One of the consequences of recent glacier recession in the Cordillera Blanca, Peru, is the risk o... more One of the consequences of recent glacier recession in the Cordillera Blanca, Peru, is the risk of glacial lake outburst floods (GLOFs) from lakes that have formed at the base of retreating glaciers. GLOFs are often triggered by avalanches falling into glacial lakes, initiating a chain of processes that may culminate in significant inundation and destruction downstream. This paper presents simulations of all of the processes involved in a potential GLOF originating from Lake Palcacocha, the source of a previously catastrophic GLOF on 13 December 1941, killing about 1800 people in the city of Huaraz, Peru. The chain of processes simulated here includes (1) avalanches above the lake; (2) lake dynamics resulting from the avalanche impact, including wave generation, propagation, and run-up across lakes; (3) terminal moraine overtopping and dynamic moraine erosion simulations to determine the possibility of breaching; (4) flood propagation along downstream valleys; and (5) inundation of populated areas. The results of each process feed into simulations of subsequent processes in the chain, finally resulting in estimates of inundation in the city of Huaraz. The results of the inundation simulations were converted into flood intensity and preliminary hazard maps (based on an intensity-likelihood matrix) that may be useful for city planning and regulation. Three avalanche events with volumes ranging from 0.5 to 3 × 10 6 m 3 were simulated, and two scenarios of 15 and 30 m lake lowering were simulated to assess the potential of mitigating the hazard level in Huaraz. For all three avalanche events, three-dimensional hydrodynamic models show large waves generated in the lake from the impact resulting in overtopping of the damming moraine. Despite very high discharge rates (up to 63.4 × 10 3 m 3 s −1), the erosion from the overtopping wave did not result in failure of the damming moraine when simulated with a hydromorphodynamic model using excessively conservative soil characteristics that provide very little erosion resistance. With the current lake level, all three avalanche events result in inundation in Huaraz due to wave overtopping, and the resulting preliminary hazard map shows a total affected area of 2.01 km 2 , most of which is in the high hazard category. Lowering the lake has the potential to reduce the affected area by up to 35 %, resulting in a smaller portion of the inundated area in the high hazard category.
Glacial lake outburst floods (GLOFs) are a great concern for the Himalaya, as they can severely d... more Glacial lake outburst floods (GLOFs) are a great concern for the Himalaya, as they can severely damage downstream populations and infrastructures. These floods originate at high altitudes and can flow down with enormous energy and change the terrain’s existing morphology. One such devastating event occurred on the night of 5 July 2016, from the inconspicuous Gongbatongsha Lake, located in the Poiqu basin, Eastern Himalaya. The Poiqu basin in the Tibetan Autonomous Region currently contains numerous big glacial lakes; however, this event originated from a small lake. The GLOF was triggered following heavy precipitation that led to a slope failure above the lake and deposition of debris into the lake, which breached the moraine dam and rapidly drained the entire lake. The flood damaged several downstream infrastructures, including the Arniko highway, the Upper Bhotekoshi hydropower plant, and several buildings as it made its way into the Bhotekoshi basin in Nepal. This study adopts a ...
It is a robust study where the causes, impacts, and implications are well presented. The authors ... more It is a robust study where the causes, impacts, and implications are well presented. The authors also point out that heavy precipitation can be an important trigger of GLOF. Meteorological conditions, especially extreme rain events, may partly melt ice in the moraine dam and weaken the moraine, or cause overfill and thermal and physical erosion of the moraine, or induce a mass movement into the lake.
Glacial lake outburst floods (GLOFs) are among the most concerning consequences of retreating gla... more 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 few decades, with particular interests in the physical drivers and mechanisms of GLOF hazard, and socioeconomic and other human-related developments that affect vulnerability 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 570 peer-reviewed GLOF studies published between 2017 and 2021 (Web of Science and Scopus databases), reviewing the content, 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 from 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 GLOFstiming and processes; (ii) modelling GLOFs and GLOF process chains; (iii) GLOF risk management, prevention and warning; (iv) human dimensions of GLOFs and GLOF attribution to climate change.
The Teesta basin in Sikkim Himalaya hosts numerous glacial lakes in the high altitude glacierized... more 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 m 3 s −1 , 8000 m 3 s −1 , and 12,487 m 3 s −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.
The existence of numerous lakes at the higher reaches of the Himalaya makes it a potential natura... more The existence of numerous lakes at the higher reaches of the Himalaya makes it a potential natural hazard, as it imposes a risk of glacial lake outburst flood (GLOF). A GLOF event may cause great loss of life and infrastructure in the low-lying areas. Hydrodynamic modeling of a natural earth dam failure helps us to understand the flow behavior of the sudden water discharge along a given river channel. Further, flood forecasting along the river channel would determine the water discharge of the dam failure event at a particular downstream point. In the present study, moraine failure using hydrodynamic modeling of the Satopanth Tal located in the Alaknanda basin, Central Himalaya is performed to estimate peak discharge at a point just downstream of the lake. Further, unsteady flow routing of the dam-break outflow discharge is performed along the river channel to estimate the peak discharge at a hydropower dam site located 21 km downstream of the lake. The simulation of the glacial lak...
The Hindu-Kush-Himalayan region is home to numerous glacial lakes. Some of these lakes could fail... more The Hindu-Kush-Himalayan region is home to numerous glacial lakes. Some of these lakes could fail and produce hazardous Glacial Lake Outburst Floods (GLOF). GLOFs are primarily triggered by an avalanche or a rockfall entering the lake that generates an overtopping displacement waves. In the present study, we investigate the susceptibility of all lakes present in the Hindu-KushKarakorum (HKH) region (Randolph Glacier inventory region 14 and 15) to the dynamic mass movement (avalanche and rockfall). Avalanche and rockfall trajectories are developed considering various depths and “Minimum Look-Up Angle” (MLUA: a term used to define the avalanche runout distance). These trajectories are also validated against the results obtained from the Rapid Mass Movement Simulation (RAMMS) model. The mass movement of avalanche or rockfall along the major axis may enhance the wave run-up leading to a higher impact on the damming structure. Therefore, each susceptible lake is critically assessed for t...
Abstract Climate change-driven retreat of glaciers is producing thousands of glacial lakes across... more Abstract Climate change-driven retreat of glaciers is producing thousands of glacial lakes across mountain regions. These lakes generally grow, coalesce into larger lakes that may produce increased downstream hazards and risks due to glacial lake outburst floods (GLOFs). This study assesses such hazards of Lower Barun Lake located near Mount Everest, Nepal. We model a series of scenarios, including two potential avalanches that enter the lake from the surrounding slope and eight potential GLOFs from the lake. To evaluate the susceptibility of the frontal moraine to overtopping, we characterize the initial avalanche-induced surge of water over the moraine caused by the kinetic energy of arriving masses and possible tsunami-like events. Further, we present physical hydrodynamic models that reveal the hazard from the potential overtopping and GLOF events along the Barun-Arun river valley. Special attention is given to analyze the flow hydraulics at six downstream settlements. To estimate potential impacts at each location, two extreme-magnitude, two high-magnitude, two moderate-magnitude, and two low-magnitude GLOFs were hydraulically evaluated for the present lake dimension and the modeled future growth of the lake. As with most hydrological processes, the magnitude and frequency of GLOFs from Lower Barun Lake have an inverse, albeit uncertain, relationship, but the potential impacts on people and infrastructure are extremely sensitive to the events’ magnitude. The flow dynamics results indicate that an overtopping flood without erosion of the damming moraine causes minimal impact in the valley. The extreme-magnitude and high-magnitude GLOF cases, where the moraine is incised, have a larger impact but differ greatly in magnitude at each of the downstream settlements. The moderate-magnitude and low-magnitude GLOFs, while the most frequent type, have limited volume and peak discharge, causing less impact downstream. Our calculations only portray the part of the hydrograph representing lake overfill due to a volume of ice or rock entering the lake, and the volume of the lake that could drain from a breach of the damming moraine down to specified depths over specified time periods.
We discuss the possible origin of the double-peaked profiles recently observed in Lyman-alpha emi... more We discuss the possible origin of the double-peaked profiles recently observed in Lyman-alpha emitters (LAEs) at the epoch of reionization (z 6.5) from obscured active galactic nuclei (AGN). In combining the extent of the Lyman-α near-zones estimated from the blue peak velocity offset in these galaxies, with the ionizing emissivity of quasars at z 6, we forecast the intrinsic UV and X-ray luminosities of the AGN needed to give rise to their double-peaked profiles. We also estimate the extent of the obscuration of the AGN by comparing their luminosities to those of similar quasar samples at these epochs. Future X-ray and radio observations, as well as those with the James Webb Space Telescope, will be valuable tools to test the AGN contribution to the intergalactic-scale ionization zones of high-redshift LAEs.
Glacial lake outburst floods (GLOFs) are a major concern throughout High Mountain Asia, where imp... more Glacial lake outburst floods (GLOFs) are a major concern throughout High Mountain Asia, where impacts can be far-reaching. 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 current lakes, and how this information can feed practically into decisionmaking and response planning. We have focused on two well-known dangerous lakes (Galongco and Jialongco), comparing 20 the consequences 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 outburst was simulated for a potential new lake forming upstream of Nyalam. Results show that although smallest in size, Jialongco, poses the greatest immediate threat to Nyalam and downstream communities, owing to the high potential for an ice avalanche to trigger an outburst. The future lake scenario would lead to flow depths and velocities that exceed either of the current scenarios, and the peak flood 25 would reach Nepal up to 20 minutes faster. Based on these findings, a comprehensive approach to disaster risk reduction is called for, combining early warning systems with effective land use zoning and capacity building programs. Such approaches address the current drivers of GLOF risk in the basin, while remaining robust in the face of future emerging threats. Keywords 30 Glacial lake outburst flood, hazard, risk, future, Himalaya authorities to take action and implement timely risk reduction measures has been acknowledged (Wang and Zhou, 2017), 55 considering the best available knowledge on existing threats (e.g.,
In this study, we examine glacier retreat and associated processes in the Lejiamayu valley, centr... more In this study, we examine glacier retreat and associated processes in the Lejiamayu valley, central Cordillera Blanca, Peru (9.27 • S; 77.48 • W) since the Last Glacial Maximum (LGM). Based on detailed mapping of wellpreserved moraines, we reconstruct glacier extent during the LGM, the Antarctic Cold Reversal (ACR) and the Little Ice Age (LIA), being 21.34 km 2 (LGM), 13.68 km 2 (ACR) and 6.84 km 2 (LIA). We document that glacier extent decreased to 2,86 km 2 since the end of the LIA in this catchment (ice loss 58%). In addition, we explore the colonization and growth of lichens and Schmidt-hammer rock test R-values over the deglaciated surfaces, suggesting a relationship to possible evironmental controls rather than to the timing of the exposure. Further, we use empirical glacier velocity-based equation to estimate maximum potential future volume of the new glacial lake forming in the upper part of the valley (4725 m a.s.l.; 2.2 Mm 3). We conclude that previous estimates of future lake volume might have been underestimated and that the sufficiency of the glacial lake outburst flood (GLOF) mitigation measures implemented at downstream located Lake Lejiacocha (4628 m a.s.l.) should be revised in future.
Kolkata Metropolitan Area (KMA) is one of the most densely populated areas in the world, where ex... more Kolkata Metropolitan Area (KMA) is one of the most densely populated areas in the world, where extreme precipitation events result in frequent waterlogging and flood inundation conditions which can adversely affect the city. In this study, we evaluate the nature and trend of annualmaximum precipitation events by employing suitable Global Circulation Models (GCMs). The trend of observed annual maximum daily rainfall from 1901 to 2013 has been analysed through linear regression, recurrence period and multi-decadal oscillation. The results show that the observed rainfall of the given region follows the natural variability and oscillation trend. TRMM time-series data (2000-2019) is employed to validate the ground-station data series using Modified Mann Kendall and Sen's Slope estimator test, which shows a correlation of 0.88. In addition, suitable bias-corrected GCMs have been selected to estimate the future precipitation in the given study area. Analysis of future rainfall for the period of 2071-2100 revealed that the RCPs are showing an increase in the extreme precipitation intensity by 1.5, 2.3 and 3 times considering RCP 4.5, 6.0 and 8.5 scenarios respectively. The presented results serve as the preliminary data for future planning and designing efficient flood management strategies in the given area to combat water-logging in KMA.
Climate change has led to the formation of numerous high-altitude lakes of glacial origin in the ... more Climate change has led to the formation of numerous high-altitude lakes of glacial origin in the Himalaya. Safed Lake is one of the largest glacial lakes, located at an elevation 4882 m a.s.l. in the state of Uttarakhand, central Himalaya, India. A temporal analysis of the lake surface using satellite imagery shows that the lake has grown more than double its size from 0.10 km2 to 0.23 km2 over the past 50 years. In this study, we performed a hazard assessment of the lake using 1D and 2D hydrodynamic modeling. We identified the potential glacial lake outburst flood (GLOF) triggering factors and evaluated the impact of a moraine breach event of the lake on the nearest village located 16.2 km downstream of the lake. A series of dynamic simulations were performed for different scenario-models based on varied breach depths, breach widths and time of moraine failure. In a worst-case GLOF scenario where breach depth reached up to 60 m, hydrodynamic routing of the breach hydrograph along t...
Hydrology and Earth System Sciences Discussions, 2019
The Cordillera Blanca in Perú has been the scene of rapid deglaciation for many decades. One of n... more The Cordillera Blanca in Perú has been the scene of rapid deglaciation for many decades. One of numerous lakes formed in the front of the retreating glaciers is the moraine-dammed Lake Palcacocha, which drained suddenly due to an unknown cause in 1941. The resulting Glacial Lake Outburst Flood (GLOF) led to dam failure and complete drainage of Lake Jircacocha downstream, and to major destruction and thousands of fatalities in the city of Huaráz at a distance of 23 km. Lake Palcacocha has dramatically regrown through further glacial retreat since then and nowadays is again considered a threat to the downstream communities. Previously, various types of computer simulations were carried out in order to quantify the possible impact of future GLOFs from Lake Palcacocha, but no attempts are made yet to back-calculate the 1941 event. Here, we chose an integrated approach to revisit the 1941 event in terms of topographic reconstruction and numerical back-calculation with the GIS-based open source mass flow/process chain simulation framework r.avaflow. Thereby we consider four scenarios: (A) and (AX) breach of the moraine dam of Lake Palcacocha due to retrogressive erosion, assuming two different fluid characteristics; (B) failure of the moraine dam caused by the impact of a landslide onto the lake; and (C) geomechanical failure and collapse of the moraine dam. The simulations largely yield empirically adequate results with physically plausible parameters, taking the documentation of the 1941 event and previous calculations of future scenarios as reference. The results of the scenarios indicate that the most likely initiation mechanism would be retrogressive erosion, possibly triggered by a minor impact wave and/or facilitated by a weak stability condition of the moraine dam. However, the involvement of Lake Jircacocha disguises part of the signal of process initiation farther downstream.
The article was published with the citation "Worni et al. (2012)". The author group of the articl... more The article was published with the citation "Worni et al. (2012)". The author group of the article would like readers to know that this information should instead read/be as follows: "Worni et al. (2013)"-Worni R, Huggel C, Stoffel M (2013) Glacial lakes in the Indian Himalayas-from an area-wide glacial lake inventory to on-site and modeling based risk assessment of critical glacial lakes. Sci Total Environ 468:S71-S84.
One of the consequences of recent glacier recession in the Cordillera Blanca, Peru, is the risk o... more One of the consequences of recent glacier recession in the Cordillera Blanca, Peru, is the risk of glacial lake outburst floods (GLOFs) from lakes that have formed at the base of retreating glaciers. GLOFs are often triggered by avalanches falling into glacial lakes, initiating a chain of processes that may culminate in significant inundation and destruction downstream. This paper presents simulations of all of the processes involved in a potential GLOF originating from Lake Palcacocha, the source of a previously catastrophic GLOF on 13 December 1941, killing about 1800 people in the city of Huaraz, Peru. The chain of processes simulated here includes (1) avalanches above the lake; (2) lake dynamics resulting from the avalanche impact, including wave generation, propagation, and run-up across lakes; (3) terminal moraine overtopping and dynamic moraine erosion simulations to determine the possibility of breaching; (4) flood propagation along downstream valleys; and (5) inundation of populated areas. The results of each process feed into simulations of subsequent processes in the chain, finally resulting in estimates of inundation in the city of Huaraz. The results of the inundation simulations were converted into flood intensity and preliminary hazard maps (based on an intensity-likelihood matrix) that may be useful for city planning and regulation. Three avalanche events with volumes ranging from 0.5 to 3 × 10 6 m 3 were simulated, and two scenarios of 15 and 30 m lake lowering were simulated to assess the potential of mitigating the hazard level in Huaraz. For all three avalanche events, three-dimensional hydrodynamic models show large waves generated in the lake from the impact resulting in overtopping of the damming moraine. Despite very high discharge rates (up to 63.4 × 10 3 m 3 s −1), the erosion from the overtopping wave did not result in failure of the damming moraine when simulated with a hydromorphodynamic model using excessively conservative soil characteristics that provide very little erosion resistance. With the current lake level, all three avalanche events result in inundation in Huaraz due to wave overtopping, and the resulting preliminary hazard map shows a total affected area of 2.01 km 2 , most of which is in the high hazard category. Lowering the lake has the potential to reduce the affected area by up to 35 %, resulting in a smaller portion of the inundated area in the high hazard category.
Glacial lake outburst floods (GLOFs) are a great concern for the Himalaya, as they can severely d... more Glacial lake outburst floods (GLOFs) are a great concern for the Himalaya, as they can severely damage downstream populations and infrastructures. These floods originate at high altitudes and can flow down with enormous energy and change the terrain’s existing morphology. One such devastating event occurred on the night of 5 July 2016, from the inconspicuous Gongbatongsha Lake, located in the Poiqu basin, Eastern Himalaya. The Poiqu basin in the Tibetan Autonomous Region currently contains numerous big glacial lakes; however, this event originated from a small lake. The GLOF was triggered following heavy precipitation that led to a slope failure above the lake and deposition of debris into the lake, which breached the moraine dam and rapidly drained the entire lake. The flood damaged several downstream infrastructures, including the Arniko highway, the Upper Bhotekoshi hydropower plant, and several buildings as it made its way into the Bhotekoshi basin in Nepal. This study adopts a ...
It is a robust study where the causes, impacts, and implications are well presented. The authors ... more It is a robust study where the causes, impacts, and implications are well presented. The authors also point out that heavy precipitation can be an important trigger of GLOF. Meteorological conditions, especially extreme rain events, may partly melt ice in the moraine dam and weaken the moraine, or cause overfill and thermal and physical erosion of the moraine, or induce a mass movement into the lake.
Glacial lake outburst floods (GLOFs) are among the most concerning consequences of retreating gla... more 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 few decades, with particular interests in the physical drivers and mechanisms of GLOF hazard, and socioeconomic and other human-related developments that affect vulnerability 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 570 peer-reviewed GLOF studies published between 2017 and 2021 (Web of Science and Scopus databases), reviewing the content, 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 from 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 GLOFstiming and processes; (ii) modelling GLOFs and GLOF process chains; (iii) GLOF risk management, prevention and warning; (iv) human dimensions of GLOFs and GLOF attribution to climate change.
The Teesta basin in Sikkim Himalaya hosts numerous glacial lakes in the high altitude glacierized... more 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 m 3 s −1 , 8000 m 3 s −1 , and 12,487 m 3 s −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.
The existence of numerous lakes at the higher reaches of the Himalaya makes it a potential natura... more The existence of numerous lakes at the higher reaches of the Himalaya makes it a potential natural hazard, as it imposes a risk of glacial lake outburst flood (GLOF). A GLOF event may cause great loss of life and infrastructure in the low-lying areas. Hydrodynamic modeling of a natural earth dam failure helps us to understand the flow behavior of the sudden water discharge along a given river channel. Further, flood forecasting along the river channel would determine the water discharge of the dam failure event at a particular downstream point. In the present study, moraine failure using hydrodynamic modeling of the Satopanth Tal located in the Alaknanda basin, Central Himalaya is performed to estimate peak discharge at a point just downstream of the lake. Further, unsteady flow routing of the dam-break outflow discharge is performed along the river channel to estimate the peak discharge at a hydropower dam site located 21 km downstream of the lake. The simulation of the glacial lak...
The Hindu-Kush-Himalayan region is home to numerous glacial lakes. Some of these lakes could fail... more The Hindu-Kush-Himalayan region is home to numerous glacial lakes. Some of these lakes could fail and produce hazardous Glacial Lake Outburst Floods (GLOF). GLOFs are primarily triggered by an avalanche or a rockfall entering the lake that generates an overtopping displacement waves. In the present study, we investigate the susceptibility of all lakes present in the Hindu-KushKarakorum (HKH) region (Randolph Glacier inventory region 14 and 15) to the dynamic mass movement (avalanche and rockfall). Avalanche and rockfall trajectories are developed considering various depths and “Minimum Look-Up Angle” (MLUA: a term used to define the avalanche runout distance). These trajectories are also validated against the results obtained from the Rapid Mass Movement Simulation (RAMMS) model. The mass movement of avalanche or rockfall along the major axis may enhance the wave run-up leading to a higher impact on the damming structure. Therefore, each susceptible lake is critically assessed for t...
Abstract Climate change-driven retreat of glaciers is producing thousands of glacial lakes across... more Abstract Climate change-driven retreat of glaciers is producing thousands of glacial lakes across mountain regions. These lakes generally grow, coalesce into larger lakes that may produce increased downstream hazards and risks due to glacial lake outburst floods (GLOFs). This study assesses such hazards of Lower Barun Lake located near Mount Everest, Nepal. We model a series of scenarios, including two potential avalanches that enter the lake from the surrounding slope and eight potential GLOFs from the lake. To evaluate the susceptibility of the frontal moraine to overtopping, we characterize the initial avalanche-induced surge of water over the moraine caused by the kinetic energy of arriving masses and possible tsunami-like events. Further, we present physical hydrodynamic models that reveal the hazard from the potential overtopping and GLOF events along the Barun-Arun river valley. Special attention is given to analyze the flow hydraulics at six downstream settlements. To estimate potential impacts at each location, two extreme-magnitude, two high-magnitude, two moderate-magnitude, and two low-magnitude GLOFs were hydraulically evaluated for the present lake dimension and the modeled future growth of the lake. As with most hydrological processes, the magnitude and frequency of GLOFs from Lower Barun Lake have an inverse, albeit uncertain, relationship, but the potential impacts on people and infrastructure are extremely sensitive to the events’ magnitude. The flow dynamics results indicate that an overtopping flood without erosion of the damming moraine causes minimal impact in the valley. The extreme-magnitude and high-magnitude GLOF cases, where the moraine is incised, have a larger impact but differ greatly in magnitude at each of the downstream settlements. The moderate-magnitude and low-magnitude GLOFs, while the most frequent type, have limited volume and peak discharge, causing less impact downstream. Our calculations only portray the part of the hydrograph representing lake overfill due to a volume of ice or rock entering the lake, and the volume of the lake that could drain from a breach of the damming moraine down to specified depths over specified time periods.
We discuss the possible origin of the double-peaked profiles recently observed in Lyman-alpha emi... more We discuss the possible origin of the double-peaked profiles recently observed in Lyman-alpha emitters (LAEs) at the epoch of reionization (z 6.5) from obscured active galactic nuclei (AGN). In combining the extent of the Lyman-α near-zones estimated from the blue peak velocity offset in these galaxies, with the ionizing emissivity of quasars at z 6, we forecast the intrinsic UV and X-ray luminosities of the AGN needed to give rise to their double-peaked profiles. We also estimate the extent of the obscuration of the AGN by comparing their luminosities to those of similar quasar samples at these epochs. Future X-ray and radio observations, as well as those with the James Webb Space Telescope, will be valuable tools to test the AGN contribution to the intergalactic-scale ionization zones of high-redshift LAEs.
Glacial lake outburst floods (GLOFs) are a major concern throughout High Mountain Asia, where imp... more Glacial lake outburst floods (GLOFs) are a major concern throughout High Mountain Asia, where impacts can be far-reaching. 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 current lakes, and how this information can feed practically into decisionmaking and response planning. We have focused on two well-known dangerous lakes (Galongco and Jialongco), comparing 20 the consequences 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 outburst was simulated for a potential new lake forming upstream of Nyalam. Results show that although smallest in size, Jialongco, poses the greatest immediate threat to Nyalam and downstream communities, owing to the high potential for an ice avalanche to trigger an outburst. The future lake scenario would lead to flow depths and velocities that exceed either of the current scenarios, and the peak flood 25 would reach Nepal up to 20 minutes faster. Based on these findings, a comprehensive approach to disaster risk reduction is called for, combining early warning systems with effective land use zoning and capacity building programs. Such approaches address the current drivers of GLOF risk in the basin, while remaining robust in the face of future emerging threats. Keywords 30 Glacial lake outburst flood, hazard, risk, future, Himalaya authorities to take action and implement timely risk reduction measures has been acknowledged (Wang and Zhou, 2017), 55 considering the best available knowledge on existing threats (e.g.,
In this study, we examine glacier retreat and associated processes in the Lejiamayu valley, centr... more In this study, we examine glacier retreat and associated processes in the Lejiamayu valley, central Cordillera Blanca, Peru (9.27 • S; 77.48 • W) since the Last Glacial Maximum (LGM). Based on detailed mapping of wellpreserved moraines, we reconstruct glacier extent during the LGM, the Antarctic Cold Reversal (ACR) and the Little Ice Age (LIA), being 21.34 km 2 (LGM), 13.68 km 2 (ACR) and 6.84 km 2 (LIA). We document that glacier extent decreased to 2,86 km 2 since the end of the LIA in this catchment (ice loss 58%). In addition, we explore the colonization and growth of lichens and Schmidt-hammer rock test R-values over the deglaciated surfaces, suggesting a relationship to possible evironmental controls rather than to the timing of the exposure. Further, we use empirical glacier velocity-based equation to estimate maximum potential future volume of the new glacial lake forming in the upper part of the valley (4725 m a.s.l.; 2.2 Mm 3). We conclude that previous estimates of future lake volume might have been underestimated and that the sufficiency of the glacial lake outburst flood (GLOF) mitigation measures implemented at downstream located Lake Lejiacocha (4628 m a.s.l.) should be revised in future.
Kolkata Metropolitan Area (KMA) is one of the most densely populated areas in the world, where ex... more Kolkata Metropolitan Area (KMA) is one of the most densely populated areas in the world, where extreme precipitation events result in frequent waterlogging and flood inundation conditions which can adversely affect the city. In this study, we evaluate the nature and trend of annualmaximum precipitation events by employing suitable Global Circulation Models (GCMs). The trend of observed annual maximum daily rainfall from 1901 to 2013 has been analysed through linear regression, recurrence period and multi-decadal oscillation. The results show that the observed rainfall of the given region follows the natural variability and oscillation trend. TRMM time-series data (2000-2019) is employed to validate the ground-station data series using Modified Mann Kendall and Sen's Slope estimator test, which shows a correlation of 0.88. In addition, suitable bias-corrected GCMs have been selected to estimate the future precipitation in the given study area. Analysis of future rainfall for the period of 2071-2100 revealed that the RCPs are showing an increase in the extreme precipitation intensity by 1.5, 2.3 and 3 times considering RCP 4.5, 6.0 and 8.5 scenarios respectively. The presented results serve as the preliminary data for future planning and designing efficient flood management strategies in the given area to combat water-logging in KMA.
Climate change has led to the formation of numerous high-altitude lakes of glacial origin in the ... more Climate change has led to the formation of numerous high-altitude lakes of glacial origin in the Himalaya. Safed Lake is one of the largest glacial lakes, located at an elevation 4882 m a.s.l. in the state of Uttarakhand, central Himalaya, India. A temporal analysis of the lake surface using satellite imagery shows that the lake has grown more than double its size from 0.10 km2 to 0.23 km2 over the past 50 years. In this study, we performed a hazard assessment of the lake using 1D and 2D hydrodynamic modeling. We identified the potential glacial lake outburst flood (GLOF) triggering factors and evaluated the impact of a moraine breach event of the lake on the nearest village located 16.2 km downstream of the lake. A series of dynamic simulations were performed for different scenario-models based on varied breach depths, breach widths and time of moraine failure. In a worst-case GLOF scenario where breach depth reached up to 60 m, hydrodynamic routing of the breach hydrograph along t...
Hydrology and Earth System Sciences Discussions, 2019
The Cordillera Blanca in Perú has been the scene of rapid deglaciation for many decades. One of n... more The Cordillera Blanca in Perú has been the scene of rapid deglaciation for many decades. One of numerous lakes formed in the front of the retreating glaciers is the moraine-dammed Lake Palcacocha, which drained suddenly due to an unknown cause in 1941. The resulting Glacial Lake Outburst Flood (GLOF) led to dam failure and complete drainage of Lake Jircacocha downstream, and to major destruction and thousands of fatalities in the city of Huaráz at a distance of 23 km. Lake Palcacocha has dramatically regrown through further glacial retreat since then and nowadays is again considered a threat to the downstream communities. Previously, various types of computer simulations were carried out in order to quantify the possible impact of future GLOFs from Lake Palcacocha, but no attempts are made yet to back-calculate the 1941 event. Here, we chose an integrated approach to revisit the 1941 event in terms of topographic reconstruction and numerical back-calculation with the GIS-based open source mass flow/process chain simulation framework r.avaflow. Thereby we consider four scenarios: (A) and (AX) breach of the moraine dam of Lake Palcacocha due to retrogressive erosion, assuming two different fluid characteristics; (B) failure of the moraine dam caused by the impact of a landslide onto the lake; and (C) geomechanical failure and collapse of the moraine dam. The simulations largely yield empirically adequate results with physically plausible parameters, taking the documentation of the 1941 event and previous calculations of future scenarios as reference. The results of the scenarios indicate that the most likely initiation mechanism would be retrogressive erosion, possibly triggered by a minor impact wave and/or facilitated by a weak stability condition of the moraine dam. However, the involvement of Lake Jircacocha disguises part of the signal of process initiation farther downstream.
The article was published with the citation "Worni et al. (2012)". The author group of the articl... more The article was published with the citation "Worni et al. (2012)". The author group of the article would like readers to know that this information should instead read/be as follows: "Worni et al. (2013)"-Worni R, Huggel C, Stoffel M (2013) Glacial lakes in the Indian Himalayas-from an area-wide glacial lake inventory to on-site and modeling based risk assessment of critical glacial lakes. Sci Total Environ 468:S71-S84.
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Papers by Ashim Sattar