Comprehensive Physical Geography Notes

UNIT I – Geography as a Discipline

  • Geography = Geo (earth) + Graphos (description) – coined by Eratosthenes (276-194 BC).

  • Explores spatial variation of all physical & human phenomena; investigates what, where, why questions.

  • Integrating discipline: interfaces with natural sciences (geology→geomorphology; meteorology→climatology; hydrology→oceanography; pedology→soil geography) + social sciences (economics→economic geography; sociology→social geography; demography→population geography; political science→political geography).

  • Dual approaches:

    • Systematic (Humboldt): study a phenomenon worldwide then typologies (e.g., natural vegetation).

    • Regional (Ritter): study all phenomena in a given region holistically.

  • Branches (Systematic): Physical (geomorphology, climatology, hydrology, soil), Human (social/cultural, population & settlement, economic, historical, political), Biogeography (plant, zoo, ecology, environmental).

  • Branches (Regional): Macro/Meso/Micro regional studies; regional planning, development, analysis.

  • Tools & techniques: Cartography, quantitative/statistical, field survey, Geo-informatics (Remote Sensing, GIS, GPS).

UNIT II – The Earth

Origin & Evolution

  • Nebular Hypothesis (Kant-Laplace 1796): planets condensed from rotating solar nebula.

  • Modern Big Bang theory (Hubble 1920): universe began 13.7 Ga; expansion continues.

  • Star & planet formation via nebula→core + rotating disc→planetesimals→accretion → planets (4.6 Ga).

  • Solar system: Sun + 8 classical planets (Pluto now dwarf) + 63+ moons + asteroids, comets, dust.

    • Inner terrestrial (Mercury–Mars) rock & metal, high density.

    • Outer Jovian / Gas Giants (Jupiter–Neptune) massive, H-He atmospheres.

  • Moon formation – Giant Impact (“The Big Splat”): Mars-sized body hit Earth → debris accreted 4.44 Ga.

Evolution of Earth systems

  • Differentiation: heavier Fe-Ni sank → core; lighter silicates rose → mantle/crust.

  • Layers: Crust (oceanic 5 km, continental 30–70 km), Mantle (incl. asthenosphere ≤400 km semi-molten), Core (outer liquid, inner solid, up to 13 g cm⁻³).

  • Atmosphere stages: loss of primordial H-He; degassing of volatiles (H₂O, CO₂, NH₃, CH₄); oxygenation via photosynthesis (~2 Ga).

  • Hydrosphere: oceans formed ≤500 Ma after Earth; water vapour condensed as temp dropped.

  • Geological Time Scale: Hadean >4 Ga, Archean, Proterozoic, Palaeozoic (Cambrian–Permian), Mesozoic (Triassic–Cretaceous), Cainozoic (Tertiary–Quaternary → modern Homo sapiens).

UNIT III – Landforms

Minerals & Rocks

  • Crust ≈ 98 % O, Si, Al, Fe, Ca, Na, K, Mg.

  • Major rock-forming mineral groups: feldspars, quartz, pyroxenes, amphiboles, micas, olivine.

  • Rock types:

    • Igneous (primary) – cooling magma; intrusive/plutonic (granite, gabbro) & extrusive/volcanic (basalt).

    • Sedimentary – lithification of detritus; mechanically formed (sandstone, shale), chemically (chert, limestone), organically (coal).

    • Metamorphic – P-V-T re-crystallisation (gneiss, schist, marble, quartzite).

  • Rock Cycle: igneous → weathered → sedimentary → metamorphic → melting → magma → igneous.

Geomorphic Processes

  • Endogenic: diastrophism (orogeny, epeirogeny, faulting), volcanism; driven by geothermal heat.

  • Exogenic: weathering, mass wasting, erosion, deposition; driven by solar energy & gravity.

    • Weathering: chemical (solution, carbonation, hydration, oxidation), physical (unloading/exfoliation, temp change, frost wedging, salt), biological.

    • Mass movements: creep, solifluction, earthflow, mudflow, landslides, rockfall.

    • Erosional agents: running water, groundwater, glaciers, wind, waves.

Selected Landforms

  • Fluvial: V-valley, gorge, canyon, potholes, waterfalls, meanders, oxbow, natural levee, delta, alluvial fan.

  • Karst: sinkholes/dolines, uvala, lapies, caves→stalactites/stalagmites.

  • Glacial: cirque, horn, U-shaped valley, fjord, moraine (lateral, medial, terminal), drumlin, esker, outwash plain.

  • Coastal: cliff, wave-cut platform, beach, spit, bar, barrier, lagoon.

  • Aeolian (desert): dunes (barchan, parabolic, seif, longitudinal, transverse), pedestal rock, playa, bajada.

UNIT IV – Climate

Atmosphere Composition & Structure

  • Gases (by volume): N₂ 78 %, O₂ 21 %, Ar 0.93 %, CO₂ 0.04 %; variable H₂O 0–4 %, O₃.

  • Layers: Troposphere (0-8/18 km, weather; lapse −6.5°C km⁻¹) → Tropopause → Stratosphere (to 50 km, Ozone) → Mesosphere (to 80 km) → Mesopause → Thermosphere/Ionosphere (80-400 km) → Exosphere.

Insolation & Heat Budget

  • Solar constant ≈ 1.94 cal cm⁻² min⁻¹ (1367 W m⁻² at TOA).

  • ~35 % reflected albedo (27 % clouds, 2 % snow, etc.), 14 % absorbed atmosphere, 51 % absorbed surface; Earth radiates 17 % direct + 34 % via atmosphere = balance 65 %.

  • Heat transfer: conduction, convection/advection, terrestrial radiation; latent heat.

Temperature & Pressure belts

  • Global distribution: equatorial low, subtropical highs 30°, sub-polar lows 60°, polar highs.

  • Forces on wind: pressure gradient, Coriolis, friction → geostrophic winds.

  • Planetary winds: trade easterlies, westerlies, polar easterlies; ITCZ migration.

  • Seasonal monsoon; local winds: land/sea breeze, mountain/valley, chinook, loo.

  • Air masses (mT, cT, mP, cP, cA); fronts (warm, cold, occluded, stationary) → mid-latitude cyclones; tropical cyclones (hurricane/typhoon) energy released by condensation.

Moisture & Precipitation

  • Humidity: absolute (g m-³), specific, relative (%).

  • Processes: evaporation, condensation (dew point) → dew, frost, fog/smog, clouds (cirrus, cumulus, stratus, nimbus).

  • Precipitation types: convectional, orographic, cyclonic; forms: rain, snow, sleet, hail.

Climate Classification (Köppen)

  • Criteria: mean monthly temp & precip; groups A Tropical, B Dry, C Warm temperate, D Cold snow-forest, E Polar, H Highland; further types Af, Am, Aw, BWh, BSh, Cfa, Cs, Cfb, Df, Dw, ET, EF.

Climate Change

  • Past variability: glacial-interglacial cycles; Little Ice Age (1550-1850);

  • ENSO (El Niño / La Niña) alters global weather.

  • Greenhouse gases (CO₂, CH₄, N₂O, CFCs) ↑ → global warming (+ 0.6 °C since 19th c.); treaties: Montreal, Kyoto.

UNIT V – Water (Oceans)

Hydrological Cycle

  • 97 % water in oceans; 2 % ice; 0.68 % groundwater; renewal constant.

  • Processes: evaporation, transpiration, condensation, precipitation, runoff, infiltration.

Ocean Relief

  • Major divisions: Continental shelf (avg 80 km wide, <200 m deep), slope (to 3000 m), deep-sea plain (abyssal 3-6 km), trenches (>6000 m; Mariana 11,022 m).

  • Minor: mid-oceanic ridges (MOR), seamounts & guyots, abyssal hills, canyons, coral reefs & atolls.

Properties of Seawater

  • Temp: surface 27 °C equator → 0 °C poles; thermocline 100-400 m; deep ocean ~4 °C.

  • Salinity: avg 35 o/oo; controls: evaporation/precip, river input, ice; high in subtropical highs (Red Sea 41), low near estuaries & poles.

Movements

  • Waves: energy, parts (crest, trough, wavelength). Break when depth <½ wavelength.

  • Tides: gravitational pull Moon+Sun + centrifugal; spring & neap; tidal range >15 m Bay of Fundy; importance navigation, power.

  • Currents: surface (wind-driven gyres; warm vs cold) & deep (thermohaline); Gulf Stream, Kuroshio, Humboldt, Benguela. Upwelling zones fertile fisheries.

UNIT VI – Life on Earth

Ecology & Ecosystems

  • Ecology: study of interactions of organisms with abiotic environment.

  • Ecosystem = biotic (producers, consumers, decomposers) + abiotic (energy, nutrients) → food chains/webs; energy flow 10 % law; detritus vs grazing chains.

  • Biomes: Forest (tropical, temperate, boreal), Grassland (savanna, steppe), Desert (hot, semi-arid, cold), Tundra, Aquatic (marine/freshwater), Highland.

Biogeochemical Cycles

  • Water global circulation.

  • Carbon: photosynthesis ↔ respiration/decay; fossil fuels.

  • Oxygen: produced photosynthesis, used respiration.

  • Nitrogen: fixation (bacteria, lightning) → nitrification, assimilation, denitrification.

  • Mineral cycles (P, S, Ca, K).

Biodiversity & Conservation

  • Levels: genetic, species (~10 million), ecosystem.

  • Importance: ecological stability, economic (food, medicine), scientific & ethical.

  • Threats: habitat loss (deforestation), over-exploitation, pollution, exotic species, climate change; categories: endangered, vulnerable, rare.

  • Hotspots (Myers): 34 now; India part of Western Ghats-Sri Lanka & Himalaya hotspots.

  • Conservation: IUCN Red List; CITES; CBD 1992; in India – Wildlife Protection Act 1972, biosphere reserves (Nilgiri, Sundarbans, Nanda Devi…).