Ch 6: Geomorphic Processes
This chapter acts as the conceptual anchor for landform evolution, detailing how endogenic tectonic forces construct the crust while exogenic weathering, mass wasting, and pedogenesis denude it.
Geomorphic Processes (Endogenic vs Exogenic)
This section establishes the foundational dichotomy between endogenic (earth-building) and exogenic (land-wearing) forces. Focus on diastrophism, including epeirogenic (continental building) and orogenic (mountain building) processes, along with volcanism. UPSC often targets the source of energy: endogenic forces are driven by radioactivity, rotational/tidal friction, and primordial heat, whereas exogenic forces are driven by solar energy and gravity. Avoid memorizing excessive geological eras; focus on the stress-strain relationship of rocks and shear strength thresholds.
Weathering Processes (Chemical, Physical, Biological)
Crucial for UPSC Prelims. Weathering types include chemical (hydration, carbonation, oxidation/reduction), physical (unloading, thermal expansion, frost wedging), and biological. UPSC tested how weathering of rocks releases nutrients (like phosphorus in biogeochemical cycles) in 2021. Pay attention to specific conditions: chemical weathering requires high moisture and temperature, while physical weathering dominates in dry/cold climates. Beware of confusing exfoliation domes (caused by unloading/thermal expansion) with chemical processes.
Exfoliation is not a single process but a common result of physical (unloading, thermal expansion) or chemical weathering, leading to the peeling of rock shells.
Mass Movements (Slow, Rapid, Landslides)
Mass movements are gravity-driven transfers of slope materials, distinct from erosion because no geomorphic agent (like wind/water) acts as a carrier. Understand the distinction between slow movements (creep, solifluction in permafrost) and rapid movements (earthflow, mudflow, debris avalanche). Landslides are exceptionally fast. Note the specific regional vulnerability of Himalayas (tectonically active, steep slopes, high rainfall) vs Western Ghats (stable but highly weathered, susceptible to debris slides during monsoons) which is a recurrent UPSC mains/prelims concept.
Gravity acts directly on the mass during mass wasting; geomorphic agents like running water, glaciers, wind, or waves do not carry the debris from place to place.
Erosion, Deposition and Soil Formation (Pedogenesis)
Soil formation (pedogenesis) is controlled by parent material, topography, climate, biological activity, and time. Note that climate (precipitation and temperature) and biological activity are active factors, while parent material, topography, and time are passive factors. Weathering is the prerequisite for soil formation. UPSC frequently tests soil profile development and the role of pioneer organisms (lichens, mosses) in biological weathering on bare rocks, bridging geography and ecology.
Topography and parent material are passive factors, while climate and organic activity are active soil-forming factors. Time acts as an independent passive variable.