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Why Are Landslides Concentrated in Certain Regions? Understanding the Global & Indian Spatial Distribution of Landslides

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Introduction

  • Landslides are among the most destructive geomorphic hazards on Earth. At their core, they represent the downslope movement of rock, soil, or debris under the influence of "gravity ( the Driving Force)"  when the natural balance of a slope is disturbed. In simple terms, a landslide occurs when the driving forces acting on a slope exceed the resisting forces that maintain its stability. Thus, landslides are not merely the movement of Earth materials but the visible manifestation of slope failure resulting from the "breakdown of equilibrium".
  1. gravity, 
  2. lithology, 
  3. geological structures, 
  4. slope gradient, 
  5. water infiltration, and 
  6. weathering interact to determine whether a slope remains stable or eventually fails.
  • Building upon that foundation, our second blog, Slope Stability: The Interplay Between Driving and Resisting Forces, examined the mechanics of slope failure through the concept of Driving Forces versus Resisting Forces, where we devoted special attention to the growing influence of anthropogenic activities and demonstrated that many of today's catastrophic landslides are no longer solely natural events. Instead, they increasingly result from human-induced disturbances such as unplanned urbanisation, indiscriminate hill cutting, infrastructure development, deforestation, mining, poor drainage, and the intensifying impacts of anthropogenic climate change. These activities disturb "the natural equilibrium" of slopes, reduce their factor of safety, and significantly increase the frequency and magnitude of landslide disasters.
  • In this third blog, we shift our focus from the mechanics of slope failure to its "spatial distribution", and here we will examine why landslides are concentrated in specific regions of the world- including India- while remaining relatively uncommon in others. Understanding this spatial pattern is essential not only for disaster risk reduction but also for-
  1. sustainable land-use planning (mainly for urban settlements), 
  2. infrastructure development, and 
  3. environmental conservation in an era of rapid climate change and expanding human intervention.


Hierarchy of Factors Controlling Landslide Occurrence

      


  • The above infographic presents the hierarchy of factors controlling landslide occurrence, with individual thought discretion as there is no scaling to determine this hierarchy, illustrating that landslides result from the interaction between driving forces and resisting forces acting on a slope. At the top of the hierarchy we have rock and soil shear strength, the primary resisting force that determines whether a slope can withstand gravitational stress. This is followed by geological structures, such as faults, joints, bedding planes, and fractures, which create natural planes of weakness within the rock mass. Slope gradient serves as the principal driving force, as steeper slopes experience greater gravitational stress. Among the triggering factors, water plays the most critical role by increasing-

  1. pore-water pressure, 
  2. adding weight to slope materials, and 
  3. reducing the effective shear strength of rocks and soils. 
  • The infographic further highlights the influence of human activities, including road cutting, excavation, mining, urbanisation, and slope loading, which artificially disturb the natural equilibrium of slopes and significantly reduce their factor of safety. 
  • Finally, dynamic processes such as-
  1. earthquakes and volcanic activity, 
  2. along with deforestation, 
  3. climate change, and 
  4. unsustainable human behaviour, further accelerate slope instability and increase the likelihood of catastrophic landslides. Overall, the infographics demonstrate that landslides are rarely the result of a single factor; instead, they occur through the combined interaction of (a) geological, (b) hydrological, (c) topographical, (d) climatic, and (e) anthropogenic processes that progressively weaken the resisting forces until they are exceeded by the driving forces.

 

Water: The Most Important Agent Linking Weathering and Landslides

  • In our first blog on Earth's geomorphic processes, we discussed the two fundamental forces responsible for shaping the Earth's surface: endogenic forces and exogenic forces. 
        

  • So, according to the above infographics, while the endogenic forces originate from within the Earth and are primarily constructive in nature—creating mountains, plateaus, and other landforms—exogenic forces are denudational or destructive forces with the primary function of wearing down, weakening, and gradually reducing the elevation and relief of the Earth's surface. In other words, every landform exposed to exogenic forces continuously undergoes modification through processes that lower its height and alter its original shape.
  • Among the various denudational processes, weathering occupies the foremost position because it initiates the weakening of rocks and soil before any erosion or mass movement can occur. Within weathering, water is by far the most influential and versatile agent, as it actively participates in all three major forms of weathering—
  1. physical, 
  2. chemical, and 
  3. biological. 
  • During physical weathering, raindrops strike the ground with kinetic energy, while flowing water in rivers and streams exerts continuous mechanical force on rocks and soil, gradually breaking them into smaller fragments. 
  1. Through repeated wetting and drying, 
  2. freezing and thawing in colder regions, and 
  3. hydraulic action, water progressively reduces the structural integrity of the slope.
  • In addition, water is equally important in chemical weathering; as rainwater infiltrates through pores, joints, fractures, and bedding planes in rocks, it reacts with minerals through processes such as hydrolysis, hydration, oxidation, carbonation, and solution. 
      

  • These reactions-
  1. decompose minerals, 
  2. weaken the rock mass, and 
  3. reduce its shear strength, as a result of which, over time, even the strongest rocks become weathered and susceptible to failure. Furthermore, because water is the fundamental prerequisite for life, it promotes the growth of vegetation, microorganisms, fungi, and other biological organisms, where plant roots penetrate cracks in rocks, widening them over time, while microbial activity accelerates mineral decomposition. 
     

  • Consequently, water also becomes the principal driver of biological weathering, making it the only natural agent that simultaneously facilitates physical, chemical, and biological degradation of rocks and soils.
  • The cumulative outcome of these weathering processes is a progressive reduction in the strength, cohesion, and resistance of rock and soil masses. As weathering intensifies, the resisting forces that maintain slope stability gradually decline. Once these resisting forces become weaker than the gravitational driving forces acting on the slope, the probability of a landslide increases significantly.


Global spatial Landslides distribution


  • Now, examine the following global landslide susceptibility map. One striking geographical pattern immediately emerges: the regions experiencing the highest frequency of landslides largely coincide with areas receiving abundant or intense rainfall. So, as shown in the above infographics-
  1. The Himalayan belt, 
  2. Southeast Asia, 
  3. Japan, 
  4. the Andes, 
  5. Central America, 
  6. the European Alps, 
  7. New Zealand, and 
  8. the Western Ghats of India are all, with their stipulated reason as mentioned over there, responsible for landslides, receive substantial precipitation,  and simultaneously exhibit high landslide susceptibility. This spatial coincidence is not accidental. It demonstrates a strong correlation between water availability and landslide occurrence. 
  • Adequate or excessive rainfall-
  1. accelerates weathering, 
  2. increases pore-water pressure, 
  3. raises the weight of slope materials, and 
  4. Finally reduces the shear strength of rocks and soils- that is, weakening the resistance force. Thus, although gravity remains the fundamental driving force behind landslides, water acts as the most critical environmental agent that prepares, weakens, and ultimately triggers slope failure. This explains why regions with abundant rainfall consistently emerge as global landslide hotspots.

 

Indian spatial Landslide distribution of Landslide-Prone Regions


  • Now, let us examine the following "Indian Landslide Zonation Map", prepared by the "Geological Survey of India (GSI)". 
       

  • A striking geographical pattern immediately emerges: the regions experiencing the highest frequency and susceptibility to landslides are-
  1. predominantly located in mountainous areas,
  2. receiving abundant or intense rainfall, 
  3. possessing steep slopes, 
  4. having weak geological formations, and 
  5. in many places, undergoing extensive human intervention. 
  • This spatial distribution is far from random; rather, it reflects the combined influence of (a) climate, (b) geology, (c) topography, (d) tectonic activity, and (e) anthropogenic disturbances that collectively govern slope stability across the Indian subcontinent.
  • "The Himalayan mountain belt", extending from-
  1. Union Territory (UT) Jammu & Kashmir -&- Ladakh, India, states such as 
  2. Himachal Pradesh, 
  3. Uttarakhand, 
  4. Sikkim, and 
  5. Arunachal Pradesh, 
  6. Nagaland, 
  7. Manipur, 
  8. Mizoram, Tripura, and
  9. Meghalaya, represent India's most extensive landslide-prone region. Why? For this answer, look into the heading "Hierarchy of Factors Controlling Landslide Occurrence", where we have discussed the "Dynamic factors", one of factor names as tectonic activities, showing as earthquake -&- Volcanic activities. 
  • So, as we discussed, these that These young fold mountains are still tectonically active, characterised by steep slopes, highly fractured and weathered rocks, numerous faults and thrusts, and intense monsoonal precipitation. Frequent earthquakes associated with the ongoing collision between the Indian and Eurasian Plates further weaken already unstable slopes with the presence of sedimentary rocks, making the Himalayas one of the most landslide-susceptible mountain systems in the world.
  • A similarly high concentration of landslides is observed throughout Northeast India, including Assam, Meghalaya, Nagaland, Manipur, Mizoram, and Tripura. This region experiences some of the highest annual rainfall on Earth, particularly in Meghalaya, while also lying within one of India's most seismically active zones. T
  • So, the combination of-
  1. steep terrain, 
  2. fragile lithology, 
  3. deep weathering, 
  4. intense monsoonal rainfall, 
  5. deforestation, 
  6. road construction, 
  7. quarrying, 
  8. rapid urban expansion, and
  9. frequent earthquakes create highly favourable conditions for recurrent landslides.
  • On the other hand, in Peninsular India, the Western Ghats emerge as another major landslide hotspot. Stretching across Maharashtra, Goa, Karnataka, Kerala, and Tamil Nadu, these escarpments receive exceptionally heavy rainfall during the Southwest Monsoon. Continuous weathering of basaltic and lateritic rocks, combined with
  1. steep slopes, 
  2. high pore-water pressure during prolonged rainfall, 
  3. deforestation, 
  4. road construction, 
  5. quarrying, and 
  6. rapid urban expansion, has significantly increased landslide frequency in recent decades. Catastrophic events in Kerala, Karnataka, and Maharashtra clearly illustrate the growing influence of anthropogenic disturbances on naturally sensitive mountain ecosystems.
  • Beyond these principal hotspots, moderate landslide susceptibility is also observed in parts of the Eastern Ghats, Chhattisgarh, Jharkhand, Odisha, West Bengal, and the Andaman & Nicobar Islands. Although these regions experience landslides less frequently than the Himalayas or the Western Ghats, localised combinations of steep terrain, weathered rock masses, heavy rainfall, coastal erosion, and human-induced slope modifications continue to generate significant landslide hazards.
  • Amid all these, one common characteristic unites nearly all these regions: they receive substantial precipitation and simultaneously exhibit high landslide susceptibility. This spatial coincidence is not accidental; rather, it demonstrates a strong correlation between water availability and landslide occurrence, when intense or prolonged rainfall-
  1. accelerates physical, chemical, and biological weathering, 
  2. increases groundwater infiltration, 
  3. elevates pore-water pressure, 
  4. raises the weight of slope materials, and 
  5. ultimately reduces the shear strength of rocks and soils—thereby weakening the resisting forces that maintain slope stability.
  • But when we dive deep into the following infographics, only then do we come to understand a comprehensive interplay of natural and anthropogenic factors responsible for this menace known as a landslide.


  • So, after all, we satisfied ourselves that rainfall alone does not fully explain the present pattern of landslides across India. In recent decades, unplanned urbanisation, indiscriminate hill cutting, road widening, hydropower projects, quarrying, mining, deforestation, poor drainage systems, and the increasing frequency of extreme rainfall events associated with anthropogenic climate change have substantially amplified the natural susceptibility of these regions. Consequently, many of today's devastating landslides are no longer purely natural phenomena; they are increasingly the result of the interaction between natural geomorphic processes and unsustainable human interventions.
  • Therefore, the Indian Landslide Zonation Map highlights a fundamental geographical principle:-
  1. Landslides are concentrated where favourable natural conditions coincide with intensive human disturbance. Understanding this spatial distribution is essential for 
  2. scientific land-use planning, 
  3. infrastructure development, 
  4. disaster risk reduction, and, as one of the most important aspects, 
  5. sustainable mountain management, particularly as climate change continues to intensify extreme weather events across the Indian subcontinent.


We are Concluding-
  • Nature creates landslide-prone landscapes, but human actions increasingly determine whether they remain stable or become disasters. Therefore, understanding the spatial distribution of landslides is not merely a geographical exercise—it is the foundation of sustainable development, resilient infrastructure, and effective disaster risk management, because when geography decides everything of the Earth then degree of accommodation with nature by the present shall decide the future of comings.


Thanks. 
Critical comments are welcome.













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