Frequency of debris flows and rockfall along the Mendoza river valley (Central Andes), Argentina: Associated risk and future scenario

The frequency of debris flows and rockfalls was estimated by temporal distribution of these events during the last 50 years. This parameter was expressed by annual probability of occurrence and mean interval of recurrence of historical events. More recurrent events in this sector of the Central Andes are associated with the Guido locality and tunnels situated along International road No. 7. Furthermore, these events are more frequent in Cordillera Frontal where the mean recurrence interval was lower than in Precordillera. The maximum interval of recurrence is rarely greater than 20 years, showing the activity of these events on human lives and infrastructure in this region. The accuracy of the determined recurrence frequency is discussed. A future scenario indicates that landslides will be probably more frequent under global climate change. As a consequence, those most vulnerable elements in the region, the international access routes, may be severely damaged in the future, implying an adverse impact in our regional economy.     

小秦岭大湖峪矿渣型泥石流的物源特征及其危险度评价

河南省灵宝市大湖峪峪道金矿开采活动强烈,采矿废渣成为当地泥石流主要的物源隐患。在2007年对峪道内采矿废渣堆进行实地调查的基础上,依据矿渣型泥石流的特点,选择渣堆规模、河道堵塞程度、渣堆稳定性、沟谷纵坡降比、河流弯曲度和沟谷汇水面积6个因子,利用层次分析法确定各因子的权重,进而对大湖峪主峪道及其支沟进行了泥石流危险度评价。结果表明,13条沟谷中有10条为高危险度区,其中东峪黑峪子沟、东峪主峪道、西峪东槽桐沟和槽桐沟均为泥石流极高危险区。大湖峪泥石流危险度评价结果为泥石流的防治和预警提供了科学依据。     

基于信息量模型的云南东川泥石流易发性评价

以东川泥石流为研究对象,选取高程、坡度、坡向、起伏度、曲率、工程岩组、距断层距离、距水系距离、土地利用类型9个影响因子,以研究区144条泥石流为样本数据,建立了东川泥石流易发性评价体系。基于GIS平台,采用信息量模型计算各个评价指标状态分级的信息量值,以小流域为评价单元使用自然间断法将研究区泥石流易发程度分为极高、高、中和低4个易发区等级。结果表明：研究区极高易发区和高易发区发生泥石流灾害数量占比94.44%,AUC值为0.876,表明选取评价指标合理,信息量模型适用于东川泥石流易发性评价研究。     

基于RS及GIS的泥石流等地质灾害三维定量评价

随着泥石流等地质灾害的频繁发生,定量分析灾害发生的风险性已经成为越来越重要的课题。综合运用RS（遥感）和GIS（地理信息系统）等技术,对地质灾害数据进行采集、存储、检索、建模、分析,以期定量评价灾害发生的风险性,并以此作为参考,给泥石流等灾害可能发生的地区提出合理建议。     

Carbonatite diversity in the Central Andes: the Ayopaya alkaline province,Bolivia

The Ayopaya province in the eastern Andes of Bolivia, 100 km NW of Cochabamba, hosts a Cretaceous alkaline rock series within a Palaeozoic sedimentary sequence. The alkaline rock association comprises nepheline-syenitic/foyaitic to ijolitic intrusions, carbonatite, kimberlite, melilititic, nephelinitic to basanitic dykes and diatremes, and a variety of alkaline dykes. The carbonatites display a wide petrographic and geochemical spectrum. The Cerro Sapo area hosts a small calciocarbonatite intrusion and a multitude of ferrocarbonatitic dykes and lenses in association with a nepheline-syenitic stock. The stock is crosscut by a spectacular REE-Sr-Th-rich sodalite-ankerite-baryte dyke system. The nearby Chiaracke complex represents a magnesiocarbonatite intrusion with no evidence for a relationship to igneous silicate rocks. The magnesiocarbonatite ( REE up to 1.3 wt%) shows strong HREE depletion, i.e. unusually high La/Yb ratios (520–1,500). Calciocarbonatites ( REE up to 0.5 wt%) have a flatter REE distribution pattern (La/Yb 95–160) and higher Nb and Zr contents. The sodalite-ankerite-baryte dyke system shows geochemical enrichment features, particularly in Na, Ba, Cl, Sr, REE, which are similar to the unusual natrocarbonatitic lavas of the recent volcano of Oldoinyo Lengai, Tanzania. The Cerro Sapo complex may be regarded as an intrusive equivalent of natrocarbonatitic volcanism, and provides an example for carbonatite genesis by late-stage crystal fractionation and liquid immiscibility. The magnesiocarbonatite intrusion of Chiaracke, on the other hand, appears to result from a primary carbonatitic mantle melt. Deep seated mantle magmatism/metasomatism is also expressed by the occurrence of a kimberlite dyke. Neodymium and strontium isotope data (_Nd 1.4–5.4, ⁸⁷Sr/⁸⁶ Sr<Bulk Earth) indicate a depleted mantle source for the alkaline magmatism. The magmatism of the Ayopaya region is attributed to failed rifting of western South America during the Mesozoic and represents the only occurrence of carbonatite and kimberlite rocks in the Andes.     

Susceptibility analysis of large-scale debris flows based on combination weighting and extension methods

Susceptibility is an important issue in debris flow analysis. In this paper, 26 large-scale debris flow catchments located in the Wudongde Dam site were investigated. Seven major factors, namely, loose material volume per square kilometer, loose material supply length ratio, average gradient of the main channel, average hill slope, drainage density, curvature of the main channel, and poor vegetation area ratio, were selected for debris flow susceptibility analysis. Geographic information system, global positioning system, and remote sensing, collectively known as 3S technologies, were used to determine major factors. Weights of major factors affecting debris flow susceptibility were determined. This paper applied the combination weighting method, which considers both the preference of the engineers for major factors and the objective major factor information by using analytic hierarchy process and entropy method. Combination weights of major factors for the investigated 26 debris flow catchments are 0.20, 0.12, 0.20, 0.10, 0.08, 0.19, and 0.11, respectively. Combination weights follow the order of loose material volume per square kilometer = average gradient of the main channel > curvature of the main channel > loose material supply length ratio > poor vegetation area ratio > average hill slope > drainage density. This paper applied extension theory, which is used to solve incompatibility and contradiction problems, to determine susceptibility. Susceptibility results show that the susceptibility of 4 debris flow catchments are very low, 13 are low, 8 are moderate, and 1 is high. Assessment results exhibit consistency with the activity analysis.     

基于FLO-2D数值模拟的工布江达县城泥石流灾害危险性评价

工布江达县位于藏东地区,雨季区内泥石流频发,对人民基本生活和区域经济建设与发展造成了严重影响。为研究藏东地区中—小型泥石流灾害对城镇居民聚集区的危害特征和潜在危险性,运用FLO-2D软件,以西藏自治区工布江达县县城周边居民分布较为集中的5条泥石流沟为研究对象,通过模拟泥石流泥深和流速等方面的冲淤特征,以县城典型泥石流沟模拟冲出结果为基础,确定泥石流强度并划定危险性分区,分析泥石流危险分区与居民聚集区之间的拓扑关系,评估县城周边泥石流危险性,为工布江达县城的城镇规划和防灾减灾提供技术参考。     

Velocity and runout simulation of destructive debris flows and debris avalanches in pyroclastic deposits,Campania region,Italy

The Campanian Apennines are characterized by the presence of monocline ridges, mainly formed by limestone. During the periods of volcanic activity of the Somma-Vesuvius and Phlegrean Fields, the ridges were mantled with pyroclastic materials in varying thickness. The pyroclastics have been involved in destructive landslides both in historical time and in the recent past (1997, 1998, 1999). The landslides occur following intense and prolonged rainfalls. In some cases, landslides extended up to 4 km into the surrounding lowlands and reached towns, causing severe destruction and over 200 deaths. Generally, the landslides begin as small debris slides that develop into large, shallow debris avalanches or debris flows involving pyroclastic horizons and colluvial soils (0.5–2 m thick) on steep and vegetated slopes, often at the heads of gullies. During motion, the landslide materials eroded vegetation and soils from the slope, so that the moving material volume tended to increase. Then, proceeding towards and beyond the base of the slopes, the phenomena evolved into hyperconcentrated streamflow due to dilution by incorporating water. The results of motion analyses are described. An empirical rheological relationship was used including two principal terms that depend on the total normal stress and on the flow velocity. On this basis, the model has simulated the velocity and duration of debris avalanches and the distribution of the deposits. The selected areas were those of Sarno/Quindici and Cervinara, where a large amount of data is available both on the material properties and geomorphological setting. It was found that the majority of the cases at the two sites can be simulated successfully with only one specific pair of rheologic parameters. This provides the possibility for first-order predictions to be made of the motion of future landslides. Such predictions will be a valuable tool for outlining potential hazard areas and designing remedial measures.     

Measuring and estimating the impact pressure of debris flows on bridge piers based on large-scale laboratory experiments

After the 2008 Wenchuan earthquake, mountainous areas in SW China are recognized as a region with highly active and perilous landslides and debris flows. The frequent impacts of debris flow are a major threat to bridge piers located in debris flow gullies. It is an important issue for guaranteeing the safety of railway bridges in areas prone to hazardous debris flows. Previous research has achieved significant results characterizing the initiation and mechanisms for debris flow, and their interactions with some structures. However, there has been little research on the dynamic pressure of debris flow on bridge pier caused by different debris flows. In this study, the measurement and estimation of the impact pressure and dynamic behavior of debris flows on scaled bridge piers were conducted. Nine pressure sensors were used to measure the impact pressure of debris flows. Flow velocities and flow depths were determined at the end of a flume using a high-speed camera. The results show that the impact pressure differed between different types of debris flows. The distribution of impact pressures from high-viscosity debris flows indicated three layers, with different features in individual event. In comparison, a layered structure was not observed in low-viscosity debris flows. Based on dimensional analyses, the impact pressure depended on Froude number (Fr) and Reynolds number (Re). For low-viscosity debris flows, the dimensionless impact pressures were power functions of Fr, while for high-viscosity debris flows, the dimensionless impact pressures were power functions of both Re and Fr. The impact frequencies of low-viscosity and high-viscosity debris flows showed considerable differences based on spectral analysis. Compared to high-viscosity debris flows, low-viscosity debris flows were characterized by relatively high velocity, strong striking pressure, and high impact frequency.     

Structure and composition of debris flows in the Eastern Sayan

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.”     

Pure risk premium rating of debris flows based on a dynamic run-out model: a case study in Anzhou,China

Natural Hazards - Debris flow risk is growing with the current increases in landscape exploitation and extreme precipitation events associated with global warming. Insurance is an efficient...     

基于面积?高程和面积?坡度积分的泥石流物质供给能力分析

松散物质是流域侵蚀演化的产物,对于泥石流流域而言,物质供给能力影响着泥石流的易发程度和活动频率。以岷江上游都江堰—汶川部分区域147个泥石流小流域为例,运用面积?高程法和面积?坡度积分对流域地貌演化阶段和侵蚀强度定量划分,并结合地貌演化阶段和侵蚀强度开展泥石流物质供给能力研究。研究结果表明:采用单一的地貌演化阶段或侵蚀强度解释泥石流的易发程度具有一定局限性,泥石流暴发主要集中于壮年期、壮年偏幼年期及侵蚀强度Ⅲ～Ⅴ级;随着物质供给能力的提升,泥石流的暴发率上升,而面积对泥石流的暴发有一定限制作用,初步确定研究区内供给能力处中、强、极强三种水平泥石流流域,其优势发育面积范围分别为:20～35 km2、10～50 km2、10～40 km2;对于物质供给能力水平较高、面积处于优势发育范围内、且长期未有明显泥石流活动迹象的流域,应进一步排查流域松散物质储量和分布特征,确定泥石流活动稳定性,采取合理的防灾减灾措施。     

昆明东川城区后山泥石流特征及成因分析

东川区是云南省也是我国泥石流暴发最强烈的地区之一。其突出特点是沟谷数量多、密度大、活动频繁、破坏损失严重、防治困难,严重威胁东川城区人民生命财产安全。论文详细分析了城区后山5条泥石流沟的暴发成因和特征。其泥石流以稀性泥石流为主,重度1.5~2.0 kN/m3之间。该区泥石流之所以如此发育,主要是地质地理环境起控制作用。东川区地质构造发育、地震频繁、山体失稳、地形高差悬殊和雨量集中且暴雨强度大等,是导致本区泥石流频繁而猛烈的根本原因。而人类不合理的经济活动则对本区泥石流的发生发展起着重要的加剧、恶化作用。论文的分析不仅对决策机构制定防治措施具有借鉴意义,且对东川城区后山“五沟”泥石流的修复治理具有重要意义。     

基于信息量的长白山地区泥石流易发性评价

长白山地区泥石流较发育,选取高程、坡度、坡向、年降水、年蒸发、泥石流点密度、人口密度、构造作用、河流作用、地层岩性、地下水类型、地貌类型、土地利用13个影响因素,以研究区110个泥石流点为样本数据,连续型指标依据各个因素分级状态下泥石流比例曲线和信息量曲线的突变点为等级划分临界值,离散型变量根据已有分类分级,建立了长白山地区泥石流易发性指标评价体系。基于信息量模型和GIS平台的栅格数据,计算各个因素分级状态下的信息量,采用自然断点法将易发性等级分为5级。结果表明:泥石流高易发区主要为地层岩性较差、靠近河流和断层的区域,土地利用类型为农业用地和居住使用地,较高易发区和高易发区占总研究区面积的19%,大部分地区较安全。采用曲线下面积即AUC值作为易发性精度验证结果,AUC值为93%,表明评价结果可靠。     

A new total volume model of debris flows with intermittent surges: based on the observations at Jiangjia Valley,southwest China

Debris flow with intermittent surges is a major natural hazard. Accurate estimation of the total volume of debris flow is a challenge for academic researchers and engineering practitioners. This paper has proposed a new model for the total volume estimation based on 15 years of observations in Jiangjia Valley, China, from 1987 to 2004. The model uses two input variables: debris flow moving time and average surge peak discharge. The Weibull distribution formula is adopted to describe the relationship between the debris flow surge peak discharge and its relative frequency. By integrating the Weibull function and two-point curve fitting, the relationship between the maximum discharge and average surge peak discharge can be established. The total debris flow volume is linked with the debris flow moving time and the average peak discharge. With statistical regression, the debris flow moving time is derived from the debris flow total time. The proposed model has fitted very well with the validation data and outperformed the existing models. This study has provided a new and more accurate way for estimating the total volume of debris flows with intermittent surges in engineering practice.     

Cenozoic basin evolution of the Central Patagonian Andes: Evidence from geochronology,stratigraphy, and geochemistry

The Central Patagonian Andes is a particular segment of the Andean Cordillera that has been subjected to the subduction of two spreading ridges during Eocene and Neogene times. In order to understand the Cenozoic geologic evolution of the Central Patagonian Andes, we carried out geochronologic(U-Pb and⁴⁰Ar/³⁹Ar), provenance, stratigraphic, sedimentologic, and geochemical studies on the sedimentary and volcanic Cenozoic deposits that crop out in the Meseta Guadal and Chile Chico areas(～47°S). Our data indicate the presence of a nearly complete Cenozoic record, which refutes previous interpretations of a hiatus during the middle Eocene-late Oligocene in the Central Patagonian Andes. Our study suggests that the fluvial strata of the Ligorio Marquez Formation and the flood basalts of the Basaltos Inferiores de la Meseta Chile Chico Formation were deposited in an extensional setting related to the subduction of the Aluk-Farallon spreading ridge during the late Paleocene-Eocene. Geochemical data on volcanic rocks interbedded with fluvial strata of the San Jose Formation suggest that this unit was deposited in an extensional setting during the middle Eocene to late Oligocene. Progressive crustal thinning allowed the transgression of marine waters of Atlantic origin and deposition of the upper Oligocene-lower Miocene Guadal Formation. The fluvial synorogenic strata of the Santa Cruz Formation were deposited as a consequence of an important phase of compressive deformation and Andean uplift during the early-middle Miocene. Finally, alkali flood basalts of the late middle to late Miocene Basaltos Superiores de la Meseta Chile Chico Formation were extruded in the area in response to the suduction of the Chile Ridge under an extensional regime. Our studies indicate that the tectonic evolution of the Central Patagonian Andes is similar to that of the North Patagonian Andes and appears to differ from that of the Southern Patagonian Andes, which is thought to have been the subject of continuous compressive deformation since the late Early Cretaceous.     

基于精确Riemann求解器的明满流过渡过程模拟

Preissmann窄缝法模拟明满流过渡过程方法简单,但存在明显的非物理振荡,抑制非物理振荡是该方法应用的关键。基于Godunov格式和精确Riemann求解器对明满流过渡过程进行模拟,针对Riemann问题代数恒等式在明满流交界处不光滑问题,提出了三阶收敛方法与二分法结合的迭代求解方法,保证迭代收敛至真实解;针对由于变量空间重构方法不能准确表达变量在空间中真实物理状态而导致的非物理振荡,提出了基于精确Riemann解的变量空间重构方法,准确表达激波间断在单元内的空间分布状态,从机理上抑制了非物理振荡。实例研究表明,数值计算结果与解析解或实测值吻合良好,研究成果为明满流过渡过程的高精度数值模拟提供了新的方法。     

Deposition and diagenesis of debris flows in Upper Ordovician limestones, Hadeland, Norway

The Upper Ordovician rocks of Hadeland, Norway, form a sequence of thin bedded nodular limestones (wackestones) and shales, hosting five distinctive sedimentary breccia complexes. These breccias contain blocks of varying sizes and shapes in a wackestone and grainstone matrix. Blocks differ in lithology, and in their included biotas and cement sequences. The thin bedded limestones are interpreted as turbidites, deposited against a background of hemipelagic calcareous shales. The breccias occupy channels cut into this sequence. The lithologies and biotas of blocks in the breccias record deposition in differing sedimentary environments, whereas their cements are the results of contrasting diagenetic histories. Blocks were eroded from a diverse and mature carbonate platform, close to sea level, which probably lay 5–10 km east of Hadeland. The breccias are interpreted as debris flow deposits, transported as channellized flows. Following channel cutting events, perhaps triggered by sea level change, channels were characterized by deposition rather than erosion. Wackestones and grainstones associated with the breccias also reflect resedimentation, their less diverse biota suggesting local derivation on the slope. The reworking of calcarenaceous muds locally produced clean washed calcarenites (now grainstones). A fall in sea level resulted in emergence of the upper slope and erosion of the debris flow complex to form caverns and fissures. As sea level rose again crinoidal calcarenites, now grainstones, were deposited within these cavities. Cement sequences in blocks record early marine and burial conditions on the shelf, and also precipitation of new marine cements following downslope transport. Those cements in lithologies formed in situ document later shallowing, culminating in emergence. The localized dissolution of cements in both blocks and associated grainstones reflects the infiltration of ‘aggressive’meteoric waters through permeable channel deposits. A subsequent rise in sea level is recorded in the generation of an additional marine cement with final burial reflected in the deposition of blocky calcite. The debris flow deposits therefore maintained their distinctive character from deposition through diagenesis.     

基于精确Riemann求解器的明满流过渡过程模拟

Preissmann窄缝法模拟明满流过渡过程方法简单,但存在明显的非物理振荡,抑制非物理振荡是该方法应用的关键。基于Godunov格式和精确Riemann求解器对明满流过渡过程进行模拟,针对Riemann问题代数恒等式在明满流交界处不光滑问题,提出了三阶收敛方法与二分法结合的迭代求解方法,保证迭代收敛至真实解;针对由于变量空间重构方法不能准确表达变量在空间中真实物理状态而导致的非物理振荡,提出了基于精确Riemann解的变量空间重构方法,准确表达激波间断在单元内的空间分布状态,从机理上抑制了非物理振荡。实例研究表明,数值计算结果与解析解或实测值吻合良好,研究成果为明满流过渡过程的高精度数值模拟提供了新的方法。