Landslides

Large, rapid, low-gradient landslides are common in clay-rich glacial sediments in northeastern British Columbia. Many of the landslides create upstream impoundments that may persist for years in small watersheds in the region. We have documented such events in the Halden Creek watershed, 60km southeast of Fort Nelson. The events are recorded geologically in two ways. First, trees are drowned in lakes dammed by the landslides and subsequently buried by deltaic sediments, where they are protected from decay. Bank erosion later exhumes the drowned trees. Second, landslide deposits with entrained wood are exposed along stream banks. We have reconstructed the recent history of landslide damming at Halden Creek by performing radiocarbon dating on exhumed trees and wood in and beneath landslide deposits at 13 sites in the watershed. Drowned trees range in age from 169±59 to 274±49 14C year bp. Wood in and below landslide deposits yielded radiocarbon ages ranging from modern to 965±49 14C year bp.

This paper describes a rockfall event in the Daisekkei Valley of Mount Shirouma-dake (2,932m), the northern Japanese Alps. The rockfall occurred on a steep cliff comprising well-jointed felsites and produced debris of ≥8,000m3. Most debris was deposited on an elongated snowpatch located immediately beneath the cliff, and it caused casualties among people who were trekking along a trail on the snowpatch. Additionally, a large rock block slipped 1km on the snowpatch. The rockfall could have been due to the differential retreat of the rockwall, which contains areas of high- and low-density joints. Seasonal and diurnal freeze–thaw activities and snow avalanches and wash appear to be important factors responsible for the retreat. Although some rock blocks that can collapse further remain on the rockwall, the position of the mountain trail in the Daisekkei Valley is fixed. Fundamental reform of tourism systems for climbers, including education on natural hazards, is required.

On July 13, 2004, heavy rainfalls because of the intensive activities of the rain front occurred in the Mid-Niigata Region, Japan. They were as much as 400mm in 24h, bringing about serious flooding by breaking the river banks. The heavy rainfalls also triggered more than 3,500 landslides. Three months later, the southern region of Mid-Niigata was attacked by an earthquake of magnitude 6.8 on the Richter scale on October 23, 2004. The main earthquakes were followed by intensive aftershocks, which continued until December 2004. By these earthquakes, variable landslides of more than 4,400 also occurred in the hilly and mountainous areas. Namely, different triggers brought about the variable landslides in the hilly mountains whose features are very similar in geological and geomorphological points of view. Therefore, these two events are very useful for clearing the difference in features of the landslides between the two. We have been researching on both landslides in the field just after both occurred and later analyzing air photographs using the geographic information system (GIS). In this paper, we describe the comparison in the distribution features using GIS analytical data between the heavy rainfall-induced and the intensive earthquake-induced landslides.

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The Qianjiangping landslide occurred after the first impoundment of the Three Gorges Reservoir in July 2003. Field investigation revealed that failure occurred when the reservoir reached 135m, but the stability of the affected slope was already reduced by pre-existing bedding-plane shears, quarrying of mudstone from the landslide toe, and previous heavy rain. A possible explanation of the rapid and long runout mechanism of the landslide is that movement on a bedding-plane shear ruptured the calcite cement and rapidly reduced the sandstone strength to residual shear strength.

Three debris-flow simulation model software have been applied to the back analysis of a typical alpine debris flow that caused significant deposition on an urbanized alluvial fan. Parameters used in the models were at first retrieved from the literature and then adjusted to fit field evidence. In the case where different codes adopted the same parameters, the same input values were used, and comparable outputs were obtained. Results of the constitutive laws used (Bingham rheology, Voellmy fluid rheology and a quadratic rheology formulation which adds collisional and turbulent stresses to the Bingham law) indicate that no single rheological model appears to be valid for all debris flows. The three applied models appear to be capable of reasonable reproduction of debris-flow events, although with different levels of detail. The study shows how different software can be used to predict the debris-flow motion for various purposes from a first screening, to predict the runout distance and deposition of the solid material and to the different behaviour of the mixtures of flows with variation of maximum solid concentration.

The summit crater of Mt Ruapehu volcano normally hosts a 15.4-ha warm lake, whose water has been repeatedly wholly or partly ejected by explosive and extrusive eruptions. Some of the larger eruptions have modified the lake outlet by burying it under unconsolidated tephra (volcanic ash and blocks), creating a dam-break flood hazard independently of the occurrence of an eruption. Eruptions in 1995 and 1996 followed this sequence; a break-out flood was anticipated and a warning system was installed to mitigate the risk from this event and subsequent lahars in the same catchment. The 11-year filling time allowed much planning and rehearsal. The warning system involved manual inspections of dam integrity, and seepage and lake-level monitoring to constrain the likely failure window, and telemetered instruments including a tripwire and geophones to detect breaching of the dam and propagation of the outbreak flood. The dam-collapse sequence, captured by a time-lapse camera, involved a series of retrogressing landslides initiated and accelerated by seepage forces and toe scour when the lake was 1.1m below overtopping. The barrier failed in two phases on 18th March, 2007, beginning at 09:55 (NZST), with rapid retreat of one of the erosion scarps on the downstream slope of the eastern barrier, initiated by internal erosion. Headward retrogression of the scarp into the barrier formed an initial breach in the dam, after which increasing outflow led to erosion and undercutting of the wider downstream toe of the western barrier. A final, larger dam breach occurred between 11:21 and 11:22 as slope instability caused retrogressive failure of the remaining barrier. Five-hundred meters downstream of the dam, a large landslide was reactivated by toe scour during the flood, contributing about a million cubic meters of solid material to the volumetric bulking of the outflow, which reached the coast, 215km away, 17 h later. The success of the planning and warning system allowed the whole event to occur with little damage to infrastructure and without causing injury. KeywordsNatural-dam collapse-Landslide retrogression-Break-out flood-Lahar-Tephra barrier-Landslide warning-Crater lake

An extreme rainfall event over the southern Shetland Islands in northern Scotland, UK, on 19 September 2003, triggered at least 20 significant peat slides and at least 15 smaller landslides of varying types. The peat slides were examined and surveyed to characterise and explain the distinctive morphological features that were produced. The failures varied in size from 0.4 to 7.3ha (2,300 to 59,000m3 displaced volumes of peat) and involved blanket peat up to 3m deep and slope gradients as low as 4°. Almost all of the failure surfaces were located at the peat–mineral interface. The morphological features included large areas (up to 0.5ha) of intact peat that moved without breaking up, linear compression and thrust features and unusual occurrences of mineral debris. These features suggest peat of high tensile strength throughout its depth and the generation of high and sometimes artesian water pressures at the base of the peat during the event. However, the variations between peat slides highlight some of the difficulties of trying to assess the susceptibility of blanket peat to failure without full knowledge of the local peat geotechnical properties and structural features within the peat mass.

In the present study, the analysis of the international landslide literature is aimed. The landslide is perhaps one of the most complex natural phenomena. Also, due to landslides, a considerable amount of loss of lives and economic losses is encountered throughout the world. Although a vast amount of landslide papers is published in international journals, a statistical assessment on this literature is not encountered. For this reason, this study is performed. For the assessment of the international landslide literature, the Science Citation Index Expanded (WOS; Web of Science) published by Institute of Scientific Information (now Thomson Scientific), USA for the period 1945–2008, is considered. A total of 3,468 publications are found and this data is stored into Oracle XE database and queried by using Structured Query Language and Procedural Language/Structured Query Language. In the following stages, some statistical analyses are performed and the possible trends are discussed.

The Abbotsford Landslide of 8 August 1979 occurred in an urban area of Dunedin, New Zealand, causing much damage to houses and urban infrastructure. Rapid failure occurred after weeks of preliminary movements, resulting in the formation of a approximately 5 million m3 block slide. It caused the loss of 69 houses, with an overall cost of about NZ $10–13 million. After several months of investigations, a commission of inquiry found that unfavorable geology (weak clay layers in a 7°-dip slope) was the underlying cause of the landslide. An old sand quarry at the toe of the slope and a leaking water main above the slide area were found to be man-made factors that contributed to the failure. Slope stability analysis showed that after sand excavation (approximately 300,000m3), the water table had to rise 0.3m less for failure to occur. Because the quarry closed 10years before the landslide occurred, it is concluded that a long-term rise in groundwater levels because of the increased rainfall over the previous decade and leakage from the water main controlled the timing of the failure and, in this sense, are considered to have triggered the landslide.

Canyon Creek drains a 79km2 watershed in northwestern Washington State. Extensive logging occurred from the mid-1960s to 1980s, which resulted in numerous slope instabilities and a several order of magnitude increase in sediment supply to the creek. On November 9, 1989, a hyperconcentrated flow with a peak discharge of 450m3/s destroyed one house on the fan. A forensic investigation of the event suggests that a temporary landslide dam may have formed at two coalescing earthflows about 4km above the fan apex. The 1989 hyperconcentrated flow caused significant aggradation on the fan. One year later to the day, a significant flood occurred, which ran over the aggraded fan surface from the 1989 event. This latter event destroyed four more homes mostly through bank erosion and rendered a section of county road impassable. FLDWAV, a flood routing model capable of simulating unsteady flow conditions, was used to model landslide dam breaches for a number of different dam heights at the earthflows. Modeling results were then combined with historic air photograph interpretation, dendrochronology, and eyewitness accounts to construct a frequency–magnitude relationship for hyperconcentrated flows at Canyon Creek. FLDWAV results were combined with a hyperconcentrated flow runout model (FLO-2D) on the fan to estimate maximum flow depth and flow velocity for the design event, a 500-year return period with a predicted peak discharge of 710m3/s. A large range of mitigation measures were reviewed, but it was concluded that buy-outs would be the most effective risk reduction measure. Property acquisition commenced in 2004.

On June 30, 2001, a debris flow occurred in the Acquabona Creek, a small catchment of the Eastern Dolomites, Italy. This debris flow originated shortly after an intense rainstorm, characterised by a peak intensity of 8.6mm per 10min; it transported a total volume of 30,000m3, consisting of poorly sorted gravely sand with boulders up to 3m in diameter. The sediment erosion yield rate reached as high as 20m3/m. In order to verify the accuracy of the field measurements, the total volume of debris deposits have was calculated using three different topographic measurement techniques: 3D laser scanning, terrestrial stereo-photogrammetry survey and total topographic station survey. Data collected so far show that no debris flow has occurred at Acquabona with a rainfall intensity lower than 4.6mm per 10min. Channel cross section measurements indicate that debris flow velocity ranges from 2.0 to 7.2m/s along the lower flow channel and peak discharge ranges between 22 and 300m3/s. Field estimates of the rheological properties indicate a yield strength ranging from 2,088 to 5,313Pa and Bingham viscosity between 70 and 337 Pa · s. It is not still possible to identify a rainfall intensity and amount threshold for debris flow triggering, but the data so far collected emphasise that debris flows do not occur with a rainfall intensity lower than 4.6mm per 10min.

On November 28, 2003, at about 00:30 PST, 35km east of Prince Rupert in northwestern British Columbia, an extremely rapid, retrogressive liquefaction earth flow, or a clay flow-slide, severed the natural gas pipeline. As a result, Prince Rupert residents were without natural gas heat for 10 days. The landslide has a steep main scarp that is 45m high by 345m wide. It consists of glaciomarine sediments mantled by rubbly colluvium lying on, and against smooth bedrock of the valley wall. It covers an area of 32ha, and displaced about 4.7M m3 of material. This displaced material flowed up and down river over a distance of 1.7km, blocked the river, and caused flooding upstream for a distance of 10km. This landslide is the most recent of four large landslides that have occurred over the last four decades in glaciomarine sediments in northwestern British Columbia.

Rock avalanches fell from Vampire (2,645m) Peak in the Southern Alps of New Zealand during January 2008. There were no direct witnesses, casualties or damage to infrastructure. Field observations indicate about 150,000m3 (±50,000) of indurated greywacke collapsed retrogressively from a 73° slope between 2,380 and 2,520m. Debris fell 800m down Vampire’s south face and out 1.7km across Mueller Glacier, with a 27.5° angle of reach. The resulting 300,000m2 avalanche deposit contains three distinct lobes. The national seismograph network recorded two pulses of avalanche-type shaking, equivalent in amplitude to a M L2.4 tectonic earthquake, for 60s on Monday 7 January at 2349hours (NZDT); then 45s of shaking at M L2.5 on Sunday 13 January at 0923hours (NZDT). Deposit lobes are inferred to relate directly with shaking episodes. The avalanche fell across the debris from an older avalanche, which was also unwitnessed and fell from a different source on Vampire’s south face between February and November 2003. The 2003 avalanche involved 120,000m3 (±40,000) of interlayered sandstone and mudstone which collapsed from a 65° slope between 2,440 and 2,560m, then fell 890m down across Mueller Glacier at a 24° angle of reach. Prolonged above-freezing temperatures were recorded during January 2008, but no direct trigger has been identified. The event appears to be a spontaneous, gravitationally induced, stress failure.

A large number of landslides induced by the 2004 Mid Niigata Prefecture earthquake resulted in the closure of 233 segments of national and prefectural routes in Higashiyama mountain district, and 61 localities were completely isolated. Since railway and road facilities follow closely the motion of soils, damage to these facilities has to be discussed in terms of soil deformations that they experienced. The example of Kizawa tunnel shows that even relatively small soil deformations can be large enough to cause serious cracking of tunnel lining.

In September 2004, rain from the remnants of Hurricanes Frances and Ivan triggered at least 155 landslides in the Blue Ridge Mountains of North Carolina. At least 33 debris flows occurred in Macon County, causing 5 deaths, destroying 16 homes, and damaging infrastructure. We mapped debris flows and debris deposits using a light-detecting and ranging digital elevation model, remote imagery and field studies integrated in a geographic information system. Evidence of past debris flows was found at all recent debris flow sites. Orographic rainfall enhancement along topographic escarpments influenced debris flow frequency at higher elevations. A possible trigger for the Wayah and fatal Peeks Creek debris flows was a spiral rain band within Ivan that moved across the area with short duration rainfall rates of 150–230mm/h. Intersecting bedrock structures in polydeformed metamorphic rock influence the formation of catchments within structural–geomorphic domains where debris flows originate.

A debris flow originating from the Alcamayo River on 10th April 2004 destroyed a part of the town of Aguas Calientes, resulting in 11 victims, and with serious affects to the tourist flow to the Machupicchu inka citadel. On the same day, as well as in January and March 2004, other similar phenomena occurred on the Cedrobamba and Leonchayoq Rivers, affecting the railway and an electrical tower, and disrupting the train service.

Heavy rain fell on the Shikoku area during Typhoon Namtheun, setting a new record for daily rainfall in Japan of 1317mm. The rain which peaked at 120mm/h, triggered numerous landslides in the Nakagawa basin of Tokushima Prefecture, Japan on August 1, 2004. Among them, four large, rapid, long-runout landslides were triggered at Kisawa village. Two people were caught in one landslide and disappeared without trace, and there was much property damage. Ring-shear tests on samples from the landslides showed that shear resistance was greatly reduced by high pore-water pressure after shear failure was triggered by the increase in ground-water level during the rain.

The international journal Landslides was initiated in April 2004. It is the core project (IPL-C100) of the International Programme on Landslides, a joint initiative of the International Consortium on Landslides and the United Nations and other global organizations. The aims of Landslides are to promote landslide sciences, technology, and capacity building and strengthen global cooperation for landslide risk reduction within the United Nations International Strategy for Disaster Reduction. This paper presents an analysis of the first 5years of Landslides, the study methods employed, the types and major causes of landslides, the number of different contributors per country, and the “times cited” per issue and most frequently cited papers and briefly discusses some of these. Strategies for future development of the journal involve obtaining input and suggestion from researchers and readers worldwide.

Data recorded by a seismic network deployed the day after the 2004 Mid Niigata Prefecture Earthquake (M6.8) in central Japan are used to determine the major source faults responsible for the mainshock and major aftershocks. Using this high-resolution seismic data, three major source faults are identified: two parallel faults dipping steeply to the west located 5km apart, and the other dipping eastward and oriented perpendicular to the west-dipping faults. The analysis also reveals that the lateral variation in seismic velocity observed at the surface extends to a depth of 15km, encompassing the source area of the mainshock. This strong heterogeneity of the crust, related to the complex geological and tectonic evolution of the area, is considered to be responsible for the prominent aftershock activity following the 2004 Niigata event.

The 2005 northern Pakistan earthquake (magnitude 7.6) of 8 October 2005 occurred in the northwestern part of the Himalayas. We interpreted landslides triggered by the earthquake using black-and-white 2.5-m-resolution System Pour l’Observation de la Terre 5 (SPOT 5) stereo images. As a result, the counts of 2,424 landslides were identified in the study area of 55 by 51km. About 79% or 1,925 of the landslides were small (less than 0.5ha in area), whereas 207 of the landslides (about 9%) were large (1ha and more in area). Judging from our field survey, most of the small landslides are shallow rock falls and slides. However, the resolution and whitish image in the photos prevented interpreting the movement type and geomorphologic features of the landslide sites in detail. It is known that this earthquake took place along preexisting active reverse faults. The landslide distribution was mapped and superimposed on the crustal deformation detected by the environmental satellite/synthetic aperture radar (SAR) data, active faults map, geological map, and shuttle radar topography mission data. The landslide distribution showed the following characteristics: (1) Most of the landslides occurred on the hanging-wall side of the Balakot–Garhi fault; (2) greater than one third of the landslides occurred within 1km from the active fault; (3) the greatest number of landslides (1,147 counts), landslide density (3.2 counts/km2), and landslide area ratio (2.3ha/km2) was found within Miocene sandstone and siltstone, Precambrian schist and quartzite, and Eocene and Paleocene limestone and shale, respectively; (4) there was a slight trend that large landslides occurred on vertically convex slopes rather than on concave slopes; furthermore, large landslides occurred on steeper (30° and more) slopes than on gentler slopes; (5) many large landslides occurred on slopes facing S and SW directions, which is consistent with SAR-detected horizontal dominant direction of crustal deformation on the hanging wall.

A seasonal rain front (Baiu front) accompanied a long-term accumulation of precipitation propagated over the wide areas of the main island of Japan during 15–24 July 2006. In Okaya City, Nagano Prefecture, several flow-type landslides occurred in the early morning of 19 July 2006, claiming eight lives. Among these landslides, a most peculiar complex earth slide–earth flow occurred on a north gentle slope of the upstream portion of the Motosawagawa River. In the source area, volcanoclastic soils overlying tuffaceous rocks at about 4-m depth slid due to the prolonged precipitation that raised the water table level in the soil. Along with the travel path, the failed materials fluidized causing the liquefaction of the volcanoclastic soils underlain by volcanic black ash soils. The resulting flow spread over a wide area up to the final deposition. Constant volume box-shear tests on undisturbed volcanoclastic soil specimens taken from the source area showed effective normal stress tended to decrease during shearing. The ring shear tests on saturated disturbed specimens produced the large loss of shear resistance, which may explain the fluidized motion of the complex landslide.

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The purpose of this paper is to present a review of peat landslide events in Ireland since 2003, when two significant events occurred. Since 2003, there have been at least 13 such events. Several of these events included more than one slide. It is also likely that there have been unrecorded slides. It seems that there is an increasing incidence of such events, but they seem to occur in clusters with intervening quiet periods. These clusters coincide with periods of intense rainfall. For many slides, at least two causal factors can be identified. Primarily these comprised intense rainfall but human activities such as road construction and peat cutting also contributed to the slides. Detailed geotechnical testing of the peat, including laboratory direct simple shear tests (DSS), is reported for two of the slides. Back-analysis of these two failures suggests that the mobilised strength of the material in the failure surface is similar to that measured in the DSS tests. However, conventional geotechnical analyses need to be treated with caution as they fail to account for the complex interactions in the sliding surface and in particular the lubricating role of water. KeywordsPeat–Translational (planar)–Undrained shear strength–Rainfall–Ireland

A gigantic rapid landslide claiming over 1,000 fatalities was triggered by rainfalls and a small nearby earthquake in the Leyte Island, Philippines in 2006. The disaster presented the necessity of a new modeling technology for disaster risk preparedness which simulates initiation and motion. This paper presents a new computer simulation integrating the initiation process triggered by rainfalls and/or earthquakes and the development process to a rapid motion due to strength reduction and the entrainment of deposits in the runout path. This simulation model LS-RAPID was developed from the geotechnical model for the motion of landslides (Sassa 1988) and its improved simulation model (Sassa et al. 2004b) and new knowledge obtained from a new dynamic loading ring shear apparatus (Sassa et al. 2004a). The examination of performance of each process in a simple imaginary slope addressed that the simulation model well simulated the process of progressive failure, and development to a rapid landslide. The initiation process was compared to conventional limit equilibrium stability analyses by changing pore pressure ratio. The simulation model started to move in a smaller pore pressure ratio than the limit equilibrium stability analyses because of progressive failure. However, when a larger shear deformation is set as the threshold for the start of strength reduction, the onset of landslide motion by the simulation agrees with the cases where the factor of safety estimated by the limit equilibrium stability analyses equals to a unity. The field investigation and the undrained dynamic loading ring shear tests on the 2006 Leyte landslide suggested that this landslide was triggered by the combined effect of pore water pressure due to rains and a very small earthquake. The application of this simulation model could well reproduce the initiation and the rapid long runout motion of the Leyte landslide. KeywordsLeyte landslides-Computer simulation-Rapid landslides-Ring shear test

A strong earthquake (M J 6.9, M W 6.6–6.7) at about 11 km depth hit the western shore of the Noto Peninsula on Honshu, Japan, at about 00:42 coordinated universal time (9:42 a.m. local time) on 25 March 2007 (the Noto Hanto Earthquake in 2007). The earthquake triggered only 61 landslides, with most traveling short distances. It caused one long run-out landslide in the Nakanoya district of Monzen town, Wajima city, Ishikawa Prefecture, when a portion of a deep-seated landslide transformed into a moderate debris slide down a channel. The rock slide occurred on a south-facing convex-shaped slope on a small spur where earthquake ground shaking likely was strongly amplified by topography. A portion of the rock slide reached a small channel floored by materials containing abundant groundwater. Constant-volume box-shear tests on normally consolidated saturated specimens revealed that the apparent angle of internal friction of the channel-floor material was 33–36° at 10-mm shear displacement and did not show much decrease in effective normal stress during shearing. In situ rock-sliding testing on the exposed channel materials showed a low kinetic-friction angle of about 21°. We suggest that an unsaturated portion of the rock slide slid down the channel, with sliding between the rock-slide mass and the channel floor. Because the slope angle of the travel path nearly equaled the kinetic-friction angle, the unsaturated rock slide mass may have traveled at a moderately slow speed, or it might have decelerated and accelerated. Slow speed is supported by accounts from local residents that suggest movement of debris continued for 3 days after the main shock.

Due to a lack of systematic observations, the intensity and volume of rock falls and rock avalanches in high mountain areas are still poorly known. Nevertheless, these phenomena could have burly consequences. To document present rock falls, a network of observers (guides, mountaineers, and hut wardens) was initiated in the Mont Blanc Massif in 2005 and became fully operational in 2007. This article presents data on the 66 rock falls (100m3 ≤ V ≤ 50,000m3) documented in 2007 (n = 41) and 2008 (n = 25). Most of the starting zones are located in warm permafrost areas, which are most sensitive to warming, and only four rock falls are clearly out of permafrost area. Different elements support permafrost degradation as one of the main triggering factors of present rock falls in high mountain areas. KeywordsRock falls-Permafrost-High alpine environments-Mountains-Mont Blanc Massif

Fox Creek is a small tributary of the Saddle River, a tributary of the Peace River in northwestern Alberta. It has several dormant landslides with degraded scarps and grabens. A new, reactivated landslide on the north bank of the Fox Creek occurred on 5 May 2007. The landslide formed two major sliding blocks. A rapid translational block slide, it mobilized 47Mm3 of displaced materials, blocked the creek, and made a natural dam with a maximum height of 19m at the tips of the displaced blocks. The rupture surfaces of the 2007 landslide were within the advance phase glaciolacustrine sediments. The residual friction angles are about 10° similar to those of the previous landslides in the Peace River Lowland. Precipitation and snow melt prior to the landslide are likely triggers of the 2007 Fox Creek landslide. The farmlands on the crest of the river valley and timber resources were impacted. The current landslide dam in Fox Creek does not have any evidence of seepage downstream; it may last for many years. Eventually, the creek will overtop and erode the dam. The same cycle of actions, landsliding, damming, and erosion will continue in the foreseeable future. Keywords: Landslide, Landslide dam, Preglacial valley, Peace River Lowland, Alberta

On the 21st of April 2007, the Aysén Fjord earthquake (Mw 6.2) in southern Chile (45.3° S, 73.0° W) triggered hundreds of landslides in the epicentral area along the fjord coast and surroundings. Some of these landslides induced large tsunami waves within the fjord causing fatalities and damaging several salmon farms, the most important economic activity of the area. The landslides included rock slides and avalanches, rock falls, shallow soil and soil–rock slides, and debris flows. The earthquake was the climax of a seismic swarm that began 3months earlier. The seismicity is associated with tectonic activity along the Liquiñe–Ofqui fault zone (LOFZ), a major structural feature of the region. The earthquake-induced landslides were mapped and classified from field observations and remote sensing analysis. The landslide areas and epicentral distances are within the expected range for the earthquake magnitude according to worldwide data, while the position of landslides on the slopes strongly suggests topographic amplification effects in triggering the failures. The location of the landslides is also clearly related to some of the main fault branches of the LOFZ. The seismic event has configured a new situation of seismic and landslide hazard in the Aysén region and along the LOFZ, where the presence of towns and economic infrastructure along the coasts of several fjords constitutes a potential risk that was not considered before this seismic event. KeywordsLandslide-Earthquake-Patagonia

A large rock and ice avalanche occurred on the north face of Mount Steele, southwest Yukon Territory, Canada, on July 24, 2007. In the days and weeks preceding the landslide, several smaller avalanches initiated from the same slope. The ice and rock debris traveled a maximum horizontal distance 5.76km with a maximum vertical descent of 2,160m, leaving a deposit 3.66km2 in area on Steele Glacier. The seismic magnitude estimated from long-period surface waves (M s) is 5.2. Modeling of the waveforms suggests an estimated duration of approximately 100s and an average velocity of between 35 and 65m/s. This landslide is one of 18 large rock avalanches known to have occurred since 1899 on slopes adjacent to glaciers in western Canada. We describe the setting, reconstruct the event chronology and present a preliminary characterization of the Mount Steele ice and rock avalanches based on field reconnaissance, analysis of seismic records and an airborne LiDAR survey. We also present the results of a successful dynamic simulation for the July 24 event.

The M s 8.0 Wenchuan earthquake or “Great Sichuan Earthquake” occurred at 14:28p.m. local time on 12 May 2008 in Sichuan Province, China. Damage by earthquake-induced landslides was an important part of the total earthquake damage. This report presents preliminary observations on the Hongyan Resort slide located southwest of the main epicenter, shallow mountain surface failures in Xuankou village of Yingxiu Town, the Jiufengchun slide near Longmenshan Town, the Hongsong Hydro-power Station slide near Hongbai Town, the Xiaojiaqiao slide in Chaping Town, two landslides in Beichuan County-town which destroyed a large part of the town, and the Donghekou and Shibangou slides in Qingchuan County which formed the second biggest landslide lake formed in this earthquake. The influences of seismic, topographic, geologic, and hydro-geologic conditions are discussed.

The 12 May 2008 M7.9 Wenchuan earthquake in the People’s Republic of China represented a unique opportunity for the international community to use commonly available GIS (Geographic Information System) tools, like Google Earth (GE), to rapidly evaluate and assess landslide hazards triggered by the destructive earthquake and its aftershocks. In order to map earthquake-triggered landslides, we provide details on the applicability and limitations of publicly available 3-day-post- and pre-earthquake imagery provided by GE from the FORMOSAT-2 (formerly ROCSAT-2; Republic of China Satellite 2). We interpreted landslides on the 8-m-resolution FORMOSAT-2 image by GE; as a result, 257 large landslides were mapped with the highest concentration along the Beichuan fault. An estimated density of 0.3 landslides/km2 represents a minimum bound on density given the resolution of available imagery; higher resolution data would have identified more landslides. This is a preliminary study, and further study is needed to understand the landslide characteristics in detail. Although it is best to obtain landslide locations and measurements from satellite imagery having high resolution, it was found that GE is an effective and rapid reconnaissance tool.

The 2008 Wenchuan earthquake (M s = 8.0; epicenter located at 31.0° N, 103.4° E), with a focal depth of 19.0km was triggered by the reactivation of the Longmenshan fault in Wenchuan County, Sichuan Province, China on 12 May 2008. This earthquake directly caused more than 15,000 geohazards in the form of landslides, rockfalls, and debris flows which resulted in about 20,000 deaths. It also caused more than 10,000 potential geohazard sites, especially for rockfalls, reflecting the susceptibility of high and steep slopes in mountainous areas affected by the earthquake. Landslide occurrence on mountain ridges and peaks indicated that seismic shaking was amplified by mountainous topography. Thirty-three of the high-risk landslide lakes with landslide dam heights greater than 10m were classified into four levels: extremely high risk, high risk, medium risk, and low risk. The levels were created by comprehensively analyzing the capacity of landslide lakes, the height of landslide dams, and the composition and structure of materials that blocked rivers. In the epicenter area which was 300km long and 10km wide along the main seismic fault, there were lots of landslides triggered by the earthquake, and these landslides have a common characteristic of a discontinuous but flat sliding surface. The failure surfaces can be classified into the following three types based on their overall shape: concave, convex, and terraced. Field evidences illustrated that the vertical component of ground shaking had a significant effect on both building collapse and landslide generation. The ground motion records show that the vertical acceleration is greater than the horizontal, and the acceleration must be larger than 1.0g in some parts along the main seismic fault. Two landslides are discussed as high speed and long runout cases. One is the Chengxi landslide in Beichuan County, and the other is the Donghekou landslide in Qingchuan County. In each case, the runout process and its impact on people and property were analyzed. The Chengxi landslide killed 1,600 people and destroyed numerous houses. The Donghekou landslide is a complex landslide–debris flow with a long runout. The debris flow scoured the bank of the Qingjiang River for a length of 2,400m and subsequently formed a landslide dam. This landslide buried seven villages and killed more than 400 people.

On June 14 2008, an Iwate–Miyagi inland earthquake that had a magnitude of 7.2 hit the eastern foot of the Ohu Mountains in Tohoku district, Japan. The seismic peak ground acceleration was greater than 1,000 gal in the Aratozawa Dam area. The earthquake triggered a massive landslide at the upper reach of the dam. The landslide had the sediment volume of over 67 million cubic meters and is considered the largest catastrophic landslide in Japan during the last 100years. This report presents a summary of our findings pertinent to the landslide’s activities based on our field investigations that started the day after the landslide. This report covers: (1) details of the land deformations caused by the landslide, (2) geological background pertinent to landslide development, and (3) estimation of the slip surface and the other physical properties of the landslide based on the analysis of the boring core specimens and landform features. The landslide is roughly divided into two sections, a lower and an upper half. The lower half moved almost simultaneously as one massive block of 700 m long, 800 m wide, and 70–80 m thick. The slip surface had developed on the very fine sand of the alternate layer of fine-grained sandstone and siltstone. The slickensided slip surface has a gradient of only 2°. This feature indicates that the type of the landslide movement is considered to be a block glide. The landslide body is nearly identical to the topography of the landslide area that was developed about 50,000 years ago. This shows the possibility that the landslide was reactivated. The upper half consists of two large ridges and the broad debris field and is 600 m long, 900 m wide, and 70–100 m thick. The maximum height of the main scarp is over 150 m. KeywordsMassive landslide–Aratozawa Dam–Translational block glide–Landform deformation–Inland earthquake

Natural landslide dams triggered by earthquakes are a common feature and a significant hazard in high-relief, tectonically active areas. The great Wenchuan Earthquake of May 12, 2008 created 256 natural dams, of which 34 presented significant risks to downstream areas in the event of their uncontrolled failure. Out of the 34 large landslide dams that warranted mitigation, we discuss Tangjiashan landslide dam in detail. Emergency response to the Tangjiashan landslide-dammed lake in the following weeks and months successfully reduced the risk, and the advantages and disadvantages of various countermeasures that were applied are summarized here. Successful strategies relied on accurate scientific assessments, on timely execution of the countermeasures, and on the correct design of sluiceway (spillway) channels across the landslide dams. Retrospective assessment indicates that the following improvements would be more beneficial: (1) Sluiceway channels utilizing a combination of cross-section types, rather than simply trapezoidal in shape; (2) increased channel slope, which is more than the original gradient of the river; (3) better protection of inlets and outlets to control the planned incision rates; and (4) channels lined to better control the incision rate. We discuss applications of the concept of artificially controlled failure, and we submit these observations for the benefit of those responding to future seismic catastrophes. KeywordsWenchuan Earthquake–Landslide-dammed lake–Emergency response–Mitigation–Artificially controlled failure

On July 12, 2008, two convective cells about 155km apart produced a brief period of intense rainfall triggering large debris flows in the southern Sierra Nevada. The northernmost cell was centered over Oak Creek Canyon, an east-flowing drainage, and its tributaries near Independence, CA, USA. About 5:00 p.m., debris flows passed down the South Fork and North Fork of Oak Creek to merge into a large single feature whose passage affected the historic Mt. Whitney Fish hatchery and blocked California State Highway 395. At about the same time, the southernmost cell was largely centered over Erskine Creek, a main tributary of the west-flowing Kern River. Debris flows issued from several branches to coalesce into a large debris flow that passed along Erskine Creek, through the town of Lake Isabella, CA, USA and into the Kern River. It was observed reaching Lake Isabella about 6:30 p.m. Both debris flows caused significant disruption and damage to local communities. KeywordsDebris flow–Sierra Nevada–Wildfire–Intense rainfall–California

The Iwate–Miyagi Nairiku Earthquake in 2008, whose seismic intensity was M. 7.2 in Japan Meteorological Agency (JMA) scale, induced innumerable landslides on the southern flank of Mt. Kurikoma volcano allocated along the Ou Backbone Range in Northeast Japan. Most landslides are detected in a hanging wall side of the seismic fault. Those landslides are classified into five types: deep-seated slide, debris slide, shallow debris slide, secondary shallow debris slide, and debris flow. Most common landslide types induced by the earthquake are shallow debris slides and subsequent debris flows. They are intensively distributed along steep gorges incising a volcanic skirt of Mt. Kurikoma, consisting of welded ignimbrite of the Pleistocene age. Debris flows are also distributed even along gentle river floors in the southern lower flank of the volcano. The area of densely distributed debris slides, shallow debris slides, and debris flows is concordant with that of severe seismic tremor. Thus, genetic processes of landslides induced by the Iwate–Miyagi Nairiku Earthquake in 2008 are attributed to multiple causative factors such as geology, topography, and seismic force.

On June 5, 2009, a catastrophic rockslide-debris flow occurred at the crest of the Jiweishan Mountain in Wulong, Chongqing, China. Approximately five million cubic meters of limestone blocks slid along a weak interlayer of bituminous and carbonaceous shale. The source mass descended from the upper part of the slope rapidly, crossing a 200-m wide and 50-m deep creek in front of it. Blocked by the opposite steep creek wall, the sliding mass changed its direction and traveled a further 2.2km along the creek in debris-flow mode, finally forming a large accumulation zone with an average depth of 30m. This is one of the most catastrophic rockslide events in recent years in China. It buried 12 houses and the entrance of an iron mining tunnel where some 27 miners were working inside. Ten people died, 64 missing, and eight wounded. Immediately after this disaster happened, the government organized an expert team to assist the rescue work. As one of the geological experts, the author did a lot of field investigations and collected first-hand information. Multi-methods including the remote sensing, 3D laser scanning, geophysical exploration, and numerical modeling were used for analyzing the characteristics and the triggering mechanism of the Wulong rockslide. The preliminary investigation results reveal that this rockslide with poor geological conditions was mainly induced by the gravitation and the karst effect and also affected by the previous mining activities. The research in this paper is meaningful and useful for further research on such kind of rockslides that are geologically similar to the Wulong rockslide. KeywordsRockslide-Debris flow-Genetic Mechanism-Mine-Wulong

From September 16 to September 20, 2010, a cold weather front went across Slovenia. A heavy 4-day rainfall totaling between 300 and 520mm caused large floods and triggered numerous rainfall-induced landslides. The damage due to the floods and landslides is estimated over 250 million Euros. One of the largest landslides covering the area of approximately 15ha was triggered on flysch bedrock, just below a limestone overthrust zone. The sliding material properties, the inclinations of the slope, and the water catchment area indicate that the landslide may transform into a fast moving debris flow. The necessary protective measures were taken to protect inhabitants and the infrastructure against the disaster. The Stogovce landslide is one of the numerous rainfall-induced landslides that have occurred in Slovenia on flysch bedrock in the last 10years. It proves that landslide risk on flysch territory is increasing. Special program of monitoring and protective measures will have to be developed in near future to protect densely populated areas against landslides as a consequence of weather extremes. KeywordsDebris flow–Mudflow–Flysch bedrock–Overthrust–Tectonic–Slovenia

More than 150 landslides originated in the eastern part of the Czech Republic (region of the Flysch Outer Western Carpathians—hereinafter, OWC) due to soil saturation caused by antecedent precipitation and long lasting and intensive rainfalls on 16–18 May 2010 (>300mm as measured by some stations). As a consequence, a multitude of small failures originated 88% of which was smaller than 104m2. Most landslides are characterised as shallow (<10m) or middle–deep (10–30m) incipient (rather short travel) landslides, debris slides and soil slips spatially clustered to a geological domain underlain by rather weak thin-bedded flysch and unconsolidated Quaternary deposits. An exception to this is represented by a kilometre-long rockslide (∼2–3milm3) affecting tectonically weakened and weathered claystone/mudstone-dominated flysch on the southern slope of Mt. Girová (the Beskydy Mountains). The rockslide is one of the largest long runout landslides in the territory of the Czech Republic activated over the past few decades as it reaches the dimensions of the largest documented Holocene long runout landslides in the Czech part of the OWC. A majority of the May 2010 landslide events developed inside older (Holocene or historic) landslide terrains, which points to their spatial persistency and recurrent nature. In spite of the fact that the May 2010 landslide event was not as destructive as some previous landslide activisation in the OWC region (e.g. July 1997 event), it left many slope failures at the initial stage of their potential future reactivation. KeywordsExtreme precipitation–Rockslide–Recurrent landslides–Flysch Carpathians–Czech Republic

The World Landslide Forum is a triennial mainstream conference aimed at gathering scientists, stakeholders, policy makers and industry members dealing with the management of landslide risk. The First World Landslide Forum, organised by the International Consortium of Landslides, UNESCO, WMO, FAO, UNISDR, UNU, UNEP, IBRD, UNDP, ICSU, WFEO, KU and the Japan Landslide Society, was held in 2008 at the United Nations University, Tokyo. The First World Landslide Forum adopted the 2008 Tokyo Declaration ‘Strengthening the International Programme on Landslides with UNISDR’. The numerous recent disasters due to landslides show that there is an urgent need to translate science into practical applications to assist communities, governments and disaster-relief organisations avert and mitigate future landslide disasters. For this reason, the explicit theme of the Second World Landslide Forum, being organised for Rome, Italy, for 3–9 October 2011, is to connect landslide scientists with landslide stakeholders in a special landslide forum to align future innovations in landslide science and technology with the future needs of humanity and the environment. KeywordsWorld Landslide Forum-Technology marketplace-Field trip-Science-Stakeholders-Decision makers

The World Landslide Forum (WLF) is a triennial mainstream conference aimed at gathering scientists, stakeholders, policy makers and industry members dealing with the management of landslide risk. The First World Landslide Forum, organised by the International Consortium of Landslides, UNESCO, WMO, Food and Agriculture Organization, UNISDR, UNU, UNEP, IBRD, UNDP, ICSU, WFEO, KU and the Japan Landslide Society, was held in 2008 at the United Nations University, Tokyo. The 1st WLF adopted the 2008 Tokyo Declaration “Strengthening the International Programme on Landslides with UNISDR”. The Second World Landslide Forum has the objective to further develop the outcomes of the First Forum in Tokyo 2008 by providing a global cross-cutting information and cooperation platform for all types of organisations representing academia, United Nations organisations, governments, private enterprises and individuals that contribute to landslide research, practice, education and decision making and are willing to strengthen landslide and other related Earth system risk reduction strategies. The emphasis of this forum will be “Putting Science into Practice” with special attention given to actual implementation of technology and research in everyday applications and procedures with the direct involvement of researchers, engineers, private enterprises, stakeholders as well as policy and decision makers. The abstract submission and pre-registration of participants was quite successful with 649 received abstracts and more than 800 participants at May 2011. The full organisation of the event is now in progress taking into consideration the new figure and interest in scientific community and stakeholders. KeywordsWorld Landslide Forum–Technology marketplace–Field trip–Science–Stakeholders–Decision makers