Geomorphic Processes — Class 11 Geography

The earth's surface is uneven because of two opposing groups of forces: endogenic forces, which build up the crust from within, and exogenic forces, which wear it down. Endogenic geomorphic processes include diastrophism (orogeny or mountain building, epeirogeny or continental uplift, earthquakes and plate tectonics) and volcanism, both energised by heat from within the earth. Exogenic processes derive their energy from the sun and from gravity-driven gradients, and are collectively termed denudation, which includes weathering, mass movements, erosion and transportation. Weathering is the in-situ mechanical disintegration and chemical decomposition of rocks; its three groups are chemical (solution, carbonation, hydration, oxidation), physical or mechanical (thermal expansion, unloading, salt weathering) and biological weathering. Weathering aids biodiversity, soil formation, mass movement and the enrichment of ores. Mass movements (creep, flow, slide and fall, including landslides, slumps and rock falls) transfer rock debris downslope under gravity. Erosion and deposition by running water, glaciers, wind, waves and groundwater shape landforms. Soil formation (pedogenesis) depends on five factors: parent material, topography, climate, biological activity and time; parent material, topography and time are passive factors, while climate and biological activity are active factors.