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Breaching of natural dams in the Hutiao Gorge of the Jinsha River across the Yulong-Haba Mountains is one of the major geomorphological events in the largest river of Asia. Catastrophic flood events have an important influence on the geomorphological evolution of the First Bend of the Yangtze River since the Last Glacial Maximum (LGM). However, detailed geomorphological evidence, ages, and depositional phases of outburst flooding remain unclear. In this paper, large-scale gravel bars overlying the river terraces and dammed lakes are analyzed within the Daju Basin. The macroscopic geomorphological characteristics of megaflood landforms with large thickness and uniform gravel bars are similar to those of Missoula and Altai megafloods. Morphological analysis shows that eddy gravel bars (EGBs) with rhythmic structure are characterized by a dome-shaped protrusion in the cross section and a gravel mound in the longitudinal section. Each bar with oblique, parallel and massive bedding was analyzed from the horizontal and vertical directions. Three dome-shaped bars clearly show at least three palaeoflood phases. Quartz grain surface macrotextures are mainly V-shaped pits and conchoidal fractures, which exhibits a high-energy environment during the flood. The stratigraphic sequence model of EGBs is dominated by coarse sand and fine gravel rhythmic bedding in high-energy eddy environments and suspended sand deposits in low-energy backwater environments. Such phenomenon reveals megaflood fluctuates, which is also confirmed by geochemical difference. The episode of natural dam break floods triggered by tectonic activity and glacier fluctuation was dated to 20–17 ka during the LGM. Sedimentary pattern of EGBs offers fresh insights into understanding the megaflood geomorphological characteristics of the upper Yangtze River and better identification similar high-energy palaeoflood landforms in the southeast Tibetan Plateau. • Eddy gravel bars of megaflood events were systemic analyzed in the First bend of Yangtze River. • Coarse sand and fine gravel rhythmic bedding were identified in high-energy eddy environments. • The episode of megafloods was dated to 20–17 ka during the Last Glacial Maximum. • Sedimentary pattern and stratigraphic sequences of megaflood gravel bars were established. • Role of megaflood events in the evolution of river geomorphology was discussed in the Hutiao Gorge. [ABSTRACT FROM AUTHOR]

Under the climate warming, the ice avalanches (IAs) and glacier lake outburst floods (GLOFs) will continue or even intensify in the future. In order to find out the number, spatial distribution, and characteristics of hidden dangers of IA and GLOF-prone lakes on the Tibetan Plateau (TP), the first inventory is presented. (1) The study has identified and analyzed 581 IAs and 369 GLOFs on the TP. IAs and GLOFs are widely distributed in the Tibet Autonomous Region (TAR), concentrating in the Yarlung Zangbo River basin and the Nyainqntanglha and Himalaya Mountain range. (2) Most of the IAs have an area of 0.1 ~ 1 km2. The IAs occur on vulnerable slopes ranging from 35 to 45°, with an elevation between 4500 and 5500 m and a north-friendly aspect. (3) Most of the GLOFs with a lake area of 0.1 ~ 0.3 km2 and a north-facing outburst direction are developed in an elevation range from 4500 to 5500 m. There are about half of the GLOF-prone lakes to be close to the front edge of the mother glaciers. (4) The front elevation of IAs changes regularly with the eastern Himalayan syntaxis region as the boundary. It generally increased from west to east on the west side, while a "V-shaped" trend first decreased and then increased, and decreased from south to north on the east side. (5) The IAs and GLOFs are mainly distributed in the southern and northwestern TP with "clustering" characters due to the topographical and climatic settings. [ABSTRACT FROM AUTHOR]

Outburst floods triggered by breaching of landslide dams may cause severe loss of life and property downstream. Accurate identification and assessment of such floods, especially when leading to secondary impacts, are critical. In 2018, the Baige landslide in the Tibetan Plateau twice blocked the Jinsha River, eventually resulting in a severe outburst flood. The Baige landslide remains active, and it is possible that a breach happens again. Based on numerical simulation using a hydrodynamic model, remote sensing, and field investigation, we reproduce the outburst flood process and assess the hazard associated with future floods. The results show that the hydrodynamic model could accurately simulate the outburst flood process, with overall accuracy and Kappa accuracy for the flood extent of 0.956 and 0.911. Three future dam break scenarios were considered with landslide dams of heights 30 m, 35 m, and 51 m. The potential storage capacity and length of upstream flow back up in the upstream valley for these heights were 142 × 106m3/32 km, 182 × 106m3/40 km, and 331 × 106m3/50 km. Failure of these three dams leads to maximum inundation extents of 0.18 km2, 0.34 km2, and 0.43 km2, which is significant out-of-bank flow and serious infrastructure impacts. These results demonstrate the seriousness of secondary hazards associated with this region. [ABSTRACT FROM AUTHOR]

• Disaster chains of two GLOFs within a river basin of Nyainqêntanglha range were identified. • Ice avalanche and landslide were identified as the dominant triggers of GLOFs. • GLOF processes and downstream impacts were assessed using a hydrodynamic model. • Fieldworks provide important insights into the recognition of cascading hazards of GLOFs. Glacial lake outburst floods (GLOFs) are a major natural hazard in high mountain regions and have caused significant loss and damage. In the past decade, two lakes (Ranzeria Co in 2013 and Jiweng Co in 2020) burst out within a single river basin in the Nyainqêntanglha range of the Tibetan Plateau. These GLOFs destroyed local infrastructure and vegetation, and eroded river banks. In this study, field measurements, satellite remote sensing, and hydrodynamic modelling were used to reveal the causes, mechanisms, and flow dynamics of both events. Field surveys in 2020 and 2022 including lake bathymetry, lake shorelines, high-resolution aerial photographs, geomorphological data, and downstream damage provided evidence to analyze the triggers and mechanisms involved in both cases. The results show that Ranzeria Co expanded by 123% in area between 1976 and 2012, and contracted by 53% in 2013 due to the outburst. The area of Jiweng Co grew by 54% from 1976 to 2020, and shrank by 57% after the dam breach. Lake levels decreased by 20.2 ± 0.3 m in 2013 for Ranzeria Co and by 25.8 ± 0.3 m in 2020 for Jiweng Co, corresponding to water volume losses of about 7.9 × 106 (68%) and 1.1 × 107 m3 (87%), respectively. Using the hydrodynamic model HEC-RAS, it was found that the GLOFs reached peak discharges of about 7,500 m3/s with an average velocity of 8.8 m/s at Ranzeria Co, and 5,100 m3/s with 3.7 m/s at Jiweng Co. The Ranzeria Co outburst involved a cascade of processes, including the collapse of the parent glacier, a displacement wave in the lake, and the overtopping of the moraine dam. The processes of the Jiweng Co outburst flood were more complex, including an unstable lateral moraine, landslides entering the lake, rising water level, dam erosion, and finally dam failure. The study provides important insights into the mechanisms of two GLOFs, which are key to assessing and managing the hazards of critical glacial lakes in the Tibetan Plateau and its surroundings. [ABSTRACT FROM AUTHOR]

Surface hazards can form hazard cascades which expand their reach. However, our understanding of their complex dynamics and ability to mitigate their impacts remain limited. In 2018, two landslides dammed the Jinsha River in the Tibetan plateau and formed landslide‐dammed lakes. Subsequent dam breaches prompted the evacuation of >120,000 people. An early warning system for floods using a regional seismic network has been proposed on the basis of catastrophic floods having been detected ∼100 km away, with seismic energy proportional to discharge. Surprisingly, we find that this catastrophic outburst flood was undetectable beyond a few kilometers, with peak seismic energy preceding peak discharge. We propose that river channel stability also controls seismic energy generation and should be considered for accurate monitoring of catastrophic floods. In contrast, we find that the various processes during dam breach can be well‐characterized seismically further away and provide warning ∼60 min before discharge exceeds monsoon flood levels. We also show that numerical modeling of dam breaches which typically lacks in situ measurements can benefit from incorporating seismic data as constraints. Finally, we show that this event drastically increased sediment fluxes ∼670 km downstream for years and may significantly reduce the capacity of hydropower plants. Our results reveal ways to improve early warning of catastrophic outburst floods and the need to consider surface hazards' long‐term impact when managing infrastructure in mountainous regions. Plain Language Summary: Mountainous regions are prone to surface hazards such as landslides and floods. However, our understanding of how these events evolve and interact is limited. In 2018, two landslides blocked a river in Tibet and created landslide‐dammed lakes. Subsequently, the dam broke and the resulting outburst floods severely damaged downstream infrastructure and led to the evacuation of >120,000 people. In contrast to what previous studies suggest, we find that this catastrophic outburst flood was undetectable beyond a few kilometers, with peak seismic energy preceding peak discharge. We propose that river channel stability also controls seismic energy generation and should be considered for accurate monitoring of catastrophic floods. Conversely, the dam breakage could be detected seismically further away and provide warning ∼60 min before discharge exceeded monsoon flood levels. Finally, we show that this event drastically increased sediment amounts downstream for years and may reduce the capacity of hydropower plants. Our results reveal ways to improve seismic monitoring and early warning of catastrophic floods and the need to consider the long‐term impact of surface hazards when managing downstream infrastructure. Key Points: Catastrophic outburst floods were surprisingly quiet with peak seismic energy preceding peak discharge due to changes in channel stabilityVarious dam breach processes can be well‐characterized seismically, which can constrain numerical modeling and provide earlier warningThese hazard cascades drastically increased sediment fluxes ≥670 km downstream for years and reduced hydropower plant capacity [ABSTRACT FROM AUTHOR]

Glacial lake outburst floods (GLOFs) are among the most severe cryospheric hazards in the Third Pole, encompassing the Tibetan Plateau and surrounding Himalayas, Hindu Kush, and Tianshan Mountains. Recent studies on glacial lake changes and GLOF characteristics and risks in this region have shown scattered and insufficiently detailed features. Here, we conduct an appraisal of the GLOF risks by combining high-resolution satellite images, case-by-case high-precision GLOF modeling, and detailed downstream exposure data. The glacial lake changes from 2018 to 2022 in the region were primarily driven by the accelerated expansion of proglacial lakes. The GLOF frequency has exhibited a significant increasing trend since 1980, with intensified activity in Southeastern Tibet and the China-Nepal border area over the past decade. Approximately 6,353 km2 of land could be at risk from potential GLOFs, posing threats to 55,808 buildings, 105 hydropower projects, 194 km2 of farmland, 5,005 km of roads, and 4,038 bridges. This study directly responds to the need for local disaster prevention and mitigation strategies, highlighting the urgent requirement of reducing GLOF threats in the Third Pole and the importance of regional cooperation. The recent accelerated expansion of glacial lakes and increased glacial lake outburst flood activities in the Tibetan Plateau and its surroundings indicate that numerous communities and infrastructure downstream are at a higher flood risk than previously understood. [ABSTRACT FROM AUTHOR]

Debris-covered glaciers have contrasting melting mechanisms and climate response patterns if compared with debris-free glaciers and thus show a unique influence on the hydrological process. Based on high-resolution satellite images and unpiloted aerial vehicle surveys, this study investigated the dynamic changes of Zhuxi Glacier, a thick debris-covered glacier in the southeastern Tibetan Plateau. Our result shows that the whole glacier can be divided into the active regime and stagnant regime along the elevation of 3400 m a.s.l. The mean surface velocity of the active regime was 13.1 m yr−1, which was five times higher than that of the stagnant regime. The surface-lowing rate of this debris-covered glacier reaches more than 1 m yr−1 and displays an accelerating trend. The majority of ice loss concentrates around ice cliffs and supraglacial ponds, the ablation hotspots. These hotspots can be roughly classified into three types, including persistent, expanding, and shrinking patterns, at different dynamic regimes on the Zhuxi Glacier. With the evolution of these hotpots and glacier dynamic changes, the supraglacial ponds showed significant change, with the total number fluctuating from 15 to 38 and the total area increasing from 1128 m2 to 95790 m2 during the past decade. The recent exponential expansion of the proglacial lake and the significant downwasting of stagnant ice inside the dammed terminus moraine possibly trigger the glacial lake outburst flood and thus threaten the security of livelihoods and infrastructure downstream. [ABSTRACT FROM AUTHOR]

Owing to intense glacial retreat and melting, it is anticipated that numerous glacial lakes will be formed in the next few decades. However, their development and distribution patterns in the Tibetan Plateau and its surroundings still need to be elucidated. In this study, a published glacier ice thickness distribution dataset was employed to fully detect overdeepened glacier beds as potential glacial lakes. We selected and expanded four morphological metrics to determine the formation probability of potential glacial lakes: surface slope, break in slope, lake area, and position on the glacier. The results revealed that 15,826 potential glacial lakes with areas >0.02 km2 exist in the Tibetan Plateau and its surroundings, covering an area of 2253.95 ± 1291.29 km2 with a water volume of 60.49 ± 28.94 km3 that would contribute to an equivalent sea level rise of 0.16 ± 0.08 mm. The experimental comparison and uncertainty assessment for the overdeepening processing showed that the different extraction methods and basic digital elevation models used could lead to non-negligible errors in the results (at least ±30%), which were ignored in previous studies, contributing to major divergences between the several current inventories of potential glacial lakes in the plateau. Notably, approximately 90% of the total area of the potential glacial lakes is concentrated in the lower half of the individual glaciers in the Tibetan Plateau and its surroundings. >70% of the potential glacial lakes and contemporary glacial lakes in this region were found to be concentrated within the 4000–5800 m elevation range. Moreover, the study identified 5361 potential glacial lakes with high or very high exposure probabilities, and their distribution was mostly determined by regional glacier resources. However, the numbers and sizes of some potential glacial lakes that are found in the Karakoram region are considered to be exaggerated because of the presence of numerous surge-type glaciers, which have not been discussed in previous studies. These results can improve our understanding of future glacial lake formation and distribution in the Tibetan Plateau and its surroundings and have implications for further implementation of effective prevention, mitigation, and adaptation measures for glacial lake outburst floods and water security. • 15,826 PGLs with areas >0.02 km2 exist in the Tibetan Plateau and its surroundings, covering an area of 2253.95 ± 1291.29 km2 with a water volume of 60.49 ± 28.94 km3. • Approximately 90% of the total area of the Potential Glacial Lakes is concentrated in the lower half of the individual glaciers in the Tibetan Plateau and its surroundings. • The number and size of some Potential Glacial Lakes found in the Karakoram region are considered exaggerated because of the presence of numerous surge-type glaciers. [ABSTRACT FROM AUTHOR]

The repeated cut-and-fill process induced by the late Quaternary glacial damming and catastrophic outburst events in the Yarlung Tsangpo Gorge (YTG) in the eastern Himalaya may reflect the interaction between rock uplift, climate change and river incision in the southeastern Tibetan Plateau. Here we provide the detailed reconstruction of the cut-and-fill history recorded at the entrance of the YTG, based on geomorphological, sedimentological and chronological analyses. The results reveal a catastrophic glacial-dam breach during the last deglaciation (∼18 ka), and the outburst flood eroded a ∼30–45 km long valley floor filled with glacial diamicton and glaciofluvial deposits, which was later further incised to form terrace T 2 with a height of ∼350 m. The second dam failure occurred at ∼5 ka, producing a spillway, forming terrace T 1 with a height of ∼100 m. The vertical incision and horizontal migration rate of the knickpoint at the glacier dams were estimated as 0.02 m/yr, and 2.5 m/yr since the last deglaciation, based on the age of the terraces and distance of the knickpoints. We consider the glacial dams to be effective in impeding headward river erosion during glacial periods. This, along with rapid river headward erosion during the last interglacial period, results in two knickpoints on the longitudinal profile due to the differences in erosion resistance. The fluvial reaches corresponding to the repeated cut-and-fill processes are confined to the center of the Namche Barwa massif, suggesting that rapid rock uplift counteracted fluvial headward erosion and maintained the stability of the bedrock knickpoint. Therefore, in comparison to glacial dams, tectonic uplift is the most important component in plateau margin stabilization. • Two primary terraces have developed in the Yarlung Tsangpo Gorge since the last glacial period. • Vertical and horizontal migration rate of the knickpoint were estimated as 0.02 m/yr, and 2.5 m/yr. • Glacial dams have impeded erosion of bedrock channels, resulting in two knickpoints on the profile. • Maintaining stability of knickpoints over millions of years requires long-term continuing rock uplift. [ABSTRACT FROM AUTHOR]

Over the past decades, the cryosphere has changed significantly in High Mountain Asia (HMA), leading to multiple natural hazards such as rock–ice avalanches, glacier collapse, debris flows, landslides, and glacial lake outburst floods (GLOFs). Monitoring cryosphere change and evaluating its hydrological effects are essential for studying climate change, the hydrological cycle, water resource management, and natural disaster mitigation and prevention. However, knowledge gaps, data uncertainties, and other substantial challenges limit comprehensive research in climate–cryosphere–hydrology–hazard systems. To address this, we provide an up-to-date, comprehensive, multidisciplinary review of remote sensing techniques in cryosphere studies, demonstrating primary methodologies for delineating glaciers and measuring geodetic glacier mass balance change, glacier thickness, glacier motion or ice velocity, snow extent and water equivalent, frozen ground or frozen soil, lake ice, and glacier-related hazards. The principal results and data achievements are summarized, including URL links for available products and related data platforms. We then describe the main challenges for cryosphere monitoring using satellite-based datasets. Among these challenges, the most significant limitations in accurate data inversion from remotely sensed data are attributed to the high uncertainties and inconsistent estimations due to rough terrain, the various techniques employed, data variability across the same regions (e.g., glacier mass balance change, snow depth retrieval, and the active layer thickness of frozen ground), and poor-quality optical images due to cloudy weather. The paucity of ground observations and validations with few long-term, continuous datasets also limits the utilization of satellite-based cryosphere studies and large-scale hydrological models. Lastly, we address potential breakthroughs in future studies, i.e., (1) outlining debris-covered glacier margins explicitly involving glacier areas in rough mountain shadows, (2) developing highly accurate snow depth retrieval methods by establishing a microwave emission model of snowpack in mountainous regions, (3) advancing techniques for subsurface complex freeze–thaw process observations from space, (4) filling knowledge gaps on scattering mechanisms varying with surface features (e.g., lake ice thickness and varying snow features on lake ice), and (5) improving and cross-verifying the data retrieval accuracy by combining different remote sensing techniques and physical models using machine learning methods and assimilation of multiple high-temporal-resolution datasets from multiple platforms. This comprehensive, multidisciplinary review highlights cryospheric studies incorporating spaceborne observations and hydrological models from diversified techniques/methodologies (e.g., multi-spectral optical data with thermal bands, SAR, InSAR, passive microwave, and altimetry), providing a valuable reference for what scientists have achieved in cryosphere change research and its hydrological effects on the Third Pole. [ABSTRACT FROM AUTHOR]

High‐resolution present‐day earth surface deformation maps from satellites provide important data constraints, which help us better understand tectonic processes and analyze seismic hazards. Here, we use Sentinel‐1 Radar images (2014–2020) and accurate positioning measurements (2009–2019) to get a high‐resolution three‐dimensional earth surface velocity map for the northeastern Tibetan Plateau, and we invert the slip rate and coupling ratio of major regional faults. We find ∼4 mm/yr uplift along an arc from the Qilianshan to Lajishan, relative to the neighboring low‐elevation area to the east, which indicates ongoing rapid orogeny. We find transient deformation along the Laohushan and 1920 M8.5 Haiyuan rupture segments of the Haiyuan fault, whereas the western Haiyuan, southern Liupanshan, central Lajishan and central‐western West Qinling faults are essentially locked above 15–20 km, suggesting a potentially high seismic hazard. Plain Language Summary: The northeast Tibetan Plateau, which is impeded by the tectonically stable Ordos block, continues to grow in response to the far‐field India‐Eurasia collision. This region has several large‐scale active faults that hosted some destructive earthquakes in the last 100 years. Although intensively studied, the fault kinematics of those seismogenic faults are still not clear, mainly because of poor observational constraints. Hence, high‐resolution present‐day deformation maps are essential to answering this question, either of scientific or societal concern. We provide satellite‐based ground deformation rate maps with mm‐accuracy for this region. They show shallow fault creep along some segments of the Haiyuan fault which is better constrained than previous results, active tectonic uplift in the Lajishan. Our work gives new constraints for the seismic hazard for the Northeastern Tibetan Plateau case. Key Points: We derive a new high‐resolution three‐dimensional present‐day deformation map for the Northeastern Tibetan PlateauGeodetic data reveals ongoing rapid uplift along an accurate orogenic belt from the eastern Qilianshan and LajishanNew constraints for the seismic hazard analysis for the Northeastern Tibetan Plateau [ABSTRACT FROM AUTHOR]

Maritime glaciers in the southeastern Tibetan Plateau (TP) have experienced important changes in mass and dynamics over the past decades, challenging the regional water supply and glacier-related hazards. However, knowledge about long-term variations in the surface velocity and mass balance of maritime glaciers remains incomplete due to the lack of representative observations in the southeastern TP. In this study, offset tracking is employed to measure spatiotemporal variation in the surface velocity of the Hailuogou Glacier (HLG) in Mount Gongga of the southeastern TP using Sentinel-1A imagery, while the time series of the HLG mass balance is reconstructed since 1950 by a physically based energy–mass balance model. Our satellite-based results find that HLG surface velocity shows significant spatial heterogeneity with a double-peak pattern along the flow line, and sustained slowdown below the icefall zone has been observed during the past nearly 40 years, although the icefall zone and the area above it have become relatively active. Our modeling indicates a persistent increase in mass loss over the last seven decades with an average rate of −0.58 m water equivalent (w.e.) year−1, which has accelerated in the past two decades. Sustained slowdown on the glacier is concomitant with pronounced negative mass balance, thereby enhancing glacier wastage in recent decades. The long-term trend in HLG mass loss is mainly driven by an increase in positive air temperature that decreases surface albedo and solid precipitation ratio and increases longwave incoming radiation, besides the influence of supraglacial debris cover. Large-scale atmospheric circulation patterns in the Eurasian region provide important implications for regional-to-local climate variability, unsustainably intensifying the trend of the negative mass balance of the HLG in the southeastern TP in the past two decades. [ABSTRACT FROM AUTHOR]

Glaciers play a vital role in the Asian mountain water towers and have significant downstream impacts on domestic, agricultural, and industrial water usage. The rate of glacier mass loss in the Southeastern Tibetan Plateau (SETP) is among the highest in Asia and has intensified in recent decades. However, a comprehensive quantification that considers both spatial and temporal aspects of glacier mass loss across the entire SETP is still insufficient. This study aimed to address this gap by utilizing geodetic datasets specific to each glacier by calibrating the Open Global Glacier Model (OGGM) driven by HAR v2 and reconstructing the glacier mass balance of 7756 glaciers in the SETP from 1980 to 2019 while examining their spatial variability. The findings reveal that the average mass balance during this period was −0.50 ± 0.28 m w.e. a−1, with an accelerated loss observed in the 2000s (average: 0.62 ± 0.24 m w.e. a−1). Notably, central glaciers in the SETP exhibited relatively smaller mass loss, indicating a gradient effect of increased loss from the central region toward the eastern and western sides. By the end of this century, the area, length, and volume of glaciers in the entire SETP region are projected to decrease by 83.57 ± 4.91%, 90.25 ± 4.23%, and 88.04 ± 4.52%, respectively. Moreover, the SETP glacier melt runoff is estimated to decrease by 62.63 ± 6.16% toward the end of the century, with the "peak water" point of glacier melt runoff predicted to occur in 2023 under the SSP585 scenario. Sensitivity experiments demonstrated that the SETP glaciers are more than three times more sensitive to temperature changes than to precipitation variations, and the observed decrease in monsoon precipitation indicates the weakening magnitude of the Indian summer monsoon in recent years. The spatially refined and high-temporal-resolution characteristics of glacier mass loss presented in this study contribute to a better understanding of specific glacier changes in the SETP. Additionally, the prediction results provide valuable references for future water resources management and policy formulation in the SETP region. [ABSTRACT FROM AUTHOR]

• New sedimentary evidences of high-magnitude floods in the Purlung Tsangpo basin. • Reconstruct the paleo-discharge of 37,000 m3/s, possibly resulting from outburst flood. • The Paleo-flood event occurred 2.2–2.6 cal kyr BP, following Holocene climate transition. Catastrophic flood events are the most devastating natural hazard in the world, and direct human observation or instrumental/systematic measurement cannot capture the full range of their frequency-magnitudes. It is essential to reconstruct large-magnitude, rare floods that are recorded in landforms and sediments. Recently, palaeohydrology studies associated with Holocene palaeofloods in Himalayan rivers have been gaining attention. Exceptional Holocene outburst floods have been invoked as a highly efficient erosion agent contributing to the rapid incision of the Tsangpo Gorge. Despite its significance, palaeoflood records upstream of Tsangpo Gorge have rarely been explored. This study presents a series of flood deposits consisting of laminated silt and sand or repeated cross-bedding sets, which points to high-magnitude flood. Inverse hydraulic modelling of the step-backwater method based on HEC-RAS software was applied to acquire the water surface profile under varying peak discharge scenarios. The discharges of palaeofloods were estimated by relating elevations of flood features to water surface profiles calculated for the reach. The result provides a minimum estimate of the peak discharge of approximately 3.70 × 104 m3/s with a maximal depth of up to 47 m. The overestimation of the peak discharge due to post-event channel incision is up to 3000 m3/s. Seven charcoal 14C dates give a narrow age range between 2.2 and 2.6 ka cal BP. This flood occurred only a few hundred years after a period of climate transition at ∼ 3 ka BP, which was prone to hydrological extremes. Since the reconstructed palaeodischarge is significantly beyond the scope of either rainfall floods or glacial lake outburst floods, it can be inferred that the breaching of an upstream landslide dam is the most reasonable origin. [ABSTRACT FROM AUTHOR]

Investigating the response of landslide activity to climate change is crucial for understanding the disastrous effects of climate change on high mountains. However, the lack of long-term, spatial-temporal consistent measurement of landslide activity prohibits the study of this relationship. In this work, we used two methods to derive the time series of a landslide's deformation and study its relationship with precipitation in the northeastern Tibetan Plateau. The small baseline subset-interferometric synthetic aperture radar (SBAS-InSAR) method with Sentinel-1A images is first applied to derive time series of the landslide's deformation from 2020 to 2021. A recently developed method to derive cumulative deformations of optical images was used with Landsat 5 and Sentinel-2 images to derive the long-term deformation time series from 1986 to 2023. Centimeter-scale deformations detected by using the InSAR method are mainly located in the upper and eastern parts of the landslide, whereas meter-scale deformations detected by using the optical method are in the middle of the landslide. Time-series results from both methods show that intra-annual initiations of the landslide's deformation occurred in rainy months (from July to October). Although there seems to be no direct relations between inter-annual deformations and precipitation, significant displacements since 2020 occurred after exceptionally wet years from 2018 (with a record-breaking precipitation year in 2020). With optical images, we found that the maximum cumulative deformation of the landslide has been >35 m since 1986 with major deformations (>20 m) found after 2020, which may indicate an imminent risk to the Lijie town near the toe of the landslide. With climate change, increased precipitation is expected in future, which may trigger more similar landslides in the vicinity of this region. This work demonstrates an executable framework to assess landslide hazard risk under climate change. [ABSTRACT FROM AUTHOR]

This study examines the Zhama ancient landslide, one of several large-scale ancient landslides with complex formation mechanisms and significant reactivation trends found in the Batang Fault zone of the eastern Tibetan Plateau. The Zhama landslide, located in Deda Township, Batang County, Sichuan Province, has a dustpan shape with dimensions of 1750 m in length, 710 m in width, and a height difference of 1000 m. Based on unmanned aerial vehicle light detection and ranging (UAV LiDAR), small baseline subset interferometric synthetic aperture radar (SBAS-InSAR), optical remote sensing interpretation, field investigation, geophysical prospecting, and drilling, the study identifies two-level sliding zones, which were found at 31.4–33.4 m and 77.7–81 m in drill hole ZK1 and at 46.6–47.6 m and 80.4–93.8 m in drill hole ZK2. The volume of the landslide is estimated to be approximately 2.5 × 107–3.1 × 107 m3. The Zhama landslide is divided into the landslide zone of depletion (I) and the landslide zone of accumulation (II), which can be further divided into the central local stability zone (II1) and the foot edge strong deformation zone (II2, II3). The surface deformation rate of the strong deformation zone (II2) at the foot edge of the Zhama ancient landslide is approximately − 65.8 mm/a. The reactivation of the landslide is influenced by heavy rainfall, earthquakes, fault activities, river erosion, and loading on the head edge of the landslide. Numerical simulations suggest that under heavy rain and seismic activities conditions, the head edge of the landslide deforms greatly, causing the middle and front slope to push and form a push-type landslide. Overall, this study sheds light on the development characteristics and reactivation mechanism of the Zhama ancient landslide, providing valuable insights into the hazards posed by large-scale ancient landslides in the Batang Fault zone. [ABSTRACT FROM AUTHOR]

With global warming, changes in glaciers and glacial lakes on the Tibetan Plateau call for a serious inspection. The Southeastern Tibetan Plateau (SETP) is a typical monsoonal marine glacier area that is extremely vulnerable to climate change. It is affected by both humid and warm Indian Ocean currents. Outlines of glaciers and glacial lakes in SETP have been extracted from Landsat satellite images with an automatic extraction method based on image compositing with Google Earth Engine and Random Forest algorithm. Alongside the outlines, meteorological data have been collected from 1990 to 2021. The results show that since 1990 the glacier area of SETP has retreated by about 2165.33 km2 (~25.28%), the glacial lake area has increased by about 36.41 km2 (~21.45%), and their number has increased by 477 (~27.32%). The reliability and scientific validity of this study is proven by comparison with existing glacier inventories. By analyzing the meteorological data, the inverse correlation between the glacier area and temperature has been found. Despite decreases in cumulative precipitation, the glacial lake level rise and consequent area expansion have been observed. A fitting equation for the response pattern of glacier changes to temperature and precipitation change is presented and will provide a basis for future studies. [ABSTRACT FROM AUTHOR]

This paper aims to introduce a numerical technique for forecasting the hazard caused by the disaster chain of landslide blocking river-dam breach floods through an integration of the distinct element method (DEM) and a well-balanced finite volume type shallow water model (SFLOW). A toppling slope in a reservoir area, the southeastern Tibetan Plateau, was chosen for the study. Creep has been observed in the potential instability area, and a possible sliding surface was identified based on the data collected from adits and boreholes. Catastrophic rock avalanches may be triggered after reservoir impoundment, and the associated landslide disaster chain needed to be predicted. First, the landslide blocking river process was modeled by the DEM using the three-dimensional particle flow code (PFC 3D). The landslide duration, runout distance, and kinematic characteristics were obtained. In addition, the landslide dam and barrier lake were constructed. Then, the cascading dam breach flood propagation was simulated using the self-developed SFLOW. The flow velocity, inundation depth, and area were obtained. The hazard maps derived from the combined numerical technique provided a quantitative reference for risk mitigation. The influences of two involved parameters on the final hazard-affected area are discussed herein. It is expected that the presented model will be applied in more prediction cases. [ABSTRACT FROM AUTHOR]

Debris-covered glaciers are a common feature of the mountain cryosphere in the southeastern Tibetan Plateau. A better understanding of these glaciers is necessary to reduce the uncertainties in regional water resource variability and to anticipate potential cryospheric risks. In this study, we quantified the seasonal thinning and surface mass balance patterns of two neighbouring debris-covered glaciers (23K Glacier and 24K Glacier) in the southeastern Tibetan Plateau with four unpiloted aerial vehicle surveys and in situ measurements. We observed that the thinning of 23K Glacier was ∼2 –7 times greater than that of the 24K Glacier for annual and cold periods. The surface velocity of the 24K Glacier is higher than that of the 23K Glacier (∼5 –6 times) for all periods. In contrast with the thinning patterns, the surface mass balance patterns of the two glaciers closely agree across the different periods. We found that the surface mass balance distribution strongly correlated with the spatial distribution of debris thickness for both glaciers. Ice cliffs and supraglacial ponds are prevalent on the surface of these glaciers (∼4.4 – 7.2±0.5 %) and enhance melt overall (enhancement factor: ∼2.5) but do not control the surface mass balance pattern of either glacier. This comparison study of two neighbouring glaciers confirms the significance of both glacier dynamics and debris thickness in controlling thinning and melt for the different debris-covered glaciers of the southeastern Tibetan Plateau in the context of climate change. [ABSTRACT FROM AUTHOR]

The Tibetan Plateau and its surroundings have recently experienced several catastrophic glacier-related disasters. It is of great scientific and practical significance to establish ground-based early warning systems (EWSs) to understand the processes and mechanisms of glacial disasters and warn against potential threats to downstream settlements and infrastructure. However, there are few sophisticated EWSs on the Tibetan Plateau. With the support of the Second Tibetan Plateau Scientific Expedition and Research Program (STPSER), an EWS was developed and implemented in the Sedongpu Valley, southeastern Tibetan Plateau, where repeated river blockages have occurred due to ice/rock collapse debris flow. The EWS collected datasets of optical/thermal videos/photos, geophone waveforms, water levels, and meteorological variables in this sparsely populated zone. It has successfully warned against three ice-rock collapse–debris flow–river blockage chain events, and seven small-scale ice-rock collapse–debris flow events. Meanwhile, it was found that the low-cost geophone can effectively indicate the occurrence and magnitude of ice/rock collapses by local thresholds, and water level observation is an efficient way to warn of river blockages. Our observations showed that there were no immediate meteorological triggers for the ice-rock collapses and associated debris flows. Several factors, such as the volume and location of the collapses and the percentage of ice content involved, influence the velocities of debris flows and the magnitude of river blockages. There are still two possible glaciers in the study area that are at risk of ice collapse. It is worth monitoring their dynamic changes using high-resolution satellite data and the ground-based EWS to safeguard the surrounding hydrological projects and infrastructure in this transboundary region. [ABSTRACT FROM AUTHOR]

In this paper, we analyze the Holocene record of extreme flood events in the upper Minjiang River valley of the eastern Tibetan Plateau, China. Slackwater deposits (SWDs), the fine-grained sediments of palaeofloods, were identified within debris flow deposits at a tributary mouth and in channel expansions along the bedrock gorge. Eight palaeoflood SWDs were dated to between 6.0 ± 0.9 ka and 4.6 ± 0.9 ka using optically-stimulated luminescence analysis in combination with the minimum age model and represent at least two phases of palaeoflood events. The palaeoflood history in the upper Minjiang River Valley is consistent with the record of the mid-Holocene flood events in the mainstream of the Yangtze River. These mid-Holocene extreme flood events were closely related to strong ENSO activity and variability of the monsoon climate in the eastern Tibetan Plateau. In our study area, minimum palaeoflood discharges were estimated as 6500–7800 m3/s by the step-backwater method. These estimated discharges are less than the values inferred for the outburst flood that occurred in the upper Minjiang River Valley in 1933. Flood-inundation maps show that palaeoflood SWDs were deposited in low-velocity backwater zones. Our palaeoflood reconstructions are important for improving regional records of maximum flood and help to develop risk analysis for rare flood events. • Sedimentary characteristics of palaeoflood records in complex environment were identified. • Palaeoflood discharges were estimated to be 6500–7800 m3/s at the three study sites. • Palaeoflood results redefine the envelope curve of the regional maximum floods. • Response of mid-Holocene (6.0–4.6 ka) extreme flood events to climate variability. • Palaeoflood reconstructions help to develop risk analysis for rare flood events. [ABSTRACT FROM AUTHOR]

The topological system of lakes and streams is the basis for deriving a multitude of patterns and processes in hydrology, geomorphology and ecology. Flow direction is key to constructing a lake‐stream topological system. However, lakes and streams are important hydrological objects that should be considered since they are linked during the process of material and energy transportation. Therefore, a flow direction algorithm that can clearly express the topological relationship of lakes and streams, was proposed here. Lakes and streams were taken as the hydrological objects in stream networks and coupled into a flow direction algorithm. A topological system was established based on the proposed algorithms. Six areas on the Tibetan Plateau were chosen as sample areas with the MERIT digital elevation model (DEM) as the DEM data source. Streams derived from flow direction data in the HydroSHEDS data set (HYDROSTREAMS) and MERIT hydro data set (MERITSTREAMS), as well as streams derived from flow direction results of the D‐infinity algorithm and priority‐flood algorithm were compared with streams derived from the proposed algorithm. The topological relationship between streams and lakes was clearly expressed by the proposed algorithm. In lake areas, the proposed algorithm showed better performance, and no parallel streams were found. In nonlake areas, the stream networks derived from these algorithms were stable. The proposed algorithm offers an opportunity to treat lakes and streams differently during simulation, thus adding to the authenticity of the simulation. Key Points: A novel flow direction algorithm considering the characteristics of lake‐stream is proposed to construct a lake‐stream topological systemThe proposed flow direction model exhibits good robustness, considering the errors in lake areas in digital elevation modelsThe constructed lake‐stream topological system can be applied in both endorheic and exorheic basins worldwide [ABSTRACT FROM AUTHOR]

Deglaciation has intensified in alpine regions with climate warming, causing increasingly intense paraglacial debris flows (PDFs). Examining the hydromechanical mechanism and initiation of PDFs is essential to disaster relief in downstream areas. However, the establishment of source initiation of PDFs and early warning criteria are hampered by a lack of in situ observations of PDFs; therefore, providing a PDF early warning is still challenging. In this study, on the basis of long-time series field monitoring of rainfall, temperature, soil moisture, and surface displacement in the Tianmo gully, southeast of the Tibetan Plateau, the initiation mechanism of PDFs and the evolutions of the effective saturation, matrix suction, and suction stress were analyzed by combining the hydromechanical coupling analysis method of a slope for a long-term sequence. The measured evidence for the formation and evolution process of slope stability in PDF source area was provided under the conditions of precipitation and ablation. Furthermore, through the inversion of the key slope stability parameters, the thresholds of the hydraulic factors for the provenance slope failure were established, which could be used for early warning of PDFs. This study provides theoretical reference and long-time field data for monitoring and early warning of PDFs in paraglacial hazard-prone areas under global warming sequences. [ABSTRACT FROM AUTHOR]

Tectonic uplift and climate changes are the two critical factors controlling the evolution of river landscapes and the formation of terraces. However, little is known about the effect of river blockage events on terrace formation along valley areas. In this paper, we investigated the geomorphology, sedimentology, and chronology of Tuanjie (seven staircases) and Taiping (three staircases) Terraces in Diexi. These represent two typical fluvial terraces in the upper Minjiang River in the eastern Tibetan Plateau. These terraces are composed, from bottom to top, of lacustrine deposits, gravels, loess, and paleosol. Taiping Terrace 3 (T3) has two sets of mud-phyllite clasts sequences. Field investigation, Digital Elevation Model (DEM) data, lithofacies, and dating results confirm that terraces T1 to T3 in Taiping correspond to terraces T5 to T7 in Tuanjie. These findings suggest that two damming and four outburst events occurred in the area during the late Pleistocene. The palaeo-dam blocked the river around 32.40±1.91 ka, followed by the first outburst at 27.11±0.18 ka. Then, the palaeo-dam blocked the river again between 27 to 17 ka, and suffered a second dam-breaking event at 17 ka. The third and fourth gradual collapse events respectively occurred at ~10 ka and ~9.35 ka. Combined with the tectonic uplift rate, river incision rate, and high-resolution climate data, our analysis shows that the blockage and collapse of the palaeo-dam have been a major factor in the formation of tectonically active mountainous river terraces. Tectonic movement and climatic fluctuations, on the other end, play a minor role. [ABSTRACT FROM AUTHOR]

Landslide dams, especially long-term stable landslide dams, have been recognized as important contributors to regional geomorphological evolution. Here, the Diexi area, a long-term stable dam-prone area located in upstream of the Minjiang River on the eastern Tibetan Plateau, was adopted to reveal reasons that landslide dams are concentrated in this area and maintain long-term stability via detailed field investigations, landslide dam sampling, unmanned aerial vehicle (UAV) images, and digital surface models (DSM). The results show the controlling factors that the slopes are prone to sliding and rock mass structure deterioration including lithological combination mode, slope structure, topographic conditions, a series of NNE-trending radial fissures and hydrological conditions. Fault activities, which have caused many earthquakes, are the main inducing factor. Landslide dams are prone to occurrence in the Diexi area owing to the combined effect of the narrow channels, the large landslide dam volume and the rock fragments. The river flow, and the landslide dam volume, material, structure, and parameters control the stability of landslide dams. The landslide dam consists of various sizes of boulders and all landslide dams exhibit an obvious inverse grading sequence, and this size combination could consume most of the flow energy, and consequently protect the dam from incision. Additionally, a total of seven knickpoints were formed by landslide dams, and the longitudinal gradient upstream of every landslide dam was found to decrease by the action of knickpoint. In the eastern margin of the Tibetan Plateau, there are numerous landslide dams existed for hundreds or thousands of years. Studies on the long-term stable landslide dams in the Diexi area could provide experience for studying similar kinds of landslide dams in this region. [ABSTRACT FROM AUTHOR]

On the southeastern Tibetan Plateau, an area widely covered by alpine glaciers, two types of debris flow generally occur: glacier-related debris flows (GDFs) and rainfall-related debris flows (RDFs). It is widely accepted that topographic conditions influence debris flow activities; however, few studies have examined the differences between such influence on GDFs and RDFs. This study investigated the GDFs and RDFs in the periglacial area of the Parlung Tsangpo Basin, and calculated 12 geomorphic indexes to reveal the topographic features associated with these two types of debris flow. It was found that lower values in the drainage area, main channel length, and relative elevation occurred in RDFs compared to the GDFs. In contrast, higher values in the channel gradient, relief ratio, and effective basin area appeared in RDFs. The discrepancy is mainly related to the different topographic and geomorphic shaping of modern glaciers. According to its geomorphological characteristics, the Parlung Tsangpo Basin can be divided into the upper V-shaped canyon section, middle wide valley section, and lower steep canyon section. The scale and frequency of debris flow in the upstream canyon region are substantially lower than those in the downstream. Moreover, the frequency and scale of RDFs are considerably different from those of GDFs, primarily because of the different geomorphic evolutionary stages of debris flow gullies in different regions. [ABSTRACT FROM AUTHOR]

Permafrost degradation increases the likelihood of glacial lake outburst floods on the Tibetan Plateau. Analyses of the freeze–thaw conditions in moraine dams and associated impacts on dam stability contribute toward reducing natural hazard risks. We used the heat transfer module of COMSOL Multiphysics to simulate the soil temperature field in the Longbasaba moraine dam, which is on the northern slope of central Himalaya. There is close agreement between the simulated and observed soil temperature values. Root mean squared errors (the square root of the mean of the square of all of the error) are below 1.30°C and mean bias errors vary from −0.10 to −0.52°C for the different soil layers. Between 1959 and 2020, active layer thickness increased at a mean annual rate of 0.024 m a−1. Under the Coupled Model Intercomparison Project Phase 6 scenarios, the buried ice inside the moraine dam is clearly melting. The maximum‐buried ice thaw depth is currently 3.4 m and at the end of the 21st century is projected to be 9.53, 16.69, and 21.83 m under SSP1‐2.6, SSP2‐4.5, and SSP5‐8.5, which indicates a continuous decrease in moraine dam stability. Plain Language Summary: Glacial Lake Outburst Floods have frequently occurred on the Tibetan Plateau in recent years and have caused many casualties and substantial property damage. Longbasaba lake is located at the end of Longbasaba glacier and is dammed by a terminal moraine complex. We used the heat transfer module of COMSOL Multiphysics simulation software to simulate the freeze–thaw process and melting of buried ice inside the Longbasaba moraine dam between 1959 and 2100 and examined dam stability. The maximum thawing depth of the dam in summer has increased over the past decades and buried ice has been melting since the mid‐1970s. Under future warming scenarios, the depth of melting inside the dam is projected to exceed the depth of freezing and the melting rate of buried ice will accelerate. This indicates that seepage and piping will increase and dam stability will continue to decrease. We must remain alert about the possibility of future dam failure. Key Points: Soil temperatures at different depths of the Longbasaba moraine dam were well simulated by COMSOL Multiphysics softwareBetween 1959 and 2020, annual active layer depth increased at a mean rate of 0.024 m a−1Under Coupled Model Intercomparison Project Phase 6 scenarios, melting of buried ice is projected to accelerate and reduce dam stability [ABSTRACT FROM AUTHOR]

Due to the heterogeneous terrains and unique alpine climate environment, the three‐dimensional differentiation of climatic impacts on vegetation change and its possible mechanism in the Pan‐Tibetan Plateau (PTP) are complex and lack adequate research. Hence, we here quantify the three‐dimensional differentiation of the contribution of climatic factors to vegetation change using the analysis of variance (ANOVA) method. Results indicate that the overall PTP has been warmer and wetter but partially drier, with a remarkable fractional vegetation coverage (FVC) increase since 2000. Moreover, the total areas with FVC changes accounting for approximately 49.3% of PTP are significantly driven by climate factors. Precipitation and potential evaporation predominate the vegetation change at relatively high altitudes and latitudes, while temperature affects the vegetation change at relatively low latitudes and parts of low elevations. Meanwhile, relative humidity dominates the vegetation change at middle altitudes and latitudes. Furthermore, the hydrothermal conditions and climate change magnitudes modulate the three‐dimensional differentiation. On the one hand, the effects of heat conditions on FVC change overwhelm the moisture conditions in alpine areas or warm and wet regions, in sharp contrast with the dominant role of water conditions in most dry areas. On the other hand, the spatial heterogeneity in climate change magnitudes influences the contribution of climatic factors in most hydrothermal conditions. Additionally, interventions challenging to quantify, such as climatic and mountainous hazards, anthropogenic activities, and vegetation feedback, will lead to the differentiation's uncertainties. Our research hopefully provides theoretical support for national ecosystem management and major construction projects across PTP. Plain Language Summary: The eco‐environmental change under the warming and humidification of the PTP, one of the most complex terrains and sensitive areas to global warming, has attracted widespread attention. The spatial distribution of vegetation response to climate change is uneven. However, attention paid to the mechanism behind spatial differentiation is insufficient. Therefore, we here develop a strategy to quantify the relative contribution of climatic factors affecting vegetation change. We disclose the overall greening as a result of the warming and wetting in PTP and propose that the relative contributions of climatic factors to vegetation change vary with latitude, longitude, and altitude. Unlike most existing research, we further explore the cause of the differentiation and attribute it to the different hydrothermal conditions and climate change magnitudes. Moreover, we detect the factors (i.e., climatic and mountainous hazards, human activities interferences, and vegetation feedback) possibly causing the uncertainties of the differentiation, shedding light on the mechanisms of vegetation response to climate change in PTP. Our research will provide theoretical support for modeling the coupling between climate change and terrestrial ecosystems, serving for regional ecological protection and major infrastructure construction. Key Points: The contributions of climatic factors to vegetation change have three‐dimensional differentiation in the Pan‐Tibetan PlateauHydrothermal conditions and climate change magnitudes modulate the differentiation of the climatic impactsInterventions, such as hazards, anthropogenic activities, and vegetation feedback, will lead to the differentiation's uncertainties [ABSTRACT FROM AUTHOR]

Glaciers across the Kashmir Himalayan region are melting at an accelerated pace compared to other regions across the Himalayan arc. This study analyzed the recession patterns of nine glaciers in the Kashmir Himalaya region over 28 years between 1992 and 2020 using satellite images and field measurements. The recession patterns were correlated with debris cover, topographic factors, and ambient black carbon (BC) concentration at glacier sites. HYSPLIT model was used to track the air mass sources at a 7-day time-step from September 1, 2014, to September 28, 2014, over the selected region. All nine glaciers revealed high recession as indicated by changes in the area (average recession: 20.8%) and snout position (~ 14 m a−1). The relative percentage of debris on each glacier varied between ~ 0% (clean glacier) and 43%. Although the investigated glaciers lie in the same climatological regime, their topographical behavior is dissimilar with mean altitude ranging between 4000 and ~ 4700 m asl and the average slope varying from 17 to 24°. All the investigated glaciers are north-facing except G3 (southerly aspect). Our results indicate anomalously high ambient BC concentrations, ranging from 500 to 1364 ng m−3, at the glacier sites, higher than previously studied for glaciers in the Himalayas and neighboring Tibetan Plateau. The backward air-mass trajectory modeling indicated both local and global sources of particulate matter in the study area. A comparative analysis of BC measurements and glacier recession with the studies conducted across high Asia indicated the influence of BC in accelerating the melting of glaciers in the Kashmir region. [ABSTRACT FROM AUTHOR]

Massive slope failures often occur along the Himalayan orogenic belt, where the Indian plate subducts beneath the Eurasian plate. On March 22, 2021, a slope failure hazard occurred at the Grand Canyon section of the Yarlung Tsangpo River, eastern Himalayan syntaxis, and blocked the river leading to a water level rise of over 10 m. We conducted an analysis of the seismic waveforms recorded by broadband seismic stations which we deployed around the Grand Canyon. These seismograms showed emergent onsets with a total duration of approximately 300 s and corroborated their origination as a glacier collapse along the remote Sedongpu basin. Based on direct measurements of seismic energy and an empirical distance attenuation function, we estimated the volume to be approximately 50 × 106 m3. The source process was interpreted as a single force with three possible stages: progressive coherent block fracturing, mass flow through the Sedongpu basin with downslope acceleration-deceleration-stable motions, and continuous flow along the river after the formation of a temporary dam at the outlet basin. [ABSTRACT FROM AUTHOR]

Glacial detachment is a newly emerged glacial hazard type, and more than 20 cases have been identified worldwide. The Xiao Ma Glacier in the Amney Machen Mountains, northeastern Tibetan Plateau, experienced an intensive detachment of the terminal low-slope glacier in 2004, forming a large dammed lake downstream and burying 2.27 km2 of grassland. An advanced multi-phase r.avaflow model was used to simulate this glacier detachment event to reconstruct its slide mechanism and dynamic process. In total, 9.77 × 106 m3 mass detached were categorized into three different phases according to their properties: the old ice remaining in the middle layer following the 1988–1997 glacier surge (47% of total volume), new ice in the upper layer originating from the 2003–2004 surge, which directly caused the 2004 detachment (48%), and subglacial water trapped in the bedrock (5%). The modeling results showed that the glacier detachment–induced debris flow reached a peak discharge of 0.25 × 106 m3/s at 40 s at the mouth of the Xiao Ma Valley, and the entire propagation process was completed within 140 s. The initially trapped meltwater dominated the debris flow state, with a maximum velocity of 103 m/s. The underlying old glacial ice was pushed and deposited to the front of the fan, and the new ice in the upper layer was primarily deposited over the middle fan. Additionally, several important parameters in the r.avaflow model were recommended for the optimal interval of values via optimality analysis, and the potential of the model to be extensively applied for large-scale risk assessment was discussed under relatively simple settings. The modeling of the 2004 Amney Machen glacier detachment has resulted in a comprehensive understanding of the dynamic processes of such events, which is significant for future glacier disaster simulation and assessment thereby improving regional strategies in hazard early warning, prevention, and mitigation. [ABSTRACT FROM AUTHOR]

The existence of glacial lakes in the southeastern Tibetan Plateau (SETP) is a potential hazard to downstream regions, as the outburst of such lakes has the potential to result in disastrous glacial lake outburst floods (GLOFs). In the present study, we conducted a comprehensive investigation of Bienong Co, a moraine-dammed glacial lake in the SETP. First, the lake basin morphology was determined, and the lake volume was estimated, showing that the maximum lake depth is ∼181 m and the lake volume is ∼102.3×106 m 3. These scenarios included the possibility of GLOFs being triggered by ice avalanches (Scenarios A1–3) from the mother glacier or by landslides from the lateral moraines (Scenarios B1–3 and C1–3). Avalanche volumes of the nine trigger scenarios were obtained from the Rapid Mass Movement Simulation (RAMMS) modeling results. Next, the Basic Simulation Environment for Computation of Environmental Flow and Natural Hazard Simulation (BASEMENT) model was used to simulate the generation and propagation of the avalanche-induced displacement waves in the lake. With the model, the overtopping flows and erosion on the moraine dam and the subsequent downstream floods were also simulated. The results indicate that the ice avalanche scenario may cause the largest mass volume entering the lake, resulting in a displacement wave up to 25.2 m in amplitude (Scenario A3) near the moraine dam. Landslide scenarios with smaller volumes entering the lake result in smaller displacement waves. Scenarios A1, A2, and A3 result in released water volumes from the lake of 24.1×106 , 25.3×106 , and 26.4×106 m 3 , respectively. Corresponding peak discharges at the moraine dam are 4996, 7817, and 13 078 m 3 s -1 , respectively. These high discharges cause erosion of the moraine dam, resulting in breach widths of 295, 339, and 368 m, respectively, with the generally similar breach depth of approximately 19 m. In landslide scenarios, only overtopping flows generated by Scenarios B3 and C3 cause erosion on the moraine dam, with breach depths of 6.5 and 7.9 m and breach widths of 153 and 169 m, respectively. According to our simulations, GLOFs generated by Scenarios A1–3 all flow through 18 settlements downstream in 20 h, threatening more than half of them. Both Scenarios B3 and C3 produce GLOFs that flow through the first eight settlements downstream in 20 h and have a relatively small impact on them. Comparisons of the area, depth, and volume of glacial lakes for which the bathymetry data are available show that Bienong Co is the deepest known glacial lake with the same surface area on the Tibetan Plateau. This study could provide a new insight into moraine-dammed glacial lakes in the SETP and be a valuable reference for GLOF disaster prevention for the local government. [ABSTRACT FROM AUTHOR]

As the Third Pole of the Earth and the Water Tower of Asia, the Tibetan Plateau (TP) nurtures large numbers of glacial lakes, which are sensitive to global climate change. These lakes modulate the freshwater ecosystem in the region but concurrently pose severe threats to the valley population by means of sudden glacial lake outbursts and consequent floods (GLOFs). The lack of high-resolution multi-temporal inventory of glacial lakes in TP hampers a better understanding and prediction of the future trend and risk of glacial lakes. Here, we created a multi-temporal inventory of glacial lakes in TP using a 30-year record of 42,833 satellite images (1990–2019), and we discussed their characteristics and spatio-temporal evolution over the years. Results showed that their number and area had increased by 3285 and 258.82 km2 in the last 3 decades, respectively. We noticed that different regions of the TP exhibited varying change rates in glacial lake size; most regions show a trend of expansion and increase in glacial lakes, while some regions show a trend of decreasing such as the western Pamir and the eastern Hindu Kush. The mapping uncertainty is about 17.5%, which is lower than other available datasets, thus making our inventory reliable for the spatio-temporal evolution analysis of glacial lakes in the TP. Our lake inventory data are publicly published, it can help to study climate change–glacier–glacial lake–GLOF interactions in the Third Pole and serve as input to various hydro-climatic studies. [ABSTRACT FROM AUTHOR]

In the past 20 years, Lebai gully (Linzhi, Tibet, China) has been affected by several debris flow events. These debris flow events caused the blockage of three-quarters of the river channel at the mouth of the Lebai gully, threatening thousands of acres of cultivated land, houses, and residents' property in the upper reaches of the Yarlung Tsangpo River. However, few investigations have been carried out on the debris flows in the Lebai gully, and the triggering mechanism of Lebai debris flows remains elusive. In this paper, we presented a detailed demonstration of the geological environment and geomorphological features of the Lebai Basin, and a detailed geohazard history of the Lebai gully was collected and presented based on interviews with local villagers. To provide information on the lithological, hydrological, and geotechnical characteristics of the terrain in Lebai gully, the electrical resistivity tomography (ERT) method was carried out to research the subsurface characteristics of debris flow fans. The ERT results illustrated the two-layered vertical strata of the debris fan, and the shallow layer of relatively low resistivity, which has thicknesses of 5–18 m, could be described as Quaternary colluvial deposits, while the deep layer of relatively high resistivity could be considered Precambrian bedrock. Taking a relatively large-scale debris flow on August 20, 2003, as an example, a detailed discussion was carried out on the possible factors triggering this event, and it was found that the Lebai debris flows were closely related to pre-event rainfall, air temperature, and antecedent earthquakes. Moreover, with the intention of evaluating the future risk of river blockage and helping to make rational decisions on developing suitable mitigation measures, the unstable deposits found in field investigations were generalized to geometric models according to their geometric characteristics, and the volumes of these unstable materials in each location were estimated using digital elevation models and geometric spatial analysis methods. A dynamic model named RAMMS was used to predict these unstable materials' dynamic processes and final deposit characteristics. The simulation results revealed a great possibility that the Yarlung Tsangpo River will be blocked at the mouth of Lebai gully in the future, and it is necessary to take further mitigation measures. The research in this paper contributes to a better understanding of the debris flows in the Lebai Basin and provides meaningful and valuable information for debris flow hazard mitigation in the future. [ABSTRACT FROM AUTHOR]

Understanding how future climate change impacts glaciers is crucial to sustainable water supplies and water resource managements. A calibrated degree-day glacier mass balance model and a volume-area scaling approach were coupled to quantitatively assess the effect of future climate change on the ice volume in the Beida River catchment, Northeast Tibetan Plateau. The results show that future mean mass loss of all glaciers will reach to 0.628±0.058, 0.676±0.058 and 0.765±0.074 ×108 m3 yr−1 under RCP 2.6, 4.5 and 8.5, respectively, with 81%–96.2% ice volume losses by the end of 21st century. Future mass balance tends to be more negative until 2050 under RCP 2.6, until 2060 under RCP 4.5, and until 2100 under RCP 8.5. Glaciers in the catchment are likely experiencing or will soon experience the most intense ice loss, which may lead to negative impact on water resources after the tipping point around 2015–2035. In the RCP 8.5 scenario, the summer mass balance decreases with elevation at the altitudinal belt of 4650∼5050 m a.s.l. due to the variation of elevation structure caused by accelerating glaciers shrinkage. Further, the simulations are sensitive to the parameterization scheme of glacier area and air temperature. The projections have the potential to significantly improve our understandings of glacier regime over data-poor regions. [ABSTRACT FROM AUTHOR]

In China, flash floods are one of the main natural disasters causing loss of life and damage to infrastructure. The threat of flash floods is exacerbated with climate change and increased human activities, such that the number of disasters has shown a clear upward trend in recent years. However, due to the scarcity of instrumental data or overly short timeseries, we are still lacking critical data to understand spatio-temporal patterns and driving factors of extreme flash floods. This missing knowledge is however crucial for a proper management of these hazards, especially in remote mountain environments. In forested catchments, dendrogeomorphology allows the reconstruction of past process activity based on growth disturbances (GDs) in trees that have been affected by past flash floods. Therefore, in our study, for the first time, we reconstruct past flash floods in the Qilian Mountains, northeast Tibetan Plateau, over past centuries. To this end, we sampled 99 Qinghai spruce (Picea crassifolia) trees affected by flash floods, with a total of 194 increment cores, and identified 302 GDs induced by past flash floods. These GDs have been caused by at least 21 flash floods that we are able to reconstruct over the last 170 years. The position of GDs within tree rings and the intra-seasonal dating of past events also allowed discussion of the likely synoptic situations that may have led to the triggering of flash floods in the past. Logistic regression analysis confirms that significant correlation exists between cumulative maximum 5-day August–September precipitation and reconstructed flash floods, which is corresponding to the majority of scars and related tangential rows of traumatic resin ducts (TRDs) found in the latewood portion of growth rings. These results support the idea that abundant precipitation occurring at the end of the summer season and early fall is the key factor driving flash floods in our study area. Our research not only fills the gaps regarding historical flash flood histories in the Qilian Mountains, but also provides a scientific basis for the region's response to climate change and flood prevention and reduction. [ABSTRACT FROM AUTHOR]

Glacier lake outburst floods (GLOFs) that result from the breaching of moraine dams are typical disasters in high mountain regions of the Tibetan Plateau, which endanger vital infrastructures such as the Sichuan-Tibet Railway and Highway. Breaching can be caused by tsunami-type waves, resulting from glaciers calving and falling into impounded lakes, which overtop and destroy their natural boundaries. In this work, we develop an equation for the overtopping volume based on the simplified geometry of fluids running up an incline. Specifically, we propose that overtopping can be viewed in terms of the run-up of solitary waves impacting a structure from which relationships with the dam and wave properties can be established. This equation is tested and verified against physical experiments and numerical simulations of waves overtopping rigid, impermeable triangular structures which serve as idealized natural dams. The proposed equation is found to adequately account for the first-order dependencies of the overtopping volume on the different dam and wave properties. We extend the applicability of this analysis to erodible dams made up of glacier tills, wherein we show the basic dependence of the overtopping volume on the erodibility of the dams and flood scales. • A quantitative relationship between the runup and overtopping volume of solitary waves is newly established. • A novel overtopping equation, developed from geometric arguments, captures its dependence on the wave and dam properties. • An empirical method relating the wave and dam properties to the outburst flood volume is proposed. [ABSTRACT FROM AUTHOR]

Due to their special geographical locations and environments, plateau lakes play a key role in maintaining regional water balance, but lake water storage changes are upsetting this balance. Based on data from lakes on the Tibetan Plateau (TP), this study used the Spatial Processes in Hydrology (SPHY) model to simulate the runoff process in the Siling Co basin from 2000 to 2016 and estimated the changes in water storage of Siling Co and the contribution of each component of runoff into the lake. The results showed that the water storage capacity of Siling Co has increased by 1.2 billion m3/yr, and the lake area continues to expand; declines in precipitation have significantly reduced baseflow (BF), rainfall runoff (RR), and snow runoff (SR), while temperature increases have raised glacier runoff (GR). The simulated average runoff showed that BF, GF, RR, and SR contribute 24%, 22%, 16%, and 38%, respectively, of the flow into Siling Co. Based on hypothetical climate change scenarios and two Shared Socioeconomic Pathways (SSP1-2.6 and SSP3-7.0) from the MRI-ESM2-0 GCMs, this study estimated that a 10% increase in precipitation could lead to a 28% increase in total runoff, while a 1 °C increase in temperature could lead to a 10% decrease in runoff. The average runoff depth of the basin is expected to increase by 30–39 mm, since the temperature and precipitation may increase significantly from 2020 to 2050. The intensification of glacial melting caused by the increase in temperature continues, posing a greater challenge to many water resources management problems caused by the expansion of lakes. [ABSTRACT FROM AUTHOR]

On October 17 and 29, 2018, two rock and ice avalanches occurred on the western slope of the Sedongpu Basin upstream of the Yarlung Zangbo River in the Tibetan Plateau. Both avalanches formed the disaster chains and damaged many bridges and roads. Both avalanches on high mountain slope at an elevation of 6000 m asl above sea level triggered long-runout disaster chains, including debris flow, river blocking and flood. In this study, the disaster characteristics and dynamic process were analyzed by multitemporal satellite imagery. The results show that both of the initial sliding bodies were composed of rock and ice. Due to the large elevation difference, the initial sliding bodies rapidly descended into valley floor and immediately transformed into a debris flow after impact and fragmentation. And then, this study divided the disaster chain into four zones by satellite images and field observation, including source zone, dynamic erosion zone, deposition and damming zone, and flash flood zone. This study also carried out the numerical simulation of the disaster by RAMMS. The numerical results reproduced the dynamical process of the debris flow. Furthermore, the potential causes of disaster, evolution process, and the geohazard tendency are discussed. [ABSTRACT FROM AUTHOR]

The hydroclimatology and hydrometeorology of flooding over the Third Pole region is poorly understood, despite its societal and environmental significance. Here we examine extreme rainfall and flooding over the eastern Tibetan Plateau (TP) based on empirical analyses of long‐term, in‐situ rainfall and stream gaging observations as well as the ECMWF Reanalysis fields. We develop a flood catalog that consists of 168 extreme rainfall‐runoff floods over the eastern TP, and characterize the synoptic conditions for flood‐producing storms based on the principal component analysis. We show the transitional pattern form Asian summer monsoons to midlatitude systems as the most frequent synoptic conditions for flooding over the eastern TP. The interplay between complex terrains and moisture transport determines the contrasting flood characteristics (in terms of intensity and spatial pattern) under different synoptic environments. We carry out high‐resolution Weather Research and Forecasting modeling analysis for four flood‐producing storms over the eastern TP. We highlight the interaction of complex terrains and nocturnal low level jets as the key mesoscale ingredients in dictating a pronounced diurnal cycle of extreme rainfall over the southeastern portion of TP. Our results establish the link between large‐scale synoptic environment, mesoscale process, and regional flood hydrology over the eastern TP, and therefore contribute to improved flood risk management practices over the Third Pole region under a changing climate. Key Points: We examine meteorological floods over the eastern Tibetan Plateau based on long‐term, in‐situ stream gaging and rainfall observationsThe transitional pattern from Asian summer monsoons to midlatitude systems is the most frequent synoptic condition for floodingThe interplay between complex terrains and moisture transport dictates contrasting flood characteristics under different synoptic patterns [ABSTRACT FROM AUTHOR]

Glaciers and glacial lakes in the Bosula Mountain Range need special attention, because their instability may cause disastrous consequences to the downstream settlements and the Sichuan-Tibet Road. The latter is a pivotal traffic line in the Southeast Tibetan Plateau. In order to investigate the state of glaciers and glacial lakes in the Bosula Mountain Range, we estimated the changes in glacier/glacial lake boundaries, glacier surface elevation, and glacier flow velocity between 2000 and 2021 based on multisource remote sensing data. Our results showed that, from the period 2000–2013 to the period 2013–2021, the average shrinking rate of glacier area increased from 0.99 km2/a to 1.74 km2/a, and the average expanding rate of glacial lake area increased from 0.04 km2/a to 0.06 km2/a. From the period 1990–2011 to the period 2015–2019, the average thinning rate of glaciers increased from 0.83 m/a to 1.58 m/a. These results indicate the Bosula Mountain Range is one of the fastest melting glacierized regions in the High Mountain Asia, and the factors that account for this may include quick temperature rise, abundant summer rainfall, and thin debris cover. In spite of strong ice melting, the observed changes in glacier boundaries, surface elevation, and flow velocity show no sign of surge activity, and the frequency of glacier lake outburst has not increased since 1989. Currently, three proglacial lakes that expanded quickly during 2000–2021 are now prominent hazards. They are directly threatened by accidental ice calving and ice avalanche, and their outburst could cause considerable damage to the downstream settlements and the Sichuan-Tibet Road. [ABSTRACT FROM AUTHOR]

Profound effects of episodic megafloods (≥106 m3/s) have been observed on Earth and Mars. Quaternary megafloods sourced from valley‐blocking glaciers on the Tibetan Plateau likely play an important role in the geomorphic evolution of the Yarlung‐Tsangpo Gorge and mountain landscape of the eastern Himalaya. We use the first 2D numerical simulation of a megaflood sourced from a reconstructed 81 km3 Tibetan lake to analyze flood hydraulics and examine the erosional and depositional potential of megafloods in mountain landscapes. The simulated flood has a duration >60 hr and a peak discharge of 3.1 × 106 m3/s. We find that the extent of inundated features like terraces, narrow valley sections, tight meander bends, and overtopped ridges influences locations of observed maximum depth (370 m), speed (76 m/s), and bed shear stress (>100 kPa), creating dynamic patterns of erosive potential. Consequently, it is difficult to predict local (≤1 km) patterns of megaflood erosional potential from either unit stream power or flood power from smaller magnitude outburst floods. However, both are useful when predicting regional (≥25 km) order‐of‐magnitude shifts in megaflood flood power. Portions of the flood domain downstream of the Gorge experience lower bed shear stresses and flood power <5 kW/m2, indicating potential for significant deposition. We suggest widespread deposition of boulders within the modern channel and fine‐grained particles on hillslopes during a megaflood likely impedes subsequent erosion and affects channel width and longitudinal form throughout the flood pathway. Our findings show the legacy of megaflooding in mountainous terrain includes both extensive erosion and deposition. Plain Language Summary: Megafloods are catastrophic floods with a fast‐moving peak discharge of at least a million cubic meters (the volume of around 400 Olympic‐sized swimming pools) per second that are usually sourced from the sudden drainage of lakes formed behind unstable landslide or glacier dams. While previous scientists have studied the flow of megafloods in other, lower relief parts of the world, little is known about how these immense floods behave in steep mountainous landscapes. We simulated a megaflood in the eastern Himalaya and found that the simulated flood had a peak discharge of 3.1 million m3/s—three times higher than predicted from simple estimates using lake volume and dam height. We find that the hydraulics of this megaflood are directly related to the shape of the river valley (i.e., whether or not the water flowed over ridges and/or terraces or whether the river path took a sharp turn) and they change continuously throughout the flood. This means the patterns of removed material after a megaflood will be directly related to shape of the flooded landscape. Additionally, we predict that megafloods leave behind a lot of sand and large boulders—deposition that might impact where the modern river can erode. Key Points: 2D hydraulic simulation of a Holocene megaflood in the eastern Himalaya produces peak discharge of 3.1 × 106 m3/s and bed shear stress >100 kPaLocal megaflood erosion will reflect interactions between valley topography and flood hydraulics more than patterns of unit stream powerMegaflood boulder/sand deposits could impede later erosion by smaller flows with potential long‐term impacts on mountain landscape evolution [ABSTRACT FROM AUTHOR]