Role Of Landslides Research Articles

Review of Assessing Slope Stability in Sabah: A Comprehensive Geotechnical Analysis

Rainfall has been recognized as the primary factor contributing significantly to landslide incidents globally. This is attributed to rainwater infiltration, resulting in fluctuations in groundwater levels, which play a crucial role in landslide occurrences. This article reviews the previous study on the relationship between rainfall intensity towards slope failure. A summary of the present research was conducted, and it is apparent that rainfall intensity is one of the elements that plays a role in landslides. Ultimately, rainfall leads to significant landslides, affecting pore pressure and frictional strength.

How the EU Soil Observatory contributes to a stronger soil erosion community

New policy developments have emerged in relation to soil conservation after 2020. The Common Agricultural Policy (CAP) 2023–2027, the proposal for a Soil Monitoring Law and the mission ‘A Soil Deal for Europe’ have shaped a new policy framework at EU level, which requires updated assessments on soil erosion and land degradation. The EU Soil Observatory (EUSO) successfully organised a scientific workshop on ‘Soil erosion for the EU’ in June 2022. The event has seen the participation of more than 330 people from 63 countries, addressing important topics such as (i) management practices, (ii) large scale modelling, (iii) the importance of sediments in nutrient cycle, (vi) the role of landslides and (v) laying the foundations for early career scientists. As a follow up, among the 120 abstracts submitted in the workshop, we received fifteen manuscripts, out of which nine were selected for publication in the present special issue. In this editorial, we summarize the major challenges that the soil erosion research community faces in relation to supporting the increasing role of soils in the EU Green Deal.

Developing a more complete understanding of tropical montane forest disturbance ecology through landslide research

Landslides are a central component of tropical montane forest disturbance regimes, including in the tropical Andes biodiversity hotspot, one of the most biodiverse ecosystems in the world. Technological developments in remote sensing have made landscape-scale landslide studies possible, unlocking new avenues for understanding montane biodiversity, ecosystem functioning, and the future effects of climate change. Here, we outline three axes of inquiry for future landslide ecology research in Andean tropical montane forest. We focus exclusively on the Andes due to the vast floral diversity and high endemicity of the tropical Andes biodiversity hotspot, and its importance for global biodiversity and regional ecosystem service provisioning; the broad elevational, latitudinal, and topographic gradients across which landslide dynamics play out; and the existence of long-term plot networks that provide the necessary baseline data on mature forest structure, composition, and functioning to contextualize disturbance impacts. The three lines of study we outline, which draw heavily on remote sensing data and techniques, will deepen scientific understanding of tropical montane forest biodiversity and ecosystem functioning, and the potential impacts of climate change on both. They are: (1) tracking landslide biodiversity dynamics across time and space with high spatial and temporal resolution satellite and unoccupied aerial vehicle imagery; (2) assessing the ecological influence of landslides through the lens of plant functional diversity with imaging spectroscopy; and (3) understanding current and predicting future landslide regimes at scale by building a living landslide inventory spanning the tropical Andes. The research findings from these three axes of inquiry will shed light on the role of landslides and the process of forest recovery from them in both the Andes and worldwide.

Evolution of cracks in the shear bands of granite residual soil

The evolution of shear bands and cracks plays an important role in landslides. However, there is no systematic method for classification of the cracks, which can be used to analyze the evolution of cracks in shear bands. In this study, X-ray computed tomography (CT) is used to observe the behavior of granite residual soil during a triaxial shear process. Based on the digital volume correlation (DVC) method, a crack classification method is established according to the connectivity characteristics of cracks before and after loading. Cracks are then divided into six classes: obsolete, brand-new, isolated, split, combined, and compound. With evolution of the shear bands, a large number of brand-new cracks accelerate the damages of materials at the mesoscale, resulting in a sharp decrease in strength. The volume of brand-new cracks increases rapidly with increasing axial strain, and their volume is greater than 50% when the strain reaches 12%, while the volume of compound cracks decreases from 54% to 21%. As cracks are the weakest areas in a material, brand-new cracks accelerate the development of shear bands. Finally, the coupling effect of shear bands and cracks destroys the soil strength.

Landslide Processes Involved in Volcano Dismantling From Past to Present: The Remarkable Open‐Air Laboratory of the Cirque de Salazie (Reunion Island)

AbstractThe Cirque de Salazie is one of the large erosional depressions of Reunion Island. Composed of a thick accumulation of loose volcaniclastic materials derived from successive volcanic flank collapses and exposed to high precipitation rates, this large depression is particularly prone to landslides. Of the 133 km2 making up this large depression, at least 19% of slopes are affected by various types of landslides. The diversity and high density of landslides is one of the main issues for inhabited areas. We examine the landslides in this area with the goal of providing key elements for better hazard assessment and understanding their role in the landscape's evolution. For over 20 years, we have been acquiring multidisciplinary data on landslides. In this cirque, eight types of landslides are identified and described following an adapted landslide classification. Using a multidisciplinary approach, we characterize and interpret the surface morphology and internal structure of three large inhabited compound landslides with volumes of 0.1 km3 moving up to 1.15 myr−1. These complex landslides provide an opportunity to investigate the influence of past slope movements on current slope movements. Furthermore, using detailed mapping and volume calculation of the landslides triggered by the last major cyclonic rainstorm, we estimate that rainfall‐triggered landslides contribute up to 20% of the long‐term erosion rate. The Cirque de Salazie is a remarkable laboratory that offers new insights and challenges for future research on landslide hazard assessment and the role of landslides in the short‐ and long‐term dismantling of volcanoes.

A visualized hybrid intelligent model to delineate Swedish fine-grained soil layers using clay sensitivity

In the current paper, a hybrid model was developed to generate 3D delineated soil horizons using clay sensitivity (St) with 1 m depth intervals in a landslide prone area in the southwest of Sweden. A hybridizing process was carried out using generalized feed forward neural network (GFFN) incorporated with genetic algorithm (GA). The model was conducted by means of seven variables consisting of the geographical coordinates and piezocone penetration test data (CPTu). The output of model (St) as a description of the effect of soil disturbance on shear strength plays a significant role in landslides in Sweden and thus can be applied for site-specific evaluation. Therefore, the use of St-based models to delineate soil layers can be a cost-effective solution to improve geo-engineering design practices and assist in the reduction of related environmental risks, such as catastrophic landslide events or excavation failures. Evaluated model performance based on different applied soil classifications showed 4.38% improvement in the predictability level of GFFN-GA compared to optimum GFFN. Accordingly, delineated soil layers were evaluated using different criteria including previous landslides as well as supplementary geophysical and geotechnical investigations. The results show that the adopted hybrid GFFN-GA is an efficient tool that can potentially be applied to delineate soil horizons for the prediction of future events.

Landslide-Induced Weathering in Tectonically Active Mountains: Evidence From Dissolved Radiogenic Uranium Isotopes

Understanding weathering processes in landslide-dominated catchments is critical for evaluating the role of landslides in chemical weathering and the global carbon cycle. Previous studies have focused on solute concentrations in landslide-impacted landscapes, but have paid less attention to developing isotopic tracers of landslide-induced weathering fluxes. Recent work found that the dissolved radiogenic uranium isotopes in river water are closely related to the denudation rates in catchments draining steep mountains where landslides are thought to be a major erosion mechanism, suggesting the potential of uranium isotopes to trace landslide-induced weathering fluxes. Here we compile the dissolved radiogenic uranium isotopes (234U/238U ratios) in the river water samples from a group of catchments with variable landslide activities in the Minjiang River Basin at the eastern margin of the Tibetan Plateau. We derive three metrics of landslide activity from the analyses of digital topography and an inventory map of the co-seismic landslides triggered by the 2008 Mw7.9 Wenchuan earthquake: the normalized volume of landslides, the mean catchment slope angle, and the fraction of slopes steeper than a threshold angle beyond which slopes are mechanically unstable. The riverine dissolved 234U/238U ratios correlate negatively with the metrics of landslide activity in each catchment, which likely reflect the influence of landslides on the dissolved 234U/238U ratios. Mechanistically, enhanced bedrock landsliding would accelerate the exposure of fresh rock, promoting bedrock weathering and congruent dissolution of 234U and 238U contained in minerals; reduced landslide activities and enhanced regolith weathering would lead to preferential accumulation of 234U against 238U in solutes through alpha-recoil ejection, thus increasing dissolved 234U/238U. Our findings provide field evidence of using the riverine dissolved 234U/238U ratio to trace weathering fluxes driven by landslides, shedding new light on chemical weathering processes in uplifting mountains.

The role of landslides in the evolution of a small mountain river valley (Polish Carpathians)

The role of landslides in the evolution of a small mountain river valley (Polish Carpathians)

Role of landslides on the volume balance of the Nepal 2015 earthquake sequence

The 7.8 Mw earthquake that struck Nepal on April 25th, 2015 triggered over 21,000 landslides over an area of more than 25,000 km2. These landslides contributed to mass wasting, partially compensating the tectonic uplift by the earthquake. In this paper we quantify the volume balance resulting from the 2015 earthquake uplift (or subsidence) and landslide erosion. Starting from a new complete earthquake-induced landslide inventory, we calculated landslide volume by adopting different strategies for low-mobility and high-mobility landslides, considering also the potential supply of sediments to the drainage network. The results show that the contribution of earthquake-induced landslides to erosion is about one order of magnitude smaller than the vertical coseismic displacement. We found landslide volume values, due to the 2015 Nepal earthquake, ranging between 251 (− 15/ + 16) Mm3 up to 1503 (− 183/ + 210) Mm3 based on the adopted method, and a volume due to coseismic vertical displacement of 2134 (± 1269) Mm3 for the whole area. The volume balance of the 2015 Nepal earthquake is strongly dominated by tectonic displacement. We show that these estimates depend on several uncertainties. We identified and quantified uncertainties related to: (1) the choice of empirical volume-area scaling relationships and their parameters; (2) the completeness and quality of landslide inventory through comparison with available inventories; (3) the approach adopted for the assessment of elongated landslide volume; (4) the InSAR displacement data.

Geotechnical studies for Landslide susceptibility in the high basin of the Oum Er Rbia river (Morocco)

ABSTRACT In the high basin of Oum Er Rbia in the Middle Atlas Mountain, the steep slopes with inherent soil lead to the formation of landslides, which could pose danger to road infrastructure and buildings. Evenly the heavy rains exceeding the saturation of soils play a key role in landslides. In this context, this study attempted to assess unconsolidated soil characteristics and their impacts on landslide susceptibility. The texture, clay mineralogy, and Atterberg limits were determined for soil samples. Atterberg limits were conducted to estimate the swell potential of the soil and eventually classify the soil samples as swelling or non-swelling. As a result of the geotechnical studies, the average of the liquid limit values was between 28% and 56%, and the mean plasticity index of the units ranged from 13% to 24% in the overlying materials in the landslide zones. XRD analysis revealed that the most dominant mineral identified was quartz; illite minerals.

CORRELATIONS BETWEEN FLUVIAL KNICKPOINTS AND RECURRENT LANDSLIDE DAMS ALONG UPPER INDUS RIVER

TThis article summarizes an investigation into the likely role of landsliding in the formation of knickpoints along the Indus River in northern Pakistan. The knickpoints and their related geomorphic parameters (channel profile, concavity, drainage area, steepness index, etc.) were extracted from ASTER Digital Elevation Models (DEMs) with 30m resolution using ArcGIS, and Matlab software. A total of 251 knickpoints were extracted from the longitudinal profile of the Indus River along a ~750km long reach upstream of Tarbela dam. The identified knickpoint locations, along with their respective normalized steepness index (ksn values), were compared with the lithologic contacts, mapped faults, a regional level landslide inventory, and the locations of prehistoric rockslides. The knickpoints identified adjacent to the prehistoric landslide dams (i.e. Katzarah and Gol-Ghone events, and Lichar Gah etc.), exhibited normalized steepness index (Ksn) in the range of 500-1800m0.9 at various locations along the river channel. The highest normalized ksn values (>1800m0.9) were observed in the tectonically-active Nanga Perbat Haramosh Massif (NPHM) region, where the river flows through narrow gorges, and/or where active thrust faults cross the river channel. The study reveals that the landslide dams appear to be one of the significant trigger factors in the formation of knickpoints along the Indus River.

Sediment yield and erosion rate estimation in the mountain catchments of the Camastra artificial reservoir (Southern Italy): A comparison between different empirical methods

The sedimentary budget assessment is an important topic for the scientific and social community, because it is crucial to understand the dynamics of orogenic belts and cope with a number of practical problems, such as soil conservation and sediment accumulation in reservoir. Sediment yield or denudation rate estimates in southern-central Italy are generally obtained either by applying simple empirical relationships based on the statistical regression between the geomorphic parameters of the drainage network and the suspended sediment yield measured at the drainage basins outlets, or by using qualitative–quantitative sediment delivery ratio or erosion models. In this work, we carry out a study of catchment dynamics and a sedimentary yield computation of several mountain catchments of the central-western sector of the Basilicata region (southern Italy), which are located upstream of an artificial reservoir. The sediment yield and erosion rate have been computed through both an indirect assessment of the suspended sediment yield, based on the Tu index (mean annual suspension sediment yield), and the application of the RUSLE and USPED empirical methods. The results obtained have been compared with the historical data of sediment accumulation, measured in the artificial reservoir of the Camastra dam where a detailed evaluation of the volumes of historical (i.e. about 40years) sediment storage was collected.The collected dataset represents a basic tool both for the investigation of the morpho-dynamics of a typical mountain catchment of the Mediterranean area and the evaluation of sediment budget related to fluvial and hillslope processes. The 38-year-long record of the sediment storage in the Camastra artificial reservoir located at the outlet of the studied mountain catchments permits the validation of empirical relationships based on the geomorphic and climatic parameters of the drainage basin. Among the three different methods of sediment yield evaluation (Tu index, RUSLE and USPED), the Tu index showed the best prediction ability, although USPED erosion model also furnished a good estimation. As also confirmed by other works, the indirect estimation of sediment yield based on Ciccacci's empirical relationships can represent a good proxy of short-term denudation rates in the Mediterranean areas with geological and geomorphological features similar to the study area but the use of empirical models with increasing complexity such as the USPED erosion model can help to explore the spatial distribution of the sediment yield sectors of the drainage basin, the erosion hot-spots, and the role of landslides in sediment mobilization and hillslope-channel connectivity processes.

Characterization of groundwater dynamics in landslides in varved clays

Abstract. Groundwater dynamics may play a significant role in landslides. A detailed model is developed of the groundwater dynamics in landslides in varved clays in the Trièves area in the French Alps. The varved clays consist of a sequence of alternating silt and clay layers, covered by a colluvium layer and intersected by fissures. The hydraulic conductivity of the clay layers is negligible compared to the silt layers. It is conceptualized that fissures form a hydraulic connection between the colluvium and the varved clays. Groundwater recharge flows through the colluvium into the fissures, where water is exchanged horizontally between the fissure and the silt layers of the varved clays. Groundwater flow in the colluvium is simulated with the Boussinesq equation, while flow in the silt layers of the varved clays is simulated with the Richards equation. Longitudinal outflow from the fissure is simulated with a linear-reservoir model. Scattered data of relatively short monitoring periods is available for several landslides in the region. A good similarity between observed and simulated heads is obtained, especially when considering the lack of important physical parameters such as the fissure width and the distance between the monitoring point and the fissure. A simulation for the period 1959–2004 showed some correlation between peaks in the simulated heads and the recorded occurrence of landslides, while the bottom of the varved clays remained saturated during the entire simulation period.

Controls on valley width in mountainous landscapes: The role of landsliding and implications for salmonid habitat

Research Article| April 01, 2013 Controls on valley width in mountainous landscapes: The role of landsliding and implications for salmonid habitat C. May; C. May 1Department of Biology, James Madison University, Harrisonburg, Virginia 22807, USA Search for other works by this author on: GSW Google Scholar J. Roering; J. Roering 2Department of Geological Sciences, University of Oregon, Eugene, Oregon 97403, USA Search for other works by this author on: GSW Google Scholar L.S. Eaton; L.S. Eaton 3Department of Geology and Environmental Science, James Madison University, Harrisonburg, Virginia 22807, USA Search for other works by this author on: GSW Google Scholar K.M. Burnett K.M. Burnett 4U.S. Forest Service Pacific Northwest Research Station, Corvallis, Oregon 97331, USA Search for other works by this author on: GSW Google Scholar Author and Article Information C. May 1Department of Biology, James Madison University, Harrisonburg, Virginia 22807, USA J. Roering 2Department of Geological Sciences, University of Oregon, Eugene, Oregon 97403, USA L.S. Eaton 3Department of Geology and Environmental Science, James Madison University, Harrisonburg, Virginia 22807, USA K.M. Burnett 4U.S. Forest Service Pacific Northwest Research Station, Corvallis, Oregon 97331, USA Publisher: Geological Society of America Received: 22 Aug 2012 Revision Received: 10 Nov 2012 Accepted: 12 Nov 2012 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2013 Geological Society of America Geology (2013) 41 (4): 503–506. https://doi.org/10.1130/G33979.1 Article history Received: 22 Aug 2012 Revision Received: 10 Nov 2012 Accepted: 12 Nov 2012 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation C. May, J. Roering, L.S. Eaton, K.M. Burnett; Controls on valley width in mountainous landscapes: The role of landsliding and implications for salmonid habitat. Geology 2013;; 41 (4): 503–506. doi: https://doi.org/10.1130/G33979.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract A fundamental yet unresolved question in fluvial geomorphology is what controls the width of valleys in mountainous terrain. Establishing a predictive relation for valley floor width is critical for realizing links between aquatic ecology and geomorphology because the most productive riverine habitats often occur in low-gradient streams with broad floodplains. Working in the Oregon Coast Range (western United States), we used airborne lidar to explore controls on valley width, and couple these findings with models of salmon habitat potential. We defined how valley floor width varies with drainage area in a catchment that exhibits relatively uniform ridge-and-valley topography sculpted by shallow landslides and debris flows. In drainage areas >0.1 km2, valley width increases as a power law function of drainage area with an exponent of ∼0.6. Consequently, valley width increases more rapidly downstream than channel width (exponent of ∼0.4), as derived by local hydraulic geometry. We used this baseline valley width–drainage area function to determine how ancient deep-seated landslides in a nearby catchment influence valley width. Anomalously wide valleys tend to occur upstream of, and adjacent to, large landslides, while downstream valley segments are narrower than predicted from our baseline relation. According to coho salmon habitat-potential models, broad valley segments associated with deep-seated landsliding resulted in a greater proportion of the channel network hosting productive habitat. Because large landslides in this area are structurally controlled, our findings indicate a strong link between geologic properties and aquatic habitat. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Influence of lixiviation by irrigation water on residual shear strength of weathered red mudstone in Northwest China: Implication for its role in landslides' reactivation

Irrigation in loess tableland areas of northwest China has induced a large number of landslides around their edges, of which loess–red mudstone landslide is one of the most frequent types. Salt sinters commonly observed at the toes of these landslides, where the weathered red mudstone (WRM) outcrops, have raised the possibility that removal of soluble salts in the WRM by irrigation water could be crucial in the reduction of its shear strength, and thus in the occurrence of these landslides. In order to investigate the effects of lixiviation by irrigation water on residual shear strength of the WRM, samples of the WRM close to two landslides in Lanzhou city, one of the largest cities in northwest China, were tested after being treated under different conditions. These included: (1) saturation with the Yellow River water, the only source of irrigation, (2) saturation with groundwater, and (3) saturation and leaching with deionized water. Based on the results of these tests, specific mechanisms of residual shear strength reduction of the WRM due to lixiviation by irrigation water were discussed in terms of physico-chemical interactions between the WRM and water. It was found that lixiviation reduced residual shear strength and residual friction angle φr′ of the WRM by up to 65% and 62% respectively, after being leached 6 times. This coincided with a dramatic dissolution and leaching of soluble salts from the WRM. Particle size distribution showed that the more the WRM was leached, the more the clay fraction and the lesser coarser fractions. This suggested that reduction in residual shear strength of the WRM could be attributed to mainly disaggregation of particles coarser than clay, and to a lesser degree to weakening of interparticle forces among individual clays. It was further postulated that variation in clay mineralogy may influence performance of particle disaggregation.

Landslides and Neotectonic Activities in the Main Boundary Thrust (MBT) Zone: Southeastern Kumaun, Uttarakhand

Abstract Main Boundary Thrust (MBT) zone is constituted of some of the landslide prone areas in southeastern part of Kumaun Sub-Himalaya. Role of landslides as natural hazard and hill slope modifying agent is well documented from various part of Himalayan region and southern hills of Kumaun particularly in the MBT zone, which are susceptible to various type of mass movement. The rocks making up the slopes has been put to a number of brittle deformation phases during the movement along the MBT, and are traversed by number of joint sets. In the open slope these intersecting joint sets forms wedges and are the most favorable site for initiation of rockfalls and other types of landslides. Landslides are taking place primarily due to high angle slopes, formation of structural wedges along the free steep slopes, sheared nature of the rocks due to proximity to the MBT and neotectonic activities along the MBT and other transverse faults. Wedge failure is a common type of landslides in rock slopes characterized by multiple joints and acts as sliding planes for the failed blocks. Field observations and wedge failure analysis indicates most of the landslides taking place in MBT zone of Kumaun Sub-Himalaya are joint controlled. Safety Factor analysis suggests MBT zone of Kumaun Sub-Himalayan region is prone to landslides and related mass movements. This zone is also neotectonically active as indicated by various geomorphic signatures such as structurally controlled drainage pattern, offsetting of fan by MBT and formation of number of small lakes.

Landslide-amplified flash floods—The June 2008 Panay Island flooding, Philippines

The role of landslides in generating or enhancing a flash flood event in Aklan, Panay Island, Philippines, resulting from Typhoon Fengshen, was investigated. The flash flood occurred between 1100h and 1400h (GMT+8) of 21 June 2008 and inundated Sitios Agbatan and Abaya in the municipality of Libacao.Peak discharges at Kipot, a channel constriction in Aklan River about 10km upstream, were independently derived using a hydrologic model (302.6m3/s) and Manning's equation (7000m3/s). The modeled flood peak reached Kipot at 0300h on 21 June 2008 and the communities between 0600h and 1000h on June 21, at the earliest. The actual flood peak arrived at Sitios Agbatan and Abaya between 1100h and 1400h on June 21, at least 1h earlier than the modeled arrival.While the flash flood may have been caused by the preceding rainfall alone (234.4mm from 0600h June 20 to 0600h June 21), the discrepancies in peak discharges and the delayed arrival time suggest the possibility of damming and eventual breaching of the dam. Evidence of the damming was found at the channel constriction in Kipot. A landslide at this site was mapped, characterized, and inferred to have completely blocked the channel and caused the damming. Implications to flash flood risk assessment are discussed.

LANDSLIDES IN A RURAL MOUNTAINOUS REGION: DAMAGING AND RESOURCE-FORMING IMPACTS (SOUTH CAUCASUS, GEORGIA)

Catastrophic loss of soils and slope sediments by landslides causes destruction of mountainous environment and outflow of population from affected areas. However, the role of landslides in mountainous regions goes beyond direct destructive activity. The sliding mass expose surfaces for weathering and accumulate loose mineral material, the vital resource for mountain biota and population thus starting new cycles in ecosystems development, forming new habitats for biota and, in some cases, new lands for farming. A chronological sequence of landslides and their adaptation for human needs was studied in Adjara province, the South Caucasus mountainous region, Georgia. As a rule, in 15 years, a thin and compacted soil layer is formed on low and mound surface of a landslide. In 30 years, people start recultivation of the landslide area. After 40–60 years, the landslide area is used as a hayfield. It usually takes 100 years to transform the area into a fully cultivated landscape typical of Mountainous Adjara.

The characteristics of the landslides triggered by the Wenchuan M s 8.0 earthquake from Anxian to Beichuan

This paper presents a quantitative analysis of the number and area of the landslides triggered by the Wenchuan M s 8.0 earthquake from Anxian to Beichuan. In this study the controlling factors of landslides are obtained from geological maps, relief amplitude, slope, and topographic roughness calculated from DEM data in ArcGis 9.2. A total of 4134 landslides are identified from digital aero-image of 1 m resolution, covering 19.7 km 2 that accounts for 6.4% of the study area. The number of landslides with areas less than 5000 m 2 is up to 85.22%. The smallest landslide is 6 m 2 and the largest 1515,000 m 2. The number of landslides which have occurred is 1.6 times more prevalent at hanging walls as opposed to foot walls. Also the relationship between the numbers of landslides and the distances to an earthquake rupture at a hanging wall is linear but exponential at a footwall. These results prove that landslide activity is more severe at hanging walls than at foot walls. The outcrop area of geologic unit is proportional to the number of landslides except the Jurassic, Triassic and Quaternary units ( R 2 = 0.952) in the study area, and landslide density is 19. Meanwhile the area of a landslide is linearly proportional to outcrop area of geologic unit except Jurassic, Lower Cambrian and Quaternary unit ( R 2 = 0.8279) in the study area and appear to indicate that the lithology does not play an important role in landslides in the study area. Earthquake-triggered landslides tend to be concentrated in specific zones associated with the event-controlling parameters such as reliefs, slopes and topographic roughness. The landslides occurred particularly in the range of 600–1293 m relief amplitudes, and the number in this range amounts to 90% of total slides in the studied region. Moreover, landslides easily occurred in the curvature 1–15 with slope between 5° and 55°. In addition, landslides also usually occurred in the range of 1–1.5 topographic roughness. Therefore these correlations provide a way to assess regional landslide hazards and are of great significance to regional geohazard planning and prediction.

飛騨山脈の花こう岩山域における斜面崩壊が線状凹地の分布に及ぼす影響

Linear depressions and associated uphill-facing scarps, which result from the gravitational deformation of rock slopes, have widely developed along the main ridge in the Mt. Eboshi area, northern Japanese Alps. The role of landslides in the development of linear depressions in granitic rocks is evaluated from the distribution of linear depressions, characteristics of landslides (form, magnitude and frequency) and characteristics of bedrock (geology, discontinuity, degree of weathering and rock mass strength). The morphology of landslides and changes in the areas of landslides from 1958 to 2004 are compared to the development of linear depressions. Most linear depressions lie parallel to the main ridge and the strike of major rock joints, although their distribution differs between the northern and southern areas. In the northern study area, linear depressions are concentrated on the gentle upper slopes and landslides have intensively occurred on the lower slopes. In contrast, the southern area shows sporadic occurrences of linear depressions on the middle to upper slopes and has experienced only minor landslides. The intensive occurrences of landslides and linear depressions in the northern area are considered to result basically from debuttress and stress-release caused by the landslide activity. In addition, the lower rock mass strength in the northern study area also promotes the development of linear depressions.