Geological and geomorphological influences on a recent debris flow event in the Ice-scoured Mountain Quaternary domain,western Scotland

Debris flows in settings that have experienced net glacial erosion within the UK's Ice-scoured Quaternary domain are the result of a complex interaction of a range of geological and geomorphological factors. On the 11^th of August 2016 a rainfall-triggered debris flow deposited 100 t of sediment onto local road and rail infrastructure blocking transport between town of Fort William and port of Mallaig in north-west Scotland. The debris flow occurred in an ice-scoured setting, where current 1:50,000-scale geological maps suggest that little or no sediment is expected on the valley slopes. In this study, we show how weathering and mass-wasting processes have interacted with bedrock structures to fill localised depressions with sediment on the upper parts of the slope. The intense rainfall event of August 2016 caused the destabilisation of this localised sediment, with eventual failure along bedrock joint surfaces resulting in two debris flows. This study demonstrates the combination of processes that can result in thick accumulations of sediment on slopes that are otherwise generally lacking in superficial sediment cover. These sediment accumulations have the potential to pose a significant landslide hazard in areas that might previously have been thought of as lower susceptibility. The research illustrates a need to improve understanding and representation of sediment thickness and distribution on hill slopes – particularly those that show an absence of superficial deposits at the scale of currently available geological maps.     

Debris flows: behaviour and hazard assessment

Debris flows are water‐laden masses of soil and fragmented rock that rush down mountainsides, funnel into stream channels, entrain objects in their paths, and form lobate deposits when they spill onto valley floors. Because they have volumetric sediment concentrations that exceed 40 percent, maximum speeds that surpass 10 m/s, and sizes that can range up to ～10⁹ m³, debris flows can denude slopes, bury floodplains, and devastate people and property. Computational models can accurately represent the physics of debris‐flow initiation, motion and deposition by simulating evolution of flow mass and momentum while accounting for interactions of debris’ solid and fluid constituents. The use of physically based models for hazard forecasting can be limited by imprecise knowledge of initial and boundary conditions and material properties, however. Therefore, empirical methods continue to play an important role in debris‐flow hazard assessment.     

Characteristics of spatial distribution of debris flow and the effect of their sediment yield in main downstream of Jinsha River,China

Debris flow hazard posts a big threat to the main downstream of Jinsha River where a number of huge power stations are under construction. The characteristics of spatial distribution of debris flows and the effect of their sediment yield on the reservoir areas have been studied. An automatic recognition module was developed to extract the geometry of debris flow channels from remote sensing data. Spatial distribution pattern of debris flows is obtained through combining the inventory database and multi-source remote sensing investigation. The distribution of debris flows has high dependency on the various factors including geology, geomorphology, climate, hydrology and human economic activities. The debris flows distributed in the study area are characterized by group and pair distribution, uncompleted deposition fans, highly controlled by faults and tectonic activities, spatial variation between left bank and right bank, and different subdivisions. The sediment yield caused by debris flow activates is evaluated using multi-year observation data from numerous observation stations. Quantitative studies have been performed on the relationship between the sediment yield and the debris flow area. A relatively fix ratio of 2.6 (×10⁴ t/km²) has been found in different subdivisions of main downstream area which shows that the source of sediment discharged into Jinsha River primarily come from debris flow activities. Another ratio is evaluated to represent the transforming possibility of debris flow materials to bed-sediment load and suspended-sediment load in the river. Based on these findings, the potential effect of sediment yield caused by debris flows on reservoir areas is discussed. The zonation map shows the different effect of debris flow sediment on different dam site area which shows a good agreement with variation of debris flow spatial distribution.     

Limits of sediment transfer in an alpine debris-flow catchment,Illgraben, Switzerland

The 9.5 km² Illgraben catchment, located in the Rhône valley in the Central Alps of Switzerland, is one of the most active debris flow torrents in the Alps. In this paper we present sediment yield data collected in 2006 for segments where hillslopes and channels form a fully connected network and contrast these with sediment yields measured for disconnected hillslopes. The data reveal that sediment yields are 1–2 orders of magnitude larger in segments where hillslopes are connected with the channel network than on disconnected hillslopes. Support for this conclusion is provided by observations made on 1959, 1999 and 2004 aerial photographs that the vegetation cover in the disconnected segments is still intact, whereas denudation rates of several centimeters per year in the connected segments have inhibited the establishment of a stable vegetation cover. Furthermore, sediment supplied from hillslopes during the past 40 years has temporarily accumulated along the Illgraben channel, indicating that the channel aggraded over this period and has not yet recovered. An implication of this observation is that initiation of debris flows in the Illgraben catchment is limited more by the availability of intense rainfall than sediment. In contrast, on disconnected hillslopes, sediment flux does not appear to be driven by precipitation.The petrographic composition of the Illgraben fan deposits indicates two distinct sediment sources, one related to rockfall and the other to landslides and debris flows. The presence of clasts from both sources implies multiple processes of erosion, deposition, mixing and re-entrainment in the catchment before the material is exported to the Illgraben fan and to the Rhône River. In addition, delivery of large amounts of coarse-grained sediment to the Rhône causes a modification of the flow pattern from meandering or anastomosing upstream to braided downstream. Hence, the direct connectivity between hillslope and channelized processes in the Illgraben catchment causes not only rapid topographic modifications in the catchment, but also morphologic adjustment in the Rhône valley downstream.     

Movement of radiocaesium fallout released by the 2011 Fukushima nuclear accident

The moment magnitude (M _w) 9.0 Tohoku-Oki Earthquake occurred on March 11, 2011, generating an unusually large tsunami. The seismic shocks and tsunami inundation severely damaged the Fukushima Daiichi Nuclear Power Plant. Radionuclide emission due to reactor breakdown contaminated wide areas of Fukushima and its surroundings. Heavy rainfall causes runoff across surface soil, and fine soil particles are susceptible to uptake by the flowing water. The high radioactivity of grains suspended in floodwater indicates that radioactive fallout was streamed into rivers in particulate form and transported downstream under high-flow conditions. Here, we investigated the diachronic mode of ¹³⁴Cs and ¹³⁷Cs in central Fukushima, through which the contaminated air mass drifted and caused wet deposition of radionuclides. Stratigraphic measurements of radioactivity in sediment cores is the method employed in this study to determine the basin-wide movement of ¹³⁴Cs and ¹³⁷Cs, to evaluate the significance of the erosion–transportation–accumulation processes on natural decontamination in terrain characterized by steep slopes and high precipitation. Stratigraphic results illustrate the process of fluvial sediment discharge, and the massive deposition of radiocaesium suggests basin-wide movement of fallout during concentrated rainfall. Grain suspension in torrential currents is an important pathway for transportation of radionuclides from land to sea, and the appearance of hotspots on floodplains and the offshore sea floor is the consequence of erosion and transportation under seasonal heavy precipitation. Radioactive horizons occur in offshore sediment columns and thus radiocaesium discharged from the estuary will persist forever under the sea floor if no artificial disturbance occurs.     

Dynamical evolution properties of debris flows controlled by different mesh-sized flexible net barriers

Because the flexible net barrier is a gradually developed open-type debris-flow counter-measure, there are still uncertainties in its design criterion. By using several small-scale experimental flume model tests, the dynamical evolution properties of debris flows controlled by large and small mesh-sized (equal to D₉₀ and D₅₀, respectively) flexible net barriers are studied, including the debris flow behaviors, segregation, and permeability of sediments, as well as the energy absorption rates and potential overtopping occurring when debris flows impact the small mesh-sized one. Experimental results reveal that (a) two sediment deposition patterns are observed depending on variations in debris flow textures and mesh sizes; (b) the aggregation against flexible net barriers is dominated by flow dynamics; (c) the segregation and permeable functions of the barrier are determined by the mesh size, concentration, and flow dynamics; and (d) the smaller mesh-sized flexible net barrier tends to be more efficient in restraining more turbulent debris flows and can absorb greater rate of kinematic energy, and finally, the great kinematic energy dissipation that occurs when secondary debris flows interact with the post-deposits in front of the small mesh-sized flexible net barrier is believed to cause the failure of overtopping phenomenon. The mesh size is concluded to be the decisive parameter that should be associated with debris flow textures to design the control functions of flexible net barriers.     

Estimation of soil erosion rates in a subtropical mountain watershed using 137Cs radionuclide

The formulation of watershed management strategies to protect water resources threatened by soil erosion and sedimentation requires a thorough understanding of sediment sources and factors that drive soil movement in the watershed. This paper describes a study of medium-term water-driven soil erosion rates in a mountainous watershed of the Shihmen Reservoir in Taiwan. A total of 60 sampling sites were selected along a hillslope. At each sampling site, the inventory ¹³⁷Cs activity was determined and then calculated with the diffusion and migration model to derive soil erosion rates. The rates are one to two orders of magnitude lower than estimates using the Universal Soil Loss Equation, a soil erosion model often used in Taiwan. Results of multiple regression analysis indicate that the spatial variability of soil erosion rates is associated with the relative position of a sampling site to the nearest ridge and soil bulk densities (r ² = 0.33, p < 0.01). Finally, the patterns of soil redistribution rates on the hillslope follow the ¹³⁷Cs hillslope model as soil erosion increases in the downslope direction. No deposition site is found at footslope because soil deposition is swept away by regular flooding along the stream channel. This study is an important first step in using ¹³⁷Cs as a tracer of soil redistribution in mountainous watersheds of Taiwan.     

Reconstruction of urban stormwater contamination of an estuary using catchment history and sediment profile dating

Cores were collected from the length of Pakuranga estuary, a small urban estuary in Auckland, New Zealand, to determine sedimentation and contaminant history, and in particular the impact of urbanization. Catchment sediment loads for the most recent history (1953–1995), including urbanization since 1960, were reconstructed using the landcover history and soil erosion modeling. Pollen and¹⁴C dating and pre-urban landcover history were used to reconstruct early estuary sedimentation (i.e., post-3000 yr BP to 1960). Heavy metal concentrations, particle size,¹³⁷Cs, pollen, and catchment sediment loads were all needed to disentangle the complex estuarine response to urbanization.¹³⁷Cs profiles did not reflect the historical fallout pattern, but deposition of¹³⁷Cs-labelled eroded catchment soil, coinciding with peaks in urban construction. Temporal variations in stormwater¹³⁷Cs concentrations are likely due to varying contributions from¹³⁷Cs-rich topsoil and¹³⁷Cs-poor subsoils. A similar pattern was observed in heavy-metal concentrations and attributed to street runoff rather than topsoil being diluted by metal-poor subsoils. Dating of the sediment profiles showed that during urbanization sedimentation rates in the tidal creek and estuary were higher than sedimentation rates associated with past agricultural landuse and the original forest landcover. Urbanization has brought about substantial environmental changes in the upper estuary through continued infilling of shallow, intertidal areas, contamination by heavy metals to levels of ecological concern, sediment textural changes, and rapid mangrove colonization of formerly bare intertidal sediments.     

Assessment of sediment and erosion rates by using the caesium-137 technique in a Chinese polygonal karst depression

Karst depressions comprise geomorphologically important sources and sinks for sediments and associated pollutants; yet the sedimentology of many depressions is not well understood in the world. In this paper, the ¹³⁷Cs technique was employed to estimate recent sedimentation rates in a Chinese polygonal karst depression. The results indicate that the sediment deposition rates ranged from 0.91 to 1.97 mm year⁻¹ from 1963 to 2007, and the average sediment deposition rate and specific deposit yield were estimated to be 1.47 mm year⁻¹ and 20 t km⁻² year⁻¹, respectively. These results are consistent with the local monitoring data of runoff fields, which confirms the validity of the overall approach. This shows that the soil loss rate is very low in some karst areas of Southwest China. Above all, the approach appears to offer valuable potential to study surface erosion by estimating sediment deposition rates of karst depressions, rather than the assessment of complicated soil erosion in stony soils of carbonate rock slopes. In addition, the space distribution of surface soil and ¹³⁷Cs inventories are affected remarkably by the inhomogeneous dissolution of limestone under the soil. It may be an important phenomenon, which exists widely in karst areas, and it is significantly different from other places.     

The application of caesium-137 measurements to estimate recent sedimentation rates in a typical karst depression of Guizhou Plateau,China

The existing traditional methods of assessing the rates of soil loss have many limitations and are difficult to apply in the karst areas of Southwest China. Karst depressions comprise geomorphologically important sources and sinks for sediments and associated pollutants, yet the sedimentology of many depressions is not well understood. In this paper, the 137Cs technique was employed to investigate recent sedimentation rates in a Chinese polygonal karst depression. The results indicated that the sediment deposition rates ranged from 0.91 to 1.97 mm?a?1 in the period from 1963 to 2007, and the average sediment deposition rate and specific deposit yield of the catchment were estimated to be 1.47 mm?a?1 and 20 t?km?2?a?1, respectively. The results obtained were consistent with the local monitoring data of runoff plots, confirming the validity of the overall approach. It was shown that soil loss rates were very low in some karst areas of Southwest China. Above all, the approach appears to offer valuable potential to study surface erosion by estimating sediment deposition rates of karst depressions, rather than the assessment of complicated soil erosion in stony soils of carbonate rock slopes. In addition, the spacial distribution of surface soil and 137Cs inventories was affected remarkably by the inhomogeneous dissolution of limestone under the soil. It may be an important phenomenon which exists widely in the karst areas and is significantly different from other places.     

137Cs示踪技术在土壤侵蚀估算中的应用研究进展

137Cs示踪技术目前已被广泛用于长期的土壤侵蚀(水蚀)估算。该技术要解决的两个关键问题是土壤137Cs基准值的确定,以及土壤的137Cs损失量与土壤侵蚀量之间的定量模型的建立。对现有的主要的定量模型进行了简述,并提出了各自的局限性。这些模型可分为经验模型和理论模型两大类,其中以理论模型中的质量平衡模型较为成熟,综合考虑了较多的侵蚀因子,如137Cs年沉降分量、土壤颗粒粒径分布差异、地表富集作用、耕作土壤在耕作活动前新沉降137Cs的侵蚀损失等。对现有模型的改进也进行了探讨,并提出了今后的一些研究重点。     

Status and Trends in Research on Deep-Water Gravity Flow Deposits

Deep-water gravity flows are one of the most important sediment transport mechanisms on Earth. After 60 years of study,significant achievements have been made in terms of classification schemes,genetic mechanisms,and depositional models of deep-water gravity flows. The research history of deep-water gravity flows can be divided into five stages: incipience of turbidity current theory; formation of turbidity current theory; development of deep-water gravity flow theory; improvement and perfection of deep-water gravity flow theory; and comprehensive development of deep-water gravity flow theory. Currently,three primary classification schemes based on the sediment support mechanism,the rheology and transportation process,and the integration of sediment support mechanisms,rheology,sedimentary characteristics,and flow state are commonly used.Different types of deep-water gravity flow events form different types of gravity flow deposits. Sediment slump retransportation mainly forms muddy debris flows,sandy debris flows,and surge-like turbidity currents. Resuspension of deposits by storms leads to quasi-steady hyperpycnal turbidity currents(hyperpycnal flows). Sustainable sediment supplies mainly generate muddy debris flows,sandy debris flows,and hyperpycnal flows. Deep-water fans,which are commonly controlled by debris flows and hyperpycnal flows,are triggered by sustainable sediment supply; in contrast,deep-water slope sedimentary deposits consist mainly of debris flows that are triggered by the retransportation of sediment slumps and deep-water fine-grained sedimentary deposits are derived primarily from finegrained hyperpycnal flows that are triggered by the resuspension of storm deposits. Harmonization of classification schemes,transformation between different types of gravity flow deposit,and monitoring and reproduction of the sedimentary processes of deep-water gravity flows as well as a source-to-sink approach to document the evolution and deposition of deep-water gravity flows are the most important research aspects for future studies of deep-water gravity flows study in the future.     

汶川震区北川9.24暴雨泥石流特征研究

2008年9月24日汶川震区的北川县暴雨导致区域性泥石流发生,这次9.24暴雨泥石流灾害导致了42人死亡,对公路和其他基础设施造成严重损毁。本研究采用地面调查和遥感解译方法分析地震与暴雨共同作用下的泥石流特征,获取的气象数据用于分析泥石流起动的临界雨量条件。本文探讨了研究区泥石流起动和输移过程,并根据野外调查,分析了泥石流形成的降雨、岩石和断层作用,特别是强降雨过程与物源区对泥石流发生的作用。根据应急调查发现北川县境内暴雨诱发的泥石流72处,其分布受岩石类型、发震断层和河流等因素控制。根据对研究区震前和震后泥石流发生的临界雨量和雨强的初步分析,汶川地震后,该区域泥石流起动的前期累积雨量降低了14.8%～22.1%,小时雨强降低25.4 %～31.6%。震区泥石流起动方式主要有二种,一是由于暴雨过程形成的斜坡表层径流导致悬挂于斜坡上的滑坡体表面和前缘松散物质向下输移,进入沟道后转为泥石流过程;二是消防水管效应使沟道水流快速集中,并强烈冲刷沟床中松散固体物质,导致沟床物质起动并形成泥石流过程。调查和分析发现沟内堆积的滑坡坝对泥石流的阻塞明显,溃决后可导致瞬时洪峰流量特别大。研究结果表明了汶川震区已进入一个新的活跃期。因此,应该开展对汶川地震区的泥石流风险评估和监测、早期预警,采取有效的工程措施控制泥石流的发生和危害。     

用137Cs计年法确定湖泊沉积物沉积速率研究进展

137Cs计年法利用137Cs固有的理化和沉降特性,在湖泊沉积物的137Cs垂直分布与大气137Cs沉降间确立对应关系,找出有异常137Cs含量的沉积层作为时标,但需注意137Cs从水体表面至湖底的时间和粘粒含量对各层137Cs含量的影响,并用其它方法校验时标的可靠性。再求取不同时标层间的年均沉积厚度,或因克服了压实效应而更能反映真实沉积速率的年均沉积通量,且结合GIS等手段进一步估算湖泊各区域的沉积总量;还可延伸研究湖泊内源污染负荷及相关环境演变和湖泊演化。但是,沉积柱样的分割厚度取多少才能既满足计年精度要求又不使工作量过大,137Cs的大气沉降时间与进入沉积物时间还与泥沙的陆地迁移时间有关,沉积物中究竟是否发生137Cs下渗及其机理等都还是此法应用中有待解决的问题。     

四川省都江堰市龙池地区泥石流危险性评价研究

汶川地震灾区震后泥石流灾害较震前活跃,对灾区泥石流危险性进行评价是灾后重建过程中合理防灾减灾的基础工作。通过研究泥石流灾害事件中的泥石流规模、泥石流沟堆积扇面积及相应的灾害损失等基础资料,提出以泥石流在泥石流沟堆积扇上的平均堆积厚度替代泥石流规模作为主要危险因子的单沟泥石流危险性评价方法。用该方法对汶川震区都江堰市龙池镇龙溪河流域2010年"8.13"泥石流事件中的29条沟谷型泥石流进行危险性评价,评价结果中9条为高度危险,12条为中度危险,8条为低度危险。用以泥石流规模为主要危险因子的单沟泥石流危险性评价方法进行对比评价,2种评价方法中有65.5%的泥石流的危险性评价结果一致。以泥石流沟堆积扇平均堆积厚度为主要危险因子的单沟泥石流危险性评价方法更能突出规模对泥石流综合危险度的贡献,能更好地反映小泥石流流域和小泥石流堆积扇的泥石流在中小规模的泥石流总量下的危险程度。     

Post‐deposition diffusion of 137Cs in lake sediment: Implications for radiocaesium dating

Peak activities of radiocaesium (¹³⁷Cs) in lake sediments have frequently been used to infer the ages of sediments deposited in the 1960s (¹³⁷Cs derived from nuclear bomb testing) or in 1986 (Chernobyl derived ¹³⁷Cs). Records of the vertical distribution of ¹³⁷Cs in sediments can thus be used to provide accurate dates for a critical period in which palaeoecological reconstructions often overlap contemporary monitoring data. However, knowledge regarding how the distribution of ¹³⁷Cs in sediments is affected by post‐depositional processes is limited to interpretations based on the ¹³⁷Cs distribution in sediments sampled at a single given date. This study assesses the extent to which the ¹³⁷Cs record in annually laminated (varved) lake sediments is affected by post‐depositional diffusion, using 11 archived sediment cores sampled between 1986 and 2007. The sediment record reveals how Chernobyl ¹³⁷Cs incorporated into the 1986 varve diffused downwards in the core at a decreasing rate over time, whereas the surface sediments continued to receive inputs of ¹³⁷Cs mobilized from the catchment soils or lake margin. In spite of these processes, all cores post‐dating the Chernobyl accident had a clear and well‐resolved peak in the 1986 varve, justifying the use of this feature as a fixed chronostratigraphic feature. Because of the very high levels of Chernobyl fallout at this site, downwards migration of Chernobyl ¹³⁷Cs has, however, completely masked the nuclear weapons ¹³⁷Cs fallout peak that had been clearly preserved in the 1964 varve of a pre‐Chernobyl core sampled just three weeks before the Chernobyl accident. In consequence, the weapons fallout marker is likely to be of little use for determining ¹³⁷Cs dates in areas strongly affected by high levels of Chernobyl fallout.     

长江河口水下三角洲137Cs地球化学分布特征

文章通过对长江口水下三角洲采集的10个柱状样放射性核素¹³⁷Cs的分析可以得知,长江口水下三角洲¹³⁷Cs剖面中均存在清晰的最大蓄积峰,其峰值比活度介于5.68±1.03～21.74±1.39Bq/kg之间,平均值为14.11±1.10Bq/kg,最大蓄积峰所处的深度为55～117cm。剖面中¹³⁷Cs最大蓄积峰应该与1963年的¹³⁷Cs散落沉降相对应。长江口水下三角洲的表层沉积物中的¹³⁷Cs比活度范围介于0～9.19±1.12Bq/kg之间,并且与长江流域其他地区的表层¹³⁷Cs比活度相一致。长江口水下三角洲可探测到的¹³⁷Cs比活度的最大深度范围在88～160cm的范围内变化,¹³⁷Cs蓄积总量为2361.30±174.38～17714.94±262.14Bq/m²,平均值为9664.97±100.05Bq/m²,¹³⁷Cs比活度的最大深度及¹³⁷Cs蓄积总量均表现出从岸向海逐渐增加的趋势。实测的¹³⁷Cs总量均大于长江流域的¹³⁷Cs背景值,说明了长江口水下三角洲的¹³⁷Cs蓄积既有大气散落直接沉降的来源,又有流域侵蚀带来的¹³⁷Cs输入,并且主要以后者为主。通过放射性核素示踪模型分析长江口水下三角洲¹³⁷Cs散落蓄积特征可以得知,长江口水下三角洲¹³⁷Cs的蓄积以长江流域来源为主,说明了放射性核素¹³⁷Cs在长江口水下三角洲沉积物中的蓄积主要受流域侵蚀因素的影响。     

浅层滑坡诱发沟谷泥石流的地形和降雨条件

2011年贵州省望谟县打易镇的大范围浅层滑坡诱发的沟谷泥石流提供了研究这类泥石流地形和降雨条件的机会。在地质条件一致和小区域内的降雨条件基本一致的情况下,地形条件就是这些泥石流暴发与否的唯一决定因素。对比一些重要的地形因素与泥石流暴发的关系,得出了由流域面积、沟床纵比降和25°~45°山坡坡度面积比组成的泥石流综合地形因子T。在地形因子T的基础上,研究获得了由前期降雨量、1 h降雨强度、年平均降雨量等组成的降雨因子R。由地形因子T和降雨因子R获得的临界条件P可以判断该区域的泥石流暴发。由于研究工作部分基于泥石流的形成机理,研究成果还可用于其他区域的泥石流形成预测,为泥石流的预测预报提供了一个较好的方法。     

Catastrophic debris flows triggered by a 14 August 2010 rainfall at the epicenter of the Wenchuan earthquake

The Wenchuan earthquake of May 12, 2008 produced large amounts of loose material (landslide debris) that are still present on the steep slopes and in the gullies. This loose material creates an important hazard as strong rainfall can cause the development of devastating debris flows that will endanger the resettled population and destroy the result of reconstruction efforts. On 14 August 2010, a total of 21 debris flows were triggered by heavy rainfall around the town of Yingxue, located near the epicenter of the Wenchuan earthquake. One of these debris flows produced a debris dam, which then changed the course of the river and resulted in the flooding of the newly reconstructed Yinxue town. Prior to this catastrophic event, debris flow hazard had been recognized in the region, but its potential for such widespread and devastating impacts was not fully appreciated. Our primary objective for this study was to analyze the characteristics of the triggering rainfall and the sediment supply conditions leading to this event. Our field observations show that even small debris flow catchment areas have caused widespread sediment deposition on the existing fans. It is concluded that the whole of the area shaken by the Wenchuan earthquake is more susceptible to debris flows, initiated by localized heavy rainfall, than had been assumed earlier. The results of this study contribute to a better understanding of the conditions leading to catastrophic debris flow events in the earthquake-hit area. This is essential for the implementation of proper early warning, prevention, and mitigation measures as well as a better land use planning in this area.     

Debris flow hazards for mountain regions of Russia: regional features and key events

The total area of debris flow territories of the Russian Federation accounts for about 10% of the area of the country. The highest debris flow activity areas located in Kamchatka-Kuril, North Caucasus and Baikal debris flow provinces. The largest debris flow events connected with volcano eruptions. Maximum volume of debris flow deposits per one event reached 500 × 10⁶ m³ (lahar formed during the eruption of Bezymyanny volcano in Kamchatka in 1956). In the mountains of the Greater Caucasus, the maximum volume of transported debris material reached 3 × 10⁶ m³; the largest debris flows here had glacial reasons. In the Baikal debris flow province, the highest debris flow activity located in the ridges of the Baikal rift zone (the East Sayan Mountains, the Khamar-Daban Ridge and the ridges of the Stanovoye Highland). Spatial features of debris flow processes within the territory of Russia are analyzed, and the map of Debris Flow Hazard in Russia is presented. We classified the debris flow hazard areas into 2 zones, 6 regions and 15 provinces. Warm and cold zones are distinguished. The warm zone covers mountainous areas within the southern part of Russia with temperate climate; rain-induced debris flows are predominant there. The cold zone includes mountainous areas with subarctic and arctic climate; they are characterized by a short warm period, the occurrence of permafrost, as well as the predominance of slush flows. Debris flow events are described for each province. We collected a list of remarkable debris flow events with some parameters of their magnitude and impact. Due to climate change, the characteristics of debris flows will change in the future. Availability of maps and information from previous events will allow to analyze the new cases of debris flows.