Mass Movement Events Research Articles

More than one landslide per road kilometer – surveying and modeling mass movements along the Rishikesh–Joshimath (NH-7) highway, Uttarakhand, India

Abstract. The rapidly expanding Himalayan road network connects rural mountainous regions. However, the fragility of the landscape and poor road construction practices lead to frequent mass movements alongside roads. In this study, we investigate fully or partially road-blocking landslides along National Highway (NH-7) in Uttarakhand, India, between Rishikesh and Joshimath. Based on an inventory of >300 landslides along the ∼250 km long corridor following exceptionally high rainfall during September and October 2022, we identify the main controls on the spatial occurrence of mass-movement events. Our analysis and modeling approach conceptualizes landslides as a network-attached spatial point pattern. We evaluate different gridded rainfall products and infer the controls on landslide occurrence using Bayesian analysis of an inhomogeneous Poisson process model. Our results reveal that slope, rainfall amounts, lithology and road widening are the main controls on landslide occurrence. The individual effects of aggregated lithozones are consistent with previous assessments of landslide susceptibilities of rock types in the Himalayas. Our model spatially predicts landslide occurrences and can be adapted to other rainfall scenarios, thus having potential applications for efficiently allocating efforts for road maintenance. To this end, our results highlight the vulnerability of the Himalayan road network to landslides. Climate change and increasing exposure along this pilgrimage route will likely exacerbate landslide risk along the NH-7 in the future.

Application of modern seismic attributes in the characterisation of mass transport deposits: Orange Basin, South Africa

Abstract The southern Orange Basin is structurally complex, with a tectonic history dating back to the Late Jurassic to Early Cretaceous. Mass movement events triggered by gravity and tectonic activities have resulted in the deposition of mass transport deposits (MTDs) on the seafloor. These MTDs have been documented as contributors to geohazards, posing risks to underwater infrastructure. Evidence of MTDs has been observed in 3D seismic surveys in the southern portion of the Orange Basin. However, limited studies have explored the geomorphological expression of MTDs using seismic attributes to delineate their shape, size, and anatomy in this region. The MTDs in the study area exhibit features such as basal shear surfaces (BSS), grooves, ramps, and striations. Four distinct mass transport packages were interpreted, primarily within the extensional regime, in the study area. These MTDs, spanning the Neogene to Coniacian periods, have thicknesses ranging from 300 m to 500 m. The MTDs are generally chaotic with semitransparent reflections. MTD D, being the largest, exhibits a maximum thickness of about 500 m and extends approximately 30 km in width.

Nature-based solutions for regulating moisture content in an expansive clay soil

Land degradation in the form of mass movement is a major challenge in the humid tropics, where intense rainfall and tropical cyclones are common. Rainfall increases soil moisture content, which often acts as a triggering factor for mass movement events, particularly in clay soils with expansive minerals, where moisture changes impact structural integrity. Growing evidence suggests that Nature-based Solutions (NbS) can regulate soil moisture levels, which can assist in maintaining cohesion and hence reduce slope instability. This paper examines soil moisture changes due to Coconut Matting (CM), Coconut Matting-Natural Vegetation Hybrid (CMNV), Natural Vegetation (NV), and Vetiver grass (VET) and discusses moisture content regulation as it relates to slope stability, with a particular focus on expansive clays. Soil moisture trends were measured for 90 days at four depths (20 cm, 40 cm, 60 cm, and 100 cm) using soil moisture loggers, while precipitation levels were monitored using a rain gauge. GLM ANOVA analysis showed a significant depth*treatment interaction (P < 0.05) on soil moisture. The Vetiver grass treatment had the lowest soil moisture levels, with a (27.62 %) reduction compared to the control (bare plot). The CMNV treatment had the second-greatest-% soil moisture reduction (7.68 %). Contrastingly, CM and NV resulted in limited moisture reduction (1.99 %) and (0.73 %) respectively. The role of Vetiver grass was therefore highlighted in mitigating water saturation towards preventing potential slope instability.

Insight into the dynamics of a long-runout mass movement using single-grain feldspar luminescence in the Pokhara Valley, Nepal

Abstract. Mass movements play an important role in landscape evolution of high mountain areas such as the Himalayas. Yet, establishing numerical age control and reconstructing transport dynamics of past events is challenging. To fill this research gap, we bring luminescence dating to the test in an extremely challenging environment: the Pokhara Valley in Nepal. This is challenging for two reasons: (i) the optically stimulated luminescence (OSL) sensitivity of quartz, typically the mineral of choice for dating sediments younger than 100 ka, is poor, and (ii) highly rapid and turbid conditions during mass movement transport hamper sufficient OSL signal resetting prior to deposition, which eventually results in age overestimation. Here, we first assess the applicability of single-grain feldspar dating of medieval mass movement deposits catastrophically emplaced in the Pokhara Valley. Second, we exploit the poor bleaching mechanisms to get insight into the sediment dynamics of this paleo-mass movement through bleaching proxies. The Pokhara Valley is a unique setting for our case study, considering the availability of an extensive independent radiocarbon dataset as a geochronological benchmark. Single-grain infrared stimulated luminescence (IRSL) signals were measured at 50 ∘C (IRSL-50) and post-infrared infrared stimulated luminescence signals at 150 ∘C (pIRIR-150). Our results show that the IRSL-50 signal is better bleached than the pIRIR-150 signal. A bootstrapped minimum age model (bMAM) is applied to retrieve the youngest subpopulation to estimate the paleodose. However, burial ages calculated with this paleodose overestimate the radiocarbon ages by an average factor of ∼23 (IRSL-50) and ∼72 (pIRIR-150), showing that dating of the Pokhara Formation with a single-grain approach was not successful for most samples. Some samples, however, only slightly overestimate the true emplacement age and thus could be used for a rough age estimation. Large inheritances in combination with the scatter in the single-grain dose distributions show that the sediments have been transported under extremely limited light exposure prior to deposition, which is consistent with the highly turbid nature of the sediment-laden flood and debris flows depositing the Pokhara gravels. To investigate the sediment transport dynamics in more detail, we studied three bleaching proxies: the percentage of grains in saturation 2D0 criteria, the percentage of best-bleached grains (2σ range of bMAM-De) and the overdispersion (OD). None of the three bleaching proxies indicate a spatial relationship with runout distance of the mass movement deposits. We interpret this as evidence for the lack of bleaching during transport, which reflects the catastrophic nature of the event. While not providing reliable burial ages of the Pokhara mass movement deposits, single-grain feldspar dating can potentially be used as an age range finder method. Our approach shows the potential of luminescence techniques to provide insights in sediment transport dynamics of extreme and rare mass movement events in mountainous regions.

Analyzing the spatial interactions between rainfall levels and flooding prediction in São Paulo

AbstractRainfall is one of the primary triggers for many geological and hydrological natural disasters. While the geological events are related to mass movements in land collapse due to waterlogging, the hydrological ones are usually assigned to runoff or flooding. Studies in the literature propose predicting mass movement events as a function of accumulated rainfall levels recorded at distinct periods. According to these approaches, a two‐dimensional rainfall levels feature space is segmented into the occurrence and non‐occurrence decision regions by an empirical critical curve (CC). Although this scheme may easily be extended to other purposes and applications, studies in the literature need to discuss its use for flooding prediction. In light of this motivation, the present study is unfolded in (1) verifying that defining CCs in the rainfall levels feature space is a practical approach for flooding prediction and (2) analyzing how geospatial components interact with rainfall levels and flooding prediction. A database containing the rainfall levels recorded for flooding and non‐flooding events in São Paulo city, Brazil, regarding the period 2015–2016, was considered in this study. The results indicate good accuracy for flooding prediction using only partial rain, which can be improved by adding physical characteristics of the flooding locations, demonstrating a direct correlation with spatial interactions, and rainfall levels.

Divergent Temporal Trends of Mercury in Arctic Char from Paired Lakes Influenced by Climate-Related Drivers.

Climate-driven changes including rising air temperatures, enhanced permafrost degradation, and altered precipitation patterns can have profound effects on contaminants, such as mercury (Hg), in High Arctic lakes. Two physically similar lakes, East Lake and West Lake at the Cape Bounty Arctic Watershed Observatory on Melville Island, Nunavut, Canada are being affected by climate change differently. Both lakes have experienced permafrost degradation in their catchments; however, West Lake has also undergone multiple underwater Mass Movement Events (MMEs; beginning in fall 2008), leading to a sustained 50-fold increase in turbidity. This provided the unique opportunity to understand the potential impacts of permafrost degradation and other climate-related effects on Hg concentrations and body condition of landlocked Arctic char (Salvelinus alpinus), an important sentinel species across the Circum-Arctic. Our objectives were to assess temporal trends in char Hg concentrations and to determine potential mechanisms driving the trends. There was a significant decrease in Hg concentrations in East Lake char, averaging 6.5%/year and 3.8%/year for length-adjusted and age-adjusted means, respectively, from 2008 to 2019. Conversely, in West Lake there was a significant increase, averaging 7.9%/year and 8.0%/year for length-adjusted and age-adjusted mean Hg concentrations, respectively, for 2009 to 2017 (the last year with sufficient sample size). The best predictors of length-adjusted Hg concentrations in West Lake were carbon and nitrogen stable isotope ratios, indicating a shift in diet including possible dietary starvation brought on by the profound increase in lake turbidity. Our study provides an example of how increasing lake turbidity, a likely consequence of climate warming in Arctic lakes, may influence fish condition and Hg concentrations. Environ Toxicol Chem 2023;42:2712-2725. © 2023 His Majesty the King in Right of Canada and The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. Reproduced with the permission of the Minister of Environment and Climate Change Canada.

Mass Movement Hazard and Exposure in the Himalaya

AbstractHimalaya is experiencing frequent catastrophic mass movement events such as avalanches and landslides, causing loss of human lives and infrastructure. Millions of people reside in critical zones potentially exposed to such catastrophes. Despite this, a comprehensive assessment of mass movement exposure is lacking at a regional scale. Here, we developed a novel method of determining mass movement trajectories and applied it to the Himalayan Mountain ranges for the first time to quantify the exposure of infrastructure, waterways, roadways, and population in six mountain ranges, including Hindu Kush, Karakoram, western Himalaya, eastern Himalaya, central Himalaya, and Hengduan Shan. Our results reveal that the exposure of buildings and roadways to mass movements is highest in Karakoram, whereas central Himalaya has the highest exposed waterways. The hotspots of exposed roadways are concentrated in Nepal, the North Indian states of Uttarakhand, Himachal Pradesh, the Union Territory of Ladakh, and China's Sichuan Province. Our analysis shows that the population in the central Himalaya is currently at the highest exposure to mass movement impacts. Projected future populations based on Shared Socio‐economic and Representative Concentration Pathways suggest that changing settlement patterns and emission scenarios will significantly influence the potential impact of these events on the human population. Assessment of anticipated secondary hazards (glacial lake outburst floods) shows an increase in probable headward impacts of mass movements on glacial lakes in the future. Our findings will support researchers, policymakers, stakeholders, and local governments in identifying critical areas that require detailed investigation for risk reduction and mitigation.

Characterizing the surge behaviour and associated ice-dammed lake evolution of the Kyagar Glacier in the Karakoram

Abstract. Glacier surges are prevalent in the Karakoram and occasionally threaten local residents by inundating land and initiating mass movement events. The Kyagar Glacier is well known for its surge history, and in particular its frequent blocking of the downstream valley, leading to a series of high-magnitude glacial lake outburst floods (GLOFs). Although the surge dynamics of the Kyagar Glacier have been broadly described in the literature, there remains an extensive archive of remote sensing observations that have great potential for revealing specific surge characteristics and their relationship with historic lake outburst floods. In this study, we propose a new perspective on quantifying the surging process using successive digital elevation models (DEMs), which could be applied to other sites where glacier surges are known to occur. Advanced Spaceborne Thermal Emission and Reflection Radiometer DEMs, High Mountain Asia 8-meter DEMs, and the Shuttle Radar Topography Mission DEM were used to characterize surface elevation changes throughout the period from 2000 to 2021. We also used Landsat time series imagery to quantify glacier surface velocities and associated lake changes over the course of two surge events between 1989 and 2021. Using these datasets, we reconstruct the surging process of the Kyagar Glacier in unprecedented detail and find a clear signal of surface uplift over the lower glacier tongue, along with uniformly increasing velocities, associated with the period of surge initiation. Seasonal variations in surface flow are still evident throughout the surge phase, indicating the presence of water at the glacier bed. Surge activity of the Kyagar Glacier is strongly related to the development and drainage of the terminal ice-dammed lake, which itself is controlled by the drainage system beneath the glacier terminus.

An impact-based forecast system developed for hydrometeorological hazards

This article describes the Impact-Based Forecast (IBF) system developed for hydrometeorological disasters in Brazil. The system was conceived on some fundamental elements: mapping risk areas for floods and mass movement events, characteristics of the vulnerability and population exposed in such areas, and implementation of a robust observational network. Data from all warnings issued between 2017 and 2021 are compared with disasters recorded during the same period. The results show the efficiency of such a system when the warning level is very high, but also the weaknesses at moderate warning levels. The system, developed for a country with a very large number of risk areas and a high level of social vulnerability of the population living in these areas, can be adapted and implemented in other countries with such similarities.

Three-dimensional distribution of mass movement signals in disturbed Picea abies (L.) Karst.

Dendrogeomorphologic approaches enable annual absolute dating of various potentially hazardous geomorphic processes. This study tested the dating precision of three commonly used dendrogeomorphic approaches used for the extraction of geomorphic signals from the tree ring series of disturbed trees. The first approach is based on the onset of reaction wood occurrence, and the other two approaches are based on the detection of abrupt changes in tree ring eccentricity. Nine 165 cm long stems of maximally 27 year old Norway spruces (Picea abies (L.) Karst.) growing on unstable slope affected by mass movement events of known age were analysed. Several sampling directions on stems were analysed to reveal the best sampling strategy for each tested approach. The relationships between stem curvature and the dating precision of the approaches were also analysed. The results of dating precision showed crucial differences between the tested approaches. Tree stem curvature did not influence dating precision. Overall, we concluded that the approaches based on eccentric increments are less precise than those based on reaction wood analysis when juvenile P. abies trees that grow on landslide slope are sampled. The importance of this study is in providing new insight into dating precision by analysing the whole tree stems of trees influenced by mass movements. This is unique since the approaches based on eccentricity increments have not been previously tested in such a detail.

A new flood chronology for KwaZulu-Natal (1836–2022): the April 2022 Durban floods in historical context

ABSTRACT In April 2022, flooding and associated geohazards caused major loss of life and extensive damage in the greater Durban region and large areas of the KwaZulu-Natal (KZN) coastal zone. Heavy rainfall that triggered the flooding and mass movement events was reported in national and international media as having ‘smashed weather records’. However, no systematic and up-to-date flood record exists for KZN to allow the April 2022 floods to be viewed within their full historical context. This study presents an historical geographic account of flooding in KZN, with a particular focus on the greater Durban region. The flood record expands upon available databases held by the South African Weather Service, drawing on missionary accounts, newspapers and personal diaries to identify all significant flood events in KZN since the mid-nineteenth century. We document 53 significant flood events from 1850-1899 (average ~1.1 per annum) and 210 from 1900-2022 (average ~1.7 per annum). Within the limits of our data, we suggest that the frequency of flooding in Durban has likely doubled over the last century. Our research confirms that the April 2022 floods were likely the most catastrophic natural disaster yet recorded in KZN, in collective terms of lives lost and overall economic impact.

Spatial and Temporal Analysis of Global Landslide Reporting Using a Decade of the Global Landslide Catalog

Rainfall-triggered landslides can result in devastating loss of life and property damage and are a growing concern from a local to global scale. NASA’s global landslide catalog (GLC) compiles a record of rainfall-triggered landslide events from media reports, academic articles, and existing databases at global scale. The database consists of all types of mass movement events that are triggered by rainfall and represents a minimum number of events occurring between 2007 and 2018. The GLC collection is no longer being compiled, and the dataset will not be updated past 2018. The research presented here evaluates global patterns in landslide reporting from events in the GLC. The evaluation includes an analysis of the spatial and temporal distribution of global landslide events and associated casualties and comparisons with other landslide inventories. This database has been used to estimate landslide hotspots, evaluate geographic patterns in landslides, and train and validate landslide models from local to global scales. The most notable landslide hotspots are in the Pacific Northwest of North America, High Mountain Asia, and the Philippines. Additionally, the relationship between country GDP and income status with landslide occurrence was determined to have a positive correlation between economic status and landslide reporting. The GLC also indicates a reporting bias towards English-speaking countries. The general goal of this research is to assess the decade of global landslide reports from the GLC and show how this database can be used for rainfall-triggered landslide research.

Simulating impact-induced shaking as a triggering mechanism for mass movements on Bennu

Observations of near-Earth asteroid Bennu have revealed a dynamic surface composed of unconsolidated material. The OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer) mission found numerous locations exhibiting evidence of mass movements of surface material. Mass movements can be a major factor in the surface evolution of a small near-Earth asteroid, and the Small Carry-on Impactor (SCI) experiment on asteroid Ryugu has shown that seismic shaking can trigger it. We selected one mass movement site on Bennu to conduct a detailed survey of the surface boulder arrangement and geomorphology. Using these data, we created dynamical simulations of mass movement events at this site initiated by seismic shaking, and we found a mass flux comparable to estimates from the site survey. The frequency ranges of the shakings are similar to what would be produced by a 0.5-m-diameter impactor, for which the expected crater size is of a scale widely seen on Bennu (32 m). In addition, the simulation exhibited the Brazil nut effect, where finer particles percolate towards greater depth, in this case up to 1.5 m. Our results demonstrate that impact-induced seismic shaking is a viable mechanism for the initiation of mass movements, and a plausible explanation for the scarcity of fine regolith, on Bennu's surface.

Christmas Mass Movements in the Italian Alps

Mass movements at high elevation during wintertime are rare events in the Italian Alps, but are generally large events compared to those occurring in other seasons. In a context of climate change, their interpretation is particularly challenging due to the risk implications during a highly tourist season in the mountains, and because their occurrence seemingly contradicts the attribution of recent mass movements in high-alpine environments to global warming. To shed some light on this topic, we reviewed 12 mass movements in the Italian Alps that occurred at elevations above 1500 m, documented from mid-December to January, henceforth during the Christmas period. The aim is to understand whether recent events may be related to ongoing climate and environmental changes. Even though the small number of analysed mass movements does not allow statistically based conclusions, some preliminary considerations could be drafted. We observe a seeming increase in the frequency and elevation of winter mass-movement events in the last two decades, with an increased number of failures involving rock slopes under permafrost conditions, and a transition from heavy-precipitations controlled mass movements to temperature-anomalies and -fluctuations controlled mass movements. We also show that any type of instability process can occur in winter, including debris flows, with rock falls/avalanches prevailing. These findings may partly stem from an increased number of mass-movement reports deriving from the growing attention in recent years to the impacts of climate change and their related risks. Considering the growing anthropic pressure on alpine areas even in winter, especially for tourism purposes, it is crucial to broaden our knowledge on winter mass movements by expanding and analysing a larger case history, through the opportunities offered by new technologies and citizen science.

Composite landslide in the dynamic alpine conditions: a case study of Urbas landslide

The alpine environment is characterized by complex geology, high-energy terrain, deeply incised river valleys with high erosional potential, extreme weather conditions and dynamic geomorphic processes. Such settings provide favourable conditions for the formation of composite landslides rather than individual slope mass movement phenomena. As an example, we present the kinematics of the composite landslide Urbas in the North of Slovenia which developed in the complex geological and morphological settings characteristic of the alpine environment. The research combines several monitoring techniques and involves the integration of both surface and subsurface displacements measured in the landslide area. The results indicate that the composite sliding process consists of several simultaneous and interrelated types of movements occurring in different segments of the unstable mass that are governed by different mechanisms of displacements, such as rockfall, sliding and debris flow. The kinematic characteristics of a deep-seated landslide that formed in such conditions vary spatially, but is rather homogenuous vertically, indicating translational type of movement. Spatial kinematic heterogeneity is primarily related to the diverse terrain topography, reflecting in different displacement trends. Based on the revealed kinematic proprieties of the sliding material, the sediment discharge illustrates the sliding material balance which estimates the volume of the retaining material that represents the potential for slope mass movement events of larger scales.

Intensification of ENSO frequency drives forest disturbance in the andes during the holocene

The biodiverse montane forests of the tropical Andes are today frequently disturbed by rainfall-driven mass movements which occur mostly during extreme El Niño events. Over the coming decades these events are projected to double under the 1.5 °C global warming scenario. The consequent increased rainfall and mass movement events likely present an elevated risk to millions of people living in the Andes. However, the impact of more frequent rainfall extremes remains unclear due to a lack of studies that directly link past changes in El Niño-Southern Oscillation (ENSO) frequency to forest and landscape disturbance patterns. Here, we present the first Holocene palaeoecological record from Laguna Pallcacocha, southern Ecuador, a key site for El Niño reconstructions. We demonstrate that for the past 10,000 years plant taxa indicative of recolonization – such as Alnus acuminata – covary with El Niño-induced flood layers in the lake. An amplified forest disturbance pattern is observed in the late Holocene, suggesting enhanced slope instability following deforestation. The temporal pattern is not explained by tree line fluctuations or human impact, while the latter does amplify the impact of ENSO on landscape disturbance. Spatial correlations between modern ENSO and precipitation are consistent with a regional comparison of Holocene records of landscape disturbance. Our results indicate that climate extremes, such as those associated with future intensification of El Niño, combined with ongoing land use change will increase the frequency of mass movements elevating risks for millions of people in the Andes.

Geomorphology and initiation mechanisms of the 2020 Haines, Alaska landslide

In early December 2020, an atmospheric river (AR) and rain-on-snow (ROS) event impacted the Haines, Alaska area, resulting in record-breaking rainfall and snowmelt that caused flooding and dozens of mass movement events. We consider the AR—a one-in-500-year event—as the trigger for the devastating Beach Road Landslide (BRLS), which destroyed or damaged four residences and took the lives of two people. The BRLS started as a debris avalanche and transitioned into a debris flow, with a total approximate landslide volume of 187,100 m3. Geomorphic analysis using lidar data identified evidence of paleo-landslides and displaced masses of rock, one of which served as the source area for the BRLS. Significant structural features in the weak ultramafic bedrock defined the head scarp area and formed the failure plane. This study illustrates the importance of identifying pre-existing landslide features and source areas likely to produce future landslides. As an increase in ROS events is projected for Southeast Alaska with warmer and wetter winters, we recommend the development of an AR scale coupled with geological information for the region, to enhance warnings to residents in landslide-prone areas.

Traces of a prehistoric and potentially tsunamigenic mass movement in the sediments of Lake Thun (Switzerland)

Mass movements constitute major natural hazards in the Alpine realm. When triggered on slopes adjacent to lakes, these mass movements can generate tsunami-like waves that may cause additional damage along the shore. For hazard assessment, knowledge about the occurrence, the trigger and the geomechanical and hydrogeological mechanisms of these mass movements is necessary. For reconstructing mass movements that occurred in or adjacent to lakes, the lakes’s sedimentary record can be used as an archive. Here, we present a prehistorical mass-movement event, of which the traces were found in an alpine lake, Lake Thun, in central Switzerland. The mass movement is identified by large blocks on the bathymetric map, a chaotic to transparent facies on the reflection seismic profiles, and by a mixture of deformed lake sediments and sandy organic-rich layers in the sediment-core record. The event is dated at 2642–2407 cal year BP. With an estimated volume of ~ 20 × 106 m3 it might have generated a wave with an initial amplitude of > 30 m. In addition to this prehistorical event, two younger deposits were identified in the sedimentary record. One could be dated at 1523–1361 cal year BP and thus can be potentially related to an event in 598/599 AD documented in historical reports. The youngest deposit is dated at 304–151 cal year BP (1646–1799 AD) and is interpreted to be related to the artificial Kander river deviation into Lake Thun (1714 AD).

Mass movements

AbstractIn this chapter, we consider key advances in the understanding of mass movements betweenc.1965 andc.2000. This period saw a burgeoning need for a greater level of understanding of mass-movement processes in response to a series of high-impact mass-movement events, and because of the need to develop infrastructure safely. A series of step changes were enabled through hillslope geomorphology (broadly defined) being open to overarching and consolidating concepts, methods and models from cognate disciplines, whilst seizing opportunities to gain insight from rapidly advancing methods increasingly focused at a scale of investigation relevant to landsliding. Byc.2000, geomorphologists had made significant contributions to our understanding of mass-movement processes and ultimately led many key conceptual advances, notably relating to: bridging across scales of hillslope investigation; linking and developing understanding of process, form and mechanisms of slope stability; and articulating the temporal characteristics of slope stability and mass movement.

Long-Term Evolution and Monitoring at High Temporal Resolution of a Rapidly Retreating Cliff in a Cold Temperate Climate Affected by Cryogenic Processes, North Shore of the St. Lawrence Gulf, Quebec (Canada)

This article focuses on the quantification of retreat rates, geomorphological processes, and hydroclimatic and environmental drivers responsible for the erosion of an unconsolidated fine-sediment cliff along the north shore of the Gulf of St. Lawrence (Quebec, Canada). Annual monitoring using field markers over a period of twenty years, coupled with photo interpretation and historical archive analysis, indicates an average annual erosion rate of 2.2 m per year between 1948 and 2017. An acceleration in retreat occurred during the last 70 years, leading to a maximum between 1997 and 2017 (3.4 m per year) and 2000–2020 (3.3 m per year). Daily observations based on six monitoring cameras installed along the cliff between 2008 and 2012 allowed the identification of mechanisms and geomorphological processes responsible for cliff retreat. Data analysis reveals seasonal activity peaks during winter and spring, which account for 75% of total erosional events. On an annual basis, cryogenic processes represent 68% of the erosion events observed and subaerial and hydrogeological processes account for 73%. Small-scale processes, such as gelifraction, solifluction, suffosion, debris collapse, and thermoabrasion, as well as mass movement events, such as slides and mudflows, induced rapid cliff retreat. Lithostratigraphy and cliff height exert an important control on erosion rates and retreat modes, which are described by three main drivers (hydrogeologic, cryogenic, and hydrodynamic processes). Critical conditions promoting high erosion rates include the absence of an ice-foot in winter, the absence of snow cover on the cliff face allowing unrestricted solar radiation, the repetition of winter warm spells, snow melting and sediment thawing, and high rainfall conditions (&gt;30 mm or SPI &gt; 2). The relationships between hydroclimatic forcing and retreat rates are difficult to establish without taking into account the quantification of the geomorphological processes involved. The absence of quantitative data on the relative contribution of geomorphological processes can constitute a major obstacle in modeling the retreat of cliffs with regard to climate change.