Rock-ice avalanches in cold high-mountain regions pose severe hazards due to their high mobility,yet the quantitative controls of particle-size ratio and ice content remain insufficiently constrained.This study invest...Rock-ice avalanches in cold high-mountain regions pose severe hazards due to their high mobility,yet the quantitative controls of particle-size ratio and ice content remain insufficiently constrained.This study investigates their coupled effects using inclinedflume experiments and Discrete Element Method(DEM)simulations,covering three gravel sizes(2-5 mm,5-7 mm,7-10 mm)and four ice-content levels(0%,20%,40%,60%).Run-out distance,velocity,energy components,flow regime(Savage number),and segregation indexαwere quantified.Increasing ice content significantly enhances mobility,but with diminishing marginal effectiveness.From 0%to 40%ice content,run-out distance increases by 41%-86%,whereas the additional increase from 40%to 60%contributes only 12%-23%.Particle-size ratio strongly governs segregation intensity.Fine-gravel groups reach segregation indices ofα=0.92-0.98,indicating nearly complete upward migration of ice,whereas medium-gravel and coarse-gravel groups exhibit much weaker segregation,stabilizing atα=0.68-0.74 and 0.60-0.69.Savage number analyses reveal marked flow-regime transitions.At 0%ice content,Savage numbers reach 1.0-1.5,indicating a collisional regime.Increasing ice content suppresses collisionality,with Savage numbers decreasing to 0.03-0.07 at 60%ice content,consistent with dense-regime flow.DEM energy analyses confirm this regime shift:for finegravel mixtures,collision energy decreases by 14%,while sliding-friction energy increases by 33%as ice content increases from 0%to 60%,reflecting enhanced overburden effects imposed by upward-segregated ice layers.Medium and coarse mixtures exhibit weaker or opposite energy-shift patterns,demonstrating strong size dependence.Mechanistically,large particle-size contrasts promote strong segregation and form dense basal rock layers that increase basal friction and reduce mobility.When particle sizes are similar or ice content is high,segregation remains limited,allowing ice to mix into the basal layer,thereby reducing basal friction and enhancing mobility.This research quantitatively demonstrates how composition controls particle spatial distribution,flow regime,and energy dissipation,offering new mechanistic insights into the propagation and deposition behaviors of rock-ice avalanches and improving hazard assessment in vulnerable high-mountain regions.展开更多
Air blasts induced by rock-ice avalanches are common natural phenomena known for their far-field destructive impact.In this study,remote sensing images,eyewitness videos and numerical modelling were comprehensively ap...Air blasts induced by rock-ice avalanches are common natural phenomena known for their far-field destructive impact.In this study,remote sensing images,eyewitness videos and numerical modelling were comprehensively applied to analyze the initiation and propagation of the 2021 Chamoli avalancheinduced air blast.Our findings indicate that air blasts are observed from the avalanche source area to the Rishiganga valley,but nearly disappear in the Dhauliganga valley.The most intense air blast is concentrated on the left side of Ronti Gad valley,with maximum velocity and pressure estimated at over 70 m/s and 20 kPa,respectively.Such high pressure results in widespread tree breakage in the area.Based on the analysis of the Chamoli event,we further discussed the potential contribution of the avalanche flow regime,avalanche dynamics and geomorphology to the destructive potential of air blasts.Rapidly moved sliding mass can impart the air blast a high initial momentum,and this process will be exaggerated when the avalanche impacts valley walls at bends.However,when the rock-ice avalanche transforms into a debris-enriched flash flood,free water within the flowing mass can displace air,inhibiting the generation of air blasts.Our work offers new insights into the generation and propagation of rock-ice avalanche-induced air blasts,underscoring the importance of including this type of hazard during avalanche risk assessment in high-altitude glacial regions.展开更多
Rock-ice avalanches have frequently occurred in the Eastern Himalayan Syntaxis region due to climate change and active tectonic movements.These events commonly trigger catastrophic geohazard chains,including debris fl...Rock-ice avalanches have frequently occurred in the Eastern Himalayan Syntaxis region due to climate change and active tectonic movements.These events commonly trigger catastrophic geohazard chains,including debris flows,river blockages,and floods.This study focuses on the Zelongnong Basin,analyzing the geomorphic and dynamic characteristics of high-altitude disasters.The basin exhibits typical vertical zonation,with disaster sources initiating at elevations exceeding 4000 m and runout distances reaching up to 10 km.The disaster chain movement involves complex dynamic effects,including impact disintegration,soil-rock mixture arching,dynamic erosion,and debris deposition,enhancing understanding of the flow behavior and dynamic characteristics of rock-ice avalanches.The presence of ice significantly increases mobility due to lubrication and frictional melting.In the disaster event of September 10,2020,the maximum flow velocity and thickness reached 40 m/s and 43 m,respectively.Furthermore,continuous deformation of the Zelongnong glacier moraine was observed,with maximum cumulative deformations of 44.68 m in the distance direction and 25.96 m in the azimuth direction from March 25,2022,to August 25,2022.In the future,the risk of rock-ice avalanches in the Eastern Himalayan Syntaxis region will remain extremely high,necessitating a focus on early warning and risk mitigation strategies for such basin disasters.展开更多
Large-scale rock-ice avalanches resulting from the interaction of tectonics and climate are characterized with high mobility,huge volumes of sediment,and rapid denudation,being a major agent of landscape evolution in ...Large-scale rock-ice avalanches resulting from the interaction of tectonics and climate are characterized with high mobility,huge volumes of sediment,and rapid denudation,being a major agent of landscape evolution in high altitude mountainous regions.Specifically,the extreme glaciated slope failures often transform into extraordinarily large and mobile debris flows,resulting in disastrous consequences such as sedimentation and desertification.Due to a dearth of on-site observation data and experimental data collection,our comprehension of the geomorphic and kinematic characteristics of rock-ice avalanches remains poor.Here we report a cluster of ancient rock-ice avalanches spreading along the Chomolhari range of the China-Bhutan Himalayas.By integrating remote sensing image interpretation with detailed field investigations,we demonstrate the geomorphic and sedimentary characteristics of four events among the avalanches.The estimated volumes of the four are 23.73 Mm³,39.69 Mm³,38.43 Mm³,and 38.25 Mm³,respectively.The presence of pre-existing moraines or alluvial fans constrained their movement,resulting in deposition features such as marginal digitated lobes at higher elevations and large depressed areas in the interior.Applying the Savage-Hutter theory,we calculate the basal friction angle and travel angle of these ancient rock-ice avalanches that are both less than 10°,affirming the similarity of these avalanches in the study area to those occurring in other regions.Our study significantly contributes to understanding the geomorphic and kinematic characteristics of rock-ice avalanches in high-altitude mountainous regions,providing valuable insights into their response to the disproportionate growth of Himalayan peaks.展开更多
Rock-ice granular flows in high-altitude cold regions exhibit extreme mobility and destructive potential,posing severe threats to lives and infrastructure.Basal stress,governing the interaction between the flow and th...Rock-ice granular flows in high-altitude cold regions exhibit extreme mobility and destructive potential,posing severe threats to lives and infrastructure.Basal stress,governing the interaction between the flow and the underlying substrate,is critical for understanding their high mobility and erosion behavior.However,systematic investigations into basal stress fluctuations and their relationship with frictional behavior in rock-ice granular flows remain scarce,particularly regarding the effects of ice content and inclination angle.In this study,a series of flume experiments were conducted with ice contents ranging from 0%to 100%and flume inclination angles of 30°–45°.A triaxial force sensor and high-speed imaging with particle image velocimetry(PIV)were employed to measure basal normal and shear stresses,flow depth,and velocity.The results reveal that both normal and shear basal stresses initially increase slightly at 10%ice content but then decrease progressively as ice content increases further,while both stresses increase monotonically with inclination angle.These variations are attributed to the combined effects of hydrostatic pressure(overburden load and flow depth)and dynamic pressure(particle collisions and flow velocity).Dimensionless normal impulse decreases with ice content,whereas dimensionless tangential impulse increases,indicating enhanced normal interactions but weakened tangential interactions at higher ice concentrations.The maximum stress and standard deviation of stress both scale linearly with the time-mean stress,confirming that stress fluctuations are governed by bulk flow conditions(density,overburden load).The effective friction coefficientμshows a linear decrease with increasing ice content and a negative correlation with the Froude number Fr.Additionally,the normalized standard deviation of normal stress correlates positively withμ,while that of shear stress correlates negatively,suggesting that normal stress fluctuations from particle-substrate collisions enhance basal friction,whereas tangential fluctuations reduce it.These findings provide quantitative insights into the basal stress dynamics of rock-ice granular flows and establish a basis for improved hazard assessment and mitigation strategies in high-altitude mountain regions.展开更多
Ice avalanches are one of the most devastating mountain hazards,and can pose a great risk to the security of the surrounding area.Although ice avalanches have been widely observed in mountainous regions around the wor...Ice avalanches are one of the most devastating mountain hazards,and can pose a great risk to the security of the surrounding area.Although ice avalanches have been widely observed in mountainous regions around the world,only a few ice avalanche events have been studied comprehensively,due to the lack of available data.In this study,in response to the recent catastrophic rock-ice avalanche(7 February 2021)at Chamoli in the India Himalaya,we used high-resolution satellite images and found that this event was actually a glacier-rock landslide,where the collapse of the rock-ice body was caused by the sliding of the bedrock beneath the glacier,for which the source area and volume loss were about 2.89×10^(5) m^(2) and 2.46×10^(7) m^(3),respectively,corresponding to an average elevation change of about−85 m.Furthermore,visual analysis of the dense time-series satellite images shows that the overall downward sliding of the collapsed rock-ice body initiated around the summer of 2017,and thereafter exhibited clear seasonality(mainly in summer).Meteorological analysis reveals a strong rainfall anomaly in the initiation period of the sliding and a remarkable winter warming anomaly in the 40 days before the collapse.Comparisons of multi-temporal digital elevation models(DEMs)further suggest that the glacier geometry in the collapsed areas was likely changing(i.e.,accelerated surface thinning in the lower part of the glaciers and insignificant change in the upper part),which is consistent with the region-wide climate warming.Finally,by combining the above findings and a geomorphic analysis,we conclude that the rock-ice avalanche event was mainly caused by the joint effects of climate and weather changes acting on a steeply sloping and fracture-prone geological condition.The findings of this study provide new and valuable evidence for the study of slope/glacier instability at high altitudes.This study also highlights that,for the Himalaya and other high mountain ranges,there is an urgent need to identify the glaciers that have a high risk of ice avalanches.展开更多
基金funded by the Natural Science Foundation of China(Grants No 42277127)。
文摘Rock-ice avalanches in cold high-mountain regions pose severe hazards due to their high mobility,yet the quantitative controls of particle-size ratio and ice content remain insufficiently constrained.This study investigates their coupled effects using inclinedflume experiments and Discrete Element Method(DEM)simulations,covering three gravel sizes(2-5 mm,5-7 mm,7-10 mm)and four ice-content levels(0%,20%,40%,60%).Run-out distance,velocity,energy components,flow regime(Savage number),and segregation indexαwere quantified.Increasing ice content significantly enhances mobility,but with diminishing marginal effectiveness.From 0%to 40%ice content,run-out distance increases by 41%-86%,whereas the additional increase from 40%to 60%contributes only 12%-23%.Particle-size ratio strongly governs segregation intensity.Fine-gravel groups reach segregation indices ofα=0.92-0.98,indicating nearly complete upward migration of ice,whereas medium-gravel and coarse-gravel groups exhibit much weaker segregation,stabilizing atα=0.68-0.74 and 0.60-0.69.Savage number analyses reveal marked flow-regime transitions.At 0%ice content,Savage numbers reach 1.0-1.5,indicating a collisional regime.Increasing ice content suppresses collisionality,with Savage numbers decreasing to 0.03-0.07 at 60%ice content,consistent with dense-regime flow.DEM energy analyses confirm this regime shift:for finegravel mixtures,collision energy decreases by 14%,while sliding-friction energy increases by 33%as ice content increases from 0%to 60%,reflecting enhanced overburden effects imposed by upward-segregated ice layers.Medium and coarse mixtures exhibit weaker or opposite energy-shift patterns,demonstrating strong size dependence.Mechanistically,large particle-size contrasts promote strong segregation and form dense basal rock layers that increase basal friction and reduce mobility.When particle sizes are similar or ice content is high,segregation remains limited,allowing ice to mix into the basal layer,thereby reducing basal friction and enhancing mobility.This research quantitatively demonstrates how composition controls particle spatial distribution,flow regime,and energy dissipation,offering new mechanistic insights into the propagation and deposition behaviors of rock-ice avalanches and improving hazard assessment in vulnerable high-mountain regions.
基金supported by the National Natural Science Foundation of China(Grant Nos.U2244227,42277126 and 41977215).
文摘Air blasts induced by rock-ice avalanches are common natural phenomena known for their far-field destructive impact.In this study,remote sensing images,eyewitness videos and numerical modelling were comprehensively applied to analyze the initiation and propagation of the 2021 Chamoli avalancheinduced air blast.Our findings indicate that air blasts are observed from the avalanche source area to the Rishiganga valley,but nearly disappear in the Dhauliganga valley.The most intense air blast is concentrated on the left side of Ronti Gad valley,with maximum velocity and pressure estimated at over 70 m/s and 20 kPa,respectively.Such high pressure results in widespread tree breakage in the area.Based on the analysis of the Chamoli event,we further discussed the potential contribution of the avalanche flow regime,avalanche dynamics and geomorphology to the destructive potential of air blasts.Rapidly moved sliding mass can impart the air blast a high initial momentum,and this process will be exaggerated when the avalanche impacts valley walls at bends.However,when the rock-ice avalanche transforms into a debris-enriched flash flood,free water within the flowing mass can displace air,inhibiting the generation of air blasts.Our work offers new insights into the generation and propagation of rock-ice avalanche-induced air blasts,underscoring the importance of including this type of hazard during avalanche risk assessment in high-altitude glacial regions.
基金granted by the National Natural Science Foundation of China(Grant Nos.U2244227 and U2244226)the National Key R&D Program of China(Grant No.2022YFC3004301)China Geological Survey Project(Grant No.DD20230538)。
文摘Rock-ice avalanches have frequently occurred in the Eastern Himalayan Syntaxis region due to climate change and active tectonic movements.These events commonly trigger catastrophic geohazard chains,including debris flows,river blockages,and floods.This study focuses on the Zelongnong Basin,analyzing the geomorphic and dynamic characteristics of high-altitude disasters.The basin exhibits typical vertical zonation,with disaster sources initiating at elevations exceeding 4000 m and runout distances reaching up to 10 km.The disaster chain movement involves complex dynamic effects,including impact disintegration,soil-rock mixture arching,dynamic erosion,and debris deposition,enhancing understanding of the flow behavior and dynamic characteristics of rock-ice avalanches.The presence of ice significantly increases mobility due to lubrication and frictional melting.In the disaster event of September 10,2020,the maximum flow velocity and thickness reached 40 m/s and 43 m,respectively.Furthermore,continuous deformation of the Zelongnong glacier moraine was observed,with maximum cumulative deformations of 44.68 m in the distance direction and 25.96 m in the azimuth direction from March 25,2022,to August 25,2022.In the future,the risk of rock-ice avalanches in the Eastern Himalayan Syntaxis region will remain extremely high,necessitating a focus on early warning and risk mitigation strategies for such basin disasters.
基金funded by the Second Tibetan Plateau Scientific Expedition and Research Program(2019QZKK0902)the National Natural Science Foundation of China(91747207,41790434)。
文摘Large-scale rock-ice avalanches resulting from the interaction of tectonics and climate are characterized with high mobility,huge volumes of sediment,and rapid denudation,being a major agent of landscape evolution in high altitude mountainous regions.Specifically,the extreme glaciated slope failures often transform into extraordinarily large and mobile debris flows,resulting in disastrous consequences such as sedimentation and desertification.Due to a dearth of on-site observation data and experimental data collection,our comprehension of the geomorphic and kinematic characteristics of rock-ice avalanches remains poor.Here we report a cluster of ancient rock-ice avalanches spreading along the Chomolhari range of the China-Bhutan Himalayas.By integrating remote sensing image interpretation with detailed field investigations,we demonstrate the geomorphic and sedimentary characteristics of four events among the avalanches.The estimated volumes of the four are 23.73 Mm³,39.69 Mm³,38.43 Mm³,and 38.25 Mm³,respectively.The presence of pre-existing moraines or alluvial fans constrained their movement,resulting in deposition features such as marginal digitated lobes at higher elevations and large depressed areas in the interior.Applying the Savage-Hutter theory,we calculate the basal friction angle and travel angle of these ancient rock-ice avalanches that are both less than 10°,affirming the similarity of these avalanches in the study area to those occurring in other regions.Our study significantly contributes to understanding the geomorphic and kinematic characteristics of rock-ice avalanches in high-altitude mountainous regions,providing valuable insights into their response to the disproportionate growth of Himalayan peaks.
基金financial support from the National Key Research and Development Program of China(Project No.2023YFC3008300,2023YFC3008302)the National Natural Science Foundation of China(Grant No.U22A20603).
文摘Rock-ice granular flows in high-altitude cold regions exhibit extreme mobility and destructive potential,posing severe threats to lives and infrastructure.Basal stress,governing the interaction between the flow and the underlying substrate,is critical for understanding their high mobility and erosion behavior.However,systematic investigations into basal stress fluctuations and their relationship with frictional behavior in rock-ice granular flows remain scarce,particularly regarding the effects of ice content and inclination angle.In this study,a series of flume experiments were conducted with ice contents ranging from 0%to 100%and flume inclination angles of 30°–45°.A triaxial force sensor and high-speed imaging with particle image velocimetry(PIV)were employed to measure basal normal and shear stresses,flow depth,and velocity.The results reveal that both normal and shear basal stresses initially increase slightly at 10%ice content but then decrease progressively as ice content increases further,while both stresses increase monotonically with inclination angle.These variations are attributed to the combined effects of hydrostatic pressure(overburden load and flow depth)and dynamic pressure(particle collisions and flow velocity).Dimensionless normal impulse decreases with ice content,whereas dimensionless tangential impulse increases,indicating enhanced normal interactions but weakened tangential interactions at higher ice concentrations.The maximum stress and standard deviation of stress both scale linearly with the time-mean stress,confirming that stress fluctuations are governed by bulk flow conditions(density,overburden load).The effective friction coefficientμshows a linear decrease with increasing ice content and a negative correlation with the Froude number Fr.Additionally,the normalized standard deviation of normal stress correlates positively withμ,while that of shear stress correlates negatively,suggesting that normal stress fluctuations from particle-substrate collisions enhance basal friction,whereas tangential fluctuations reduce it.These findings provide quantitative insights into the basal stress dynamics of rock-ice granular flows and establish a basis for improved hazard assessment and mitigation strategies in high-altitude mountain regions.
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.41988101&42001381)the China Post-Doctoral Program for Innovative Talents(Grant No.BX20200343)+1 种基金the China Post-Doctoral Science Foundation(Grant No.2020M670480)The TanDEM-X data were provided as part of a science data project conducted by the German Aerospace Center(Grant No.NTI_BIST7136).
文摘Ice avalanches are one of the most devastating mountain hazards,and can pose a great risk to the security of the surrounding area.Although ice avalanches have been widely observed in mountainous regions around the world,only a few ice avalanche events have been studied comprehensively,due to the lack of available data.In this study,in response to the recent catastrophic rock-ice avalanche(7 February 2021)at Chamoli in the India Himalaya,we used high-resolution satellite images and found that this event was actually a glacier-rock landslide,where the collapse of the rock-ice body was caused by the sliding of the bedrock beneath the glacier,for which the source area and volume loss were about 2.89×10^(5) m^(2) and 2.46×10^(7) m^(3),respectively,corresponding to an average elevation change of about−85 m.Furthermore,visual analysis of the dense time-series satellite images shows that the overall downward sliding of the collapsed rock-ice body initiated around the summer of 2017,and thereafter exhibited clear seasonality(mainly in summer).Meteorological analysis reveals a strong rainfall anomaly in the initiation period of the sliding and a remarkable winter warming anomaly in the 40 days before the collapse.Comparisons of multi-temporal digital elevation models(DEMs)further suggest that the glacier geometry in the collapsed areas was likely changing(i.e.,accelerated surface thinning in the lower part of the glaciers and insignificant change in the upper part),which is consistent with the region-wide climate warming.Finally,by combining the above findings and a geomorphic analysis,we conclude that the rock-ice avalanche event was mainly caused by the joint effects of climate and weather changes acting on a steeply sloping and fracture-prone geological condition.The findings of this study provide new and valuable evidence for the study of slope/glacier instability at high altitudes.This study also highlights that,for the Himalaya and other high mountain ranges,there is an urgent need to identify the glaciers that have a high risk of ice avalanches.
