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A landslide is the movement of rock, earth, or debris down a sloped section of land.

Earth Science, Geology, Geography, Human Geography, Physical Geography

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Morgan Stanley

A landslide is the movement of rock , earth , or debris down a sloped section of land. Landslides are caused by rain , earthquakes , volcanoes , or other factors that make the slope unstable . Geologists , scientists who study the physical formations of the Earth , sometimes describe landslides as one type of mass wasting . A mass wasting is any downward movement in which the Earth 's surface is worn away. Other types of mass wasting include rockfalls and the flow of shore deposits called alluvium . Near populated areas, landslides present major hazards to people and property. Landslides cause an estimated 25 to 50 deaths and $3.5 billion in damage each year in the United States.

What Causes Landslides?

Landslides have three major causes: geology , morphology , and human activity.

Geology refers to characteristics of the material itself. The earth or rock might be weak or fractured , or different layers may have different strengths and stiffness.

Morphology refers to the structure of the land. For example, slopes that lose their vegetation to fire or drought are more vulnerable to landslides. Vegetation holds soil in place, and without the root systems of trees , bushes , and other plants , the land is more likely to slide away.

A classic morphological cause of landslides is erosion , or weakening of earth due to water. In April 1983, the town of Thistle, Utah, experienced a devastating landslide brought on by heavy rains and rapidly melting snow . A mass of earth eventually totaling 305 meters wide, 61 meters thick, and 1.6 kilometers long (1,000 feet wide, 200 feet thick, and one mile long) slid across the nearby Spanish Fork River, damming it and severing railroad and highway lines. The landslide was the costliest in U.S. history, causing over $400 million in damage and destroying Thistle, which remains an evacuated ghost town today.

Human activity, such as agriculture and construction , can increase the risk of a landslide. Irrigation , deforestation , excavation , and water leakage are some of the common activities that can help destabilize, or weaken, a slope.

Types of Landslides

There are many ways to describe a landslide. The nature of a landslide's movement and the type of material involved are two of the most common.

Landslide Movement

There are several ways of describing how a landslide moves. These include falls , topples , translational slides , lateral spreads , and flows. In falls and topples, heavy blocks of material fall after separating from a very steep slope or cliff. Boulders tumbling down a slope would be a fall or topple. In translational slides, surface material is separated from the more stable underlying layer of a slope. An earthquake may shake the loosen top layer of soil from the harder earth beneath in this type of landslide. A lateral spread or flow is the movement of material sideways, or laterally. This happens when a powerful force, such as an earthquake, makes the ground move quickly, like a liquid.

Landslide Material

A landslide can involve rock, soil, vegetation, water, or some combination of all these. A landslide caused by a volcano can also contain hot volcanic ash and lava from the eruption . A landslide high in the mountains may have snow and snowmelt . Volcanic landslides, also called lahars , are among the most devastating type of landslides. The largest landslide in recorded history took place after the 1980 eruption of Mount St. Helens in the U.S. state of Washington. The resulting flow of ash, rock, soil, vegetation and water, with a volume of about 2.9 cubic kilometers (0.7 cubic miles), covered an area of 62 square kilometers (24 square miles).

Other Factors

Another factor that might be important for describing landslides is the speed of the movement. Some landslides move at many meters per second, while others creep along at an centimeter or two a year. The amount of water, ice , or air in the earth should also be considered. Some landslides include toxic gases from deep in the Earth expelled by volcanoes. Some landslides, called mudslides , contain a high amount of water and move very quickly. Complex landslides consist of a combination of different material or movement types.

Martian Landslide In December 2008, scientists announced that they had found evidence of the largest landslide ever. Because of a giant asteroid impact billions of years ago, the smooth northern hemisphere of Mars is sharply separated from the irregular southern highlands. Arabia Terra, a previously unexplained plateau between the two regions, is thought to have been formed by an enormous landslide immediately after the impact. The land mass that slid north to form Arabia Terra was the size of the entire United States!

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Settlements and slides: a large landslide case study from the Central Cordillera of the Philippines

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Gareth James Hearn , Jonathan Roy Hart; Settlements and slides: a large landslide case study from the Central Cordillera of the Philippines. Quarterly Journal of Engineering Geology and Hydrogeology 2019;; 53 (1): 62–73. doi: https://doi.org/10.1144/qjegh2019-050

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The Central Cordillera of Luzon in the Philippines is home to some of the most complex geology, active plate margin tectonism, heaviest rainfall and steepest terrain in the world. It also hosts a thriving agricultural community that has developed its agrarian, municipal and transport infrastructure in a landscape of marginal stability and extreme geomorphological sensitivity. The village of Pilando occupies a saddle on a prominent ridge where it is crossed by the Halsema Highway. As a result of landslide displacements, both the highway and the village have been subsiding for several decades and many dwellings have had to be abandoned. From topographical survey and visual observation, average rates of settlement vary between c. 0.1 and 0.4 m a −1 . The apparent depth and areal extent of ground movement are such that attempts to stabilize the area would be both impracticable and uneconomic. Realignment and relocation are options that might be considered but many adjacent slopes are unstable or have failed in the past and those that have not are highly sensitive to earthworks and drainage disturbance. Unfortunately, there are many areas of the Central Cordillera that are affected by similar slope instability problems. The interpretation of satellite imagery available on Google Earth, supported by geomorphological field observation, can assist in the delineation and assessment of these notably unstable areas for land use planning and slope management purposes.

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The effect of topography on landslide kinematics: a case study of the Jichang town landslide in Guizhou, China

  • Recent Landslides
  • Published: 10 January 2020
  • Volume 17 , pages 959–973, ( 2020 )

Cite this article

  • Jian Guo   ORCID: orcid.org/0000-0002-5586-1321 1 ,
  • Shujian Yi 2 , 3 ,
  • Yanzhou Yin 2 , 3 ,
  • Yifei Cui   ORCID: orcid.org/0000-0002-9559-5988 4 ,
  • Mingyue Qin 2 , 3 ,
  • Tonglu Li 1 , 5 &
  • Chenyang Wang 4  

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On July 23, 2019, a large-scale landslide occurred in Jichang town, Shuicheng County, Liupanshui City, Guizhou Province in China. The landslide, which moved along two gullies, resulted in strong punching-shear, induced scarping on vegetation and large destruction of houses, and finally formed a deposit with a volume of 2 × 10 6  m 3 . This research aims to understand the effect of topography on landslide kinematics. To achieve this aim, a detailed field investigation was first carried out with an unmanned aerial vehicle (UAV) aerial photography survey, resident interviews, and field sampling. The rainfall analysis indicates the effective rainfall within 7 days before landslides was 70.14 mm which exceeded the rainfall threshold of 54.3 mm in this region, which finally triggered the landslide. Traditional soil mechanic tests were then performed to identify the soil properties of the source material. Combined with numerical simulation using the nonlinear shallow water equation, the whole process of landslides was divided into four stages: instability stage, acceleration stage, transformation stage, and impact and accumulation stage. The simulations results show the landslide block slid with a low velocity of 8 m/s for about 100 m. Then, Froude number of landslide increases from 2 to 3 when passing the high and steep terrain, indicating that landslide change to inertial dominated with potential same Froude behavior of classic debris flow. The rupture mass slid with the peak velocity of 23 m/s and diverged in two gullies and ran out for about 600 m. The maximum velocity is 23 m/s in east gully while only 15 m/s in west gully. Compared with deep and incised valleys in the west, shallow and straight valley in the east decreases the deposit depth and further increases the velocity of landslide material with increased runout distance. This research may provide a fast flow path of back analyzing geo-hazards on complex terrain and serve as a basis for future research on long runout landslides.

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The study here is funded by the National Natural Science Foundation of China (41790434) and the Chinese Academy of Sciences (XDA23090401), as well as the Major International (Regional) Joint Research Project (No. 41520104002), the Key Research Program of Frontier Sciences, CAS (QYZDY-SSW-DQC006), and the National Key R&D program of China (No. 2017YFC1501302).

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Department of Geological Engineering, Chang’an University, Xi’an, 710064, China

Jian Guo & Tonglu Li

Key Laboratory of Mountain Surface Process and Hazards/Institute of Mountain Hazards and Environment, Chinese Academy of Sciences, Chengdu, 610041, China

Shujian Yi, Yanzhou Yin & Mingyue Qin

University of Chinese Academy of Sciences, Beijing, 100049, China

State Key Laboratory of Hydroscience and Engineering, Tsinghua University, Beijing, 100084, China

Yifei Cui & Chenyang Wang

Water Cycle and Geological Environment Observation and Research Station for the Chinese Loess Plateau, Ministry of Education, Zhengning, 745399, China

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Guo, J., Yi, S., Yin, Y. et al. The effect of topography on landslide kinematics: a case study of the Jichang town landslide in Guizhou, China. Landslides 17 , 959–973 (2020). https://doi.org/10.1007/s10346-019-01339-9

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Received : 19 October 2019

Accepted : 18 December 2019

Published : 10 January 2020

Issue Date : April 2020

DOI : https://doi.org/10.1007/s10346-019-01339-9

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Landslides are generated by natural causes and by human action, causing various geomorphological changes as well as physical and socioeconomic loss of the environment and human life. The study, characterization and implementation of techniques are essential to reduce land vulnerability, different socioeconomic sector susceptibility and actions to guarantee better slope stability with a significant positive impact on society. The aim of this work is the bibliometric analysis of the different types of landslides that the United States Geological Survey (USGS) emphasizes, through the SCOPUS database and the VOSviewer software version 1.6.17, for the analysis of their structure, scientific production, and the close relationship with several scientific fields and its trends. The methodology focuses on: (i) search criteria; (ii) data extraction and cleaning; (iii) generation of graphs and bibliometric mapping; and (iv) analysis of results and possible trends. The study and analysis of landslides are in a period of exponential growth, focusing mainly on techniques and solutions for the stabilization, prevention, and categorization of the most susceptible hillslope sectors. Therefore, this research field has the full collaboration of various authors and places a significant focus on the conceptual evolution of the landslide science.

1. Introduction

Landslides are disasters that cause damage to anthropic activities and innumerable loss of human life globally [ 1 ]. Mass movement processes cause significant changes in the Earth’s relief, causing economic losses due to landslides in mountainous areas with a dense population [ 2 , 3 ], and even in the direct and indirect cost of buildings or infrastructure on an urban scale [ 4 , 5 , 6 ].

In the evolution of the reliefs, landslides are considered to be intrinsic processes, and among other dynamics, they favor the formation of valleys [ 7 ], and the contribution of river sediments and ecological renewal. The degree of physical, biological and chemical weathering, earthquakes, and extraordinary rains (among other natural processes) can cause slope instability [ 8 , 9 ].

Landslides have caused costly damage and loss of life worldwide, yet the most devastating disasters occur in developing countries [ 10 ]. Therefore, the implementation of techniques to reduce geological risks and natural vulnerability is essential for developing disaster prevention and mitigation strategies on various scales [ 11 , 12 , 13 , 14 ].

This research field has different approaches and objectives that have evolved over the last decades [ 15 ]. Some studies have been based on satellite images in remote sensing [ 16 ], geomorphological mapping [ 17 , 18 ], its relationship with earthquakes [ 9 ], continuous monitoring of places susceptible to landslides [ 19 , 20 ], triggering of landslides due to extraordinary precipitation events [ 21 , 22 , 23 ] and various methods for stabilizing slopes [ 24 , 25 ].

There are other studies of a preventive nature, such as real-time warnings of landslides due to the action of rains in winter [ 26 ] and in unsaturated areas above the water table [ 27 ], which are of great support for adequate management of these disasters. The consequences caused by landslides (centralized in an environmental and socioeconomic framework) show that their impacts have greater intensity in areas with higher population density [ 28 ]. Across the world, there is a great number of landslides that have affected the population from cold, temperate and tropical regions [ 13 , 29 , 30 , 31 , 32 , 33 , 34 , 35 ].

According to the United States Geological Survey (USGS), the material involved in a landslide and its type of mass movement is a significant basis for the classification of landslides [ 36 ]. Therefore, given the internal mechanics that predominates in mass movements, the landslides are classified as: falls, topples, slides, spreads, and flows ( Figure 1 ).

An external file that holds a picture, illustration, etc.
Object name is ijerph-18-09445-g001.jpg

Classification scheme based on the literature review of the USGS landslide manual. Source: [ 36 ].

The academic field of landslides is broad, where some researchers have made efforts to understand their structure [ 37 ], addressing literature reviews [ 11 ] and their classification [ 36 , 38 , 39 ], as well as the bibliometric analysis of various landslide concepts through the Science Citation Index-Expanded (SCIE) and Social Sciences Citation Index (SSCI) databases (1991–2014) [ 13 ]. Over time, various studies have been carried out regarding landslides, but very few have highlighted their structure and intellectual growth. Therefore, a new bibliometric study would allow a new approach to its structure and updates on its different research scopes.

The use of bibliometric methods is considered for the analysis of scientific activity in an academic field. Derek J. de Solla Price initially exhibited the bibliometric analysis in 1965 [ 40 ]. The proposal focuses on the quantitative evaluation of an academic field of study by analyzing its structure, characteristics and existing relationships, which allows examining its behaviour between the disciplines of a specific field of study [ 41 , 42 ]. The bibliometric analysis allows identifying research areas (current and future) and the analysis of their multidisciplinary production, achieving a more systematic comprehensive evaluation in the field of study [ 43 , 44 ].

Due to the above, the research question arises: How has the intellectual/conceptual structure of the various types of landslides developed over time?

The present study aims to evaluate the intellectual structure of the landslide through performance analysis and bibliometric mapping to determine the development, patterns and trends of its scientific structure. Thus, to analyze the scientific production and intellectual structure of the field of study, managing to provide a transparent, updated, reliable and high-quality study for its transdisciplinary use.

This study has been structured in five sections, starting with an introductory framework of the problem, highlighting its objective and investigative question to support at the end of this work, followed by Section 2 , in which the materials and the implemented methodology are described (three phases: research criteria and source identification, software and data extraction, and data analysis and interpretation). Section 3 represents the results and their analysis, to later be discussed in Section 4 and, finally, Section 5 concludes with the scientific trends of this research field.

2. Materials and Methods

A systematic review allows an exploration of the intellectual territory of existing studies in the face of a problem raised, evaluating the contributions and synthesizing the data obtained to provide reliable knowledge of a particular field of study [ 45 , 46 ]. This exhaustive and rigorous procedure is similar to the protocol presented in the bibliometric analysis [ 47 , 48 ].

The bibliometric analysis allows evaluating the scientific production of journals [ 49 , 50 ] or understanding the intellectual structure of various fields of knowledge such as management [ 51 , 52 , 53 ], environment [ 54 , 55 , 56 ], natural science [ 57 ] and health [ 58 ]. Employing analytical techniques that allow an exploration of the tendencies of investigation and interpretation of new perspectives in the investigative field [ 59 , 60 ].

The methodology proposed in this work is shown in Figure 2 . Its structure comprises three phases that allow the proposed bibliometric analysis to be carried out: (i) Research criteria; (ii) reprocessing of data and software; and (iii) analysis and interpretation of data.

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Bibliometric research methodology applied in this study.

2.1. Phase I. Research Criteria and Database Use

For this research, a bibliographic search of the classification of landslides was established based on the internal mechanics of the mass movement. These requirements are encompassed by the USGS, which establishes a classification according to the internal mechanics present in landslides, such as fall, topple, slide, spread and flow [ 36 ]. The selection of these terms allows the compilation of the base documents to be considered in this study.

The selection of documents should be made based on choosing a reliable, quality database with comprehensive coverage. The databases used for bibliometric studies are the Web of Science and Scopus, which differ in volume of information, journal coverage and subject areas [ 61 ]. The Scopus database was selected due to its comprehensive coverage in years, journals in various areas of knowledge [ 62 , 63 , 64 , 65 ], an intuitive search system, easy data download and high-quality standards [ 66 , 67 ], which allows a more precise bibliometric evaluation in the domain of any subject to be analyzed.

The search carried out in Scopus focuses on the titles of the publications that contain the term “landslide” with the terms of: fall, fall, slide, spread and flow. The search topic is as follows: (TITLE (fall*) OR TITLE (topple*) OR TITLE (slide*) OR TITLE (spread*) OR TITLE (flow*) AND TITLE (landslide*)).

The landslide research field is vast, so it is necessary to obtain more exact results and synthesize the study approach; therefore, the search in Scopus focuses only on the title of the publications with the previously established terms [ 68 , 69 ]. In this way, a total of 661 publications were obtained, to which inclusion criteria such as all types of document, language, years and study area were applied [ 13 ], in addition to an exclusion criterion such as the year 2021 (year still in progress), obtaining a final database of 641 documents.

2.2. Phase II. Data and Software Reprocessing

The selected records are downloaded in csv format (comma separated values) from the Scopus database for analysis using the Microsoft Excel software from Office 365 ProPlus [ 70 ]. Since the downloaded database contains miles of data from various variables (e.g., authors name, document title, year, keywords, abstracts, among others), a review and cleaning of the data is required to ensure precision in analysis results [ 71 , 72 ]. Cleaning consists of eliminating duplicated values, incomplete or erroneous records that cannot be completed manually [ 73 ]. A total of 9 deleted records and 632 documents to be analyzed were established.

The new csv files were entered in VOSviewer, an open access and reliable software that allows the construction and visualization of bibliometric networks in various fields of study, allowing a comprehensive bibliometric mapping in any research branch [ 74 , 75 ]. This software allows an analysis of the structure of the research field through co-occurrence [ 76 ], co-citations [ 77 , 78 , 79 , 80 ], and bibliographic coupling [ 81 ]. This software has been used in different scientific areas such as: sustainability [ 82 ], natural and cultural resources [ 83 ], geosciences [ 55 , 84 ], medicine [ 76 ] and the circular economy [ 85 ], among others. Its analysis is carried out only for articles in English, obtaining a total of 354 documents.

2.3. Phase III. Data Analysis and Interpretation

The results were examined using the two classic approaches to bibliometric analysis: Performance Analysis and Science Mapping [ 42 , 86 ].

  • Performance analysis allows an evaluation of its scientific production (authors, countries, journals) and its scientific impact [ 87 , 88 ];
  • sciences mapping allows the graphic representation of the cognitive structure of the study field and its evolution [ 41 , 89 ]. It is considered to apply a triangulation method that allows an analysis of this structure by examining its micro (keywords), meso (articles and authors) and macro (journals) components [ 90 ].

3.1. Performance Analysis

3.1.1. scientific production.

From 1952 to 1990 ( Figure 3 ), landslides have been analyzed from a descriptive perspective, considering the internal mechanics and the mass movement type that is generated according to the lithology and the material involved [ 91 , 92 , 93 ]. Its leading causes are determined, such as the hydraulic gradient and earthquakes [ 94 , 95 , 96 , 97 ]. There is also the beginning of geotechnical and geomorphological studies and the elaboration of models to understand the internal mechanics of the different triggered landslides [ 93 , 98 , 99 ]. Given this analysis, this period is considered to be the beginning of studies that will be the basis for further research.

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Growth of scientific production of landslides.

Figure 3 shows a progressive growth in 1990–2020, determining three different periods that frame the studies.

Period I (1990–2000) focuses on researches related to the debris flows, managing to generate models for the understanding and prediction of landslides, and the volume of material deposited in a sector [ 100 , 101 ]. It considers different aspects such as the mechanical process of mass movement [ 102 , 103 ], data in the field (rainfall, vegetation cover, slope inclination, distance, elevation), coefficient of internal friction, among others [ 104 , 105 , 106 , 107 ]. This period is the basis for continuous studies and analysis of future landslide models.

In period II (2001–2010), the exponential research growth and a significant focus on the classification of landslides is observed. These classifications focus on the area of engineering and speed of landslide for the elaboration of physical models [ 108 ], considering the material involved (gravel, sand, silt and clay) and its variations (debris, earth and mud, peat and rock), thus managing to formalize definitions that allow identifying the present types of landslides [ 109 , 110 , 111 , 112 ]. In 2008, a relevant study to the global analysis of rainfall was presented, which made it possible to study rainfall and its influence on shallow landslides and debris flows [ 113 ]. These studies are the basis of all landslide warning systems throughout the world [ 114 , 115 , 116 ]. From this, the mathematical prediction models have been considered of great importance worldwide, calculating and predicting the trajectory, speed and depth that landslides would have [ 117 , 118 , 119 ].

Finally, period III (2011–2020) focuses on the improvement and combination of different numerical models, managing to represent the reality of the environment and the mechanical behavior of the landslides for their respective analysis in field and risk assessment [ 120 , 121 , 122 , 123 ]. In this way, at the end of this period, these investigations and improved models allow us to understand the behavior of different landslides types [ 124 , 125 , 126 ]. In addition, the geomorphological, tectonic and hydrodynamic processes involved in mass movement processes were explained in detail [ 127 , 128 ]. Different experimental research was conducted considering the pressure of the pore fluid, type of grain, rainfall and a large amount of on-site and laboratory investigations, assuring the validity of the results [ 129 , 130 , 131 , 132 , 133 , 134 ].

3.1.2. Language and Types of Documents

In the areas of knowledge related to Life Science and Earth Science, the English language is predominant [ 135 ]. Landslide is no exception; despite presenting studies in 15 languages, 81.8% of its studies are written in English. This predilection for language is due to its relevance in scientific communication as there is an overrepresentation of English-speaking journals, and it is the common nexus for international collaboration [ 136 , 137 ]. The second language is Chinese (13.45%), due to its high national collaboration on topics of debris flow and flow-type landslides in national indexed journals (e.g., Yantu Lixue/Rock and Soil Mechanics, Yanshilixue Yu Gongcheng Xuebao/Chinese Journal of Rock Mechanics and Engineering, Journal of Natural Disasters).

Another characteristic of landslide studies is that they mostly constitute journal articles (74%) since these documents are considered certified knowledge, as they are examined by peer reviewers who have expertise in the field of knowledge [ 138 ]. Other types of documents are shown in Figure 4 .

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Types of scientific publications.

3.1.3. Contribution by Country

The analysis of the contribution of the countries allows us to understand their relationships in knowledge generation [ 87 ]. This product is developed by the collaboration of 64 countries (see Figure 5 ), in which most of the research is related to developed countries. The map was generated through ArcMap 10.5 software, using data from the authors’ affiliations.

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Contribution by countries, world map.

China has the most significant academic contribution on landslides ( Figure 5 ), collaborating with 47 countries, especially Italy, the United Kingdom and the United States. The contributions with Italy are related to numerical modelling in the propagation of flow-like landslides [ 139 , 140 , 141 ]. Concerning the United Kingdom, studies focus on modelling debris flow and submarine landslides and as a flow influenced by precipitation, earthquakes, or tectonic movements, e.g., [ 142 , 143 , 144 ]. The third international partner, the United States, focuses on landslide monitoring and numerical modelling based on the smoothed particle hydrodynamics (sph) method, e.g., [ 145 , 146 , 147 ]. China has experienced sustained economic growth over the last 30 years, allowing broad knowledge development in various academic fields [ 148 ].

In Italy, as the second country with more contributions in the analyzed topic, representative authors such as Guzzetti F., Cuomo S., Cascini L., Sorbino G., Crosta G.B. present studies focused on numerical modelling, the application of sph and GEOtop-FS, run-out analysis and trigger factors in shallow landslides and debris flows [ 117 , 118 , 119 , 149 , 150 ]. Japan is the third country with a scientific contribution, with authors such as Imaizumi F., Sassa K., Wuang G. who highlight the effects of landslides and shallow landslides as a consequence of deforestation, groundwater flow, earthquakes, rainfall and flow path [ 151 , 152 , 153 , 154 , 155 ]. Other countries contributing in this area can be observed in Figure 5 .

3.2. Bibliometric Mapping Analysis

The construction of bibliometric maps, depending on what is established in the methodology. Only articles and the English language are considered given their broad domain in various areas of knowledge [ 156 , 157 ].

3.2.1. Co-Occurrence Author Keyword Network

This type of analysis allows visualizing the study area (its history and evolution) and its possible trends [ 158 , 159 , 160 ].

Figure 6 shows the co-occurrence network of author keywords, where 25 nodes (represents each author-keyword with at least four co-occurrences) and four clusters (groupings of nodes of the same color) are observed [ 161 ]. The figure allows a visualization of the intellectual structure of landslides to be examined in greater detail.

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Visualization of the co-occurrence network by assigning a representative color for each cluster. Red color (shallow landslide), green color (flow like landslide), blue color (debris flow) and yellow color (landslide).

Cluster 1 (red color) shows studies of landslides caused by precipitation and pore pressure in the subsoil studied, due to the topography and water flow caused by rainfall [ 94 , 115 , 162 , 163 , 164 ]. These studies were carried out based on: (i) post-failure in deposits of colluvial, weathered and pyroclastic origin [ 118 ]; (ii) simulation of the probability of occurrence in hydrographic basins using GEOtop-FS [ 117 ]; (iii) the quantification of morphology and hydrological conditions [ 165 ]; and (iv) an evaluation of susceptibility and slope stability for landslide prevention [ 166 ]. Other studies reflect the slope instability that can cause significant hazards, mainly influenced by the deposit type, the rapid flows generated by seismic movements [ 167 , 168 , 169 ], large-scale deforestation [ 170 ], groundwater fluctuation, and different triggering scenarios [ 132 , 171 ].

Studies focusing on this cluster have led to improved mapping, understanding, interpretation and prediction of landslides, such as the movement direction through the hydraulic gradient [ 172 ], the influence of rainfall, soil saturation [ 125 , 173 ] and continuous monitoring for preventive decisions in potential hazardous landslides [ 174 ].

Cluster 2 (green color) focuses on landslides with a non-Newtonian flow behavior, demonstrated through numerical modelling, geological study and its geodynamic behavior [ 121 , 175 , 176 , 177 ]. These movements and trajectories are influenced by different factors such as: (i) rheology and topography [ 139 ]; (ii) hydrometeorological events such as heavy rainfall [ 113 , 178 ]; (iii) soil saturation in gravelly and sandy materials [ 178 ]; (iv) pore pressure impact caused by earthquakes [ 155 , 179 , 180 ]; and (v) the frontal plowing phenomenon [ 140 ]. These landslides have a natural, rapid and irregular behavior with devastating dynamics. This cluster provides the scientific community with resources to understand flow-like landslides through numerical and 3D models [ 181 ]. Models considering the smoothed particle hydrodynamics (SPH) [ 77 , 182 , 183 , 184 ] and the use of satellite images using methods such as InSAR [ 185 , 186 , 187 ]. These studies have allowed the modelling of submarine landslides [ 188 , 189 ] and landslides in landfills caused by seismic action [ 182 ]. In addition, they facilitate the affected area mapping and evaluate the intensity of the danger for the planning of adequate risk management [ 190 ].

Cluster 3 (blue color), these landslides can be generated by: (i) earth rubble and intense added rainfall [ 131 , 191 ] or when they come in contact with the mainstream [ 116 ]; (ii) failures in the landslide dam [ 192 , 193 ]; and (iii) the material traction on a slope, liquefaction or even due to temperature changes [ 105 ]. For its understanding, various experiments were carried out, such as the use of differential equations for the dynamics of the system [ 129 ], analysis of the theory of the critical state in the mobilization of debris flows due to the increase in the basal pressure of pores [ 194 ], and the generation of dynamic models to understand the evolution of the system [ 112 ]. For a further understanding of debris flow, maps used that are supported by Geographic Information Systems (GIS) [ 195 , 196 ], geophysical studies [ 197 ] and statistical methods such as logistic regression (LR) [ 198 , 199 ] and Multivariate Adaptive Regression Splines (MARS) were explored [ 200 ], allowing us to understand the formation or prevention of landslide dams [ 201 , 202 , 203 ] and debris flows, which can also be generated by shallow landslides, which are identified through susceptibility mapping [ 124 , 204 , 205 ].

Cluster 4 (yellow color), covers the topics written in other clusters given its great diversity or classification [ 36 ]. Its studies focus on numerical simulations for the understanding and prediction of landslides [ 206 , 207 , 208 ], which allows an understanding of the groundwater flow affectation [ 209 , 210 ], the infiltration of water by rainfall [ 211 , 212 ] and wave propagation (tsunamis) due to the collapse of slopes in bodies of water [ 181 , 213 ]. Recently, scientific contributions regarding landslides have been present. Multiphase flow models present submarine landslides, especially on the type and size of particles (rheology) [ 188 ]. Regarding groundwater or what is percolated by high rainfall, it is considered in Critical Rainfall Threshold (CRT) analysis, monitoring system by video camera systems and the generation of two-dimensional mathematical models by the finite difference method [ 214 , 215 , 216 ].

3.2.2. Co-Citation Analysis

Co-citation analysis is one of the most widely used methods in bibliometric analysis [ 41 ]. It allows us to explore the relationships between documents, to know the knowledge base and the intellectual structure of a field of study [ 217 , 218 ]. Co-citation analyzes the number of times two documents are co-cited by another subsequent document [ 79 ]. When frequently cited in other publications, documents show a close relationship, which allows us to consider that they belong to the same field of research [ 219 , 220 ]. However, this relevance does not imply that the ideas shared by the various authors coincide with each other [ 221 ].

In this work, two co-citation methods are used: author co-citation analysis and Journal co-citation analysis, which are presented below:

Author Co-Citation Analysis (ACA)

This analysis is an adaptation of work by H. Small [ 79 ], done by White and Griffith [ 222 ] using the authors of the papers. ACA considers that by citing two authors more frequently in several papers, it is very likely that their fields of research are similar [ 223 ]. This makes it possible to discover the co-citation groups of reference authors that make up the knowledge base of the intellectual structure studied [ 73 , 224 ]. Furthermore, it allows the discovery of the academic community linked to confirming this knowledge base [ 225 ].

Figure 7 shows this co-citation network of authors. Its construction is carried out with the VOSviewer software version 1.6.17, which uses a proprietary technique called VOS to allow a grouping of the units of analysis using similarities [ 74 ]. The nodes represent the authors’ names, which may represent topics, schools of thought or specialties [ 226 ]. The structure presents six clusters, with 235 authors possessing more than 20 co-citations.

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Visualization of the co-citation network assigning a representative color for each cluster. according to the number of interconnected authors. Red, green, blue, yellow, purple and light blue (in order of highest importance by VOSviewer software version 1.6.17).

Cluster 1 (red color) consists of 60 authors. The studies in this cluster focus on the research area of shallow landslides and debris flow influenced by rainfall or hydrological triggers [ 227 , 228 , 229 ]. These authors include Guzzetti F. (157 co-citations), in studies related to precipitation and shallow landslides [ 113 , 230 ]; Crosta G.B. (128) in numerical modelling and debris flow [ 231 , 232 ]; and Godt J.W. (107), in map generation and modelling of shallow landslides for landslide risk prevention and assessment [ 233 , 234 ].

Cluster 2 (green color) has 44 authors. This cluster has studies focused on the internal mechanics of landslides and debris flows, and the factors that affect the movement or detachment of material [ 235 , 236 , 237 , 238 , 239 ], in addition, it considers the run-out analysis of rock and soil slides [ 121 , 240 , 241 ]. These research topics are cover by various authors such as Sassa K., Xu Q and Wang G. with 131, 97 and 90 citations.

Cluster 3 (blue color) consists of 39 authors, some of the authors, such as: Pastor M. (126), consider the stabilization of slopes using models [ 119 , 242 , 243 , 244 ], while Cascini L. (122) and Evans S.G. (115), focus on modelling and studies regarding debris flow [ 245 , 246 , 247 , 248 , 249 , 250 ].

Cluster 4 (yellow color) is distant from the rest of the clusters, located at the extreme right of Figure 7 . This cluster comprises 37 authors, such as Masson D.G. (79 co-citations) and his studies in the underwater landslides are influenced by groundwater [ 251 , 252 , 253 ]. Grilli S.T. (49) and Hager W.H. (46) focus on the generation of modelling and numerical simulations linked to the movement of underwater masses and subsequent tsunamis [ 254 , 255 , 256 ].

Cluster 5 (purple color) is in the central part of the structure and has 32 authors, such as Hungr O. (259), who researches runout analysis and the generation of models for risk assessment [ 257 , 258 , 259 ]. Iverson R.M. (248) and Reid M.E. (77) focused on the study of debris flow and hydrological factors such as groundwater hydraulics [ 260 , 261 , 262 ].

Cluster 6 (light blue color) has 23 authors, such as Takahashi T. (73), Rickenmann D. (61) and Sidle R.C. (61), where the topics of interest highlight the study and analysis of debris flow [ 263 , 264 , 265 ].

Journal Co-Citation Analysis (JCA)

This analysis considers the relevance and similarity of journals in a field of study to reveal the intellectual structure [ 225 , 266 ]. JCA studies the number of times two journals are co-cited by another journal, revealing the various research fields that make up the intellectual structure [ 67 , 267 ].

Figure 8 shows this co-citation network of journals. The VOSviewer software version 1.6.17 is used to construct and visualize the connections between the various journals represented by nodes. This network shows 69 journals with at least 20 co-citations displayed in four clusters.

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Visualization of the co-citation network assigning a representative color for each cluster (topics) and nodes (journals). According to the structure built using the VOSviewer software version 1.6.17. The colors red, green, blue and yellow appear in order of importance.

Cluster 1 of red color consists of 20 journals with 1239 citations, in which the following stand out: “Journal of Geophysical Research” in the category of Agricultural and Biological Sciences, Earth and Planetary Sciences, and Environmental Science; the “Journal of Fluid Mechanics” in Physics and Astronomy; and the “Journal of Hydraulic Engineering” in Environmental Science. The latter converge in the category of Engineering.

Cluster 2 (green color) contains 20 journals and 3526 citations, focusing mainly on the category of Earth and Planetary Sciences, such as the journals of: “Engineering Geology”, “Geomorphology” and “Landslides”.

Cluster 3 (blue color) focuses on the Earth and Planetary Sciences category and consists of 17 journals with 622 citations such as: “Marine Geology”, “Geological Society of America Bulletin” and “Geology”.

Cluster 4 (yellow color) has 12 journals and 834 citations, such as “Canadian Geotechnical Journal”, in the Engineering category, and “Environmental and Engineering Geoscience”, which have a focus on Environmental Sciences. These are intertwined with the “Geotechnique” journal in the Earth and Planetary Sciences category, reflecting the interconnection with the other clusters in Figure 8 .

4. Discussion

This study shows a consistent increase in scientific research on a landslide, thanks to the contribution of 64 countries spread over five continents ( Figure 5 ), in 15 languages, mostly in scientific articles and in the English language.

During the 90s, scientific production entered an introductory period, where Iverson R.M., Crosta G., and other authors contributed to the scientific community with the results of their analyses and studies (theoretical, laboratory and field) on the dynamic behavior of debris flows and landslides [ 101 , 105 ]. According to the Scopus database, this scientific production has experienced considerable growth since 2001 (representing 90.2% of publications).

In the decade 2001–2010, scientific research increased ( Figure 3 ), prioritizing the update of old studies such as the global rainfall threshold [ 113 ], the classification of landslides [ 109 ] and the generation of models [ 117 , 119 ], which in this period are essential for understanding and preventing landslides. Over the last decade (2011–2020), the increase in its scientific production has been stable, improving the development and combination of models generated in the previous period [ 125 , 126 ]. In this way, the analysis of landslides and the dynamic behavior of the debris flow, shallow landslides and their movement as a flow was perfected ( Figure 6 ).

The analysis of the intellectual structure of this field of study is conducted through three scientific maps:

In the analysis of co-occurrence of authors keywords, the application of geographic information systems (gis) and numerical simulations are a means for the study and analysis of landslides, debris flow and flow-like landslides, e.g., [ 184 , 213 ]. The sph (smoothed particle hydrodynamic) method is also part of this type of analysis, in conjunction with implementing sector rheology, e.g., [ 149 ]. Numerical models are the most common method for analyzing the main issues in each cluster, focusing on modelling, erosion, slope stabilization and rainfall among others, for such study, e.g., [ 174 ].

Secondly, the author co-citation analysis allows an observation of the interconnections that the various authors have in the entire landslide field ( Figure 7 ), which has international collaboration mainly from countries in Asia, Europe and North America ( Figure 5 ). One of the main topics of study is the shallow landslides, which since 1988 has focused on the analysis of propagation and transformation in debris flows [ 268 ]. This issue is related to the duration and intensity of rainfall analyzed by Guzzetti, et al., (2008) [ 113 ]. The authors characteristic of this analysis, such as Sassa (green cluster), Hungr (purple cluster), Takahashi (sky cluster), Guzzetti (red cluster), among others ( Figure 7 ), focus on the main hydrological and hydraulic, seismic and geomechanical factors causing the shallow landslide, debris flow, and consequently, the development of numerical models for risk prevention and assessment [ 229 , 232 , 234 , 235 , 238 , 241 , 264 , 265 , 269 ]. These topics are related to the red and blue clusters in Figure 6 .

In addition, the existence of small groups that are isolated from those previously mentioned is observed, which we detail below: (a) the group of Pastor, Cascini and Evans (blue cluster, Figure 7 ), they analyzed issues related to landslide dams, erosion, the susceptibility and stabilization of slopes referring to debris flows (blue cluster, Figure 6 ) [ 244 , 250 ], which is done through simulations [ 243 , 245 ] and mathematical models (e.g., smoothed-particle hydrodynamics—SHP [ 119 , 245 ]). (b) Masson, Grilli and Hager’s group (yellow cluster, Figure 6 ) study the action of groundwater and its influence on mass movement (underwater and on the surface), which can trigger the generation of tsunamis or the propagation of landslides such as flows, which can be analyzed using models and numerical simulations [ 251 , 254 , 255 , 256 ]. These topics are closely related to the green and yellow clusters ( Figure 6 ).

Third, in the journal co-citation analysis ( Figure 8 ), the red cluster is observed with a broad domain about the rest of the clusters in the categories of: Engineering, Agricultural and Biological Sciences, Physics and Astronomy, Earth and Planetary Sciences, and Environmental Science. Another field of study is that of Earth and Planetary Sciences (green and blue cluster, Figure 8 ), focusing on the hydraulic and geotechnical properties of the material and its formation environment (geological and geomorphological) [ 270 , 271 , 272 ]. The green and blue clusters are intertwined with the yellow cluster (Earth and Planetary Sciences, Figure 8 ), focusing on understanding landslides, improving the models in the assessment, and their classification [ 273 , 274 , 275 ]. Instead, given the diversity of the landslide science representing the red cluster ( Figure 8 ), it focuses on the behavior of the landslide, similar to that of a flow and the engineering analysis of the mechanical and hydraulic characteristics of the material [ 276 , 277 , 278 , 279 , 280 ]. This study is related to the group of authors Masson, Grilli and Hager (yellow cluster, Figure 7 ).

In this way, the entire intellectual structure and its topics of interest are analyzed, such as shallow landslide, debris flow, landslide and flow like landslide ( Figure 4 ), which cover the five classifications made by the USGS (fall, topple, slide, spread, and flow) ( Figure 1 ) [ 36 ].

5. Conclusions

This work analyses the scientific production of the research field of landslides, according to the classification addressed by the USGS. It allows an exploration and analysis of the intellectual structure of 632 publications from the Scopus database, which is feasible for a bibliometric study. When performing the performance analysis, its constant evolution is visualized between 1952–2020 ( Figure 3 ), with a significant increase in the last 20 years. The 74% corresponds to scientific articles ( Figure 4 ), the majority of which are in English. The scientific contribution is concentrated in 64 countries, led by China ( Figure 5 ).

The debris flow is a type of landslide generated by various causes, such as precipitation and collapse of landslide dams. This field of study analyzes the material’s hydraulics, geodynamics and geological properties in the face of hydrometeorological and seismic events, which are an essential part of the propagation of landslides with a flow behavior and subsequent generation of debris flow ( Figure 6 ). Some authors present studies related to the subject, such as Guzzetti F., Crosta G.B., Godt J.W., Sassa K. and Wang G., among others (see Figure 7 ).

The shallow landslide is an area of study supported since 1980 by Nel Caine and by Guzzetti et al., 2008, who analyze this type of landslides as a consequence of the duration and intensity of rains. This research area is in a period of growth. Therefore, it links the material’s hydrological processes and hydraulic conditions as its main triggering factors. Therefore, the implementation of numerical models for slope stabilization and risk prevention enhances their importance ( Figure 6 ). In addition, the group of co-cited authors, such as Guzzetti, Crosta and Godt (red cluster, Figure 7 ), analyze a large part of these landslides, which may be the basis for understanding debris flow formation and other types of landslide.

It is essential to mention that the intellectual structure of this research field made it possible to point out or list topics of interest that can increase scientific knowledge of this subject, such as:

  • The analysis of the hydraulic properties and the circumstances by which landslides can be generated as a flow;
  • a deeper analysis in the study of shallow landslides and their propagation in debris flow and flow-like landslides;
  • analysis of landslides from the point of view of rheology, focusing on the movement of materials caused by earthquakes and rainfalls, among others;
  • generation of models through the Smoothed-Particle Hydrodynamics (SPH) method, which has been widely used for cases such as debris flow, shallow landslides, and other types of mass movements such as flows;
  • implementation of satellite images in the areas of the different landslides, where the most widely implemented methods are: Interferometric Synthetic Aperture Radar (InSAR), Unmanned Aerial Vehicle (UAV), and Geographic Information System (GIS);
  • stabilization studies in landslide dams, which can be caused by rainfalls and subsequent generation of debris flow;
  • a technical and geological analysis on topics related to submarine landslides, among which run-out analysis and the propagation of tsunamis due to landslides and earthquakes stand out, this being an area of study that is evolving.

We consider that this study is a contribution to the academic literature due to: (i) The possibility of getting to know different researchers in specific topics of this field of study, which allows the establishment of collaboration networks; (ii) to know the experiences validated by the different authors, using techniques and methods of study that enrich scientific knowledge; and (iii) the study serves as a guide for novice researchers who wish to know in brief outlines this general structure of knowledge.

Finally, there are some limitations to this work: (a) restriction due to the classification of landslides, only to the contribution of the USGS; and (b) the use of the database (Scopus), without considering other existing bases in the academic world such as the Web of Science or Dimensions. Considering these limitations, future research is estimated using different databases and other classifications related to landslides.

Acknowledgments

This research study was possible with the valuable contribution of the “Registry of geological and mining heritage and its impact on the defence and preservation of geodiversity in Ecuador” academic research project by ESPOL University under grant nos. CIPAT-01-2018, the support of NOVA Science Research Associates and Geo-resources and Applications GIGA, ESPOL.

Author Contributions

Conceptualization, P.C.-M., N.M.-B., A.Q.-R., F.M.-C. and B.A.-M.; methodology, P.C.-M., N.M.-B., F.M.-C. and B.A.-M.; software, N.M.-B. and B.A.-M.; validation, N.M.-B. and B.A.-M.; formal analysis, P.C.-M., N.M.-B., A.Q.-R., F.M.-C. and B.A.-M.; investigation, P.C.-M., N.M.-B., A.Q.-R., F.M.-C. and B.A.-M.; data curation, N.M.-B. and B.A.-M.; writing—original draft preparation, P.C.-M., N.M.-B., A.Q.-R., F.M.-C. and B.A.-M.; writing—review and editing, P.C.-M., N.M.-B., A.Q.-R., F.M.-C. and B.A.-M.; visualization, N.M.-B. and B.A.-M.; supervision, P.C.-M., N.M.-B. and F.M.-C. All authors have read and agreed to the published version of the manuscript.

This research received no external funding.

Institutional Review Board Statement

Informed consent statement, data availability statement, conflicts of interest.

The authors declare no conflict of interest.

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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Proceedings of The Hong Kong Engineers Engineering for Public Safety Conference, HKIE April 1997

Managing Slope Safety in a High Density City Prone to Landslips

by Dr Andrew Malone Geotechnical Engineering Office

Hong Kong's terrain and climate make the territory very prone to landslips and significant risk has been created through the post-war urban development of its steep hillsides. However, progressively, the government has introduced slope safety measures over the last 30 years.

Today, Hong Kong has a well developed slope safety system aimed at reducing risk and addressing public attitudes to risk. The system is managed by the Geotechnical Engineering Office. The aims are to be achieved through the setting of safety standards, policing actions, providing public educational and information services and the management of upgrading works programmes for old man-made slopes in private and public ownership.

The purpose of this paper is to outline Hong Kong's slope safety system and evaluate its effectiveness in lay terms.

Figure 1. Landslip fatalities.

Hong Kong's landslip problem

Landslips have been responsible for the death of more than 470 people in Hong Kong since 1948 (Figure 1). Although landslips are common on undeveloped natural hillsides, nearly all of these deaths result from the collapse of man-made slopes, i.e. cut slopes, fill slopes and retaining walls created by the process of hillside development. There is evidence from analysis of fatal landslips that the origin of a significant portion of Hong Kong's landslip risk lies in the nature of hillside development works in the post-war decades, along with lack of adequate subsequent maintenance (Hong Kong Government, 1972a, 1972b and 1977; Geotechnical Engineering Office 1993a, 1993b, 1994, 1996a and 1996b, Chan et al., 1996).

Creation of a policing body

The two most destructive landslips in the recent history of Hong Kong took place on 18 June 1972, the third day of a severe rainstorm associated with a trough of low pressure. Shortly after 1 pm, a major landslip occurred in the Sau Mau Ping Resettlement Estate in the Kowloon foothills. The failure involved the collapse of the side-slope of a 40 m-high road embankment constructed on sloping ground. The resulting flowslide destroyed many huts in a licensed temporary housing area, killing 71 people and injuring 60 others (Hong Kong Government, 1972a). Hours later, another major landslip occurred, in a private residential district on a steep hillside Lit Po Shan Road in the Mid-levels area of Hong Kong Island. Sixty-seven people were killed and 20 injured when an Occupied 12-storey private apartment building was demolished under the impact of an extremely rapid flowslide (Hong Kong Government 1972b). The landslip, illustrated in Figure 2, was initiated on the hillside above by the collapse of a steep cutting in a works site for a private building.

Figure 2. The landslip at Po Shan Road, Hong Kong Island which occurred on 18 June 1972.

A commission of enquiry, set up amidst the ensuing public outcry, reported in August and by the end of the year a group of civil engineers had been assigned to the building control office to vet the geotechnical aspects of private development submissions.

Four years later another destructive landslip occurred in the Sau Mau Ping Resettlement Estate, on the morning of 25 August 1976 following heavy rainfall associated with a Severe Tropical Storm. At least four landslides took place in the estate resulting from the collapse of the side-slopes of highway embankments formed of earth fill. Three of these turned into flowslides, the most hazardous occurring on the face of a 35 m-high embankment above an occupied public housing block. The debris moved downwards as 'a large sheet' until arrested by the building, the ground floor rooms of which were inundated by fluid mud, trapping many occupants; eighteen people were killed and 24 seriously injured. Subsequent investigation found that the collapse had occurred because the earth fill forming the face of the slope was in a loose condition, having been placed by end-tipping without compaction, contrary to good practice (Hong Kong Government, 1977). The 1976 Sau Mau Ping landslip brought the number of landslip fatalities in a four year period to greater than 175 (Figure 1). Immediately after the landslip the Governor established an Independent Review Panel on Fill Slopes, comprised largely of overseas geotechnical experts, which recommended the creation of a central policing body to regulate the whole process of investigation, design, construction, monitoring and maintenance of slopes in Hong Kong.

The geotechnical control body, created in July 1977, has since evolved in response to experience and through reform initiatives (Malone & Ho, 1994) and today, Hong Kong has a well-developed slope safety regime. The GEO manages the safety regime, which will be referred to as the 'Slope Safety System'. The aims are twofold: to reduce risk and to address public attitudes to risk. Along with GEO as safety manager, the main action parties in respect of slope safety are the private owners and government agencies that are responsible for the construction of slopes and the maintenance of their stability.

The Slope Safety System

To recap, post-war site formation and subsequent maintenance by private owners and Government departments went largely unregulated before the creation of the civil engineering unit in the building control office in 1972 and then the central policing body in 1977. By this date a very large amount of development had already taken place on hillslopes. Some of the developments constructed on hillslopes during the unregulated period turned out to contain design, construction or maintenance defects, when judged on modem standards, causing failure with attendant harm and damage.

Therefore, when the policing body was established it was given two main duties; to establish a control regime for new works on hillslopes, to prevent any increase in risk due to new works, and to be the manager of a slope retrofit programme, under which substandard works of the past would be brought up to modem standards by their owners, with a corresponding reduction in risk. These duties remain the major elements of GEO's work in terms of resources deployed. GEO took on new tasks in the 1980s with the introduction of squatter safety clearances and in the 1990s with its educational initiatives, initially targeted at slope owners to promote good maintenance practice. Today GEO's slope safety functions are fourfold: policing slope safety, setting safety standards and research, carrying out works projects and providing educational and information services. The contribution which each of these components makes towards the two aims of the Slope Safety System (reducing risk and addressing public attitudes) is illustrated in Table 1.

Table 1. The Slope Safety System

Evaluation of the Slope Safety System to date

To evaluate the Slope Safety System to date it is necessary to begin by examining evidence of change in global landslip risk (i.e. landslip risk for the entire territory) in the last 20 years and then to go on to examine, if possible, the efficiency and effectiveness of the component parts of the system.

If landslip risk has been reduced by the Slope Safety System, the trend depicted in Figure 3 ought to be apparent. This trend is based on the premise that risk grew broadly in proportion to population until arrested by the intervention of the Slope Safety System. It is postulated that without the Slope Safety System, landslip risk would have continued to increase with continuing growth in population, the encroachment of development onto steeper terrain, the increase in the number of man-made features and their deterioration due to lack of maintenance.

Figure 3. Hypothetical risk trend.

To measure change in risk with time, quantified risk analyses (QRAs) must be carried out for different times and this work has not yet been done. Evaluation will therefore have to rely for the present on indication of risk rather than calculation of risk by QRA.

A reducing trend with time in the amount of harm and damage occurring annually due to landslips, when normalized for rainfall, would be a prima facie indication of a reduction in risk. Trends in data can be revealed by plotting rolling averages (i.e. moving averages) and this technique is adopted here, using a 15- year datum period after trying several other periods. The plots in Figures 4 and 5 utilize landslip fatality data for the whole territory and rainfall data from the Royal Observatory Tsim Sha Tsui gauge. The past 15-year rolling averages of annual number of landslip fatalities are given in Figure 4. In an attempt to discern trends in rainfall the 15-year rolling averages of the annual number of heavy rainfall events, defined as 24-hour rainfall greater than 175 mm (Figure 5), and the 15-year rolling average annual rainfall are also plotted (Figure 5). The former criterion is chosen because the occurrence of 175 mm of rain in 24 hours at Tsim Sha Tsui is the main Landslip Warning criterion and the data is readily available.

Figure 4. Past 15-year rolling average of annual number of landslip fatalities.

Figure 5. Rainfall trends.

The trend in 15-year rolling annual fatalities resembles that shown in Figure 3 but there is no corresponding reduction in annual rainfall or the number of heavy rainfall events. This finding may be interpreted as indicating a reduction in risk. Another indication of reduction in risk would be any reducing trend in territorial landslip fatality rate with increasing territorial population. The data are plotted in Figure 6. The trends evident in Figures 4 and 6 provide prima facie evidence of significant risk reduction since the end of the 1970s.

Figure 6. Trend of fatalities with population growth.

In evaluating the efficiency of the Slope Safety System as a whole in terms of outcome, the fundamental question is 'is Hong Kong getting value for money in terms of cost/benefit?'

Projecting forward the fatality rate trend prior to the 1980s it appears that an annual fatality rate (15-year rolling average) of the order of twenty-five fatalities per year might have been reached by 1996. In fact the actual annual fatality rate in 1996 (15-year rolling average) was of the order of three fatalities per year. Taking these figures, attributing the reduction to the Slope Safety System, making assumptions about the 19-year cost of the Slope Safety System and charging its entire cost to saving life only, it is estimated that up to the end of 1996 each life saved has cost about $20 million. This price would probably be regarded as cost-effective by the stakeholders. Judged on the UK Health and Safety Executive's tolerability rationale (commonly known as the ALARP or 'as low as reasonably practical' rationale) $20 million is higher than but not grossly disproportionate to the values of statistical life assumed in risk assessments for technological hazards in Hong Kong current practice. Therefore, purely on the ALARP rationale, the need is indicated for continuing investment in landslip risk reduction in Hong Kong.

Conclusions

The trends indicated in Figures 4 and 6 provide prima facie evidence of significant risk reduction in the past twenty years which may be attributed to the Slope Safety System introduced progressively since the late 1970s. Crude calculations indicate that the risk reduction effort has been cost-effective and should be continued.

Acknowledgements

The paper is published with the permission of the Director of Civil Engineering of the Hong Kong Government.

1. Chan, Y.C., Pun, W.K., Wong, H.N., Li, A.C.O. & Yeo, K.C. (1996) Investigation of some major slope failures between 1992 and 1995. Geotechnical Engineering Office, Hong Kong, 97 p. (GEO Report No. 52). 2. Geotechnical Engineering Office (1993a) Report on the Rainstorm of May 1982, by M.C. Tang (1993), 129 p. plus 1 drg. (Reprinted, 1995). 3. Geotechnical Engineering Office (1993b) Report on the Rainstorm of August 1982, by R.R. Hudson (1993), 93 p. plus 1 drg. (Reprinted, 1995). 4. Geotechnical Engineering Office (1994) Report on the Kwun Lung Lau Landslide of 23 July 1994, Volume 2: Findings of the Landslide Investigation. Geotechnical Engineering Office, Hong Kong, 379 p. (Chinese version, 358 p). 5. Geotechnical Engineering Office (1996a) Report on the Fei Tsui Road Landslide of 13 August 1995, Volume 2: Findings of the Landslide Investigation. Geotechnical Engineering Office, Hong Kong, 68 p. (Chinese version, 64 p). 6. Geotechnical Engineering Office (1996b) Report on the Shum Wan Road Landslide of 13 August 1995, Volume 2: Findings of the Landslide Investigation. Geotechnical Engineering Office, Hong Kong, 51 p. (Chinese version, 49 p). 7. Hong Kong Government (1972a) Interim Report of the Commission of Inquiry into the Rainstorm Disasters, 1972. Hong Kong Government Printer, 22 p. 8. Hong Kong Government (1972b). Final Report of the Commission of Inquiry into the Rainstorm Disasters, 1972. Hong Kong Government Printer, 94 p. (Also published in Chinese, 99 p.) 9. Hong Kong Government (1977). Report on the Slope Failures at Sau Mau Ping, August 1976. Hong Kong Government Printer, 105 p. plus 8 drgs. 10. Malone, A.W. & Ho, K.K.S. (1995). Learning from Landslip Disasters in Hong Kong. Built Environment, 21, no 2/3, 126-144.

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What is Landslide?

Have you seen or heard of a mass movement land? Have you noticed the news that some roads in the mountains were closed due to landslides? Well, in this article, we will only discuss this mass movement of landmass. We will learn about the meaning of landslides, the impact of landslides, the causes of landslides, efforts to prevent or overcome them and so on. This article will help you understand a very important geographical phenomenon, namely landslides and related concepts.

Landslides are a natural phenomenon, but it involves many human activities which lead to the mass movement of landmass. In recent times we find the causes of landslides increasing day by day and the primary cause is deforestation. To survive, one needs to keep a check on these human activities.

More on the Topic

The movement of the rocks or debris etc., on a slope downwards, is called a landslide. It is a type of "mass wasting ", which refers to the movement of any mass, soil, or rocks under the influence of gravity. It is one of the natural hazards and can be a disaster if the damages occur in large amounts.

According to the Oxford learners dictionary, "landslides is a mass of earth, rock, etc. that falls down the slope of a mountain or a cliff ".

Types of Landslides

They can occur because of various reasons. We can classify them into four categories which are mentioned below:

Falls Landslides  

It means falling of some material or debris or rocks etc., from a slope or a cliff which leads to a collection of this debris at the base of the slope.

(Image will be Uploaded soon)

Topple Landslides

These can occur because of some fractures between the rocks and the tilt of the rocks because of gravity without collapsing. Here, we see the forward rotational movement of the material.

It is a kind of landslide when a piece of the rock slides downwards and gets separated from it.

It happens on flat terrain and gentle slopes and can occur because of softer material.

Causes of Landslide

Landslides are caused by various factors, which are mentioned below:

It can be caused because of heavy rain.

Deforestation is also one of the main reasons for landslides because trees, plants, etc., keep the soil particles compact and due to deforestation, the mountain slopes lose their protective layers because of which the water of the rain flows with unimpeded speed on these slopes.

It can be caused by earthquakes as well.

For example, in the Himalayas, the tremor occurred because earthquakes unstabilized the mountains, which led to landslides.

Volcanic eruptions in specific regions can also cause landslides.

Landslides often occur in mountain regions while making roads and construction; a large number of rocks has to be removed, which can cause landslides over there.

In the regions of North East India, landslides occur because of shifting agriculture.

Due to the increasing population, a large number of houses are being created, which leads to the creation of a large amount of debris which can cause landslides.

Effects of Landslide

Let us look at the effects of landslides in points:

Landslides can disturb the social and economic environment with the number of other damages which are mentioned below:

Short Term Impacts

The natural beauty of the area is damaged.

Loss of life and property

Destruction of railway lines

Channel blocking because of the falling of rocks.

It leads to the diversion of river water, which can cause floods as well.

Long Term Impacts

Landscape changes can be permanent.

The loss of fertile land or cultivation land.

Erosion and soil loss can lead to environmental problems.

Population shifting and migration.

Effects on the sources of water.

Some roads can be damaged or closed permanently.

Prevention and Mitigation

The following measures can be taken in this regard:

The country should identify the vulnerable areas and actions should be taken in this regard on a priority basis.

Early warning systems and monitoring systems should be there.

Hazard mapping can be done to identify the areas which are more prone to landslides.

Restriction on the construction in the risky areas should be imposed.

Afforestation programs should take place.

Restricting development in landslide areas and protecting the existing ones.

The country should specify codes or standards etc. For the construction of the buildings and other purposes in such areas of risk.

Insurance facilities should be taken by the people to deal with the loss.

Terrace farming should be adopted in hilly areas.

Response teams should be quick to deal with landslides if they occur.

Landslides in India

It is one of the natural hazards in India, which affects 15% of the geographical area of our country. Due to several factors, India is divided into the following vulnerability zones, which are shown in the table below:

Did You Know?

The North India Flood Mudslides that occurred in Kedarnath, India in June 2013 was one of the deadliest landslides in the world. Around 5700 people died in this disaster. It was one of the worst disasters ever to occur in India.

Thus, in this article, we have covered a very important topic namely landslides. We have covered its related concepts like causes, effects, prevention, and mitigation, etc. Hence, it is very important to learn these kinds of topics. These notes will help you in Geography, Environment, and Disaster Management. So, we have read about the landslide information, effects of landslides, etc. Let's look at some FAQs in the following.

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FAQs on Landslide

1. What is meant by a landslide?

Also known as a mass movement of landmass, Rocks, rubble, etc. A landslide is called an avalanche. It is a kind of "mass movement" which refers to the movement of any kind of mass, soil or rock under gravity. This is a natural hazard and can be catastrophic if the damage is large. Landslides mostly happen in hilly regions. Many factors involve landslides and we need to be careful and aware of these factors. We can learn in detail about landslides on the website of Vedantu for free.

2. What are the causes and effects of landslides?

Landslides can be caused by a combination of factors, both man-made and geological. Landslides must occur when the subsoil loses its ability to withstand the pressure of the part above it. It is estimated that it will surrender by force, and depending on the earth, the earth can only cover a short distance or even a few kilometers.

Some cases are more tragic than others due to soil moisture and other conditions, but in all cases, the worst-case scenario needs to be prepared. Landslides are caused by heavy rains, earthquakes, deforestation, volcanic eruptions, construction of roads, buildings or houses, and so on. causing. It can have a variety of short-term and long-term effects on the environment, area and people. Can cause loss of property and life. Can damage the natural environment, means of transportation or communication can block roads, railroads, rivers and so on.

3. Is it possible to predict landslides?

Landslide prone areas are quite predictable but timing is not. One of the main ways to predict them is to look at areas where they have appeared before. Areas that have experienced landslides are likely to occur in the future. Scientists are studying existing landslides to see the factors that caused them to collapse. Mountain slopes, hills or cliffs. Existing drainage. Erosion, which is especially common near riverbanks and rocky sides. Excessive rainy season.

A place that is saturated with water that is not wet. Mountainous area with freezing point. Man-made projects such as road construction in steep areas, quarrying and mining. It's important to remember that our landscape is constantly evolving, so landslides can happen almost anywhere if the environment allows them.

4. What are Countermeasures and protection against landslides?

Landslides are a constant threat to human life and livelihoods throughout much of the world, especially in some areas where population and economic growth are high. This risk is mainly mitigated by preventive measures, such as limiting or even removing people from areas previously affected by landslides, limiting certain types of land use where slope stability is present, and setting up warning systems based on slope control. soil conditions such as rock and soil pressure, slope displacement and groundwater levels.

There are also various direct methods to prevent landslides; This includes changes in slope geometry, the use of materials to strengthen slope materials, installation of structures such as poles and retaining walls, grouting at rock joints and fractures, bending of debris and drainage paths on the surface and underwater. Such a direct method is limited by the cost, extent and frequency of landslides and the size of the human settlement at risk.

landslide case study geography

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Landslide case study

Cantata La Contain is a very small community, located on the southern California coastline between Ventura and Santa Barbara. The community lies on a narrow strip of land about 250 meters (820 feet) wide between the shoreline and abutting a 180-meter 1590 Ft) high bluff. The top of the bluff is covered by avocado and citrus orchards. The bluff above La Contain has a slope of approximately 35 degrees and consists of roll cemented marine sediments

On March 4, 1995, the hill behind La Contain failed, moving tens of meters in minutes, and buried nine homes with no loss of life. The County of Ventura immediately declared the whole community a Geological Hazard Area, imposing building restrictions on the community to restrict new construction.

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Days later, on March 10, a subsequent debris flow from a canyon to the northwest damaged five additional houses in the north-western part of La Contain. The dimensions of the slides were approximately 120 meters (390 feet) wide, 330 meters 1 ,080 feet) long, and 30 meters (98 Ft) deep.

The deposit covered approximately 4 hectares (9. 9 acres), and the volume was estimated to be approximately 1. 3 million cubic meters of sediment. The landslide slumped as a coherent mass of material.

Eased on the opinion that surface water infiltration from irrigation contributed to the landslide, seventy-one homeowners sued La Contain Ranch Co. In Bateman v. La Contain Ranch Co. The Judge ruled that irrigation was not the major cause of the slide and that the ranch owners were not responsible.

The 2005 La Contain Landslide occurred at the end of a 1 5-day period of near-record rainfall levels.

From December 27, 2004 through January 10, 2005, the nearby city of Ventura received 378 millimeters (14. 9 inches) of rainfall, only slightly less than its mean annual total of 390 millimeters (15. 4 inches). On January 10, 2005, the south-eastern portion of the 1995 landslide deposit failed, resulting in shallow, rapid fluid flow, unlike the 1995 landslide.

The volume of the landslide was estimated to be approximately 200,000 pubic meters with a surface 350 meters (1 , 1 50 feet) long and 80-100 meters (260- 330 Ft) wide. The landslide destroyed 13 houses and severely damaged 23 others.

There were 10 confirmed fatalities. Subsequently, residents formed the La Contain Community Organization (LOCO) to coordinate with government officials to determine the best way to protect the community. In March 2006, Governor of California, Arnold Schwarzenegger, allocated $667,000 for a scientific study to determine control measures to be taken to prevent future landslides.

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Pennington Point, Sidmouth, Devon

Landslide case study

Active coastal landsliding at Pennington Point was caught on camera by local resident, Eve Mathews, showing a dramatic series of rock falls onto the beach. Pennington Point lies just east of the town of Sidmouth on the south-east Devon coast. The landslide has been entered into the BGS National Landslide Database as ID 16367/1.

Pennington Point location map.

Pennington Point location map. BGS © UKRI.

Falls began to take place began in February 2009 and continued during March. Due to the speed of this type of landslide, it very unusual to be caught on film and these images provide a rare insight into the process as it happens.

Landslides along this section of coast are common; another fall occurred nearby at Hangar Point around the same time. The famous Axmouth to Lyme Regis undercliff lies just to the east, representing a 1 km stretch of coast formed entirely from ancient landslides. This stretch is particularly famous for the 1839 Bindon landslide , which attracted much public attention at the time. Sidmouth and Pennington Point are also part of the UNESCO Jurassic Coast World Heritage Site , which is important for its sequence of Triassic, Jurassic and Cretaceous rocks but also for and its many large-scale landslides.

fall at Pennington Point. (Photo: © Eve Mathews)

Rock fall at Pennington Point. © Eve Mathews.

Pennington Point lies close to the boundary of the Otter Sandstone Formation (part of the Sherwood Sandstone Group ) and the Sidmouth Mudstone Formation (part of the Mercia Mudstone Group ). The Otter Sandstone Formation forms continuous coastal exposures from the River Otter and is predominantly a sandstone with conglomerates and mudstones. The overlying Sidmouth Mudstone Formation comprises red mudstones.

Photographs

The following sequences of images were captured on 5 February 2009. The images show how the fall developed and how much material was involved.

Sequence of rock fall observed by local resident. (Photo: © Eve Mathews).

© Eve Mathews.

Sequence of rock fall observed by local resident. (Photo: © Eve Mathews).

There was a further small rock fall on 19–20 February 2010, which brought the edge of the cliff nearer to the footpath.

Photograph taken the week before the rock fall © Eve Mathews.

Photograph taken the week before the rock fall. © Eve Mathews.

Photograph taken after the rock fall on 20th February 2009 © Eve Mathews.

Photograph taken after the rock fall on 20 February 2009. © Eve Mathews.

Contact the Landslide Response Team

You may also be interested in, landslide case studies.

The landslides team at the BGS has studied numerous landslides. This work informs our geological maps, memoirs and sheet explanations and provides data for our National Landslide Database, which underpins much of our research.

Debris flow on A83

Understanding landslides

What is a landslide? Why do landslides happen? How to classify a landslide. Landslides in the UK and around the world.

Holbeck Hall Landslide

How to classify a landslide

Landslides are classified by their type of movement. The four main types of movement are falls, topples, slides and flows.

Storegga landslide

Landslides in the UK and around the world

Landslides in the UK, around the world and under the sea.

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COMMENTS

  1. A hill slope failure analysis: A case study of Malingoan village

    1. Introduction. Landslide is a common natural disaster often in hilly terrain, which causes huge loss of natural resources and human life (Ering & Babu, Citation 2016).It is mainly attributed by natural factors, such as earthquakes and rainfall occurred on these regions (Collins & Znidarcic, Citation 2004; Rahardjo, Li, Toll, & Leong, Citation 2001).A sudden downward movement of the ...

  2. Landslide case studies

    100 mi Leaflet | Powered by Esri | Esri, HERE, Garmin, FAO, NOAA, USGS The landslides team at the BGS has studied numerous landslides. This work informs our geological maps, memoirs and sheet explanations and provides data for our National Landslide Database , which underpins much of our research.

  3. Landslide

    6 - 12+ Subjects Earth Science, Geology, Geography, Human Geography, Physical Geography Photograph Proof of a Landslide This landslide left behind a trail of roots that now serve as a memorial for the foliage that once covered this area. Mudslides like this one are the fastest-moving type of landslide, or "mass wasting."

  4. The Aberfan disaster, 1966

    Landslide case study Share this article On 21 October 1966, the worst mining-related disaster in British history took place in Aberfan, a small village in South Wales. This harrowing and tragic event started when the nearby colliery ran out of tipping space in the valley floor in 1916.

  5. (PDF) Post landslide Investigation of Shallow Landslide: A case study

    Geology Geoscience Landslides Post landslide Investigation of Shallow Landslide: A case study from the Southern Western Ghats, India Authors: Sarun Savith Sree Sankaracharya University of...

  6. Settlements and slides: a large landslide case study from the Central

    Settlements and slides: a large landslide case study from the Central Cordillera of the Philippines Gareth James Hearn; Jonathan Roy Hart Author and Article Information Quarterly Journal of Engineering Geology and Hydrogeology (2020) 53 (1): 62-73. https://doi.org/10.1144/qjegh2019-050 Article history Cite Share Permissions Abstract

  7. Unit 4: Anatomy of a tragic slide: Oso Landslide case study

    Part 1: Preparatory activity. In each of the five study sites that students have looked at in Units 2 and 3, there is a significant mass wastage somewhere in the map area. In order to prepare for Unit 4, have students prepare five-minute presentations on one those mass-wastage events (except the Northern Washington one, as the rest of Unit 4 is ...

  8. Case study: Scottish landslides

    Case study: Scottish landslides - Local and global effects of climate change - Higher Geography Revision - BBC Bitesize Higher Local and global effects of climate change Case study: Scottish...

  9. Landslides

    Cambridge University Press Earth and environmental science Geomorphology and physical geography Look Inside Landslides Types, Mechanisms and Modeling Editors: John J. Clague, Simon Fraser University, British Columbia Douglas Stead, Simon Fraser University, British Columbia View all contributors Date Published: March 2018 availability: Available

  10. The effect of topography on landslide kinematics: a case study of the

    On July 23, 2019, a large-scale landslide occurred in Jichang town, Shuicheng County, Liupanshui City, Guizhou Province in China. The landslide, which moved along two gullies, resulted in strong punching-shear, induced scarping on vegetation and large destruction of houses, and finally formed a deposit with a volume of 2 × 106 m3. This research aims to understand the effect of topography on ...

  11. Worldwide Research Trends in Landslide Science

    1. Introduction. Landslides are disasters that cause damage to anthropic activities and innumerable loss of human life globally [].Mass movement processes cause significant changes in the Earth's relief, causing economic losses due to landslides in mountainous areas with a dense population [2,3], and even in the direct and indirect cost of buildings or infrastructure on an urban scale [4,5,6].

  12. Landslide

    landslide, the movement downslope of a mass of rock, debris, earth, or soil (soil being a mixture of earth and debris). Landslides occur when gravitational and other types of shear stresses within a slope exceed the shear strength (resistance to shearing) of the materials that form the slope. Shear stresses can be built up within a slope by a ...

  13. PDF IB Geography Hazards & Disasters Case Study Summary Sheet for Freetown

    IB Geography - Hazards & Disasters Case Study Summary Sheet for Freetown Landslide, Sierra Leone (LIC) Where did it happen? Freetown is the capital and largest city of Sierra Leone. It is a major port city on the Atlantic Ocean and is located in the Western Area of the country.

  14. Cyclone Idai Case Study

    At least 180 people in Zimbabwe known to have been killed by landslides triggered by Idai. Nasa satellite images depict the extensive landslide activity associated with Cyclone Idai. The landslides were partly caused by deforestation. People were still being rescued a week and a half after the storm.

  15. L'Aquila Earthquake 2009

    The L'Aquila Earthquake - Background. On 6 April 2009, a magnitude 6.3 earthquake struck L'Aquila in central Italy, killing 309 people. The main shock happened in the early morning hours at 3.32 am when most people were sleeping, extensively damaging the 13th-century city of L'Aquila, located only about 60 miles (100 km) northeast of Rome.

  16. Holbeck Hall, Scarborough

    Holbeck Hall, Scarborough Landslide case study Share this article The Holbeck Hall landslide, south of Scarborough in North Yorkshire, attracted considerable interest when it destroyed the four-star Holbeck Hall Hotel between 3 and 5 June 1993.

  17. Geography Case Studies

    Geography Case Studies - A wide selection of geography case studies to support you with GCSE Geography revision, homework and research. Twitter; Facebook; Youtube; 0 Shopping Cart ... Landslide at West Bay, Dorset; Hornsea 360 Gallery; Malham Gallery; Mappleton Gallery; Old Harry Rocks Gallery; Skipsea Gallery; Spurn Point;

  18. Geohazards [Landslides

    Figure 1. Landslip fatalities. Hong Kong's landslip problem Landslips have been responsible for the death of more than 470 people in Hong Kong since 1948 (Figure 1).

  19. Landslide

    More on the Topic. The movement of the rocks or debris etc., on a slope downwards, is called a landslide. It is a type of "mass wasting ", which refers to the movement of any mass, soil, or rocks under the influence of gravity. It is one of the natural hazards and can be a disaster if the damages occur in large amounts.

  20. A Level Geography Montecito Landslides Case Study

    Death toll= 23 people and injured 163 people (hospitalised) Debris flows were up to 15 feet in height of mud, tree branches and boulders and moved at over 20 mph into the lower areas of Montecito. 20,000 people lost power. A 30-mile section of Route 101 from Santa Barbara to Ventura was shut as it filled with 2 feet of mud and debris.

  21. Folkestone Warren, Kent

    Share this article. The Folkestone Warren landslide is a very large, deep-seated coastal landslide that is well known to geologists and engineers. It is about 3 km wide and up to 350 m in length. There are nine surveys in the BGS National Landslide Database: IDs 1774/1 to 1774/9. The village of Capel-le-Ferne is situated behind the landslide at ...

  22. Landslide case study

    Landslide case study Cantata La Contain is a very small community, located on the southern California coastline between Ventura and Santa Barbara. The community lies on a narrow strip of land about 250 meters (820 feet) wide between the shoreline and abutting a 180-meter 1590 Ft) high bluff.

  23. Pennington Point, Sidmouth, Devon

    Landslide case study. Share this article Facebook Twitter Pinterest WhatsApp Email Copy Link. Active coastal landsliding at Pennington Point was caught on camera by local resident, Eve Mathews, showing a dramatic series of rock falls onto the beach. Pennington Point lies just east of the town of Sidmouth on the south-east Devon coast.

  24. With drop in illegal fishing comes rise in piracy, study in Indonesia finds

    The authors of the new study, however, make the case that the negative association between maritime piracy and illegal fishing boils down to it being easier for individuals fishing illegally to ...