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Exogenic processes UPSC: Weathering , erosion, deposition, and mass movements
Exogenic processes, driven primarily by solar energy and gravitational forces, are fundamental mechanisms that shape the Earth’s surface. These processes include weathering, erosion, deposition, and mass movements, each playing a distinct role in transforming landscapes. For UPSC aspirants, understanding these processes is critical, as they form the basis of geomorphology, influence ecological systems, and impact human settlements and economic activities. The interplay of these processes explains the formation of diverse landforms, soil fertility, and natural hazards, making them integral to topics like disaster management, environmental conservation, and sustainable development.
Table of Contents
Weathering: The Breakdown of Earth’s Surface
Weathering refers to the in-situ disintegration and decomposition of rocks at or near the Earth’s surface. It is classified into three types: physical weathering, chemical weathering, and biological weathering.
Physical weathering, also known as mechanical weathering, involves the breakdown of rocks without altering their chemical composition. Key mechanisms include thermal expansion and contraction, where temperature fluctuations cause rocks to expand during the day and contract at night, leading to stress and fractures. This is prominent in arid regions like the Thar Desert. Frost action occurs in temperate or high-altitude areas, where water seeps into rock cracks, freezes, and expands, exerting pressure on the rock. This process is significant in the Himalayas. Salt crystallization involves the growth of salt crystals in porous rocks, common in coastal regions like Gujarat and Tamil Nadu, where saline groundwater evaporates, leaving salts that wedge apart mineral grains.
Chemical weathering alters the chemical composition of rocks through reactions with water, oxygen, and acids. Oxidation occurs when minerals like iron react with oxygen, leading to rust-like deposits, as seen in lateritic soils of Karnataka and Odisha. Hydrolysis involves the reaction of minerals with water, forming new compounds; for example, feldspar in granite weathers into clay minerals. Carbonation is the reaction of carbonate rocks like limestone with carbonic acid (formed when CO2 dissolves in water), leading to the creation of karst landscapes such as the Krem Liat Prah caves in Meghalaya. Acid rain, caused by industrial emissions, accelerates chemical weathering in urban areas, damaging historical monuments like the Taj Mahal.
Biological weathering results from the activities of living organisms. Plant roots grow into rock fractures, exerting pressure and splitting rocks—a process common in the Western Ghats. Burrowing animals like earthworms and termites expose rocks to further weathering. Lichens and microorganisms secrete organic acids that dissolve minerals, contributing to soil formation. Human activities such as mining and deforestation also accelerate biological weathering by disturbing rock structures.
Erosion: The Transport of Weathered Material
Erosion involves the removal and transport of weathered material by natural agents like water, wind, ice, and gravity. The effectiveness of erosion depends on factors such as slope gradient, climate, vegetation cover, and human intervention.
Water erosion is the most widespread agent, particularly in India’s monsoon-driven climate. Sheet erosion removes thin layers of topsoil from flat or gently sloping lands, degrading agricultural productivity in states like Punjab and Haryana. Rill erosion forms small channels on slopes, while gully erosion creates deep trenches, as observed in the Chambal Ravines of Madhya Pradesh. River erosion shapes valleys and floodplains; for instance, the Brahmaputra’s lateral erosion causes bank collapse and displacement in Assam. Coastal erosion, driven by waves and currents, threatens regions like Kerala’s Alappuzha and the Sundarbans delta.
Wind erosion dominates arid and semi-arid regions. Deflation lifts and removes fine particles, creating desert pavements in Rajasthan. Abrasion involves wind-blown sand grinding against rock surfaces, forming yardangs and mushroom rocks in the Rann of Kutch. Loess deposits, though rare in India, are fine silt transported over long distances.
Glacial erosion occurs in high-altitude regions like the Himalayas. Plucking involves ice freezing onto rock fragments and tearing them away, while abrasion by ice-embedded debris carves U-shaped valleys and cirques. The Gangotri Glacier exemplifies these processes, contributing to the formation of the Bhagirathi River.
Gravitational erosion includes landslides and rockfalls, where material moves downslope due to gravity. This is discussed in detail under mass movements.
Deposition: The Settling of Eroded Material
Deposition occurs when transporting agents lose energy, leading to the accumulation of sediments. This process creates distinct landforms and fertile soils, vital for agriculture and ecosystems.
Fluvial deposition forms alluvial plains, such as the Indo-Gangetic Plains, where rivers like the Ganga and Indus deposit silt, creating some of the world’s most fertile soils. Deltas, like the Sundarbans, develop at river mouths where sediment load exceeds the river’s capacity to carry it. Oxbow lakes and levees are other depositional features.
Aeolian deposition results in sand dunes and loess plains. Rajasthan’s Thar Desert features barchans and longitudinal dunes, while semi-arid regions like Gujarat have loamy soils from windblown silt.
Glacial deposition leaves behind moraines, drumlins, and eskers. The Kashmir Valley contains karewa deposits, ancient glacial sediments that support saffron cultivation.
Coastal deposition forms beaches, spits, and tombolos. Marina Beach in Chennai and Chilika Lake’s sandbars exemplify such features.
Lacustrine deposition in lakes creates flat plains, as seen in the Kashmir Valley’s Dal Lake surroundings.
Mass Movements: Downslope Transport of Material
Mass movements involve the large-scale movement of soil, rock, or debris downslope under gravity. These include rapid events like landslides and slow processes like soil creep, significantly impacting topography and human settlements.
Landslides are sudden movements of rock or debris, often triggered by heavy rainfall, earthquakes, or human activities. The Himalayas, particularly Uttarakhand and Himachal Pradesh, are prone to landslides due to steep slopes, fragile geology, and monsoonal rains. The 2013 Kedarnath disaster, triggered by cloudbursts, caused massive landslides and loss of life. Debris flows and mudflows are common in the Western Ghats during monsoons, disrupting transport and agriculture.
Slumps involve rotational movement of material along curved surfaces, common in coal-rich areas like Jharkhand, where mining weakens slopes. Rockfalls occur in steep terrains, such as the Nilgiri Hills, where weathered rocks detach and fall.
Soil creep is the gradual downhill movement of soil due to freeze-thaw cycles, wetting-drying, or animal activity. Though imperceptible, it tilts structures and fences over time, affecting regions like Meghalaya’s Shillong Plateau. Solifluction, a type of creep in water-saturated soils, occurs in periglacial regions of Ladakh.
Economic and Environmental Significance
Exogenic processes have profound implications for India’s economy and environment. Weathering enriches soil fertility, supporting agriculture in regions like the Deccan Plateau, where black cotton soils form from basalt weathering. Erosion and deposition shape river basins critical for irrigation and hydropower. The Ganga-Brahmaputra delta’s fertile soils sustain rice and jute cultivation, while coastal deposits support mangrove ecosystems like the Sundarbans, a UNESCO World Heritage Site.
However, these processes also pose challenges. Soil erosion reduces agricultural productivity, costing India nearly 0.8% of its GDP annually. States like Madhya Pradesh and Rajasthan face desertification due to wind erosion. Landslides disrupt transportation and damage infrastructure, particularly in the Himalayan states. The 2014 Malin landslide in Maharashtra buried an entire village, highlighting the need for disaster preparedness.
Depositional landforms like deltas and floodplains are densely populated, making them vulnerable to flooding. The Kosi River’s shifting course in Bihar exemplifies how deposition can lead to recurrent floods, displacing millions. Coastal deposition, while creating habitats, also leads to siltation in ports like Kolkata, affecting maritime trade.
Human Interventions and Government Initiatives
Human activities often exacerbate exogenic processes. Deforestation in the Himalayas accelerates landslides, while over-irrigation in Punjab induces soil salinization. Urbanization increases impervious surfaces, intensifying water erosion and urban flooding, as seen in Mumbai and Chennai.
The Indian government addresses these challenges through policies like the National Landslide Risk Management Strategy, which focuses on hazard mapping, early warning systems, and community awareness. The Soil Health Card Scheme promotes sustainable farming to reduce erosion. Afforestation programs like Green India Mission aim to stabilize slopes and enhance groundwater recharge.
The National Disaster Management Authority (NDMA) oversees landslide mitigation, advocating for slope stabilization techniques like terracing and gabion walls. Coastal Zone Management Plans regulate construction activities to prevent erosion, guided by the CRZ Notification, 2019.
Conclusion
Exogenic processes are dynamic forces that continually reshape India’s physical and human landscapes. For UPSC aspirants, comprehending the mechanisms of weathering, erosion, deposition, and mass movements is essential to analyze geomorphic hazards, agricultural sustainability, and environmental policies. These processes underscore the delicate balance between natural systems and human activities, emphasizing the need for integrated approaches to land use, disaster resilience, and ecological conservation. As climate change intensifies rainfall variability and glacial melt, understanding exogenic processes becomes even more critical for shaping India’s sustainable future.