Global Promotion of Understanding and Reducing Landslide Disaster Risk: Two Years on P-LRT

Abstract

This article presents an overview and a concise review of a global promotion of understanding and reducing landslide disaster risk, based on 2 years of publication of Progress in Landslide Research and Technology (P-LRT). The Vol. 1 Issue 1, Vol. 1 Issue 2, Vol. 2 Issue1 and Vol. 2 Issue 2 of P-LRT were comprised of a total of ninety-seven articles from thirty-six countries/regions from Africa, Asia, Europe, North America, Oceania, and South America. The first four issues embody recent progress in landslide research and technology for practical applications and the benefit for the society contributing to the Kyoto Landslide Commitment 2020.

1 Introduction

The Vols 1 and 2 of P-LRT: Progress in Landslide Research and Technology were composed of the contributions of ninety-seven relevant articles from thirty-six countries/regions worldwide, as shown in Fig. 1. The articles represented a total of forty-four original articles, ten review articles, four landslide lessons, a total of twenty-two articles on the projects of the International Programme on Landslides (IPL) and the World Centres of Excellence on Landslide Risk Reduction (WCoEs), and Kyoto Landslide Commitment, six teaching tools, six technical notes and case studies, and five world landslide reports from a total of four hundred and twenty-seven researchers/practitioners.

Fig. 1

Global promotion of understanding and reducing landslide disaster risk: Countries/regions with contributions to P-LRT highlighted in red

The themes were diverse and ranged from early warning and real-time prediction to climate change, UNESCO, experimental and numerical analysis, standards and patents, landslide-induced tsunami, hazard map**, resilience and sustainability, advanced monitoring technology, earthquake-induced landslide, rainfall-induced landslide, giant landslides on volcanic islands and mountains, rockslide, reservoir landslide and landslide dam, cultural heritage, landslide-structure interaction, risk communication, education and network, design and countermeasures, and socio-economic significance. An overview and a concise review of each theme above can be described as below.

2 Global Promotion of Understanding and Reducing Landslide Disaster Risk

2.1 Early Warning and Real-Time Prediction

The development and implementation of Landslide Early Warning Systems (LEWSs) in low-, lower-middle-, upper-middle-, and high-income countries (LICs, MICs, UMIs, and HICs) were reviewed by Alcántara-Ayala and Garnica-Peña (2023a, b, c) in light of the integrated disaster risk reduction (DRR) strategies perspective in line with the Sendai Framework for Disaster Risk Reduction (SFDRR) 2015–2030, addressing future challenges for the successful implementation and development of LEWSs. A recent development of real-time high-resolution predictions of orographic precipitation was presented by Onishi et al. (2023) and Bandara and Onishi (2023), based on the robust cloud microphysics for facilitating early warning of landsides due to orographic rainfall (Fig. 2). Gariano et al. (2023) presented an implementation of and challenges in defining frequentist rainfall thresholds using the statistics and an automatic tool for a landslide early warning system to forecast the occurrence of rainfall-induced landslides in two pilot areas in India. Konagai et al. (2023a) reported an outline of the joint research project between Japan and Sri Lanka, aiming at develo** critical technologies for the early warning system against rainfall-induced landslides in Sri Lanka. Ha et al. (2023) proposed a landslide early warning system based on a landslide susceptibility map using a spatial multi-criteria evaluation (SMCE) method and an empirical rainfall threshold, showing the reliability of predicting the spatial and temporal occurrences of landslides in a case study in Vietnam. Fathani et al. (2023) presented an implementation of a new standard for community-based landslide early warning systems, the ISO (International Organization for Standardization) 22327:2018, to be used by communities vulnerable to landslides, and by government and non-governmental organizations at central, provincial, districts, sub-district, and village levels to reduce the possibility of injuries, loss of life, and damage to property and the environment. Ramesh et al. (2023a) proposed an Internet of Things (IoT) solution for building the real-time landslide monitoring and early warning system to provide community-scale disaster resilience, demonstrating the capability of the IoT system to gather spatiotemporal triggers for multiple types of landslides, detection and decision of specific scenarios, and the impact of real-time data on mitigating the landslide disaster (Figs. 3 and 4).

Fig. 2

Scales of atmospheric simulations. The nesting domain system is used in MSSG multiscale simulations. (a) Global simulations use Yin-Yang grid system, (b) regional simulations use the conventional longitude-latitude orthogonal grid system, (c) local (urban) simulations allow building and residential topography resolved. (Figure 1 in Bandara and Onishi 2023)

Fig. 3

Landslide Tracker: A Crowdsourced Mobile Application (Fig. 19 in Ramesh et al. 2023a)

Fig. 4

Comprehensive Landslide Early Warning System (Fig. 20 in Ramesh et al. 2023a)

2.2 Climate Change

The prevalence of landslides in hilly and mountainous regions has increased due to climate change-induced extreme hydro-meteorological conditions. Wijaya et al. presented such climate change-induced regional landslide hazard and exposure assessment (Fig. 5) in mountainous regions under extreme rainfalls in Nepal, to aid climate resilient road infrastructure planning. Based on the extreme rainfall scenarios for the baseline period 1976–2005 and future horizons of 2030, 2050 and 2080, they developed high-resolution landslide hazard models adopting the Frequency Ratio (FR) and Analytical Hierarchical Process (AHP) methods, showing a significant increase of the landslide hazard under the future climate change scenarios. Beroya-Eitner et al. (2023) presented the projected decrease in rainfall and landslide susceptibility in a study area in the Philippines, whereas other hazards such as drought and water shortage might increase, which underscores the need for a multi-hazard assessment that takes into account the complex interrelationships between different hazards under changing climate. Abolmasov et al. (2023a) presented the framework of a project titled “Mainstreaming Climate Resilience in the Road Transportation Management in Serbia (CliRtheRoads)” comprising of a web portal for data entry and management for authorised users, a publicly available web-GIS application, a mobile GIS application, and a back-end landslides database, to support decision- makers for better road management in climate changing conditions.

Fig. 5

Landslide hazard and exposure maps for (a) baseline period (1976–2005), (b) time horizon 2030s for RCP4.5, (c) time horizon 2030s with RCP8.5, (d) time horizon 2050s for RCP4.5, (e) time horizon 2050s for RCP8.5, (f) time horizon 2080s for RCP4.5 and (g) time horizon 2080s for RCP8.5. RCP denotes representative concentration pathways. (Figure 7 in Wijaya et al. 2023)

2.3 UNESCO

Delgado et al. (2023) reported the establishment of the Disaster Risk Reduction Unit in UNESCO and UNESCO’s contribution to global resilience at all levels through multi-hazard, multi-discipline, and multi-stakeholder DRR mechanisms pertaining to landslide hazard under climate change, health, and sustainable development.

2.4 Experimental/Numerical Analysis

The application of spectral element method (SEM) in slope instability analysis was presented by Tiwari and Bhandary (2023), where the SEM procedure has three major benefits over the existing FEM procedures: (1) geometrical flexibility, (2) high computational efficiency, and (3) reliable spectral accuracy, which could be used in an effective design and implementation of various slope stability analysis. The use of experimental models to calibrate numerical models for slope stability and deformation analysis was presented by Tiwari and Tran (2023), showing how various soil and ground parameters influence the stability of slopes and how numerical models can be calibrated with the experimental modeling results to apply the calibrated numerical models for field slopes/landslides. Ajmera et al. (2023) presented the teaching tool and manual of LS-RAPID, an integrated simulation model capable of capturing the entire landslide process starting from a state of stability to landslide initiation and movement to the mass deposition, illustrating the applications to (1) a rainfall-induced failure, (2) an earthquake-induced failure, and (3) the case study of the Atami debris flow, as supplemented by the video tutorials.

Large-scale cree** landslides were experimentally simulated in Bhandary (2023), based on a modified ring shear machine, showing a comprehensive understanding on the residual-state creep deformation behavior of clayey materials for predicting landslide creep displacement and failure. Tan and Tang (2023) presented an in-situ triaxial creep test on gravelly slip zone soil of a giant landslide in the Three Gorges area of China, showing that the sliding zone soil behavior matches the observed landslide behavior. Loi et al. (2023) presented the teaching tool for the undrained dynamic-loading ring-shear testing with video to experimentally study landslide dynamics involving the entire process from the initial stage of stress before landslide occurrence and stress changes due to static, dynamic loading or pore pressure changes or other types of stress loading to the formation of a sliding surface and the steady-state shear resistance.

The sliding-surface liquefaction (SSL) concept (Fig. 6) and the undrained steady-state shear-strength to understand and reduce rapid landslide disaster risk were presented by Sassa et al. (2023a). SSL occurs even in dense sandy layers. SSL is caused by a series of phenomena, (1) grain-crushing due to shearing under overburden pressure in the shear zone, (2) volume reduction in the shear zone, (3) generation of high pore-water pressure in the shear zone, and (4) liquefaction of the shear zone material. After SSL, a mass of soil layer above the liquified sliding surface moves at high speed, and the generated pore pressure reaches a certain constant value which is the undrained steady-state shear-strength (USS).

Fig. 6

Illustration and experimental data for the sliding-surface liquefaction (Fig. 3 in Sassa et al. 2023a)

The resultant feature of rapid and long- travelling landslides poses a high risk to people living in/near slopes.

Recent advancements in shear strength interpretation, testing, and use for landslide analysis were presented by Tiwari and Ajmera (2023), based on various soil testing involving direct shear tests, triaxial tests, ring shear tests, and cyclic simple shear tests. They summarized correlations developed in the literature to estimate various shear strengths, including the fully softened and residual shear strengths of soil (Fig. 7).

Fig. 7

Shear stress—shear displacement (left) and shear-stress-normal stress (right) relationship for over-consolidated and normally consolidated soils (Fig. 7 in Tiwari and Ajmera 2023)

The behaviour of small-scale slope models supported by various remedial measures under artificial rain in 1 g conditions was presented and discussed in Arbanas et al. (2023), showing the impact of the appropriate mitigation measures on retaining the stability of the slopes, which otherwise collapsed, and hence reducing landslide disaster risk. Ariyarathna and Sasahara (2023) presented a procedure of data processing for the improvement of failure time prediction of a landslide using the velocity and acceleration of the displacement based on a small-scale slope model experiment and a field experiment on a natural slope.

2.5 Standards and Patents

Landslide-related patent documents were extracted from open-access databases in order to evaluate how well they relate to the field of landslide research and technology (Mikoš 2023a), showing potential of such intellectual property to find more application in real word solutions when planning and executing landslide disaster risk reduction.

A list of twenty-two international standards containing landslide-related terms (landslide, debris flow, rock fall) was presented by Mikoš (2023b), using the Online Browsing Platform by the International Organization for Standardization (ISO). A new standard published as ISO 22327:2018 empowers individuals and communities vulnerable to landslides to act in sufficient time, and in appropriate ways to reduce the possibility of injuries, loss of life, and damage to property and the environment, thereby strengthening the communities’ resilience to landslide disasters (Fathani et al. 2023).

2.6 Landslide-Induced Tsunamis

Sassa (2023a, b) and Sassa et al. (2022, 2023b) presented some recent advances, the current state and challenges in understanding and reducing the disaster risk of landslide-induced tsunamis (e.g. Figs. 8 and 9), based on a global review and the outcome of a global panel discussion organized across America, Europe, and Asia and the review of the World Tsunami Awareness Day Special Event of the Fifth World Landslide Forum. Kawamura et al. (2023) reported ongoing persistent slope failures at the toe of a giant submarine slide in the Ryukyu trench that generated the AD 1771 Meiwa tsunami, based on the three dive surveys using a manned submersible in the trench. Dang et al. (2023) presented the development and application of the LS-Tsunami simulation code as a teaching tool, which utilizes landslide motion data from LS-RAPID to model landslide-induced tsunamis, illustrating several case studies (e.g. Fig. 10).

Fig. 8

Comparing the locations of multiple tsunami generations, alongshore distributions and directions with the locations, distributions and directions where the coastal lands collapsed and flowed due to the occurrence of liquefaction in the 2018 Indonesia Sulawesi earthquake (Fig. 4(c) in Sassa and Takagawa 2019) (Fig. 8 in Sassa et al. 2023b)

Fig. 9

Global distribution of mapped submarine landslides (SLs): Green, SLs on passive margins; Yellow, SLs located along convergent margins; Orange, SLs on strike slip margins; purple, volcanoes; Red, tsunamis associated with SLs (Tappin and Grilli 2020). Submarine landslide tsunamis (in red) are mainly located along convergent margins, but also along passive and strike slip margins and on flanks of volcanoes (Fig. 17 in Sassa et al. 2023b)

Fig. 10

Simulation of tsunami-like wave across the Truong River propagating from the landslide (from Duc et al. 2020) (Fig. 27 in Dang et al. 2023)

2.7 Hazard Map**

Moncayo and Ávila (2023) presented the analysis of the database of 123 landslides from the Andean region of Colombia, where the empirical-statistical modeling incorporated landslide travel distances associated with landslide volume, slope angle, maximum landslide height, and geomorphological environment, resulting in a hazard map to identify possible zones affected by landslide processes in this area. Bornaetxea et al. (2023a) presented a landslide inventory map** for the rocky mountains in British Columbia, Canada, based on the 1286 landslides in a 1200 km² area by classifying them into 11 categories and three levels of certainty. Nguyen et al. (2023a, b) presented the application of an Analytical Hierarchy Process (AHP) for landslide susceptibility map**, showing significant effects of the rainfall frequency on landslide susceptibility in a mountainous region of central Vietnam. The AHP method was used to construct the landslide susceptibility maps in the Republic of Serbia (Abolmasov et al. 2023b) and in the tropical zone of Vietnam (Tien et al. 2023) based on the landslide identification using the unmanned aerial vehicles (UAV) and landslide map** through the World Digital 3D and Google Earth maps. Mihalić Arbanas et al. (2023) presented the application of data and information from landslide inventory and landslide susceptibility maps (Fig. 11) based on LIDAR (Light Detection and Ranging) and DTM (Digital Terrain Model) for spatial and urban land-use planning in Croatia. The quality of a large-scale landslide susceptibility map** was discussed by Krkač et al. (2023), based on a case study from Croatia, showing the impact of the spatial accuracy of the input data on the landslide susceptibility assessment. Bornaetxea et al. (2023b) and Bernat Gazibara et al. (2023b) presented a tool for the statistically-based landslide susceptibility zonation, LAND-SUITE, with its applications to the Gipuzkoa province in Spain and the Hrvatsko Zagorje area in Croatia. Paulín et al. (2023a, b) presented the landslide susceptibility assessment based on the digital terrain models (DTMs) derived from UAV and the multiple logistic regression (MLR) model with its application to areas affected by rockfalls and shallow landslides in State of Morelos and on the south flank of Pico de Orizaba volcano with more than six hundred landslides mapped into GIS and grouped into landform units, Mexico. Thirugnanam (2023) presented a review of the use of deep learning for landslide detection and landslide susceptibility map**, emphasizing the need for further development.

Fig. 11

Landslide susceptibility map of Croatia, original scale 1:100,000 (Bernat Gazibara et al. 2022) (Fig. 7 in Mihalić Arbanas et al. 2023)

Bernat Gazibara et al. (2023a) presented the landslide and soil erosion inventory map** (Fig. 12) based on the visual interpretation of high-resolution remote sensing data in a case study from Istria, Croatia, showing the potential for the future landslide and erosion hazards management. Vacha et al. (2023) presented the post-wildfire monthly erosion rates at the catchment scale on GIS in the north-western Italian Alps, highlighting the marked increase (more than 20 times) in erosion rates in the post-fire scenario than the pre-fire one.

Fig. 12

Example of landslide map** in areas affected by gully and combined erosion on LiDAR DTM derivatives (Fig. 9 in Bernat Gazibara et al. 2023a)

Erzagian et al. (2023) developed a landslide susceptibility map using the frequency ratio (FR) approach, where the controlling factors involving elevation, slope, aspect, lithology, lineament density, distance from streams, distance from roads, land use, and rainfall (Fig. 13), were combined with seven hundred and forty-four landslide data though GIS in the Kulon Progo Mountains Area, Indonesia. The frequency ratio (FR) approach combined with the fractal analysis considering the spatial relationship between past landslides and four landslide factors: distance to roads, distance to faults, distance to drainage, and distance to geological boundaries was presented by Duong et al. (2023a), to produce a landslide susceptibility map in Cao Bang province, Vietnam. Michel (2023) presented a consequence - frequency matrix approach as a tool to assess landslides risk and susceptibility with its application to Pont Bourquin Landslide in the Swiss Prealps, Switzerland. Beroya-Eitner et al. (2023) presented the rainfall-induced landslide susceptibility maps in Davao Oriental, Philippines in the historical period 1986–2005 and in the projected period 2046–2065, showing a decrease in the landslide susceptibility by the mid-twenty-first century (Fig. 14).

Fig. 13

Landslide-controlling factor maps: (a) elevation; (b) slope; (c) aspect; (d) lithology; (e) lineament density; (f) distance from streams; (g) distance from roads; (h) land use, and (i) rainfall (Fig. 3 in Erzagian et al. 2023)

Fig. 14

Modified rainfall-induced landslide susceptibility maps of Davao Oriental (a) Historical (1986–2005), (b) Projected under RCP4.5 (2046–2065), and (c) Projected under RCP8.5 (2046–2065). A decrease in landslide susceptibility is expected by the mid-twenty-first century, mainly in Baganga, Cateel and Caraga, following a decrease in extreme rainfall in the area. (Figure 8 in Beroya-Eitner et al. 2023)

The rainfall-induced shallow landslide susceptibility map was produced for land-use planning in the High City of Antananarivo, Madagascar (Frodella et al. 2023a, Fig. 15).

Fig. 15

Shallow landslide susceptibility map of the Analamanga Hill (modified after Frodella et al. 2022) (Fig. 3 in Frodella et al. 2023a)

2.8 Resilience and Sustainability

The use of natural-hazard-related-web-observatory as sustainable development took was discussed by Mikoš et al. (2023) to support the implementation of sustainable development at different scales, where the information gathered on the internet is structured, and shown using geolocators for different regions and/or countries susceptible to landslides. UNESCO’s new disaster risk reduction unit aims to contribute to global resilience against multi-hazards involving landslides (Delgado et al. 2023).

The sustainability of geosynthetics-based solutions to mitigate landslide disaster risk was presented by Damians et al. (2023) by identifying the sustainability factors to consider when applying geosynthetics and showing how a value integrated model for sustainability evaluations (MIVES) methodology (Fig. 16) can be applied to evaluate and compare alternative methods for remediation of landslides.

Fig. 16

Sustainability assessment flow chart or requirements tree proposal for landslide applications (modified from Damians et al. 2018) (Fig. 4 in Damians et al. 2023)

Restoration works including the road cut slope protections, data gathering of constructed slopes, data evaluation, and design of remedial measures for mountainous regions/countries also contribute to the development of the landslide disaster resilience (Dias et al. 2023). Ramesh et al. (2023b) presented a framework to build and strengthen community-scale landslide resilience (Fig. 17) using a citizen-science approach involving a landslide tracker mobile app, social media data analysis, and community involvement, with its application to two case study areas Munnar and Chandmari in India, which can help policymakers, community leaders, change makers, administrative officials, and researchers in disaster management.

Fig. 17

Proposed framework for involving citizens in building community-scale landslide resilience (Fig. 1 in Ramesh et al. 2023b)

2.9 Advanced Monitoring Technology

Huntley et al. (2023a,b,c,d) reported an effective monitoring technology and practices involving the satellite Interferometric Synthetic Aperture Radar (InSAR) interferograms, UAV time-series photograms and the remotely piloted aircraft system (RPAS), and the ground-based real-time kinematic global navigation satellite system (RTK-GNSS) surveys to describe the form and function of a wide range of rapid and slow-moving landslides, combined with the field-based geological observations, terrain classification and boreholes, for the railway transportation corridors in southwestern British Columbia, Canada (e.g. Figs. 18 and 19). Casagli et al. (2023) reported advanced monitoring techniques to estimate the temporospatial deformational evolution of landslide events by using the ground-based InSAR (GB-InSAR, Fig. 20), LIDAR, persistent scatterer InSAR (PS-InSAR), UAVs equipped with different sensors, GPS antennas, infrared thermography and traditional instrumentation (e.g. strain gauges, inclinometers, piezometers), providing the satellite-based services at regional scale in Italy. Trofymchuk et al. (2023) reported the application of landslide monitoring comprised of the PS-InSAR, GIS database and DEM to the stability assessment of St. Andrew’s Church in Ukraine. The application of an advanced PS-InSAR, SqueeSAR algorithm, to the Humarri slide in the Hunza-Nagar River valley in northern Pakistan was presented by Poggi et al. (2023). Hoang et al. (2023) applied an automatic real-time landslide monitoring system with multiple GPS antennas to the Alishan highway traversing steep slo** land in Chiayi County, Taiwan. Fukuhara et al. (2023) presented the use of multi-point Micro Electro Mechanical Systems (MEMS) tilt sensors to detect the spatiotemporal variation of the behavior of vulnerable slopes. Thanh et al. (2023) showed a community-level monitoring network comprised of the UAVs, ALOS World 3 Digital (AW3D) Data, and Google earth images, with its application to mountainous areas in northern Vietnam. Bernat Gazibara et al. (2023a) presented the application of high-resolution remote sensing involving the LIDAR data and orthophoto images to small and shallow landslides and soil erosion processes in the Istrian flysch area in Croatia.

Fig. 18

Ripley Landslide surface displacement data derived from UAV overflights in 2016 and 2018 and multi-beam bathymetry data collected in 2018; plotted with RTK-GNSS (average annual rate for 2017, 2018 and 2019) and d-GNSS displacement data (November 2018 to June 2019, expressed as cm year⁻¹). Stable d-GNSS unit—yellow dot; active d-GNSS unit—black and white dot; inactive d-GNSS—black dot. Active GCP - blue dot (modified from Huntley et al. 2021) (Fig. 4 in Huntley et al. 2023b)

Fig. 19

3D RPAS deformation over North Slide between 2019-09-19 and 2021-09-28. Vectors indicate horizontal deformation from MicMac digital image correlation and colour scale represents difference in DSMs. Hill-shade transparency is applied for context (Fig. 5 in Huntley et al. 2023c)

Fig. 20

Annual cumulative displacements of the Ruinon slide area measured by the GBInSAR system from 2014 to 2019 (a–f) (Fig. 1a–f in Casagli et al. 2023)

2.10 Earthquake-Induced Landslide

Wang and Nam (2023) reported the characteristics of the landslide disasters caused by the 2018 Eastern Iburi Earthquake in Hokkaido Japan, pertaining to the distinctive properties of the widely distributed, weathered Plinian Ta-d tephra deposits from the Tarumae volcano and their impact on the spatial clustering of the Iburi landslides, together with the implementation of a countermeasure by removing the surficial volcanic ashes over the slopes (Fig. 21).

Fig. 21

The photos showing the slopes after removing the surficial volcanic ashes (Fig. 7 in Wang and Nam 2023)

Konagai et al. (2023b) reported the post-earthquake deformations that can last for months in the grounds that have undergone liquefaction and spread laterally due to earthquakes (Fig. 22), by showing two case studies of the 2018 Sulawesi Earthquake, Indonesia and the 2015 Gorkha earthquake, Nepal. Konagai (2023) also reported the characteristics of the landslides in the 2004 Mid-Niigata Prefecture Earthquake, Japan, showing an estimate of the coseismic displacements and stress changes with their impact on the post-earthquake rehabilitations. Higaki et al. (2023) presented a review of the mega slide of Unzen-Mayuyama of Quaternary volcanic rock due to the 1792 earthquake, and the numerous shallow landslides that disrupted highway and rail traffic due to the 2016 Kumamoto earthquake, Japan (Fig. 23) as well as the subsequent unmanned slope stabilization works (Fig. 24) with earth retaining walls, embankments and re-vegetation.

Fig. 22

Line-of-sight (LOS) deformations on two different days after the earthquake (October 12, 2018, and January 4, 2019): Yellow polygons show locations of extensive flow slides. (Konagai et al. 2022) (Fig. 5 in Konagai et al. 2023b)

Fig. 23

A slope failure induced by the mainshock near the Aso-Ohashi Bridge (Modified from the Kyushu Regional Development Bureau, MLIT 2021) (Fig. 10 in Higaki et al. 2023)

Fig. 24

Countermeasures adopted for the stabilization of each block (Embarkment and steel-reinforced soil at the lower slope and earth removal and soil sha** at the head slope) (Kyushu Regional Development Bureau, MLIT 2021) (Fig. 15 in Higaki et al. 2023)

2.11 Rainfall-Induced Landslide

Gratchev et al. (2023) presented the mechanisms of rainfall-induced shallow landslides in Australia, showing an important role of the formation of wetting (moisture) front, increases in water content, and the excess pore water pressure generation in jointed, bedded, and weathered sandstone deposits. Konagai et al. (2023a) reported a review of the rapid and long-travelling landslides that took place at Aranayake 2016 and Athwelthota 2017 in Sri Lanka and the joint research framework between Japan and Sri Lanka for develo** essential technologies for an effective early warning system against such rainfall-induced landslides (Fig. 25). The effect of rainfall frequency on the susceptibility of rainfall-induced landslides was investigated by Nguyen et al. (2023a, b), using the Regional Frequency Analysis (RFA) in a case study for a mountainous region in Central Vietnam. The characteristics of suffusion landslides associated with the rise in groundwater level due to rainfall in the European part of Russia was presented by Zerkal and Barykina (2023). Yasufuku and Alowiasy (2023) and Higaki et al. (2023) presented the characteristics of heavy rainfall-induced landslides that took place in Kyusyu Island and Hiroshima, Japan, during the last decade, together with the mitigation and prevention measures adopted in those areas respectively. Duong et al. (2023b) presented the deterministic and probabilistic slope stability analysis using finite element (FEM) and limit equilibrium (LEM) methods in connection with the landslide events triggered by heavy rainfalls in the Sapa district, Vietnam, showing consistency with the actual landslides. Tofani et al. (2023) presented a high-resolution slope stability simulator (HIRESSS) model for analyzing the occurrence of shallow landslides during a rainfall event with its application to the Aosta Valley region in the northwest of the Alpine chain, showing a satisfactory validation against the 2009 event with a complete database of the landslides (Fig. 26). The historical and future rainfall-induced landslide susceptibility map** of Davao Oriental, Philippines was presented by Beroya-Eitner et al. (2023) and described in the sections “Climate Change” and “Hazard Map**” above. The rainfall-induced landslide hazard map based on the comparison between rainfall data and the recorded landslide events (Fig. 27) was generated for land-use planning in the High City of Antananarivo, Madagascar (Frodella et al. 2023a) and described in the section “Hazard Map**” above.

Fig. 25

Pilot study sites: (Left) Alanayake landslide in 2016, and (Right) Athwelthota landslide in 2017 (credit NBRO) (Fig. 10 in Konagai et al. 2023a)

Fig. 26

HIRESSS 24-hr map of failure probabilities for the day of April 27 (Fig. 4 in Tofani et al. 2023)

Fig. 27

Comparison between rainfall data from September 2014 to January 2020 (Daily and cumulated data from Climate Engine, 2015), the recorded landslide events (dashed black arrows), and the recorded Cyclones (red arrows), reported in Frodella et al. (2021) (a) (the Dashed brown arrow represents the Winter 2015 landslide event) (Fig. 5a in Frodella et al. 2023a)

2.12 Giant Landslides on Volcanic Islands and Mountains

Rowberry et al. (2023) presented a comprehensive online database of giant landslides on volcanic islands, describing a total of seventy-five landslide events from the Atlantic Ocean and Mediterranean Sea, sixty-seven landslide events from the Pacific Ocean, and forty landslide events from the Indian Ocean (Fig. 28). Ríos and Ávila (2023) presented the landslide risk assessment based on the two landslide events that took place in 2019 and 2020 in the city of Pereira in the Central Cordillera of the Colombian Andes mountainous region composed of volcanic soils.

Fig. 28

Distribution of giant landslides on volcanic islands from the Atlantic and Indian Oceans (Left) and the Pacific Ocean (Right). Source: Global relief model derived from Global Bathymetry and Topography at 15 Arc Sec: SRTM15+ V2.1 (Tozer et al. 2019) (Figs. 4 and 5 in Rowberry et al. 2023)

2.13 Rockslide

Abe et al. (2023) presented the role of translational rockslides in the evolution of cuesta topography based on the field surveys in Japan, Taiwan, Switzerland, and Nepal, showing a common feature such that rockslides on cuesta’s back slopes slide along the same laminar rock joints over a long term, thus maintaining the cuesta landscape. Strom (2023) presented large-scale rockslides, rock avalanches and manifestations of active tectonics leading to the compilation of a complete rockslide database of the entire Central Asia Region involving Afghanistan, China, Kazakhstan, Kyrgyzstan, Tajikistan, and Uzbekistan (e.g. Fig. 29). Dias et al. (2023) presented the characteristics of rock failures along mountainous road side slopes in Sri Lanka, comprised of wedge failure, translational slides and falling rocks (Fig. 30). The characteristics of a deep-seated weathered rockslide that occurred in 2020 on a natural slope near a highway to Sapa town in the northwestern Vietnam was presented by Nguyen et al. (2023a, b), together with the remedial measures adopted with ground anchors, soil nails and drainage pipes to stabilize the slope. Wang et al. (2023) presented the spatial distribution, emplacement processes and mechanisms of the rock avalanches in the Tibetan Plateau of China (Fig. 31), involving the sedimentary structures of four typical rock avalanches with jigsaw structures, inner shear zones, diapiric structures, convoluted laminations, and faults, based on the remote sensing analysis, map** using a fixed-wing UAV and detailed field investigations. Gallego et al. (2023) investigated potential rock slope instabilities that may affect the conservation of an archaeological site, which is described in “Cultural Heritage” below.

Fig. 29

The 7.5 km long Chukurchak rock avalanche, Tien Shan, Kyrgyzstan. Headscarp is marked by elevation marks 2970 and 2250 m a.s.l., while other elevation marks are placed at the front of rock avalanche branches (Fig. 8 in Strom 2023)

Fig. 30

Example of rock formed failures along the road side slope. Wedge failure, translational slides and falling rocks are very much significant along the road sides. High hazard potential zone can be observed due to foliated and jointed rock formations (Fig. 13 in Dias et al. 2023)

Fig. 31

Typical rock avalanches distributed in the Tibetan Plateau, China (a: Luanshibao rock avalanche; b: Nyixoi Chongco rock avalanche; c: Tagarma rock avalanche; d: Iymek rock avalanche) (Fig. 3 in Wang et al. 2023)

2.14 Reservoir Landslide and Landslide Dam

Tang et al. (2023) presented some key techniques of reservoir landslide prevention and control by considering seven evolution modes for rock slides and the optimal control measures suitable for each evolution mode and different evolution stages (e.g. Fig. 32) as established in the Three Gorges Reservoir area (TGRA), China. The characteristics and the stability evaluation methods for the reservoir landslides (e.g. Fig. 33) in the TGRA were also summarized in Tang (2023). Based on a four year field observation and monitoring, Barjasteh (2023) presented the stability analysis of Ambal Salt Ridge in the Gotvand dam reservoir, Southern Iran, where the 2019 flooding event increased the landslide displacement and the situation is expected to be more critical under a moderate to high future earthquake in a tectonically active zone of the Zagros Fold Belt. Zerkal et al. (2023) reported the recent activity and analysis of the Buzulgan landslide (Fig. 34) that resulted in the formation of a landslide dam and its influence on the future debris flow hazard for the Tyrnyauz town in Northern Caucasus, Russia, showing the possible inundation zones. Sattar and Konagai (2023) reported the post-formation behaviour of the Hattain Bala landslide dam formed by the 2005 Kashmir earthquake and the post-breaching situation of the landslide dam in Kashmir, Pakistan.

Fig. 32

Cross section of the Hongshibao landslide, whose toe is affected by fluctuations of the TGR level. Drainage ditches, retaining walls, lattice beams and stabilizing piles were constructed to stabilize this actively cree** landslide (Tang et al. 2019) (Fig. 2 in Tang et al. 2023)

Fig. 33

Front view of the landslide, looking NW (after Tang et al. 2017) (Fig. 14 in Tang 2023)

Fig. 34

General view on the Buzulgan landslide (2020) (Photo of O.V. Zerkal) (Fig. 4 in Zerkal et al. 2023)

2.15 Cultural Heritage

Elshayeb (2023) presented the development of landslide risk assessment during the last 30 years for the various Egyptian cultural heritage sites, leading to a better preservation of the temple of Queen Hatshepsut at Eldeir Elbahary, the Tomb of Ramses I at the Valley of the Kings and the Serapeum Tomb in Saqqara, Egypt. Frodella et al. (2023b) presented an overview of the last decade’s activities for the conservation of Georgian rupestrian cultural heritage sites associated with the slope instability processes by integrating field surveys, close-range remote sensing involving the infrared thermography and UAV digital photogrammetry, and laboratory analyses for geotechnical-mineralogical and geological characterization, leading to the implementation of deep anchoring and retaining walls to protect the cultural heritage sites (Fig. 35). Based on the in-situ and laboratory tests on rock blocks and discontinuities, Gallego et al. (2023) reported the weathering and erosion-induced rock degradation processes and their impact on the potential slope instabilities affecting the AIUla archaeological sites in a rock cut landscape (Fig. 36) shaped for thousand years in the Kingdom of Saudi Arabia.

Fig. 35

General master plan for the proposed mitigation measures for the whole Vardzia Monastery (Fig. 11 in Frodella et al. 2023b)

Fig. 36

General view of AlUla Old Town and the dangerous Western cliff (Fig. 21 in Gallego et al. 2023)

2.16 Landslide-Structure Interaction

Cuomo et al. (2023) presented the analysis of landslide-structure interaction for flow-like landslides against protection barriers, based on a general conceptual scheme (Fig. 37), empirical, analytical and numerical approaches including the estimate of the amount of landslide volume overtop** the barrier. Perna et al. (2023) presented the Material Point Method (MPM) based modelling of landslide-structure interaction, showing that landslide pore water pressures undergo significant tempo-spatial evolution during a dynamic impact on the structure. Ng et al. (2023) presented the impact mechanisms of water, dry granular and two-phase debris flows on barriers of varying stiffness, openings and numbers based on physical and numerical results to mitigate debris flows, showing that debris flow composition governs the impact dynamics on barriers (Fig. 38).

Fig. 37

General conceptual scheme for Landslide Structure Interaction (LSI) (Fig. 1 in Cuomo et al. 2023)

Fig. 38

A schematic diagram of the multiple barrier framework for both dry granular and two-phase flows. The framework includes (1) impact model, (2) overflow and landing kinematics, and (3) subsequent barrier impact (Fig. 7 in Ng et al. 2023)

2.17 Risk Communication, Education and Network

Arbanas and Mihalić Arbanas (2023) reported the 10th Anniversary of the Adriatic-Balkan Network (ABN) in the framework of International Consortium on Landslides (ICL) by showing the establishment, objectives and activities of ABN during the last ten years with the organization of biannual Regional Symposiums on Landslides in Croatia, Serbia, Slovenia, and Bosnia and Herzegovina. Nishikawa (2023) presented the need to effectively raise public awareness about landslides by showing the application of an Ichi-Nichi-Mae (The Day Before the Disaster) Project for landslide awareness and risk communication with the episodes by the survivors of landslides. Ahmed et al. (2023) reported the use of qualitative social science tools and techniques via key informant interviews to investigate the anthropogenic-induced landslide disasters in Chittagong hill districts, Bangladesh, showing that climate change-induced erratic rainfall is leading to more rainfall-induced landslides and presenting the recommendations to stop illegal hill cutting and deforestation and to raise risk awareness and coordination among the communities. Thanh et al. (2023) presented a community level landslide risk reduction program comprised of the creation of a communication- based evacuation map** (CBEM) and the engagement of residents in slope disaster risk reduction in a mountainous area of northern Vietnam. Garnica-Peña and Alcántara-Ayala (2023) reported the expansion of the urban area of a community where in the last decade, landslides have not occurred in a mountainous zone highly susceptible to the hillslope instability in México by showing a key recommendation to implement a landslide disaster risk awareness program and include education programs at all levels. Based on diverse web tools and databases, Mikoš (2023c) presented an assessment of worldwide efforts in reduction at higher education levels and beyond, by focusing on the higher education study programmes offering courses on slope stability and landslide mitigation. Munasinghe et al. (2023) presented an outcome of a literature survey to consolidate a common set of risk assessment perspectives and approaches for measuring landslide disaster risk by using the PICO (Population, Intervention, Compression Intervention, and Outcome) method, identifying the future requirements of risk critical curve, judgment curve, and risk matrix (Fig. 39). Kamal et al. (2023) presented the refugees’ perception of landslide disasters based on a structured questionnaire and survey of 400 people from the Rohingya camps in Cox’s Bazar, Bangladesh, showing through a regression analysis (Proportional Odds Model) that exposure to previous landslides, mitigation measure quality, and emergency managers’ roles were crucial in defining people’s risk perception compared to the demographic characteristics of the Rohingya population.

Fig. 39

Risk perspectives connections (a mind map) (Fig. 4 in Munasinghe et al. 2023)

2.18 Design and Countermeasures

Cuomo et al. (2023) presented different tools and options to design a protection barrier against flow-like landslides, where the different approaches adopted for analysis are summarized in “Landslide-Structure Interaction” above. Higaki et al. (2023) presented an overview of the emergent and permanent countermeasures adopted following the 2018 heavy rainfall-induced landslide disaster in Hiroshima, Japan, involving channel stabilization works using large sandbags to channel water downstream safely, installation of warning devices such as wire sensors to detect the occurrence of debris flows, and construction of 20 Sabo dams to trap sediments produced during heavy rains to protect the downstream area from the landslide and debris flow impacts (Fig. 40). Hirota et al. (2023) presented the application of vegetation works to protect unstable cutting slopes along highway where slope failures have repeatedly occurred in rainy seasons in Gangthangkha, Wangdue, Bhutan, by showing the site-specific optimal selection of seeds and methods suitable for the landslide stabilization due to vegetation (Fig. 41). Arbanas et al. (2023) presented a series of model slope experiments with various countermeasures where a gabion wall and buttressing embankment were installed in sandy and silty slopes and a pile wall with counterfort was constructed in a clayey slope (Fig. 42), showing that appropriate countermeasures realized the stability of the slope, which otherwise collapsed. Ng et al. (2023) presented the design of debris-resisting single and multiple barriers by proposing a new dimensionless overflow number with a threshold value of unity to design a rigid barrier for regulating discharge of debris material downstream while reducing the debris flow impact force. Tang et al. (2023) presented an optimal design and arrangement of stabilizing piles for the prevention and control of reservoir landslides with their applications to Hongshibao landslide (Fig. 32) and Majiagou landslide in the Three Gorges Reservoir area (TGRA), China.

Fig. 40

Installation plan of sabo dams for disaster recovery in the catchment of debris-flow affected streams (Modified from the Chugoku Regional Development Bureau, MLIT 2019) (Fig. 25 in Higaki et al. 2023)

Fig. 41

Sequence of events at the site of vegetation works, Gangthangkha, Wangdue. (a) Slope before vegetation works, (b) Finished vegetation works, (c, d) Photos about a month after the vegetation works) (Fig. 22 in Hirota et al. 2023)

Fig. 42

Views at buttressing embankment behind the gabion wall in a silty slope and at pile wall, buttressing counterfort and excavated trenches in a clayey slope (Figs. 8g and 9e in Arbanas et al. 2023)

2.19 Socio-Economic Significance

Parkash (2023) presented the archival records of socio-economically and environmentally significant landslides in India, by classifying a total of 412 landslides as low, moderate and high socio-economic significance to differentiate the degree of damages and losses, including both direct and indirect costs together with the key lessons learned from these events (Table 1).

Table 1 Criteria for classifying socio-economically and environmentally significant landslides in India (Table 1 in Parkash 2023)

3 Conclusion

This article has presented an overview and a concise review of two years of publication of Progress in Landslide Research and Technology (P-LRT). The themes for the Vols. 1 and 2 of P-LRT were indeed diverse as described above, with a total of four hundred and twenty-seven researchers/practitioners from thirty-six countries/regions from Africa, Asia, Europe, North America, Oceania, and South America, contributing to the Vols 1 and 2 of the ICL Open Access Book Series. It is hoped that P-LRT will continue to serve as a common platform for the publication of recent progress in landslide research and technology for practical applications and the benefit for the society contributing to the Kyoto Landslide Commitment 2020 for the global promotion of understanding and reducing landslide disaster risk.