Session NH3.2

[Programme]

NH3.2 | Large mass movements monitoring, modeling and early warning

Large mass movements monitoring, modeling and early warning

Co-organized by GM4

Convener: Giovanni Crosta | Co-conveners: Christian Zangerl, Irene Manzella

Orals

| Thu, 18 Apr, 10:45–12:25 (CEST)

Room 1.15/16

Posters on site

| Attendance Thu, 18 Apr, 16:15–18:00 (CEST) | Display Thu, 18 Apr, 14:00–18:00

Hall X4

Posters virtual

| Attendance Thu, 18 Apr, 14:00–15:45 (CEST) | Display Thu, 18 Apr, 08:30–18:00

vHall X4

Large mass movements in rock, debris and ice in glacial masses, represent enormous risks. These complex systems are difficult to describe, investigate, monitor and model. Hence a reliable model of these phenomena requires acquisition and analysis of all available data to support successive steps up to the management of Early Warning systems.
Large instabilities affect all materials (rock, weak rocks, debris, ice), from low to high altitudes, evolving as slow or fast complex mass movements. This and the complex dependency on forcing factors result in different types and degrees of hazard and risk. Some aspects of these instabilities are still understudied and debated, because of difficult characterization and few cases thoroughly studied. Regional and temporal distribution, relationships with controlling and triggering factors are poorly understood resulting in poor predictions of behavior and evolution under present and future climates. How will it change their state of activity under future climatic changes? How this will impact on existing structures and infrastructures? How can we improve our predictions? Relationships among geological and hydrological boundary conditions and displacements are associated to evolution in space and time of hydro-mechanical controls . Even for well studied and active phenomena warning thresholds are mostly qualitative, based on semi-empirical approaches. Hence a multidisciplinary approach and robust monitoring data are needed. Many modeling approaches can be applied to evaluate instability and failure, considering triggerings, failure propagation, leading to rapid mass movements . Nevertheless, these approaches are still phenomenological and have difficulty to explain the observed behavior. Impacts of such instabilities on structures represents a relevant risk but also an opportunity in terms of investigations and quantitative measurements of effects on tunnels, dams, roads. Design of these structures and knowledge of their expected performance is fundamental.
We invite to present case studies, sharing views and data, to discuss monitoring and modeling approaches and tools, to introduce new approaches for thresholds definition, including advanced numerical modeling, Machine Learning for streamline and offline data analyses, development of monitoring tools and dating or investigation techniques.

Orals: Thu, 18 Apr | Room 1.15/16

10:45–10:55

EGU24-2036

ECS

On-site presentation

Spatio-temporal distribution of extreme rock-ice avalanches in the Cordillera Blanca (Peru)

Benjamin Lehmann, Swann Zerathe, Ronald Concha, Julien Carcaillet, Pierre G. Valla, Juan C. Torres-Lázaro, W. Harrinso Jara, and Manuel Cosi

The Cordillera Blanca, located in Peru between latitudes 8-10°S, is the most glacierized intertropical mountain range in the world, with peaks over 6,000 meters still carrying numerous glaciers today. Ongoing climate change has resulted in a 41.50% reduction in glacier extent from 1962 to 2020, increasing natural hazards such as icefall, glacial lake overflow flooding, and rock avalanches. These events mainly affect the highest reliefs, but can reach the low elevation valleys, where around 300,000 inhabitants are exposed. Since the 1950s, these hazards have caused tens of thousands of casualties, including two major disasters: rock-ice avalanches from the northern summit of Huascaran (6,757m) traveling over considerable distances and destroying populated areas such as Ranrahirca (1962) and Yungay (1970), resulting in approximately 7,000 casualties in total.

In this context, our objective is to construct a comprehensive "spatio-temporal" inventory of substantial rock-ice avalanches (volume > 10⁶ m³) within the Cordillera Blanca. Our aim is to enhance our understanding of their spatial distribution, temporal frequency, and magnitude while pinpointing potential triggering factors. Our specific focus involves investigating potential correlations between avalanche records and climatic oscillations spanning the past hundred thousand years. The primary area of interest is the Yungay site, situated directly downstream from Huascaran North, where successive debris avalanche (historical and paleo) have accumulated, forming debris cones that extend across several square kilometers. Preliminary field observations have identified numerous large boulders indicative of events surpassing the reported magnitude for historical avalanches and their associated deposits.

Employing a multi-method approach that integrates fieldwork, remote sensing, geochronology, and numerical modeling, we intend to assess rock-avalanche deposits and volumes. A preliminary field mission conducted in August 2023 in Yungay facilitated the mapping and sampling of approximately 30 boulders of pluri-decametric size for surface-exposure dating (in situ ¹⁰Be on quartz). Anticipating dating results by early 2024, one of the primary expected outcomes of this study is to achieve a comprehensive reconstruction of the geomorphic response of the high Cordillera Blanca during past climate oscillations. This understanding will contribute to better anticipating the future evolution of natural hazards within the context of ongoing global climate warming, glacial retreat, and accelerated permafrost degradation. Additionally, our objective is to characterize the triggering mechanisms for low-frequency (recurrence time >100 yr) high-magnitude (volume >10⁶ m³) events.

How to cite: Lehmann, B., Zerathe, S., Concha, R., Carcaillet, J., Valla, P. G., Torres-Lázaro, J. C., Jara, W. H., and Cosi, M.: Spatio-temporal distribution of extreme rock-ice avalanches in the Cordillera Blanca (Peru), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2036, https://doi.org/10.5194/egusphere-egu24-2036, 2024.

10:55–11:05

EGU24-5778

ECS

On-site presentation

Monitoring 4D landslide displacement using very high resolution Pléiades satellite remote sensing.Case study of the La Valette landslide, French Alps

Sheng Fu, Steven M. de Jong, Wiebe Nijland, Mathieu Gravey, Philip Kraaijenbrink, and Tjalling de Haas

Slow-moving landslides may pose a substantial threat to communities and infrastructure, with annual creeping distances ranging from a few mm to 100 m. To protect local communities from the landslide motion, landslide displacement monitoring is necessary. However, traditional field investigations are time- and labor-consuming, which may limit the understanding of the landslide evolution and thereby mitigation. Here we propose a 4D landslide displacement framework using optical very high resolution (0.5m) Pléiades satellite constellation imagery. We use our method to monitor the annual movement of the ‘La Valette’ landslide, southern French Alps, between 2012 and 2022. During this period, the landslide moved most actively during the years 2012 and 2013, with average 3D displacement rates of 1.22 and 0.89 cm / day, respectively. Furthermore, we found a decelerating trend in movement rate from 2012 to 2022, which we attribute to warmer weather, decreasing precipitation rates, drier air conditions, and the implementation of a drainage installation. Our study demonstrates the great potential of very-high resolution satellite imagery for near-real time monitoring of 4D landslide displacement, which may benefit research and may contribute to the mitigation of damage and fatalities of slow-moving landslides.

How to cite: Fu, S., de Jong, S. M., Nijland, W., Gravey, M., Kraaijenbrink, P., and de Haas, T.: Monitoring 4D landslide displacement using very high resolution Pléiades satellite remote sensing.Case study of the La Valette landslide, French Alps, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5778, https://doi.org/10.5194/egusphere-egu24-5778, 2024.

11:05–11:15

EGU24-6091

On-site presentation

Monitoring impending rock slope failure in alpine scenarios: impact of high spatial and temporal resolution satellite SAR imagery in the investigation of the June 15, 2023, failure event in Brienz/Brinzauls, Swiss Alps

Andrea Manconi, Yves Bühler, Valentyn Tolpekyn, Melanie Rankl, and Michael Wollersheim

Rock slope failures are the catastrophic expression of long-term geomorphological processes occurring in alpine regions. Their impact is often limited to single slopes; however, rock and debris material can occasionally travel very long distances and affect landscape, infrastructures, as well as endanger human life several kilometers away from the source area. Monitoring the evolution of surface activity is recognized as a suitable method to timely identify changes potentially leading to such failure events. Satellite based remote sensing, and in particular Synthetic Aperture Radar (SAR), has shown to be an efficient alternative to in-situ sensors to monitor displacements, especially in situations where the area of interest is large and/or barely accessible. Despite the advent of satellite missions like the ESA Copernicus Sentinel-1, operational monitoring and early warning on single slopes exhibiting surface displacement acceleration potentially leading to failure is still not viable from satellite radars. This is mainly because of the current limitations in spatial and temporal resolution, which prevent obtaining the accuracy and the timeliness often needed for such scenarios.

Here we demonstrate how high spatial and temporal resolution SAR imagery can improve monitoring and characterization of the evolution of a rock slope instability prior and after catastrophic failure. We benefit from ICEYE imagery (X-Band, SPOT mode, 5x5 km scene size, ~50cm resolution) acquired over the Brienz/Brinzauls slope instability in the Swiss Alps between March and August 2023. Among 100 SAR images, we have identified a subset of 30 datasets (ascending orbit, left looking) providing an optimal viewing of the moving slope and imaging the area of interest with revisit times ranging from 3 days to a few hours. We use digital image correlation to measure surface displacements and change detection analyses to map rockfall activity and the slope failure event on June 15^th, 2023. We also applied SAR interferometry on data pairs exhibiting suitable perpendicular baselines and computed topographic models at different times and determine failed volumes. The latter have been validated with local terrain models based on photogrammetric drone flights. We discuss the results obtained with ICEYE imagery versus the possibilities with Sentinel-1 data and focus on advantages and specific problems. Our results provide an important step forward towards the use of satellite SAR imagery for operational landslide monitoring scenarios and in the identification and forecasting of catastrophic slope failure events in alpine areas.

How to cite: Manconi, A., Bühler, Y., Tolpekyn, V., Rankl, M., and Wollersheim, M.: Monitoring impending rock slope failure in alpine scenarios: impact of high spatial and temporal resolution satellite SAR imagery in the investigation of the June 15, 2023, failure event in Brienz/Brinzauls, Swiss Alps , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6091, https://doi.org/10.5194/egusphere-egu24-6091, 2024.

11:15–11:25

EGU24-15258

ECS

On-site presentation

Effects of rainfall Intensity-Duration on landslides’ velocity variations: insights from long-term monitoring of case studies in Emilia-Romagna and South Tyrol (Italy)

Melissa Tondo, Vincenzo Critelli, Marco Mulas, Francesco Lelli, Giuseppe Ciccarese, Giovanni Truffelli, Volkmar Mair, and Alessandro Corsini

What is known, nowadays, is that shallow landslides are mostly influenced by intense short-duration rainfall events while deep-seated ones are mainly affected by long-duration cumulated rainfall. However, the correlation between precipitation and displacement rates, especially for deep-seated landslides, is still poorly investigated on a quantitative basis. In order to understand the mechanisms of acceleration and deceleration of landslides and how they are related to rainfall regimes, long-term, possibly continuous, monitoring of displacement is essential. This contribute aims to present and discuss this issue based on results from about 15 long-term monitored landslides, ranging from earthslides-earthflows to deep-seated rockslides, located in Emilia-Romagna region and South Tyrol. Displacement time series in these case studies have been collected with different in-situ techniques such as principally periodic and continuous GNSS and Robotic Total Stations (RTS), covering periods up to more than ten years. After analysing displacement plots, each identified acceleration event was correlated to rainfall by considering the last significant precipitation event antecedent to the first date of velocity variation, recorded by local meteo stations. Then, Duration (h) and Intensity (mm/h) were retrieved for each event and an Intensity-Duration (ID) plot was built with all data together. It could be observed that the ID-points were distributed along a line with extremely slow deep-seated landslides on one side and rapid earthslides-earthflows on the other, representing the two opposites of the spectrum. Secondly, another aspect that was considered in this framework is the difference between velocity variations of monitored points (such as GNSS benchmarks or RTS prisms) and the velocity of movement propagation along the landslide body. Examples on this topic are presented from Ca’ Lita and Corvara landslides, located in Emilia-Romagna and South Tyrol, respectively. Landslides response to precipitation events is the result of a complex combination of geological, geomorphological, geotechnical, and meteo-climatic factors. In accordance with ID-points distribution, the lower the surface of movement the lower duration and intensity are needed to enhance instability and displacement rates. On the other hand, the interaction with rainfall is not as immediate for deep-seated landslides, making their interpretation more complex. This study presents (i) a summary of all the recorded velocity variations affecting the proposed case studies, and (ii) an interpretation of their behavior in terms of acceleration and precipitation conditions.

How to cite: Tondo, M., Critelli, V., Mulas, M., Lelli, F., Ciccarese, G., Truffelli, G., Mair, V., and Corsini, A.: Effects of rainfall Intensity-Duration on landslides’ velocity variations: insights from long-term monitoring of case studies in Emilia-Romagna and South Tyrol (Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15258, https://doi.org/10.5194/egusphere-egu24-15258, 2024.

11:25–11:35

EGU24-2625

On-site presentation

Rheological behavior of Crushed Rock Flows

wei hu and Mauri McSaveney

The enduring mystery surrounding the unexpectedly high mobility of expansive geophysical flows has persistently tantalized researchers since Albert Heim's investigation following the catastrophic landslide at Elm, Switzerland. Despite numerous claims of resolution, the mechanism underpinning this remarkable mobility has remained elusive. To delve into the flow dynamics of crushable dense granular material exhibiting high mobility, a series of high-speed rotary shear experiments was conducted using various mineral particles. Our findings revealed a more explicable flow behavior when interpreting shear resistance as viscous rather than purely frictional. Notably, we observed a dramatic decrease in viscosity for crushable materials, stabilizing at a consistently low level, crucial in dictating the remarkable fluidity observed in large-scale geophysical flows like rock avalanches. The flow exhibited two distinct phases, demarcated by a critical point of weakening within accumulated strain for crushable material. The initial phase reflected a simple Newtonian or non-Newtonian-like flow, while the subsequent phase was more intricate, displaying a profound viscosity drop stabilizing at a constant level under substantial strain. This discovery holds significant implications for understanding hypermobile geophysical phenomena, including rock avalanche dynamics, natural faulting, and crater collapse. In particular, we demonstrate that the behavior of rock avalanches is similar to that of complicated fluids with extensive weakening and that the viscosity of this special “liquid” is as low as 500 Pa·s. This finding can also help improve the accuracy and reliability of the numerical simulation of rock avalanches by using the viscous model obtained from the experiments.

How to cite: hu, W. and McSaveney, M.: Rheological behavior of Crushed Rock Flows, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2625, https://doi.org/10.5194/egusphere-egu24-2625, 2024.

11:35–11:45

EGU24-11468

On-site presentation

Dynamic simulation of rock-avalanche fragmentation

Shiva P. Pudasaini, Martin Mergili, Qiwen Lin, and Yufeng Wang

Fragmentation is a common phenomenon in rock avalanches with complex features. The fragmentation intensity and process determines exceptional spreading and mobility of rock-avalanches in the run-out zone. However, studies focusing on the simulation of these phenomena are still limited and no operational dynamic simulation model including the effects of fragmentation has been proposed yet. By enhancing the mechanically controlled landslide deformation model, we propose a novel, unified dynamic simulation method for rock-avalanche fragmentation during propagation. Our formally derived method relies on the continuum mechanics that is applicable to rock masses of any size. The model includes three important aspects: mechanically controlled rock mass deformation, the momentum loss while the rock-mass fiercely impacts the ground, and the energy transfer during fragmentation resulting in the generation of dispersive lateral pressure. We reveal that the dynamic fragmentation, resulting from the overcoming of the tensile strength of the rock mass by the impact on the ground, leads to spreading, thinning, and run-out of the rock avalanche, and to its hypermobility. The elastic strain energy release caused by fragmentation is an important process. Energy conversion between the front and rear parts of the mass caused by the fragmentation process results in the forward movement of the frontal material and the hindered motion of the rear portion of the rock avalanche. Our new model describes this by amplifying the lateral pressure gradient in the opposite direction: enhanced for the frontal particles and reduced for the rear particles after the fragmentation process. The main principle is the switching between the compressional stress and the tensile stress, and therefore from the controlled deformation to substantial spreading of the frontal part of the mass in the flow direction while backward stretching of the rear part of the rock mass. In principle, observations in the laboratory and field events support our simulation results.

How to cite: Pudasaini, S. P., Mergili, M., Lin, Q., and Wang, Y.: Dynamic simulation of rock-avalanche fragmentation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11468, https://doi.org/10.5194/egusphere-egu24-11468, 2024.

11:45–11:55

EGU24-15459

ECS

On-site presentation

Multiscale Numerical Modeling of Ultrasound-Induced Granular Avalanches

Hugo A. Martin, Anne Mangeney, Xiaoping Jia, Bertrand Maury, Aline Lefebvre-Lepot, Yvon Maday, and Paul Dérand

Understanding the mechanisms of seismic-wave-induced triggering of landslides and earthquakes at micro-strain amplitudes is crucial for quantifying seismic hazards. Granular materials, as an out-of-equilibrium and metastable model system, offer insights into landslides and fault dynamics within the unjamming transition framework from solid to liquid states. Recent experiments suggest that ultrasound-induced granular avalanches result from reduced interparticle friction via shear acoustic lubrication. However, investigating crack growth or slip at the grain contact scale in optically opaque granular media remains challenging.

We present a new multiscale numerical modeling of 2D dense granular flows triggered by basal acoustic vibrations of an inclined plane. We introduce a time-scale separation method, addressing the characteristic scales of grain motion on one hand and the propagation of acoustic vibrations on the other. Our approach results from the coupling between the Convex Optimization Contact Dynamics model (COCD) and the computation of vibration modes.

Numerical simulations of ultrasonic vibrations in the millisecond range and flow onset in the second range reveal a correlation between local rearrangements at the grain scale and continuous flows at the macroscopic scale. Ultrasounds primarily propagate through strong-force chains, while a decrease in interparticle friction occurs in weak contact forces perpendicular to these chains. This friction reduction initiates local rearrangements leading to continuous flows through a percolation process with a delay dependent on proximity to failure. Ultrasound-induced flow, compared to gravity-driven flow, appears more spatially uniform, suggesting the role of effective temperature induced by ultrasonic vibration. The simulations align well with experimental observations of granular flows triggered by ultrasound below avalanche angles, supporting the validity of our numerical method.

How to cite: Martin, H. A., Mangeney, A., Jia, X., Maury, B., Lefebvre-Lepot, A., Maday, Y., and Dérand, P.: Multiscale Numerical Modeling of Ultrasound-Induced Granular Avalanches, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15459, https://doi.org/10.5194/egusphere-egu24-15459, 2024.

11:55–12:05

EGU24-11528

On-site presentation

Landslide mobility enhanced by dynamic basal liquefaction of underlying sediments

Mark Reid and Brian Collins

Far-traveled landslides greatly increase hazard and risk. Although pervasive liquefaction in debris flows and flow slides can dramatically boost their mobility, the effects of liquefaction on the mobility of coherent landslides is more difficult to forecast. In 2014, the Oso landslide in Washington State, USA failed rapidly and swept across more than 1 km of the adjacent flat alluvial valley, killing 43 people. We mapped over 350 sand boils that emanated from the alluvium under the debris-avalanche hummock deposit. Although transient, these sand boils represent definitive evidence of sub-bottom (basal) liquefaction of the alluvium beneath the overriding slide. The hummocks in the slide mass were not liquefied and they commonly rafted upright vegetation, including coniferous trees, and intact layered glacial sediments across the valley floor. A liquefied base provides little shear resistance, greatly enhancing slide mobility. Our extensive laboratory testing and numerical modeling revealed that several mechanisms may have enhanced basal liquefaction at Oso: rapid undrained loading, shearing of contractive alluvial sediments, and cyclical loading from ground shaking associated with rapid emplacement.

Here we further investigate the potential for a rapidly moving slide mass to dynamically liquefy underlying alluvial sediments through undrained loading. We use a fully coupled poro-elastic numerical model with parameters determined by laboratory tests of the valley alluvium at the Oso landslide site. Given a landslide speed of 10 m/s, estimated from seismic records of the event, our modeling demonstrates that rapid loading induces transiently elevated pore-fluid pressures nearly equal to the overriding landslide load. These pore-fluid pressures are capable of liquefying the saturated alluvium, reducing its shear strength, and enhancing mobility. Both landslide speed and the hydraulic conductivity of the underlying alluvium strongly modulate the potential for liquefaction. Slower landslide speeds and/or greater alluvial hydraulic conductivity allow simulated pore pressures from loading to dissipate before reaching liquefaction levels. Only specific combinations of these parameters promote basal liquefaction. Such basal liquefaction effects may enhance the mobility of other slides traveling rapidly across saturated alluvium in adjacent valley floors.

How to cite: Reid, M. and Collins, B.: Landslide mobility enhanced by dynamic basal liquefaction of underlying sediments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11528, https://doi.org/10.5194/egusphere-egu24-11528, 2024.

12:05–12:15

EGU24-12171

ECS

On-site presentation

Detecting Mass Movements using Fractal-based algorithm

Quratulain Jaffar, Qi Zhou, and Hui Tang

Rapid climate change is triggering an increase in the frequency and magnitude of catastrophic mass movements on the Earth's surface. Real-time detection of these hazards can improve existing early warning systems and mitigate risks to both humans and society. However, effectively isolating seismic signals from mass movements within continuous seismic recordings remains a significant challenge due to persistent background noise interference. Therefore, It is essential to develop robust detection algorithms for automatic detection. To address this issue, this study proposes the utilization of fractal geometry, which offers a quantitative description of the intricate structures and patterns within a signal across different scales. By using fractal dimensions, this approach aims to differentiate the seismic signal from background noise, because noise typically has a higher fractal dimension than the seismic signal. Two methods, namely, i) variogram estimator and ii) detrended fluctuation analysis, are investigated and applied to the continuous seismic data recorded in the Illgraben catchment in Switzerland to compute the fractal dimension. The findings demonstrate that both methods exhibit power law behaviors in spatio-temporal data, unveiling consistent patterns across scales. The observed variation in fractal dimensions along the seismic traces suggests the reliability of this approach, showcasing reduced susceptibility to false positive detection errors even in the presence of high noise levels. Furthermore, this study also aims to categorize various types of mass movements. This involves defining distinct ranges of fractal dimensions derived from measured data, facilitating the differentiation of various types of mass movements.

How to cite: Jaffar, Q., Zhou, Q., and Tang, H.: Detecting Mass Movements using Fractal-based algorithm, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12171, https://doi.org/10.5194/egusphere-egu24-12171, 2024.

12:15–12:25

EGU24-13255

On-site presentation

Unifying endo-exo classification of episodic landslide movements

Qinghua Lei and Didier Sornette

Landslides, a widespread form of mass wasting, involve complex gravity-driven downslope movements developing over days to years before the final major collapse, which are commonly boosted by external events like precipitations and earthquakes. The reasons behind these episodic movements, characterised by alternating cycles of accelerating and decelerating creeps (marked by intermittent bursts of displacement followed by sustained periods of relaxation dynamics), and how these relate to the final instability, remain poorly understood. Here, we propose the new “endo-exo” classification of landslide bursts, based on the dynamical signatures of pre- and post-burst displacement rates. The underlying concept is based on the existence of cascades of triggered frictional slip and damage responses around a burst. The general theory of multiple cascades of triggered events predicts the existence of four classes of bursts: (i) exogenous non-critical, (ii) exogenous critical, (iii) endogenous non-critical, and (iv) endogenous critical, with respective displacement rates relaxing as power laws around the time t_c of the burst respectively as (i) 1/(t–t_c)^1+ϑ for t > t_c, (ii) 1/(t–t_c)^1–ϑ for t > t_c, (iii) 1/t–t_c⁰, and (iv) 1/t–t_c^1–2ϑ, thus depending on a single parameter ϑ. We test these predictions on the precursory and recovery signatures associated with bursts recorded in the long-term monitoring dataset of a rainfall-induced landslide at Preonzo, Switzerland, which exhibited significant episodic movements over many years prior to a catastrophic failure in 2012. Exogenous critical bursts (ii), provoked by external rainfall events, occur abruptly and relax gradually with a power-law exponent around 0.5. In contrast, for endogenous critical bursts (iv) that occur spontaneously under no external triggering, the landslide progressively accelerates prior to the burst and then slowly decelerates afterwards, showing a semi-symmetrical acceleration-deceleration behaviour governed by a small power-law exponent around 0.1. The longer-lived influence of an endogenous critical burst (as reflected by its small relaxation exponent) results from the precursory process that impregnates the system much more than its exogenous counterpart. Additionally, we document a unique exogeneous subcritical burst (i) triggered by the sudden collapse of a downslope sector; it is characterised by an immediate peak followed by a rapid recovery with a power-law exponent around 1.4, consistent with the absence of cascading failures. Endogenous non-critical bursts (iii) are largely driven by fluctuations and thus show no time-dependent recovery. The obtained power laws for these different burst classes are compatible with the existence of a single exponent ϑ ≈ 0.4±0.1, providing strong support for our theory. Our novel conceptual framework points at the existence of a deep quantitative relationship between episodic landslide movements, external triggering events (e.g. rainfall, snowmelt, and seismicity), and internal frictional slip, damage, and healing processes within the landmass.

How to cite: Lei, Q. and Sornette, D.: Unifying endo-exo classification of episodic landslide movements, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13255, https://doi.org/10.5194/egusphere-egu24-13255, 2024.

Posters on site: Thu, 18 Apr, 16:15–18:00 | Hall X4

Display time: Thu, 18 Apr, 14:00–Thu, 18 Apr, 18:00

X4.29

EGU24-1624

ECS

Reconstructing the history of landslides in northern Japan through dendrogeomorphology

Reona Kawakami, Ching-Ying Tsou, Yukio Ishikawa, Ami Matsumoto, Shigeru Ogita, Kazunori Hayashi, and Daisuke Kuriyama

Dendrogeomorphology serves as a method to determine the timing of historical landslide events. This approach entails scrutinizing the spatial and temporal aspects of landslide occurrences by investigating their impact on tree growth by analyzing variations in tree-ring width, recovery timeline of injured tree stem, as well as the age of tree invasion and establishment in areas affected by landsliding. The method's advantage lies in its capacity to yield a large number of samples where trees are growing. This study encompasses research conducted in both the Sansukezawa landslide in Aomori Prefecture and the Kamitokitozawa landslide in Akita Prefecture, Japan. The examination includes an analysis of the reactions of a combined total of 187 tilted deciduous broadleaved trees and coniferous trees aged between 10⁰ and 10² years in response to landslide events. The findings, revealed by variations in tree-ring width, suggested multiple landslide occurrences at the Sansukezawa landslide between 1901 and 2000. The magnitude of these events varied, encompassing localized activities such as the enlargement of landslide scarps to more extensive landslide movements. In the Kamitokitozawa landslide area, the development of impending landslide events, inferred from the recovery timeline of injured tree stems, included scarp expansion. There were five instances of landslide activities recorded during the period from 1999 to 2019.

How to cite: Kawakami, R., Tsou, C.-Y., Ishikawa, Y., Matsumoto, A., Ogita, S., Hayashi, K., and Kuriyama, D.: Reconstructing the history of landslides in northern Japan through dendrogeomorphology, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1624, https://doi.org/10.5194/egusphere-egu24-1624, 2024.

X4.30

EGU24-2327

Riverbed Sediment Topography Mapping Using UAV LiDAR and Insights into Sediment Redistribution Following an Extreme Rainfall Event and Dam Failure

Yu-Chang Chan and Cheng-Wei Sun

Accurate characterization of riverbed sediment is crucial for monitoring cross-sectional changes in rivers and modeling water dynamics, especially during large water discharge events. The UAV LiDAR technique, with recent advancements, offers enhanced capabilities for detailed riverbed topography mapping by eliminating surface vegetation. Despite its potential, the adoption of UAV LiDAR for riverbed cross-sectional profiling has faced delays and skepticism in regular practices. In this study, we applied the UAV LiDAR technique to measure the riverbed topography of a relatively wide river in the Ilan plain, northeast Taiwan. Our findings reveal that UAV LiDAR provides significantly more detailed results compared to Airborne LiDAR and surpasses topography measurements obtained through photogrammetry. The accuracy of UAV LiDAR-derived point clouds outperforms photogrammetry, especially when ground control points for the work of photogrammetry are insufficient or poorly distributed. Despite challenges posed by water bodies absorbing LiDAR signals, UAV LiDAR allows the production of complete riverbed topography, offering reliable estimates during dry seasons. Utilizing UAV LiDAR data, we conducted a comprehensive analysis of both cross-sectional and longitudinal riverbed profiles. The longitudinal profiles exhibit wavy frequencies associated with sediment transport processes, opening avenues for further investigation. Additionally, we evaluated Digital Elevation Models (DEMs) of Differencing (DoD) using previously acquired Airborne LiDAR point clouds. The DoD analysis unveiled the substantial magnitude of sediment movement and redistribution following an extreme rainfall event and dam failure, with a height difference exceeding 9m. This analysis, extending along the river's longitudinal profile, serves as a ground-truth field dataset illustrating how extreme rainfall events can trigger large sediment movements, posing potential hazards to the residents near rivers. Our study demonstrates the utility of UAV LiDAR in high-resolution mapping of riverbed sediment topography and provides valuable insights into sediment dynamics under extreme events, contributing to improved monitoring and hazard assessment practices.

How to cite: Chan, Y.-C. and Sun, C.-W.: Riverbed Sediment Topography Mapping Using UAV LiDAR and Insights into Sediment Redistribution Following an Extreme Rainfall Event and Dam Failure, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2327, https://doi.org/10.5194/egusphere-egu24-2327, 2024.

X4.31

EGU24-2547

ECS

SAR Monitoring and Finite Element based Stability Modeling for the Zero Landslide in the Darjeeling Himalayas, India

Suvam Das, Koushik Pandit, Debi Prasanna Kanungo, and Shantanu Sarkar

Landslides are one of the recurring geological hazards in the Indian Himalayas, often leading to loss of life and economy. For the present study, the Zero landslide located in the Darjeeling Himalayas, India has been investigated. This landslide was first activated on July 16, 2014 and its subsequent occurrences have affected a total area of 1×10⁵ sq.m. Field investigations revealed that a local school building, its nearby roads and a few residential buildings are at risk from this landslide. Therefore, monitoring and stability modeling becomes imperative to assess the associated hazard level. For the studied case, the Small Baseline Subset Interferometric Synthetic Aperture Radar (SBAS-InSAR) technique was applied to monitor the surface level deformation. For this purpose, Sentinel-1 SLC images captured from January 2022 to November 2023 were collected, and processed using the HyP3 and OpenSARLab platforms. The SBAS-InSAR results revealed maximum subsidence i.e., Line-of-Sight (LOS) velocity (cm/y) of –8.2 and –11.5 for ascending and descending orbit directions, respectively. The presence of transverse tension cracks in the crown and flanks of this landslide supports the SBAS-InSAR results and indicate an active sliding. Furthermore, to assess the slope stability, continuum based two-dimensional finite element modeling (FEM) was carried out. For this, the Shear Strength Reduction (SSR) method was employed in the FE analysis to compute the safety factors for different scenarios. To incorporate material properties within the configured FEM, the Mohr-Coulomb strength criterion was used for soil overburden, and the Generalized Hoek-Brown strength criterion was used for bed-rock profile. The FE analysis revealed a critical Factor of Safety (FoS) value of 1.07 for dry condition and 0.78 for wet condition (R_u). The obtained FoS values suggest that the studied slope section is marginally stable in dry condition; however, instability may be induced during a rainfall event in future. Based on these findings, the design and implementation of landslide risk mitigation measures have been encouraged prior to any major landslide event at the study location.

How to cite: Das, S., Pandit, K., Kanungo, D. P., and Sarkar, S.: SAR Monitoring and Finite Element based Stability Modeling for the Zero Landslide in the Darjeeling Himalayas, India, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2547, https://doi.org/10.5194/egusphere-egu24-2547, 2024.

X4.32

EGU24-3883

Evolution of large-scale landslide at Tuchang creek, Taiwan

Chia-Ming Lo and Yu-Chen Wu

The D077 study area is located on the right bank of Tuchang Creek in Wufeng Township, Hsinchu County, Taiwan. Two large-scale landslide events occurred in the D077 study area in 2004 and 2013, causing 14 casualties and disrupting traffic, seriously threatening downstream settlements. Until now, the rock slopes in the D077 study area are still in a state of toppling deformation and instability. In view of this, this study used multi-stage remote sensing, terrain analysis, geological survey, geophysical prospecting, drilling, and other data in the analysis of the evolution of large-scale landslides at D077 study area. The results show that the evolution of large-scale landslides (the D077 study area contains three sliding masses: S1, S2, and S3) can be divided into six periods: (1) the period of severe erosion of Tuchang creek and Chingchuan anticline, (2) rock mass decompression and toppling deformation period, (3) development of wedge failure trend of rock slopes at S1 sliding mass, (4) movement of S1 sliding mass and violent erosion of the S2 sliding mass slope toe, (5) toppling deformation develops rapidly at S2 sliding mass, (6) movement of S2 sliding mass and S3 sliding mass toppling deformation continues to develop. In the future, we predict that S2 and S3 will again cause debris sliding and large-scale rock mass sliding. This activity is also expected to threaten the safety of inhabitants and property in downstream of Tuchang creek.

Key words: large-scale landslide, toppling deformation, remote sensing, geological survey, geophysical prospecting, drilling

How to cite: Lo, C.-M. and Wu, Y.-C.: Evolution of large-scale landslide at Tuchang creek, Taiwan, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3883, https://doi.org/10.5194/egusphere-egu24-3883, 2024.

X4.33

EGU24-4336

Study on energy and displacement evolution of rock slope during the development of landslide by multi-scale modeling

Yu Chen Wu and Chia ming Lo

Slope monitoring is a commonly way to mitigate the hazard of landslide. The displacement is one of the main parameters being used in slope monitoring, however it is not significant until landslide occurs. According to the literature, energy will accumulate, transfer and dissipate during the development of landslide. So, it is possible to take energy as one of parameters used in slope monitoring if it’s property was understood sufficiently. This study is aimed to find the relationship between energy evolution, displacement of sliding mass and mechanical behavior of rock materials during the development of landslide. In addition, the energy data and displacement data were compared to find the difference between them. Science the mechanical properties of rock mass is affected by scale, four kind of numerical models were created using different scales. Then the energy data and displacement data of specific particles inside each models were recorded during the simulation. The small-scale models include direct shear test model and uniaxial compression test model. The large-scale models include simplified toppling failure model and full-scale landslide model. The results show that in the large-scale models, the variation of energy data is more significant than displacement data. However, in the small-scale models, the variation of displacement data is more significant.

How to cite: Wu, Y. C. and Lo, C. M.: Study on energy and displacement evolution of rock slope during the development of landslide by multi-scale modeling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4336, https://doi.org/10.5194/egusphere-egu24-4336, 2024.

X4.34

EGU24-4996

A simplified calculation method for high-steep soil slope stability due to groundwater rise from irrigation

(withdrawn after no-show)

Jianqi Zhuang

X4.35

EGU24-6050

A case study integrating in-situ monitoring data and numerical simulation method to slope stability assessment of a remote village in southwest Taiwan

Huai-Houh Hsu, Ting-Wei Chen, Chen-Hsun Hsieh, Chia-Chi Chang, and Tsung-Yi He

The Baoshan Village, a remote village deep in southwest Taiwan, is located near the Tengjhih National Forest Recreation Area. The strata at the site of this study belong to the Miocene Changshan Formation. Its lithology is mainly slate, occasionally intercalated with thin sandstone layers, and the Chaochou Fault passes through it on the east side. Headward erosion and weathering effects made landfall while heavy rainfall and typhoons hit Taiwan. Typhoon Morakot (2009) impacted Taiwan and brought catastrophic damage. Landslides and significant damage happened in the Baoshan Village neighborhood. This study compiles the long-term in-situ monitoring data of the Baoshan Village from 2018 to the present. Monitoring results show that the east side of the Baoshan Elementary School has an apparent slide surface at a depth of 46m. The limit equilibrium method is adopted for the numerical simulation of slope stability by the digital elevation model (DEM), site investigations, and monitoring data. Results show that Baoshan Village contains many potential slide surfaces distributed in different areas, three of which have high potential sliding surfaces. The assessment of slope stability analysis can provide a tremendously meaningful reference for disaster mitigation of Baoshan Village.

How to cite: Hsu, H.-H., Chen, T.-W., Hsieh, C.-H., Chang, C.-C., and He, T.-Y.: A case study integrating in-situ monitoring data and numerical simulation method to slope stability assessment of a remote village in southwest Taiwan, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6050, https://doi.org/10.5194/egusphere-egu24-6050, 2024.

X4.36

EGU24-6304

ECS

Physics-based uncertainty modeling of deep-seated landslides using InSAR: A case of El Forn (Andorra)

Rachael Lau

Deep-seated landslide monitoring can require extensive insitu monitoring tools, typically involving equipping boreholes with extensometers, thermometers, and piezometers – proving to be an expensive and labor-intensive task. This work focuses on assessing deep-seated landslide stability by using the physics-based modeling, in partnership with Interferometric Synthetic Aperture Radar (InSAR), as a diagnostic tool for assessing stability in remote regions. We use the case of the insitu monitored El Forn landslide in Canillo, Andorra. We used available Sentinel-1 data to create a velocity map from deformation time series in 2019 and inputted it into a calibrated physics-based predictive model. Using the correlation between the model’s velocity, the insitu observed velocity and the velocity derived from InSAR, we create a normalized real-time risk map of the landslide.

How to cite: Lau, R.: Physics-based uncertainty modeling of deep-seated landslides using InSAR: A case of El Forn (Andorra), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6304, https://doi.org/10.5194/egusphere-egu24-6304, 2024.

X4.37

EGU24-8090

ECS

The discovery of a large-scale gravitational collapse in the Gulf of Squillace, Calabria region (central Mediterranean)

Giacomo Mangano, Silvia Ceramicola, Tiago M. Alves, Massimo Zecchin, Dario Civile, Anna Del Ben, and Salvatore Critelli

The discovery of a large-scale gravitational complex, named in this work Squillace Complex, has been reported in the Gulf of Squillace, Southern Italy, spanning from the continental shelf (c. 1.5 km from the coastline) to the distal sector, covering an area of roughly 600 km². The integration between seismic reflection data, borehole and bathymetric information has revealed that this complex exhibits a NE-trending headwall domain made up of sinuous and continuous seafloor scarps linked to a E-W morphological high, via a basal detachment layer between the Messinian evaporites and Tortonian shaleys.

The initiation of the Squillace Complex dates back to the Zanclean (~ 4 Ma) and persisted in movement through the Gelasian (~ 2.1 Ma) at an average rate of 1.9 mm/year. Later in the Calabrian (Middle Pleistocene), the movement underwent a braking and continued sliding to the present day at a reduced rate of 0.1 mm/year. The gravitational collapse of the Squillace Complex aligns temporally with distinct contractional/transpressional events impacting the Calabrian region. These events resulted from basin shortening under a setting of Calabrian Arc stop migration, as well as tectonic uplift affecting the study area since 0.45 million years ago.

In contrast, the diminished movement observed in the Squillace Complex since the Calabrian (Middle Pleistocene) has been inferred as a consequence of conditions of basin stretching in the framework of Ionian plate rollback beneath the Calabrian Arc.

How to cite: Mangano, G., Ceramicola, S., Alves, T. M., Zecchin, M., Civile, D., Del Ben, A., and Critelli, S.: The discovery of a large-scale gravitational collapse in the Gulf of Squillace, Calabria region (central Mediterranean), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8090, https://doi.org/10.5194/egusphere-egu24-8090, 2024.

X4.38

EGU24-11027

ECS

Deep-seated gravitational slope deformations of Friuli Venezia Giulia Region (NE Italy)

Christian Leone, Stefano Devoto, and Luca Zini

Deep-seated Gravitational Slope Deformations (DGSDs) are common phenomena and are observed across various mountain belts worldwide. These phenomena are characterized by the presence of multiple landforms which are important for the recognition of the occurrence of DGSDs. The latter pose significant geological hazard due to their impact on society, economy and environment. They can affect vast areas, potentially endangering large sections of infrastructure, transportation routes, settlements and natural habitats. Furthermore, they cause collateral landslides that can evolve in catastrophic events.

In the past, a comprehensive inventory detailing DGSDs at the scale of the entire European Alps was compiled. This work shows a relatively limited DGSD population in Friuli Venezia Giulia, if compared to other mountain areas such as Central or Western Alps. The final objective of this study is to produce a detailed inventory of DGSDs that affect Alps of Friuli Venezia Giulia Region. Preliminary activities were aimed to desk activities such as analysis of historical documents, reports, aerial images and geomorphological interpretation of LiDAR-derived DTMs. We identified during preliminary activities several DGSDs and tens of possible gravity-induced landforms such as double ridges, ridge top depressions, uphill and downhill-facing scarps, trenches, toe bulges and persistent discontinuities. These gravity-induced features were validated by extensive field surveys carried out in 2023 and the beginning of 2024, also using HR images provided by low-altitude UAV surveys. DGSDs and their landforms were mapped and stored in a GIS.

DGSDs of Friuli Venezia Giulia Alps are favored by: (i) exceptionally high mean annual precipitation (ranging from 1400 to 3400 mm/y), (ii) the presence of several regional faults, (iii) the high-energy relief, (iv) the presence of different rock units (rigid materials and plastic terrains).

How to cite: Leone, C., Devoto, S., and Zini, L.: Deep-seated gravitational slope deformations of Friuli Venezia Giulia Region (NE Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11027, https://doi.org/10.5194/egusphere-egu24-11027, 2024.

X4.39

EGU24-14609

The Parraguirre ice-rock avalanche 1987, semi-arid Andes, Chile - A holistic revision

Johannes J. Fürst, David Farías-Barahona, Lucía Scaff, Thomas Bruckner, and Martin Mergili

On November 29 in 1987, a massive ice-rock avalanche detached near Cerro Rubicano in the Dry Andes east of Santiago de Chile. The avalanche developed into a highly destructive debris flow, which reached a run-out distance of more than 50 km resulting in important damage of infrastructure and causing numerous fatalities. In the wake of the event, several studies have shed light on the event history as well as on the geological, volcano-seismic, meteorological and glacio-hydrological pre-conditioning. Although the El-Niño event, that prevailed in 1987, and the presence of glaciers are considered important factors for the development of such a massive debris flow, a holistic analysis of observational evidence, meteorological conditions and debris-flow simulations remains, to this day, absent.

Here, we present new insights obtained from historic aerial photographs and satellite imagery, climate reanalysis, weather stations, hydrographic monitoring and physically-based debris-flow modelling. First, we are able to better constrain the trigger volume and to delineate a first map of the impact area. Second, time records and modelling results affirm the assumed multi-stage character of the event. Third, we postulate that the Parraguirre event can be considered a compound weather event, pre-conditioned by anomalously high temperatures and exceptionally deep snow cover in the days and weeks before the devastating debris flow.

How to cite: Fürst, J. J., Farías-Barahona, D., Scaff, L., Bruckner, T., and Mergili, M.: The Parraguirre ice-rock avalanche 1987, semi-arid Andes, Chile - A holistic revision, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14609, https://doi.org/10.5194/egusphere-egu24-14609, 2024.

X4.40

EGU24-16450

ECS

Assessing river morphological changes induced by large ice-rock avalanches: The 2021 Chamoli disaster region using UAV-LIDAR data.

Sahil Kaushal and Yunus Ali Pulpadan

X4.41

EGU24-18109

ECS

Paleo-landslides in the southern France (Larzac plateau)

Kévin Elkharrat, Catherine Homberg, Sara Lafuerza, Nicolas Loget, Muriel Gasc-Barbier, and Stephanie Gautier

The Larzac carbonate plateau (France) is subject to numerous slope instabilities on its edges, ranging from toppling to landslides. Due to their extremely slow slip rates (3mm/year), these last large rotational instabilities remain poorly understood, particularly in terms of characterisation and dynamics. Our study focuses on several deep paleo-landslides of this type, located in two valleys: the Lergue and the Laurounet. These landslides evolved in sedimentary rocks including the highly fractured Jurassic carbonates overlying the Triassic sandstones and the thick Triassic clays. This work aims to study the initial phase mechanisms. In a climate change context, with extreme precipitations as in southern France (“cevenol events”), understanding paleo-landslide mechanisms has an added value in the comprehension of the future slope stability in similar geological contexts.

We used a multi-method approach to characterize the investigated landslides. Remote sensing and field surveys allowed mapping of the landslides, identification of geomorphological features, main and secondary scarps, and their associated slide blocks. Rock mass fracturing was characterized at localities in and away from the landslides. Mechanical characterization was obtained through the Rock Mass Rating (RMR)/Geological Strength Index (GSI) and laboratory tests. Finally, terrestrial cosmogenic nuclides (³⁶Cl for carbonate surfaces) were used to determine the exposure age of the landslide scarps.

The investigated million-cubic-meter landslides show upslope and secondary circular scarps with counter-slope slide blocks, signifying rotation. However, at deeper levels, the failure surface flattens within the evaporite-rich clays. Dating two paleo-landslides places their occurrence between 10 and 18 kyrs, suggesting the Late Pleistocene/Holocene transition. A directional correlation is evidenced between the dense NNW-SSE joint network that cut the carbonates and N-S faults with the landslide scarps. The study suggests that landslides exhibit a rotational-translational mechanism, influenced by lithological differences between fractured carbonate units and weak underlying clays. This reaffirms the significance of clays in landslide failure, with evaporite levels playing a role in deep rupture surface branching in certain cases. Furthermore, a major structural control is evidenced, with the faults serving for initiation or as lateral ramps of the landslides depending on their orientation relative to the slope. Dating results suggest that increasing precipitation could have led to slope failures.

These geological constraints were employed to test scenarios for the initiation of the rotational-translational landslides of the Larzac carbonate plateau using the distinct elements method 3DEC. Field data supplied geometry, while the mechanical parameters of the multi-layer rock mass were estimated based on the RMR and GSI data. The three families of discontinuities, layering planes, and the sub-vertical NNW-SSE and WSW-ENE joints were also included, as well as the in-situ pore pressure. The stability analysis revealed the significant impact of joints/faults and lithology contrast on the stability and geometry of the failure surface. This study illustrates how landslides can be related to a combination of predisposing parameters such as structural inheritance and variation of properties in the heterogeneous rock mass that control their modes of failure and geometries.

How to cite: Elkharrat, K., Homberg, C., Lafuerza, S., Loget, N., Gasc-Barbier, M., and Gautier, S.: Paleo-landslides in the southern France (Larzac plateau), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18109, https://doi.org/10.5194/egusphere-egu24-18109, 2024.

Posters virtual: Thu, 18 Apr, 14:00–15:45 | vHall X4

Display time: Thu, 18 Apr, 08:30–Thu, 18 Apr, 18:00

vX4.30

EGU24-18344

ECS

Locating Sediment Evacuation Zones – A Prefatory Action for Early Warning System Development in Mountainous landscapes

Arkaprabha Sarkar, Vimal Singh, and Sukumar Parida

The past decade has seen an alarming rise in the number of extreme events, most of which are high magnitude hydrological events triggered by focused precipitation, glacial lake outburst or both. During such event large amount of debris is mobilized and get deposited in downstream reaches. Studies have quantified the volumes of debris exported by the events and have shown them to possess potential for future hazard (e.g., Hooke, 2019; Sarkar and Singh, 2022; Westoby et al., 2023). However, a pressing question that remains unaddressed is regarding the identification of storage sites of these sediments prior to the event.

We have employed the concept of index of connectivity (IC) to locate sediment stored in the landscape. We have altered the relationships of the upslope and downslope components of the basic framework of index of connectivity (Borselli et al., 2008), and normalized the values to obtain a dimensionless storage potential index (SPI) that indicates the proneness of a point to arrest sediment flux and disrupt the routing process. Using the SPI and normalized IC, we have formulated a Sediment Evacuation Susceptibility Index (ESI_S), the values of which ranges between -1 to 1; lower ESI_S values indicate stable zones with higher thresholds of evacuation, and vice versa.

The model has been tested in a small catchment (~93 km²) known as Pranmati catchment in NW Himalayas, India. Our results show that significant volume of sediment gets arrested along the margins of land cover units that have contrasting impedance to sediment transportation. Sediment flux also gets arrested in isolated pockets (e.g., grassland patches) within forested land. Croplands tend arrest and store sediment due to intense anthropogenic modification of hillslopes. Landslide talus deposits are a potential sediment storage unit. Mid-slope regions of hillslope transects tend to have high storage potential. These sites get connected during extreme hydrological conditions and release the stored sediments. Landslides debris deposits are found to be highly stable. However, parts of the hillslope in the vicinity of the stream network have a very high susceptibility to evacuation. The results have been validated in field with reference to two major local high magnitude flash flood events. The evacuation susceptibility assessment can be the first step for risk identification, development of an early warning system for flood hazards and disaster mitigation.

References

Borselli, L., Cassi, P., & Torri, D. (2008). Prolegomena to sediment and flow connectivity in the landscape: A GIS and field numerical assessment. Catena, 75(3), 268-277.

Hooke, J. M. (2019). Extreme sediment fluxes in a dryland flash flood. Scientific Reports, 9(1), 1686.

Sarkar, A., & Singh, V. (2022). Characterisation and Assessment of a Flash Flood in the Himalaya: Understanding the Significance of High Magnitude Events in Sediment Mobilisation. Journal of the Geological Society of India, 98(5), 678-686.

Westoby, M. J., Dunning, S. A., Carrivick, J. L., Coulthard, T. J., Sain, K., Kumar, A., ... & Shugar, D. H. (2023). Rapid fluvial remobilization of sediments deposited by the 2021 Chamoli disaster, Indian Himalaya. Geology, 51(10), 924-928.ter, Indian Himalaya. Geology, 51(10), 924-928.

How to cite: Sarkar, A., Singh, V., and Parida, S.: Locating Sediment Evacuation Zones – A Prefatory Action for Early Warning System Development in Mountainous landscapes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18344, https://doi.org/10.5194/egusphere-egu24-18344, 2024.

vX4.31

EGU24-20856

ECS

“Identification and Characterization of Paleoalluvial Events in the Ranrahírca Hydrographic Unit, Cordillera Blanca, Perú”

W. Harrinson Jara Infantes, Manuel Cosi Cosi, Juan C. Torres, Benjamin Lehmann, Swann Zerathe, Hilbert Villafane, Enver Melgarejo, Adriana Caballero, Sara Cachay, and Leila Mamani

Abstracts

The Cordillera Blanca, located in Peru, is a mountain range with peaks exceeding 6000 meters, preserving tropical glaciers on its surface. Currently, due to global climate change resulting from both natural and anthropogenic causes, glaciers are rapidly losing surface area and volume. Over a period of 58 years, between 1962 and 2020, the Cordillera Blanca (CB) has lost 301.4 km2 of glacier surface, equivalent to 41.50% of the total area. This has led to an increased occurrence of ice and rock avalanches, triggering violent overflow events of glacial lakes and alluvial processes. In this context, the Hydrographic Unit (HU) Ranrahírca has recorded the occurrence of two extreme avalanche events originating from the North Peak of Nevado Huascarán, corresponding to the 1962 event in Ranrahírca and the 1970 event in Yungay.

The objective is to identify, differentiate, categorize, and correlate unconsolidated deposits with different historical alluvial events (Paleoalluvions) of significant magnitude that occurred on the north peak of Nevado Huascarán, Cordillera Blanca. This involves a detailed grain size analysis of soils, with emphasis on lithology, dimensions, shape, and degree of weathering of the clasts in their composition, as well as their fine material content, aiding in temporally situating the origin event. The primary study area is the Yungay district, located at the lower part of Nevado Huascarán, where Quaternary material from various paleoalluvions has accumulated in a fan-shaped pattern in the lower part of the Ranrahírca HU. This area extends for several kilometers, currently encompassing the urban areas of Yungay and Ranrahírca.

To achieve this, fieldwork was conducted in August 2023 in the Yungay and Ranrahírca areas. Seven (07) chronostratigraphic columns were surveyed, and thirteen (13) soil samples were collected from different cut sections of slopes. These efforts have allowed the differentiation of various paleoalluvionic events and, in some cases, evidence the transition between them.

Keywords: Cordillera Blanca, rock-ice paleoavalanche, grain size analysis, chronostratigraphic column.

How to cite: Jara Infantes, W. H., Cosi, M. C., Torres, J. C., Lehmann, B., Zerathe, S., Villafane, H., Melgarejo, E., Caballero, A., Cachay, S., and Mamani, L.: “Identification and Characterization of Paleoalluvial Events in the Ranrahírca Hydrographic Unit, Cordillera Blanca, Perú”, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20856, https://doi.org/10.5194/egusphere-egu24-20856, 2024.