A 90,000-year tephrostratigraphic framework of Aso Volcano, Japan

A detailed 90,000-year tephrostratigraphic framework of Aso Volcano, southwestern Japan, has been constructed to understand the post-caldera eruptive history of the volcano. Post-caldera central cones were initiated soon after the last caldera-forming pyroclastic-flow eruption (90 ka), and have produced voluminous tephra and lava flows. The tephrostratigraphic sequence preserved above the caldera-forming stage deposits reaches a total thickness of 100 m near the eastern caldera rim. The sequence is composed mainly of mafic scoria-fall and ash-fall deposits but 36 silicic pumice-fall deposits are very useful key beds for correlation of the stratigraphic sequence. Explosive, silicic pumice-fall deposits that fell far beyond the caldera have occurred at intervals of about 2500 years in the post-caldera activity. Three pumice-fall deposits could be correlated with lava flows or an edifice in the western part of the central cones, although the other silicic tephra beds were erupted at unknown vents, which are probably buried by the younger products from the present central cones. Most of silicic eruptions produced deposits smaller than 0.1 km³, but bulk volumes of two silicic eruptions producing the Nojiri pumice (84 ka) and Kusasenrigahama pumice (Kpfa; 30 ka) were on the order of 1 km³ (VEI 5). The largest pyroclastic eruption occurred at the Kusasenrigahama crater about 30 ka. This catastrophic eruption began with a dacitic lava flow and thereafter produced Kpfa (2.2 km³). Total tephra volume in the past 90,000 years is estimated at about 18.1 km³ (dense rock equivalent: DRE), whereas total volume for edifices of the post-caldera central cones is calculated at about 112 km³, which is six times greater than the former. Therefore, the average magma discharge rate during the post-caldera stage of Aso Volcano is estimated at about 1.5 km³/ky, which is similar to the rates of other Quaternary volcanoes in Japan.     

The Mogangling giant landslide triggered by the 1786 Moxi M 7.75 earthquake,China

A good understanding of seismic giant landslides could provide favourable guidance for seismic stability evaluation of nearby slopes. Here, an excellent example of a catastrophic seismic landslide named the Mogangling giant landslide (MGL), located upstream along the Dadu River and triggered by the 1786 Moxi M 7.75 earthquake, is analysed for its deposit characteristics, failure mechanism and dammed lake. The MGL, with a volume of approximately 4500?×?10⁴ m³, 450 m long and 1000 m wide, blocked the Dadu River completely and caused over 100 000 deaths when the landslide dam broke. The MGL occurred on the upper part of a narrow granite ridge; a potentially unstable wedge-shaped rock mass was separated from the remaining massif by unloading fissures and an active fault (Detuo fault) that just crossed the slope foot. The Moxi earthquake coupled with strong site amplification triggered the MGL, which blocked the Dadu River; the elevation of the dam crest was approximately 130 m higher than the present river level. The dammed lake had a volume of approximately 9.504?×?10⁸ m³, an area of 19.91 km² and a length of approximately 31 km; the peak flow of the outburst flood was larger than 7100 m³/s. After hundreds of years of concave bank erosion, the deposit is divided into the right bank deposit (main deposit) and left bank deposit (residual deposit).

     

贵州省六盘水水城高位远程滑坡流态化运动过程分析

高位远程滑坡是中国西南山区常见的一类灾难性地质灾害,其发生往往伴随有碰撞解体效应,导致滑体碎裂化,转化为碎屑流或泥石流,具有流化运动堆积的特征。2019年7月23日发生于中国贵州省六盘水市水城县的鸡场镇滑坡是典型的高位远程流态化滑坡,滑坡前后缘高差430 m,水平运动距离1340 m,堆积体体积200×104 m3,导致21幢房屋被掩埋,51人遇难。基于野外详细调查和滑前滑后地形对比,采用DAN-W软件对水城滑坡的整个运动堆积过程进行了模拟,结果显示:水城滑坡在滑源区残留堆积体厚度最大为27 m,堆积区最大堆积厚度为15 m,滑坡碎屑流前缘最大运动速度为27 m/s,最大动能为6.57×106 J;滑坡高位剪出,由于势能转化为动能,滑坡快速达到速度峰值,并铲刮地表松散土层;由于强降雨,滑体高速运动使基底孔隙水来不及排出,导致基底摩擦力下降,降低能量损耗,滑体解体促进颗粒流化运动,减少了摩擦,也是滑坡远程运动的重要原因。      

Large scale failure of the external waste dump at the “South Field” lignite mine, Northern Greece

This paper presents the failure process of the external waste dump of the South Field Mine, the major open pit mine in Greece. The waste materials of the mine were deposited in three phases, forming an average inclination slope 10% and a total height of 110 m from the ground surface. The failure occurred when the third phase of the deposit was initiated. The high moisture content of the waste materials and their deposition over a spring, choking its flow, had as a result the development of high pore water pressure in clayey and marly materials in the base of the deposit. As a consequence, a large scale slope failure incident occurred. The landslide involved the mobilization of waste material in the order of 40 Mm³, while the material that moved outside the boundaries of the waste dump was in the order of 2.5 Mm³. The stability of the waste dump was investigated using the limit equilibrium analysis and different types of models.Limit equilibrium analyses were performed using different methods and considering the clay layer of small shear resistance that exists in the base of the deposit. They do not indicate activation of failure mechanism, only that there is a combination of high pore water pressure that developed in the deposit because the covering of the spring with the clayey materials of the dump.     

Application of DDA to simulate characteristics of the Tsaoling landslide

This study simulates the kinematic behavior of sliding blocks of rock in the earthquake-induced Tsaoling landslide using seismic discontinuous deformation analysis (DDA). We assume sliding rocks are elastic blocks. Detailed joint shear strength parameters are set in DDA in a manner compatible with what is known about the Tsaoling landslide mechanisms. Landslide run-out distance, information from survivors, and the post-failure topography are used to constrain the computational results. Calculations demonstrate that sliding rocks from the ground surface decoupled from those near the basal shear surface during the landslide. Local residents survived because surficial rocks were never deeply buried during the landslide. Additionally, shear strength parameters of material in the deposition area strongly govern final deposit topography. Computational results correlate well with actual post-failure topography.     

Evaluation of potential landslide damming: Case study of Urni landslide,Kinnaur, Satluj valley,India

This work aims to understand the process of potential landslide damming using slope failure mechanism,dam dimension and dam stability evaluation. The Urni landslide, situated on the right bank of the Satluj River, Himachal Pradesh(India) is taken as the case study. The Urni landslide has evolved into a complex landslide in the last two decade(2000-2016) and has dammed the Satluj River partially since year 2013,damaging ～200 m stretch of the National Highway(NH-05). The crown of the landslide exists at an altitude of ～2180-2190 m above msl, close to the Urni village that has a human population of about 500.The high resolution imagery shows ～50 m long landslide scarp and ～100 m long transverse cracks in the detached mass that implies potential for further slope failure movement. Further analysis shows that the landslide has attained an areal increase of 103,900 ± 1142 m^2 during year 2004-2016. About 86% of this areal increase occurred since year 2013. Abrupt increase in the annual mean rainfall is also observed since the year 2013. The extreme rainfall in the June, 2013; 11 June(～100 mm) and 16 June(～115 mm),are considered to be responsible for the slope failure in the Urni landslide that has partially dammed the river. The finite element modelling(FEM) based slope stability analysis revealed the shear strain in the order of 0.0-0.16 with 0.0-0.6 m total displacement in the detachment zone. Further, kinematic analysis indicated planar and wedge failure condition in the jointed rockmass. The debris flow runout simulation of the detached mass in the landslide showed a velocity of ～25 m/s with a flow height of ～15 m while it(debris flow) reaches the valley floor. Finally, it is also estimated that further slope failure may detach as much as 0.80 ±0.32 million m^3 mass that will completely dam the river to a height of 76±30 m above the river bed.     

贵州水城“7.23”高位远程滑坡冲击铲刮效应分析

以2019年贵州水城“7.23”滑坡为例,采用现场调查、无人机航测和数值模拟技术,分析了滑坡的运动过程和冲击铲刮特征,结果表明:（1）水城“7.23”滑坡属典型的高位远程滑坡,滑体高位启动后冲击下方凸起山脊,铲刮地表残坡积土层,并解体形成碎屑流,最大铲刮深度可达11 m;（2）模拟结果显示,滑坡运动最大速度为30 m?s-1,最大动能达8 900 kJ,铲刮体积达46×104 m3,最终体积为116×104 m3,灾害放大效应明显;（3）水城滑坡的冲击铲刮过程可分为冲击嵌入→剪切推覆→裹挟混合三个阶段。      

The past valley glacier network in the Himalayas and the Tibetan ice sheet during the last glacial period and its glacial-isostatic, eustatic and climatic consequences

Since 1973 new data were obtained on the maximum extent of glaciation in High Asia. Evidence for an ice sheet covering Tibet during the Last Glacial Period means a radical rethinking about glaciation in the Northern Hemisphere. The ice sheet's subtropical latitude, vast size (2.4 million km²) and high elevation (6000 m asl) are supposed to have resulted in a substantial, albedo-induced cooling of the Earth's atmosphere and the disruption of summer monsoon circulation. Moraines were found to reach down to 460 m asl on the southern flank of the Himalayas and to 2300 m asl on the northern slope of the Tibetan Plateau, in the Qilian Shan region. On the northern slopes of the Karakoram, Aghil and Kuen-Lun mountains, moraines occur as far down as 1900 m asl. In southern Tibet radiographic analyses of erratics suggest a former ice thickness of at least 1200 m. Glacial polish and roches moutonnées in the Himalayas and Karakoram suggest former glaciers as thick as 1200–2700 m. On the basis of this evidence, a 1100–1600 m lower equilibrium line (ELA) has been reconstructed, resulting in an ice sheet of 2.4 million km², covering almost all of Tibet. Radiometric ages, obtained by different methods, classify this glaciation as isotope stage 3–2 in age (Würmian = last glacial period). With the help of 13 climate measuring stations, radiation- and radiation balance measurements have been carried out between 3800 and 6650 m asl in Tibet. They indicate that the subtropical global radiation reaches its highest energies on the High Plateau, thus making Tibet today's most important heating surface of the atmosphere. At glacial times 70% of those energies were reflected into space by the snow and firn of the 2.4 million km² extended glacier area covering the upland. As a result, 32% of the entire global cooling during the ice ages, determined by the albedo, were brought about by this area — now the most significant cooling surface. The uplift of Tibet to a high altitude about 2.75 Ma ago, coincides with the commencement of the Quaternary Ice Ages. When the Plateau was lifted above the snowline (= ELA) and glaciated, this cooling effect gave rise to the global depression of the snowline and to the first Ice Age. The interglacial periods are explained by the glacial-isostatic lowering of Tibet by 650 m, having the effect that the initial Tibet ice – which had evoked the build-up of the much more extended lowland ices – could completely melt away in a period of positive radiation anomalies. The next ice age begins, when – because of the glacial-isostatic reverse uplift – the surface of the Plateau has again reached the snowline. This explains, why the orbital variations (Milankovic-theory) could only have a modifying effect on the Quaternary climate dynamic, but were not primarily time-giving: as long as Tibet does not glaciate automatically by rising above the snowline, the depression in temperature is not sufficient for initiating a worldwide ice age; if Tibet is glaciated, but not yet lowered isostatically, a warming-up by 4 °C might be able to cause an important loss in surface but no deglaciation, so that its cooling effect remains in a maximum intensity. Only a glaciation of the Plateau lowered by isostasy, can be removed through a sufficiently strong warming phase, so that interglacial climate conditions are prevailing until a renewed uplift of Tibet sets in up to the altitude of glaciation.An average ice thickness for all of Tibet of approximately 1000 m would imply that 2.2 million km³ of water were stored in the Tibetan ice sheet. This would correspond to a lowering in sea level of about 5.4 m.     

Catastrophic rockslide-debris avalanche at St. Bernard, Southern Leyte, Philippines

On 17 February 2006, a rockslide-debris avalanche cascaded down the steep slope of Mt. Can-abag, burying the entire village of Guinsaugon in St. Bernard, Southern Leyte, Philippines. Casualties include 139 dead with 980 still missing and presumed dead, making it perhaps the most catastrophic landslide in Philippine history. The landslide started at the ridge top along a fault plane associated with the active Philippine Fault Zone. It started as a block slide that transformed into an avalanche. The entire event lasted for only a few minutes. Estimated maximum landslide velocity is 120–130 m/s. The landslide left behind a deep, wedge-shaped scarp. The central part of the deposit exhibits a hummocky topography typical of avalanches, in contrast to the flatter surface of the debris-flow-type marginal deposit. High amounts of soil in the matrix were derived from the scouring of ancient landslide deposits and rice fields in the valley. The landslide has a total area of 3.2 km² and a runout distance of 4.1 km. Estimated volume of debris is approximately 20 Mm³. At least four streams were dammed by the landslide debris. Intense precipitation and earthquakes preceding the landslide are the potential triggers. Preliminary back analyses assuming a planar and wedge slip surface yielded very low factors of safety even under dry conditions. A more rigorous analysis of the failure mechanism of the landslide is needed.     

Large block slide at San Juan Grijalva, Northwest Chiapas, Mexico

On November 4, 2007, a large block slide occurred on the south face of the Cerro La Pera at San Juan Grijalva (SJG), northwest Chiapas, Mexico. The SJG landslide has an area of 1.11 km² and a volume of 50 Mm³, making it one of the largest landslide of its type in the twentieth century. The landslide created a dam over 80 m high and 1,170 m wide across the Grijalva River, backing up the water and forming a 49 km² lake. Landslide-generated tsunamis up to 15 m high destroyed the village of SJG, and the newly formed lake flooded 21 villages located upstream. The landslide killed 16 people and caused around 3,600 to be evacuated with incalculable economic losses. It was perhaps the most catastrophic landslide in the history of Mexico. The probable trigger of the landslide was cumulative precipitation of about 67% of the average annual rainfall over the preceding 30 days. The associated potentially causative factors include a M4.5 earthquake that occurred 5 days before the landslide and a water-level drawdown at the Grijalva River generated by the release of water from the Pe?itas dam located 14 km downstream.     

Dynamic process of the Wenjiagou rock landslide in Sichuan Province,China

A rock avalanche is a geological event that is always sudden, rapid and with a long run-out, and can result in large loss of lives and property. The Wenjiagou rock avalanche was a high-speed rock landslide caused by a strong earthquake, in Mianzhu, Sichuan Province, southwest China. In this study, we reproduce the movement and deposition processes of the sliding mass by numerical simulation. We analyze the effects of the friction coefficient of each slip surface and the strength of the parallel bonds and contact stiffness between particles on the dynamic process and deposit features using three-dimensional particle flow code (PFC3D). The simulation results agree with the field measurements when the friction coefficient is 0.2, parallel bond strength is 2 MPa, and contact stiffness is 2?×?10⁸ kN/m. The landslide lasted about 115 s from the initial movement to the final deposition at the exit of the valley. The maximum velocity of the sliding mass was 114 m/s.     

Geo-diversity and its hydrological response in relation to landslide susceptibility in the Himalaya: a GIS-based case study

Assessment and inventory of landslide susceptibility are essential for the formulation of successful disaster mitigation plans. The objective of this study was to assess landslide susceptibility in relation to geo-diversity and its hydrological response in the Lesser Himalaya with a case study using Geographic Information System (GIS) technology. The Dabka watershed, which constitutes a part of the Kosi Basin in the Lesser Himalaya, India, in the district of Nainital, has been selected for the case illustration. The study constitutes three GIS modules: geo-diversity informatics, hydro informatics and landslide informatics. Through the integration and superimposing of spatial data and attribute data of all three GIS modules, Landslide Susceptibility Index (LSI) has been prepared to identify the level of susceptibility for landslide hazards. This resonance study, carried out over a period of five years (2007–2011), found that areas of most stressed geo-diversity (comprising very steep slopes above 30°, geology of Lower Krol and Lariakanta formation, geomorphology of moist areas and debris sites, land use of barren land with a very high drainage frequency and spring density) have a high landslide susceptibility because of high rate of average runoff (33 l/s/km²), flood magnitude (307.28 l/s/km²), erosion (398 tons/km²) and landslide density (5–10 landslides/km²). The areas of least stressed geo-diversity (comprising gentle slopes below 10°, geology of Kailakhan and Siwalik formation, geomorphology of depositional terraces, land use of dense forest with low drainage frequency and spring density) have the lowest landslide susceptibility because of the low rate of average runoff (6.27 l/s/km²), flood magnitude (20.49 l/s/km²), erosion (65.80 tons/km²) and landslide density (1–2 landslides/km²).     

Investigation on causes of the Siruyeh Landslide, West Semirom (Iran)

The Siruyeh landslide occurred at the eastern side of the Siruyeh valley, 22 km west of Semirom city, south of Esfahān on 25th March, 2005 with large dimensions (2,400 m long, 450 m wide with total area of 1 km²). The sliding mass blocked the Siruyeh River making a 35-m-high natural dam and 6-acre lake 570,000 m³ in volume that poses a potential threat for the area. The landslide occurred in soil and intensely weathered marls of the Tarbur and Kashkan Formations (upper Cretaceous–Paleocene age). The overall comparison and interpretation of the gathered evidence from satellite images, field trips, and laboratory tests show that the most important factors involved in triggering the Siruyeh landslide in order of importance are heavy precipitation and snow melt and intense concentration of faults and fractures as well as weathered and weak lithology.     

三眼峪特大泥石流形成的物源条件分析

通过对舟曲县"8.8"特大山洪泥石流三眼峪沟进行现场调查,从泥石流的岩土体类型及特征、地质构造、水文地质、新构造运动及地震等方面,对物源条件的地质环境背景进行了总结.调查结果表明:①三眼峪沟泥石流的松散固体物质主要包括崩塌堆积物、滑坡堆积物、残坡积物和冲洪积物.②三眼峪沟松散固体物质总量4079.42×104m3,流域...     

甘肃永靖黑方台4·29罗家坡黄土滑坡的特征

2015年4月29日上午,甘肃省永靖县盐锅峡镇黑方台滑坡高频发区的党川村罗家坡同一斜坡处连续发生了2次大规模黄土滑坡,总体积约65×10~4m~3,最大滑距630 m,摧毁14户居民房屋和3家工厂.通过现场详细调查、取样试验、1∶500地形测量、滑坡影像、视频等资料分析,对灌溉引发的罗家坡黄土滑坡的特征、滑动过程、形成机理进行了探讨.结果表明:第1次滑坡经过近2 a变形过程,整体突然失稳,高速远程滑动;第2次滑坡变形时间仅3 h,分块逐步滑动,滑动历时长而过程复杂,总体为低速远程滑动.高陡的地形和强度低、水敏感性强的土体是滑坡发生的基础,黄土台塬区长期农业灌溉是引发因素,大量水体入渗形成了20余米厚的饱和软弱基座,使抗剪强度降低,导致斜坡失稳滑动.黄土滑坡高速远程滑动的主要原因是滑坡剪出口位置高,滑动势能大,释放条件好,剪出口下部陡坡段为主要加速段;前方有开阔的滑动空间且有一定坡度、平缓的滑道;滑体底部饱和软弱黏性土在滑道上持续产生超孔隙水压力、液化等低摩阻效应,是远程滑动的润滑剂.同时,两次滑体间还存在冲击加速和能量传递作用.     

Investigation and dynamic analysis of a catastrophic rock avalanche on September 23, 1991, Zhaotong,China

At 6:10 p.m. on September 23, 1991, a catastrophic rock avalanche occurred in Zhaotong, Yunnan, southwestern China. Over 216 people were killed when the Touzhai village was overwhelmed directly in the path of the landslide. The landslide involved the failure of about 12 Mm³ of jointed basaltic rock mass from the source area. The displaced materials ran out a horizontal distance of 3650 m over a vertical distance of 960 m, equivalent to a Fahrböschung of 14.7°, and covered an area of 1.38 km². To provide information for hazard zonation of similar type of potential landslides in the same area, we used a dynamic model (DAN-W) with three alternative rheological models to simulate the runout behaviour of the displaced landslide materials and found that a combination of the frictional model and Voellmy model could provide the best performance in simulating this landslide. The simulated results indicated that the duration of the movement is estimated at about 175 s for a mean velocity 21 m/s.     

Topographical changes revealed by high-resolution airborne LiDAR data: The 1999 Tsaoling landslide induced by the Chi–Chi earthquake

The 1999 Chi–Chi earthquake triggered the catastrophic Tsaoling landslide in central Taiwan. We mapped the landslide area and estimated the landslide volume, using a high-resolution digital elevation model from airborne LiDAR (Light Detection And Ranging), aerial photographs and topographic maps. The comparison between scar and deposit volumes, about 0.126 km³ and 0.150 km³ respectively, suggests a coseismic volume increase of 19% due to decompaction during landsliding. In July 2003, the scar and deposit volumes were about 0.125 km³ and 0.110 km³ respectively. These estimates suggest that 4 years after the event, the volume of landslide debris removed by river erosion was nearly 0.040 km³. These determinations are confirmed by direct comparison between the most accurate topographic models of the post-landslide period, indicating a very high erosion rate at the local scale (0.01 km³/year) for the deposit area of the landslide. Such a large value highlights the importance of landslide processes for erosion and long-term denudation in the Taiwan mountain belt.     

Deep-rooted piercement structures in deep sedimentary basins — Manifestations of supercritical water generation at depth?

Deep-rooted enigmatic piercement structures in sedimentary basins, including ‘mud volcanoes’, ‘shale diapirs’, ‘salt diapirs’, and ‘asphalt volcanoes’, range in size from less than 1 km², surface area, up to 64 km², and have often an unknown depth of penetration due to incomplete imaging. We propose that they form a family associated with fluid flow. Our argument is based partly on their inferred location (above deep faults) and on the chemical analysis of emitted products, which includes liquid clays, brines and other substances from salt diapirs, and asphalt and light oils from the asphalt volcanoes. We explain these compositions by chemical alteration caused partly by supercritical water, a phase of water existent at high pressure and temperature, locally and temporarily achieved at depths generally beyond 10 km below surface, i.e., at the sediment–crust boundary. Our hypothesis overcomes some of the problems with interpreting fluid flow products, which are otherwise very difficult to explain. In case this hypothesis can be further verified, the family could perhaps be called ‘hydrothermally associated piercement structures’.     

Environmental impact of the 1.8 ka Taupo eruption, New Zealand: Landscape responses to a large-scale explosive rhyolite eruption

Large-scale ignimbrite eruptions from rhyolitic caldera volcanoes can trigger geologically instantaneous changes in sedimentary systems over huge areas by either burying existing environments or overloading them with vast quantities of unconsolidated particulate material. The post-eruption readjustment of the landscape to such perturbations is one of the most dramatic processes in physical sedimentology, exemplified here by the 1.8 ka Taupo eruption in the central North Island of New Zealand. This eruption generated voluminous fall deposits, then climaxed with emplacement of a c. 30 km³ non-welded ignimbrite over a near-circular area of c. 20 000 km². Approximately 90% of the area, but < 50% of the ignimbrite volume, is represented by a landscape-mantling unit that covered the pre-eruption topography to a depth varying from c. 10 m in proximal areas to less than 15–30 cm distally. The remainder of the ignimbrite deposit is represented by landscape-modifying material that ponded in valley bottoms and depressions to thicknesses of up to 70 m, with no systematic variation in thickness with distance from source.The headwaters of many of the North Island's largest rivers were impacted by both the primary pyroclastic fall and flow material. Large-scale post-eruption remobilisation of this material, coupled with the re-establishment of fluvial systems, occurred in a distinct sequence as recorded by the evolution of sedimentary facies in different sub-environments. Following an initial period dominated by mass flows, re-establishment of fluvial systems began with the headward erosion of box canyons through the ponded ignimbrite deposits, a process often associated with the break-out of temporary lakes. Aggradational streams developed in these channels rapidly evolved from shallow, ephemeral, sediment-laden outbursts associated with flash flood events to deeper, permanent braided rivers, before declining sediment yields led to retrenchment of single thread rivers and a return to pre-eruption gradients and bedloads years to decades later. Typically the modern profile of many streams and rivers follow closely their pre-eruption profiles, and incision and erosion is overwhelmingly confined to the deposits of the eruption itself.Although the general remobilisation pattern is similar for all impacted river systems, detailed studies of the Waikato, Rangitaiki, Mohaka, Ngaruroro and Whanganui catchments show that the relative timing and scale of each eruption response phase differs between each catchment. These reflect differences in catchment physiography and hydrology, and the volume and type of pyroclastic material deposited in each. Ultimately, the landscape response reflects the relative spatial distributions of, and the volumetric ratios between, the volumes of pyroclastic debris, water, and accommodation space in the basin (cf. Kataoka and Manville, this volume).