Glacial Lake Outburst Flood Hazard Research Articles

Transboundary hazard and downstream impact of glacial lakes in Hindu-Kush Karakoram Himalayas

Glacial Lake Outburst Floods (GLOFs) can generate catastrophic flash floods when the damming structure is breached or overtopped. Some of these glacial lakes are located in transboundary regions where floods originating from the lake in one country could inundate a neighboring country, devastating the population and infrastructure of both nations and influencing socio-political relationships. Therefore, assessing the lakes' hazard is crucial. This study investigates transboundary glacial lakes, considering their GLOF hazard, including potential mass movement intrusion, moraine's stability, upstream and downstream process cascades, downstream flood extents, and the exposure and vulnerability of the downstream infrastructure and affected population. GLOF exposure assessments were carried out to identify exposed buildings, bridges, and hydropower systems in transboundary regions. China currently has the highest number of transboundary lakes, with most of them potentially impacting India and Nepal. Most of the transboundary lakes in China, and many in India and Nepal, are susceptible to mass movements. Among the 230 transboundary glacial lakes in the Hindu Kush Karakoram Himalaya, 55 lakes can potentially impact other glacial lakes along their flow path, creating a cascade of events. Five transboundary lakes could potentially impact over 1000 buildings, and 16 lakes could impact over 500 buildings. A total of 35 lakes can impact at least one hydropower station along their flow path, and 4 lakes can impact two hydropower stations. This research emphasizes the critical importance of conducting comprehensive risk analyses of GLOFs in transboundary regions to inform policy-makers. It calls for investing in broad-scale assessments and data-driven decision-making for mitigating and adapting to GLOF risks effectively. Finally, by raising awareness among policy-makers, the study aims to drive actions that safeguard communities and infrastructure vulnerable to GLOF.

Glacial Lake Outburst Flood Monitoring and Modeling through Integrating Multiple Remote Sensing Methods and HEC-RAS

The Shishapangma region, situated in the middle of the Himalayas, is rich in glacial lakes and glaciers. Hence, glacial lake outburst floods (GLOFs) have become a top priority because of the severe threat posed by GLOFs to the downstream settlements. This study presents a comprehensive analysis of GLOF hazards using multi-source remote sensing datasets and designs a flood model considering the different breaching depths and release volumes for the Galong Co region. Based on high-resolution optical images, we derived the expanding lake area and volume of glacial lakes. We monitored deformation velocity and long-term deformation time series around the lake dam with Small BAseline Subset Interferometric Synthetic Aperture Radar (SBAS-InSAR). The glacier thinning trend was obtained from the difference in the Digital Elevation Model (DEM). We identified potential avalanche sources by combining topographic slope and measurable deformation. We then carried out flood modeling under three different scenarios using the hydrodynamic model HEC-RAS for Galong Co, which is formed upstream of Nyalam. The results show that the Nyalam region is exposed to high-intensity GLOFs in all scenarios. The larger breaching depth and release volumes caused a greater flow depth and peak discharge. Overall, the multiple remote sensing approaches can be applied to other glacial lakes, and the modeling can be used as a basis for GLOF mitigation.

GLOF hazard, exposure, vulnerability, and risk assessment of potentially dangerous glacial lakes in the Bhutan Himalaya

Deglaciation due to atmospheric warming has led to the formation and expansion of numerous glacial lakes, especially in the eastern Himalaya. Many of these glacial lakes are susceptible to glacial lake outburst floods (GLOFs), which can cause far-reaching impacts on downstream infrastructure and livelihoods. This study is a comprehensive assessment of GLOF susceptibility, hazard, exposure, vulnerability, and risk for four potentially dangerous glacial lakes (Bechung Tsho, Raphstreng Tsho, Thorthomi Tsho, and Lugge Tsho) located in the Lunana glacier complex of the Phochu basin in Bhutan. Exposure and risk assessments were based on modelled GLOF hydrodynamics, infrastructure data, population and housing census data. Among the four glacial lakes, Thorthormi Tsho and Lugge Tsho are relatively more susceptible to outburst floods than Raphstreng Tsho and Bechung Tsho. Outflow flood volumes from these lakes range between 6 × 105 and 3 × 108 m3 which can potentially impact over 16,000 people, two hydropower projects, numerous other infrastructures, and agricultural land up to 150 km downstream of the lakes. The GLOF exposed elements are largely in Punakha and Wangdue Phodrang districts, which are located 90 and 100 km downstream of the Lunana glacier complex respectively. Among 17 subdistrict blocks within the basin, one (Lunana) lies in a very high GLOF risk area, while 9 others are in the high GLOF risk zone. The study highlights the importance of multi-source data in improving the knowledge of downstream GLOF risk and serves as a base for improving GLOF risk reduction strategies in high mountain regions.

Assessment of potential present and future glacial lake outburst flood hazard in the Hunza valley: A case study of Shisper and Mochowar glacier

In Himalayas, new glacial lake formation and expansion of existing glacial lakes have occurred as a consequence of the increasing temperature and glacier recession. These lakes have the potential to release catastrophic volumes of water and trigger a glacial lake outburst flood (GLOF). GLOFs can cause devastating downstream impacts including loss of lives, damage to infrastructure, and economic loss. The risk associated with GLOFs is evident in the case of the Mochowar and the Shisper glaciers of the Hunza valley in the Karakoram ranges. The present study is divided in two parts: 1) investigation of the recent GLOF event from the Shisper glacier ice-dammed lake on 7th May 2022. 2) identification of an overdeepening site for future lake formation at the Mochowar glacier and its future GLOF susceptibility; We used the Himalayan Glacier Thickness Mapper (HIGTHIM) to calculate the thickness of Mochowar glacier and identify an overdeepening site at its terminus. This site could host a glacial lake of area 0.22 km2 and a mean depth of 58.97 m that can release a potential flood volume leading to cascading effects with the Shisper ice-dammed lake that further increases the GLOF susceptibility. The GLOF susceptibility of this future lake was determined to be high based on a multi-criterion decision analysis. The recent GLOF event of 7th May 2022 occurred from the Shisper glacier ice-dammed lake. We applied a 2D hydrodynamic model for investigating this GLOF episode and estimated a release volume of 6.23 × 106 m3, with a modelled peak discharge of approximately 1505 m3 s−1.

Glacial lake outburst flood risk assessment using remote sensing and hydrodynamic modeling: a case study of Satluj basin, Western Himalayas, India.

Glacier-associated hazards are becoming a common and serious challenge to the high mountainous regions of the world. Glacial lake outburst floods (GLOFs) are one of the most serious unanticipated glacier hazards, with the potential to release a huge amount of water and debris in a short span of time, resulting in the loss of lives, property, and severe damage to downstream valleys. The present study used multi-temporal Landsat and Google earth imageries to analyze the spatio-temporal dynamism of the selected glacial lake (moraine-dammed) in the Satluj basin of Western Himalayas. Furthermore, GLOF susceptibility of the lake was assessed using a multi-criteria decision-based method. The results show that the lake area has increased from 0.11 to 0.26 km2 over the past 28years from 1990 to 2018. The susceptibility index value for the lake was calculated as 0.75, which indicates that the lake is highly susceptible to the GLOF. The depth and volume of the lake were estimated to be 16m and 57 × 105 m3, respectively, using an empirical formula. HEC-RAS, HECGeo-RAS, and Arc-GIS software were utilized in this study to perform unsteady flow analysis and to determine the GLOF impact on the downstream area. The worst-caseGLOF scenario(breach width of 75m) was revealed during an overtopping failure of the moraine dam, resulted in a peak discharge of 4060 m3/s and releasing a total watervolume of 57 × 105 m3. The breach hydrograph has been routed to calculate the spatial and temporal distribution of peak flood, inundation depth, velocity, water surface elevation, and flood peak arrival time along the river channel. The analysis further reveals that the routed flood waves reach the nearest settlement, i.e., Rajpur town, situated at a distance of 102km in the downstream valley of the lake at 6h after the beginning of the lake breach event with a peak discharge/flood of 1757 m3/s and maximum flow velocity of 1.5m/s. With the ongoing climate warming and glacier retreat, moraine-dammed lakes are becoming more hazardous and thus increasing the total threat. Therefore, it is mandatory to monitor and assess such lakes at regular intervals of time to lessen the disastrous impacts of GLOFs on the livelihood and infrastructure in the downstream valleys. The findings of this study will aid in the creation of risk management plans, preparatory tactics, and risk reduction techniques for GLOF hazards in the region.

Quantitative susceptibility assessment of the breach of moraine-dammed lakes due to glacier avalanches

Glacial lake outburst floods (GLOFs) have caused tens of millions of dollars of damage to infrastructure and have killed thousands of people worldwide. The objective of this study was to quantify the hazard posed by the occurrence of a GLOF due to an ice avalanche into an ice-free moraine-dammed lake, producing a surge wave and raising the water level. This study was carried out in the Himalayan region and in the western cordillera of North America. Some simplifications and combinations of parameters were made to reduce the number of parameters as much as possible. We selected seven factors for the quantitative susceptibility assessment of the GLOF hazard: the dangerous glacier slope factor S, temperature factor T, aspect factor Y, glacier aspect factor X, runout factor of the dangerous glacier R, ratio of the volume factor of the dangerous glacier to the volume of the lake V, and the downstream slope factor of the dam D (lake parameter). A machine learning model (a support vector machine, SVM) was used to create a susceptibility assessment model. Data for 21 drained and 50 undrained ice-free moraine-dammed lakes in the Himalayan region were used for the training of the GLOF susceptibility assessment model. In addition, data for 19 drained and 43 undrained ice-free moraine-dammed lakes in the western cordillera of North America were used to test the GLOF susceptibility assessment model. The susceptibility assessment factor P1 is a combination of these seven factors. The probability of GLOF occurrence increases as the P1 value increases. Using three critical P1 values, we divided the GLOF occurrence probability into four grades: low, medium, high, and very high probability of occurrence. The threshold values for the western cordillera of North America were 6.1–15.4% lower than the corresponding critical values for the Himalayan region because the annual temperature variation is larger in Canada than in Tibet. Thus, this assessment model can be used to assess the susceptibility of other areas of the world to GLOFs when annual temperature variations are considered.

Glacial Lake Outburst Flood Hazard and Risk Assessment of Gangabal Lake in the Upper Jhelum Basin of Kashmir Himalaya Using Geospatial Technology and Hydrodynamic Modeling

Climate warming-induced glacier recession has resulted in the development and rapid expansion of glacial lakes in the Himalayan region. The increased melting has enhanced the susceptibility for Glacial Lake Outburst Floods (GLOFs) in the region. The catastrophic failure of potentially dangerous glacial lakes could be detrimental to human life and infrastructure in the adjacent low-lying areas. This study attempts to assess the GLOF hazard of Gangabal lake, located in the Upper Jhelum basin of Kashmir Himalaya, using the combined approaches of remote sensing, GIS, and dam break modeling. The parameters, such as area change, ice thickness, mass balance, and surface velocity of the Harmukh glacier, which feeds Gangabal lake, were also assessed using multitemporal satellite data, GlabTop-2, and the Cosi–Corr model. In the worst-case scenario, 100% volume (73 × 106 m3) of water was considered to be released from the lake with a breach formation time (bf) of 40 min, breach width (bw) of 60 m, and producing peak discharge of 16,601.03 m3/s. Our results reveal that the lake area has increased from 1.42 km2 in 1972 to 1.46 km2 in 1981, 1.58 km2 in 1992, 1.61 km2 in 2001, 1.64 km2 in 2010, and 1.66 km2 in 2020. The lake area experienced 17 ± 2% growth from 1972 to 2020 at an annual rate of 0.005 km2. The feeding glacier (Harmukh) contrarily indicated a significant area loss of 0.7 ± 0.03 km2 from 1990 (3.36 km2) to 2020 (2.9 km2). The glacier has a maximum, minimum, and average depth of 85, 7.3, and 23.46 m, respectively. In contrast, the average velocity was estimated to be 3.2 m/yr with a maximum of 7 m/yr. The results obtained from DEM differencing show an average ice thickness loss of 11.04 ± 4.8 m for Harmukh glacier at the rate of 0.92 ± 0.40 m/yr between 2000 and 2012. Assessment of GLOF propagation in the worst-case scenario (scenario-1) revealed that the maximum flood depth varies between 3.87 and 68 m, the maximum flow velocity between 4 and 75 m/s, and the maximum water surface elevation varies between 1548 and 3536 m. The resultant flood wave in the worst-case scenario will reach the nearest location (Naranaag temple) within 90 min after breach initiation with a maximum discharge of 12,896.52 m3 s−1 and maximum flood depth and velocity of 10.54 m and 10.05 m/s, respectively. After evaluation of GLOF impacts on surrounding areas, the area under each inundated landuse class was estimated through the LULC map generated for both scenarios 1 and 2. In scenario 1, the total potentially inundated area was estimated as 5.3 km2, which is somewhat larger than 3.46 km2 in scenario 2. We suggest a location-specific comprehensive investigation of Gangbal lake and Harmukh glacier by applying the advanced hazard and risk assessment models/methods for better predicting a probable future GLOF event.

Glacial lake outburst flood hazard under current and future conditions: worst-case scenarios in a transboundary Himalayan basin

Abstract. Glacial lake outburst floods (GLOFs) are a major concern throughout High Mountain Asia, where societal impacts can extend far downstream. This is particularly true for transboundary Himalayan basins, where risks are expected to further increase as new lakes develop. Given the need for anticipatory approaches to disaster risk reduction, this study aims to demonstrate how the threat from a future lake can be feasibly assessed alongside that of worst-case scenarios from current lakes, as well as how this information is relevant for disaster risk management. We have focused on two previously identified dangerous lakes (Galongco and Jialongco), comparing the timing and magnitude of simulated worst-case outburst events from these lakes both in the Tibetan town of Nyalam and downstream at the border with Nepal. In addition, a future scenario has been assessed, whereby an avalanche-triggered GLOF was simulated for a potential large new lake forming upstream of Nyalam. Results show that large (>20×106 m3) rock and/or ice avalanches could generate GLOF discharges at the border with Nepal that are more than 15 times larger than what has been observed previously or anticipated based on more gradual breach simulations. For all assessed lakes, warning times in Nyalam would be only 5–11 min and 30 min at the border. Recent remedial measures undertaken to lower the water level at Jialongco would have little influence on downstream impacts resulting from a very large-magnitude GLOF, particularly in Nyalam where there has been significant development of infrastructure directly within the high-intensity flood zone. Based on these findings, a comprehensive approach to disaster risk management is called for, combining early warning systems with effective land use zoning and programmes to build local response capacities. Such approaches would address the current drivers of GLOF risk in the basin while remaining robust in the face of worst-case, catastrophic outburst events that become more likely under a warming climate.

Progress and challenges in glacial lake outburst flood research (2017–2021): a research community perspective

Abstract. Glacial lake outburst floods (GLOFs) are among the most concerning consequences of retreating glaciers in mountain ranges worldwide. GLOFs have attracted significant attention amongst scientists and practitioners in the past 2 decades, with particular interest in the physical drivers and mechanisms of GLOF hazard and in socioeconomic and other human-related developments that affect vulnerabilities to GLOF events. This increased research focus on GLOFs is reflected in the gradually increasing number of papers published annually. This study offers an overview of recent GLOF research by analysing 594 peer-reviewed GLOF studies published between 2017 and 2021 (Web of Science and Scopus databases), reviewing the content and geographical focus as well as other characteristics of GLOF studies. This review is complemented with perspectives from the first GLOF conference (7–9 July 2021, online) where a global GLOF research community of major mountain regions gathered to discuss the current state of the art of integrated GLOF research. Therefore, representatives from 17 countries identified and elaborated trends and challenges and proposed possible ways forward to navigate future GLOF research, in four thematic areas: (i) understanding GLOFs – timing and processes; (ii) modelling GLOFs and GLOF process chains; (iii) GLOF risk management, prevention and warning; and (iv) human dimensions of GLOFs and GLOF attribution to climate change.

Social vulnerability assessment of Glacial Lake Outburst Flood in a Northeastern state in India

The Himalayas are experiencing rapid climate change that is significantly contributing to glacier retreat, formation of new glacial lakes, and enlargement of the existing ones. The presence of glacial lakes in the Himalayan region makes it a potential threat for the downstream community, as the catastrophic failure of the lake causes the Glacial Lake Outburst Flood (GLOF), which significantly damages the low-lying areas. Devising appropriate risk reduction strategies for the downstream community to the GLOF hazard is the prime concern for the policymakers. In this study, we have assessed the social vulnerability of the downstream community of Chungthang town of Sikkim Himalaya. Many settlements at Chungthang are potentially exposed to the future GLOF of South Lohnak Lake, one of the fastest-growing glacial lakes in Sikkim, India. A sample size of 90 households have been selected and classified into migrated and permanent residents for the study. Primary data have been collected by using a semi-structured questionnaire. Results revealed that, in Chungthang migrated population are more vulnerable because of their low adaptive capacity and high exposure to the GLOF of South Lohnak lake in Sikkim. The study suggests some important mitigation measures to decrease the vulnerability of the vulnerable community by improving some of the important socioeconomic indicators.

Dam type and lake location characterize ice-marginal lake area change in Alaska and NW Canada between 1984 and 2019

Abstract. Ice-marginal lakes impact glacier mass balance, water resources, and ecosystem dynamics and can produce catastrophic glacial lake outburst floods (GLOFs) via sudden drainage. Multitemporal inventories of ice-marginal lakes are a critical first step in understanding the drivers of historic change, predicting future lake evolution, and assessing GLOF hazards. Here, we use Landsat-era satellite imagery and supervised classification to semi-automatically delineate lake outlines for four ∼5-year time periods between 1984 and 2019 in Alaska and northwest Canada. Overall, ice-marginal lakes in the region have grown in total number (+183 lakes, 38 % increase) and area (+483 km2, 59 % increase) between the time periods of 1984–1988 and 2016–2019. However, changes in lake numbers and area were notably unsteady and nonuniform. We demonstrate that lake area changes are connected to dam type (moraine, bedrock, ice, or supraglacial) and topological position (proglacial, detached, unconnected, ice, or supraglacial), with important differences in lake behavior between the sub-groups. In strong contrast to all other dam types, ice-dammed lakes decreased in number (six fewer, 9 % decrease) and area (−51 km2, 40 % decrease), while moraine-dammed lakes increased (56 more, 26 % and +479 km2, 87 % increase for number and area, respectively) at a faster rate than the average when considering all dam types together. Proglacial lakes experienced the largest area changes and rate of change out of any lake position throughout the period of study and moraine-dammed lakes which experienced the largest increases are associated with clean-ice glaciers (<19 % debris cover). By tracking individual lakes through time and categorizing lakes by dam type, subregion, and topological position, we are able to parse trends that would otherwise be aliased if these characteristics were not considered. This work highlights the importance of such lake characterization when performing ice-marginal lake inventories and provides insight into the physical processes driving recent ice-marginal lake evolution.

160 glacial lake outburst floods (GLOFs) across the Tropical Andes since the Little Ice Age

Assessing the extent to which glacial lake outburst floods (GLOFs) are increasing in frequency in modern times and whether their incidence is driven by anthropogenic climate change requires historical context. However, progress on this issue is hampered by incomplete GLOF inventories, especially in remote mountain regions. Here, we exploit high-resolution, multi-temporal satellite and aerial imagery, and documentary data to identify GLOF events across the glacierized Cordilleras of Peru and Bolivia, using a set of diagnostic geomorphic features. A total of 160 GLOFs from 151 individual sites are characterised and analysed, tripling the number of previously reported events. We provide statistics on location, magnitude, timing and characteristics of these events with implications for regional GLOF hazard identification and assessment. Furthermore, we describe several cases in detail and document a wide range of process chains associated with Andean GLOFs. • Our inventory consists of 160 glacial lake outburst floods (GLOFs). • About two thirds of these have not been identified previously in the literature. • We analyze spatial and temporal patterns of GLOF occurrence. • We characterize pre-conditions, triggers and mechanisms of GLOFs.

Contemporary glacial lakes in the Peruvian Andes

Glacier recession in response to climate warming has resulted in an increase in the size and number of glacial lakes. Glacial lakes are an important focus for research as they impact water resources, glacier mass balance, and some produce catastrophic glacial lake outburst floods (GLOFs). Glaciers in Peru have retreated and thinned in recent decades, prompting the need for monitoring of ice- and water-bodies across the cordilleras. These monitoring efforts have been greatly facilitated by the availability of satellite imagery. However, knowledge gaps remain, particularly in relation to the formation, temporal evolution, and catastrophic drainage of glacial lakes. In this paper we address this gap by producing the most current and detailed glacial lake inventory in Peru and provide a set of reproducible methods that can be applied consistently for different time periods, and for other mountainous regions. The new lake inventory presented includes a total of 4557 glacial lakes covering a total area of 328.85 km2. In addition to detailing lake distribution and extent, the inventory includes other metrics, such as dam type and volume, which are important for GLOF hazard assessments. Analysis of these metrics showed that the majority of glacial lakes are detached from current glaciers (97%) and are classified as either embedded (i.e. bedrock dammed; ~64% of all lakes) or (moraine) dammed (~28% of all lakes) lakes. We also found that lake size varies with dam type; with dammed lakes tending to have larger areas than embedded lakes. The inventory presented provides an unparalleled view of the current state of glacial lakes in Peru and represents an important first step towards (1) improved understanding of glacial lakes and their topographic and morphological characteristics and (2) assessing risk associated with GLOFs.

Analyzing glacial lake outburst flood triggers for sustainable disaster risk mitigation: an interpretive structural modelling based approach

PurposeClimate change and global warming pose a serious threat to the community as deglaciating environments trigger glacial lake outburst floods (GLOFs). The Sendai framework underpins the role of disaster risk reduction (DRR) for sustainable development, thereby calling for the development of GLOF hazard and risk assessment procedures. This study aims to delineate the enablers of GLOF risk and establish a contextual relationship between them.Design/methodology/approachThe risk enablers are identified from the extant GLOF literature, and the experts from disaster management area are consulted to explore the underlying contextual relationship among them. An interpretive structural model is developed from the responses to analyze the contextual relationships among the risk enablers.FindingsThe interpretive structural modeling results manifest that seismic activity, temperature and precipitation events, and proximity are key drivers that trigger flash floods from the lakes and an effective assessment of these triggers may contribute significantly to GLOF risk mitigation.Originality/valueThe study models the complex relationship among the risk enablers for a glacial flood hazard that find commonality across all geographic contexts. The findings provide the practitioners of DRR useful insights into these factors and their subsequent impact on others, while conducting hazard assessment of glacial lakes that may contribute to the sustainable development of settlements lying downstream to glacial lakes.

Prevalent risk of glacial lake outburst flood hazard in the Hindu Kush–Karakoram–Himalaya region of Pakistan

Prevalent risk of glacial lake outburst flood hazard in the Hindu Kush–Karakoram–Himalaya region of Pakistan

Future Glacial Lake Outburst Flood (GLOF) hazard of the South Lhonak Lake, Sikkim Himalaya

The Teesta basin in Sikkim Himalaya hosts numerous glacial lakes in the high altitude glacierized region, including one of the largest and the fastest-growing South Lhonak Lake. While these lakes are mainly located in remote and unsettled mountain valleys, far-reaching glacial lake outburst floods (GLOFs) may claim lives and damage assets up to tens of kilometers downstream. Therefore, evaluating GLOF hazard associated with current and potential future glacier-retreat-driven changes is of high importance. In this work, we assess the future GLOF hazard of the South Lhonak Lake by integrating glacier and hydrodynamic modeling to calculate the lake's future volume and hydraulic GLOF characteristics and impacts along the valley. We identify the increased susceptibility of the lake to potential avalanche impacts as the lake grows in the future. Here we model six avalanche scenarios of varying magnitudes to evaluate the impact-wave generated in the lake and overtopping flow at the dam. Avalanche simulations indicate that the frontal moraine is susceptible to overtopping. The overtopping flow hydraulics is evaluated along the channel assuming no erosion of the moraine. Further, we consider three lake-breach scenarios to model GLOFs originating from the lake, flow propagation, and its downstream impacts. The uncertainty in the breach parameters including breach width and time of failure are calculated to estimate the upper and the lower hydraulic limits of potential future GLOF events. Further, the uncertainty in the flow hydraulics was evaluated using dynamic flood routing of six GLOFs that originate from the lake. Hydrodynamic GLOF modeling resulted in a predicted peak discharge of 4311 m3s−1, 8000 m3s−1, and 12,487 m3s−1 for breach depths of 20 m, 30 m, and 40 m respectively. The large-potential scenario suggests that maximum flow depth and flow velocity at Chungthang, a town proximally located to a major hydropower station built-in 2015, could reach up to 25–30 m and 6–9 m s−1, respectively. Mapping infrastructure exposed to GLOFs in the Teesta valley shows that many settlements and assets located along the river channel at Chungthang are potentially exposed to future GLOFs, indicating the need to conduct a full environmental impact assessment and potentially undertake GLOF risk mitigation measures.

Expansion and hazard risk assessment of glacial lake Jialong Co in the central Himalayas by using an unmanned surface vessel and remote sensing

Glacial lake outburst floods (GLOFs) are a severe hazard in the Himalayas. Glacial lake expansion and the corresponding volume increase play major roles in GLOFs as well as climate change. Furthermore, mass movement and dam conditions play a major role in the GLOF initiation process. Recently, because of global warming, glacial lakes in the central Himalayas have been expanding rapidly. Owing to a lack of systematic assessment and meticulous field surveys, people living downstream are at great risk of GLOFs. Comprehensive investigations and assessment of the relationships among lake expansion, lake dam conditions, and GLOF risk are urgently needed. In this study, we surveyed Jialong Co, a typical end-moraine dammed lake in Poiqu River in the central Himalayas by using Landsat and Sentinel satellite images from the past 32 years, field work, and depth measurements using an unmanned surface vessel on August 28, 2020. The results showed that Jialong Co had experienced slow–quick–slow expansion, increasing in area from 0.13 ± 0.03 to 0.60 ± 0.02 km2. The lake bathymetric map revealed that the lake volume was (3.75 ± 0.38) × 107 m3 in 2020. Lake expansion occurred in the area from which the mother glacier retreated, indicating a close connection between the lake and its mother glacier and revealing that topography controlled the lake expansion process. Furthermore, thorough field work revealed that outlet dynamics and external water erosion are vulnerable elements in the disaster chain that initiate and affect the GLOF hazard of Jialong Co. Overall, this case study could help scholars understand the expansion mechanism of end-moraine dammed lakes and aid in hazard assessment of glacial lakes in the central Himalayas.

Future glacial lakes in High Mountain Asia: an inventory and assessment of hazard potential from surrounding slopes

AbstractBedrock overdeepenings exposed by continued glacial retreat can store precipitation and meltwater, potentially leading to the formation of new proglacial lakes. These lakes may pose threats of glacial lake outburst floods (GLOFs) in high mountain areas, particularly if new lakes form in geomorphological setups prone to triggering events such as landslides or moraine collapses. We present the first complete inventory for future glacial lakes in High Mountain Asia by computing the subglacial bedrock for ~100 000 glaciers and estimating overdeepening area, volume and impact hazard for the larger potential lakes. We detect 25 285 overdeepenings larger than 104m2with a volume of 99.1 ± 28.6 km3covering an area of 2683 ± 773.8 km2. For the 2700 overdeepenings larger than 105m2, we assess the lake predisposition for mass-movement impacts that could trigger a GLOF by estimating the hazard of material detaching from surrounding slopes. Our findings indicate a shift in lake area, volume and GLOF hazard from the southwestern Himalayan region toward the Karakoram. The results of this study can be used for anticipating emerging threats and potentials connected to glacial lakes and as a basis for further studies at suspected GLOF hazard hotspots.

Can a dam type of an alpine lake be derived from lake geometry? A negative result

Glacial lake outburst floods (GLOFs) represent one of the most serious hazard and risk in deglaciating high mountain regions worldwide and the need for GLOF hazard and risk assessment is apparent. As a consequence, numerous region- and nation-wide GLOF assessment studies have been published recently. These studies cover large areas and consider hundreds to thousands of lakes, prioritizing the hazard posed by them. Clearly, certain simplification is required for executing such studies, often resulting in neglecting qualitative characteristics which would need manual assignment. Different lake dam types (e.g., bedrock-dammed, moraine-dammed) are often not distinguished, despite they control GLOF mechanism (dam overtopping/dam breach) and thus GLOF magnitude. In this study, we explore the potential of easily measurable quantitative characteristics and four ratios to approximate the lake dam type. Our dataset of 851 lakes of the Cordillera Blanca suggests that while variances and means of these characteristics of individual lake types differ significantly (F-test, t-test), value distribution of different geometrical properties can’t be used for the originally proposed purpose along the spectra. The only promising results are obtained for extreme values (selected bins) of the ratios. For instance, the low width to length ratio indicates likely moraine-dammed lake while the high value of ratio indicating round-shape of the lake indicates increased likelihood of bedrock-dammed lake. Overall, we report a negative result of our experiment since there are negligible differences of relative frequencies in most of the bins along the spectra.

Increased outburst flood hazard from Lake Palcacocha due to human-induced glacier retreat

A potential glacial lake outburst flood from Lake Palcacocha (Cordillera Blanca, Peru) threatens Huaraz, a city of 120,000 people. In 1941, an outburst flood destroyed one-third of the city and caused at least 1,800 fatalities. Since pre-industrial times, Lake Palcacocha has expanded due to the retreat of Palcaraju glacier. Here we used observations and numerical models to evaluate the anthropogenic contribution to the glacier’s retreat and glacial lake outburst flood hazard. We found that the magnitude of human-induced warming equals between 85 and 105% (5–95% confidence interval) of the observed 1 °C warming since 1880 in this region. We conclude that it is virtually certain (>99% probability) that the retreat of Palcaraju glacier to the present day cannot be explained by natural variability alone, and that the retreat by 1941 represented an early impact of anthropogenic greenhouse gas emissions. Our central estimate is that the overall retreat is entirely attributable to the observed temperature trend, and that the resulting change in the geometry of the lake and valley has substantially increased the outburst flood hazard. Human-induced warming is responsible for the retreat of Palcaraju glacier and the associated increase in glacial lake outburst flood hazard, according to an analysis of observations and numerical models.