The Nenang Ravine Small Nature Reserve is located in Tohlung Dechen District,Lhasa City,Xizang,approximately 38 kilometers from downtown Lhasa.Being called the small nature reserve,it refers to an emerging type of nat...The Nenang Ravine Small Nature Reserve is located in Tohlung Dechen District,Lhasa City,Xizang,approximately 38 kilometers from downtown Lhasa.Being called the small nature reserve,it refers to an emerging type of natural protection reserve that is smaller in scale and independently established by local governments at or under county level.展开更多
Debris flows in Jiangjia Ravine in Yunnan province, China are not only triggered by intense storms but also by short-duration and low-intensity rainfalls. This reflects the significance of antecedent rainfall. This pa...Debris flows in Jiangjia Ravine in Yunnan province, China are not only triggered by intense storms but also by short-duration and low-intensity rainfalls. This reflects the significance of antecedent rainfall. This paper tries to find the debris flow- triggering threshold by considering antecedent rainfall through a case study in Jiangjia Ravine. From 23 debris flow events, the I-D （Intensity-Duration） threshold was found, which is very dose to the line of 95th percentile regression line of rainfall events, representing that 95% of rainfalls can potentially induce debris flows and reflects the limitation of I-D threshold application in this area. Taking into account the effect of antecedent rainfall, the debris flowtriggering threshold for rainfall quantity and intensity is statistically and empirically derived. The relationships can be used in debris flow warning system as key thresholds. Coupling with the rainfall characteristics in this area, new thresholds are proposed as triggering and warning thresholds.展开更多
Characteristics of planar velocity distribution of viscous debris flow were analyzed using the measured data at Jiangjia Ravine, Yunnan, China. The velocity data were measured through using two radar velocimeters. The...Characteristics of planar velocity distribution of viscous debris flow were analyzed using the measured data at Jiangjia Ravine, Yunnan, China. The velocity data were measured through using two radar velocimeters. The cross-sectional mean velocities were calculated and used to examine Kang et al＇s （2004） relationship, which was established for converting the flow velocity at river centerline measured by a radar velocimeter into the mean velocity based on the stop-watch method. The velocity coefficient, K, defined by the ratio of the mean velocity to the maximum velocity, ranges from 0.2 to 0.6. Kang et al＇s （2004） relationship was found being inapplicable to flows with K smaller than 0.43. This paper contributes to show the complexity of the planar velocity distribution of viscous debris flows and the applicability of Kang et al＇s relationship.展开更多
Jiangjia Ravine is a world-famous debris flow valley in Dongchuan,Yunnan Province,China.Every year large numbers of landslides and collapses happened and caused enormous damages to people's properties and lives.Wi...Jiangjia Ravine is a world-famous debris flow valley in Dongchuan,Yunnan Province,China.Every year large numbers of landslides and collapses happened and caused enormous damages to people's properties and lives.With longtime observation and testing in Jiangjia Ravine we had found out one kind of special landslide which had the characteristics of landslide and collapse.Landslide and collapse supplied sufficient materials for debris flow.When a debris flow broke out,some kind of intergrowth existed among rainfall,landslide and debris flow.In order to study the intergrowth and some key parameters,we carried out artificial rainfall landslide tests and model experiments to observe the phenomena such as collapse,surface slide and surface flow.By observing the experimental phenomena and monitoring water contents,the transformation process among landslide deposits and debris flow under the condition of rainfall had been analyzed.Research results revealed the relationship of this kind of intergrowth among rainfall,landslide and debris flow in Jiangjia Ravine.Meanwhile,it was found that this kind of intergrowth relationship existed only when the moisture content was in a certain range.That is,the critical state seemed to be existed in the transformation process.展开更多
Five leucaena trees of similar age were chosen in Jiangjia Ravine of Dongchuan,Yunnan Province,China,near which the soil samples were collected by digging profiles 2m in depth and 1m in width.In each section,soil samp...Five leucaena trees of similar age were chosen in Jiangjia Ravine of Dongchuan,Yunnan Province,China,near which the soil samples were collected by digging profiles 2m in depth and 1m in width.In each section,soil samples at different depths were taken for direct shear experiments to determine the root amount and mechanical composition.It is found that the cohesion and internal friction angle of the undisturbed soil are related to the root amount,depth,clay content and breccias content.Cohesion correlates negatively with root content,a finding that differs from that of other researchers.In addition,internal friction angle correlates positively with all these factors.展开更多
Zelongnong Ravine,a branch ravine of Brahmaputra,is an old large glacier debris-flow ravine.Debris-flows with medium and/or small scales occur almost every year;multiple super debris-flows have also broken out in hist...Zelongnong Ravine,a branch ravine of Brahmaputra,is an old large glacier debris-flow ravine.Debris-flows with medium and/or small scales occur almost every year;multiple super debris-flows have also broken out in history,and have caused destructive disaster to local residents at the mouth of ravine and blocked Brahmaputra.The huge altitude difference and the steep slope of the Zelongnong Ravine provide predominant energy conditions for the debris-flow.The drainage basin is located in the fast uplifted area,where the complicated geologic structure,the cracked rock,and the frequent earthquake make the rocks experience strong weathering,thus plenty of granular materials are available for the formation of debris-flows.Although this region is located in the rain shadow area,the precipitation is concentrated and most is with high intensity.Also,the strong glacier activity provides water source for debris-flow.According to literature reviews,most debris-flows in the ravine are induced by rainstorms,and their scales are relatively small.However,when the melted water is overlaid,the large scale debris-flows may occur.Parametric calculation such as the flow velocity and the runoff is conducted according to the monitoring data.The result shows that large debris-flows can be aroused when the rainstorm and the melted water are combined well,but the possibility of blocking off Brahmaputra is rare.The occurrence of the super debris-flows is closely related to the intense glacier activity(e.g.,glaciersurge).They often result in destructive disasters and are hard to be prevented and cured by engineering measures,due to the oversized scales.The hazard mitigation measures such as monitoring and prediction are proposed.展开更多
Objective One of major challenges in paleoenvironmental reconstruction using travertine in the Huanglong area is whether one can accurately determinate the age of travertine through high-precision and high-resolution...Objective One of major challenges in paleoenvironmental reconstruction using travertine in the Huanglong area is whether one can accurately determinate the age of travertine through high-precision and high-resolution dating techniques. Previous works of 14C or ESR chronology, however, have shown that the variation of deposition ages of travertine was displayed inconsistent with each other even conflict. For instance, （1） The oldest travertine age （80 ka） located in the middle of this travertine succession is departure from sequential deposition; （2） Top or boundary ages in this sedimentary section, even with the same dating method （14C）, are three times errors, moreover, the age of the depositional sequence is not continuous. We report here the U230Th ages in lowest boundary of travertine in Dawanzhangjia Valley, Huanglong, China, to discuss the effectiveness of U-series dating for cold-water travertine and the significance of age for vicissitude of paleoenvironment.展开更多
Gravelly soils are made up of gravel, sand, silt and clay. They are widely used in engineering applications such as rock-fill dams with clay cores, which are the main researches at present. The strength and mechanical...Gravelly soils are made up of gravel, sand, silt and clay. They are widely used in engineering applications such as rock-fill dams with clay cores, which are the main researches at present. The strength and mechanical properties of the gravelly soils are affected by the content of coarse grain, fine particles, and their adhesive states. These Properties can be verified by laboratory unconsolidated undrained triaxial tests with grain size less than 5 mm and by large scale direct-shear tests with original grain content. Fine particles of the loose gravelly slopes are released under rainfalls, alternated the structures and mechanical properties, even affected the slope stability. There are a series of large scale direct-shear tests with different coarse grain contents to study the influence of fine particles releasing and migration, results showed the strength behavior of the gravelly soils were affected by the coarse grain content （5） and the inflection coarse grain contents. In order to study the erosion features of the gravelly soil slopes on rainfall conditions and the slopes stability alteration, we had carried out one sort of artificial rainfall local and model experiments, the runoff sediment contents were monitored during the experiments. Result showed that the shapes of the slopes surface transformed periodically, runoff sediment contents were divided into five phases according to the experiment phenomena, runoff sediment contents maintained downtrend during the rain time and the downtrend was obviouslyinterpreted by one descend belt no matter the rainfall intensity and the slope angels. Particle size analysis released the deposit on the slope surface lost almost all of the clay, most of the silt and sand after the experiments, this meant the fine particles releasing, migration and accumulation process on condition of rainfall resulted in the instability factor of the slopes even induced landslide or debris flow.展开更多
The structural features of soil in debris flow-triggering region play an important role in the formation and evolution of debris flow. In this paper, a case study on the fractal of soil particle-size distribution （PS...The structural features of soil in debris flow-triggering region play an important role in the formation and evolution of debris flow. In this paper, a case study on the fractal of soil particle-size distribution （PSDFs） and pore-solid （PSFs） in Jiangjia Ravine was conducted. The results revealed that the soil in Jiangjia Ravine had significant fractal features and its PSDF and PSF had the same variation trend despite different type of soils in debris flow-triggering region： residual soil （RS） 〉 debris flow deposit （DFD）~clinosol （CL）, their fractal dimension of PSDFs are respectively between 2.62 and 2.96, 2.52 and 2.68, 2.37 and 2.52; and the fractal dimension of PSFs are respectively between 2. 75 and 2.95, 2. 57 and 2. 72, 2.59 and 2.64. The fractal dimension of soil reflected its complexity as a self-organizing system and was closely related to the evolution of soil in debris flow- triggering region.展开更多
The Bathonian GSSP is defined at the base of limestone bed RB071 in the Ravin du Bès Section,Bas-Auran area,southern Subalpine Chains(France).This section satisfies most of the requirements recommended by the Int...The Bathonian GSSP is defined at the base of limestone bed RB071 in the Ravin du Bès Section,Bas-Auran area,southern Subalpine Chains(France).This section satisfies most of the requirements recommended by the International Commission on Stratigraphy.The exposure extends over 13 m in thickness.展开更多
文摘The Nenang Ravine Small Nature Reserve is located in Tohlung Dechen District,Lhasa City,Xizang,approximately 38 kilometers from downtown Lhasa.Being called the small nature reserve,it refers to an emerging type of natural protection reserve that is smaller in scale and independently established by local governments at or under county level.
基金support from the Key Deployment Project of Chinese Academy of Sciences(Grant No.KZZD-EW-05-01)National Key Technologies R&D Program of China(Grant No.2012BAK10B04)data support from the Dongchuan Debris Flow Observation Station
文摘Debris flows in Jiangjia Ravine in Yunnan province, China are not only triggered by intense storms but also by short-duration and low-intensity rainfalls. This reflects the significance of antecedent rainfall. This paper tries to find the debris flow- triggering threshold by considering antecedent rainfall through a case study in Jiangjia Ravine. From 23 debris flow events, the I-D （Intensity-Duration） threshold was found, which is very dose to the line of 95th percentile regression line of rainfall events, representing that 95% of rainfalls can potentially induce debris flows and reflects the limitation of I-D threshold application in this area. Taking into account the effect of antecedent rainfall, the debris flowtriggering threshold for rainfall quantity and intensity is statistically and empirically derived. The relationships can be used in debris flow warning system as key thresholds. Coupling with the rainfall characteristics in this area, new thresholds are proposed as triggering and warning thresholds.
基金the National Natural Science Foundation of China (50221903, 50309007)
文摘Characteristics of planar velocity distribution of viscous debris flow were analyzed using the measured data at Jiangjia Ravine, Yunnan, China. The velocity data were measured through using two radar velocimeters. The cross-sectional mean velocities were calculated and used to examine Kang et al＇s （2004） relationship, which was established for converting the flow velocity at river centerline measured by a radar velocimeter into the mean velocity based on the stop-watch method. The velocity coefficient, K, defined by the ratio of the mean velocity to the maximum velocity, ranges from 0.2 to 0.6. Kang et al＇s （2004） relationship was found being inapplicable to flows with K smaller than 0.43. This paper contributes to show the complexity of the planar velocity distribution of viscous debris flows and the applicability of Kang et al＇s relationship.
基金financially supported by the National Natural Science Foundation of China(Grant No.50709035,40672193)the Youth Science and Technology Dawn Plan of Wuhan,China(Grant No.20065004116-42)
文摘Jiangjia Ravine is a world-famous debris flow valley in Dongchuan,Yunnan Province,China.Every year large numbers of landslides and collapses happened and caused enormous damages to people's properties and lives.With longtime observation and testing in Jiangjia Ravine we had found out one kind of special landslide which had the characteristics of landslide and collapse.Landslide and collapse supplied sufficient materials for debris flow.When a debris flow broke out,some kind of intergrowth existed among rainfall,landslide and debris flow.In order to study the intergrowth and some key parameters,we carried out artificial rainfall landslide tests and model experiments to observe the phenomena such as collapse,surface slide and surface flow.By observing the experimental phenomena and monitoring water contents,the transformation process among landslide deposits and debris flow under the condition of rainfall had been analyzed.Research results revealed the relationship of this kind of intergrowth among rainfall,landslide and debris flow in Jiangjia Ravine.Meanwhile,it was found that this kind of intergrowth relationship existed only when the moisture content was in a certain range.That is,the critical state seemed to be existed in the transformation process.
基金supported by the National Natural Science Foundation of China (Grant No.40771025)National Key Basic Research and Development Program (Grant No.2008CB425802)the Chinese Academy of Sciences important direction for knowledge engineering projects(Grant No.KZCX2-YW-332)
文摘Five leucaena trees of similar age were chosen in Jiangjia Ravine of Dongchuan,Yunnan Province,China,near which the soil samples were collected by digging profiles 2m in depth and 1m in width.In each section,soil samples at different depths were taken for direct shear experiments to determine the root amount and mechanical composition.It is found that the cohesion and internal friction angle of the undisturbed soil are related to the root amount,depth,clay content and breccias content.Cohesion correlates negatively with root content,a finding that differs from that of other researchers.In addition,internal friction angle correlates positively with all these factors.
基金supported by the National Natural Science Foundation of China(Grant No.40871024 & 40971014)
文摘Zelongnong Ravine,a branch ravine of Brahmaputra,is an old large glacier debris-flow ravine.Debris-flows with medium and/or small scales occur almost every year;multiple super debris-flows have also broken out in history,and have caused destructive disaster to local residents at the mouth of ravine and blocked Brahmaputra.The huge altitude difference and the steep slope of the Zelongnong Ravine provide predominant energy conditions for the debris-flow.The drainage basin is located in the fast uplifted area,where the complicated geologic structure,the cracked rock,and the frequent earthquake make the rocks experience strong weathering,thus plenty of granular materials are available for the formation of debris-flows.Although this region is located in the rain shadow area,the precipitation is concentrated and most is with high intensity.Also,the strong glacier activity provides water source for debris-flow.According to literature reviews,most debris-flows in the ravine are induced by rainstorms,and their scales are relatively small.However,when the melted water is overlaid,the large scale debris-flows may occur.Parametric calculation such as the flow velocity and the runoff is conducted according to the monitoring data.The result shows that large debris-flows can be aroused when the rainstorm and the melted water are combined well,but the possibility of blocking off Brahmaputra is rare.The occurrence of the super debris-flows is closely related to the intense glacier activity(e.g.,glaciersurge).They often result in destructive disasters and are hard to be prevented and cured by engineering measures,due to the oversized scales.The hazard mitigation measures such as monitoring and prediction are proposed.
基金supported by National Natural Science Foundation of China (grants No. 41572035, 41472309, 41603041 and 41741026)the Open Funds of State Key Laboratory of Loess and Quaternary Geology (grant No. SKLLQG1620)
文摘Objective One of major challenges in paleoenvironmental reconstruction using travertine in the Huanglong area is whether one can accurately determinate the age of travertine through high-precision and high-resolution dating techniques. Previous works of 14C or ESR chronology, however, have shown that the variation of deposition ages of travertine was displayed inconsistent with each other even conflict. For instance, （1） The oldest travertine age （80 ka） located in the middle of this travertine succession is departure from sequential deposition; （2） Top or boundary ages in this sedimentary section, even with the same dating method （14C）, are three times errors, moreover, the age of the depositional sequence is not continuous. We report here the U230Th ages in lowest boundary of travertine in Dawanzhangjia Valley, Huanglong, China, to discuss the effectiveness of U-series dating for cold-water travertine and the significance of age for vicissitude of paleoenvironment.
基金financially supported by National Natural Science Foundation of China (Grant Nos. 41172283, 41372313)National Basic Research Program of China (2012CB026103)
文摘Gravelly soils are made up of gravel, sand, silt and clay. They are widely used in engineering applications such as rock-fill dams with clay cores, which are the main researches at present. The strength and mechanical properties of the gravelly soils are affected by the content of coarse grain, fine particles, and their adhesive states. These Properties can be verified by laboratory unconsolidated undrained triaxial tests with grain size less than 5 mm and by large scale direct-shear tests with original grain content. Fine particles of the loose gravelly slopes are released under rainfalls, alternated the structures and mechanical properties, even affected the slope stability. There are a series of large scale direct-shear tests with different coarse grain contents to study the influence of fine particles releasing and migration, results showed the strength behavior of the gravelly soils were affected by the coarse grain content （5） and the inflection coarse grain contents. In order to study the erosion features of the gravelly soil slopes on rainfall conditions and the slopes stability alteration, we had carried out one sort of artificial rainfall local and model experiments, the runoff sediment contents were monitored during the experiments. Result showed that the shapes of the slopes surface transformed periodically, runoff sediment contents were divided into five phases according to the experiment phenomena, runoff sediment contents maintained downtrend during the rain time and the downtrend was obviouslyinterpreted by one descend belt no matter the rainfall intensity and the slope angels. Particle size analysis released the deposit on the slope surface lost almost all of the clay, most of the silt and sand after the experiments, this meant the fine particles releasing, migration and accumulation process on condition of rainfall resulted in the instability factor of the slopes even induced landslide or debris flow.
文摘The structural features of soil in debris flow-triggering region play an important role in the formation and evolution of debris flow. In this paper, a case study on the fractal of soil particle-size distribution （PSDFs） and pore-solid （PSFs） in Jiangjia Ravine was conducted. The results revealed that the soil in Jiangjia Ravine had significant fractal features and its PSDF and PSF had the same variation trend despite different type of soils in debris flow-triggering region： residual soil （RS） 〉 debris flow deposit （DFD）~clinosol （CL）, their fractal dimension of PSDFs are respectively between 2.62 and 2.96, 2.52 and 2.68, 2.37 and 2.52; and the fractal dimension of PSFs are respectively between 2. 75 and 2.95, 2. 57 and 2. 72, 2.59 and 2.64. The fractal dimension of soil reflected its complexity as a self-organizing system and was closely related to the evolution of soil in debris flow- triggering region.
基金supported by the CGL2004-0694/BTE(MEC-CSIC)and CGL2008-01273/BTE(MICINN)projectsgrants from the 2006 and 2007 Geoconservation Projects,respectively coordinated at the Madrid and Torino universities.
文摘The Bathonian GSSP is defined at the base of limestone bed RB071 in the Ravin du Bès Section,Bas-Auran area,southern Subalpine Chains(France).This section satisfies most of the requirements recommended by the International Commission on Stratigraphy.The exposure extends over 13 m in thickness.
