanisms of long-runout landslides in Valles Marineris, Mars

Long-runout landslides with transport distances of >50 km are ubiquitous in Valles Marineris (VM), yet the transport mechanisms remain poorly understood. Four decades of studies reveal significant variation in landslide morphology and emplacement age, but how these variations are related to landslide transport mechanisms is not clear. In this study, we address this question by conducting systematic geological mapping and compositional analysis of VM long-runout landslides using high-resolution Mars Reconnaissance Orbiter imagery and spectral data. Our work shows that: (1) a two-zone morphological division (i.e., an inner zone characterized by rotated blocks and an outer zone expressed by a thin sheet with a nearly flat surface) characterizes all major VM landslides; (2) landslide mobility is broadly dependent on landslide mass; and (3) the maximum width of the outer zone and its transport distance are inversely related to the basal friction that was estimated from the surface slope angle of the outer zone. Our comprehensive Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) compositional analysis indicates that hydrated silicates are common in landslide outer zones and nearby trough-floor deposits. Furthermore, outer zones containing hydrated minerals are sometimes associated with longer runout and increased lateral spreading compared to those without detectable hydrated minerals. Finally, with one exception we find that hydrated minerals are absent in the inner zones of the investigated VM landslides. These results as whole suggest that hydrated minerals may have contributed to the magnitude of lateral spreading and long-distance forward transport of major VM landslides.

Rainfall-induced landslides and debris flows in Mengdong Town, Yunnan Province, China

On 2 September 2018, an intense rainstorm swept Mengdong Town in Yunnan Province of China, inducing a serious landslide and debris flow disaster with 10 deaths and 11 missing. Image interpretation, field survey, and slope stability analysis were used to examine the characteristics and initiation mechanism of this hazard. A total of 1774 landslide scars were identified, the area of which occupied 8.26% of the study region. Due to the spatial inhomogeneity of precipitation, these scars mainly concentrated along valleys in the lower part of the study area. Besides, well-forested hillslopes were more prone to landslides, indicating the limited role of trees in stabilizing slopes in extreme rainfall events. The initiation of landslides is mainly attributed to the week cohesion of the saturated clayey sand beneath the root zone, where the tensile resistance of roots was absent, and the increase of positive pore water pressure. Additionally, 288 landslide scars were situated adjacent to roads, demonstrating that the road construction activity had intensified the landslide disaster. Owing to the relatively low mobility of landslides, a considerable portion of landslide debris deposited on the valley floor in smaller watersheds (< 6.03 hm(2)), while the remaining portion entered high-order channels. In these channels, where stream power was relatively large, the woody debris and soil carried by landslides were entrained by streamflow, and debris flows were formed. Moreover, the magnitude of debris flow was amplified by the vertical and lateral erosion of the stream channel.

Mobility of dry granular flows of varying collisional activity quantified by smart rock sensors

Highly instrumented particles (i.e., “smart rocks”) were included in monodisperse dry granular landslide experiments to quantify the collisional nature of such flows and to investigate the influence of collisional flow on the mobility of landslides. The total number of particles comprising a constant source volume of 0.4 m3 was varied by filling the volume with monodisperse particles of nominal diameters of 3, 6, 13 or 25 mm. Successively raising the total particle count resulted in flows that were increasingly thick relative to the respective particle size. Raw resultant acceleration data from the embedded smart rock sensors indicate that for each increase in grain size, there were increases in both the magnitude and frequency of particle collisions. Light detection and ranging (LiDAR)-generated point clouds of the landslide deposits indicated that increases in mobility and spreading, compared using differences in travel angle, were directly proportional to increases in collisional activity. By changing the size of the landslide particles from 3 to 25 mm, the travel angle at the gravity centre (αg) was observed to decrease from 27.8° to 25.3° (Δαg = −9.0%) and the Fahrböschung angle (α) was observed to decrease from 25.0° to 21.4° (Δα = −14.4%).

Effects of granular collisions on the rapid coarse-grained materials flow

A continuum model to predict the mobility of landslides is developed according to the formulation by Savage and Hutter as well as the main ‘microscopic aspects’ affecting the rapid sliding of granular masses. Conservation of mass and momentum equations, describing the geometry and velocity evolution during the motion, are re-written by considering the effects of collisions between solid grains (‘granular temperature’ and ‘dispersive pressures’) typically occurring within a basal thin ‘shear’ layer, causing a ‘fluidification’ effect and corresponding energy dissipations. To this purpose, a ‘frictional−collisional’ rheological law allowing to simulate the energy dissipation related to grain inelastic collisions and friction, simultaneously acting within the basal ‘shear layer’, is developed and applied. The interstitial pressures, and their possible increment along curved paths related to centrifugal force, and the mass variation due to erosion/deposition processes are also considered. The numerical simulation of a documented experimental test is finally carried out.

An empirical power density-based friction law and its implications for coherent landslide mobility

An empirical power density-based friction law and its implications for coherent landslide mobility

Simulating the Xinmo landslide runout considering entrainment effect

This paper investigates the setting, causes, and main dynamic characteristics of the landslide that occurred at Xinmo village, Diexi, Sichuan province, China, on June 24, 2017. By comparing the pre- and post-sliding DEMs, the landslide involved the failure of ≈ 3.0 × 106 m3 rock mass from its source area, and had a final volume of ≈ 6.3 × 106 m3. The landslide runout extended 2800 m horizontally and 1200 m vertically, and covered an area of ≈ 143.1 × 104 m2. Field investigation indicates that entrainment was one of the major causes of the increase in volume of landslide. To reproduce the behavior of the landslide runout, a depth-averaged continuum model that takes entrainment into consideration is applied. The simulated results generally agree well with the characteristics of the sliding path and distribution of the landslide deposit as observed in the field. It is demonstrated that entrainment plays a significant role in landslide mobility and volume. The final volume of the landslide is calculated about 6.21 × 106 m3, which has more than double its initial volume.

Experimental analysis of tsunamis generated by the impact of landslides with high mobility

Landslides into water can generate massive tsunamis which are major natural hazards in coastal regions. In this study, waves were generated in a series of 41 laboratory experiments by releasing 4 different slide volumes ranging from 0.1-0.4 m3 of highly mobile material down a 6.73 m long slope into a reservoir of depth varying from 0.15-0.65 m, to achieve a wide range of dimensionless landslide parameter values. Water is used as the sliding material and with zero internal shear strength it is representative of the upper limit of high landslide mobility. The slide characteristics of thickness and velocity were measured at impact using high speed cameras and the time series of the resulting changes in water surface elevation were measured using nine wave probes along the 33.8 m long flume. The experimental results indicate that in the near-field the maximum wave amplitude is dependent on the landslide thickness and velocity and is relatively independent of the reservoir water depth. As waves propagate to the far-field, the depth-limited breaking reduces the wave amplitude, such that the maximum wave amplitude is highly dependent on the reservoir depth. The wave breaking limit, which differentiates the breaking from the non-breaking waves, is defined by the relationship am/h = 0.6 that is very closely adhered to for all source volumes and reservoir depths. The time and length over which the waves are generated are determined from the digital imagery, and are used to describe the scales of the momentum transfer. These observations are compared with previously published empirical and theoretical equations for granular landslides and positively buoyant avalanches, indicating that water is a useful source material for simulating highly mobile landslides. Since these parameters are difficult to obtain in field cases, a simplification of the theoretical equation is presented and this yields reasonable results for the maximum wave amplitude generated by slides with high mobility.

The 2016 Lamplugh rock avalanche, Alaska: deposit structures and emplacement dynamics

Supraglacial landslides result from the catastrophic failure of periglacial rock slopes and deposit large volumes of rock and ice onto the glacier surface. The most remarkable features of these landslides are their prominent long flowbands and a high mobility that exceeds that of their counterparts in other environments. Based on field surveys, high-resolution digital elevation models, and continuous seismic data, we show that the emplacement dynamics of the 2016 rock avalanche on Lamplugh Glacier were characterized by two distinct stages. During the first stage, the debris traveled about 5 km from the base of the slope. Clear long-period seismic signals during this stage record strong interactions of the rock avalanche debris with the ground, suggesting dynamic processes such as grain collisions and fragmentation. The second stage was essentially aseismic at long periods and dominated by low-friction sliding at slow deceleration rates. A higher density of flowbands and increased entrainment of snow from the runout path characterize the morphology of this second-stage distal deposition. Around the margins, lobes are offset by up to 400 m along major strike-slip faults, whereas within individual lobes, offsets between flowbands are much less pronounced (0 to < 10 m). The two-stage emplacement model may explain the higher apparent mobility of supraglacial landslides.

How does a cluster of buildings affect landslide mobility: a case study of the Shenzhen landslide

Urban landslides always occur where development has taken place on pre-existing unstable land. Due to rapid urbanization, human activities expand onto sloping terrain and disturb the geological environment, increasing the urban landslide risk. When a rapid flow-like landslide occurs, the landslide mobility can be affected by the presence of buildings located along its flow path. In this paper, the effect of building blockage on landslide mobility and the associated energy dissipation mechanisms are evaluated based on a well-documented landslide, which happened on 20 December 2015 in Shenzhen, China. The landslide flow process is reproduced by three-dimensional terrain analyses using LS-DYNA, considering three scenarios; namely, green field, movable buildings, and fixed buildings. Simulations show that the presence of densely located buildings significantly affects flow pattern, travel distance, deposition, and energy transfer mechanism. A fully developed debris fan in the flat area is observed in the green field case. The buildings in the runout path decelerate the flow process, leading to lower landslide mobility and less volume deposited in the accumulation zone. The shortest runout distance and widest and thickest deposits are observed in the fixed buildings case. The debris fan in the movable buildings case is closer to reality. Fixed buildings pose more constraint on surface moving material, leading to the largest deformation, largest internal energy, and smallest kinetic energy of the soil mass. The dissipation of the largest frictional energy occurs in the movable buildings case due to the long sliding distance of the damaged buildings. The internal energy of the landslide mass dominates the energy transfer mechanism. The results presented here indicate the need to consider building clusters when conducting urban landslide hazard mapping and risk assessment.