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The term debris flow is associated with a wide variety of phenomena as debris slides, debris torrents, debris floods, mudflows, mudslides, hyper-concentrated flows and lahars (in volcanic slopes). In historical times, they frequently occurred in Campania Region (Southern Italy) producing damage and casualties. In this paper, more than 200 events described as “debris flow” between 1924 and 2020 were collected. They are mainly located in the central sector of the region, which is characterized by pyroclastic deposits resting on steep carbonate and volcanic slopes and highly prone to hydrogeological hazards. Debris flow events registered in the region were classified as “gravity processes” (flow-like landslides, FL) or “fluvial processes” (flash floods, FF). This classification is fundamental for designing effective early warning systems and risk mitigation plans, since the two phenomena are triggered by different types of rainfall events and are responsible for damages of different magnitude. In this study, a large rainfall database was explored to identify the time scales and seasonality of the two classes of rainfall events, respectively triggering the two phenomena.

Tailing dam failures are most common worldwide that should be. The recent disasters of Fundao dam (2015) and Corrego do Feijao dam (2019) are among the worst of these disasters in terms of human, social, environmental, and economic costs. The Corrego do Feijao dam collapsed at 12:28 p.m. on Jan. 25, 2019, killing 272 people, with 11 still missing. The dam had 76 m high, with a crest of 720 m. It stored 12 Mt iron ore tailings, mostly composed by sand to silt-sized hematite, goethite, and quartz. Its sudden collapse provoked (a) a rotational slide which destroyed the complete dam structure; (b) a debris avalanche; (c) a debris flow; and (d) a mudflow, composed by a mixture between tailings material and the soil. The debris flow velocity is estimated to be at least 90 km/h in the first 500 m downstream of the dam. CENACID team subdivided into the affected area into zones of destructive capability (ZDC), from ZDC1 to ZDC4, in order of increasing destructivity. The ZDC4 comprises both a debris avalanche and an extremely high-energy debris flow, where basal and lateral erosion predominates. In the ZCD3, the material is transitioning from low-energy debris flow to mud flow because of the increase of soil mixed with the tailings. The ZDC2 comprises high-energy mudflow, with predominance of deposition over erosion. The ZDC1 is a low-energy mudflow that is deposited in the Paraopeba River. In the river channel, the finer sediment has been carried downwards either as a bedload or as a suspension load. The qualitative preliminary analysis of this anthropogenic gravitational mass movement enhances our understanding of this type of disaster. This initial quantitative analysis is important to improve the risk analysis in tailings dam failure events.

Among the natural disasters on the planet, especially in the mountainous and foothill regions, it is widespread erosive-debris flow events, which have the most significant environmental and economic damage to humanity. Georgia is no exception. This paper aims to develop a new methodology to calculate the predictive quantities of debris flow, essential for implementing anti-debris flow measures. Based on the available data and various calculations, a completely new empirical approach has been adopted to calculate predictive quantities of debris flow spent, predicting debris flow spent in the mountains and foothill regions of Georgia. The suggested methodology reflects the physics of debris-flow processes at a very high level and can be applied to calculate debris flow in various world regions.

This study analyses the Devdoraki Glacier surge type catastrophes since 1776, lead to human casualties, destruction of settlements and the international road in the Georgian Caucasus. According to archival data, at least six ice and ice-rock avalanches fell from the Devdoraki Glacier onto the Tergi (Terek) River valley during the period 1776–1876, the largest on June 18, 1776 and on August 13, 1832. The first blocked the Tergi River for three days and was breached catastrophically; the second was ~100 m high and ~2 km wide and its breach started after 8 hours. The most recent hazard occurred on May 17, 2014 killing nine people, and destroyed the Trans-Caucasus gas pipeline, Dariali Hydropower Plant (HPP) and international road. Using aerial and satellite imagery – Landsat, ASTER, SENTINEL along with the 30 m resolution Advanced Spaceborne Thermal Emission and Reflection Radiometer Global Digital Elevation Model (ASTER GDEM; 17 November 2011) we have reconstructed this event. On the basis of subsequent detailed field observations, new geological and tectonic maps of the study region have been compiled. After that collapse we have registered ~180 m advance of the Devdoraki Glacier snout between 2014 and 2015, which was mostly caused by rock-ice avalanche deposits. This part of the glacier should be monitored continuously as it can raise debris flow activity in the future. We consider the main hypotheses behind these events, namely a) tectonic and seismic, b) permafrost, c) volcanic and d) morphological factors; interpret the data for mechanisms and velocities of the catastrophic movement and argue that the 2014 event should not be classified as a glacier surge, although the possibility of similar glacial surges can not be excluded. The Kazbegi-Jimara massif should be considered as a natural laboratory that enables the investigation of rock-ice avalanches and glacial mudflows.

Counteracting the phenomenon of debris flow is implemented in various ways. As international practice has shown, hydrotechnical constructionsoccupy a special place among structures regulating debris flow. Despite the large variety of constructions, each of them has a strictly defined purpose. The specifics associated with the hazards of debris flow in a given area are taken into account when selecting such a construction. The work indicates the expediency of applying semi-cylindrical openweb constructions to regulate debris flow. The methodology of selecting the design elements is presented. A specific example of the construction calculation and graphic illustrations are presented.

Presented are the results from studying transported and suspended load formed during the debris flows and floods within the basins of small rivers in the central part of the Sayan-Baikal Stanovoi Highlands. In studying deposits of suspended and transported load exposed by profiles on alluvial fans, the age of the debris flow event was determined by radiocarbon dating of organic matter of buried soils. The turbidity of the flow, its speed, water discharge, pH, total mineralization of water and mudflow suspensions, and particle size distribution of suspended material were estimated for suspended load as part of the research. With a normal and reduced runoff, the water in the rivers of the central part of the Sayan-Baikal Stanovoi Highlands is transparent and clean. Visible turbidity of water appears with the formation of a high water resulting from atmospheric precipitation and snowmelt. In the rivers under investigation, the turbidity at the peak of the flood or debris flow was about 7 thou g/m3, with the maximum turbidity not exceeding 25 thou g/m3 (the Slyudyanka river, 1960). The particle size of suspended material varied from silt sand to heavy sandy loam and light loam. The research has shown that suspended load, along with tractional load, plays a significant role in the formation of accumulative landforms. This is especially evident in the lower parts of the cones, where they are able to be deposited as layers reaching several meters.

Over the last decades, numerous extreme climate events such as extreme temperatures, droughts, heavy precipitation, and storms associated with climate change have been recorded in many countries, including Bulgaria. As a result, geomorphological hazards such as landslides, debris flows, mudflows, high-speed soil erosion, etc. often occur on the territory of the country. The debris flow is one of the most common hazardous processes in small catchments of the main river basins in Bulgaria. The Kresna Gorge located in the middle part of Struma River valley is a typical area with such processes which often cause the damages to the E79 international highway. The purpose of the present study is to characterize debris flows in Kresna Gorge (southwestern part of Bulgaria) by comparative analysis between the two events (occurred on May 24, 2009 and July 28, 2019). In order to achieve the aim of the study the geomorphological features and flow type of 2019 event were identified and the results were compared with the previous publications which investigated the event on May 24, 2009. In the present paper, the sediments and the type of transportation of the investigated event (July 2019) were determined by grain-size and clast-shape analysis. The impact of weather conditions on debris flow occurrence was shown by the analysis of the synoptic conditions on the day before the event. The results of the study bring to clarifying the geological-geomorphological and meteorological factors for the occurrence of debris flow and are important for geomorphological hazard management.

Geological hazard posed by landslides, debris flows, rock avalanches and mudflows has always been and still represents a major threat for communities all over the world, causing extensive damage and often times the destruction of infrastructures and facilities. Over the last decades, the protection of the population from geohazards and the safe operation of infrastructures have become a significant priority for most countries in the world. Geological-related, adverse phenomena are more frequent in mountainous countries with high rainfall amounts and complicated geological settings. The above-mentioned geological hazards can also be favoured by climate change, earthquakes, as well as by pervasive human activities. Georgia belongs to one of the most complicated regions among the world’s mountainous countries: thousands of settlements, buildings, roads, oil and gas pipelines, high-voltage power lines are prone to geohazards, that can trigger disasters and lead to widespread losses of life and property. Consequently, geohazard assessment is an important step towards the management and mitigation of adverse, natural events. In the present work, we introduce a set of new hazard maps for geological hazard assessment, compiled by employing methods applied at the national level, with a particular focus on landslides and mudflows.

Wildfires increase flow and sediment load through removal of vegetation, alteration of soils, decreasing infiltration, and production of ash commonly generating a wide variety of geophysical flows (i.e., hyperconcentrated flows, mudflows, debris flows, etc.). Numerical modellers have developed a variety of Non-Newtonian algorithms to simulate each of these processes, and therefore, it can be difficult to understand the assumptions and limitations in any given model or replicate work. This diversity in the processes and approach to non-Newtonian simulations makes a modular computation library approach advantageous. A computational library consolidates the algorithms for each process and discriminates between these processes and algorithms with quantitative non-dimensional thresholds. This work presents a flexible numerical library framework (DebrisLib) to simulate large-scale, post-wildfire, non-Newtonian geophysical flows using both kinematic wave and shallow-water models. DebrisLib is derived from a variety of non-Newtonian closure approaches that predict a range of non-Newtonian flow conditions. It is a modular code designed to operate with any Newtonian, shallow-water parent code architecture. This paper presents the non-Newtonian model framework and demonstrates its effectiveness by calling it from two very different modelling frameworks developed by the U.S. Army Corp of Engineers (USACE), specifically, within the one-dimensional and two-dimensional Hydrologic Engineering Centre River Analysis System (HEC-RAS) and two-dimensional Adaptive Hydraulics (AdH) numerical models. The development and linkage-architecture were verified and validated using two non-Newtonian flume experiments selected to represent a range of non-Newtonian flow conditions (i.e., hyperconcentrated flow, mudflow, debris flow) commonly associated with post-wildfire flooding.

Debris flow is a geological phenomenon occurring in nature under the action of gravitational forces over a sloping surface and exists in different forms, e.g. landslides, rockfalls, debris avalanches or mudslides. The significance of studying debris flow lies in the effective estimation of flow-height, front velocities, impact pressures and amount of material deposition at the runout zone, which are essential for designing barriers, rock fence or rock sheds as protective measures against such mass movements. A numerical framework can be adopted to solve the field equations associated with the debris flow phenomenon in conjunction with a suitable material model mimicking the constitutive behaviour of the flowing mass. The front velocity and debris runout length are better predicted when the momentum balance equation takes into account the flow resistance due to turbulence, which inherently results in a nonhomogeneous distribution of the flow viscosity. Moreover, due to the heterogeneous nature of the debris mixture there appears to be no plausible reason for the mechanical model to assume a homogeneous rheological parameter. The influence of nonhomogeneous viscosity on the dynamics of debris flow has been explored in this work, through Newtonian, single-phase, multi-material, laminar-flow simulations. An efficient adaptive-mesh hybrid finite-element/control volume (FE/CV) framework—Fluidity, which enables full Eulerian-based large deformation analysis has been utilised for this purpose. Based on the results obtained, it is noticed that the viscous nature of the lower layer primarily dictates the final flow pattern of the debris.

A giant debris flow occurred in the Laomao Mountain area of Dalian city on July 27, 1981, which caused considerable losses of human lives and damages to properties. The average precipitation of Dalian has increased in recent years as compared with the annual mean precipitation. Increased and concentrated rainfall indicates a high possibility of debris flow outbreak in the Laomao Mountain area. The topography and material conditions of the debris flow gully in Matun village in Wafangdian city, Wanjialing town, Laomao Mountain area lead to the development and occurrence of mudslides. This study analyzed the development conditions of the debris flow gully in Matun village and conducted a risk evaluation of the debris flow gully by analytic hierarchy process and fuzzy comprehensive evaluation based on field survey in the study area. The results indicate that the debris flow gully in Matun village is highly dangerous, and debris flow occurs during heavy rainfall. In addition, the breakout of debris flow can threaten human life and property.

Based on the catastrophic June 28, 2014, Arshan debris flows in the Eastern Sayan Mountains, the structure and lithological composition of the debris are studied and a debris flow defense system is proposed. Among five debris flows in this region, two flows 4.1 and 5.6 km long are scrutinized. The grain size and mineral composition of fans and mudflows, as well as their evolution scenario are studied. The paper also examines the engineering-geological features of debris flow sediments and their textural-structural and physical alterations in the course of settling. Specific attention is devoted to the lithological and climatic constraints of debris flows. It is noted that sediments of recent mudflows are characterized by a high underconsolidation and deliquescence, promoting the formation of high-plastic and fluidal zones that can migrate actively. The approach proposed for debris flow defense measures lies in the construction of flow diversion dams designed for orienting the debris flows toward the “debris dump site.”

In this paper, with debris flow in Zhouqu as the research object, combined with experiments such as cation exchange capacity (CEC), mineral chemical composition and water quality analysis, relation between water and salt in solid source forming debris flow was studied via soil column leaching test and soluble salt analysis, and internal characteristics of debris flow was accordingly showed. It was found that, the soil was loose, and the content of gravel and sand was high, and the content of fine particle was low. The soluble contents at the slope of the accumulation body were described as, collapsed accumulation body > landslide accumulation body, slope toe > slope top, gentle slope > steep slope, also related to length of the slope. The results indicated that accumulations released a large number of base ion after intense weathering, which migrated with water, concentrated and enriched at the slope toe. Saline soil with high salt content collapsed when encountering water and then formed mudflow, thus becoming the internal power to trigger and initiate debris flow to some extent.

Postwildfire debris flows are frequently triggered by runoff following high-intensity rainfall, but the physical mechanisms by which water-dominated flows transition to debris flows are poorly understood relative to debris flow initiation from shallow landslides. In this study, we combined a numerical model with high-resolution hydrologic and geomorphic data sets to test two different hypotheses for debris flow initiation during a rainfall event that produced numerous debris flows within a recently burned drainage basin. Based on simulations, large volumes of sediment eroded from the hillslopes were redeposited within the channel network throughout the storm, leading to the initiation of numerous debris flows as a result of the mass failure of sediment dams that built up within the channel. More generally, results provide a quantitative framework for assessing the potential of runoff-generated debris flows based on sediment supply and hydrologic conditions.

Extended horizons of 0.5–2-m-thick soft-sediment deformation structures, which were earlier described as the effects of strong earthquakes in the Late Pleistocene, are studied in glaciolacustrine deposits of the Khibiny massif (central part of the Kola Peninsula). The unstructured horizon of coarse-fragmental inclusions is found everywhere over the folds, which makes it possible to consider these structures as the result of debris flow impact on consolidated bottom sediments probably caused by glacial mudflow. Despite intense and instantaneous crumpling of sediments, no liquefaction or fluidization phenomena typical of seismites are recognized in the deformation structures. Thus, the new data on the genesis of folded horizons in glaciolacustrine sediments in the Khibiny massif does not confirm the high seismic potential of this region.

The Post-Forum Study Tour following the 4th World Landslide Forum 2017 in Ljubljana (Slovenia) focuses on the variety of landslide forms in Slovenia and its immediate NW surroundings, and the best-known examples of devastating landslides induced by rainfall or earthquakes. They differ in complexity of the both surrounding area and of the particular geological, structural and geotechnical features. Many of the landslides of the Study Tour are characterized by huge volumes and high velocity at the time of activation or development in the debris flow. In addition, to the damage to buildings, the lives of hundreds of people are also endangered; human casualties occur. On the first day, we will observe complex Pleistocene to recent landslides related to the Mesozoic carbonates thrust over folded and tectonically fractured Tertiary siliciclastic flysch in the Vipava Valley (SW Slovenia), serving as the main passage between the Friulian lowland and central Slovenia, and thus also an important corridor connecting Northern Italy to Central Europe. A combination of unfavourable geological conditions and intense short or prolonged rainfall periods leads to the formation of different types of complex landslides, from large-scale deep-seated rotational and translational slides to shallow landslides, slumps and sediment gravity flows in the form of debris or mudflows. The second day of the study tour will be held in the Soča River Valley located in NW Slovenia close to the border with Italy, where the most catastrophic Stože landslide in Slovenia recently caused the deaths of seven people, and the nearby Strug landslide, which is a combination of rockfall, landslide and debris flow. The final day of the Post-Forum Study Tour will start in the Valcanale Valley located across the border between Slovenia and Italy, severely affected by a debris flow in August 2003. The flow caused the deaths of two people, damaged 260 buildings; large amounts of deposits blocked the A23 Highway, covering both lanes. In Carinthia (Austria), about 25 km west of Villach, the Dobrač/Dobratsch multiple scarps of prehistoric and historic rockslides will be observed. Dobratsch is a massive mountain ridge with a length of 17 km and a width of 6 km, characterized by steep rocky walls. The 3-day study tour will conclude with a presentation of the Potoška planina landslide, a slide whose lower part may eventually generate a debris flow and therefore represents a hazard for the inhabitants and for the infrastructure within or near the village of Koroška Bela.

The Wulipo landslide, triggered by heavy rainfall on July 10, 2013, transformed into debris flow, resulted in the destruction of 12 houses, 44 deaths, and 117 missing. Our systematic investigation has led to the following results and to a new understanding about the formation and evolution process of this hazard. The fundamental factors of the formation of the landslide are a high-steep free surface at the front of the slide mass and the sandstone-mudstone mixed stratum structure of the slope. The inducing factor of the landslide is hydrostatic and hydrodynamic pressure change caused by heavy continuous rainfall. The geological mechanical model of the landslide can be summarized as “instability - translational slide - tension fracture - collapse” and the formation mechanism as “translational landslide induced by heavy rainfall”. The total volume of the landslide is 124.6×104 m3, and 16.3% of the sliding mass was dropped down from the cliff and transformed into debris flow during the sliding process, which enlarged 46.7% of the original sliding deposit area. The final accumulation area is found to be 9.2×104 m2. The hazard is a typical example of a disaster chain involving landslide and its induced debris flow. The concealment and disaster chain effect is the main reason for the heavy damage. In future risk assessment, it is suggested to enhance the research on potential landslide identification for weakly intercalated slopes. By considering the influence of the behaviors of landslide-induced debris flow, the disaster area could be determined more reasonably.

Debris flows are one of the most dangerous and common hydrological phenomena in mountainous regions. They are extremely various in their type and character, but they are always mountain flows consisting of a mixture of water and loose-fragmental debris. The problem of calculation and forecasting the mudflows still remains intractable. There are several reasons for that: Firstly, the representatives of the whole spectrum of the Earth Sciences (Hydrology, Geology, Geomorphology, Geography, Mechanics, Rheology) deal with this problem from their point of view. Secondly, systematic monitoring of passing debris flows are currently held only in several countries only (USA, Canada, Austria, Switzerland, Japan, China), because they require significant funding. Thirdly, the calculation methods, having been accepted for the present time, give certain errors. In this article, the results of the artificially triggered debris flow experiments conducted in 1972–1976 in the Chemolgan river basin, organized by the Kazakh Research Hydrometeorological Institute are described. These were the first full-scale experiments with the detailed recording of the numerous debris flows characteristics ever conducted. The movie is attached as supplementary material to the Editorial of the Special Issue. The information about the used measurement equipment, the obtained characteristics of debris flows, the debris flow classification accepted as a result of the experiments is given. Conducting such experiments in nature allowed us to assess various aspects of the formation of these natural phenomena and made it possible to build the mathematical models of the debris flow processes.

Potential triggering of mudflows by geodynamic and seismotectonic factors was assessed for the NE flank of the Baikal rift system, specifically for the junction area of the SW segment of the Chara depression, the Kodar ridge and the Muya-Chara inter-basin zone. The debris flow hazard in the study area is high due to geodynamic and seismotectonic activity and the regional permafrost, hydrological and climatic conditions. In 2001, debris flow damaged the railway section of the Baikal-Amur Mainline (BAM) on the northern shore of the Bolshoe Leprindo lake. To ensure stable railway operations, BAM must be protected from landslides and debris flows. Appropriate preventive actions need to be developed with respect to the correctly assessed current state of the local natural environment, which results from complex interactions between endogenous and exogenous processes. In our study, the Late Cenozoic geodynamics, faulting and seismicity are considered as the most important factors for the occurrence of landslides and mudflows on the southern slopes of the Kodar ridge. The relief in the study area develops in geodynamic conditions predetermined by active stretching of the crust, accompanied by uplifting of the rift shoulder with a large height gradient. The study area is a narrow segment of the zone of dynamic influence of the Baikal rift system. It has a dense network of faults activated in the Late Cenozoic and the fault segments active in Holocene, as deformation caused by the divergent movements of the Siberian and Transbaikalia lithospheric blocks concentrates in this narrow zone. We studied several fault systems, including those activated in the Late Cenozoic, which are related to abundant zones of high fracturing, fragmentation and disintegration of rocks to dust-size particles, accompanied by the most intensive physical weathering in such zones. In the Chara depression and the surrounding uplifts, modern seismicity and paleoseismicity are determined by differentiated movements along the active faults. In the modern and Holocene stages, during and after frequent seismic shocks (including strong ones) in the study area, loose debris materials are inten­sely displaced by gravity, accumulate in negative-relief forms, and provide an important source of solids for debris flows. The Stanovoi Plateau is currently experiencing a period of intensified tectonic and seismic activity, which contributes to favorable conditions for the occurrence of mudflows.

Xingguo County is located in the middle and low hilly mountainous areas. The area of the landslide, collapse and debris flow geological disasters is large. The sudden geological disasters such as landslides and mudslides caused by heavy rainfall are increasing year by year. This study mainly used high-altitude aerial imagery (0.5m) and Landsat 8 OLI satellite imagery covering Xingguo County as the data source, carried out remote sensing interpretation of geological environment background conditions and geological disasters in the whole area, and carried out on-site verification. At the same time, the correlation between the stratigraphic structure, topography and other factors in the study area and the spatial distribution characteristics of geological disaster points are discussed. The results show that: (1) based on remote sensing image interpretation of 377 geological disaster points; 83 landslide points, 229 hidden danger points, 17 collapse points, 26 hidden danger points, 1 hidden danger point, ground collapse point 1 At 20 places in the geological environment. (2) From the results of remote sensing interpretation, the types of geological disasters in the work area are mainly landslides and landslide hazards (including collapse type), and there are fewer collapses, collapses and debris flow hazards, and most landslide hazard points are unstable. (3) From the distribution of geological disasters, it is mainly within the scope of artificial influence. The construction of excavation slopes on the roads leads to instability of the slopes and induces disasters under the influence of rainfall. In addition, there are a large number of artificial mining mines in the work area. These places are also prone to geological disasters due to unreasonable mining and subsequent prevention and control work. (4) Areas with strong human activities, areas near the fault structure and water system roads are the main influencing factors for geological disasters in the work area.

The term "mudslide" seems to be favored by news media for all localized processes in which damage is caused by moving earth materials, regardless of whether the processes involved mud or sliding. The term came into prominence sixty years ago when an atmospheric river moved over southern California with disastrous landslides, debris flows, and floods. Very costly floodlike damage resulting from "mudslides" was added to the National Flood Insurance Program coverage as a result of the 1969 disaster. Landslides were, and still are, excluded from the flood insurance program and other insurance instruments. Because of lack of clarity in what range of phenomena was intended to be covered by the flood insurance program, a panel of experts assembled by the National Research Council (NRC) categorized the continuum of moving water to moving earth into (1) clear-water floods, (2) mud floods, (3) mud flows, and (4) other landslides. These categories recognize the lack of clear distinction between slope-movement classifications and floodlike damage caused by more fluid "landslides." Earth materials in the most recent landslide classification are subdivided into rock and soil; soil is further subdivided into debris and earth. Debris is composed of mineral fragments with 20 to 80 percent coarser than sand size, whereas earth is 80 percent sand and finer fragments. Mud was used in older geology-based classifications in a way similar to earth (e.g., mudstone). Mud is not a technical term in engineering usage. Sediment-water mixtures with sufficient water to behave hydraulically were called mud floods by the NRC. Mud flows differ from mud floods by having viscoplastic behavior, which allow mud flows to support fragments with densities greater than water during transportation and when the mass comes to rest. Mud flows and debris flows have a velocity-dependent strength (matrix viscosity) and a velocity-independent strength (shearing resistance of the mass). As a mud flow or debris flow slows to a stop, the velocity-dependent strength goes to zero; however, dense fragments do not sink or settle into the mass because of its static shearing resistance. The deposits of this spectrum of processes have distinctive sedimentary structures: clear-water flood deposits are stratified, graded, and fining upward; debris-flow deposits are unsorted, unstratified, and fully matrix supported; hyperconcentrated-flow deposits are fully clast supported. Debris-flow deposits may contain megaclasts, if they are available in the source area. Geoscientists and engineers need to understand contemporary terms used in the media to communicate with emergency managers and a variety of non-specialists, but also should recognize characteristics that are associated with specialized technical terms.

On 28 June 2014, debris flows brought large volumes of loose material into the Kyngarga river valley. The material was sourced from rock collapse and rock sliding on the valley slopes and delivered mainly to the river by debris flows from the side valleys of the river basin. Our field studies and analysis of the satellite images revealed that the potential debris volume received by the river amounted to about 1x106 m3. The morphometric parameters of the Kyngarga river basin are favorable for the river-channel processes associated with floods, debris flows and water-rock flows.

On the night of June 28, 2014, near the village of Arshan in Tunkinsky district, Republic of Buryatia in eastern Siberia, two types of debris flows were formed as a result of intense storm precipitation: 1) debris floods along the river Kyngarga; 2) debris flows along the valleys originating from the cirques of the southern slope of the Tunkinsky Goltsy range, which went in the south-west direction towards the village. A year later, July 14, 2015, in the village of Arshan a debris flood occurred in the river Kyngarga. During the Holocene debris flows have occurred repeatedly, traces of which are seen in the sections of loose deposits. Their age was defined with the help of radiocarbon analysis of buried soil horizons. A historical analysis of debris flow activity on the territory for more than a century was made using published scientific works. Natural factors for the formation of debris flow situation were considered (synoptic and climatic conditions, hydrology, geology and landscape structure were evaluated). Reasons for the most recent debris flows were defined. A detailed analysis was given of the valleys of a number of rivers where results of debris flows were the most destructive. As a result of the debris flow along the river Kharimta, realignment of the river network took place. Consequences of debris flows for the natural environment and infrastructure of the village of Arshan were evaluated. It is considered that the partial destruction of the village of Arshan is a distinct possibility in the near future due to debris flows from cirque #1.

The Oso, Washington, USA, landslide occurred on the morning of Saturday, 22 March 2014 and claimed the lives of 43 people. The landslide began within an ~ 200-m-high hillslope comprised of unconsolidated glacial and previous landslide/colluvial deposits; it continued as a debris avalanche/debris flow that rapidly inundated a neighborhood of 35 single-family residences. An intense three-week rainfall that immediately preceded the event most likely played a role in triggering the landslide; and other factors that likely contributed to destabilization of the landslide mass include alteration of the local groundwater recharge and hydrogeological regime from previous landsliding, weakening and alteration of the landslide mass caused by previous landsliding, and changes in stress distribution resulting from removal and deposition of material from earlier landsliding. Field reconnaissance following the event revealed six distinctive zones and several subzones that are characterized on the basis of geomorphic expression, styles of deformation, geologic materials, and the types, size, and orientation of vegetation. Seismic recording of the landslide indicate that the event was marked by several vibration-generating episodes of mass movement. We hypothesize that the landslide occurred in two stages, with the first being a sequential remobilization of existing slide masses from the most recent (2006) landslide and from an ancient slide that triggered a devastating debris avalanche/debris flow. The second stage involved headward extension into previously unfailed material that occurred in response to unloading and redirection of stresses.

Hundreds of settlements, agricultural lands, roads, oil and gas pipelines’ routes, towers of high voltage transmission lines, hydro-technical-meliorative objects, mountain resorts, etc. are periodically experiencing strong influence of landslide-gravitational and debris flow/mudflow processes (often with catastrophic results). Almost all landscape-geographic zones—from Black Sea coastal region, to mountainous-nival, where geo-ecological situation is severely complicated, are located in dangerous area of disaster. Negative social-economic, demographic and ecological consequences caused by debris flow/mudflows and landslide-gravitational processes, are seen in all spheres of human activity. In mountainous regions there is especially complicated situation, where in conditions of extreme activation of disaster, in many cases population displacement and transfer to other regions is needed. Because of it, in second half of 20th century, tens of villages in mountainous regions were desolated and agricultural lands were abandoned. Most alarming scenario is that such events are accompanied by loss of human lives. Only after 1995 up until now geological and geo-morphological processes in Georgia caused loss of lives of more than 139 persons. Even in conditions of routine activation of disaster, total economical damages reach tens of millions of dollars, and in case of extreme development—hundreds of millions.

The frequency of huge debris flows greatly increased in the epicenter area of the Wenchuan earthquake. Field investigation revealed that runoff during rainstorm played a major role in generating debris flows on the loose deposits, left by coseismic debris avalanches. However, the mechanisms of these runoff-generated debris flows are not well understood due to the complexity of the initiation processes. To better understand the initiation mechanisms, we simulated and monitored the initiation process in laboratory flume test, with the help of a 3D laser scanner. We found that run-off incision caused an accumulation of material down slope. This failed as shallow slides when saturated, transforming the process into debris in a second stage. After this initial phase, the debris flow volume increased rapidly by a chain of subsequent cascading processes starting with collapses of the side walls, damming and breaching, leading to a rapid widening of the erosion channel. In terms of erosion amount, the subsequent mechanisms were much more important than the initial one. The damming and breaching were found to be the main reasons for the huge magnitude of the debris flows in the post-earthquake area. It was also found that the tested material was susceptible to excess pore pressure and liquefaction in undrained triaxial, which may be a reason for the fluidization in the flume tests.

Pyroclastic soils mantling a wide area of the Campanian Apennines are subjected to recurrent instability phenomena. This study analyses the 5 and 6 May 1998 event which affected the Pizzo d’Alvano (Campania, southern Italy). More than 400 slides affecting shallow pyroclastic deposits were triggered by intense and prolonged but not extreme rainfall. Landslides affected the pyroclastic deposits that cover the steep calcareous ridges and are soil slip-debris flows and rapid mudflows. About 30 main channels were deeply scoured by flows which reached the alluvial fans depositing up to 400 000 m3 of material in the piedmont areas. About 75% of the landslides are associated with morphological discontinuities such as limestone cliffs and roads. The sliding surface is located within the pyroclastic cover, generally at the base of a pumice layer. Geotechnical characterisation of pyroclastic deposits has been accomplished by laboratory and in situ tests. Numerical modelling of seepage processes and stability analyses have been run on four simplified models representing different settings observed at the source areas. Seepage modelling showed the formation of pore pressure pulses in pumice layers and the localised increase of pore pressure in correspondence of stratigraphic discontinuities as response to the rainfall event registered between 28 April and 5 May. Numerical modelling provided pore pressure values for stability analyses and pointed out critical conditions where stratigraphic or morphological discontinuities occur. This study excludes the need of a groundwater flow from the underlying bedrock toward the pyroclastic cover for instabilities to occur.

In Georgia, landslide and debris flow/mudflow processes and water erosion are at the top of problems due to related eco-geological disaster risks and negative impact. By the scale of development of these events and their negative impact on the population and economy of the country, Georgia occupies leading position among high land countries of the world. Besides, the almost whole territory of the country is under the risk of earthquakes, the magnitude of which is 7–9. Impact of such earthquakes is directly stimulating and provoking gravitational landslide and debris flow processes. In Georgia major part of the population, agricultural lands, roads, oil and gas pipelines, hydro-technical – melioration facilities, power transmission lines and mountain tourism zones periodically are subjected to disastrous processes and the areas under the risk are expanding substantially. Around 70% of the territory of the country, about 3000 settlements (62%) are under the risk of geological disasters; 14,2% of agricultural lands were seriously damaged by geological processes and require conducting of cardinal protective measures; and 13,1% of agricultural lands are located within the high risk area. Consequently, more than 80% of the economic damage was caused to mountainous regions and the majority of eco-migrants are from highland areas. This causes vacation of villages.

The March 13th 1888 collapse of Ritter Island in Papua New Guinea is the largest known sector collapse of an island volcano in historical times. One single event removed most of the island and its western submarine flank, and produced a landslide deposit that extends at least 70 km from the headwall of the collapse scar. We have mapped and described the deposits of the debris avalanche left by the collapse using full-coverage multibeam bathymetry, side-scan sonar backscatter intensity mapping, chirp seismic-reflection profiles, TowCam photographs of the seafloor and samples from a single dredge. Applying concepts originally developed on the 1980 Mount St. Helens collapse landslide deposits, we find that the Ritter landslide deposits show three distinct morphological facies: large block debris avalanche, matrix-rich debris avalanche and distal debris flow facies. Restoring the island's land and submarine topography we obtained a volume of 4.2 km3 for the initial collapse, about 75% of which is now forming the large block facies at distances less than 12 km from the collapse scar. The matrix-rich facies volume is unknown, but large scale erosion of the marine sediment substrate yielded a minimum total volume of 6.4 km3 in the distal debris flow and/or turbidite deposits, highlighting the efficiency of substrate erosion during the later history of the landslide movement. Although studying submarine landslide deposits we can never have the same confidence that subaerial observations provide, our analysis shows that well-exposed submarine landslide deposits can be interpreted in a similar way to subaerial volcano collapse deposits, and that they can in turn be used to interpret older, incompletely exposed submarine landslide deposits. Studying the deposits from a facies perspective provides the basis for reconstructing the kinematics of a collapse event landslide; understanding the mechanisms involved in its movement and deposition; and so providing key inputs to tsunami models.

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. (C) 2014 Elsevier B.V. All rights reserved.

On 27 July 2011, a total of 33 debris flows occurred in Umyeonsan, Seoul, Korea, resulting in 16 fatalities and extensive damage to houses, roads, and other properties. The debris flows originated during an intense rainstorm with a peak intensity of 112.5 mm/h and a cumulative rainfall of 306.5 mm over 16 h. The debris flows were triggered by a combination of two processes: (1) shallow translational landslides in colluvium at the ridge crest along a fault plane associated with the Chugaryeong Fault Zone and (2) the progressive entrainment of loose material due to surface water runoff in the channel. The ensuing debris flows extensively eroded the colluvial deposits overlying the bedrock along their paths and transported large quantities of soil and woody debris. Two watersheds with catastrophic debris flows in the study area were chosen for a forensic investigation to analyze the geomorphological features of the debris flow gullies and to study several factors influencing the debris flows. The debris flow activity was found to be primarily related to rainfall, as well as to the loose, compressible colluvium overlying the gneiss bedrock, the watershed topography with >30° slopes, and the vegetation.

In recent years, traffic lines are rapidly thrusting into the hilly regions[1]. It’s not hard to list such cases that bridges have been damaged by mud-rock flow. In this paper, it is studied that the dynamic response of the solid T-pier to mud-rock flow. a finite element method is applied to analyse the effects of the stress and strain of an T-pier under the impact action of mud-rock flow with different velocity.

Chushui Creek in Shengmu Village, Nantou County, Taiwan, was analyzed for recurrent debris flow using numerical modeling and geographic information system (GIS) spatial analysis. The two-dimensional water flood and mudflow simulation program FLO-2D were used to simulate debris flow induced by rainfall during typhoon Herb in 1996 and Mindulle in 2004. Changes in topographic characteristics after the debris flows were simulated for the initiation of hydrological characteristics, magnitude, and affected area. Changes in topographic characteristics included those in elevation, slope, aspect, stream power index (SPI), topographic wetness index (TWI), and hypsometric curve integral (HI), all of which were analyzed using GIS spatial analysis. The results show that the SPI and peak discharge in the basin increased after a recurrence of debris flow. The TWI was higher in 2003 than in 2004 and indicated higher potential of landslide initiation when the slope of the basin was steeper. The HI revealed that the basin was in its mature stage and was shifting toward the old stage. Numerical simulation demonstrated that the parameters’ mean depth, maximum depth, affected area, mean flow rate, maximum flow rate, and peak flow discharge were increased after recurrent debris flow, and peak discharge occurred quickly.

Doktorski rad razmatra različite teorijske i praktične aspekte modeliranja poplavnih valova i tokova krupnozrnatog nekoherentnog (eng. Debris flow) i sitnozrnatog koherentnog materijala (eng. Mud flow, Earth flow) kao jednih od značajnijih mogućih prirodnih pojava na srednjem i donjem toku vodotoka Rječine. Rad se temelji na prikupljenim meteorološkim, hidrološkim i geotehničkim podacima, te rezultatima matematičkih i fizikalnih modela za različite scenarije kretanja poplavnih vodnih valova, propagacije toka krupnozrnatog i sitnozrnatog materijala na srednjem i donjem toku Rječine, od akumulacije Valići do urbanog dijela grada Rijeke uključujući i moguće scenarije posljedica tih aktivnosti. Metode istraživanja bazirane su većinom na ulaznim podacima sakupljenim terenskim mjerenjima na području istraživanja. Baza podataka sadrži osnovne informacije o postojećem stanju područja klizišta Grohovo i vodotoka Rječina, uključujući njihovu prirodu, veličinu, lokaciju i povijest, sve dostupne podatke o prethodnim istraživanjima (fotografije, povijesne spise, izvještaje, povratne analize područja i sl.), te podatke u realnom vremenu sa instaliranih mjernih uređaja (meteoroloških stanica, Mini i Baro Diver instrumenata, ombrografa, limnigrafa, ADCP mjerača protoka i sl.) za praćenje promjena na predmetnoj lokaciji. Metode istraživanja uključuju površinska istraživanja, podzemna istraživanja (mjerenje razine podzemnih voda na području klizišta Grohovo), 2D numeričko modeliranje poplavnih valova i tokova krupnozrnatog materijala primjenom SPH 2D simulacijskog programa na bazi SPH (eng. Smoothed Particle Hydrodinamics) metode i SOLFEC (eng. Solver for Finite Element Computation) simulacijskog programa na bazi neglatke kontaktne mehanike (eng. Non Smooth Contact Dynamics - NSCD), te GIS (eng. Geographic Information System) tehnologije. Na osnovi ulaznih hidroloških i geoloških podataka kreirani su numerički modeli tečenja nevezanog krupnozrnatog i sitnozrnatog materijala. Pri izradi numeričkih modela primijenjene su najčešće korištene empirijske metode erozijskih zakona (erozijski zakon po Egashiri, Voellmyu, Hungru), a predložen je i novi erozijski zakon. Na kraju rada su dane smjernice za analizu hazarda i rizika od djelovanja poplava te tokova krupnozrnatog i sitnozrnatog materijala na ispitivanom području. Uz pomoć dobivenih simulacijskih prikaza toka krupnozrnatog i sitnozrnatog materijala kvantificiran je vjerojatan volumen deponiranog materijala, brzine toka, dubine deponiranog materijala, kao i doseg toka takvih tipova tečenja na analiziranom području za nekoliko mogućih scenarija katastrofalnih pojava. Neki od scenarija obrađenih i analiziranih u radu vezani su za posljedice kolapsa brane Valići uslijed unosa flišne klizne mase u akumulaciju, nastanak plimnog vala i njegova propagacija prema urbanom dijelu grada Rijeke, kao i mogućnost formiranja toka krupnozrnatog materijala na srednjem dijelu toka Rječine nastalog uslijed miješanja akumulacijske vode i klizne mase nestabilnih padina. Predmetne analize omogućuju kvantifikaciju pojedinih ulaznih parametara koji iniciraju nastanak tokova krupnozrnatog i sitnozrnatog materijala. Odnosi definiranih parametara omogućuju uspostavljanje korelacija između geomorfoloških i hidrogeoloških uvjeta, te specifičnosti terenskih uvjeta s parametrima tla karakterističnim za nastanak tokova krupnozrnatog i sitnozrnatog materijala. Definiranjem kritičnih geomorfoloških i hidrogeoloških parametara tla koji uvjetuju pojavu tokova krupnozrnatog i sitnozrnatog materijala na flišnom području omogućena je procjena hazarda i mjere za ublažavanje hazarda. Pritom je provedena gruba analiza rizika na srednjem i donjem toku Rječine, pri čemu su definirani glavni elementi rizika. Dodatno su opisani uzroci mogućih nastanka analiziranih prirodnih hazarda, te smjernice za njihovu sanaciju i očuvanje od posljedica mogućih hazarda u budućnosti., The doctoral thesis discusses the different theoretical and practical aspects of flood waves modeling and propagation of coarse incoherent materials (debris flow modeling) and fine-grained cohesive material (mud flow modeling) as two potentially significant natural phenomena in the middle and lower part of the Rječina River. This doctoral thesis was based on the collection of meteorological, hydrological and geotechnical data, and consequently the development of physical and mathematical models for different movement scenarios of flood water waves, debris and mudflow propagation on the Rječina River, from the position of Valići accumulation to the urban part of the Rijeka City, including possible result scenarios of these activities. Research methods are based on the input data collected from terrain measurements in the defined area. The database contains basic information on the current state of Grohovo landslide area and Rječina River, including their nature, size, location and history, all available information on previous research (photographs, historical documents, reports, feedback analysis of areas, etc.), as well as real-time information from the built-measuring devices (meteorological stations, Mini and Baro Diver instruments, ombrografs, limnigrafs, satellite, radar, ADCP flow meter, etc.) to track changes at the location. Research methods include surface and underground research (measuring of groundwater levels in the area of the Grohovo landslide), 2D numerical modeling of flood waves and debris flows propagation (application of Smoothed Particle Hydrodinamics method (SPH) and SOLFEC (Solver for Finite Element Computation) simulation program based on Non Smooth Contact Dynamics - NSCD), and GIS (Geographic Information System) technology. Based on the input of hydrological and geological data, numerical models for debris flow and mudflow propagation were created. In developing numerical models, most commonly used empirical methods of the erosion law (Egashira, Hungr, and Voellmy erosion law) have been applied, as well as the implementation of the new erosion law. Based on that were given the guidelines for hazard and risk analysis of the flash-flood and debris flow effects on the investigated area. With the help of the debris and mudflow simulation display we quantified the volume of deposited materials, the flow velocity, the depth of the deposited materials, as well as run-out distance of debris and mudflow on the analyzed area for several possible scenarios of catastrophic phenomena. Some of the scenarios processed and analyzed in this doctoral thesis are related to the consequences of the Valići dam collapse (due to input flysch sliding mass into the accumulation), the formation of a tidal wave and its propagation to the urban part of the Rijeka City, as well as the possibility of forming the debris flow propagation in the middle part of the Rječina River due to mixing of water from the accumulation and initiating the sliding mass on the unstable flysch slopes. This analysis enables the quantification of individual input parameters that initiate the formation of debris flow and mudflow. The relationships of defined parameters allow the establishment of correlations between geomorphological and hydrogeological conditions, as well as the specifics of terrain conditions with the parameters of the soil characteristic for the formation of debris flow and mudflow. The definition of critical geomorphological and hydrogeological parameters of soil that encourage the emergence of debris flow and mudflows in flysch area enabled the assessment of hazards and hazard mitigation measures for the investigated area. In this regard a rough risk analysis of possible consequences on the middle and lower part of the Rječina River was conducted, whereby the main elements of risk were defined. Additionally, the causes of possible occurrence of natural hazards were described, as well as guidelines for their rehabilitation and preservation of the possible hazard consequences in the future.

Assessment of Data Analysis Practices in Debris Flow Modeling Debris flows can seriously damage infrastructure and potentially be responsible for the loss of life. Accurate estimates of debris volumes are necessary to design debris basins. The design accuracy of debris basins is currently limited by practices used in collecting data and then in the use of the data for model development. The goal of this research was to assess two current practices in debris flow collection and modeling. The specific objectives were: (1) to demonstrate that spurious modeling of debris production rates is not a good practice for estimating debris volumes; (2) to show that watershed burn can significantly influence the generation of debris volumes; and (3) to show the effect of the data collection interval on the accuracy of predicting debris volumes. Models to predict expected debris volumes for five regions of Southern California were developed using data from 35 existing debris basins. The correlation coefficients ranged from 0.26 to 0.91. Simulations were conducted to analyze the following data collection intervals: 1-year, 2-year, and random, with the following record lengths: 15, 30, 50, and 70 years. Results showed that both the data collection interval and the record length influence the magnitude of predicted debris volumes. These analyses also showed that prediction accuracy is greatly affected by current data collection and modeling practices.