Remote Sensing Approaches and Related Techniques to Map and Study Landslides

Landslide is one of the costliest and fatal geological hazards, threatening and influencing the socioeconomic conditions in many countries globally. Remote sensing approaches are widely used in landslide studies. Landslide threats can also be investigated through slope stability model, susceptibility mapping, hazard assessment, risk analysis, and other methods. Although it is possible to conduct landslide studies using in-situ observation, it is time-consuming, expensive, and sometimes challenging to collect data at inaccessible terrains. Remote sensing data can be used in landslide monitoring, mapping, hazard prediction and assessment, and other investigations. The primary goal of this chapter is to review the existing remote sensing approaches and techniques used to study landslides and explore the possibilities of potential remote sensing tools that can effectively be used in landslide studies in the future. This chapter also provides critical and comprehensive reviews of landslide studies focus¬ing on the role played by remote sensing data and approaches in landslide hazard assessment. Further, the reviews discuss the application of remotely sensed products for landslide detection, mapping, prediction, and evaluation around the world. This systematic review may contribute to better understanding the extensive use of remotely sensed data and spatial analysis techniques to conduct landslide studies at a range of scales.

Characterization of Susceptible Landslide Zones by an Accumulated Index

In order to characterize the landslide susceptibility in the central zone of Guerrero State in Mexico, a spatial model has been designed and implemented, which automatically generates cartography. Conditioning factors as geomorphological, geological, and anthropic variables were considered, and as a detonating factor, the effect of the accumulated rain. The use of an inventory map of landslides that occurred in the past (IL) was also necessary, which was produced by an unsupervised detection method. Before the design of the model, an analysis of the contribution of each factor, related to the landslide inventory map, was performed by the Jackknife test. The designed model consists of a susceptibility index (SI) calculated pixel by pixel by the accumulation of the individual contribution of each factor, and the final index allows the susceptibility cartography to slide in the study area. The evaluation of the obtained map was performed by applying an analysis of the frequency ratio (FR) graphic, and an analysis of the receiver operating characteristic (ROC) curve was developed. Studies like this can help different safeguarding institutions, locating the areas where there is a greater vulnerability according to the considered factors, and integrating disaster attention management or prevention plans.

Modeling Antecedent Soil Moisture to Constrain Rainfall Thresholds for Shallow Landslides Occurrence

Rainfall-triggered shallow landslide events have caused losses of human lives and millions of euros in damage to property in all parts of the world. The need to prevent such hazards combined with the difficulty of describing the geomorphological processes over regional scales led to the adoption of empirical rainfall thresholds derived from records of rainfall events triggering landslides. These rainfall intensity thresholds are generally computed, assuming that all events are not influenced by antecedent soil moisture conditions. Nevertheless, it is expected that antecedent soil moisture conditions may provide critical support for the correct definition of the triggering conditions. Therefore, we explored the role of antecedent soil moisture on critical rainfall intensity-duration thresholds to evaluate the possibility of modifying or improving traditional approaches. The study was carried out using 326 landslide events that occurred in the last 18 years in the Basilicata region (southern Italy). Besides the ordinary data (i.e., rainstorm intensity and duration), we also derived the antecedent soil moisture conditions using a parsimonious hydrological model. These data have been used to derive the rainfall intensity thresholds conditional on the antecedent saturation of soil quantifying the impact of such parameters on rainfall thresholds.

Landslide Potential Evaluation Using Fragility Curve Model

The geological environment of Taiwan mainly contains steep topography and geologically fragile ground surface. Therefore, the vulnerable environmental conditions are prone to landslides during torrential rainfalls and typhoons. The rainfall-induced shallow landslide has become more common in Taiwan due to the extreme weathers in recent years. To evaluate the potential of landslide and its impacts, an evaluation method using the historical rainfall data (the hazard factor) and the temporal characteristics of landslide fragility curve (LFC, the vulnerability factor) was developed and described in this chapter. The LFC model was based on the geomorphological and vegetation factors using landslides at the Chen-Yu-Lan watershed in Taiwan, during events of Typhoon Sinlaku (September 2009) and Typhoon Morakot (August 2009). The critical hazard potential (Hc) and critical fragility potential (Fc) were introduced to express the probability of exceeding a damage state of landslides under certain conditions of rainfall intensity and accumulated rainfall. Case studies at Shenmu village in Taiwan were applied to illustrate the proposed method of landslide potential assessment and the landslide warning in practice. Finally, the proposed risk assessment for landslides can be implemented in the disaster response system and be extended to take debris flows into consideration altogether.

Long-Term Monitoring of Slope Movements with Time-Domain Reflectometry Technology in Landslide Areas, Taiwan

The study employs time-domain reflectometry (TDR) technology for landslide monitoring to explore rock deformation mechanism and to estimate locations of potential sliding surfaces in several landslide areas, Taiwan, over ten years. Comparing to laboratory and field testing, sliding surfaces in landslide areas occurred mainly at two types, namely shear and extension failure. The TDR technology is used for field monitoring to analyze locations of sliding surfaces and to quantify the magnitude of the sliding through laboratory shear and extension tests. There are several TDR-monitoring stations in six alpine landslide areas in the middle of Taiwan for long-term monitoring. A relation between TDR reflection coefficients and shear displacements was employed for a localized shear deformation in the field. Furthermore, the type of a cable rupture for the TDR monitoring in landslides can be determined as shear, extension, or compound failure through the field TDR waveforms. Overall, the TDR technology is practically used for a long-term monitoring system to detect the location and magnitude of slope movement in landslide areas.

The Translatory Wave Model for Landslides

The Saint-Venant equations are usually the basis of numerical models for landslide flows. They are nonstationary and nonlinear. The theory for translatory waves in a prismatic channel and a funneling channel can be used for landslides using the assumption of either turbulent or laminar flow in the slide. The mathematics of translatory waves traveling over dry land or superimposed on another flow are developed. This results in a new slope factor controlling the flow velocity, together with the Chezy coefficient used in previous applications of the translatory wave theory. Flow times for the slide to reach a given destination, slide depth, and velocity can be calculated using the initial magnitude of the flow in the slide. The instabilities of the wave tail are discussed. Three case studies are presented: a submarine slide that started the Tohoku tsunami in Japan, the Morsárjökull rock avalanche in SE Iceland, and the Móafellshyrna slide in central N Iceland.

Translational Rock-Block Slides in a Tertiary Flyschoid Complexes of Southern Piedmont Region (North-West Italy)

The southern Piedmont Region (north-west Italy) is characterized by a hilly zone called “Langhe” that covers an area of about 2300 km2 and is bordered by Tanaro River at north and west, by Orba River at east, and by Apennine mountains at south. The Langhe is rolling hills famous for their excellent wine, populated by many small inhabited centers since ancient times. An idea of the Langhe geomorphology can be gained by studying the word “Langa”: it may have been derived from either “landa,” which means a wild and uninhabited place or from “lingua,” which means a strip of land. The morphology of the Langhe hills is characterized by asymmetrical valleys with steep south-east facing slopes and more gentle north-west facing slopes: their profile is defined “saw toothed” by local inhabitants. The asymmetric shape is clearly conditioned by the geology. Severe hydrological events occurred in the last 100 years in Piedmont in particular on May 1926, February and March 1972, February 1974, and November 1994. During these long rainy periods, on the gentler slopes, translational rock-block slides involve tertiary flyschoid complexes represented by rhythmic series of deposits with varied grain size. These landslides often damage or destroy buildings and roads, even if rarely claim human lives.

Techniques to Evaluate and Remediate the Slope Stability in Overconsolidated Clay

In this chapter, the origin and remediation of an important sliding in the overconsolidated Boom Clay in Kruibeke (Belgium) is discussed. Local and environmental factors caused an unstable slope about 30 m deep, A larger sensitivity to erosion resulted finally in the instability of the slope. Because of the formation of fine cracks in the soil there was a possibility for the water to penetrate in the clay close to the surface, resulting in the presence of higher water pressures. Also, the presence of the excavator on top of the slope during exploitation had an important impact on the stress state of the soil. Both an analytical and numerical approach were used to estimate the factor of safety. Because of the change of the soil characteristics, the factor of safety decreases, which can be estimated through a numerical analysis (using the Strength Reduction Method). This chapter also discussed the applied techniques for the remediation using numerical analysis. Also, the importance of the field test is discussed. An integrated approach, using numerical analysis and field tests in combination, is capable of predicting the instability. This approach can also be used to evaluate the stability of the slope after remediation.