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Mountain Landslides: An Overview of Common Types and Future Impacts
Abstract
This chapter begins by giving a brief overview of the forces involved in the geodynamics of mountains and mountain ranges, including the processes needed for the generation of mass movement processes. In the remaining parts of this chapter, the following issues associated with mountain landslides are addressed: the anatomy of landslides, common landslide materials, and landslide movement types, along with landslide causes and triggers. The purpose of the final section of this chapter is to reflect on the extent to which the increasing intensity of human activities on mountainscapes, particularly climate change and urbanization, has magnified potential disaster risk for downslope settlements.
... In fact, floods are compounding the risk of TC, exacerbating their economic and social impacts on vulnerable communities . Moreover, mass movement processes are common during the influence of cyclones producing huge impacts Geertsema and Alcántara-Ayala, 2023). In addition, under-developed countries often have limited access to healthcare and resources in general, making it difficult for residents to recover from the damage caused by these storms causing residual vulnerabilities (Sharifi et al., 2021). ...
Tropical cyclones (TC) pose a persistent natural hazard to Costa Rica. Exposure to natural hazards, such as mass movements and floods, is compounded by a growing urban population and inadequate land use planning. This study conducted a comprehensive analysis of the economic impacts of TC of Costa Rica from Hurricane Joan in 1988 to Hurricane Eta in 2020, assessing the impact by municipality and economic sector using baseline information of the Ministry of National Planning and Economic Policy. According to the study, road infrastructure (933.8 US million), agriculture (280.5 US million), river rehabilitation (153.96 US million), housing 98.26 (US million), and health (81.74 US million) were among the sectors most severely affected by TC over the past 30 years. The Pacific basin municipalities in Costa Rica were found to be the most vulnerable, primarily due to the indirect impacts of TC. The study's results offer useful information on the economic sectors and municipalities that are most exposed from TC in Costa Rica and provide a replicable methodology for other regions and countries facing similar tropical phenomena.
Stability assessment of rock slopes in the tectonically active western Himalayas region is extremely crucial, as this area has undergone multiple deformation phases that have resulted in intricate geological conditions, as observed along the Bandipora to Gurez road in J&K, India. The region's rugged and treacherous terrain is susceptible to frequent slope failures, which frequently result in disruption of traffic, loss of life, property damage, and environmental degradation. Utilizing field observations and considering variations in geological and geotechnical conditions, we conducted a detailed study of twenty slope facets. This study involved employing the rock mass rating (RMR) and kinematic analysis to classify the causes, types of failure, and potential failure directions. The RMR values derived from the study lie between 89 and 16, reflecting a spectrum of rating from very good to very poor. Higher values suggest the presence of completely stable areas, while lower values suggest the presence of completely unstable areas. The kinematic analysis depicts that the rock slopes are prone to planar and wedge failure. The kinematic analysis further shows that joint planes intersect with each other in different directions resulting in different potential failure modes. The current study is poised to help not only in risk reduction but also in supporting the ongoing civil projects in this area. Our findings indicate that immediate mitigation measures are imperative for the state highway to avert slope failure and ensure its long-term stability.
Landslides pose a formidable natural hazard. Accurate risk assessment of landslides triggered by precipitation heavily relies on hydrometeorological factors, specifically precipitation and soil moisture. However, the insufficient ground-based observations and the coarse spatio-temporal resolution hinder the performance of landslide prediction. It is not clear what hydrometeorological thresholds and triggering mechanisms are more likely to trigger landslides in China, particularly in the context of rapid urbanization. To address these questions, this study investigated 1504 shallow landslide events in Chinese urban and non-urban areas from 2007 to 2019. It utilized daily 1 km soil moisture at various depths (20–100 cm) and multi-source precipitation datasets, including gauge-based gridded dataset, in conjunction with three multi-source fusion precipitation products (Multi-Source Weighted-Ensemble Precipitation − MSWEP, the Climate Hazards Group InfraRed Precipitation with Station dataset − CHIRPS, and the Integrated Multi-satellitE Retrievals for Global Precipitation Measurement − GPM-IMERG), along with dynamic urban impervious area datasets. It aims to determine the optimal multi-source precipitation predictor, the critical soil moisture depth that triggers landslides, and to establish the hydrometeorological thresholds for landslides. Additionally, the impact of urbanization on landslide occurrences was estimated by comparing antecedent precipitation accumulation, soil moisture, and impervious surface ratio dynamics between urban and non-urban areas. The results indicated that a combination of 2-day cumulative CHIRPS precipitation and 100 cm soil moisture provided the most accurate predictions for landslides in urban regions of China (accuracy = 88.5 %), outperforming interpolated ground-based observations and other fusion products. Specifically, landslides become more prone when antecedent cumulative rainfall surpasses 97.42 mm in 2 days and soil moisture exceeds 39.6 % m/m saturation in China. Urban areas experienced high antecedent precipitation levels, lower precipitation (64.40 mm) threshold and soil moisture threshold (38.9 %), and shorter durations at landslide sites compared to non-urban areas (71.90 mm, 41.4 %, and 7 days, respectively). The process of urbanization is observed to decrease soil moisture levels while concurrently elevating rainfall amounts. This phenomenon, combined with anthropogenic activities, including distance from roads and urban impervious surface expansion, contributes to 44.6 % of the causes of landslides by reducing slope stability and increasing the presence of loose material. These findings have implications for landslide warnings in urban areas with limited measurements and contribute to understanding urbanization’s impact on landslide risks in developing nations.
Continued retreat and disappearance of glaciers cause fundamental changes in cold mountain ranges and new landscapes to develop, and the consequences can reach far beyond the still ice-covered areas. A key element is the formation of numerous new lakes where overdeepened parts of glacier beds become exposed. With the first model results from the Swiss Alps around 2010 of distributed glacier thicknesses over entire mountain regions, the derivation of glacier beds as potential future surface topographies became possible. Since then, climate-, water-, and hazard-related quantitative research about future lakes in deglaciating mountains all over the world rapidly evolved.
Currently growing and potential future open water bodies are part of new environments in marked imbalance. The surrounding steep icy slopes and peaks are affected by glacial debuttressing and permafrost degradation, with associated long-term stability reduction. This makes the new lakes potential sources of far-reaching floods or debris flows, and they represent serious multipliers of hazards and risks to down-valley humans and their infrastructure. Such hazard and risk aspects are also of primary importance where the lakes potentially connect with hydropower production, freshwater supply, tourism, cultural values, and landscape protection.
Planning for sustainable adaptation strategies optimally starts from the anticipation in space and time of possible lake formation in glacier-covered areas by numerical modeling combined with analyses of ice-morphological indications. In a second step, hazards and risks related to worst-case scenarios of possible impact and flood waves must be assessed. These results then define the range of possibilities for use and management of future lakes. Careful weighing of both potential synergies and conflicts is necessary. In some cases, multipurpose projects may open viable avenues for combining solutions related to technical challenges, safety requirements, funding problems, and societal acceptance. Successful implementation of adaptive projects requires early integration of technical-scientific and local knowledge, including the needs and interests of local users and decision makers, into comprehensive, participatory, and long-term planning. A key question is the handling of risks from extreme events with disastrous damage potential and low but increasing probability of occurrence.
As future landscapes and lakes develop rapidly and are of considerable socioeconomic and political interest, they present often difficult and complex situations for which solutions must be found soon. Related transdisciplinary work will need to adequately address the sociocultural, economic, and political aspects.
Glacier and permafrost hazards in cold mountain regions encompass various flood and mass movement processes that are strongly affected by rapid and cumulative climate-induced changes in the alpine cryosphere. These processes are characterized by a range of spatial and temporal dimensions, from small volume icefalls and rockfalls that present a frequent but localized danger to less frequent but large magnitude process chains that can threaten people and infrastructure located far downstream. Glacial lake outburst floods (GLOFs) have proven particularly devastating, accounting for the most far-reaching disasters in high mountain regions globally.
Comprehensive assessments of glacier and permafrost hazards define two core components (or outcomes):
1. Susceptibility and stability assessment: Identifies likelihood and origin of an event based on analyses of wide-ranging triggering and conditioning factors driven by interlinking atmospheric, cryospheric, geological, geomorphological, and hydrological processes.
2. Hazard mapping: Identifies the potential impact on downslope and downstream areas through a combination of process modeling and field mapping that provides the scientific basis for decision making and planning.
Glacier and permafrost hazards gained prominence around the mid-20th century, especially following a series of major disasters in the Peruvian Andes, Alaska, and the Swiss Alps. At that time, related hazard assessments were reactionary and event-focused, aiming to understand the causes of the disasters and to reduce ongoing threats to communities. These disasters and others that followed, such as Kolka Karmadon in 2002, established the fundamental need to consider complex geosystems and cascading processes with their cumulative downstream impacts as one of the distinguishing principles of integrative glacier and permafrost hazard assessment.
The widespread availability of satellite imagery enables a preemptive approach to hazard assessment, beginning with regional scale first-order susceptibility and hazard assessment and modeling that provide a first indication of possible unstable slopes or dangerous lakes and related cascading processes. Detailed field investigations and scenario-based hazard mapping can then be targeted to high-priority areas. In view of the rapidly changing mountain environment, leading beyond historical precedence, there is a clear need for future-oriented scenarios to be integrated into the hazard assessment that consider, for example, the threat from new lakes that are projected to emerge in a deglaciating landscape. In particular, low-probability events with extreme magnitudes are a challenge for authorities to plan for, but such events can be appropriately considered as a worst-case scenario in a comprehensive, forward-looking, multiscenario hazard assessment.
Disaster risk management and climate change adaptation are integrated, interinstitutional, multisectoral, and interdisciplinary processes. They generally give rise to public policies with the same goals. It is not very appropriate to refer to slope instability or landslide adaptation in a general sense without alluding to disaster risk management. Promoting risk management is equivalent to promoting adaptation, although the risk derived from slope instability is not always associated with climate change.
The increase in intensity and frequency of precipitation as a result of global warming is a driver of the slope instability hazard and therefore the associated risk for exposed elements. However, the increase in the hazard is also due to environmental degradation and human action and therefore this hazard is considered to be socio-natural. On the other hand, the increase in risk is also due to the increase in vulnerability, which is the result of social processes and inappropriate land use. In other words, this type of risk is not simply the result of climate variability and climate change.
The effectiveness of risk management or of adaptation is chiefly related to the use of correct information and a suitable application of models that provide an accurate diagnosis for appropriate decision making. The use of information that fails to give rise to clear intervention actions leads to maladaptation. An appropriate hazard and risk assessment contributes to adequate spatial planning, the relocation of exposed human settlements, the improvement of neighborhoods, the design and construction of erosion control and stability works, and the implementation of both structural and non-structural preventive measures, collective insurance, and landslide warning systems, among others.
Hazard intervention, the reduction of vulnerability, and an increase in resilience are goals of both risk management and planned adaptation. However, there are also examples of autonomous adaptation associated with the way some communities have implemented slope instability prevention measures and effective community warning systems, which have appropriately involved the population. For slope instability or landslides, the risk, as well as risk management and adaptation actions, are essentially local.
From a slope instability lens (although this may extend to the remaining sectors), risk management must be considered, for all intents and purposes, to be an adaptation and development strategy. Risk is a common denominator in management from the perspective of different approaches, disciplines and sectors, such as social and economic development, infrastructure, environmental protection, spatial planning, sustainability, resilience, climate change adaptation, and risk management itself, among others. A fragmented view of the issue is inappropriate and ineffective. In an ideal scenario, disaster risk management would be increasingly promoted as a development, sustainability, and transformation strategy that, in addition to being a strategy for anticipating risks associated with climate change, would also contribute to the rendering of ecosystem services and increasing sustainability in obtaining resources for future generations.
In the semiarid Southwestern USA, wildfires are commonly followed by runoff-generated debris flows because wildfires remove vegetation and ground cover, which reduces soil infiltration capacity and increases soil erodibility. At a study site in Southern California, we initially observed runoff-generated debris flows in the first year following fire. However, at the same site three years after the fire, the mass-wasting response to a long-duration rainstorm with high rainfall intensity peaks was shallow landsliding rather than runoff-generated debris flows. Moreover, the same storm caused landslides on unburned hillslopes as well as on slopes burned 5 years prior to the storm and areas burned by successive wildfires, 10 years and 3 years before the rainstorm. The landslide density was the highest on the hillslopes that had burned 3 years beforehand, and the hillslopes burned 5 years prior to the storm had low landslide densities, similar to unburned areas. We also found that reburning (i.e., two wildfires within the past 10 years) had little influence on landslide density. Our results indicate that landscape susceptibility to shallow landslides might return to that of unburned conditions after as little as 5 years of vegetation recovery. Moreover, most of the landslide activity was on steep, equatorial-facing slopes that receive higher solar radiation and had slower rates of vegetation regrowth, which further implicates vegetation as a controlling factor on post-fire landslide susceptibility. Finally, the total volume of sediment mobilized by the year 3 landslides was much smaller than the year 1 runoff-generated debris flows, and the landslides were orders of magnitude less mobile than the runoff-generated debris flows.
Climate change has increased the likelihood of the occurrence of disasters like wildfires, floods, storms, and landslides worldwide in the last years. Weather conditions change continuously and rapidly, and wildfires are occurring repeatedly and diffusing with higher intensity. The burnt catchments are known, in many parts of the world, as one of the main sensitive areas to debris flows characterized by different trigger mechanisms (runoff-initiated and debris slide-initiated debris flow). The large number of studies produced in recent decades has shown how the response of a watershed to precipitation can be extremely variable, depending on several on-site conditions, as well as the characteristics of precipitation duration and intensity. Moreover, the availability of satellite data has significantly improved the ability to identify the areas affected by wildfires, and, even more importantly, to carry out post-fire assessment of burnt areas. Many difficulties have to be faced in attempting to assess landslide risk in burnt areas, which present a higher likelihood of occurrence; in densely populated neighbourhoods, human activities can be the cause of the origin of the fires. The latter is, in fact, one of the main operations used by man to remove vegetation along slopes in an attempt to claim new land for pastures or construction purposes. Regarding the study area, the Camaldoli and Agnano hill (Naples, Italy) fires seem to act as a predisposing factor, while the triggering factor is usually represented by precipitation. Eleven predisposing factors were chosen and estimated according to previous knowledge of the territory and a database consisting of 400 landslides was adopted. The present work aimed to expand the knowledge of the relationship existing between the triggering of landslides and burnt areas through the following phases: (1) Processing of the thematic maps of the burnt areas through band compositions of satellite images; and (2) landslide susceptibility assessment through the application of a new statistical approach (machine learning techniques). The analysis has the scope to support decision makers and local agencies in urban planning and safety monitoring of the environment.
Permafrost and glaciers are being degraded by the warming effects of climate change. The impact that this degradation has on slope stability in mountainous terrain is the subject of ongoing research efforts. The relatively new availability of high-resolution (≤ 10 m) imagery with worldwide coverage and short (≤ 30 days) repeat acquisition times, as well as the emerging field of environmental seismology, presents opportunities for making remote, systematic observations of landslides in cryospheric mountainous terrain. I reviewed the literature and evaluated landslide activity in existing imagery to select five ~ 5000-km2 sites where long-term, systematic observations could take place. The five proposed sites are the northern and eastern flanks of the Northern Patagonia Ice Field, the Western European Alps, the eastern Karakoram Range in the Himalayan Mountains, the Southern Alps of New Zealand, and the Fairweather Range in Southeast Alaska. Systematic observations of landslide occurrence, triggers, size, and travel distance at these sites, especially if coupled with observations from in situ instrumental monitoring, could lead to a better understanding of changes in slope stability induced by climate change. The suggested sites are not meant to be absolute and unalterable. Rather, they are intended as a starting point and discussion starter for new work in this expanding landslide research frontier.
Cascading hazard processes refer to a primary trigger such as heavy rainfall, seismic activity, or snow melt, followed by a chain or web of consequences that can cause subsequent hazards influenced by a complex array of preconditions and vulnerabilities. These interact in multiple ways and can have tremendous impacts on populations proximate to or downstream of these initial triggers. High Mountain Asia (HMA) is extremely vulnerable to cascading hazard processes given the tectonic, geomorphologic, and climatic setting of the region, particularly as it relates to glacial lakes. Given the limitations of in situ surveys in steep and often inaccessible terrain, remote sensing data are a valuable resource for better understanding and quantifying these processes. The present work provides a survey of cascading hazard processes impacting HMA and how these can be characterized using remote sensing sources. We discuss how remote sensing products can be used to address these process chains, citing several examples of cascading hazard scenarios across HMA. This work also provides a perspective on the current gaps and challenges, community needs, and view forward toward improved characterization of evolving hazards and risk across HMA.
Most landslides and debris flows worldwide occur during or following periods of rainfall, and many of these have been associated with major disasters causing extensive property damage and loss of life [...]
Landslides are a ubiquitous hazard in terrestrial environments with slopes, incurring human fatalities in urban settlements, along transport corridors and at sites of rural industry. Assessment of landslide risk requires high-quality landslide databases. Recently, global landslide databases have shown the extent to which landslides impact on society and identified areas most at risk. Previous global analysis has focused on rainfall-triggered landslides over short ∼ 5-year observation periods. This paper presents spatiotemporal analysis of a global dataset of fatal non-seismic landslides, covering the period from January 2004 to December 2016. The data show that in total 55 997 people were killed in 4862 distinct landslide events. The spatial distribution of landslides is heterogeneous, with Asia representing the dominant geographical area. There are high levels of interannual variation in the occurrence of landslides. Although more active years coincide with recognised patterns of regional rainfall driven by climate anomalies, climate modes (such as El Niño–Southern Oscillation) cannot yet be related to landsliding, requiring a landslide dataset of 30+ years. Our analysis demonstrates that landslide occurrence triggered by human activity is increasing, in particular in relation to construction, illegal mining and hill cutting. This supports notions that human disturbance may be more detrimental to future landslide incidence than climate.
On interannual to decadal time scales, the climate mode with many of the strongest societal impacts is the El Niño–Southern Oscillation (ENSO). However, quantifying ENSO's changes in a warming climate remains a formidable challenge, due to both the noise arising from internal variability and the complexity of air-sea feedbacks in the tropical Pacific Ocean. In this work, we use large (≥30-member) ensembles of climate simulations to show that anthropogenic climate change can produce systematic increases in ENSO teleconnection strength over many land regions, driving increased interannual variability in regional temperature extremes and wildfire frequency. As the spatial character of this intensification exhibits strong land-ocean contrasts, a causal role for land-atmosphere feedbacks is suggested. The identified increase in variance occurs in multiple model ensembles, independent of changes in sea surface temperature variance. This suggests that in addition to changes in the overall likelihoods of heat and wildfire extremes, the variability in these events may also be a robust feature of future climate.
The 2008 M w 7.9 Wenchuan Earthquake (Sichuan, China) was possibly the largest and most destructive recent earthquake as far as the geo-hazards are concerned. Of the nearly 200,000 landslides triggered originally, many remobilized within a few years after the initial event by rainfall, which often caused catastrophic debris flows. The cascades of geo-hazards related to the Wenchuan Earthquake motivated research worldwide to investigate the triggering and mechanisms of co-seismic landslides, their rainfall-induced remobilization, the generation of debris flows, the evolution of their controlling factors, and the long-term role of earthquakes in shaping the topography. On the eve of the 10th anniversary of the 2008 Wenchuan Earthquake, we present a short review of the recent advances in these topics, discuss the challenges faced in the earthquake-related geo-hazards mitigation practice, and suggest priorities and guidelines for future research.
Regardless of the exact definition used or the type of landslide under discussion, understanding the basic mechanics and processes of a typical landslide is critical. With an increasing awareness and mandate to fully understand new building site characteristics, improve existing critical infrastructure and appreciating the importance of an area’s landslide history, typing landslides according to shared characteristics gives vital information about the future performance of a site, in relation to potential landslide hazards. We provide here, a basic primer for an understanding of the similarities and differences of the nature and physics of landslide movement. Type of material, speed of motion, slope angle, potential frequency of occurrence, weather and climatic influences, and man-made disturbances as well as other factors have a bearing on landslide motion, size and impact, yet we can generally group and categorize most landslides into more understandable groupings. Landslide typology is constantly evolving and becoming more exact, given the expanding tools of site investigation, improving computer and GIS modeling, and careful peer analysis.
Canada has a geological history that lead to the formation of sensitive clay deposits. These deposits are notorious for their large landslides. This paper presents an overview of the different types of large landslide occurring in sensitive clays located in Eastern Canada and on the West Coast of Canada. The geological formation and resulting stratigraphy of sensitive clay deposits for each region are described. Typical landslide types and their particular morphology along with their failure mechanisms are illustrated for each region. The paper discusses and concludes on the similarities and the differences of the various types of landslides in these separate areas, portraying sensitive clay landslides across Canada. RÉSUMÉ L'histoire géologique du Canada a menée à la formation de dépôts d'argiles sensibles. Ces dépôts sont tristement connus pour les grands glissements de terrain qui y surviennent. Cet article présente un survol des différents types de grands glissements de terrain qui surviennent dans l'est du Canada et sur la côte ouest du Canada. La géologie et la stratigraphie des dépôts d'argiles sensibles de chacune de ces régions sont décrites. Les différents types de grands glissement, leur morphologie particulière, de même que le mode de rupture sont illustrés pour ces deux régions. L'article discute et conclu sur les similarités et les différences des types de glissements survenant dans ces deux régions distinctes, donnant un portrait des glissements dans les argiles sensibles au Canada.
Glacier outburst floods are sudden releases of large amounts of water from a glacier. They are a pervasive natural hazard worldwide. They have an association with climate primarily via glacier mass balance and their impacts on society partly depend on population pressure and land use. Given the ongoing changes in climate and land use and population distributions there is therefore an urgent need to discriminate the spatio-temporal patterning of glacier outburst floods and their impacts. This study presents data compiled from 20 countries and comprising 1348 glacier floods spanning 10 centuries. Societal impacts were assessed using a relative damage index based on recorded deaths, evacuations, and property and infrastructure destruction and disruption. These floods originated from 332 sites; 70% were from ice-dammed lakes and 36% had recorded societal impact. The number of floods recorded has apparently reduced since the mid-1990s in all major world regions. Two thirds of sites that have produced > 5 floods (n = 32) have floods occurring progressively earlier in the year. Glacier floods have directly caused at least: 7 deaths in Iceland, 393 deaths in the European Alps, 5745 deaths in South America and 6300 deaths in central Asia. Peru, Nepal and India have experienced fewer floods yet higher levels of damage. One in five sites in the European Alps has produced floods that have damaged farmland, destroyed homes and damaged bridges; 10% of sites in South America have produced glacier floods that have killed people and damaged infrastructure; 15% of sites in central Asia have produced floods that have inundated farmland, destroyed homes, damaged roads and damaged infrastructure. Overall, Bhutan and Nepal have the greatest national-level economic consequences of glacier flood impacts. We recommend that accurate, full and standardised monitoring, recording and reporting of glacier floods is essential if spatio-temporal patterns in glacier flood occurrence, magnitude and societal impact are to be better understood. We note that future modelling of the global impact of glacier floods cannot assume that the same trends will continue and will need to consider combining land-use change with probability distributions of geomorphological responses to climate change and to human activity.
Among the more complex and devastating interactions between climate and hydromorphological processes in mountain environments are landslide lake outburst floods (LLOFs), resulting from mass movements temporarily blocking a drainage system. This work reviews these processes in the Himalayas and highlights the high frequency of this type of phenomenon in the region. In addition, we analyse two recent catastrophic trans-national LLOFs occurring in the Sutlej river basin during 2000 and 2005. Based on high resolution satellite images, Tropical Rainfall Measuring Mission (TRMM), Moderate-Resolution Imaging Spectroradiometer (MODIS) derived evolution of snowline elevation and discharge data we reconstruct the timing and hydrometeorological conditions related to the formation and failure of landslide dams. Results showed that the 2005 flood, originating from the outburst of the Parchu lake, was not related to heavy precipitation, but was likely enhanced by the rapid and late snowmelt of an unusually deep and widespread snowpack. The flood in 2000 was triggered by the outburst of an unnamed lake located on the Tibetan plateau, identified here for the first time. In this case, the outburst followed intense precipitation in the lake watershed, which raised the level of the lake and thus caused the breaching of the dam. As stream gauges were damaged during the events detailed discharge data is not available, but we estimated the peak discharges ranging between 1100 m3·s-1 and 2000 m3·s-1 in 2005, and 1024 m3·s-1 and 1800 m3·s-1 in 2000. These events caused significant geomorphic changes along the river valleys, with observed changes in channel width exceeding 200 m. Results also demonstrate that remotely-sensed data enables valuable large-scale monitoring of lake development and related hydrometeorological conditions, and may thereby inform early warning strategies, and provide a basis for flood risk reduction measures that focus on disaster preparedness and response strategies.
Although the 1963 Vajont Slide in Italy has been extensively studied for over 50 years, its regional geological and geomorphological context has been neglected. In this paper, we use field observations and remote sensing data to elucidate the interaction between endogenic and exogenic processes that brought the north slope of Monte Toc to failure. We present the first detailed pre- and post-failure engineering geomorphology maps of the slide area. The maps delineate two main landslide blocks, several sub-blocks, compressional and extensional zones, and secondary failures in the deposit. The maps provide new insights into the kinematics, dynamics and evolution of the slide. Finally, we discuss the origin of Vajont Gorge and a prehistoric failure that occurred at the same location as the 1963 slide. We propose, as part of a newly developed multi-stage landscape evolution sequence, that the prehistoric failure was a deep-seated gravitational slope deformation (sackung) that initiated during deglaciation and continued to slowly move until the catastrophic failure in 1963. We argue that the gorge was created by these deep-seated slow movements.
Keywords Vajont Slide . Engineering geomorphology . Regional geomorphology . Endogenic processes . Exogenic processes . Sackung . Rock slope damage
About one third of the global permafrost region is situated in mountainous terrain, and in Canada, large areas underlain by permafrost have mountainous topography. Although mountain topography and terrain-related mass movements yield a much greater diversity of ground materials and temperatures per unit area than encountered in polar lowlands, the governing physical principles are the same. Permafrost in mountainous regions thereby enriches the variety of perma-frost-related phenomena encountered beyond what is typically found in lowland areas. Permafrost thaw in mountains is relevant as it may increase the potential for geohazards such as debris flows, rock falls, rock avalanches, and displacement waves. There are also implications for hydrology, water quality, and ecosystems. We argue for better integration of permafrost research in mountainous regions with mainstream permafrost research and education in Canada. RÉSUMÉ Environ un tiers des terrains à pergélisol sont situés en zones montagneuses. Au Canada, de vastes zones à pergélisol ont des reliefs montagneux. Bien que les topographies montagneuses et les mouvements de masse associés produisent une plus grande diversité de matériel et de température par unité de surface que celle observée dans les plaines polai-res, les principes physiques les gouvernant demeurent les mêmes. Le pergélisol des zones montagneuses vient donc enrichir la diversité des phénomènes liés au pergélisol au-delà de ce qui est typiquement observé dans les plaines. Le dégel du pergélisol en régions montagneuses est important, car il peut accroître le potentiel de risques géologiques, tels que les coulées de débris, les chutes de pierres, et les éboulements de roches. Il a également des implications pour l'hydrologie, la qualité de l'eau, et les écosystèmes. Nous recommandons une meilleure intégration des travaux sur le pergélisol en régions montagneuses au sein de l'éducation et de la recherche généraliste sur le pergélisol au Canada.
Despite their often dangerous and unpredictable nature, landslides provide fascinating templates for studying how soil organisms, plants and animals respond to such destruction. The emerging field of landslide ecology helps us understand these responses, aiding slope stabilisation and restoration and contributing to the progress made in geological approaches to landslide prediction and mitigation. Summarising the growing body of literature on the ecological consequences of landslides, this book provides a framework for the promotion of ecological tools in predicting, stabilising, and restoring biodiversity to landslide scars at both local and landscape scales. It explores nutrient cycling; soil development; and how soil organisms disperse, colonise and interact in what is often an inhospitable environment. Recognising the role that these processes play in providing solutions to the problem of unstable slopes, the authors present ecological approaches as useful, economical and resilient supplements to landslide management.
Lahars are rapid flows of mud-rock slurries that can occur without warning and catastrophically impact areas more than 100 km downstream of source volcanoes. Strategies to mitigate the potential for damage or loss from lahars fall into four basic categories: (1) avoidance of lahar hazards through land-use planning; (2) modification of lahar hazards through engineered protection structures; (3) lahar warning systems to enable evacuations; and (4) effective response to and recovery from lahars when they do occur. Successful application of any of these strategies requires an accurate understanding and assessment of the hazard, an understanding of the applicability and limitations of the strategy, and thorough planning. The human and institutional components leading to successful application can be even more important: engagement of all stakeholders in hazard education and risk-reduction planning; good communication of hazard and risk information among scientists, emergency managers, elected officials, and the at-risk public during crisis and non-crisis periods; sustained response training; and adequate funding for risk-reduction efforts. This paper reviews a number of methods for lahar-hazard risk reduction, examines the limitations and tradeoffs, and provides real-world examples of their application in the U.S. Pacific Northwest and in other volcanic regions of the world. An overriding theme is that lahar-hazard risk reduction cannot be effectively accomplished without the active, impartial involvement of volcano scientists, who are willing to assume educational, interpretive, and advisory roles to work in partnership with elected officials, emergency managers, and vulnerable communities.
Landslides affect the following elements of the environment: (1) the topography of the earth’s surface; (2) the character and quality of rivers and streams and groundwater flow; (3) the forests that cover much of the earth’s surface; and (4) the habitats of natural wildlife that exist on the earth’s surface, including its rivers, lakes, and oceans. Large amounts of earth and organic materials enter streams as sediment as a result of this landslide and erosion activity, thus reducing the potability of the water and quality of habitat for fish and wildlife. Biotic destruction by landslides is also common; widespread stripping of forest cover by mass movements has been noted in many parts of the world. Removal of forest cover impacts wildlife habitat.
The ecological role that landslides play is often overlooked. Landslides contribute to aquatic and terrestrial biodiversity. Debris flows and other mass movement play an important role in supplying sediment and coarse woody debris to maintain pool/riffle habitat in streams. As disturbance agents landslides engender a mosaic of seral stages, soils, and sites (from ponds to dry ridges) to forested landscapes.
Large rock and soil landslides are an important part of the geodiversity in Nahanni National Park in Canada’s Northwest Territories. Here we describe five notable events, including two in soil, two in rock, and one involving rock and soil. Three of the events resulted in landslide dams. The Ram Plateau flowslide involved a collapse of a scree slope and fine textured soil over massive ground ice. This complex landslide continues to move in response to permafrost thaw and seasonal moisture. The Wrigley landslide is a large debris slide, involving thick till that dammed Wrigley Creek. The Cathedral Creek rock slide is a dip slope failure which dammed two large creeks. Cliff collapse of limestone on the Ram Plateau transformed into a rock avalanche, which dammed a stream. The Grizzly landslide involved both rock and soil. It is a large rock slide—earth flow in which, we suspect, undrained loading played an important role.
The travel angles of landslides continue to be an important parameter in risk analyses. We report on travel angles of 112 long runout landslides in the Canadian Cordillera, expanding on our 2008 study of 61 landslides. The lowest travel angles we report belong to the following groups (in ascending order) sensitive glaciomarine sediments, early deglacial earth flows in lake sediments, diamicts derived from clay shales (they may involve permafrost), glaciolacustrine sediments, earth flows generated by rock slides, confined and unconfined debris flows generated by rock slides, rock avalanches on glaciers, dry planar rock avalanches, and undifferentiated rock avalanches.
Glacial lake outburst floods (GLOFs) are highly mobile mixtures of water and sediment that occur suddenly and are capable of traveling tens to hundreds of kilometers with peak discharges and volumes several orders of magnitude larger than those of normal floods. They travel along existing river channels, in some instances into populated downstream regions, and thus pose a risk to people and infrastructure. Many recent events involve process chains, such as mass movements impacting glacial lakes and triggering dam breaches with subsequent outburst floods. A concern is that effects of climate change and associated increased instability of high mountain slopes may exacerbate such process chains and associated extreme flows. Modeling tools can be used to assess the hazard of potential future GLOFs, and process modeling can provide insights into complex processes that are difficult to observe in nature. A number of numerical models have been developed and applied to simulate different types of extreme flows, but such modeling faces challenges stemming from a lack of process understanding and difficulties in measuring extreme flows for calibration purposes. Here we review the state of knowledge of key aspects of modeling GLOFs, with a focus on process cascades. Analysis and simulation of the onset, propagation, and potential impact of GLOFs are based on illustrative case studies. Numerical models are presently available for simulating impact waves in lakes, dam failures, and flow propagation but have been used only to a limited extent for integrated simulations of process cascades. We present a spectrum of case studies from Patagonia, the European Alps, central Asia, and the Himalayas in which we simulate single processes and process chains of past and potential future events. We conclude that process understanding and process chain modeling need to be strengthened and that research efforts should focus on a more integrative treatment of processes in numerical models.
The goal of this article is to revise several aspects of the well-known classification of landslides, developed by Varnes (1978). The primary recommendation is to modify the definition of landslide-forming materials, to provide compatibility with accepted geotechnical and geological terminology of rocks and soils. Other, less important modifications of the classification system are suggested, resulting from recent developments of the landslide science. The modified Varnes classification of landslides has 32 landslide types, each of which is backed by a formal definition. The definitions should facilitate backward compatibility of the system as well as possible translation to other languages. Complex landslides are not included as a separate category type, but composite types can be constructed by the user of the classification by combining two or more type names, if advantageous.
Landslides convert potential energy into kinetic energy and are thus important agents of topographic change and landscape evolution. They are deformations of Earth's surface that refl ect patterns of regional seismic, climatic, and lithospheric stress fi elds on sloping terrain. Landslides involve fracturing of the lithosphere ranging from microscopic rock fragmentation to giant submarine slope failures, thus spanning more than 26 orders of magnitude in volume. Here I synthesize major rate constraints on landslide distribution, size, and impacts that help gauge their relevance in the Earth system with a focus on the lithosphere, the hydrosphere, and the biosphere. Given sufficient size or frequency, landslides help sculpt local topography, trigger shallow crustal response, limit volcanic edifi ce growth, modulate bedrock incision as well as water and sediment fl ux in river systems, trigger far-reaching processes such as tsunamis or catastrophic outburst fl ows, condition rates of soil production, and alter hillslope and riparian habitats. Most importantly, landslides remain a signifi cant hazard to people, housing, infrastructure , and land use in many parts of the world.
Hummocks are topographic features of large landslides and rockslide-debris avalanches common in volcanic settings. We use scaled analog models to study hummock formation and explore their importance in understanding landslide kinematics and dynamics. The models are designed to replicate large-scale volcanic collapses but are relevant also to non-volcanic settings. We characterize hummocks in terms of their evolution, spatial distribution, and internal structure from slide initiation to final arrest. Hummocks initially form by extensional faulting as a landslide begins to move. During motion, individual large blocks develop and spread, creating an initial distribution, with small hummocks at the landslide front and larger ones at the back. As the mass spreads, hummocks can get wider but may decrease in height, break up, or merge to form bigger and long anticlinal hummocks when confined. Hummock size depends on their position in the initial mass, modified by subsequent breakup or coalescence. A hummock has normal faults that flatten into low-angle detachments and merge with a basal shear zone. In areas of transverse movement within a landslide, elongate hummocks develop between strike–slip flower structures. All the model structures are consistent with field observations and suggest a general brittle-slide emplacement for most landslide avalanches. Absence of hummocks and fault-like features in the deposit may imply a more fluidal flow of emplacement or very low cohesion of lithologies. Hummocks can be used as kinematic indicators to indicate landslide evolution and reconstruct initial failures and provide a framework with which to study emplacement dynamics.
A landslide is the movement of a mass of rock, earth or debris down a slope.
The Todagin Creek landslide is located at 57.61° N 129.98° W in Northwest British Columbia. A seismic station 90 km north
of the landslide recorded the event at 1643 hours coordinated universal time (UTC; 0943 hours Pacific daylight time (PDT))
on October 3, 2006. The signal verifies the discovery and relative time bounds provided by a hunting party in the valley.
The landslide initiated as a translational rock slide on sedimentary rock dipping down slope at 34° and striking parallel
to the valley. The landslide transformed into a debris avalanche and had a total volume estimated at 4 Mm3. An elevation drop of 771 m along a planar length of 1,885 m resulted in a travel angle (fahrböschung) of 21.3°. The narrowest
part of the landslide through the transport zone is 345 m. The widest part of the divergent toe of the landslide reaches a
width of 1,010 m. Landslide debris impounded a lake of approximately 32 ha and destroyed an additional 67 ha of forest. The
impoundment took 7 to 10 days to fill, with muddied waters observed downstream on October 13. No clear linkage exists with
precipitation and temperature records preceding the landslide, but strong diurnal temperature cycles occurred in the days
prior to the event. The Todagin Creek area appears to have an affinity for large landslides with the deposits of three other
landslides >5 Mm3 observed in the valley.
Terzaghi (Geotechnique 12 (1962) 251) and Young (Young, A., 1972. Slopes. Oliver and Boyd, Edinburgh, 288 pp.) described the stable forms of slopes in sedimentary rock masses, assuming penetrative discontinuities, which are parallel to bedding and joints which are perpendicular to bedding. The only movements considered were slides along bedding. Experience in the Canadian Rockies indicates that the cohesionless rock masses that exist at or above tree line may also move by toppling, buckling and sliding along joints. These processes also act to limit the inclinations of stable slopes. Rock strength is a factor in the critical height of a slope that buckles. The processes can be represented as fields on a process diagram, a plot of slope inclination against bedding dip, using the basic friction angles of the rocks present.The process diagram also separates five common mountain peak shapes, which form on homoclinal sequences of beds. Castellate and Matterhorn mountains occur in sub-horizontal beds, cuestas develop in gently to moderately dipping beds. Hogbacks formed in moderately to steeply dipping beds have similar slope angles on both cataclinal and anaclinal slopes. Dogtooth mountains occur in steeply dipping sub-vertical beds.
Earth's climate is warming and will continue to warm as the century progresses. High mountains and high latitudes are experiencing the greatest warming of all regions on Earth and also are some of the most sensitive areas to climate change, in part because ecosystems and natural processes in these areas are intimately linked to the cryosphere. Evidence is mounting that warming will further reduce permafrost and snow and ice cover in high mountains, which in turn will destabilize many slopes, alter sediment delivery to streams, and change subalpine and alpine ecosystems. This paper contributes to the continuing discussion of impacts of climate change on mountain environments by comparing and discussing processes and trends in the mountains of western Canada and the European Alps. We highlight the effects of physiography and climate on physical processes occurring in the two regions. Processes of interest include landslides and debris flows induced by glacier debuttressing, alpine permafrost thaw, changes in rainfall regime, formation and sudden drainage of glacier- and moraine-dammed lakes, ice avalanches, glacier surges, and large-scale sediment transfers due to rapid deglacierization. Our analysis points out the value of integrating observations and data from different areas of the world to better understand these processes and their impacts.
Water bodies impounded by glaciers, moraines, and ice jams on rivers can drain suddenly, with disastrous downstream consequences. Lakes can form at the margins of an alpine glacier or ice cap, on its surface, or at its base. Smaller pockets of water may also be present within some glaciers. In all cases, these water bodies might drain by enlarging subglacial tunnels or by mechanical collapse of the glacier dam. Many formerly stable glacier lakes have failed over the past century, in some cases repeatedly, as Earth’s atmosphere has warmed and glaciers thinned and receded. The peak discharge, duration, and volume of a subglacial outburst flood depend mainly on (1) the geometry and rate of development of the tunnel at the base of the glacier and (2) the size and geometry of the impounded water body. Discharge commonly increases exponentially during the outburst, but ends quickly when the lake empties or when the drainage tunnel is plugged by collapse of the tunnel roof or closes due to plastic ice flow. Some glacier outburst floods result from the mechanical collapse of the ice dam. In such cases, the peak flow is achieved rapidly during the collapse. Outburst floods from glacier lakes attenuate due to temporary storage of floodwaters in channels and on valley floors.
Many hazardous lakes are dammed by lateral and end moraines that formed in the past two centuries when valley and cirque glaciers retreated from advanced positions reached during the Little Ice Age. Moraine dams are susceptible to failure because they are steep and relatively narrow, because they comprise loose poorly sorted sediment, and because they may contain ice cores or interstitial ice. These dams generally fail by overtopping and incision. The triggering event may be a heavy rainstorm, strong winds, or an ice avalanche or landslide into the lake that generates waves that overtop the dam. Melting of moraine ice cores and piping are other possible failure mechanisms. Outflow from a moraine-dammed lake increases as the breach enlarges and then decreases as the level of the lake falls. The moraine breach may become armored, preventing further incision, or the hydraulic gradient at the breach may decrease to a point that erosion ceases.
Outburst floods from glacier- and moraine-dammed lakes typically entrain, transport, and deposit large amounts of sediment. If the channel is steeper than about 0.10-0.15 and contains abundant loose sediment, the flood likely will transform into a debris flow. Such flows may be larger and more destructive than the flood from which they formed. A period of protracted warming is required to trap lakes behind moraines and create conditions that lead to dam failure. The warming also forces glaciers to retreat, prompting ice avalanches, and landslides that have destroyed many moraine dams.
The present time is a significant stage in the adjustment of mountain slopes to climate change and specifically atmospheric warming. This review examines the state of understanding of the responses of mid-latitude alpine landscapes to recent cryospheric change and summarizes the variety and complexity of documented landscape responses involving glaciers, moraines, rock and debris slopes, and rock glaciers. These indicate how a common general forcing translates into varied site-specific slope responses according to material structures and properties, thermal and hydrological environments, process rates, and prior slope histories. Warming of permafrost in rock and debris slopes has demonstrably increased instability, manifest as rock glacier acceleration, rockfalls, debris flows, and related phenomena. Changes in glacier geometry influence stress fields in rock and debris slopes, and some failures appear to be accelerating toward catastrophic failure. Several sites now require expensive monitoring and modeling to design effective risk-reduction strategies, especially where new lakes form and multiply hazard potential, and new activities and infrastructure are developed.
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Owing to the nature of landslide triggering mechanisms, lack of realistic documentation on the impact of landslide disasters at global, national and subnational scales has existed for many years. Data from two sources was used to examine the discrepancies about the impact of landslide disasters by considering both, high magnitude-low frequency and high frequency-low magnitude events. Analysis of this landslide disaster data for thirteen countries (Argentina, Bolivia, Chile, Colombia, Costa Rica, Ecuador, Guatemala, Mexico, Nepal, Nicaragua, Perú, Sri Lanka, and Venezuela) revealed larger differences than those previously reported. Variation among number of landslide disasters between databases was expressed in three orders of magnitude, whereas number of human losses differed in two orders of magnitude, and people affected in one.
Volcanic debris avalanches (VDA) are, on the one hand, stunning natural phenomena, but, on the other, can pose serious threats to people and infrastructure. This first chapter aims to introduce a collection of themed papers gathered in a book, each illustrating the advancements of a different aspect of VDA research. As a state-of-the-art collection, the 11 papers provide a powerful tool for the volcanological community to enhance our understanding of their history and global distribution, collapse initiation and cyclic occurrence, problems with terminology, transport processes and deposit characteristics, climate impacts, application of numerical tools, and the records of marine and ringplain settings.
There is a recognised need for bridging the gap between science and policy making aiming at the reduction of landslide disaster risk. A growing body of literature articulates the significance of scientific contributions on landslide risk assessment at different spatial-temporal scales. However, most studies in this field have mainly focused on landslide hazards, whereas vulnerability has not been treated in much detail. The present study aimed to portray the challenge involved within the integrated landslide disaster risk management sphere to avoid the configuration of new disaster risk. It should be understood whereby that landslide exposure is exacerbated by current population growth and the intensification of the use of land and resources linked to profitable activities, which in turn lead to rural transformation and a greater extent of socioeconomic occupation of depreciated land in areas susceptible to hazards, urban sprawling and even expensive housing on unstable slopes. This analysis provides evidence about the need to encourage integrated landslide disaster risk management (ILDRiM), not only in the sense of reducing existing risk, but to prevent new landslide disaster risk. Thereupon, recognising and addressing landslide root causes and disaster risk drivers strongly intertwined to exposure and vulnerability should be prioritised, whereas the need of informed disaster risk governance must neither be neglected.
Large slope collapses have been known to trigger extreme rushes of air loaded with projectiles (airblasts) capable of causing destruction and fatalities far beyond run-out of the rock mass. An appraisal of the likelihood of a destructive airblast should be a component of landslide risk assessments. Yet there is an absence of risk studies directly examining landslide-related airblasts. In this work we back-analyze an unreported airblast in the Sikkim Himalayas (India) and several other airblasts documented around the world. We explore the conditions a large slope collapse should meet to trigger a significant airblast, and we establish a semi-empirical relationship linking the potential energy in a collapse with airborne trajectory and the extent of the related airblast. The collapse of thousands or millions of cubic meters falling from a significant height results in a sudden release of energy (1011J to 1013J) and a high degree of comminution of rocks, causing a violent displacement of air. Average wind speeds of airblasts following impacts with airborne trajectory can be double the speed of rock avalanches. The size of the damage zone depends on the potential energy of the falling rock mass and can be amplified or reduced depending on how confined the valley is where the airblast occurs.
Rock slides quite commonly transform into flow-like landslides along their runout paths. At three initial rock slides in northern British Columbia, which occurred between 2002 and 2005, around 50–70% of the entire runout distance is composed of debris avalanche and debris flow deposits, which is comparable to other composite landslides around the world. Saturated ground conditions at the time of rock sliding make entrainment or undrained loading as agents of flow transformation from initially dry rock slides to partially saturated debris avalanches, respectively, fully saturated debris flows likely. Hummocks occur as clusters within the rock slide parts, whereas the flow-like depositions have more subdued morphologies. We show that late- or post-emplacement motion of individual hummocks is possible and can even divert in direction from the dominant landslide trajectory by responding to the underlying topographic gradient. Analyses of the well-preserved deposits suggest hummock formation above a basal sliding plane (low-angle normal fault) and along subordinate shear zones (high-angle normal faults) within a largely translational mass movement, thereby supporting the hypothesis of hummock formation proposed by Paguican et al. (2014). Pebbles on top of rock slide-debris avalanche boulders and on top of snapped-off trees record much higher dynamic debris flow heights. These and other features are not recorded on ancient landslides due to rapid erosion.
Fire danger rating has become the cornerstone of national fire management programs, and operational systems have been available for over 40 years. Fire danger information is used across a broad spectrum of fire management decision making including daily operations, seasonal strategic planning, and long-term fire and land management planning under future climate change. There are many different national fire danger rating systems in use worldwide. Early warning of extreme fire danger is critical for fire managers to mitigate or prevent wildfire disaster. Early warning is provided using forecasted fire weather, which is further enhanced with remotely sensed fire activity and fuels information in fire early warning systems. Fire danger and early warning systems can operate at global to local levels, depending on fire management requirements. Current operational systems and applications are reviewed.
More frequent more intense storms predicted by climate models for the Pacific Northwest of North America could increase the regional landslide hazard. The impacts of one such storm are examined on Vancouver Island, British Columbia, during which 626 mapped landslides occurred, encompassing >5 km2 total area and generating >1.5 × 106 m3 of sediment. The relationship between rainfall intensity, air temperature and wind speed obtained from mesoscale numerical weather modelling is examined relative to landslide incidence within steep terrain. A critical onset of rainfall intensity between 80 and 100 mm in 24 h that results in a rapid increase in landslides with increasing precipitation is demonstrated. The argument is presented that this result is more useful for landslide management decisions than a minimum threshold. The component of wind-driven rain was calculated, and results indicated that wind caused increased concentrations of rainfall associated with the occurrence of landslides. Approximately half the landslides studied were not related to rainfall alone, but to rain on snow, and we argue that wind played a crucial role. This often neglected component of hydrological analysis remains a major challenge as the role of snow transition zones and a warming climate in coastal mountain watersheds is considered.
In this paper, we develop a mechanical model that relates the destabilization of thawing permafrost rock slopes to temperature-related effects on both, rock- and ice-mechanics; and laboratory testing of key assumptions is performed. Degrading permafrost is considered to be an important factor for rock–slope failures in alpine and arctic environments, but the mechanics are poorly understood. The destabilization is commonly attributed to changes in ice-mechanical properties while bedrock friction and fracture propagation have not been considered yet. However, fracture toughness, compressive and tensile strength decrease by up to 50% and more when intact water-saturated rock thaws. Based on literature and experiments, we develop a modified Mohr–Coulomb failure criterion for ice-filled rock fractures that incorporates fracturing of rock bridges, friction of rough fracture surfaces, ductile creep of ice and detachment mechanisms along rock–ice interfaces. Novel laboratory setups were developed to assess
the temperature dependency of the friction of ice-free rock–rock interfaces and the shear detachment of rock–ice interfaces. In degrading permafrost, rock-mechanical properties may control early stages of destabilization and become more important for higher
normal stress, i.e. higher magnitudes of rock–slope failure. Ice-mechanical properties outbalance the importance of rock-mechanical components after the deformation accelerates and are more relevant for smaller magnitudes. The model explains why all magnitudes of rock–slope failures can be prepared and triggered by permafrost degradation and is capable of conditioning long para-glacial response times. Here, we present a synoptic rock- and ice-mechanical model that explains the mechanical destabilization processes operating in warming permafrost rocks.
Of the numerous kinds of dams that form by natural processes, dams formed from landslides, glacial ice, and late-neoglacial moraines present the greatest threat to people and property. Landslide dams form a wide range of physiographic settings. The most common types of mass movements that form landslide dams are rock and debris avalanches; rock and soil slumps and slides; and mud, debris, and earth flows. The most common initiation mechanisms for dam-forming landslides are excessive rainfall and snowmelt and earthquakes. Natural dams may cause upstream flooding as the lake rises and downstream flooding as a result of failure of the dam. Although data are few, for the same potential energy at the dam site, downstream flood peaks from the failure of glacier-ice dams are smaller than those from landslide, moraine, and constructed earth-fill and rock-fill dam failures.
Data from 40 historical world-wide earthquakes were studied to determine the characteristics, geologic environments, and hazards of landslides caused by seismic events. This sample of 40 events was supplemented with intensity data from several hundred United States earthquakes to study relations between landslide distribution and seismic parameters. Fourteen types of landslides were identified in the earthquakes studied. The most abundant of these were rock falls, disrupted soil slides, and rock slides. The greatest losses of human life were due to rock avalanches, rapid soil flows, and rock falls. Correlations between magnitude (M) and landslide distribution show that the maximum area likely to be affected by landslides in a seismic event increases from approximately 0 at M ≅ 4.0 to 500,000 km2 at M = 9.2.
Threshold magnitudes, minimum shaking intensities, and relations between M and distance from epicenter or fault rupture were used to define relative levels of shaking that trigger landslides in susceptible materials. Four types of internally disrupted landslides—rock falls, rock slides, soil falls, and disrupted soil slides—are initiated by the weakest shaking. More coherent, deeper-seated slides require stronger shaking; lateral spreads and flows require shaking that is stronger still; and the strongest shaking is probably required for very highly disrupted rock avalanches and soil avalanches.
Each type of earthquake-induced landslide occurs in a particular suite of geologic environments. These range from overhanging slopes of well-indurated rock to slopes of less than 1° underlain by soft, unconsolidated sediments. Materials most susceptible to earthquake-induced landslides include weakly cemented rocks, more-indurated rocks with prominent or pervasive discontinuities, residual and colluvial sand, volcanic soils containing sensitive clay, loess, cemented soils, granular alluvium, granular deltaic deposits, and granular man-made fill. Few earthquake-induced landslides reactivate older landslides; most are in materials that have not previously failed.
This study examines the geomorphic effects of large (>106 m3) rock-slope failures on long profiles of rivers in the Swiss Alps and the New Zealand Southern Alps. Regression of channel slope versus drainage basin area objectively highlights knickpoints separating incised from aggraded reaches that often correspond to locations of large rock-slope failures. For a fixed concavity index, the highest values of the steepness index and erosion index along a given profile spatially coincide with breach channels cut into formerly river-damming rockslide debris as old as 10 k.y. Assuming that the knickpoints do not predate slope failure, data show that high profile steepness and inferred specific stream power are not always the cause, but often a result, of large river-blocking rock-slope failure in mountain basins. Omission of rockslide data from slope-area plots lowers the steepness index and increases the concavity index on average, yet only in few cases more than one standard deviation.