Quantitative risk analysis for landslides ? Examples from Bíldudalur, NW-Iceland

International audienceAlthough various methods to carry out quantitative landslide risk analyses are available, applications are still rare and mostly dependent on the occurrence of disasters. In Iceland, two catastrophic snow avalanches killed 34 people in 1995. As a consequence the Ministry of the Environment issued a new regulation on hazard zoning due to snow avalanches and landslides in 2000, which aims to prevent people living or working within the areas most at risk until 2010. The regulation requires to carry out landslide and snow avalanche risk analyses, however, a method to calculate landslide risk adopted to Icelandic conditions is still missing. Therefore, the ultimate goal of this study is to develop such a method for landslides, focussing on debris flows and rock falls and to test it in Bíldudalur, NW-Iceland. Risk analysis, beside risk evaluation and risk management, is part of the holistic concept of risk assessment. Within this study, risk analysis is considered only, focussing on the risks to life. To calculate landslide risk, the spatial and temporal probability of occurrence of potential damaging events, as well as the distribution of the elements at risk in space and time, considering also changing vulnerabilities, must be determined. Within this study, a new raster-based approach is developed. Thus, all existent vector data are transferred into raster data using a resolution of 1m x 1m. The specific attribute data are attributed to the grid cells, resulting in specific raster data layers for each input parameter. The calculation of the landslide risk follows a function of the input parameters hazard, damage potential of the elements at risk, vulnerability, probability of the spatial impact, probability of the temporal impact and probability of the seasonal occurrence. Finally, results are upscaled to a resolution of 20m x 20m and are presented as individual risk to life and object risk to life for each process. Within the quantitative landslide risk analysis the associated uncertainties are estimated qualitatively. In the study area the highest risks throughout all of the analyses (individual risk to life and object risk to life) are caused by debris flows, followed by rock falls, showing that risk heavily varies depending on the process considered. The resultant maps show areas, in which the individual risk to life exceeds the acceptable risk (defined in the aforementioned regulation), so that for these locations risk reduction measures should be developed and implemented. It can be concluded that the newly developed method works satisfactory and is applicable to further catchments in Iceland, and potentially to further countries with different environmental settings

Evolution of natural risk: research framework and perspectives

International audienceThis study presents a conceptual framework for addressing temporal variation in natural risk. Numerous former natural risk analyses and investigations have demonstrated that time and related changes have a crucial influence on risk. For natural hazards, time becomes a factor for a number of reasons. Using the example of landslides to illustrate this point, it is shown that: 1. landslide history is important in determining probability of occurrence, 2. the significance of catchment variables in explaining landslide susceptibility is dependent on the time scale chosen, 3. the observer's perception of the geosystem's state changes with different time spans, and 4. the system's sensitivity varies with time. Natural hazards are not isolated events but complex features that are connected with the social system. Similarly, elements at risk and their vulnerability are highly dynamic through time, an aspect that is not sufficiently acknowledged in research. Since natural risk is an amalgam of hazard and vulnerability, its temporal behaviour has to be considered as well. Identifying these changes and their underlying processes contributes to a better understanding of natural risk today and in the future. However, no dynamic models for natural risks are currently available. Dynamic behaviour of factors affecting risk is likely to create increasing connectivity and complexity. This demands a broad approach to natural risk, since the concept of risk encapsulates aspects of many disciplines and has suffered from single-discipline approaches in the past. In New Zealand, dramatic environmental and social change has occurred in a relatively short period of time, graphically demonstrating the temporal variability of the geosystem and the social system. To understand these changes and subsequent interactions between both systems, a holistic perspective is needed. This contribution reviews available frameworks, demonstrates the need for further concepts, and gives research perspectives on a New Zealand example

Recent landslide activity in Manaihan, E Belgium

peer reviewedPast landslides have been recognized in the Battice area in E-Belgium. In contrast to the other inactive landslides, the Manaihan landslide responded immediately to heavy rainfall events in the last two decades. This study aims to map its spatial extent and the dominant surface features; to measure surface displacement using GPS; to investigate subsurface structure with Cone penetration test (CPT) and corings; and to determine the depth of the shear surface by inclinometers. Results show a partial landslide reactivation. Surface velocities range between 20 and 40 cm/year and are strongly dependent on winter rainfall. CPT results give clear boundaries between the landslide mass and the undisturbed bedrock in the head scarp. Distinct shear surfaces have been determined with displacement rates up to 15.8 mm in 21 days. Further research should apply geophysical methods for two-dimensional information on the ground, investigate geotechnical properties of the landslide mass, model slope instability, and determine the influence of a sewage pipe crossing the central landslide mass as a potential cause for landslide activity

A multi-risk methodology for the assessment of climate change impacts in coastal zones

Climate change threatens coastal areas, posing significant risks to natural and human systems, including coastal erosion and inundation. This paper presents a multi-risk approach integrating multiple climate-related hazards and exposure and vulnerability factors across different spatial units and temporal scales. The multi-hazard assessment employs an influence matrix to analyze the relationships among hazards (sea-level rise, coastal erosion, and storm surge) and their disjoint probability. The multi-vulnerability considers the susceptibility of the exposed receptors (wetlands, beaches, and urban areas) to different hazards based on multiple indicators (dunes, shoreline evolution, and urbanization rate). The methodology was applied in the North Adriatic coast, producing a ranking of multi-hazard risks by means of GIS maps and statistics. The results highlight that the higher multi-hazard score (meaning presence of all investigated hazards) is near the coastline while multi-vulnerability is relatively high in the whole case study, especially for beaches, wetlands, protected areas, and river mouths. The overall multi-risk score presents a trend similar to multi-hazard and shows that beaches is the receptor most affected by multiple risks (60% of surface in the higher multi-risk classes). Risk statistics were developed for coastal municipalities and local stakeholders to support the setting of adaptation priorities and coastal zone management plans

Developing a spatiotemporal model to integrate landslide susceptibility and critical rainfall conditions. A practical model applied to Rio de Janeiro municipality

Despite being a landscape evolution element, landslides pose a significant threat to infrastructure, property, and human life around the globe. In Brazil, this has been a major source of concern for many years. Over the last decades, especially in the humid areas of Brazil, landslide occurrences have become more frequent and catastrophic (Pelech et al., 2019). Especially in large and medium-sized cities, poorly-regulated living conditions and a progressing global warming scenario will likely increase the frequency, magnitude, and possibly damagecaused by landslides (Marengo et al., 2021). On the other hand, despite the efforts of local authorities to forecast and mitigate the phenomena, not enough is currently being done in terms of preparedness for future events, especially concerning research (Dias et al., 2021).Due to the geomorphological and climatic settings, the municipality of Rio de Janeiro (~1,200 km²) is often affected by landslides (Coelho Netto et al., 2007; 2009). According to the Brazilian Institute of Geography and Statistics (IBGE, 2021), the municipality has 6.7 million inhabitants, of which circa 20-25% lives in the favelas. These communities, usually located on hill slopes, face diverse challenges such as poor basic infrastructure, lack of sanitation systems, and high criminality, which tend to diminish the inhabitants’ awareness of potential landslide hazards. On the other hand, the municipality of Rio de Janeiro has systematically tracked rainfall data for the last decades. Such data comprises 33 stations, recording measurements every 15 minutes. Rainfall data is availablefor a few decades and comprise 33 stations recording measurements every 15 minutes. Also, the availability of high-resolution DTM and DEM (obtained through LiDAR with a 15 cm resolution), orthoimagery updated quasiyearly, and a suitable landslide inventory, turns Rio de Janeiro into a promising real-life laboratory for suggesting and enhancing modeling solutions that may provide valuable tools for landslide emergency preparedness, management, and response.Building upon the findings of Steger et al, 2022, the present research represents a joint effort to suggest a methodological framework to develop a dynamic landslide model that integrates static predisposing factors with dynamic rainfall conditions. Data-driven methods (e.g., Generalized Additive Models) will be used to establish statistical relationships between the static factors, the dynamic rainfall conditions prior to a potential landslide, and the landslide occurrence in space and time. The outcomes may be used by stakeholders to strategically prepare for potential rainfall events leading to landslides and possibly to improve early warning systems. Data collection and preparation are currently happening, and the analysis will follow. Partial results will be presented at the 6th World Landslide Forum

Oxidation of uranium nanoparticles produced via pulsed laser ablation

An experimental apparatus designed for the synthesis, via pulsed laser deposition, and analysis of metallic nanoparticles and thin films of plutonium and other actinides was tested on depleted uranium samples. Five nanosecond pulses from a Nd:YAG laser produced films of {approx}1600 {angstrom} thickness that were deposited showing an angular distribution typical thermal ablation. The films remained contiguous for many months in vacuum but blistered due to induced tensile stresses several days after exposure to air. The films were allowed to oxidize from the residual water vapor within the chamber (2 x 10{sup -10} Torr base pressure). The oxidation was monitored by in-situ analysis techniques including x-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and scanning tunneling microscopy (STM) and followed Langmuir kinetics

Probabilistic landslide ensemble prediction systems: lessons to be learned from hydrology

Landslide forecasting and early warning has a long tradition in landslide research and is primarily carried out based on empirical and statistical approaches, e.g., landslide-triggering rainfall thresholds. In the last decade, flood forecasting started the operational mode of so-called ensemble prediction systems following the success of the use of ensembles for weather forecasting. These probabilistic approaches acknowledge the presence of unavoidable variability and uncertainty when larger areas are considered and explicitly introduce them into the model results. Now that highly detailed numerical weather predictions and high-performance computing are becoming more common, physically based landslide forecasting for larger areas is becoming feasible, and the landslide research community could benefit from the experiences that have been reported from flood forecasting using ensemble predictions. This paper reviews and summarizes concepts of ensemble prediction in hydrology and discusses how these could facilitate improved landslide forecasting. In addition, a prototype landslide forecasting system utilizing the physically based TRIGRS (Transient Rainfall Infiltration and Grid-Based Regional Slope-Stability) model is presented to highlight how such forecasting systems could be implemented. The paper concludes with a discussion of challenges related to parameter variability and uncertainty, calibration and validation, and computational concerns.</p

Engineering behaviour and mechanical - empirical relationships for a problematic New Zealand tropical residual soil

Unlike sedimentary clays, many residual soils do not exhibit clear mechanical-empirical relationships to assist in their engineering characterisation. In contrast, this paper discusses one residual clay in which such relationships may be determined, and examines whether the effects of structure in this clay may be assessed using a framework previously developed for sedimentary clays. The Northland Allochthon residual clay of New Zealand is a problematic soil of the fersiallitic type, prone to slope instability. Atterberg limit tests on soils from five field sites in the same geological unit show considerable variation, but that they are mechanically related. Triaxial tests were performed on reconstituted and intact soil specimens from one field site. Normalization of the strength envelope using the equivalent stress on the intrinsic compression line suggests that soil structure, destroyed in reconstituted specimens, plays a role in the shear strength of this soil in its intact state. Overconsolidated behaviour, in the absence of geological preloading, suggests the existence of a pseudo-preconsolidation pressure associated with weathering processes. The results show that the saturated mechanical behaviour of this residual soil is in line with that of sedimentary clays and that mechanical-empirical relationships developed for such clays may be applied in this case

Ectomycorrhizal fungi alter soil food webs and the functional potential of bacterial communities.

Most of Earths trees rely on critical soil nutrients that ectomycorrhizal fungi (EcMF) liberate and provide, and all of Earths land plants associate with bacteria that help them survive in nature. Yet, our understanding of how the presence of EcMF modifies soil bacterial communities, soil food webs, and root chemistry requires direct experimental evidence to comprehend the effects that EcMF may generate in the belowground plant microbiome. To this end, we grew Pinus muricata plants in soils that were either inoculated with EcMF and native forest bacterial communities or only native bacterial communities. We then profiled the soil bacterial communities, applied metabolomics and lipidomics, and linked omics data sets to understand how the presence of EcMF modifies belowground biogeochemistry, bacterial community structure, and their functional potential. We found that the presence of EcMF (i) enriches soil bacteria linked to enhanced plant growth in nature, (ii) alters the quantity and composition of lipid and non-lipid soil metabolites, and (iii) modifies plant root chemistry toward pathogen suppression, enzymatic conservation, and reactive oxygen species scavenging. Using this multi-omic approach, we therefore show that this widespread fungal symbiosis may be a common factor for structuring soil food webs.IMPORTANCEUnderstanding how soil microbes interact with one another and their host plant will help us combat the negative effects that climate change has on terrestrial ecosystems. Unfortunately, we lack a clear understanding of how the presence of ectomycorrhizal fungi (EcMF)-one of the most dominant soil microbial groups on Earth-shapes belowground organic resources and the composition of bacterial communities. To address this knowledge gap, we profiled lipid and non-lipid metabolites in soils and plant roots, characterized soil bacterial communities, and compared soils amended either with or without EcMF. Our results show that the presence of EcMF changes soil organic resource availability, impacts the proliferation of different bacterial communities (in terms of both type and potential function), and primes plant root chemistry for pathogen suppression and energy conservation. Our findings therefore provide much-needed insight into how two of the most dominant soil microbial groups interact with one another and with their host plant