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Outburst floods generated by dam breaches associated with debris flow may have long-lasting effects on the formation and development landscape and the safety of human beings, increasing the difficulty of disaster prevention and mitigation. However, little was considered about channel aggradation contributing downstream damage of outburst flood. Therefore, we investigated a debris flow dam's breaching and flooding process triggered by a 50-year heavy rainfall occurring on 17th June 2020 in Danba, China. The 6-m dam and a concomitant 1.04 × 106 m3 barrier lake were formed by a tributary debris flow blocking the Xiaojin river. We used the dam breach overtopping and two-dimensional hydrodynamic models to simulate the whole process. The dam breach event persisted for 4.5 h with an outburst flood peak discharge of 823.5 m3/s, equal to a 20-year flood. It was noted that numerous sediments of approximately 5 × 106 m3 were transported to the downstream channel, elevating the main channel bed and the terrace by 10–15 m and 2–5 m, respectively. Averaged transportation efficiency of an outburst flood is 1269.73 times greater than a 20-year seasonal flood. We simulated representative seasonal floods and outburst floods based on the pre-beach river geometry, which shows that previous channel capacity is sufficient to convey seasonal floods and the outburst flood. However, the outburst flood could easily submerge terraces and living land using after-breach geometry. Due to river aggradation lifting river elevation, deposited riverbed promotes sediment and flood evolute to living land, resulting in amplified damage. Additionally, we collected 59 dam breaches and demonstrated that local riverbed slopes could increase more than 100 times. During dam breaches, the sharp slope plays a key role in high sediment transportation efficiency. This study can promote understanding the formation and development of channel aggradation triggered by outburst flood and provide more reasonable considerations for disaster prevention and mitigation triggered by outburst flood hazard chain. [ABSTRACT FROM AUTHOR]

Cryospheric responses to climate warming include glacier retreat, altitude‐dependent thermal instability, and abundant meltwater, which increase the frequency of catastrophic glacier hazard chain (CGHC) events. Here we investigated the formation mechanism of a special CGHC event in 2018, in the Sedongpu Glacier, Eastern Himalayas, China. Based on the multi‐source remote sensing, seismic signal analysis, and numerical simulation, we conducted long‐term retrospective analysis and co‐event process reconstruction. The results show that the event could be divided into two phases. First, the hanging glacier with a volume of 8.5 × 106 m3 collapsed onto the downstream trunk glacier. Next, ∼1.17 × 108 m3 eroded materials from the impacted glacier transformed into debris flow and traveled downstream 8 km. During the cascading process, ice‐rock avalanche momentum and glacier velocity are key factors in determining CGHC formation and eventual volume. Our study helps better understand the domino effects of the CGHC disaster. Plain Language Summary: Glacier instability in cryosphere is significantly influenced by global warming. The glacial lake outburst floods are the most widely studied and catastrophic events resulting from this instability, but they are not the only ones. In recent years, increasing catastrophic glacier hazard chain (CGHC) events have reminded us of disasters during climate warming, especially in the Himalayas region. Here, we report a typical CGHC event in the Eastern Himalayas, where the retreated glaciers are widely distributed. Based on our observations and simulations, we completed the retrospective analysis of CGHC through its formation conditions, evolution process, and specific kinematic process. These analyses help us understand the driving mechanism, the volume‐increasing effect, and the super‐fluidity of CGHC. Our findings help improve such hazard chain identification and mitigation in the Eastern Himalayas and glacierized environments elsewhere in the world. Key Points: New insights of Ice‐rock avalanche hazard chain on retreated hanging glacier in Eastern HimalayaErosion process on the trunk glacier led to a volume‐increasing and super‐fluidity of catastrophic glacier hazard chain (CGHC)The pre‐evolution and formation of CGHC were closely related to climate warming [ABSTRACT FROM AUTHOR]

In the context of Western China's unique geography, recurrent landslide disasters pose substantial threats to both resident safety and economic stability. The escalating frequency of these incidents emphasizes the critical need for innovative disaster research, particularly focused on the concept of a disaster chain. This research aims to enhance disaster preparedness and management strategies with the ultimate goal of minimizing losses. On the basis of predecessors, this study changes the previous analysis forms of single or partial disaster events, innovatively collects all secondary disaster events derived from the landslide disaster chain, and builds an evolutionary network model. In concrete terms, our study concentrates on the Baige landslide within the Qinghai-Tibet Plateau, pinpointing sub-hazard events as crucial disaster nodes within the landslide. By establishing directed connections, we have developed a comprehensive landslide disaster chain evolution network model firmly grounded in the principles of disaster chain dynamics and complex network theory. This model encompasses 31 distinct disaster nodes and 77 connecting edges. To assess the inherent risks in the landslide catastrophe chain, we conducted a thorough analysis considering node access degree and clustering coefficients. Critical nodes driving economic losses, such as floods, debris flows, secondary landslides, and downstream water damage, were identified. Additionally, we isolated vulnerable connections within the evolving network, evaluating the susceptibility of each edge. Our research underscores the significance of proactive measures, including pre-disaster monitoring, early warning systems, and timely post-disaster information dissemination. Implementing these actions can play a pivotal role in mitigating the impact of landslide disasters, preserving lives and sustaining regional prosperity. [ABSTRACT FROM AUTHOR]

In this study, the 1991 rock avalanche, in Touzhai, Zhaotong, Yunnan, China, was considered the study object. The investigation of the landslide accumulation body revealed that the Touzhai rock avalanche accumulation body has the characteristics of wide gradation and poor sorting. A combination of field investigations, indoor and outdoor experiments, and numerical simulations were used to invert the occurrence and spreading range of rock avalanche-debris flow hazards. To invert and analyze its dynamics and the crushing process, a three-dimensional discrete element modeling was performed on the real terrain data. Simulation results showed that the movement time of the numerically simulated Touzhai rock avalanche was approximately 200 s. After 50 s of movement, the peak velocity reached 32 m/s, and the velocity gradually decayed after the sliding mass rubbed violently against the valley floor and collided with the mountain. Due to the meandering nature of the gully, the sliding mass makes its way down the gully and constantly collides with the mountain, making particles appear to climb, with some particles being blocked by the valley. After 150 s of movement, the average velocity rate decreased substantially, and the landslide-avalanche debris reached the mouth of the trench. After 200 s of movement, the average sliding velocity tends to 0 m/s, where the avalanche debris tends to stop and accumulate. When the rock avalanche movement reaches the mouth of the gully, the avalanche debris spreads to the sides as it is no longer bounded by the hills on either side of the narrow gully, eventually forming a 'trumpet-shaped' accumulation, and the granular flow simulation matched the findings of the landslide site accumulation. [ABSTRACT FROM AUTHOR]

On 17 June 2020, a large ancient landslide over the Aniangzhai (ANZ) slope, Danba County, Sichuan Province, China, was reactivated by a series of multiple phenomena, including debris flow triggered by heavy rainfall and flooding. In this study, Synthetic Aperture Radar (SAR) images acquired by the Sentinel-1A/B satellite and optical images captured by the PlanetScope satellites were jointly used to analyze and explore the deformation characteristics and the Spatial-Temporal evolution of the ANZ landslide before and after the multi-hazard chain. Several areas of pre-failure movements were found from the multi-temporal optical images analysis before the reactivation of the ANZ landslide. The large post-failure surface deformation over the ANZ slope was also retrieved by the optical pixel offset tracking (POT) technique. A major northwest movement with the maximum horizontal deformation of up to 14.4 m was found. A time-series InSAR technique was applied to analyze the descending and ascending Sentinel-1A/B datasets spanning from March 2018 to July 2020, showing that the maximum magnitudes of the Line of Sight (LoS) displacement velocities were −70 mm/year and 45 mm/year, respectively. The Spatial-Temporal evolution over the ANZ landslide was analyzed based on the time-series results. No obvious change in acceleration (precursory deformation) was detected before the multi-hazard chain, while clear accelerated deformation can be observed over the slope after the event. This suggested that heavy rainfall was the most significant triggering factor for the generation and reactivation of the ANZ landslide. Other preparatory factors, including the deformation behavior, the undercutting and erosion of the river and the outburst flood, the local terrain conditions, and earthquakes, might also have played an important role in the generation and reactivation of the landslide. [ABSTRACT FROM AUTHOR]

Mountain mudslides have emerged as one of the main geological dangers in the Yanshan region of China as a result of excessive rains. In light of this, a multi-step debris flow hazard assessment method combining optimal weights and a topological object metamodel is proposed based on game theory ideas. First of all, based on the geological environment research in Yanshan area, this paper determines the mudslide danger evaluation indexes according to the field investigation and remote sensing image data, then combines them with the theory of topological object element evaluation, utilizes the idea of game theory, and carries out the optimal combination of the weight coefficients derived from hierarchical analysis and the CRITIC method to obtain the final comprehensive weights of the indexes, and forms the combination-assigning topological object element of the mudslide danger topological model. The results suggest that improved weight coefficients can increase topological evaluation precision, which is more in line with objective reality than the traditional method and has some application utility. [ABSTRACT FROM AUTHOR]

Unlike strong earthquake-triggered or heavy rainfall-triggered landslides, silent large-scale landslides (SLL) occur without significant triggering factors and cause unexpected significant disaster risks and mass casualties. Understanding the initiation mechanism of SLLs is crucial for risk reduction. In this study, the mechanism of the Zhaobishan SLL was investigated, and the SLL was jointly controlled by weak-soil (fractured rock mass) and strong-water (abundant water replenishment) conditions under the impact of active tectonism and complex hydraulic properties. Strong tectonic uplift, high fault density, and historical earthquakes led to weak-soil conditions conducive to the Zhaobishan SLL. The combined effect of unique lithology, antiform, and cultivated land contributed to the water replenishment characteristics of extensive runoff confluence (3.16 times that of the landslide body) and supported long-distance groundwater replenishment, thereby forming strong-water conditions for the landslide. The amplified seepage amount caused the strength of the soil mass on the sliding surface to decrease to 0.4 times its initial strength, eventually triggering the Zhaobishan SLL, which occurred 4.6 days after the peak rainfall. Moreover, the landslide deposits have accumulated on the semi-diagenetic clay rock, thereby controlling the subsequent recurring debris flows in the Lengzi Gully. To reduce disaster risk of SLL in vulnerable mountainous regions, the water confluence area behind the main scarp of the landslides and the hysteresis characteristics between landslides and peak rainfall should be further considered, and recurring debris flows following massive landslides also should be focused. [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]

In the Eastern Himalayas syntaxes (Tibet Plateau, China), increasing periglacial debris flows have been documented in recent decades, but minimal research has focused on the material properties and the topography of initiation areas. In this work, we applied a series of satellite images from 2000 to 2021 to examine the hanging glacier status and debris-flow initiation conditions in Sanggu watershed. Five large-scale debris flow events in 2003, 2015, 2018, 2020, and 2021 were interpreted. Visual interpretation, together with pixel dichotomy model and the COSI-Corr method, demonstrated that debris flows mainly initiated from the periglacial environment of catchments I and II. Since 2000, the glacier has exhibited general shrinkage, punctuated by occasional advance. The failure potential, expressed as the product of changed glacier area and topographic slope, positively relates to the inundation area of debris flows. This result implies that either abrupt glacier advancement or retreat may result in large debris flows, and glacier terminus position may serve as the main driving factor for debris flow initiation. Importantly, a lower limited area-slope initiation condition was developed in this work, which may provide a reference point for identifying possible failure areas of periglacial debris. The results of this work contribute to knowledge about the material properties and magnitude prediction of periglacial debris flows in alpine watersheds. [ABSTRACT FROM AUTHOR]

Understanding the impact forces exerted by debris flows is limited by a lack of direct field measurements and validated numerical models. In this study, we use real‐time impact‐force measurements and field observations of debris flows recorded by a sensor network in Jiangjia Ravine, China, to quantify the impact‐force distribution of natural debris flows. We observed one debris flow event during and after a storm on 25 August 2004, including 42 short‐duration surges and seven long‐duration surges, and impact‐force signals were successfully recorded for 38 surges. Our observed debris flows comprise high‐viscosity laminar flows with high sediment concentration and frequent solid‐to‐solid interactions. We identified a large magnitude (up to 1 kN), high‐frequency (greater than 1 Hz) fluctuating component of the impact force that we interpret as solid particle impact on the sensors. The variability of particle impact forces increases with the mean impact force. Our results show that a log‐logistic distribution can describe the probability density distribution of impact forces. Solid‐dominated surges and fluid‐dominated intersurge flows have similar impact‐force distributions, but surges usually have heavy tails. We created a dimensionless number to describe the impact force and correlated it against existing dimensionless parameters. Finally, we develop a simple particle impact model to understand the relationship between flow dynamics and the impact force inside debris flows that could be applied to improve debris‐flow flume experiments and design debris‐flow hazard mitigation measures. Plain Language Summary: Debris flows are fast‐moving mixtures of dirt and water that can cause huge damage to buildings and infrastructures and harm people. For effective hazard protection, we need to understand the impact forces exerted by debris flows. In this study, we measured impact forces at the high temporal resolution of 49 debris‐flow surges during and after a storm on 25 August 2004, recorded by a sensor array in Jiangjia Ravine, southwestern China. We develop statistical descriptions of the mean and the variability of the force and derive a relationship between flow dynamics and the impact force using a simple particle impact model. Our results could be applied to improve the future design of debris‐flow hazard mitigation measures. Key Points: Log‐logistic distribution is a good fit for debris‐flow impact force probability density functionsDebris‐flow surges and intersurge flows have similar impact force distribution, but surges usually have heavy tailsA simple particle impact model can explain the debris‐flow impact force signal [ABSTRACT FROM AUTHOR]

In Tibet Plateau, China, debris flows have been commonly documented in the marine monsoon climate region, yet few cases were recorded in continental climate regions, such as the mountain belt of Kallash and Back-Himalayas. In July 2021, prolonged low-intensity rain in Angla Mountain, another short-duration intensive rain in Purang County, initiated runoff-triggered debris flows. In this work, we are mainly concerned with the differences in the triggering rainfall condition and local landscape dissection with respect to the freeze–thaw state. The results reveal that the low triggering rainfall of debris flows at Angla Mountain may attribute to the long freeze–thaw duration. The high triggering rainfall of debris flows in Purang County may attribute to the high saturated hydraulic conductivity and short freeze–thaw duration. Nevertheless, freeze–thaw duration, together with the low saturated hydraulic conductivity, may result in heavy landscape dissection of Angla Mountain. The Melton's ruggedness number of catchments in the two areas is greater than some suggested criteria, indicating they are susceptible to debris flows. Debris flow deposits have low proportions of grain size fractions < 0.1 mm and higher fractions of 1–10 mm in size. Field measurement of a slope debris flow found that the mean diameter decreases as the slope gradient decreases and channel geometry widens. Such changes in gradient and channel geometry may lead to a volumetric concentration decrease, and the deposits become finer. This work preliminarily contributes to know about the effect of a freeze–thaw state on the triggering rainfall of debris flows and local landscape dissection in the continental climate region, Tibet Plateau, China. [ABSTRACT FROM AUTHOR]

Highlights: The topography and climate background determine that the hazard happens periodically, and these factors are fundamental for the weak vulnerability in the Sedongpu basin; The dynamic glacier simulations with the Elmer/Ice model showed that the glacier surface velocity can reach 19 cm/d on the Dongpu glacier; Heavy rain and an earthquake were triggering factors of the ice avalanche that led to the glacial debris flow. In this paper, the glacial debris flow blockage event, on 17 October 2018, in the Sedongpu basin of the Yarlung Zangbo River is taken as an example to analyse the occurrence and development of glacier hazards in this region. Multi-sources including remote sensing products, DEM, earthquake records and meteorological data were used to analyse the characteristics and mechanism of glacier hazards. The Elmer/Ice dynamic model was chosen to simulate the glacial surface velocity. It was found that topography and climate background determine that the hazard happens periodically. Based on the meteorological records of the Linzhi station, the warming rate was greater than 0.40 °C/10a during the period 1960–2017. The short-term heavy rainfall with daily values of 9.3 mm before the blockage event was also regarded as a factor. Both heavy rain and earthquake were triggering factors of the ice avalanche that led to the glacial debris flow. The glacier surface velocity of the Dongpu glacier simulated by Elmer/Ice model can reach 19 cm/d. This study has extensive applicability significance in glacier hazard mitigation under a changing climate. [ABSTRACT FROM AUTHOR]

On July 25, 2020, a debris flow occurred in the Wujia Gully, Sichuan Province, China. The last debris flow in this gully occurred 70 years ago and severely impacted the area downstream. The primary goal of this study was to analyze the impact of the topography on the movement process of the debris flow. To gain a precise understanding, a dataset was compiled, including metrological data, field data, accounts from locals, field sampling to obtain specific information using Unmanned Aerial Vehicle (UAV) photography, and the rheological properties of the debris flow slurry obtained through soil mechanics and rheological experiments. The movement process of the debris flow was simulated using the depth-integrated continuum approach. Based on numerical simulation analysis, the influence of the Wujia gully's topography on the debris flow's dynamic process was examined. It was found that the debris flow in the Wujia Gully was a typical viscous debris flow, and the debris flow slurry had the properties of a Bingham fluid. The dynamic process of the debris flow was divided into four stages: an acceleration stage, a deceleration stage in the channel, a smooth movement stage, and a slow accumulation stage. The topography was the main factor controlling the formation of the four stages of the dynamic process. Furthermore, Manning's resistance coefficient did not change the debris flow's dynamic process, but it significantly affected the velocity and duration of each stage. The results of this study provide a reference for future research on debris flow kinematics and flow channels of typical slope debris flows and their movement processes. [ABSTRACT FROM AUTHOR]

There has been an increased attention on hyperpycnal flows due to its importance in delivering large volumes of sediments into deep-water. The process and products of hyperpycnal flow in tectonically-active margins are still poorly understood, and potentially constitute one of the most important deep-water mechanisms in rift basins. This study integrates core data, well-logging and 3D seismic data to investigate the hyperpycnal flow process and dispersal pattern on the Eocene Dongying rift margin. 17 facies, including 5 conglomerate facies, 9 sand facies and 3 mud facies are identified, interpreted as the product of debris flows, traction currents, turbidity currents, transitional flows and lofting plumes, and suggesting the complex blend in flood-triggered hyperpycnal flow on rift margin. Two different hyperpycnal flow types are identified and a related process model is proposed based on facies sequence, distribution, transport mechanism and flood discharge analysis, including seasonal-flood triggered hyperpycnal flow (SHF) and outburst-flood triggered hyperpycnal flow (OHF). The evolution of the hyperpycnal system suggests two dispersal styles, including proximal sublacustrine fan dominated by OHF and distal sublacustrine fan dominated by SHF, respectively. Climate and tectonic movements are suggested to be the main factors controlling hyperpycnal flow generation and deposition on rift margins. The relatively arid climate enhanced seasonal-flood activity and associated sustained and stable SHF, which further prompt distal sublacustrine fan development during a weak rifting period. On the other hand, the generation of outburst-floods can be attributed to the enhanced fault activity, which corresponds to the periodical tectonic movements in the basin. As a result, proximal sublacustrine fans tend to develop in near-shore topographic lows down-dip of syn-depositional faults due to increased tectonic activities, accommodation and enhanced OHF. A deep-water depositional model is proposed for hyperpycnal systems on rift margins by emphasizing the variety in sedimentary process and dispersal patterns controlled by climate and tectonics forces, which may provide new insights into hyperpycnal flow theories and deep-water exploration in world rift basins. • Dispersal pattern and process of a faulted margin hyperpycnal system have been investigated from a lacustrine rift basin. • Two different types of hyperpycnal flows on a rift basin margin are identified and a related process model is proposed. • Two different dispersal patterns in a deep-lacustrine hyperpycnal system are documented and analysed. • Climate and fault movements controlling hyperpycnal flow types, processes and dispersal patterns on tectonic active margins. [ABSTRACT FROM AUTHOR]

Debris flows can be extremely destructive because they can increase in magnitude via progressive entrainment. In this paper, a total of 18 landslide-type debris flows and 268 channelized debris flows in Wenchuan earthquake and Taiwan region, as well as other regions were collected to analyze the entrainment rate of debris flows in each triggering condition. Results show that there is a power relationship between volume of initial triggered mass and final deposited debris for landslide type debris flow. The debris flows during 2008 and 2013 in Wenchuan earthquake-region have smaller entrainment rate than that from 2001 t0 2009 in Taiwan. The entrainment rate of debris flow events from 2001 to 2009 in Taiwan shows a decaying tendency as elapsed time. Comparison of the entrainment rate in the two earthquake-hit regions with other regions proves that entrainment rate has a close relation with major sediment availability and secondary rainstorm conditions. [ABSTRACT FROM AUTHOR]

The debris flow, which was triggered in the Wenjia Gully on August 13, 2010, is an extreme example of mass movement events, which occurred after the Wenchuan earthquake of May 12, 2008. This Earthquake triggered in the Wenjia Gully the second largest co-seismic landslide, which can be classified as a rockslide-debris avalanche. A lot of loose sediments was deposited in the basin. In the main so called Deposition Area II of this landslide, with a volume of 30 × 10 m, flash floods can easily trigger debris flows because of the steep bottom slope and the relative small grain sizes of the sediments. The largest debris flow of August 13, 2010 destroyed the most downstream dam in the catchment during a heavy rain storm. The debris flow with a peak discharge of 1,530 m/s and a total volume of 3.1 × 10 m caused the death of 7 persons, 5 persons were missing, 39 persons were injured and 479 houses buried. After three rainy seasons, only 16 % of the landslide-debris deposition was taken away by 5 large-scale debris flow events. Since the threshold for rainfall triggered debris flows in the Wenjia Gully and other catchments drastically decreased after the Wenchuan Earthquake, new catastrophic events are expected in the future during the rainy season. [ABSTRACT FROM AUTHOR]

On Monday, May 12, 2008, a devastating mega-earthquake of magnitude 8.0 struck the Wenchuan area, northwestern Sichuan Province, China. The focal mechanism of the earthquake was successive massive rock fracturing 15 km in depth at Yingxiu. Seismic analysis confirms that the major shock occurred on the Beichuan-Yingxiu Fault and that aftershocks rapidly extended in a straight northeast-southeast direction along the Longmenshan Fault zone. Fatalities approaching a total of 15,000 occurred, with a significant number resulting from four types of seismically triggered geohazards-rock avalanches and landslides, landslide-dammed lakes ('earthquake lakes'), and debris flows. China Geological Survey has identified 4,970 potentially risky sites, 1,701 landslides, 1,844 rock avalanches, 515 debris flows, and 1,093 unstable slopes. Rock avalanches and landslides caused many fatalities directly and disrupted the transportation system, extensively disrupting rescue efforts and thereby causing additional fatalities. Landslide-dammed lakes not only flooded human habitats in upstream areas but also posed threats to potentially inundated downstream areas with large populations. Debris flows become the most remarkable geohazards featured by increasing number, high frequency, and low triggering rainfall. Earthquake-triggered geohazards sequentially induced and transformed to additional hazards. For example, debris flows occurred on rock avalanches and landslides, followed by landslide-dammed lakes, and then by additional debris flows and breakouts of the landslide-dammed lakes and downstream flooding. Earthquake-induced geohazards occurred mainly along the fault zone and decreased sharply with distance from the fault. It can be anticipated that post-earthquake geohazards, particularly for debris flows, will continue for 5-10 years and even for as long as 20 years. An integrated strategy of continuing emergency response and economic reconstruction is required. The lesson from Wenchuan Earthquake is that the resulted geohazards may appear in large number in active fault regions. A plan for geohazard prevention in the earthquake-active mountainous areas is needed in advance. [ABSTRACT FROM AUTHOR]

This paper assesses the probability of the main stream in the Dujiangyan-Wenchuan reach of the Minjiang River becoming blocked by debris flows in response to the Wenchuan Earthquake of 12 May 2008, on the basis of analyses of remote sensing data and ground investigations. Background information of debris flow gullies was developed from field investigations and high-resolution remote sensing image interpretation, and was used to estimate the maximum discharge per unit width by means of the revised model of debris flow magnitude according to the situation after the Earthquake. Based on improved discrimination equations of river blocking induced by debris flow, 29 debris flow gullies were evaluated and classified as four probability levels: extreme high, high, moderate and low. The results show that most of the debris flow gullies were at or over moderate hazard level, accounting for 72.4% of the total area. The present results provide a scientific basis for the prevention, elusion and mitigation of debris flow hazards and will contribute to the reconstruction of an earthquake prone area. [ABSTRACT FROM AUTHOR]