A combined field/remote sensing approach for characterizing landslide risk in coastal areas

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record.Understanding the key factors controlling slope failure mechanisms in coastal areas is the first and most important step for analyzing, reconstructing and predicting the scale, location and extent of future instability in rocky coastlines. Different failure mechanisms may be possible depending on the influence of the engineering properties of the rock mass (including the fracture network), the persistence and type of discontinuity and the relative aspect or orientation of the coastline. Using a section of the North Coast of Cornwall, UK, as an example we present a multi-disciplinary approach for characterizing landslide risk associated with coastal instabilities in a blocky rock mass. Remotely captured terrestrial and aerial LiDAR and photogrammetric data was interrogated using Geographic Information System (GIS) techniques to provide a framework for subsequent analysis, interpretation and validation. The remote sensing mapping data was used to define the rock mass discontinuity network of the area and to differentiate between major and minor geological structures controlling the evolution of the North Coast of Cornwall. Kinematic instability maps generated from aerial LiDAR data using GIS techniques and results from structural and engineering geological surveys are presented. With this method, it was possible to highlight the types of kinematic failure mechanism that may generate coastal landslides and highlight areas that are more susceptible to instability or increased risk of future instability. Multi-temporal aerial LiDAR data and orthophotos were also studied using GIS techniques to locate recent landslide failures, validate the results obtained from the kinematic instability maps through site observations and provide improved understanding of the factors controlling the coastal geomorphology. The approach adopted is not only useful for academic research, but also for local authorities and consultancy's when assessing the likely risks of coastal instability

Types of Landslides along Lake Balaton, Hungary

Landslides are often triggered by various mechanisms such as precipitation, increase in the groundwater table, surface load, etc. and are classified according to the geometry and intensity of the motion. This paper provides an inventory considering all these factors by interpreting landslide records and available maps of the lakeside banks of the largest lake in Central Europe, Lake Balaton. Landslides in these areas severely damaged roads and railway networks. These disasters are linked to the mass movements of hundreds of m3 in the past years. The study area, the coastal regions of the lake, is divided into three geographically and geologically different sections (Eastern Basin, North Coast, South Coast). The landslide forms and the proportion of various movements and their timing also differ in these areas: at the south coast, falls and toppling prevail, while in the eastern basin, slidings prevail. The leading cause of mass movements is soaking and human interventions in all areas. Continuous monitoring of these landslide-prone areas contributes to the prediction of sliding and help in the design of remediation actions

Modelling discontinuity control on the development of Hell’s Mouth landslide

none5sìThis paper focuses on numerical modelling and back analysis of the Hell’s Mouth landslide to provide improved understanding of the evolution of a section of the north coast of Cornwall, UK. Discontinuity control is highlighted through the formation of a ‘zawn’ or inlet, the occurrence of two successive landslides and evidence of ongoing instability through opening of tension cracks behind the cliff top. Several integrated remote sensing (RS) techniques have been utilised for data acquisition to characterise the slope geometry, landslide features and tension crack extent and development. In view of the structural control on the rock slope failures, a 3D distinct element method (DEM) code incorporating a discrete fracture network and rigid blocks has been adopted for the stability analysis. The onset and opening of tension cracks behind the modelled slope failure zones has also been studied by analysing the displacements of two adjoining landslide blocks, between which, a joint-related tension crack developed. In addition, a sensitivity analysis has been undertaken to provide further insight into the influence of key discontinuity parameters (i.e. dip, dip direction, persistence and friction angle) on the stability of this section of the coastline. Numerical modelling and field observations indicate that block removal and preferential erosion along a fault resulted in the formation of the inlet. The development of the inlet provides daylighting conditions for discontinuities exposed on the inlet slope wall, triggering the initial landslide which occurred on 23rd September 2011. Numerical modelling, and evidence from a video of the initial landslide, suggests that the cliff instability is characterised by a combination of planar sliding, wedge sliding and toppling modes of failure controlled by the discrete fracture network geometryopenHe, Lingfeng; Coggan, John; Stead, Doug; Francioni, Mirko; Eyre, MatthewHe, Lingfeng; Coggan, John; Stead, Doug; Francioni, Mirko; Eyre, Matthe

Application of Remote Sensing Data for Evaluation of Rockfall Potential within a Quarry Slope

This is the final version. Available on open access from MDPI via the DOI in this recordIn recent years data acquisition from remote sensing has become readily available to the quarry sector. This study demonstrates how such data may be used to evaluate and back analyse rockfall potential of a legacy slope in a blocky rock mass. Use of data obtained from several aerial LiDAR (Light Detection and Ranging) and photogrammetric campaigns taken over a number of years (2011 to date) provides evidence for potential rockfall evolution from a slope within an active quarry operation in Cornwall, UK. Further investigation, through analysis of point cloud data obtained from terrestrial laser scanning, was undertaken to characterise the orientation of discontinuities present within the rock slope. Aerial and terrestrial LiDAR data were subsequently used for kinematic analysis, production of surface topography models and rockfall trajectory analyses using both 2D and 3D numerical simulations. The results of an Unmanned Aerial Vehicle (UAV)-based 3D photogrammetric analysis enabled the reconstruction of high resolution topography, allowing one to not only determine geometrical properties of the slope surface and geomechanical characterisation but provide data for validation of numerical simulations. The analysis undertaken shows the effectiveness of the existing rockfall barrier, while demonstrating how photogrammetric data can be used to inform back analyses of the underlying failure mechanism and investigate potential runout

Modelling discontinuity control on the development of Hell’s Mouth landslide

This is the final version. Available on open access from Springer via the DOI in this recordThis paper focuses on numerical modelling and back analysis of the Hell’s Mouth landslide to provide improved understanding of the evolution of a section of the north coast of Cornwall, UK. Discontinuity control is highlighted through the formation of a ‘zawn’ or inlet, the occurrence of two successive landslides and evidence of ongoing instability through opening of tension cracks behind the cliff top. Several integrated remote sensing (RS) techniques have been utilised for data acquisition to characterise the slope geometry, landslide features and tension crack extent and development. In view of the structural control on the rock slope failures, a 3D distinct element method (DEM) code incorporating a discrete fracture network and rigid blocks has been adopted for the stability analysis. The onset and opening of tension cracks behind the modelled slope failure zones has also been studied by analysing the displacements of two adjoining landslide blocks, between which, a joint-related tension crack developed. In addition, a sensitivity analysis has been undertaken to provide further insight into the influence of key discontinuity parameters (i.e. dip, dip direction, persistence and friction angle) on the stability of this section of the coastline. Numerical modelling and field observations indicate that block removal and preferential erosion along a fault resulted in the formation of the inlet. The development of the inlet provides daylighting conditions for discontinuities exposed on the inlet slope wall, triggering the initial landslide which occurred on 23rd September 2011. Numerical modelling, and evidence from a video of the initial landslide, suggests that the cliff instability is characterised by a combination of planar sliding, wedge sliding and toppling modes of failure controlled by the discrete fracture network geometry

Understanding the retreat of the Jurassic Cantabrian coast (N. Spain): comprehensive monitoring and 4D evolution model of the Tazones Lighthouse landslide

Forecasting coastal dynamics and sea cliff retreat under different sea level rise scenarios requires a good understanding of the conditioning factors and their relative contribution to cliff stability. The so-called Jurassic Cantabrian Coast extends along 76 km of the coastline of the Asturias region (N Spain) and is well-known worldwide due to its paleontological heritage, in particular the presence of dinosaur remains and footprints. The abundance of stratigraphic, paleontological and tectonic studies contrasts with the scarcity of studies focused on the stability of this rocky coastline where cliffs predominate, sometimes exceeding 120 m in height. In fact, evidence of current and recent instability processes can be observed along the entire coastline. In this regard, continuous monitoring is crucial to understand ongoing instabilities in rocky coastlines, as in these settings some instabilities might initiate as slow movements that induce subtle topographic changes whose detection from either satellite or aerial imagery is problematic due to the spatial and temporal resolutions.This research is part of 1) the “COSINES” Project [CGL2017-83909-R], Call 2017 for RETOS Projects funded by the Spanish Economy, Industry and Competitiveness Ministry-Ministerio de Economía, Industria y Competitividad (MINECO), the Spanish Research Agency-Agencia Estatal de Investigación (AEI) and the European Regional Development Found (FEDER) and 2) the GEOCANCOSTA research group, supported by the Asturian Regional Government (Spain) [grant number GRUPIN-IDI-2018-184]

Understanding the retreat of the Jurassic Cantabrian coast (N. Spain): Comprehensive monitoring and 4D evolution model of the Tazones Lighthouse landslide

Forecasting coastal dynamics and sea cliff retreat under different sea level rise scenarios requires a good understanding of the conditioning factors and their relative contribution to cliff stability. The so-called Jurassic Cantabrian Coast extends along 76 km of the coastline of the Asturias region (N Spain) and is well-known worldwide due to its paleontological heritage, in particular the presence of dinosaur remains and footprints. The abundance of stratigraphic, paleontological and tectonic studies contrasts with the scarcity of studies focused on the stability of this rocky coastline where cliffs predominate, sometimes exceeding 120 m in height. In fact, evidence of current and recent instability processes can be observed along the entire coastline. In this regard, continuous monitoring is crucial to understand ongoing instabilities in rocky coastlines, as in these settings some instabilities might initiate as slow movements that induce subtle topographic changes whose detection from either satellite or aerial imagery is problematic due to the spatial and temporal resolutions. This contribution presents a 4D evolution model of a key site, the Tazones Lighthouse landslide, located on the Cantabrian Coast of Asturias (N Spain), which affects subvertical rocky cliffs sculpted in the Jurassic bedrock made of alternating sandstone and marl. A high resolution multiapproach methodology was developed in order to understand its structure and kinematic characteristics, including: i) interpretation of aerial photographs and unmanned aerial photogrammetric surveys (UAV); ii) 22 monthly monitoring campaigns by total station; iii) 5 manual boreholes; iv) geomechanical characterization of the cliff bedrock; v) geomorphological evidence mapping; vi) analysis of landscape deformations obtained from UAV; and vii) precipitation, soil moisture and significant wave height (Hs) data analysis. The results show that the slope evolves by means of a complex-type mass movement, which combines translational and sliding mechanisms, and occupies tens of thousands of square meters. DTM and fieldwork analysis indicate that mass movement is mainly controlled by bedrock discontinuities (S0, 360/15-17; J1, 262/85; J2 166/75). The most important accelerations of slope movement correlate very well with rainfall, soil moisture and waves. Thus, the largest displacements occurring in January and October–November 2019, coincide with 2 periods of storms (maximum 24-h rainfall of 64.5 mm and 82.1 mm and maximum Hs of 6.54 and 9.09, respectively) and soil moisture values above 90%. Half of the markers moved more than 1 m and one of them exceeded 15 m. The 4D model obtained after the interpretation of the Tazones Lighthouse slope whole dataset, allows an understanding of how the surrounding cliffs have evolved in the past, fundamental to predicting their future behaviour."COSINES" Project GRUPIN-IDI-2018-184 Spanish Economy, Industry and Competitiveness Ministry-Ministerio de Economia, Industria y Competitividad (MINECO)Spanish Research Agency-Agencia Estatal de Investigacion (AEI)European Regional Development Found (FEDER)Asturian Regional Government (Spain) CGL2017-83909-

Application of unmanned aerial vehicle data and discrete fracture network models for improved rockfall simulations

This is the final version. Available from the publisher via the DOI in this record.In this research, we present a new approach to define the distribution of block volumes during rockfall simulations. Unmanned aerial vehicles (UAVs) are utilized to generate high-accuracy 3D models of the inaccessible SW flank of the Mount Rava (Italy), to provide improved definition of data gathered from conventional geomechanical surveys and to also denote important changes in the fracture intensity. These changes are likely related to the variation of the bedding thickness and to the presence of fracture corridors in fault damage zones in some areas of the slope. The dataset obtained integrating UAV and conventional surveys is then utilized to create and validate two accurate 3D discrete fracture network models, representative of high and low fracture intensity areas, respectively. From these, the ranges of block volumes characterizing the in situ rock mass are extracted, providing important input for rockfall simulations. Initially, rockfall simulations were performed assuming a uniform block volume variation for each release cell. However, subsequent simulations used a more realistic nonuniform distribution of block volumes, based on the relative block volume frequency extracted from discrete fracture network (DFN) models. The results of the simulations were validated against recent rockfall events and show that it is possible to integrate into rockfall simulations a more realistic relative frequency distribution of block volumes using the results of DFN analyses

Regional earthquake induced landslide susceptibility : lessons from the 2016 Mw 7.8 Kaikōura earthquake.

Coseismic landslides are one of the most impactful secondary hazards resulting from large earthquakes. Determining the physical factors that dictate landslide hazard during earthquakes is critical to improving landslide susceptibility models and hazard plans. The 2016 Mw 7.8 Kaikōura earthquake in the northeast South Island of New Zealand ruptured more that 20 on- and off-shore faults, and triggered more than 30,000 landslides. The exceptional documentation of faults and landslides from the event and the diversity of lithology and topography in the Kaikōura region present an opportunity to better understand seismic hazard and landslide susceptibility. This thesis presents a detailed analysis of landslide susceptibility from the Kaikōura earthquake with a primary focus on two factors which influence the distribution of landslides from the Kaikōura earthquake: surface fault ruptures and coastlines. Distance to a surface fault rupture, which may include the influence of both ground motion and physical properties of the fault zone, exerts one of the strongest empirical controls on the distribution of earthquake induced landslides from the Kaikōura earthquake. Quantifying coseismic deformation fields about faults is one way to define a categorical predictor for the fault zone in landslide susceptibility analysis. Distributed displacement around the Papatea fault in 2016 was characterised using 3-D displacement fields to estimate the potential extent of the fault zone. The magnitude of displacement was compared to currently defined ‘fault avoidance zones’ which capture the majority of, but not all, significant distributed displacement from the Kaikōura earthquake. The same estimation of distributed displacement was then measured across 13 additional fault ruptures from the Kaikōura earthquake to determine the width of off-fault displacement and deformation, which is a proxy for the fault damage zone around surface fault ruptures. A higher density of earthquake induced landslides observed within this zone across ruptures cannot be fully explained by the attenuation of shaking in current strong ground motion models. Comparative logistic regression models of regional landslide susceptibility were developed to further examine the relative influence of ground motion and the fault damage zone as well as the effect of other factors like distance to the coastline. Models confirm the observed contribution of the fault damage zone around faults but also suggest that strong ground motion plays a more significant role in the overall distribution of landslides. Improved ground motion models, based on more robust observational ground motion data and quantification of near-fault site effects, will be key to furthering our understanding of landslide susceptibility around faults. There was an order of magnitude greater number of landslides from the Kaikōura earthquake on slopes within 1 km of the coast as compared to slopes from 1 to 3 km from the coast. Coastal slopes introduce a variety of site-specific landslide forcings, for example wave action, and susceptibility factors, like increased moisture, but these factors are rarely incorporated into regional earthquake induced landslide susceptibility studies. Comparative logistic regression models of landslide susceptibility suggest that slope angle dominates both inland and coastal landslide susceptibility in the Kaikōura region. Average slope is steeper along the uplifted Kaikōura coast – a legacy effect of past wave action, erosion, and relict landsliding. While most coastal slopes in the Kaikōura region are buffered from wave action by uplifted shore platforms, at Conway Flat, south of Kaikōura, coastal cliffs are exposed to wave action at high tide. The edge of the coastal cliff top was repeatedly mapped at Conway Flat using a 72- year record of historical aerial imagery and recent lidar. In this location, the Kaikōura earthquake produced nearly 25% of cumulative coastal cliff retreat over the last 72 years. More than 50% of retreat at Conway Flat since 1950 can be traced back to strong ground motion in earthquakes. Estimates of strong ground motion recurrence and potential coseismic retreat can be used alongside current estimates of cliff retreat to gauge the influence of earthquakes on steep coastline evolution globally. The results of this work have improved our understanding of coseismic landslide susceptibility on a regional scale and offer some insights into the fundamental processes governing slope failure in large earthquakes. These types of contributions help to bridge the divide between practical and fundamental science aims (e.g., between empirical and physics-based, or regional and site-specific models) and represent critical steps towards increasing resilience to earthquakes