Landforms: Earth’s Living Canvas

Distribution of Major Tectonic Plates

• Plate tectonics is one of the most important scientific theories in Earth science — it explains how the Earth’s surface is constantly changing over time.
• The Earth’s outer layer, the lithosphere, is divided into large and small plates that move over the semi-fluid layer beneath them — the asthenosphere.
• The Continental Drift Theory was proposed by Alfred Wegener in 1912 — he suggested all continents were once joined in a single landmass called Pangaea and later drifted apart.
• Evidence for continental drift: matching coastlines, fossils and rock formations — but Wegener could not explain the mechanism behind the movement.
• The Seafloor Spreading Theory, proposed by Harry Hess and Robert S. Dietz in the 1950s, provided the missing mechanism — new oceanic crust is formed at mid-ocean ridges due to volcanic activity; supported by magnetic striping on the ocean floor.
• Convection Currents in the mantle: heat from Earth’s core creates convection currents — hot material rises, cooler material sinks, creating circular motion that drives plate movement.
• Types of plate boundaries: Divergent (plates move apart), Convergent (plates collide), Transform (plates slide past each other).
• This theory helps explain earthquakes, volcanic activity, mountain formation and ocean trench formation — making it one of the most important theories in geology.

Interior of the Earth — Crust, Mantle and Core

• Our earth has a layered structure comprising three main layers: Crust, Mantle and Core.
• The Crust is the solid outer covering — average thickness varies from 5 to 40 kilometres; thicker under continents, thinner under oceans; made up of a great variety of rocks; sustains all life.
• In between the crust and the mantle is the Mantle — average thickness about 2,900 km; divided into upper mantle and lower mantle.
• The crust is separated from the mantle by the Mohorovicic Discontinuity (Moho) — named after geologist Andrija Mohorovicic who discovered it.
• The innermost shell is called the Core — about 3,500 km thick; the densest layer, made up of metals; sometimes called the metallic core.
• The core is divided into: Outer core — mainly composed of iron; exists in a liquid state; and Inner core — composed of nickel and iron; behaves like a solid due to extremely high pressure.
• Because of the presence of metals (nickel and iron), the earth acts like a magnet.
• As we move towards the centre of the earth, the density of the different layers goes on increasing.
• Temperature increases at the rate of 1°C for every 32 metres as one moves down the earth’s surface.

An Effect of Weathering and Erosion

• Various processes go on changing the surface of the earth constantly — some work beneath the crust (volcanic activity, earthquakes), others work on the surface (weathering, erosion, mass movements).
• External processes play a vital role in modifying the surface of the earth and help in the formation of soil.

• Natural processes which take place gradually on the surface of the earth are called external processes — weathering, erosion and mass movements are some such external processes.

• The process by which rocks exposed on the surface get broken into smaller pieces in situ (in the same place) is known as weathering.

• Change in temperature and pressure — continuous heating and cooling of rocks makes them break apart.
• Water collects in cracks and pores of rocks; when temperature falls, it freezes and expands, widening cracks — called frost-action.
• Air loaded with sand works like sandpaper — strikes rock surfaces especially during storms, abrading and breaking rocks.
• Seeds deposited in small holes in rocks — roots of plants go deep into cracks and break rocks into pieces.
• Animals and humans also break rocks into pieces by their mechanical actions.

• 1. Physical Weathering — disintegration of rocks without any change in chemical composition; peeling of outer layers called exfoliation, common in granitic rocks; in cold lands, water freezes in cracks and expands — called frost-action.
• 2. Chemical Weathering — due to chemical reaction of water or air, portions of rocks are dissolved producing cavities, sinkholes and caverns; soluble minerals like rock-salt, limestone and sandstone dissolve into water and are removed.
• 3. Biological Weathering — animals and plants break rocks; roots of plants produce acidic juices which cut into rock-material and slowly break the rocks; burrowing animals like rabbits and rats also contribute.

• The act of carrying away the weathered particles from one place to another is called erosion.
• Rivers, rainwater, glaciers, waves and winds carry away weathered particles from place to place.
• Rate and ratio of erosion depends upon: (i) Rainfall; (ii) Temperature; (iii) Slope of land; (iv) Type of soil; (v) Presence of vegetation cover; (vi) Change in land use pattern.
• Where the Great Himalayas now stand, there was once a deep sea called ‘Tethys’ — proof of the power of weathering and erosion over millions of years.

• Mass movements bring changes in the earth’s surface — caused by gravity which pulls all materials downwards.
• Very common in mountainous regions like Uttarakhand, Himachal Pradesh and Jammu and Kashmir.
• Landslide — dry soil and rock pieces move down a steep slope.
• Earth flow — rock materials like clay and silt, saturated with water, move down a gentle slope.
• Mud-flow — water-saturated rock debris move down channels on steep hillsides.

• Denudation means making nude or bare — five agents: Rivers, Rain water, Ice or Glaciers, Sea waves and Winds.
• 1. Rivers — transport huge quantities of broken rocks to lowlands; erode land into gorges and valleys.
• 2. Rainwater — seeps underground through fissures; forms springs, caves and other landscape features in hilly areas with soluble rocks like limestone.
• 3. Ice or Glaciers — moving mass of ice on mountains; when they melt they give birth to rivers; erodes V-shaped valleys into U-shaped valleys.
• 4. Seawaves — causes erosion of the coast; also deposits material along the shore — work comprises erosion, transportation and deposition.
• 5. Winds — most significant in desert areas like Thar Desert in Rajasthan and Sahara in Africa; remove dry particles of dust or sand very easily.

• By cutting trees indiscriminately, man turns the land into wasteland — no trees means no rain, land is automatically degraded.
• Indiscriminate building activities not only swallow the land but render surrounding land degraded.
• Dirty and poisonous effluents from factories collecting in surrounding areas completely degrade land.
• Dumping of city waste on any land completely leads to its degradation.

The Course of a River from its Source in the Mountains to its Mouth at the Sea

• (1) The Upper Course or the Mountain Stage — slope is very steep; river rushes down with great speed; busy in erosion and transportation; develops gorges, V-shaped valleys, waterfalls and rapids; a series of rapids are called cascades; Angel Falls (Venezuela — 980 metres) is the highest waterfall in the world.
• (2) The Middle Course or the Plain Stage — slope is not steep; river becomes gradual; overflows its bank depositing alluvial sediments forming flood plains; irregularities of ground force river to swing making big loops called meanders.
• (3) The Lower Course or the Delta Stage — last stage before river merges into sea; speed slows down; river divides into many channels called distributaries; deltas formed — contain deposits of alluvium and are very fertile.

Mountain Glacier Moving Through a Valley

• Mountain Glaciers — move down from mountain tops along valleys; melt at edges giving birth to rivers; Rivers Ganga and Yamuna arise from melting of mountain glaciers; erodes V-shaped valley into U-shaped valley.
• Continental Glaciers — comparatively bigger in size and slower in movement; occupy large areas exceeding thousands of square kilometres; thick ice sheets covering entire land surface; generally occur in Polar Regions.

Major Landforms of the Earth — Mountains, Plateaus and Plains

• Mountains — high landmass with sharply sloping surfaces; three types: Fold Mountains (Himalayas, Alps, Appalachians, Ural); Block Mountains (Rhine valley, Vosges); Volcanic Mountains (Mt. Kilimanjaro — Africa, Mount Fujiyama — Japan). Young mountains like Himalayas have pointed peaks; old mountains like Aravalli have rounded tops due to erosion.
• Plateaus — broad, level stretch of upland; also called tableland; the Deccan Plateau extends over thousands of kilometres in India; the Tibet Plateau is the highest in the world — called the ‘Roof of the World’; generally rich in mineral deposits.
• Plains — flat, low-lying vast expanse of land; formed by major rivers depositing silt; the Great Northern Plain of India is formed by deposits brought by river Ganga and her tributaries; the Hwang-Ho Plain (China) and Nile Valley Plain (Egypt) are also formed by rivers; plains are most suitable for human habitation — very thickly populated and fertile.

• Natural disasters are powerful events caused by natural processes of the Earth — widespread destruction, loss of life, and damage to the environment and property.
• Events such as earthquakes, landslides, avalanches, GLOFs and dust storms are examples of natural hazards that significantly affect human settlements and natural ecosystems.
• Understanding these disasters is important for disaster preparedness, risk reduction and effective management.

Earthquake — Epicenter, Focus and Seismic Waves

• Both the earth’s surface and interior are unstable — a sudden shaking of earth is a result of this instability and sudden release of energy.
• An earthquake causes trembling of the ground — buildings, trees, poles, dams begin to shake depending on the intensity.

• Man has not yet been able to invent any instrument that can predict the sudden outburst of earthquake energy — thus earthquake is regarded as a ‘sudden-onset hazard’.
• Over 1 million earthquakes occur at any time of the year in any part of the world including oceans — underwater earthquakes generate tsunamis.
• At least four dozen of these are described as highly hazardous to life and property of the people.
• In some western countries and USA, loud sirens have begun to be played as warning systems — but only few prove correct.

• Earthquake prone zones are today well marked in maps — settlements along geological fault-lines are most vulnerable to: earthquakes, landslides, and floods on account of breach of river banks or dams.
• Vulnerability depends on density of human settlements, soil and rock types — disintegrated rocks, sedimentary rock strata, alluvial and windblown soil are more vulnerable.
• A U.S. Geological Survey publication has shown that earthquake waves could shake a section of the crest 2000 metres thick.
• Geology of the area directly affects the intensity of the shock — steepness of the slope makes an earthquake shock more vulnerable.

• Panic: Vibratory waves cause panic among animals and humans alike — more damage is done by the panic.
• Physical damage: Collapse of buildings, cracks in ground, roads, bridges, walls, water tanks, bunds, rivers and dams.
• Public health: Hazards of disease on account of pollution of water bodies, breakdown of sewage and sanitary pipes, leading to epidemics.
• Civic services and conveyances: Water pipes, sewers, electric connections, roads disrupted — transmission towers and transformers also collapse.
• Disruption of economic activities: Farming, business, trade and services severely affected.
• Fire: Collapse of containers of inflammable substances like gas, petrol, kerosene, chemicals — tremors, heat and suffocation cause further damage.

• Engineered structures should be designed and built to withstand ground shaking — architectural and engineering inputs to improve building design and construction practice.
• Soil type must be analysed before construction — structures must not be built on soft soil; buildings on soft soil are more likely to get damaged even if the earthquake is not strong.
• Similar problem in alluvial plains and on river banks — heavy damages sustained when ground is soft.

• Public awareness and education: Information about time of actual shock and its intensity should be made public over radio, television and newspapers well in advance.
• Awareness should include: real cause of earthquake; Do’s and Don’ts during and after earthquake; awareness about risks and geology of the area; sensitization of engineers, architects, masons, doctors, government functionaries, bankers and financiers.

Landslides — Sudden Movement of Rock and Debris Down Slopes

• A landslide is a sudden movement of masses of rock, earth or debris with a force of their own weight down mountain slopes or river banks.
• People in hilly terrains or along river banks experience landslides often — also take place in areas of surface excavation for highways, buildings, fly-overs, underground railways, open pit mines.
• Landslides are a major natural disaster in the Himalayas, Western Ghats and North Eastern region covered by Pooravanchal Mountains.
• They cause damage to life, property, crops almost perennially — damage transportation and communication networks, causing long traffic jams.

• Landslides occur due to heavy rains, heavy snowfall, earthquakes, floods and volcanoes — most occur without any prior warning.
• There are no clearly established warning systems — hence, prediction of landslides is difficult.
• Areas of high risk can be determined by utilising information on geology, hydrology, vegetation cover, past occurrence and consequences in the region.

• Drainage corrections: Reduce water infiltration by allowing excess water to drain off; maintenance of natural drainage channels in vulnerable slopes.
• Engineered structures: Buildings with strong foundations; underground installations fitted flexibly to withstand forces caused by landslides.
• Retaining walls: Built along a slope to stop land from slipping — visible along roads at hill stations like Shimla.
• Building bylaws and codes: Bureau of Indian Standards and Indian Meteorological Department have prepared earthquake prone zone maps — codes and bylaws should be widely publicised and vigorously followed.
• Vegetation cover: The easiest, cheapest and most effective way of arresting landslides — through afforestation and avoiding grazing along mountain slopes.

• Land-Use Practices: Preserving and protecting natural vegetation; check/ban on deforestation; grazing of sheep and goats along mountain slopes should be banned; denuded upper slopes must be reforested; blockage of natural drainage should be avoided while constructing roads, canals, buildings.
• Hazard Mapping: Taken up by Government agencies, NGOs and others to locate regions prone to landslides — helps avoid construction of roads, buildings and bridges in landslide-prone areas.
• Awareness generation: Public awareness about causes, effects and areas prone to landslides is essential — imminent danger should be forecasted so that people may take safety measures.

Avalanche — Sudden Flow of Snow and Ice Down a Mountain Slope

• An avalanche is a sudden and rapid flow of snow, ice, and sometimes rocks down a mountain slope.
• One of the most dangerous natural hazards in mountainous regions — can occur naturally or be triggered by human activities such as skiing, snowmobiling, or construction.

• 1. Heavy Snowfall: Large amount of fresh snowfall increases weight on existing snow layers, making them unstable.
• 2. Weak Snow Layers: If a weak layer forms beneath a heavier layer, it can collapse and trigger an avalanche.
• 3. Temperature Changes: Rapid warming causes snow to melt and lose bonding strength; sudden cooling creates fragile layers within the snowpack.
• 4. Steep Slopes: Most common on slopes between 30 and 45 degrees — gravity can easily pull the snow downward.
• 5. Human Activities: Skiers, mountaineers, vehicles or construction activities can disturb the snowpack and trigger avalanches.
• 6. Earthquakes or Vibrations: Natural vibrations from earthquakes or loud sounds may initiate avalanches in unstable snow conditions.

• 1. Monitoring and Early Warning Systems: Regular observation of snow conditions, weather forecasting and avalanche prediction systems help warn people in advance.
• 2. Controlled Avalanches: Authorities sometimes deliberately trigger small avalanches using explosives to prevent buildup of large, dangerous snow masses.
• 3. Protective Structures: Snow fences, retaining walls, avalanche barriers and diversion dams protect roads, railways and settlements.
• 4. Land Use Planning: Avoiding construction in high-risk avalanche zones reduces exposure to danger.
• 5. Afforestation: Planting trees on mountain slopes helps stabilise snow and reduce the likelihood of avalanches.
• 6. Public Awareness and Training: Educating people about avalanche risks, safety measures and rescue techniques (such as carrying avalanche beacons and probes) improves survival chances.

Glacial Lake — Massive Release of Water from a Glacial Lake

• A Glacial Lake Outburst Flood (GLOF) is a sudden and massive release of water from a glacial lake formed when melting glaciers accumulate water behind natural dams made of ice or loose rock debris (moraines).
• GLOFs are among the most dangerous natural hazards in mountainous regions — particularly in the Himalayas, Andes and other glacier-fed areas.
• When the natural dam fails, enormous volumes of water rush downstream causing severe flooding, destruction of infrastructure, loss of life and environmental damage.
• With rising global temperatures accelerating glacier melt, the risk of GLOFs has increased in many parts of the world.

• 1. Melting of Glaciers: Climate change leads to rapid glacier melting, increasing water volume and raising pressure on the natural dam.
• 2. Weak Moraine Dams: Glacial lakes blocked by loose piles of rocks and debris (moraines) which are unstable and prone to collapse.
• 3. Ice Avalanches or Landslides: Falling ice, rocks or landslides into the lake create large waves that overtop and breach the dam.
• 4. Earthquakes: Seismic activity can weaken or crack the natural dam, triggering sudden water release.
• 5. Heavy Rainfall or Rapid Snowmelt: Excess water from intense rainfall or sudden temperature rise increases water levels beyond the dam’s capacity.

• 1. Regular Monitoring and Risk Assessment: Satellite imagery, field surveys and remote sensing help identify potentially dangerous glacial lakes and monitor water levels.
• 2. Early Warning Systems: Installing sensors and alarm systems downstream alerts communities in case of sudden lake discharge.
• 3. Controlled Drainage: Constructing drainage channels, tunnels or siphon systems can safely reduce water levels in high-risk lakes.
• 4. Strengthening Natural Dams: Reinforcing moraine dams with protective structures reduces likelihood of sudden collapse.
• 5. Land Use Planning: Avoiding construction and settlement in flood-prone downstream areas minimises damage and loss.
• 6. Community Awareness and Preparedness: Educating local populations about evacuation routes and emergency response plans improves safety and resilience.

Duststorm — Strong Winds Lifting Large Amounts of Dust and Sand

• Duststorms are severe environmental disasters — strong winds lift large amounts of dust and sand from dry, bare soil into the atmosphere; reduce visibility and severely affect human life, agriculture, infrastructure and the environment.
• Most common in arid and semi-arid regions — pose serious health risks including respiratory problems such as asthma, bronchitis and eye infections; damage crops, degrade soil fertility and contaminate water sources.

• The primary causes are both natural and human-induced.
• Naturally — prolonged drought, high temperatures and strong winds create dry and loose soil conditions; sparse vegetation cover in desert regions also contributes.
• Human activities such as deforestation, overgrazing, poor agricultural practices, urbanisation and excessive land clearing further increase soil erosion and desertification.
• Climate change increases temperatures and alters rainfall patterns — leading to more frequent droughts and degraded land surfaces.

• Afforestation and reforestation programs should be promoted to stabilise soil and act as windbreaks.
• Sustainable land management — crop rotation, conservation tillage and controlled grazing help maintain soil structure and reduce erosion.
• Early warning systems and improved weather forecasting to alert communities in advance.
• Public awareness campaigns — staying indoors and using protective masks during storms.
• Regional cooperation is important because duststorms often cross national boundaries — sustainable environmental practices and strengthened disaster preparedness can significantly reduce harmful impacts.