Runout Distance Research Articles

Gravity-driven sliding and associated deformations along complex submarine slopes: a laboratory modeling approach based on constraints observed offshore Martinique Island (Lesser Antilles)

Submarine gravity-driven sliding of sediments are common processes in the vicinity of volcanic islands. In the Lesser Antilles arc, the Montagne Pelée volcano on Martinique Island underwent several flank-collapse events during its long-term eruptive history, resulting in debris avalanches. When the debris avalanches entered into the seawater, they were emplaced over the unstable slope of the volcano, triggering a seafloor sediment failure and massive landslides downslope. Using a laboratory modeling approach, we simulated the gravity-driven sliding of a sand layer lying above a silicone layer. The experiments were performed using various slope geometries (slope lengths and number of slope breaks separating the slopes with different angles), under both dry and aqueous conditions, and while varying the amount of additional sand inputs upslope. The resulting deformations were characterized in each experiment in order to compare the obtained structures with those shown by the seismic lines offshore to the west of Martinique Island. During all the experiments, a compressional frontal deformation zone made of several reverse faults formed downslope, often near the slope breaks. Downslope, a portion of the sediments was mostly displaced and poorly deformed in a damping zone, while an extensional deformation zone formed upslope. The displacements of the surficial markers were measured through time to characterize the sliding dynamics. Our study demonstrates that the slope geometry and additional sand inputs primarily favor and increase the sliding deformation, whereas the hydrostatic pressure plays a secondary catalytic role over time. These results provide new constraints on the driving factors and their consequences on gravity-driven sliding in terms of deformations and runout distance over time. This may have a significant impact on the associated hazard assessment related to offshore infrastructures, in a region known for its seismic and volcanic risks.

Keynote lecture. A general two phase depth integrated model considering pore water pressure and dewatering

Debris flows can be considered a type of landslide with large velocities and long run-out distances. There are many types of debris flows, depending on the properties of the solid and fluid components of the mixture. The triggering and propagation of debris flows can be studied using a single 3D mathematical model. The computational cost can be very high because of their length, and depth-integrated models provide a good combination of accuracy and cost. Both types of models can be combined in the analysis, using 3D models for initiation and at singular points where more accuracy is wanted. As in a chain where the strength is never higher than that of the weaker link, we have to ensure that all the models are accurate enough in a joint model. This paper deals with a new depth-integrated model which can take into account the changes caused by dewatering in a debris flow.

Pilot study to explain runout distances of debris flow and immature debris flow considering depositing rate

In Japan, many debris flows and sediment-laden floods cause serious damage to human life and property. Effective measures require high-accuracy reproduction and prediction of runout distance (bed variation reach) via numerical simulations. One possible method to increase the accuracy of numerical simulation results involves reviewing the methods used to evaluate depositing rate for flows that contain many different sizes of sediments. This study performed experiments using an artificial channel and high-speed cameras to identify parameters that govern depositing rate. The channel implemented exhibited a change in slope point; thus, the slope of the upper reach differed from the slope of the lower reach. The experiments showed that the equation representing depositing rate is closely related to flow velocity. Additionally, the equation of depositing rate can be determined if other parameters are consistently considered.

A Study on the Comparative Analysis of the FLO-2D Model According to Debris Flow Sediment Amount

It is very important to predict the extent of the damage in order to reduce or prevent damage by the debris flow. In the Republic of Korea, various methods are used to understand the characteristics and to estimate the occurrence of the debris flow in an undamaged area, such as simulating disasters using the estimation of debris flow sediment amount based on field survey data. In this study, the runout distance of debris flow was analyzed by using different methods for estimating the debris flow sediment amount, at Wondeok-eup, Samcheok-si, Gangwon-do, where debris flow occurred due to Typhoon Mitak in 2019. The simulation results of the damage area were compared with the actual damage area. The result showed that the simulations generally corresponded to the actual area of damage caused by the sedimentation of debris flow. However, the estimation of damage area varied according to the used method of calculating the debris flow sediment amount.

Proposal of Hazard Connectivity Index for debris flow disaster management

The concept of connectivity and its index have been widely discussed and applied to environmental studies such as ecology, hydrology, geomorphology and hydrosedimentology. Supposing that this concept is very useful also in disaster risk management, we define the hazard connectivity associated to debris flows as the connectivity degree between the debris flow occurrence (trajectory) and the point of interest (location of house, person, and so on). Based on this definition, the Hazard Connectivity Index (HCI) associated to debris flow is proposed as: HCI = L/(x+L), where x is the shortest distance between the debris flow trajectory and the point of interest; and L is the runout distance of the debris flow or just mass movement. The HCI value varies from 0 to 1, being that its higher value indicates larger hazard condition. The HCI application to one case study showed that it can be useful in the analysis of the debris flow related hazard.

Granular column collapse: The role of particle size polydispersity on the velocity and runout

Geophysical mass flows involve particles of different sizes, a property termed polydispersity. The granular column collapse is a simplified experiment for studying transitional granular flows. Our research focuses on the role that polydispersity has on the velocity and runout distance of dry and immersed granular columns, undergoing a numerical and experimental study. Our results highlight that polydispersity does not have a strong effect on the collapse of dry columns. On the contrary, the collapse sequence of immerse granular columns strongly depend on the polydispersity level.

Revealing the role of forests in the mobility of geophysical flows

Forests cover 39% of low-altitude mountainous areas globally, and they are considered natural barriers against geophysical flows. Owing to the complexity of flows, the protective effects of forests can hardly be considered in hazard management. In this study, the interactions between granular geophysical flows and forests are explored using a MPM-DEM simulator from a viewpoint of supersonic bow shocks. We show that bow shocks can be approximated by a non-linear analytical framework based on the Mach cone theory. To generate evidence of flow–forest interactions, a new experimental model forest is built. Then, a computational model of granular impact on trees is calibrated and solved by the MPM-DEM method. The results reveal that interactions between overlapping bow shocks considerably affect the flow mobility. Bow shocks either reduce flow momentum or concentrate momentum to increase the runout distance by a factor of up to 1.5 compared with the runout distance of a non-forested area. The revealed bow shock effects on flow momentum can guide the assessment of cultivated forests in impeding geophysical flows. The revealed bow shocks and their ability to change the flow runout highlight the need to explore new models other than classical models based only on basal friction.

Diachronic quantitative snow avalanche risk assessment as a function of forest cover changes

This work proposes a holistic quantitative snow avalanche risk assessment that evaluates, at reasonable computational costs and for various types of buildings, the impact of forest cover changes on the probability distribution of runout distances, impact pressures and subsequent risk estimates. A typical case study of the French Alps shows that, from a completely deforested to a completely forested path, avalanche risk for a building located downslope decreases by 53–99%, depending on how forest cover is accounted for in avalanche statistical–dynamical modeling. Local forest cover data inferred from old maps and photographs further demonstrates that a 20–60% risk reduction actually occurred between 1825 and 2017 at the site because of the afforestation dynamics, with significant modulations according to the considered building technology. These results (1) assert the protective role of forests against snow avalanches, (2) highlight the potential of combining nature-based solutions with traditional structural measures to reduce risk to acceptable levels at reasonable costs, (3) suggest a significant decrease in risk to settlements in areas that encountered similar forest cover changes and (4) open the door to the quantification of long-term avalanche risk changes as a function of changes of all its hazard, vulnerability and exposure drivers in various mountain context.

The Suitability of UAV-Derived DSMs and the Impact of DEM Resolutions on Rockfall Numerical Simulations: A Case Study of the Bouanane Active Scarp, Tétouan, Northern Morocco

Rockfall simulations constitute the first step toward hazard assessments and can guide future rockfall prevention efforts. In this work, we assess the impact of digital elevation model (DEM) resolution on the accuracy of numerical rockfall simulation outputs. For this purpose, we compared the simulation output obtained using 1 m, 2 m and 3 m resolution UAV-derived DEMs, to two other models based on coarser topographic data (a 5 m resolution DEM obtained through interpolating elevation contours and the Shuttle Radar Topographic Mission 30m DEM). To generate the validation data, we conducted field surveys in order to map the real trajectories of three boulders that were detached during a rockfall event that occurred on 1 December 2018. Our findings suggest that the use of low to medium-resolution DEMs translated into large errors in the shape of the simulated trajectories as well as the computed runout distances, which appeared to be exaggerated by such models. The geometry of the runout area and the targets of the potential rockfall events also appeared to be different from those mapped on the field. This hindered the efficiency of any prevention or correction measures. On the other hand, the 1m UAV-derived model produced more accurate results relative to the field data. Therefore, it is accurate enough for rockfall simulations and hazard research applications. Although such remote sensing techniques may require additional expenses, our results suggest that the enhanced accuracy of the models is worth the investment.

A multi-step hazard assessment for debris-flow prone areas influenced by hydroclimatic events

Hazard assessment studies are fundamental to identifying disaster-prone areas, especially in locations with high environmental and socioeconomic vulnerability. This study proposes a multi-step debris-flow hazard assessment, based on the combination of Logistic Regression (LR) analysis, numerical simulation and rainfall back-analysis. A landslide-prone area of 84 km2 is chosen as test-site, including 20 river catchments and one of the largest petrochemical plants in Latin America. Rainfall is the main influencing factor in debris-flow initiation, as highlighted by the LR analysis, followed by soil cover and slope. The analysis also indicated the catchments more susceptible to debris flows and the simulation results show that the average runout distance in these catchments is 470 m, with an average peak flow height of 5 m and a peak velocity of 23 m s−1. Debris flows are triggered by short duration (<48 h), high-intensity (>200 mm) precipitation, with return periods that vary from 3 to 10 years. Five levels of hazard (very low to very high) are, then, proposed for the study site, based mainly on 48-h accumulated rainfall and flow properties. Industrial and residential areas in the projected debris-flow route generally exhibit the highest overall hazard levels, as many were developed in the depositional area of debris flows and near fluvial courses, where associated floods and flash floods may occur. As pointed out by recent studies, an increase in the frequency of extreme precipitation events is projected in the Serra do Mar region and when the general short return period of the debris-flow triggering rainfall is considered (<10 years), large magnitude (>105 m3) debris flows are likely to occur in the near future.

Rainfall-Induced Landslides from Initialization to Post-Failure Flows: Stochastic Analysis with Machine Learning

Rainfall-induced landslides represent a severe hazard around the world due to their sudden occurrence, as well as their widespread influence and runout distance. Considering the spatial variability of soil, stochastic analysis is often conducted to give a probability description of the runout. However, rainfall-induced landslides are complex and time-consuming for brute-force Monte Carlo analyses. Therefore, new methods are required to improve the efficiency of stochastic analysis. This paper presents a framework to investigate the influence and runout distance of rainfall-induced landslides with a two-step simulation approach. The complete process, from the initialization of instability to the post-failure flow, is simulated. The rainfall infiltration process and initialization of instability are first solved with a coupled hydro-mechanical finite element model. The post-failure flow is simulated using the coupled Eulerian–Lagrangian method, wherein the soil can flow freely in fixed Eulerian meshes. An equivalent-strength method is used to connect two steps by considering the effective stress of unsaturated soil. A rigorous method has been developed to accurately quantify the influence and runout distance via Eulerian analyses. Several simulations have been produced, using three-dimensional analyses to study the shapes of slopes and using stochastic analysis to consider uncertainty and the spatial variability of soils. It was found that a two-dimensional analysis assuming plain strain is generally conservative and safe in design, but care must be taken to interpret 2D results when the slope is convex in the longitudinal direction. The uncertainty and spatial variability of soils can lead to the statistic of influence and runout distance. The framework of using machine-learning models as surrogate models is effective in stochastic analysis of this problem and can greatly reduce computational effort.

Emplacement age of the Markagunt gravity slide in southwestern Utah, USA

AbstractThe Markagunt gravity slide (MGS) is a large‐volume landslide in southwestern Utah that originated within the Oligocene‐Miocene Marysvale volcanic field. Gravity slides are single emplacement events with long runout distances and are now recognized as a new class of volcanic hazard. Accumulation of volcanic material on a structurally weak substrate along with voluminous shallow intrusive events led to collapse. Here, 40Ar/39Ar data for landslide‐generated pseudotachylyte, the landslide‐capping Haycock Mountain Tuff and the deformed Osiris Tuff are combined with a Bayesian age model to determine an emplacement age of 23.05 + 0.22/−0.20 Ma for the MGS. The results suggest a lag time of &lt;200 kyr between the caldera‐forming eruption of the Osiris Tuff, additional buildup of the unstable volcanic pile and subsequent mass movement.

A numerical study on the effects of particle size distribution on run-out distance of granular flow

The discrete element method is a powerful numerical tool widely employed in granular flow simulations. To reduce computational costs, either monodisperse granular models or models with a limited number of particle sizes are used to estimate the risk of sediment-related disasters. This highlights the need for a thorough understanding on the effects of particle size distribution on the accuracy of granular simulations. In this study, a series of granular flow simulations was conducted with different particle size distributions. The results clearly indicate that the run-out distance strongly depends on the number of particle sizes and is underestimated in the conditions employed by the monodisperse granular model. The longest run-out distance was observed in case that the bidisperse granular model was employed, whereas run-out distance tends to a constant value when polydisperse granular model was employed. Because particle size segregation was observed during the flow, a series of vibration simulations was also conducted to estimate the degree of the size segregation. It was shown that each granular model has an inherent degree of size segregation. From the results of the granular flow simulations and vibration simulations, it was confirmed that the inherent degree of the size segregation clearly affects the run-out distance.

Lateral Extent of Pyroclastic Surge Deposits at Ubehebe Crater (Death Valley, California) and Implications for Hazards in Monogenetic Volcanic Fields

AbstractHazard assessments in monogenetic volcanic fields require estimates of the runout of pyroclastic surges that result from phreatomagmatic explosive activity. Previous assessments used runout distances of 1–4 km, with large cases up to 6 km. Surge deposits at Ubehebe Crater (∼2100 y.b.p., Death Valley, California) have been traced ∼9 km from the crater center, and likely originally extended 1–3 km farther. There is no evidence that the Ubehebe Crater activity was unusually energetic; rather, its distal deposits are better preserved than those at most maar volcanoes because of its young age and the arid environment. Numerical simulations illustrate how low temperatures facilitate long runout of phreatomagmatic surges due to reduced expansion of entrained air compared to hot surges, allowing cool surges to retain higher densities than ambient air. We suggest that hazard assessments for volcanic fields with phreatomagmatic, maar‐forming eruptions should consider runout distances in the range of 10–15 km.

Buffer Zone Prediction for Simulated Earthquake-Induced Slope Failures in Mesilou, Kundasang, Sabah, Malaysia

The research area is located at Mesilou, Kundasang, Sabah at 1400 meters to 2000 meters from the sea level. It focuses on slopes of Pinousuk Gravel Unit, tilloid deposits from the glaciation of Mount Kinabalu during Late Pleistocene age. Four slopes were chosen for the estimation of ‘buffer zone’ of earthquake-induced slope failures. The simulation of the earthquake is conducted by using shaking table method and the earthquake event occurred in the research area on year 2018. The analysis shows the location of the buffer zones are within 1.5 meters to 13.5 meters from the toe of the slope, where the run-out distance is farther with the increment of shaking’s duration and slope height. Simulation analysis shows that all slopes have detrimental impact of the settlement area of Kg. Mesilou, Kundasang but only 60% to 87% of respondents are still staying in the area. However, 74% to 84% of respondents are willingly to relocate if given new disaster-free settlements.

A methodology to predict the run-out distance of submarine landslides

In this paper, the method of computational fluid dynamics (CFD) is proposed to simulate a fluidized submarine landslide with shear thinning non-Newtonian fluids over a seabed under different contact conditions in the ambient water. The CFD method is first validated using data of physical channel and non-Boussinesq lock-exchange experiments with different rheological characteristics and is found to provide good accuracy. Various CFD-based experiments with different initial velocities of the submarine landslide and different seabed contact conditions are then performed systematically. During the movement of the submarine landslide in ambient water, stress state and causes of the submarine landslide mass are revealed, and the submarine landslide-seabed contact relation is clarified as a decisive influencing factor. Furthermore, based on the principle of energy conservation, a methodology to predict the run-out distance of the submarine landslide mass by using the initial geometry of the submarine landslide masses with different scales and the total initial kinetic energy (including the initial kinetic energy and the gravitational potential energy difference caused by the self-slumping) of the submarine landslide mass is presented, equations to quantify the process are established, and the proposed methodology and equations are validated by the numerical result, which provides a significant basis for the prediction of marine engineering geological and hydrodynamic hazards with special reference to submarine landslides.

A new two-layer two-phase depth-integrated SPH model implementing dewatering: Application to debris flows

Debris flows can be considered a type of landslide with large velocities and long run-out distances. There are many types of debris flows, depending on the properties of the solid and fluid components of the mixture. The triggering and propagation of debris flows can be studied using a single 3D mathematical model. The computational cost can be very high because of their length, and depth-integrated models provide a good combination of accuracy and cost. Both types of models can be combined in the analysis, using 3D models for initiation and at singular points where more accuracy is wanted. As in a chain where the strength is never higher than that of the weaker link, we have to ensure that all the models are accurate enough in a joint model. This paper deals with a new depth-integrated model which can take into account the changes caused by dewatering in a debris flow. An important limitation of existing two-phase models allowing different velocities of solid and water particles is that when water abandons the mixture, porosity decreases and tends to zero. Here, a two-layer model is introduced, including an unsaturated upper layer on top of a saturated layer.

Volcanic crisis management supported by near real-time lava flow hazard assessment at Piton de la Fournaise, La Réunion

Since 1979, Piton de la Fournaise (La Réunion) has erupted on average two times per year, with 95 % of these eruptions occurring within an uninhabited caldera. However, lava flows have occasionally impacted populated regions on the island, as in 1977 and 1986. Since 2014, an integrated satellite data–driven multinational response to effusive crises has been developed to rapidly assess lava inundation area and flow runout distance. In 2018, this protocol was implemented as a standalone software to provide a lava flow hazard map showing the probability of flow coverage and runouts as a function of discharge rate. Since 2019, the produced short-term hazard map is shared with local civil protection in the first few hours following the start of an eruption to aid in mitigation actions. Multiple exchanges between scientists, the observatory, and civil protection has improved the delivered hazard map, ensuring a common understanding, a product which is of use and usable, and helping to build effective mitigation strategies at Piton de la Fournaise. In this work we illustrate this effective near real-time protocol with case studies and document how the produced short-term hazard map has been tailored to meet the needs of civil protection.

Multi-Scenario Analysis of Rockfall Hazard for a Historical Vaulted Masonry Building in Sumela Monastery

ABSTRACT Sumela Monastery located in the northeast city of Trabzon is one of the most-visited touristic places in Turkey. As it is located in a mountainous area, rockfall hazards have become a crucial problem that the Monastery complex faces, especially in the last decade. Due to several rockfall cases, the monastery was closed for visitors in 2015 to take preventative measures. The current study examines the whole stages assessing and eliminating rockfall hazards that a historical Vaulted masonry building in the Sumela Monastery is exposed to. First of all, field studies were conducted to determine the kind and type of rockfall hazard. For this purpose, the regional geology of the area was evaluated and due to the inaccessibility of the region, industrial climbers were recruited to climb the slope above the Historical Vaulted building to determine the locations, dimensions, and risk level of the risky blocks that threatened the building. After that, the terrain of the risky area was modeled with Unmanned Aerial Vehicle (UAV) using the digital photogrammetry method. In the last step of the field studies, samples were taken to determine the mechanical and physical properties of the rocks and several laboratory tests were conducted. In the second part of the study, probabilistic analyses of 2400 rockfall simulations with eight different trajectories were conducted to calculate the maximum run-out distance, velocity, kinetic energy, and bounce heights of falling blocks. In the third part, to evaluate the damage status on the vaulted building, six different possible rockfall scenarios determined by the rockfall analysis were simulated using the Finite Element Method. After determining the rock block size that would not cause significant damage to the building, the cleaning and controlled removal method of the risky blocks was determined. In the last stage, controlled crushing and removing practices for risky rock blocks were carried out and the building was restored. Consequently, the rockfall hazard for the historical Vaulted building was eliminated and the monastery complex opened for visitors in 2021.

Comparison of full-scale rockfall tests with 3D complex-shaped discrete element simulations

Trajectory analysis is often needed to handle rockfall hazards. It is crucial to understand and to refine ground and rock interactions during a rockfall, which can be related to the elements involved. They include the topology, ground and rock nature, but also the volume and shape of the falling blocks. This work focuses on replicating field observations using a 3D discrete elements model (DEM) in order to further analyze the possible rockfall deposition areas, which may not be accessible due to the limited number of experimental data available. The numerical model implements blocks of more realistic shapes that were reconstructed from in situ blocks obtained by photogrammetry. The dissipation of kinetic energy at the collision point is suitably managed. In the experimental campaign, dozens of boulders (rock block) releases were conducted on two slope profiles of a quarry located in Authume (France). Block passing heights, velocities and runout distances were assessed at specific ground points. We analyzed lateral spreads, propagation distances, and energy balances computed for 3 different block geometries. These numerical results were confronted with experimental observations. Although time-consuming compared to lumped mass and rigid body dynamics models where the impact duration is zero, the DEM used in this work is versatile thanks to an explicit consideration of geometrical effects throughout the life of multiple contacts. It allows to simulate quite accurately a multitude of configurations. Among the properties of the terrain and the blocks, geometric features are shown to be crucial. For the sake of efficiency, a simplified shape coefficient based on block’s elongation is proposed.