Landslides – Disaster Risk Reduction

Remote sensing can broadly be described as the detecting and measuring of electromagnetic energy emitted or reflected from distant objects. The measured electromagnetic energy which comes from different portions of the electromagnetic spectrum can be used to retrieve information on the properties of the earth surface. The purpose of this chapter is to present an overview of the current application of remote sensing to landslides detection (section 2), monitoring (section 3) and hazard analysis (section 4) and to illustrate how researchers around the world are currently using remote sensing techniques to map, monitor and manage landslides (section 5).

Generation of landslide maps is of great significance for land use planning, engineering works design and civil protection and risk reduction programmes. Landslide maps may portray past and current landslide occurrence mainly in the form of inventories, zonation of the spatial probability of future landslide occurrence in the form of susceptibility maps, zonation of its spatio-temporal probability in the form of landslide hazard maps, and the expected damage or losses by landslides as risk maps.

This chapter introduces the interrelated concepts of mapping landslide inventories, susceptibility, hazard and risk. It further presents main landslide inventory methods, contents and tools. Then it discusses the differences between landslide susceptibility and hazard mapping and provides an overview of some of the most commonly used methods of susceptibility and hazard analysis, from qualitative (heuristic) approaches to quantitative (statistical and physically based) models. It also introduces the concept of landslide risk and discusses some qualitative and quantitative approaches to risk assessment and mapping. Finally, it provides case study examples of landslide mapping approaches and programmes.

Landslide risk reduction is a societal pressing need in for counties and also areas along coasts, lakes, rivers in relatively flat countries. Engineering measures to stabilize dangerous slopes needs very high cost and not feasible for many cases. Monitoring, Prediction, Early Warning is the most economical landslide risk reduction measure which is applicable for both developed and developing countries. This chapter presents monitoring of triggering factors, slope deformation, other indicators in indoor experiments, field experiments as well as in natural condition. Methodology of prediction and early warning is examined based on these monitoring and topographical, geological and hydrological conditions.

Various manifestations of large-scale slope processes are described. Though many of them are prehistoric they exemplify the phenomena that have the highest potential to cause a humanitarian, economic or environmental catastrophe. They are described, based on the contributions of the 1st WLF participants.

The impact of natural hazards on our cultural heritage represents an important theme, involving a multi-disciplinary approach. In case of landsliding, engineering geologists can play a key role, through the identification of relationships between soil and structures. This chapter starts from the large perspective of UNESCO Convention (

1972

), as a bird’s-eye view of the general problem of heritage conservation, arriving at the presentation of a series of case histories from different countries. This varied approaches to the problem of landslides and cultural heritage reflects the multitudes of interests associated with this topics.

Landslides occur frequently in connection with other types of hazardous phenomena such as earthquakes and volcanic activities. Strong earthquakes often cause a large number of landslides, including large-scale landslides, in mountainous areas. Volcanic activities could trigger giant landslides or debris avalanches on mountain slopes. It is not uncommon that such large-scale landslides cause river blockage and form natural dams, which are vulnerable to collapse by overtopping and breaching. The sudden collapse of a landslide dam can cause a catastrophic flood in the downstream area. Submarine landslides are also common phenomena. Large-scale submarine landslides cause catastrophic tsunamis. In assessing those catastrophic cases as a whole, it is necessary to pay special attention to extremely high threats to vulnerable settlements in hazardous areas. The risk assessment of such complicated combined landslide disasters around the world, particularly in developing countries, is a significant step for identifying the appropriate mitigation strategy against catastrophic damage. In recent decades we have experienced remarkable disasters induced by landslides. For example, a huge number of landslides were induced by the Chi-Chi earthquake in Taiwan (1999), by the Mid-Niigata Prefecture earthquake in Japan (2004) and the Northern Pakistan earthquake (2005). Most recently the Wenchuan earthquake occurred with magnitude 8.0 in central part of China on May 12, 2008. This gigantic earthquake caused a tremendous number of landslides, as seen in the satellite picture in Fig. 23.1. Large-scale landslides occurred in volcanic areas, such as at Stromboli Volcano in Italy (2002) (Fig. 23.2) and on Leyte Island in Philippines (2006) (Fig. 23.3). Whole such events manifest the significance of a thematic session within the First World Landslide Forum focussing on the issue of risk mitigation targeting “landslides and multi-hazards”.

While rainfall is not the only triggering mechanism for debris flows, it is a significant one over a large part of the world. A better understanding of storm characteristics that commonly result in debris flows can improve preparedness and warning systems. Current research indicates that identifying regional variability in triggering storms events would advance risk reduction. Models that permit macro-scale analysis of debris flow initiation and mobilization enable researchers to better define the more vulnerable areas for future debris flow occurrence and the relative effectiveness of countermeasures. Similarly, a better understanding of debris flow occurrence within the broader continuum of erosion processes makes it possible to both understand their initiation and their impact on the fluvial environment. Large-scale human alteration of vegetation for forestry, agriculture or wildfire influences the probability that subsequent rainfall will induce debris flows. Understanding the interaction of vegetation, earth materials and rainfall provides a means for how these anthropogenic actions are influencing existing levels of debris flow hazard.

Landslides continue to be a major natural disaster causing loss of life, extensive human suffering and economic losses, despite advances in understanding of mechanisms, monitoring and mitigation technologies related to landslides. Sharing the globally accumulated expertise and implementing this knowledge effectively in different local contexts is the major challenge now facing landslide loss reduction efforts. Landslides characteristics differ according to climatic, geological and geographical conditions. They are also affected by different triggering mechanisms depending on the livelihood practices, infrastructure development and population density in each locality. Landslide risk reduction practices and institutional arrangements have evolved in different countries in response to varied landslide experiences brought about by these different geo-physical characteristics and drivers. An objective analysis of the practices adopted worldwide would provide invaluable guidance to develop pragmatic landslide risk reduction strategies and responsible institutions, especially in the developing countries where the impacts are greatest and the vulnerabilities are the highest, especially with increasing hazard potential due to climate change. This chapter describes national programs and methodologies adopted in landslide risk reduction in various countries as a contribution in this direction

Education is the key element for reducing disasters caused by natural hazards including landslides and achieving human security in the pursuit of sustainable development. The Hyogo Framework for Action 2005–2015 and “Words Into Action: A Guide for Implementing the Hyogo Framework” prepared by UN/ISDR emphasize the role of formal and non-formal education and awareness raising as a core component of risk reduction initiatives.

Past experience, projects, and programs have revealed enormously positive effects of education for vulnerability reduction and disaster risk management. Children and adults who know how to react in case of a disaster, community leaders who have learned to warn their people in time, and whole social layers who have been taught how to prepare themselves for natural hazards have contributed to better mitigation strategies and dissemination of information on the dangers of hazards. Education and knowledge have provided people with tools for vulnerability reduction and life-improving self-help strategies. Furthermore, more stable and disaster resilient education facilities, such as school buildings, provide a shelter in case of hazards and must be strengthened and improved through better engineering and technical knowledge.

Education also plays a substantial role in improving risk assessment procedures in nearby communities, in encouraging people to engage in building up resiliency and to generally reduce risk elements in communities. For education on risk reduction to have its desired impact on communities, it needs to reach out to the remotest development worker in the field. Such education needs to be made accessible and affordable for frontline practitioners who operate at community level and are often far removed from conventional knowledge centers such as universities.

Thus, while there is no argument that education is important, and it works, the challenge is how to effectively incorporate education for disaster reduction in the national and local government policy and programs, and how to reduce the gap between knowledge and practice through experiencing learning. A pro-active co-learning approach of linking school and formal education to community is the essential for the success of disaster education.

Numerous national and international organizations and initiatives – mainly under the umbrella of the UN “International Strategy for Disaster Reduction” (ISDR) – have engaged themselves in contributing to a “safer” world by promoting research projects on and preventive measurements against landslides. Other Organizations, undertakings or agencies like UNESCO, the World Bank-Global Facility for Disaster Reduction and Recovery (GFDRR), the United Nations University (UNU), the International Geoscience Programme (IGCP), the UN-International Year of Planet Earth (IYPE, 2008), the International Hydrological Programme (IHP), the International Flood Initiative (IFI), the International Sediment Initiative (ISI), the Disaster and Mitigation Programmes of World Meteorological Organization (WMO) and the International Science Council (ICSU), the Integrated Global Observing Strategy (IGOS) of the Global Earth Observation System of Systems (GEOSS), or the “Joint Technical Committee on Landslide and Engineered Slopes” of the International Society of Soil Mechanics and Geotechnical Engineering (ISSGME), the International Association of Engineering Geologists and the Environment (IAEG) and the International Society for Rock Mechanics (ISRM) are heavily involved in landslide risk mitigation measures.

Representatives of selected organizations, initiatives or undertakings are invited to present their recent activities and findings during a Round Table at the 1st World Landslide Forum.

A global review on the current status of Institutional and Legislative Systems for landslide mitigation and risk reduction management has revealed that countries go through time-consuming processes to create and update policies, legislations and strategies. As such, the concept of a template for policy and institutional framework, as well as subsequent transformation to a National Slope Master Plan has been recommended. The template will serve as a blueprint to generate political commitment, which will enable the allocation of resources from the main stakeholders both in terms of manpower and budget. This will then facilitate the setting-up of a lead organisation or agency to ensure good governance to champion landslide mitigation and risk reduction. With a proper budget for the lead organisation, they can recruit the best candidates with attractive remuneration and sustainable career path for the efficient implementation of the National Slope Master Plan.

In addition, the template for this Master Plan will streamline the preparation of a local legal and regulatory framework, etc. to secure resources and provide best practices from lessons learned locally and internationally. The involvement and technical support of international agencies like ICL will expedite the development of reference knowledge kits and guidelines for adoption and adaptation. This will also assist other countries in need of support, especially those from developing and under-developed countries.

Pronounced step-wise atmospheric warming during the 20th century reduced ice cover in most of Earth’s mountains by 25–50 percent. Net changes in temperatures responsible for this remarkable deglacierization are less than 2°C, a small fraction of the warming that occurred at the end of the Pleistocene. Yet the effects of warming of the past century have been profound. Alpine permafrost, which expanded during the Little Ice Age, is now thinning. Large areas at high elevations may become completely free of permafrost by the end of the 21st century. Loss of alpine permafrost and glacier downwasting appear to be partly responsible for accelerated mass wasting and catastrophic slope failures in high mountains in recent decades. New lakes appeared during the Little Ice Age when glaciers advanced across streams and rivers and blocked drainage. Most of these lakes drained one or more times during the past century, producing catastrophic floods orders of magnitude larger than normal nival or rainfall floods. In some instances, lakes have appeared upvalley of former, drained ones as glaciers have continued to retreat under a warming climate. Lakes also formed behind Little Ice Age end moraines when glaciers retreated in the early 20th century. Moraine dams are vulnerable to failure because they are steep-sided and consist of loose sediment. Outburst floods from lakes dammed by glaciers and moraines erode, transport, and deposit huge amounts of sediment over distances of tens of kilometers. They broaden floodplains, destroy pre-flood channels, and create a new braided planform. Outburst floods from glacier- and moraine-dammed lakes have claimed thousands of lives in the Andes and Himalayas and continue to be a hazard in these and other mountain ranges.

The Session, Socioeconomic Impacts of Landslides, was organized to provide discussions on the socioeconomic impact of landslide events as well as best practice for mitigation of the risk associated with landslides. Social and economic losses, and their quantification, the consequences of landslides on infrastructure development, and land use policy, are critical aspects of socio-economic issues related to landslides. In addition the session will include case studies on recovery and resettlement, measures to reduce social vulnerability, investments for landslide risk mitigation and reduction, and insurance issues for landslide risk mitigation and reduction.

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.

Correction of an existing landslide or the prevention of a pending landslide is a function of a reduction in the driving forces or an increase in the available resisting forces. Any remedial measure used must involve one or both of the above parameters.

According to IUGS WG/L, landslide remedial measures are arranged in four practical groups, namely: modification of slope geometry, drainage, retaining structures and internal slope reinforcement. This chapter discusses the planning and designing aspects of the landslide remedial measures in each group and presents some illustrative examples. In addition, debris flow mitigation measures are discussed in some detail. Back analysis of failed slopes is an effective tool for reliable design of the remedial measures while advanced numerical methods are nowadays frequently used to design safe and cost effective landslide remedial measures.

Selection of an appropriate remedial measure depends on: (a) engineering feasibility, (b) economic feasibility, (c) legal/regulatory conformity, (d) social acceptability, and (e) environmental acceptability. There are a number of levels of effectiveness and levels of acceptability that may be applied in the use of these measures, for while one slide may require an immediate and absolute long-term correction, another may only require minimal control for a short period.

As many of the geological features, such as sheared discontinuities are not known in advance, it is more advantageous to put remedial measures in hand on a “design as you go basis”. That is the design has to be flexible enough to accommodate changes during or subsequent to the construction of remedial works.

Landslide hazard can be influenced by natural resource management and rural development related activities, such as forest management, road construction, agricultural practices and river management. Vegetation cover and its utilizations may play a role in mitigating the risk of landsliding. Moreover and above all, it does play a role in mitigating the processes leading to increased landslide hazard, such as gully erosion. Thus, forest management and development are of particular concern. But all people living in mountain areas rely on the soil stability for their livelihoods, and their livelihoods may influence this soil stability. Therefore all related activities have to be done on an appropriate way in order to promote soil and slope stability.

To identify best adapted practices in a particular area, to organize spatially the different land uses and to promote the implementation of the identified best practices, the ideal scale is the watershed. It allows addressing upstream-downstream linking issues, such as landslides, and provides a framework for sound land use planning. However, it is not always possible to implement actions exactly with the watershed boundaries.

From the lack of knowledge regarding the scientific evidence of the role of forests against landslides to the institutional challenge of implementing watershed scaled policies, many progresses have to be done regarding this issue. But the already existing scientific knowledge, the integrated projects which are already implemented and the results which are obtained are encouraging. Above all, they show that fundamental research, socio-economic levers and institutional development have to be carried out and developed in a sound way, towards a better understanding of all the natural and man-made processes and a better management of all natural resources, in particular water and soil of the mountain areas.