Physical geography fundamentals (geomorphology, oceanography)
Geomorphology and oceanography fundamentals for UPSC: plate tectonics, landforms, ocean relief, salinity, currents, and tides, with exam-tuned framing.
The Earth's interior and plate tectonics
Geomorphology begins with the structure of the Earth. The 1909 discovery by Andrija Mohorovicic of a seismic-velocity discontinuity (the Moho) separated crust from mantle; the Gutenberg discontinuity (1914) marks the mantle-core boundary, and the Lehmann discontinuity (1936) the outer-inner core boundary. Seismic waves are the principal evidence: primary (P) waves are longitudinal and travel through solids and liquids; secondary (S) waves are transverse and cannot pass through the liquid outer core, producing the S-wave shadow zone beyond 103 degrees, while the P-wave shadow zone lies between 103 and 142 degrees. These facts are perennial Prelims fodder.
Alfred Wegener proposed Continental Drift in 1912 (Pangaea, Panthalassa, the Tethys Sea), citing the jig-saw fit of Atlantic coasts, the Glossopteris flora, and matching Gondwana glacial deposits. Harry Hess's Sea-Floor Spreading hypothesis (1962), confirmed by the Vine-Matthews-Morley palaeomagnetic stripes (1963) and the dating of basalt by drilling, supplied the mechanism Wegener lacked. By 1967-68 these merged into Plate Tectonics theory (Morgan, McKenzie, Le Pichon).
Plate boundaries and resulting landforms
Three boundary types must be memorised with examples. Divergent (constructive) boundaries form mid-ocean ridges such as the Mid-Atlantic Ridge and the East African Rift Valley. Convergent (destructive) boundaries take three forms: oceanic-continental collision builds fold mountains and trenches (the Andes, the Peru-Chile Trench); oceanic-oceanic collision builds island arcs (Japan, the Philippines, the Mariana Trench, deepest at the Challenger Deep, ~11,000 m); continental-continental collision built the Himalayas from the Indian plate's northward drift into Eurasia (collision beginning ~50 million years ago). Transform (conservative) boundaries, where plates slide laterally, are exemplified by the San Andreas Fault. The Himalayas remain seismically active; the Indian plate moves north-northeast at roughly 5 cm/year.
Exogenetic landforms
Weathering (physical, chemical, biological) and erosion shape the surface. Fluvial landforms progress from V-shaped valleys, gorges, and waterfalls in the youthful stage to meanders, ox-bow lakes, and floodplains in maturity, and deltas and natural levees in old age. Karst (limestone) topography yields sinkholes, caverns, stalactites and stalagmites. Glacial action produces U-shaped valleys, cirques, aretes, moraines, drumlins, and fjords. Aeolian (wind) processes in arid regions create barchans, seif dunes, yardangs, and loess deposits like those of northern China. Coastal landforms include sea cliffs, stacks, spits, and tombolos. The Davisian "Geographical Cycle" of erosion (W.M. Davis, 1899) and Penck's later critique frame how these stages are described in Mains answers. A candidate should connect process to landform precisely, because UPSC increasingly asks application questions rather than rote definitions.