Ch 7: Landforms and their Evolution
This chapter establishes the core geomorphic framework for identifying and distinguishing erosional and depositional landforms shaped by running water, groundwater, glaciers, waves, and winds, which UPSC tests through structural and classification questions.
Running Water
UPSC frequently tests the distinction between erosional and depositional landforms created by rivers. Focus on the evolutionary stages (Youth, Mature, Old) and specific features like V-shaped valleys, gorges, canyons, potholes, and plunge pools as erosional elements. Traps exist in confusing incised/entrenched meanders (which occur due to tectonic uplift) with normal flood plain meanders. Depositional features like alluvial fans, deltas, natural levees, and point bars must be thoroughly memorized. Skip mathematical stream-ordering equations, but pay close attention to the structural differences between alluvial fans (coarse, high slope) and deltas (fine-grained, flat).
A gorge is a deep valley with very steep to straight sides and is almost equal in width at its top as well as its bottom. A canyon is characterized by steep step-like side slopes and is typically wider at its top than at its bottom.
Groundwater (Karst Topography)
Karst topography requires specific chemical weathering conditions (carbonation of limestone/dolomite). Memorize the physical structure of erosional features like swallow holes, sinkholes, uvalas, lapies, and limestone pavements. Depositional features include stalactites, stalagmites, and pillars. UPSC tests the exact mechanism of cave formation and the spatial distribution of calcium carbonate deposition. Be aware of the trap where uvalas (coalesced sinkholes) are falsely defined as depositional features.
The term Karst is derived from the Karst region of Yugoslavia along the Adriatic Sea, where typical limestone formations with underground dissolution are found.
Glaciers
Glacial geomorphology features prominently in both Prelims (landform matches) and Mains (glaciology). Focus on erosional features like cirques, tarns, horns, serrated ridges (arêtes), and glacial troughs (U-shaped valleys). Depositional features are highly tested, especially moraines (lateral, terminal, medial), eskers, outwash plains, and drumlins. Ensure you do not confuse eskers (depositional) with arêtes (erosional). Also note the 'basket of eggs' topography reference for drumlins.
Drumlins are smooth oval shaped ridge-like features composed mainly of glacial till with some masses of gravel and sand. The stoss end facing the glacier is steeper than the down-glacier lee end.
Waves and Currents
This section details the dynamics of high rocky coasts (emergent/submergent) versus low sedimentary coasts. Erosional features include cliffs, wave-cut platforms, sea caves, arches, and stacks. Depositional features are beaches, dunes, bars, barrier bars, spits, and lagoons. UPSC often tests these concepts in the context of coastal vulnerability, CRZ regulations, and shoreline changes. Focus on the contrasting evolution of high vs. low coasts.
Winds
Arid geomorphology relies on wind as the primary agent alongside sheetwash erosion. Key erosional features are pediments, pediplains, playas, deflation hollows, and mushroom rocks. Depositional features include sand dunes like barchans, seifs, transverse dunes, and loess deposits. A major trap is the orientation of barchans: their wings/horns always point downwind, which is frequently reversed in trick questions.
Barchans are crescent-shaped dunes with points or wings directed downstream (in the direction of wind flow), whereas parabolic dunes are reverse with their tips pointing upstream.