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.

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.

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.

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.

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.

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.

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.

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.

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.

The Chamoli disaster of 2021 in the Rishiganga valley, triggered by a massive ice-rock avalanche, displayed a characteristic example of the complex dynamic in the glacier and fluvial systems under a warming climate. Here, we present cutting-edge UAV-LiDAR technology to examine the post-disaster morphological changes in the headwater river systems of Rishiganga, specifically focusing on river incision and channel morphological changes. Employing multi-period digital elevation models, we present the region's substantial increases in river incision and channel widening. A considerable increase in river width was also recorded following the event. Our research concludes that landslides act as a significant control of channel morphology in the Himalayan terrain. By unravelling the complex dynamics of river morphology caused by extreme events, this study contributes significantly to the literature in the context of bedrock river incision and landscape evolution.

How to cite: Kaushal, S. and Pulpadan, Y. A.: Assessing river morphological changes induced by large ice-rock avalanches: The 2021 Chamoli disaster region using UAV-LIDAR data., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16450, https://doi.org/10.5194/egusphere-egu24-16450, 2024.

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.

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.

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.