The term “landslide” describes a wide variety of processes that results in the downward and outward movement of slope-forming materials, including rocks, soil, artificial fill or a combination of these (USGS).
The areas of the World prone to landslides are mountains and hills, particularly deforested mountainsides, areas with coarse-grained soil or lack of vegetation. Several studies have shown that more than 12 per cent of India’s land area is susceptible to landslides.
The major landslide-prone areas of India include the Western Ghats (Nilgiris), Konkan region (Tamil Nadu, Karnataka, Kerala, Maharashtra and Goa), Eastern Ghats (Araku region of Andhra Pradesh), Eastern Himalayas (Darjeeling, Sikkim and Arunachal Pradesh), North-west Himalayas (Uttrakhand, Himachal Pradesh and Jammu & Kashmir).
Landslides have been declared the third most fatal disaster in the World. In the world, around 300 people die every year due to landslides and $400 billion are annually spent on landslide mitigation and disaster management.
Types of Landslides (USGS)
Slides: It is a type of mass movement where the sliding material detaches or breaks from the underlying stable material. It can be divided into rotational slides and translational slides. In a rotational slide, the movement is rotational, and its axis is parallel to the ground surface and transverse across the slide. Translational slides do not show any rotation, for example, block slides, where single unit slides as a coherent mass.
Falls: When rock, soil and debris break away from cliffs and slopes and start moving suddenly. It may be the result of an earthquake, weathering or gravity.
Flows: It is divided into five basic categories that fundamentally vary from each other.
Debris Flow: Rapid mass movements of a combination of loose soil, organic matter, and water that flow downslope.
Debris Avalanche: It is a type of extremely rapid debris flow.
Earth Flow: It is mainly found in rocks primarily composed of clay and fine-grained materials. The materials flow after liquefaction. In some cases, the dry flow may also be possible.
Mud Flow: It is a type of earth flow where the material is more saturated with water and contains half sand and remaining silt and clay-sized particles. Mudflow and Debris flow is also called “Mudslides”.
Creep: It is a very slow movement. This is caused by shear stress. There are three types of creeps- i) seasonal, ii) continuous, and iii) progressive.
Topples: It includes forward spinning and movement of huge masses of earth, debris and rocks from a slope; it occurs when topples fails.
Spreads: They are a little distinctive because it takes place on a very gentle slope or flat terrain. It is caused by shear force or tensile fractures, leading to lateral extensions.
Causes of Landslides
Earthquakes: It is linked with tectonic forces. It is a major contributor to global landslide events. The 2011 earthquake in Sikkim led to several landslides and mudslides.
Climate: The most important component of climate is precipitation. Intense rainfall leads to ground saturation and increases in the groundwater table, ultimately leading to soil run-off. Heavy rainfall, specifically in the upper reaches of the Himalayas, causes frequent landslides of this nature in Nepal, Uttrakhand and Himachal Pradesh.
Weathering and Erosion (Weathered Material): Disintegration of rocks develop weak regolith that is more susceptible to landslides. Erosion wipes out lateral and latent support and facilitates landslides.
Volcanic Eruptions: They can also trigger landslides. If the eruption occurs and conditions are wet, the ash and mud coming out of volcanoes may start flowing.
Gravity: Steep slopes, in combination with a gravitational pull can cause massive landslides.
Human Interferences: It includes mining and excavation using blasting techniques, cutting and clearing of forest areas, construction of roads, land use and land-cover changes, building reservoirs and water leakage from the reservoirs may also lead to landslides.
Landslide Hazard
Major landslides in the past have occurred in the Andes Mountains, the Pacific Ring of Fire, and tropical regions of Central America, Africa and Asia. Landslide hazard refers to the potential occurrence of a damaging landslide within a given area. Such damage could include loss of life or injury, property damage, social and economic disruption or environmental degradation.
Loss of Human Life: In Ningxia (China) (1920), the 8.5 Magnitude earthquake caused 675 major loess-linked landslides that killed more than 100,000 people. In June 2013, mudslides in Kedarnath (India) killed around 5000 people. One of the worst tragedies occurred in Malpa (Uttrakhand) in August 1998, when nearly 380 people were killed due to massive landslides. This included 60 pilgrims going to Mansarovar in Tibet.
Major Landslides of the World
| Year | Place | Casualties |
| 1248 | Mount Granier (France) | 1000+ |
| 1919 | Kelud (Indonesia) | 5110 |
| 1920 | Haiyuan (China) | >100000 |
| 1933 | Diexi (China) | 3100 |
| 1941 | Huaraz (Peru) | 4000-6000 |
| 1949 | Gharm (Tajikistan) | 7200 |
| 1962 | Ranrahirca (Peru) | 4000-5000 |
| 1970 | Yungay (Peru) | >22000 |
| 1985 | Armero (Colombia) | 23000 |
| 1999 | Vargas (Venezuela) | 30000 |
| 2013 | Kedarnath (India) | 5700 |
The decimation of Infrastructure and Economic Loss: It can cause serious property damage. It can decimate roads, railways, telephone lines, buildings, homes and other infrastructure. The rehabilitation also involves a heavy capital investment that puts an extra burden on already cash-crunched state governments in India.
Risk Reduction Measures
- Hazards mapping and preparation of hazard Zonation Maps
- Afforestation and prevent deforestation
- Strengthening land-use regulations
- Relocation of vulnerable settlements
- Retention wall and nets
- Strengthening of weak structures
- Drainage Control Measures
- Community education and awareness
Read More in Geomorphology
- Earth Movements: Meaning and Types
- Epeirogenic Earth Movements
- Orogenic Earth Movements
- Cymatogenic Earth Movements
- Concept of Stress and Strain in Rocks
- Folds in Geography
- Fault in Geography
- Mountain Building Process
- Morphogenetic Regions
- Isostasy: Concept of Airy, Pratt, Hayford & Bowie and Jolly
- Continental Drift Theory of Alfred Lothar Wegener (1912)
- Plate Tectonics: Assumptions, Evidences, Plate Boundaries and Features Formed
- Volcanoes: Process, Products, Types, Landforms and Distribution
- Earthquakes: Processes, Causes and Measurement
- Plate Tectonics and Earthquakes
- Composition and Structure of Earth’s Interior
- Artificial Sources to Study Earth’s Interior
- Natural Sources to Study Earth’s Interior
- Internal Structure of Earth
- Chemical Composition and Layering of Earth
- Weathering: Definition and Types
- Mass Wasting: Concept, Factors and Types
- Models of Slope Development: Davis, Penck, King, Wood and Strahler
- Davis Model of Cycle of Erosion
- Penck’s Model of Slope Development
- King’s Model of Slope Development
- Alan Wood’s Model of Slope Evolution
- Strahler’s Model of Slope Development
- Development of Slope
- Elements of Slope
- Interruptions to Normal Cycle of Erosion
- Channel Morphology and Classification
- Drainage System and Drainage Pattern
- River Capture or Stream Capture
- Stream Channel Pattern
- Fluvial Processes and Landforms: Erosional & Depositional
- Delta: Definition, Formation and Types
- Aeolian Processes and Landforms: Erosional & Depositional
- Desertification: Definition, Problem and Prevention
- Glacier: Definition, Types and Glaciated Areas
- Glacial Landforms: Erosional and Depositional
- Periglacial: Meaning, Processes and Landforms
- Karst Landforms: Erosional and Depositional
- Karst Cycle of Erosion
- Coastal Processes: Waves, Tides, Currents and Winds
- Coastal Landforms: Erosional and Depositional
- Rocks: Types, Formation and Rock Cycle
- Igneous Rocks: Meaning, Types and Formation
- Sedimentary Rocks: Meaning, Types and Formation
- Metamorphic Rocks: Types, Formation and Metamorphism
- Morphometric Analysis of River Basins
- Soil Erosion: Meaning, Types and Factors
- Urban Geomorphology: Concept and Significance
- Hydrogeomorphology: Concept, Fundamentals and Applications
- Economic Geomorphology: Concept and Significance
- Geomorphic Hazard- Earthquake: Concept, Causes and Measurement
- Geomorphic Hazard- Tsunami: Meaning and Causes
- Geomorphic Hazard- Landslides: Concept, Types and Causes
- Geomorphic Hazard- Avalanches: Definition, Types and Factors
- Integrated Coastal Zone Management: Concept, Objectives, Principles and Issues
- Watershed: Definition, Delineation and Characteristics
- Watershed Management: Objective, Practice and Monitoring
- Applied Geomorphology: Concept and Applications