On September 9, 2021, a catastrophic landslide occurred in Zhanjiaping Village, Zhenba County, Shaanxi Province, China, blocking the Yushui River and forming a landslide barrier lake. To gain a deeper understanding of this catastrophic event, we have utilized a combination of engineering geological exploration, multi-source remote sensing and geotechnical testing techniques to elucidate the dynamic evolution and formation mechanisms of the landslide. Zhanjiaping landslide is located in the core of the Luoquanyan Syncline within the Daba Mountain foreland arc structure zone, with the plunge direction of 319° and plunge of 11° along the fold axis. Zhanjiaping landslide is developed in the ancient landslide area, which is a typical sliding and tension-fracturing landslide with a very gentle sliding surface, and the volume of the landslide is estimated to be 7.44 × 10⁶ m³. The strata in the landslide area exhibits a layered structure with alternating soft and hard formations. Under the influence of continuous rainfall, the steep slopes on the north flank of the Luoquanyan Syncline were destabilized along the bedding planes of the underlying mudstone, and forming a deposit on the gentle slope to the northeast of Zhanjiaping Village in the syncline core area. Then, affected by the landslide impact loading and rainfall infiltration, the strength of the contact surface between the paleoslide body and bedrock in the core area of Luoquanyan Syncline decreases, leading to the resurrection of the ancient landslide. However, blocked by the south flank of Luoquanyan Syncline, the downward sliding of the slide body was impeded, which in turn to both sides to undergo multiple extrusion and braking phenomena. This study provides a case study of a small landslide destabilization that eventually triggered the resurrection of a large-scale ancient landslide under the control of geological structure, which can provide a reference for the prevention and control of similar landslide disasters.

How to cite: Yu, Z., Zhan, J., and Peng, J.: Activation mechanism and failure process of an ancient landslide induced by landslide impact loads in China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4468, https://doi.org/10.5194/egusphere-egu24-4468, 2024.

Glacier lake outburst floods (GLOF) are mass flow hazards of severe destructive potential and far reach that can cause extensive damage to the natural and built environment posing a threat to people and their livelihoods. Diverse risk management measures have been proposed and been implemented in order to reduce the risks associated with GLOFs. However, systematic studies on the effectiveness and cost-benefit of such measures in the contest of disaster risk management (DRM) are largely lacking.

Here we model, map and evaluate GLOF risk measures and analyse how the implementation of different GLOF DRM measures alters GLOF risk. We compare cost and benefit of five potential measures in the mountainous Ala-Archa catchment in the Kyrgyz range south of Bishkek, the capital of the Kyrgyz Republic. Using the RAMMS debris flow software, the extent of two GLOF scenarios are modelled for the situations of (i) no DRM measure (current state), (ii) lake volume reduction, (iii) a deflection dam, (iv) a retention dam and reservoir, (v) an Early Warning System, and (vi) land use planning.

We analyse the effect of the different DRM measures by examining the three components of risk, namely hazard, exposure and vulnerability. We estimate the expected cost of the respective DRM measures and compare it to the costs of the potential damage caused by the GLOF scenarios. While we assess hazard and exposure quantitatively, we analyse vulnerability in a qualitative way, based on socio-economic characteristics such as age, gender, education, economic diversity and dependency.

With increasing numbers of glacier lakes and potential disastrous lake outbursts linked to climate change, often combined with increasing exposure of infrastructure and human assets, cost effective GLOF DRM is of growing importance.  While the absolute numbers based on the exposed assets, cost and damage will differ for other settings, the conceptual approach of this case study can be applied to other mountainous catchments. This study’s main findings serve as a basis for decision making in similar settings with stakeholders aiming for cost-effective GLOF risk management.

How to cite: Niggli, L., Zaginaev, V., Frey, H., Allen, S., and Huggel, C.: Modelling and evaluating GLOF risk management measures in the Kyrgyz Ala-Archa valley, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10680, https://doi.org/10.5194/egusphere-egu24-10680, 2024.

The retreat of glaciers has emerged as a significant threat in recent decades, leading to the emergence and growth of glacial lakes. Many of these lakes are vulnerable to Glacial Lake Outburst Floods (GLOFs) as a result of challenging geotectonic settings and adverse climatic environments. Satellite imageries, Digital Elevation Models (DEMs), seismic and meteorological data were utilized in this study to asses the vulnerability posed by more than 1300 glacial lakes in the Northwest Himalayas (NWH) to a potential GLOF event in the future. We employed the Analytic Hierarchy Processes (AHP) - Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) and AHP - Complex Proportional Assessment of Alternatives (COPRAS) approaches to identify Potentially Dangerous Glacial Lakes (PDGLs), using 15 key conditioning factors.  Over 20 lakes were identified as having very high risk to GLOFs, while more than 130 lakes were classified as being at a high risk. The upper Indus basin possessed the most number of vulnerable lakes, which are at a greater risk of experiencing a probable GLOF event, followed by the Jhelum basin. To authenticate our results, we examined the past GLOFs incidents and our analysis revealed that most of the previous GLOFs are classified as PDGLs falling into either the very high or high risk categories. The findings of this study will provide valuable insights for stakeholders and decision makers enabling them to implement preventive measures to mitigate risks during a potential GLOF event in future.

How to cite: Upadhyaya, A. and Rai, A. K.: Identification of Potentially Dangerous Glacial Lakes (PDGLs) in the Northwest Himalayas , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15032, https://doi.org/10.5194/egusphere-egu24-15032, 2024.

The rapid retreat of glaciers due to warmer temperatures has resulted in an increase in both number, size and volume of glacial lakes across the Andes. Indeed, a recent study found that Patagonian lakes have more than doubled in volume during the last three decades. These lakes, constrained by unstable moraine dams or ice walls, hold the potential for catastrophic outbursts, known as Glacial Lakes Outburst Flood (GLOF) events. Glacial inventories are available since 1986 for Central Andes, Northern Patagonia and Southern Patagonia and GLOF occurrence and distribution has been widely studied for Chilean and Argentinian Andes. However, very few information on glacial lakes and related GLOF events exists in the Cordillera Darwin. Although the sudden release of immense volumes of water, sediments, and debris in such a remote area does not have the potential of affecting communities and infrastructures downstream, as in more populated areas, it still poses severe threats to the fiords ecosystems. Here we present the detection and analysis of a GLOF event at Alemania (Roncagli) glacier, in the south-western flank of the Cordillera Darwin, occurred in April 2023. The GLOF event was initially identified through FerryBox data collected across the Beagle Channel and subsequently confirmed using satellite imagery, analysing changes in the area of Lake Martinic, where the secondary front of Alemania glacier terminates. Moreover, a detailed analysis of 35 satellite images reveals a regular occurrence of such events since 2018, emphasising the repetitive nature of GLOFs at Alemania Glacier and its potential of disrupting the Beagle Channel ecosystem. 

How to cite: Schliermann, M., Tabone, I., Farias-Barahona, D., Arndt, J. E., and Giesecke, R.: Detection and analysis of GLOF events at Alemania (Roncagli) Glacier, Cordillera Darwin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16448, https://doi.org/10.5194/egusphere-egu24-16448, 2024.

In High Mountain Asia (HMA), rising temperatures and retreating glaciers are leading to the formation of new glacial lakes and the expansion of existing ones. The sudden release of water from such lakes can lead to devastating glacial lake outburst floods (GLOF) threatening people and infrastructure for many kilometers downstream. Therefore, it is important to obtain information on future glacial lakes, e.g., their location, area, and volume as well as the timing of their development. This data can in turn be used to estimate the range and destructive potential of future GLOF events, which is crucial for the sustainable development of settlements and infrastructures.

Dam failures at glacial lakes and the subsequent flooding events are often investigated using two-dimensional models (e.g. HEC-RAS). These 2D models are based on the solution of the shallow water equations, which assume that the vertical velocity of the water is always much lower than the horizontal velocity. In case of a moraine failure, however, high vertical accelerations are observed in the behavior of the dam break wave in mountainous terrain, which violates the shallow water equations. To overcome these shortcomings of 2D models, fully three-dimensional Computational Fluid Dynamic (CFD) models can be used, which are based on the solution of the Navier-Stokes equations along with the volume of fluid method to locate the interface between water and air.

In our research project, we use the 3D open-source CFD model OpenFOAM to determine the possible range of GLOF events at future glacial lakes in HMA. To capture the different climate pathways and the corresponding differences in lake volume, we use previously published data on the evolution of future glacial lakes over the course of the 21st century under different SSP scenarios. To account for the uncertainties of future moraine height or composition, we simulate different moraine failure scenarios resulting in different magnitudes of GLOFs. These simulations allow us to determine the velocity of the initial break wave and identify potential inundation areas. By intersecting the resulting flood map with land-use and land-cover maps (while taking into consideration the potential changes in this data during the coming decades), we can estimate affected agricultural land and potentially damaged infrastructures. Our findings can contribute to helping local communities adapt to emerging challenges, implement risk minimization measures, and enhance sustainable development in HMA.

How to cite: Furian, W., Sauter, T., and Schneider, C.: Three-dimensional simulations of future GLOF events in High Mountain Asia under different SSP scenarios, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17940, https://doi.org/10.5194/egusphere-egu24-17940, 2024.

Nepal faces a spectrum of climate-related challenges, such as floods, landslides, and droughts, causing substantial economic and environmental consequences. The country’s vulnerability to climate change is intensified by its geographic features and inadequate preparedness, underscoring the significance of studying compound extremes for water resources management and disaster mitigation. The susceptibility to climate change, coupled with geographic vulnerability heightened by extreme weather events, like floods and landslides, poses significant threats to Nepal’s socioeconomic development, necessitating further research. Studying compound extremes is crucial due to the escalating disastrous effects of cascading disasters, impacting agriculture, food security, and water resources. This study utilizes observed and model data to analyze compound heatwaves and extreme precipitation events, categorizing extreme precipitation as values surpassing the 95^th percentile and defining heatwaves as three or more consecutive days with maximum temperatures exceeding the 95^th percentile. Station data from 1981-2020 along with CMIP6 13 models data from 1951-1982 for past event analysis and from 2015 to 2100 for future projections reveal varying trends in heatwaves, extreme precipitation, and compound events across Nepal. Different models indicate diverse distributions of heatwaves and wet extremes, with some regions experiencing a decline in heatwave events in the past. The sensitivity of compound events to lagging periods is evident, resulting in a shift from 15 to 30 days and a subsequent increase in compound events. SSP scenarios project an overall rise in compound heatwaves and extreme precipitation in the future, emphasizing the risk of cascading disasters and urging stakeholders and governments to implement robust disaster risk reduction and management strategies. The study underscores the complexities of extreme events in Nepal’s climate data and model results, stressing the importance of considering spatial, temporal, and modeling factors for effective climate change impact adaptation and mitigation.

How to cite: Neupane, B. P., Guntu, R. K., and Agarwal, A.: Frequency analysis of compound heat and wet extremes over Nepal, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11236, https://doi.org/10.5194/egusphere-egu24-11236, 2024.