Mobility Of Debris Flows Research Articles

Determining the debris flow yield strength of weathered soils: a case study of the Miryang debris flow in the Republic of Korea

Debris flow hazards are often interpreted through back-calculated simulation analysis or empirical methods. The mobility of a debris flow is greatly influenced by mechanical and hydrological parameters. The strength parameters play important roles in the debris flow initiation and flow stages. In particular, the rheological parameters of yield strength and plastic viscosity directly affect the debris flow runout distance and velocity. One of the most important parameters to consider when evaluating debris flow hazards is the shear strength. This strength is called the residual shear strength in the failure stage and the yield strength in the post-failure stage. The residual shear strength obtained from ring shear tests can be related to the initiation of mass movements; the yield strength obtained from rheological tests can be related to the mobilization of debris flows. The residual shear stresses obtained from ring shear tests of weathered soils typically range between 10 and 100 kPa and strongly depend on the normal stress and shear velocity. When progressive slope failure (i.e., strain-softening behavior) occurs at a relatively shallow slope depth (e.g., < 1 m), the soil strength ranges from approximately 5–10 kPa. If the liquid limit state (i.e., solid‒liquid transition) is reached, the shear strength of the soil is approximately 2 kPa. Once the soil fails and mixes with ambient water along the slip surface, the yield strength decreases dramatically, resulting in high mobilization. A suggestion on how strength parameters can be applied to estimate debris flow mobility is presented by considering the 2011 Miryang debris flow, which occurred in weathered soil deposits in Miryang city, Republic of Korea. The best approach for debris flow yield strength estimation would be to consider the residual shear strength in the initiation stage, the yield strength in the flow stage, and the reduction in yield strength with the entrainment effect of the flow in the rapid fluidization stage.

Probabilistic assessment of postfire debris-flow inundation in response to forecast rainfall

Abstract. Communities downstream of burned steep lands face increases in debris-flow hazards due to fire effects on soil and vegetation. Rapid postfire hazard assessments have traditionally focused on quantifying spatial variations in debris-flow likelihood and volume in response to design rainstorms. However, a methodology that provides estimates of debris-flow inundation downstream of burned areas based on forecast rainfall would provide decision-makers with information that directly addresses the potential for downstream impacts. We introduce a framework that integrates a 24 h lead-time ensemble precipitation forecast with debris-flow likelihood, volume, and runout models to produce probabilistic maps of debris-flow inundation. We applied this framework to simulate debris-flow inundation associated with the 9 January 2018 debris-flow event in Montecito, California, USA. When the observed debris-flow volumes were used to drive the probabilistic forecast model, analysis of the simulated inundation probabilities demonstrates that the model is both reliable and sharp. In the fully predictive model, however, in which debris-flow likelihood and volume were computed from the atmospheric model ensemble's predictions of peak 15 min rainfall intensity, I15, the model generally under-forecasted the inundation area. The observed peak I15 lies in the upper tail of the atmospheric model ensemble spread; thus a large fraction of ensemble members forecast lower I15 than observed. Using these I15 values as input to the inundation model resulted in lower-than-observed flow volumes which translated into under-forecasting of the inundation area. Even so, approximately 94 % of the observed inundated area was forecast to have an inundation probability greater than 1 %, demonstrating that the observed extent of inundation was generally captured within the range of outcomes predicted by the model. Sensitivity analyses indicate that debris-flow volume and two parameters associated with debris-flow mobility exert significant influence on inundation predictions, but reducing uncertainty in postfire debris-flow volume predictions will have the largest impact on reducing inundation outcome uncertainty. This study represents a first step toward a near-real-time hazard assessment product that includes probabilistic estimates of debris-flow inundation and provides guidance for future improvements to this and similar model frameworks by identifying key sources of uncertainty.

Exploring debris flow deposit morphology in river valleys: Insights from physical modeling experiments

A comprehensive understanding of the deposit morphodynamics of debris flows in river valleys is crucial for disaster prevention and mitigation in mountainous areas. However, debris flows in river valleys are complex and variable, and the influence of the composition and terrain on deposit mechanisms and morphology remains unclear. In this study, a series of laboratory experiments were conducted to investigate the impact of the water content, slope, and grain size distribution on the deposit morphology of debris flows in river valleys. In the experiments, debris flows form narrow and elongated shuttle-shaped deposits upon entering river valleys. Increased water content and slope enhance the mobility of debris flows, resulting in wider deposit widths, gentler deposit slopes, and larger deposit areas. An increase in the gravel fraction partially facilitates the movement and deposition of debris flows. However, a large number of coarse particles may increase internal friction within the debris flow, hindering the spread of deposits and resulting in a relatively concentrated deposit with a steeper morphology. Furthermore, the debris flow regime shifts from friction to collision as the water content, slope, and gravel fraction increase. Debris flows dominated by collision forces exhibit higher mobility and a wider impact area, potentially leading to more severe disaster consequences. Compared with unconfined debris flows, the deposit area of debris flows in the river valley is smaller, and the deposit width to height ratio is larger. There is a power function relationship between deposition area and Savage number in river valleys. Additionally, particle sorting and flow regime transformation during the movement and deposition of debris flows can significantly impact the morphology and internal structure of the deposits in river valleys and then affect the development of debris flow dam breaching. In summary, this study utilized experiments to simulate natural debris flows, offering fresh insights into the depositional behavior of debris flows in river valleys.

The mechanisms of high mobility of a glacial debris flow using the Pudasaini-Mergili multi-phase modeling

Glacial debris flows with high mobility and long run-out distance have posed a growing threat to human life and critical infrastructure under climate change. The dynamics and mobility of glacial debris flows are related to many physical factors, among which initial ice/water content, phase transition, and entrainment might be the most important. A typical glacial debris flow occurred on 10 September 2020 near Namcha Barwa Peak in Tibet Plateau and travelled about 10 km under no precipitation condition. The major unsolved mechanical questions for the high mobility of this glacial debris flow include: What is the primary water source of this glacial debris flow? How do the water and ice affect the dynamics of the glacial debris flow? Which physical factor dominates the high mobility characteristics of the glacial debris flow? To answer these questions and deepen our understanding, we adopted the Pudasaini and Mergili (2019) advanced multi-phase mass flow model implemented in the computational tool (r.avaflow) to back-calculate this event. Through well-designed numerical experiments, we revealed that the initial water content is the major water source of this glacial debris flow event. We analyzed the impact of the initial ice/water fraction, phase transition, and entrainment on the mobility of the glacial debris flow. Results show that the initial ice/water content and entrainment are critical to the mobility of the glacial debris flow in the initial and later transport stage, respectively, while the phase transition only plays a minor role. Our study promotes mechanical understanding of the high mobility of this kind of glacial debris flow events.

Evolution of debris flow activities in the epicentral area, 10 years after the 2008 Wenchuan earthquake

The occurrence of debris flows after the earthquake not only damaged infrastructure but also caused large numbers of casualties. Analyzing the evolution of debris flows after the Wenchuan earthquake is significant for understanding the long-term impacts of the earthquake on the subsequent debris flow activities. This study made a continuous track of mass movements of loose deposits in all debris flow gullies from 2008 to 2018 along Provincial Road 303 (PR303) after the Wenchuan earthquake according to remote sensing images interpretation and field investigations. Four aspects, i.e. vegetation recovery, source materials, runout characteristics, and human activities were analysed to describe the evolution laws based on the 10-year inventory of debris flows. The loose deposits on the hillslope were found to be gradually transported into channels. A declining trend of mass transport rate from 2010 (24.5%) to 2018 (6.5%) was found. The occurrence frequency, magnitude, and mobility of debris flows were found to decrease. Recovery of vegetation made the loose deposits stable, whereas human activities of excavation of debris flows deposits promoted the occurrence of landslides. Three stages were divided for debris flows activities: the active period (2010–2014), the unstable period (2014–2017), and the recession period (after 2017). The decreasing trend of debris flows in the future is predicted.

Effects of flow-bed interactions on barrier impact

Debris flow mobility is governed by complex interactions at the flow-bed interface. These interactions may cause flow bulking and increase in momentum. Both factors need to be considered for the design of barriers installed along the flow path. In this study, channelized debris flow over a wet erodible bed impacting a terminal flexible barrier is modelled in a 28-m-long and 2-m-wide flume facility with 20o slope inclination in Hong Kong. Tests with flow volumes of 6 m3 and 9 m3 overriding both erodible and non-erodible beds are conducted. The change in normalised flow energy over the erodible bed section, the change in flow momentum and the impact dynamics on the terminal barrier is assessed.

The Rosetta Stone Project – Integrating experimental results on debris flow mechanics across the scales: Next results

We present the combined efforts of a research network designed to address the many challenges in the experimental modelling of debris flow phenomena. The approach has been to use apparatuses of different functional arrangement and at different scale with identical and commonly sourced flow materials from the highly idealised (dry, coarse and uniform) to the highly complex (well graded, segregating, fluid saturated). Here we briefly present some key findings of the network and point to the research questions that are currently being addressed. This complementary view of experimental debris flows helps to constrain methodological artefacts/scale effects and to identify key processes responsible for the diverse appearance and often high mobility of debris flows.

Effects of bed permeability and roughness on the mobility of submarine debris flows: experimental insights

Effects of bed permeability and roughness on the mobility of submarine debris flows: experimental insights

Numerical investigation on the role of check dams with bottom outlets in debris flow mobility by 2D SPH

Check dams with bottom outlets are widely used in debris flow gullies to minimize the damage caused by debris flows. However, the bottom size is often based on empirical criteria due to the lack of knowledge of the interaction between the debris flow and the check dam with the bottom outlet. In this study, the interaction between a viscous debris flow and check dams with bottom outlets is investigated via flume tests using 2D smoothed particle hydrodynamics. The normalized height of the bottom outlet is varied from 0 to 1, and slope angles from 15 to 35° are considered. Based on the numerical results, the jump height decays with the increasing normalized height of the bottom outlet and this trend can be approximated by a power law function. When the normalized height of the bottom outlet is less than 0.15, the performance is similar to that of a closed check dam. The flow regulation and sediment trapping functions of the check dam may fail when the normalized height of the bottom outlet is greater than 0.6. These results show that the energy breaking, flow regulation, and sediment trapping functions of check dams with bottom outlets operate well when the normalized height of the bottom outlet is in the range 0.15–0.6. Even if model limitations require further efforts to validate the findings of this study, they provide a basis for the rational design of check dams with bottom outlets.

Numerical investigation of debris flows using a two-phase continuum model incorporating a visco-inertial rheology

The motion of debris flows is controlled by the interaction of their fluid and solid components. In this work, a general two-phase model framework (Pudasaini, 2012) is adopted which captures the coupled effects of the individual phase dynamics to the overall mobility. While solving the model equations, the fluid phase is treated as a viscous Newtonian liquid while the solid phase is considered to be a granular material obeying a recently developed visco-inertial constitutive rheology. Solid and fluid components in the mixture are coupled through the interaction forces, namely buoyancy, drag, and virtual mass. The model is calibrated against results from instrumented flume experiments and from field measurements of saturated, channelized debris flows. The numerical model captures the enhanced mobility of debris flows due to the presence of interstitial fluid and provides better predictions of the flow dynamics relative to those obtained from single-phase frameworks. Better modeling agreement is obtained for granular-fluid flows with relatively high fluid content. The model is then used to simulate real debris flow events, including a case that occurred in the proximity of the Sichuan-Tibet Railway, where good agreement with reported field measurements is obtained. This modeling framework is expected to improve mitigation strategies for debris flows hazards.

Insights on the growth and mobility of debris flows from repeat high-resolution lidar

Insights on the growth and mobility of debris flows from repeat high-resolution lidar

Post‐Wildfire Generation of Debris‐Flow Slurry by Rill Erosion on Colluvial Hillslopes

AbstractLandscapes after wildfire commonly experience accelerated hillslope erosion, which often contributes to the mobilization and volume of debris flows. However, quantitative studies of the erosion and its relationship to rainfall, runoff, and landscape characteristics have been limited to a narrow range of physiographic conditions. We estimated the volume and delivery rate of slurry (a water‐sediment mixture) supplied to stream channels during a post‐wildfire rainstorm that generated large debris flows in six catchments above Montecito, CA, in 2018. We mapped the distribution of rills and measured their cross‐sectional geometries to quantify the influences of runoff, lithology, and hillslope characteristics on the sediment volumes released by rill erosion, and we scaled the results up to the 19.5 km2 of burned hillslopes in the source catchments. We computed the likely rate of surface runoff during the rainstorm and developed an empirical model for the evolution of a representative hillslope‐spanning rill to illustrate the magnitude and speed of the erosion process. Rilling was the dominant form of erosion across the hillslopes of the source catchments, and the rapid evacuation and mixing of water and sediment during rill formation supplied a slurry with high solids concentrations to stream channels. Colluvium on shale formations was more continuous, finer‐grained, and probably less permeable than colluvium on sandstones, and these differences affected the extent and dimensions of rills. As a result, shale hillslopes were the dominant source of slurry to the debris flows and supplied over twice as much slurry per unit burn area as sandstones.

Control factors for mobility of dense and dilute debris flows

<p indent=0mm>Debris flow is a commonly occurring geological hazard in mountainous areas. The solid-liquid coupling makes the debris flows distinct from other geophysical fluids such as debris avalanches and floods. Owing to the complexity of this solid-liquid interaction, current research of debris-flow mobility focuses mainly on dense debris flows with a volumetric solid concentration of ~0.6. However, few studies focus on the physical processes occurring in the transition from dense to dilute debris flows with volumetric solid concentrations of 0.6–0.4. The objectives of this study are to explore the effects of changes in volumetric solid concentration on pore water pressure response and debris-flow mobility and to reveal the mechanisms in the transition from dense to dilute debris flows. Taking the debris-flow volumetric solid concentration and fluid viscosity as variables, a series of well-instrumented flume experiments is conducted. The results show that the high mobility of debris flow is closely related to the state of liquefaction. In the transition from dense to dilute debris flows, the shear dilatancy (state of solid particles) shifts from positive (dilation) to negative (contraction). As a result, the increase in pore water pressure causes the debris flow to liquefy, and the mobility surges accordingly. According to the calculated and measured shear stresses, it is apparent that the shear resistance of dense (dilute) debris flows is dominated by friction between the particles (viscous drag). An employed rheological model shows that the shear resistance in dense debris flows is insufficient for describing the rheological behavior of dilute flows. Models considering the interaction between particles, including friction and collision, and the viscosity of the fluid phase are warranted in future research.

Exploring new methods to analyse spatial impact distributions on debris‐flow fans using data from south‐western British Columbia

AbstractPredicting the spatial impact of debris flows on fans is challenging due to complex runout behaviour. Debris flow mobility is highly variable and flows can sporadically avulse the channel. For hazard and risk assessments, practitioners typically base the probability of spatial impact or avulsion on their experience and expert judgement. To support decision‐making with empirical observations, we studied spatial impact distributions on 30 active debris‐flow fans in south‐western British Columbia, Canada. We mapped 146 debris‐flow impact areas over an average observation period of 74 years using orthorectified airphotos, satellite imagery, topographic base maps, LiDAR data, orthophotos, and field observations. We devised a graphical method to convert our geospatial mapping into spatial impact heat maps normalized by fan boundaries, enabling comparison of runout distributions across different fans. About 90% of the mapped debris flows reached beyond the mid‐points of fans, while less than 10% avulsed more than half‐way across the fan relative to the previous flow path. Most avulsions initiated at distances of 20% to 40% of the maximum fan length from the fan apex and upstream of the fan intersection point. Large volume events tend to be more mobile in the down‐fan direction, but the relation between volume and cross‐fan runout (e.g., avulsions) is more complex. Differences in spatial impact distributions can be explained, in part, by the degree of fan incision and whether a fan is truncated at its toe by a river or lake. There were no significant differences in spatial impact distributions based on the geology of the source area, sediment supply condition, or hydrogeomorphic process classification.

Debris Flow Characteristics in Flume Experiments Considering Berm Installation

This study was conducted to identify the characteristics and mobility of debris flows and analyze the performance of a berm as a debris flow mitigation measure. The debris flow velocity, flow depth, Froude number, flow resistance coefficients, and mobility ratio were accordingly determined using the results of flume tests. To analyze the influence of the berm, the results for a straight channel test without a berm were compared with those for a single-berm channel test. The debris flow velocity was observed to increase with increasing channel slope and decreasing volumetric concentration of sediment, whereas the mobility ratio was observed to increase with increasing channel slope and volumetric concentration of sediment. In addition, it was confirmed that the installation of a berm significantly decreased the debris flow velocity and mobility ratio. This indicates that a berm is an effective method for reducing damage to areas downstream of a debris flow by decreasing its potential mobility. By identifying the effects of berms on debris flow characteristics according to the channel slope and volumetric concentration of sediment, this study supports the development of berms to serve as debris flow damage mitigation measures.

Effective Hydrological Events in an Evolving Mid‐latitude Mountain River System Following Cataclysmic Disturbance—A Saga of Multiple Influences

AbstractCataclysmic eruption of Mount St. Helens (USA) in 1980 reset 30 km of upper North Fork Toutle River (NFTR) valley to a zero‐state fluvial condition. Consequently, a new channel system evolved. Initially, a range of streamflows eroded channels (tens of meters incision, hundreds of meters widening) and transported immense sediment loads. Now, single, large‐magnitude, or multiple moderate‐magnitude events are needed to accomplish substantial channel modification. Three large floods (two ≥100‐year events; one ∼10–25‐year event along lower Toutle River) from 1996 to 2015 indicate flood effectiveness in this environment is affected by both geomorphic and environmental factors. The largest and smallest of these floods (February 1996, November 2006) transported the most sediment by single floods since 1982; erosion and sediment transport by an ∼100‐year flood in December 2015 was not exceptional. Strong coupling between NFTR and its tall corridor banks, local geologic and hydraulic conditions promoting threshold erosion, event sequencing, and possibly a longitudinal gradient in stream power are important factors affecting event effectiveness on channel modification. In addition, environmental factors have also been influential, as variations in snowpack, storm trajectories and rainfall distributions, and episodic mobilization of debris flows have also influenced geomorphic response. Other factors such as vegetation anchoring, strong channel–hillside coupling, disparities between flood frequencies and perturbation relaxation times, and large variations in flood duration do not appear to be critical influences. Climate forecasts for warmer temperatures and a shift from snowfall to rainfall at high elevations may promote further acute geomorphic responses.

Influence of biopolymers on the rheological properties of seafloor sediments and the runout behavior of submarine debris flows

Submarine debris flows are mass movement processes on the seafloor, and are geohazards for seafloor infrastructure such as pipelines, communication cables, and submarine structures. Understanding the generation and run-out behavior of submarine debris flows is thus critical for assessing the risk of such geohazards. The rheological properties of seafloor sediments are governed by factors including sediment composition, grain size, water content, and physico-chemical conditions. In addition, extracellular polymeric substances (EPS) generated by microorganisms can affect rheological properties in natural systems. Here we show that a small quantity of EPS (~ 0.1 wt%) can potentially increase slope stability and decrease the mobility of submarine debris flows by increasing the internal cohesion of seafloor sediment. Our experiments demonstrated that the flow behavior of sediment suspensions mixed with an analogue material of EPS (xanthan gum) can be described by a Herschel–Bulkley model, with the rheological parameters being modified progressively, but not monotonously, with increasing EPS content. Numerical modeling of debris flows demonstrated that the run-out distance markedly decreases if even 0.1 wt% of EPS is added. The addition of EPS can also enhance the resistivity of sediment to fluidization triggered by cyclic loading, by means of formation of an EPS network that binds sediment particles. These findings suggest that the presence of EPS in natural environments reduces the likelihood of submarine geohazards.

Grain‐energy release governs mobility of debris flow due to solid–liquid mass release

AbstractDebris flows often exhibit high mobility, leading to extensive hazards far from their sources. Although it is known that debris flow mobility increases with initial volume, the underlying mechanism remains uncertain. Here, we reconstruct the mobility–volume relation for debris flows using a recent depth‐averaged two‐phase flow model without evoking a reduced friction coefficient, challenging currently prevailing friction‐reduction hypotheses. Physical experimental debris flows driven by solid–liquid mass release and extended numerical cases at both laboratory and field scales are resolved by the model. For the first time, we probe into the energetics of the debris flows and find that, whilst the energy balance holds and fine and coarse grains play distinct roles in debris flow energetics, the grains as a whole release energy to the liquid due to inter‐phase and inter‐grain size interactions, and this grain‐energy release correlates closely with mobility. Despite uncertainty arising from the model closures, our results provide insight into the fundamental mechanisms operating in debris flows. We propose that debris flow mobility is governed by grain‐energy release, thereby facilitating a bridge between mobility and internal energy transfer. The initial volume of debris flow is inadequate for characterizing debris flow mobility, and a friction‐reduction mechanism is not a prerequisite for the high mobility of debris flows. By contrast, inter‐phase and inter‐grain size interactions play primary roles and should be incorporated explicitly in debris flow models. Our findings are qualitatively encouraging and physically meaningful, providing implications not only for assessing future debris flow hazards and informing mitigation and adaptation strategies, but also for unravelling a spectrum of earth surface processes including heavily sediment‐laden floods, subaqueous debris flows and turbidity currents in rivers, reservoirs, estuaries, and ocean. © 2020 John Wiley &amp; Sons, Ltd.

Epithermal clast coating inside the rock avalanche-debris flow deposits from Mount Meager Volcanic Complex, British Columbia (Canada)

The observational and semi-quantitative sedimentological analyses of the lithofacies assemblage contribute to describe at different scales the breccia matrix along the sheared and transformed contact between rock avalanche deposits and trailing debris flow deposits emplaced by a large landslide at Mt. Meager volcano in British Columbia in 2010. An inverted cataclastic gradient of crushed breccias in a fluidized and mixed matrix implies a structurally controlled flow regime and rapid deposition. The coating matrix changed the initial polymodal distribution of the debris-flow lithofacies. Clast shape evolution helps to characterize the cataclastic sorting during transport and fluidized disaggregation. A plot of matrix percent against matrix/gravels helps to distinguish primary hot fracturing of about 61% from initial dilation and sheared fracturing involving ~22% matrix. Extensional disaggregation between 73 and 79% matrix is related to hydromagmatic fragmentation within an epithermal system. Clayey mineral assemblages identified by XRD patterns are related to colloidal aluminium gel, cataclastic shear bands, and quartz microstructures in epithermal breccia zones (pH = 2–3, 200–350 °C, <10–20 GPa).Microstructural analysis differentiates the inner rim of coated clasts from their border and the surrounding matrix in impact melt breccias. Sequential coating stages are inferred during the propagation of the shock wave with an oscillatory relative speed during the inter-seismic period. We differentiate: 1) shock faulting which contributes to the impacted quartz (10–35 GPa) in a devitrified matrix and pseudotachylite coating related to frictional melting at the margin of a conduit; 2) shock response (85 GPa) in epithermal vein with calcic spheroids, CO2 dissociation, and basaltic melt (70–101 GPa, >1500 °C); and 3) the secondary fracturing with flash heating and pressure pulse during cavitation (ΔP ~ 10 GPa, >1000–1500 °C), which generates pockets of partial melting, quartz spheroids, and a roll-over effect for the inner rim of coated clasts. The formation of impact melt breccias and the debris flow are related to the slowing elastic impact wave with an oscillatory relative speed during the inter-seismic period along a proximal strike-slip fault.This study helps identify how the proximal rock avalanche transformed into a highly mobile debris flow, larger examples of which pose a hazard to the town of Pemberton, at a distance of 65 km from Mt. Meager.

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.