[Show abstract][Hide abstract] ABSTRACT: Many glacier dams on major rivers at the southeastern edge of the Tibetan Plateau had been previously determined through remote sensing and glacier terminal position calculation. It was hypothesized that such damming substantially impeded river incision into the plateau interior. Investigation on the large glacial-dammed lake at the entrance of Tsangpo gorge is critical for understanding this hypothesis. So far, the issues, such as age, lake surface elevation, and stages of this dammed lake, are still in debate. Our field survey of lacustrine deposits and loess distribution along the middle Yarlung Tsangpo River and its tributary, Nyang River, suggested that the lake surface elevation was at about 3180masl. The 23 quartz optically stimulated luminescence (OSL) and 4 organic AMS 14C ages all fall into the Last Glacial period (~41-13ka). The OSL and 14C ages are in general agreement with each other where applicable. There might be only one long damming event because the ages of lacustrine deposits from 2970 to 3100masl are similar, and every lacustrine section is sustained for a long time. The estimated lake surface area was 1089km2, and the volume was ~170km3, which differ from previous estimations which suggested two-stage (about early Holocene and 1.5ka) lakes, and the largest lake surface elevation reached 3500m.
[Show abstract][Hide abstract] ABSTRACT: Landslide dams commonly form when mass earth or rock movements reach a river channel and cause a complete or partial blockage of the channel. Intense rainfalls can induce upstream flows along a sloping channel that significantly affect downstream landslide dams. If a series of landslide dams are collapsed by incoming mountain torrents (induced by intense rainfall), large debris flows can form in a very short period. Furthermore, the failure of these dams can amplify the magnitude and scale of debris flows in the flow direction. The catastrophic debris flows that occurred in Zhouqu County, China on 8 August 2010 were caused by intense rainfall and the upstream cascading failure of landslide dams along the gullies. Incorporating the role of outburst floods associated with the complete or partial failure of landslide dams is an interesting problem usually beyond the scope of analysis because of the inherent modeling complexity. To understand the cascading failure modes of a series of landslide dams, and the dynamic effect these failures have on the enlargement of debris flow scales, experimental tests are conducted in sloping channels mimicking field conditions, with the modeled landslide dams distributed along a sloping channel and crushed by different upstream flows. The failure modes of three different cascades of landslide dams fully or partially blocking a channel river are parametrically studied. This study illustrates that upstream flows can induce a cascading failure of the landslide dams along a channel. Overtopping is the primary failure mechanism, while piping and erosion can also induce failures for different constructed landslide dams. A cascading failure of landslide dams causes a gradually increasing flow velocity and discharge of the front flow, resulting in an increase in both diameter and percentage of the entrained coarse particles. Furthermore, large landslide blockages can act to enhance the efficiency of river incision, or conversely to induce aggradation of fluvial sediments, depending on the blockage factor of the landslide dams and upstream discharge.
International Journal of Sediment Research 08/2015; 30(3). DOI:10.1016/j.ijsrc.2014.09.003 · 0.72 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The Jiangjia Gully (JJG), Yunnan Province, China, is one of several debris flow gullies that characterize the topography of mountainous areas in China. Rainfall-triggered debris flows are frequent in the JJG. In order to model and predict these debris flow occurrences, we analyzed precipitation parameters (including intensity–duration thresholds and rainfall event–duration thresholds) that triggered past debris flow events in the JJG. Since the JJG is unique, any model used for predicting debris flows in this gully must be developed using data from only this gully. Furthermore, the effects of normalized precipitation and antecedent precipitation on debris flows in the JJG were considered. Debris flow data and precipitation data were compiled from 47 debris flow events in 1993, 1994, 1998-2001, 2004 and 2006 in JJG. All of these debris flows were triggered following a precipitation event with a duration of 6 hours or less, with most of the precipitation events exhibiting a duration of 3 to 6 hours. Only three rainfall events with a duration of less than 1 hour and average intensity between 1.0 and 42.0 mm/h produced debris flows. The 90%, 70% and 50% probability curves for debris flow events were then constructed. Intensity-duration (I-D) and rainfall event-duration (RE-D) thresholds were then used for debris flow modeling based on preliminary tests and comparisons. Antecedent precipitation was found to not be a significant factor in triggering debris flows in the JJG; however, intraday precipitation played a significant role. Normalized precipitation threshold curves from adjacent areas were not well-correlated with the patterns observed in the JJG. Determination of unique thresholds for each gully is necessary for developing an effective prediction system.
[Show abstract][Hide abstract] ABSTRACT: A miniaturized flume experiment was carried out to measure impact forces of viscous debris flow. The flow depth (7.2–11.2 cm), velocity (2.4–5.2 m/s) and impact force were recorded during the experiment. The impact process of debris flow can be divided into three phases by analyzing the variation of impact signals and flow regime. The three phases are the sudden strong impact of the debris flow head, continuous dynamic pressure of the body and slight static pressure of the tail. The variation of impact process is consistent with the change in the flow regime. The head has strong–rapid impact pressure, which is shown as a turbulent-type flow; the body approximated to be a steady laminar flow. Accordingly, the process of debris flows hitting on structures was simplified to a triangle shape, ignoring the pressure of the tail. In order to study the distribution of the debris flow impact force at different depths and the variation of impact process over time, the impact signals of slurry and coarse particles were separated from the original signals with Wavelet analysis. The slurry's dynamic pressure signal appears to be a smooth curve, and the peak pressure is 12–34 kPa when the debris flow head hit the sensors, which is about 1.54 ± 0.36 times the continuous dynamic pressure of debris flow body. The limit application of the empirical parameter α of hydraulic formula was also noted. We introduced the power function relationship of α and the Froude number of debris flows, and proposed a universal model for calculating dynamic pressure. The impact pressure of large particles has the characteristic of randomness. The mean frequency of large particles impacting on the sensor is 210 ± 50–287 ± 29 times per second, and it is 336 ± 114–490 ± 69 times per second for the debris flow head, which is greater than that in the debris flow body. Peak impact pressure of particles at different flow depths is 40–160 kPa, which is 3.2 ± 1.5 times the impact pressure of the slurry at the bottom of flow, 3.1 ± 0.9 times the flow in the middle, and 3.3 ± 0.9 times the flow at the surface. The differences of impact frequency indicate that most of the large particles concentrate in the debris flow head, and the number of particles in the debris flow head increases with height. This research can supports the study of solid–liquid two phase flow mechanisms, and helps engineering design and risk assessment in the debris flow prone area. This article is protected by copyright. All rights reserved.
[Show abstract][Hide abstract] ABSTRACT: Over 240 debris flows occurred in hill-slopes, gullies ( indicated those with single-channel) and watersheds (indicated those with tributaries and channels) on July 10th 2013 in the Wenchuan county, and caused 29 casualties and about 633×106 USD losses. This work aimed to analyze characteristics, hazards and causes of these events and explore mitigating measures based on field investigation and remote sensing images interpretation. The debris flows contained clay content of 0.1%∼3.56%, having densities of 1.72∼2.14 t/m3, velocities of 5.0∼12.7 m/s, discharges of 335∼2353 m3/s and sediment yields of 0.10∼1.26×106 m3, and also numerously occurred in large watersheds with the area over 10 km2. Large debris flows formed 3 hazard-chains in slopes, gullies, watersheds and rivers, which all evolved in dammed lakes and outburst flood, and 26 dammed lakes and 10 newly ones were generated along the rivers of Min and Yuzi. The remarkable spatial difference of loose solid materials accumulation and intense rainfall, with the cumulative of about or more than 150 mm and the hourly of over 16mm, caused debris flows in the sections from Yingxiu to Miansi and Gengda. The damages on buildings, reconstructions, highways, factories and hydro power station originated from the impacting, scouring, burying of debris flows, the submerging of dammed lake and the scouring of outburst flood, and the huge losses came from the ruinous destructions of control engineering works of debris flows as well as the irrational location and low-resistant capabilities of reconstructions. For hazards mitigating of debris flows in long term, the feasible measures for short term, including risk-reassessing of foregone and potential hazard sites, regional alarming system establishing and integrated control in disastrous sites, and middle-long term, including improving reconstruction standard, rationally disposing river channel bed rise and selecting appropriate reconstruction time and plans, were strongly suggested.
[Show abstract][Hide abstract] ABSTRACT: In present paper, 3D finite element (FE) method is used to determine plastic limit load solutions for pipe bends under combined bending and torsion moment. With a detailed analysis and comparison, a common awareness for loading effect is showing which will raise researchers concern. By the way, past solutions are not appropriate to estimate FE results. In this respect of finite element analysis, overall yielding considering the spread process of yield region from crown to the straight pipe shows these promising finite element results. A wide range of non-dimensional parameters for pipe bends are considered and plastic limit load solutions are suggested. The results show that r/t is the main factor affecting the limit loads. Plastic limit load is independent on the loading path and material constants by normalizing. Results show that the circular interaction rule is a great approximation for pipe bends under combined bending and torsion moment. A series of approaches are confirmed in order to validate our finite element method on plastic limit analysis. Based on the finite element results, approximate plastic limit load solutions are proposed. Present work will further improve the limit load solution for pipe bends under complex loading conditions.
International Journal of Mechanical Sciences 12/2014; 92. DOI:10.1016/j.ijmecsci.2014.12.011 · 2.03 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Debris flows are typically caused by natural terrain landslides triggered by intense rainfalls. If an incoming mountain torrent flows along sloping channels at high velocity, huge amounts of sediment (from landslide dams and eroded channel beds) will be entrained into the flows to form debris flows. It is likely that large debris flows are due to the failure of many landslide dams of different scales (due to bank slides or collapses), bed erosion, and solid transport. The catastrophic debris flows that occurred in Wenjia Gully (Wenchuan Earthquake Area), China on August 13, 2010 (two years after the mega earthquake), were caused by intense rainfall and the serious erosion of sloping channels. In the wake of the incident, experimental tests were conducted to better understand the process of sediment erosion and entrainment on the channel bed and the formation of debris flows. The results show that the bed erosion, bank collapses and channel widening caused by erosion accounted for the triggering and scale amplification of downstream debris flows in the Wenjia Gully event. This study illustrates how the hazardous process of natural debris flows can begin several kilometers upstream, and how such a complex cascade of geomorphic events (failure of landslide dams and erosion of the sloping bed) can lead to catastrophic discharges. Neglecting recognition of these hazardous geomorphic and hydrodynamic processes may result in high cost.
[Show abstract][Hide abstract] ABSTRACT: Avalanches and landslides caused by the Wenchuan earthquake in the Longmen Mountains area provide abundant loose solids for debris flows, and a large number of debris flows have occurred during the period 2008–2012. The engineering measures in certain gullies failed, causing serious damage and loss of life. Judging from the debris flow characteristics in the Wenchuan earthquake area, engineering measures should be better constructed after the active period of debris flows in severely affected areas. To reduce debris flow disasters, this paper proposes a mitigation method and design principle based on the transport capacity of the main river. A series of check dams with various opening sizes was designed by investigating and analyzing existing cases. Furthermore, a new type of drainage channel with prefabricated reinforced concrete boxes is proposed. Finally, a case study of the Xiaogangjian Gully, which is a typical debris flow gully in the Wenchuan earthquake area, is presented. This system of engineering measures is based on the main river's transport capacity and consists of five check dams with various opening sizes, a drainage channel with sidewalls constructed of prefabricated reinforced concrete boxes, and a debris flow basin at the base of the main gully. The debris flow mitigation measures constructed in the Xiaogangjian Gully effectively resisted a debris flow with a 50-year return period that was triggered by rainfall on July 26, 2012. Specifically, these measures effectively protected a highway and minimized debris flow damage. Thus, the layout and engineered structures involved in this new engineering technique can provide a reference design for debris flow hazard mitigation.
[Show abstract][Hide abstract] ABSTRACT: The formation of landslide dams is often induced by earthquakes in mountainous areas. The failure of a landslide dam typically results in catastrophic flash floods or debris flows downstream. Significant attention has been given to the processes and mechanisms involved in the failure of individual landslide dams. However, the processes leading to domino failures of multiple landslide dams remain unclear. In this study, experimental tests were carried out to investigate the domino failure of landslide dams and the consequent enlargement of downstream debris flows. Different blockage conditions were considered, including complete blockage, partial blockage and erodible bed (no blockage). The mean velocity of the flow front was estimated by videos. Total stress transducers (TSTs) and Laser range finders (LRFs) were employed to measure the total stress and the depth of the flow front, respectively. Under a complete blockage pattern, a portion of the debris flow was trapped in front of each retained landslide dam before the latter collapsed completely. This was accompanied by a dramatic decrease in the mean velocity of the flow front. Conversely, under both partial blockage and erodible bed conditions, the mean velocity of the flow front increased gradually downward along the sloping channel. Domino failures of the landslide dams were triggered when a series of dams (complete blockage and partial blockage) were distributed along the flume. However, not all of these domino failures led to enlarged debris flows. The modes of dam failures have significant impacts on the enlargement of debris flows. Therefore, further research is necessary to understand the mechanisms of domino failures of landslide dams and their effects on the enlargement of debris flows.
International Journal of Sediment Research 09/2014; 29(3):414–422. DOI:10.1016/S1001-6279(14)60055-X · 0.72 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: An Ms7.0 earthquake, focal depth 13 km, struck Lushan on April 20, 2013, caused 196 deaths and 21 missing, 13,484 injuries, and affected more than two million people. A field investigation was taken immediately after the quake, and the induced hazards were analyzed in comparison with the Wenchuan earthquake. We have identified 1,460 landslides and avalanches and four dammed lakes, which were generally small and concentrated on high elevation. Avalanches and rockfalls developed in cliffs and steep slopes of hard rocks, including Jinjixia of Baosheng Town and Dayanxia of Shuangshi Town, Lushan, and the K317 section the Xiaoguanzi section north to Lingguan Town along the provincial highway S210. Landslides were relatively less, mainly in moderate and small scales, developing in sandstone, shale, and loose colluviums. Only one single large landslide was observed to turn into debris slide-flow. Dammed lakes were formed by avalanches and landslides, all in small size and of low danger degree. The earthquake-induced hazards distributed in belt on the hanging wall along the faults, and their major controlling factors include tectonics, lithology, structure surface, and landform. More than 99 % landslides were within 30 km to the epicenter, and 678 within 10 km, accounting for 46 % of the total; about 50 % landslides were distributed on slopes between 35° and 55°, and 11 % on slope exceeding 75°; 60 % on slopes at the altitudes between 1,000 and 1,500 m, 77 % on slopes between 900 and 1,500 m; and 24 and 62 % in hard rocks and section between hard and soft rocks, respectively. Compared with the case of Wenchuan earthquake, both the number and extension of landslides and avalanches in Lushan earthquake-affected area are much smaller, only 5.53 % in number and 0.57 % in area. The earthquake has increased the instability of slope and potentiality of landslide and debris flow. Accordingly, the active period is expected to be relatively short comparing with that in Wenchuan earthquake-hit area. However, the insidious and concealed hazards bring difficulty for risk investigation.
[Show abstract][Hide abstract] ABSTRACT: Buildings are the element of greatest concern with regard to debris flow hazard risk, and their destruction is mainly caused by the collapse of walls and reinforced concrete (RC) columns. This research classifies the failure modes of the columns in a typical beam–column-framed building based on field investigations and historical data. It also proposes the collapse mechanism for columns damaged by debris flow, with reference to their failure modes. Based on the collapse mechanism, three typical types of RC columns with different strengths, which are usually used in many mountainous areas of Western China, were selected for the damage analysis. The critical velocity of debris flow and the diameter of particles were obtained using theories of material and structural mechanics. The results showed that the critical bearing condition of columns can be indicated by the formation of plastic hinges along columns and by the shear damage in the column section. The development of plastic hinges was mainly determined by the debris flow velocity and diameter and the impact location of large boulders. The energy of viscous debris flow is much larger than that of the dilute flow, and there will be more severe damage for columns under viscous flow impact. The critical velocities for three plastic hinge collapses are about twice those of two plastic hinge collapses. If the diameter of the boulders is larger than 0.5 m, the impact force of the large boulders plays a major role in the column collapse. Otherwise, both the dynamic pressure of debris flow and the impact force of boulders are responsible for column failure. Finally, the critical condition of column failure was applied to Zhouqu’s debris flow hazard. The calculated critical velocity is consistent with the value given by field investigation, which implies that this study can be used for risk analysis and damage estimation in a debris-flow-prone area.
[Show abstract][Hide abstract] ABSTRACT: In areas hit by the 2008 Wenchuan earthquake that occurred in Sichuan Province, China, debris flows are often generated from landslide deposits during heavy rainstorms. The broadly graded and unconsolidated landslide deposits respond to rainfall in very complex mechanical and hydraulic manners. An artificial rainfall test was conducted to simulate the rainfall infiltration and surface runoff processes occurring on the landslide deposit slope at the Wenjiagou Gully, China, with heavy rainfall rates (140 mm/h) incorporated. An innovative flume was designed to collect the slope interflow and surface runoff separately. Sensors to monitor the pore water content (PWP) and volumetric water content (VWC) were deployed. The results indicated that there were four stages in the hydrological response of landslide deposits during the artificial rain event: infiltration, a slow increase in interflow (surface runoff begins), a rapid increase in interflow (surface runoff slowly increases) and a steady state. Bed gradient increase will lead to PWP rapidly ascending and regressive failure happening. Concomitant with the observed increases in PWP and VWC, the shear strength of the landslide deposits decreased and led to the occurrence of small-scale shallow failures. Surface runoff, interflow and fine particle migration effects are presented to interpret the process of shallow failure. And although shallow slope failure is the result of interaction with the above three factors induced by rainfall, the key underlying factor is the characteristically loose structure of landslide deposits.
[Show abstract][Hide abstract] ABSTRACT: Declining vegetation coverage caused by serious soil erosion in dry-hot river valley of the Jinsha River has resulted in a vicious cycle of environmental deterioration and aggravated soil erosion. In order to identify the relationship between vegetation succession and transformation of soil erosion, the methods of “space replacing time” and 137Cs technique have been used to analyze community structure of vegetation and distribution characteristics of 137Cs contents in the slopes and vegetation units of five succession stages, which included native grassland, shrub, sapling forest, half-mature forest and near mature forest in Jiangjiagou gully, Dongchuan city, Yunnan province. We found, during the course of succession, the number of species in communities increased with vegetation development and succession, but the 137Cs loss decreased with vegetation succession. Following the succession, near mature forest had the highest 137Cs inventory and native grassland had the lowest 137Cs inventory in both slopes and vegetation units. Principal component analysis showed that 137Cs inventory was significantly positively correlated with average crown diameter of tree (ACDT), species number, tree coverage and average tree height. Average crown diameter of shrub (ACDS) and average shrub height were also positively related to 137Cs inventory but to a lesser extent. Based on the results of our study, we illustrated the improvement of soil erosion control through soil conservation and water regulation with vegetation succession. Consequently, the results suggest that community features significantly affect soil erosion, through which we can evaluate and predict the soil erosion intensity of different vegetation.
[Show abstract][Hide abstract] ABSTRACT: The Donghekou landslide-debris flow was a remarkable geological disaster triggered by the Wenchuan earthquake in 2008. The dynamic process of a rapid landslide-debris flow is very complicated and can be divided into two aspects: the slope dynamic response of the earthquake and the mass movement and accumulation process. A numerical method combined with a finite difference method (FDM) and discrete element method (DEM) for simulation of landslide-debris flow under seismic loading is presented. The FDM and DEM are coupled through the critical sliding surface, initiation time and velocity. The dynamic response of the slope is simulated by the finite difference method, and critical sliding surface is determined using the earthquake response spectrum method. The landslide initiation time and the velocity are determined by time-history analysis. The mass movement and accumulation process is simulated using the discrete element method. Simulation results demonstrate that the maximum amplification coefficient of dynamic acceleration for the Donghekou slope is approximately 3.909, the initiation time of landslide is approximately 6.0 s, and the average initial velocity of the sliding mass is approximately 0.85 m/s. The failure of the slope is the result of elevation-orientated amplification effect and the sliding mass triggered with a small initial velocity. The numerical simulated result of the maximum sliding velocity is approximately 66.35 m/s, and the mass is disintegrated rapidly because of collision and free fall. The landslide velocity decreases when the flowing mass reaches a lower slope angle and gradually comes to a stop, and the total travel distance is approximately 2400 m.
Journal of Asian Earth Sciences 10/2013; 76:70-84. DOI:10.1016/j.jseaes.2013.08.007 · 2.74 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Many mountain towns in China are located on the joint alluvial fans of multiple and adjacent past debris flows, making them vulnerable to large, multiple, and simultaneous debris flows during heavy rainfall. Without emergency management planning, such flows, often appearing with interconnecting and chain-reaction processes, can lead to extensive loss of life and property. In the Wenchuan earthquake-affected area, such disasters are common. We analyzed the compound effects of simultaneous debris flow events, and proposed three quantitative methods of debris risk assessment based on kinetic energy, flow depth, and inundation depth. Validated using a field study of actual debris flow disasters, these analyses are useful in determining the type, quantity, distribution, economic worth, and susceptibility of hazard-affected objects in a region. Subsequently, we established a method to determine the vulnerability of different hazard-affected objects, particularly concerning the susceptibility indexes of buildings or structures. By analyzing the elements underlying hazard formation conditions, damage potential, and the socio-economic conditions of mountain townships, we proposed a systematic and quantitative method for risk analysis of mountain townships. Finally, the proposed method was applied to a case study of Qingping Township, which was affected by 21 simultaneous debris flows triggered by a 50-year return period precipitation event. The proposed method analyzed the superposition and chain-reaction effects of disasters and divided the affected area of the township into three risk zones. The analysis indicated that the calculated risk zones coincide with the actual distribution and severity of damage in the debris flow event, which suggests that the risk assessment is consistent with results from the actual disaster.
[Show abstract][Hide abstract] ABSTRACT: Understanding the characteristics and mechanics of granular avalanches along sloping channels is fundamental and vital for the study of different geophysical flows in the field. By using the discrete element method (DEM), three-dimensional (3D) granular (mass) flows along a sloping channel are numerically modelled to study the contact behaviour between solid particles. The evolution of 3D unsteady granular flows from a quasi-static state to an inertial flow is systematically investigated through numerical simulations. Captured velocity profiles along the flow height show variation in the flow regimes, while utilisation of the definition of the Savage number allows study of the vibration of solids inside a granular body along the sloping channels. These numerical results are compared with field measurements to observe the effect of channel confinement on the solids discharge per unit width of granular flows. This particulate study illustrates that, for unsteady granular flows, solid particles in the front head are more collision dominated, with shear rates and Savage numbers greatly enhanced. Also, the solids discharge inside a granular body is not uniformly distributed. Finally, channel width acts as a confinement to the granular debris flow, which can significantly affect sediment transport.
[Show abstract][Hide abstract] ABSTRACT: The damming of rivers by landslides resulting in the formation of a lake was one of the typical secondary geological hazards triggered by the Wenchuan earthquake which occurred on May 12, 2008. Some landslide-dammed lakes were at a high risk of causing further damage since the rainstorm season was expected soon after the earthquake. Understanding the dynamic processes in the formation of landslide-dammed lakes is helpful in planning the mitigation measures. The Yangjiagou landslide-dammed lake was selected as a case study to investigate the typical processes of dam formation. The dynamic simulation of the formation of the Yangjiagou landslide-dammed lake was divided into two steps: the landslide step and the overflow/overtopping step. Two-dimensional discrete element method (DEM) was adopted to investigate the mechanics of the Yangjiagou landslide. The landslide process was found to be controlled by the bond strength and residual friction coefficient of the DEM models. Computational results show that the formation of the landslide dam took approximately 35 s. The maximum velocity of a typical particle was approximately 26.8 m/s. The shallow-water equation and finite difference method were used to analyze the hydrodynamic mechanisms of the overflow process of the landslide-dammed lake. Computational results show that overflow would have occurred 15.1 h after the river was blocked, and overtopping failure occurs for the landslide dam in the rainstorm season when the water flow is large enough, causing a major disaster.
[Show abstract][Hide abstract] ABSTRACT: During the last 70 years of general climatic amelioration, 18 glacial-lake outburst floods (GLOFs) and related debris flows have occurred from 15 moraine-dammed lakes in Tibet, China. Catastrophic loss of life and property has occurred because of the following factors: the large volumes of water discharged, the steep gradients of the U-shaped channels, and the amount and texture of the downstream channel bed and bank material. The peak discharge of each GLOF exceeded 1000 m3/s. These flood discharges transformed to non-cohesive debris flows if the channels contained sufficient loose sediment for entrainment (bulking) and if their gradients were >1%. We focus on this key element, transformation, and suggest that it be included in evaluating future GLOF-related risk, the probability of transformation to debris flow and hyperconcentrated flow. The general, sequential evolution of the flows can be described as from proximal GLOFs, to sedimentladen streamflow, to hyperconcentrated flow, to non-cohesive debris flow (viscous or cohesive debris flow only if sufficient fine sediment is present), and then, distally, back to hyperconcentrated flow and sediment-laden streamflow as sediment is progressively deposited. Most of the Tibet examples transformed only to non-cohesive debris flows. The important lesson for future hazard assessment and mitigation planning is that, as a GLOF entrains (bulks) enough sediment to become a debris flow, the flow volume must increase by at least three times (the "bulking factor"). In fact, the transforming flow waves overrun and mix with downstream streamflow, in addition to adding the entrained sediment (and thus enabling addition of yet more sediment and a bulking factor in excess of three times). To effectively reduce the risk of GLOF debris flows, reducing the level of a potentially dangerous lake with a siphon or excavated spillway or installing gabions in combination with a downstream debris dam are the primary approaches.