Geomorphology Cheatsheet

Cheatsheet Content

### Earth's Interior #### Internal Structure of The Earth - Layers: Crust, Mantle, Outer Core, Inner Core (concentric layers with unique physical/chemical properties). - **Crust:** Silicate solid. - **Mantle:** Viscous molten rock. - **Outer Core:** Viscous liquid. - **Inner Core:** Dense solid. - **Mechanical Divisions:** Lithosphere, Asthenosphere, Mesospheric Mantle, Outer Core, Inner Core. - **Chemical Divisions:** Crust, Upper Mantle, Lower Mantle, Outer Core, Inner Core. ##### The Crust - Outermost layer, 0.5-1.0% of Earth's volume, Liquids > Gases). - Velocity: 5-8 km/s (crust) to 13.5 km/s (lower mantle), 11 km/s (inner core). - Used for earthquake warning (arrive before destructive S/surface waves). 2. **S-waves (Secondary waves):** - Transverse/shear/distortional waves (particle displacement perpendicular to wave propagation). - Create troughs/crests. - High frequency, slightly more destructive than P-waves. - **Cannot pass through fluids (liquids/gases).** - Travel at varying velocities (proportional to shear strength). ##### Surface waves (L-Waves) - Interact with surface rocks, generate new waves that move only along surface. - Slowest, recorded last. - Long period waves (long wavelength). - Low-frequency transverse waves. - Develop near epicenter, affect only surface, die out at shallow depths. - Lose energy slowly with distance. - Largest particle motion, **most destructive.** - **Love Waves:** Fastest surface wave, moves ground side-to-side. - **Rayleigh Waves:** Rolls along ground (up-down, side-to-side in wave direction), causes most shaking/damage. ##### How Do Seismic Waves Help In Understanding The Earth’s Interior? - Differences in arrival times, unexpected paths (refraction), and shadow zones allow mapping of interior. - Velocity discontinuities indicate changes in composition/density. - Wave motion discontinuities indicate phase changes. ##### Emergence of Shadow Zone of P-Waves & S-Waves - **S Wave Shadow Zone:** Entire zone beyond 103° does not receive S-waves (because S-waves can't travel through liquid outer core). Led to discovery of liquid outer core. - **P Wave Shadow Zone:** Band between 103° and 142° from epicenter. P-waves are refracted at mantle-outer core transition. - **No Shadow Zone:** Seismographs within 103° receive both P and S-waves (crust and mantle are solid). - **Shadow Zone For Both P Wave and S Wave:** Zone between 103° and 142° receives P-waves but not S-waves, providing clues about solid inner core. ### Earth’s Magnetic Field (Geomagnetic Field) #### Magnetosphere - Region above ionosphere, defined by Earth's magnetic field in space. - Extends tens of thousands of km, protects Earth from solar wind/cosmic rays (prevents atmospheric stripping). - Shaped like a hemisphere facing Sun, with a magnetotail on opposite side. - **Magnetopause:** Boundary where solar wind pressure balances Earth's magnetic field. - **Bow Shock:** Area where solar wind slows abruptly before magnetopause. - **Magnetosheath:** Turbulent magnetic region between magnetopause and bow shock. - **Plasmasphere:** Region inside magnetosphere with low-energy charged particles, rotates with Earth (60 km to 3-4 Earth radii, includes ionosphere). - **Auroras:** Luminous glow in upper atmosphere from charged particles (solar wind) interacting with atmospheric atoms near magnetic poles. #### Magnetosphere and Solar Wind - **Geomagnetic Storms:** Periods of intense solar activity (coronal mass ejections) cause rapid drop in Earth's magnetic field. - Effects: Ionosphere heating/distortion (disrupts long-range radio), increased satellite drag, GPS disruption, high astronaut radiation, power grid voltage spikes (blackouts). - A planet's magnetic field protects its atmosphere from solar wind stripping. #### Van Allen Radiation Belt - Zones of charged particles (from solar wind) captured by Earth's magnetic field. - Two concentric regions: Inner (1-2 Earth radii), Outer (4-7 Earth radii). - Deflect energetic particles, protecting atmosphere. - Endanger satellites (require shielding). Spacecraft beyond LEO face cosmic ray/solar particle hazards. #### Magnetic Field of Solar System Objects - **Moon:** Very weak, no magnetic dipole, not strong enough to prevent atmospheric stripping. - **Mercury:** Approx. magnetic dipole, 1.1% of Earth's field, can't sustain atmosphere due to Sun's proximity. - **Mars:** No intrinsic global magnetic field, weak magnetosphere, thin atmosphere. - **Venus:** Lacks magnetic field, ionosphere separates atmosphere from solar wind, dense atmosphere despite no field. - **Jupiter, Saturn, Uranus, Neptune:** Significant magnetic fields. #### Dynamo Theory: Generation of Earth’s Magnetic Field and Sustaining it - Mechanism: Convection in liquid outer core + Coriolis effect generates and sustains Earth's magnetic field (geodynamo). - Temperature/pressure/composition differences cause convection currents in molten iron. - Flow of liquid iron generates electric currents, which produce magnetic fields. Charged metals create their own currents, continuing the cycle. - Coriolis force aligns separate magnetic fields, producing one vast planetary field. #### Magnetic Poles - **North Magnetic Pole:** Geomagnetic field lines directed vertically downwards. - **South Magnetic Pole:** Geomagnetic field lines directed vertically upwards. - Magnetic Dip Poles: Where compass needle points straight down/up. - Earth's magnetic field is not perfectly symmetrical; magnetic poles are not antipodal but near geographic poles. - Earth's North magnetic pole is actually the South pole of its magnetic field (attracts North pole of compass). - **Geomagnetic Poles:** Intersections of Earth's surface and axis of hypothetical bar magnet at center. Tilted ~11° to rotational axis. - North geomagnetic pole = South pole of Earth's magnetic field. - South geomagnetic pole = North pole of Earth's magnetic field. - **Geomagnetic Reversal:** Change in Earth's magnetic field where magnetic north/south interchange. Occurs roughly every 200,000-300,000 years (not periodic like Sun's 11-year cycle). - **Normal Polarity:** Earth's North Magnetic Pole near Geographic North Pole. - **Reverse Polarity:** Earth's North Magnetic Pole near Geographic South Pole. - **Current Location:** North Magnetic Pole rapidly drifting towards Siberia. South Magnetic Pole off Antarctica. #### Compass - Compass needle points towards magnetic north (Earth's magnetic south pole). - **Magnetic Declination:** Angle between magnetic north and true north (changes with time). Ships must correct for this. - **Magnetic Inclination (Dip Angle):** Angle made with horizontal by Earth's magnetic field lines (angle of compass needle in vertical orientation). 0° at magnetic equator, 90° at magnetic poles. Aviation corrects for this. ### Geomorphic Movements - Earth's crust/surface constantly evolving due to **endogenic** (internal) and **exogenic** (external) forces. - Changes can be slow (weathering, folding), gradual (erosion), or sudden (earthquakes, volcanoes). - **Geomorphic agents:** Mobile media (water, glaciers, wind, waves) that remove, transport, deposit material. - **Geomorphic processes:** Physical/chemical processes on surface (folding, faulting, weathering, erosion). - **Geomorphic movements:** Large-scale changes from geomorphic processes. #### Endogenic Geomorphic Movements - Large-scale movements on Earth's crust/surface from forces deep below. - **Ultimate energy source:** Earth's internal heat (radioactive decay, gravitation). - Temperature/pressure differences create density differences, driving **convection currents** in mantle. - Convection currents move lithospheric plates (tectonics), causing endogenic movements. - Earth's rotation (Coriolis effect) influences convection current paths, determining nature/location of movements. - Divided into **diastrophic movements** (gradual, long-term) and **sudden movements** (short-term, rapid). ##### Diastrophism - Deformation of Earth's crust: folding, faulting, warping, fracturing. - Processes that move, elevate, or build up crustal portions. 1. **Orogenic processes:** Mountain building via severe folding (long, narrow belts). 2. **Epeirogenic processes:** Uplift/warping of large crustal parts (simple deformation). 3. **Earthquakes & Volcanism:** Local, relatively minor movements. 4. **Plate Tectonics:** Horizontal movements of crustal plates. - Evidence: Bent, broken, or tilted sedimentary rocks. ##### Epeirogenic or Continent Forming Movements - Radial movements (towards/away from center). - Cause upheavals or depressions (undulations of long wavelengths, little folding). - Affect broad central parts of continents (cratons). - **Uplift:** Raised beaches, elevated wave-cut terraces, sea caves, fossil beds above sea level (e.g., Kathiawar coast). - **Subsidence:** Submerged forests/valleys/buildings (e.g., Rann of Kachchh, peat/lignite beds below sea level). ##### Orogenic or Mountain-Forming Movements - More complex crustal deformation, associated with crustal thickening (plate convergence). - Act tangentially to Earth's surface, form orogenic belts (mountain ranges) via folding/faulting, magma intrusion, volcanism. - **Tension** produces fissures. - **Compression** produces folds. ##### Sudden Movements - Occur mostly at lithospheric plate margins, rapid deformation. - Plate margins unstable due to pressure from mantle convection currents. ###### Earthquakes - Sudden release of accumulated stress in rocks (folding, faulting, other changes) via weak zones on surface (seismic waves). - Can cause uplift/subsidence (e.g., New Zealand uplift, Japan subsidence). - Effects: Change in contours, river courses, shorelines, glacial surges, landslides, soil creeps. ###### Volcanoes - Molten rock (magma) escapes through crustal vents/fissures, accompanied by steam, gases, pyroclastic material. #### Exogenic Geomorphic Movements - Processes on Earth's crust/surface from forces above (wind, water). - Examples: Weathering, erosion. - Effects typically small/slow but cause severe long-term fatigue. - Sun's energy (weather patterns, winds, precipitation) causes stress, leading to exogenic movements. ##### Denudation - General term for all exogenic processes (weathering, erosion). - "Denude" = strip off/uncover. - Depends on physical (folds, faults, joints, hardness, permeability) and chemical (corrosion susceptibility) rock properties. ##### Weathering - Disintegration of rocks, soil, minerals by physical (heat, pressure) and chemical (leaching, oxidation, hydration) agents. - **In-situ/on-site process** (little material motion), unlike erosion which carries material away. - Three major groups: chemical, physical/mechanical, biological. Often occur together. - **Significance:** First step in soil formation, weakens rocks (aids resource exploitation), natural soil enrichment, mineral enrichment (leaching unwanted minerals). ##### Physical Weathering Processes - Mechanical disintegration from molecular stresses (temperature, shear, freeze-thaw, wet-dry, salt crystallization, biological activity). - **Exfoliation Due to Pressure Release/Unloading:** Intrusive rocks brought to surface, overlying load removed, vertical pressure release causes expansion/fracturing parallel to surface. Sheets of rock break away ("sheeting"). - **Exfoliation Due to Thermal Stress Weathering:** Expansion/contraction from diurnal/seasonal temperature changes. Surface layers expand more, causing peeling. Effective in dry climates/high elevations. - **Granular Disintegration:** In coarse-grained rocks, different minerals expand/contract differentially, causing grain-by-grain separation. - **Frost Weathering:** Ice-related processes (shattering, wedging, freeze-thaw). Water in cracks freezes (expands), exerting pressure. - **Frost Wedging:** Cracks forced apart by repeated freeze-thaw. - **Block Separation (Freeze-Thaw):** Rocks weaken along joints, break into angular pieces. - **Shattering:** Disintegrates rocks along weak zones, produces angular pieces (scree piles at mountain foot). - **Salt Weathering:** Saline solutions seep into cracks, evaporate, leave salt crystals. Crystals expand (crystallization, heating), splitting grains ("granular disintegration/foliation"). Common in arid climates. - **Mass Wasting (Slope Failure)/Mass Movements:** Mass movement of unconsolidated material (soil, sand, regolith) down a slope under gravity. Includes creep, flow, slide, fall. - Occurs when gravitational force > shearing resistance. - Timescales: Seconds (debris/mudflows) to hundreds of years (creeps). - **Causes:** Weak materials, thinly bedded rocks, faults, steep slopes, abundant rain, lack of vegetation, removal of support, increased gradient, overloading (natural/artificial), earthquakes, explosions, seepage. - **Slow Movements:** - **Creep:** Extremely slow, imperceptible movement of soil/rock debris on moderate slopes (e.g., leaning fence posts). - **Solifluction:** Slow downslope flow of saturated fine-grained rock debris/soil (common in moist temperate areas with surface melting). - **Rapid Movements:** Prevalent in humid regions, gentle to steep slopes. - **Earthflow:** Water-saturated clayey/silty earth moves down low-angle terraces/hillsides (slumps, arcuate scarps). - **Mudflows:** Saturated weathered material flows down channels (no vegetation, heavy rain). Very destructive (lahars from volcanoes). - **Debris Avalanche:** Rapid flow of debris on steep slopes (humid regions, with/without vegetation), faster than mudflow. - **Landslides:** Relatively rapid, perceptible movements of dry materials. - **Slump:** Slipping of rock debris with backward rotation. - **Debris Slide:** Rapid rolling/sliding without backward rotation. - **Debris Fall:** Nearly free fall from vertical face. - **Rockslide:** Sliding of individual rock masses along bedding/joint/fault surfaces. - Mass movements are gravity-aided, not erosion by geomorphic agents. Weathering aids them. - **Landslides in India:** Frequent in Himalayas (tectonically active, sedimentary rocks, steep slopes). Also in Western Ghats/Nilgiris (steep cliffs, mechanical weathering, heavy rain). Anthropogenic activities (road construction, tourism, plantation agriculture) exacerbate. ##### Chemical Weathering - Chemical decomposition of rocks/soil (loosening bonds). - Processes: Dissolution, solution, carbonation, hydration, oxidation, reduction. Interrelated, hasten weathering. - Acids (microbial/plant), water, air (O2, CO2), heat speed up reactions. - **Natural Dissolution:** Minerals (nitrates, sulfates, potassium) dissolve naturally in rains, leaving no residue (accumulate in dry regions). - **Solution Weathering:** Solvent is acidic solution (higher H+ conc.). - **Carbonation:** Atmospheric CO2 forms weak carbonic acid in rain, dissolves soluble rocks (limestone) to calcium bicarbonate (solution weathering). Speeds up with lower temp. (colder water holds more CO2). Forms caves (Karst topography). - **Anthropogenic Solution Weathering (Acid Rain):** SO2, NOx in atmosphere react to form stronger acids (pH ### Tectonics - Study of forces and processes (mantle convection, plate collisions, folding, faulting, volcanism) that control Earth's crustal structure and evolution. - Deals with large-scale lithospheric deformation. - Study of: 1. Folding/faulting (mountain building - orogeny). 2. Large-scale crustal movements (epeirogenic). 3. Growth/behavior of cratons (old continental cores). 4. Sudden horizontal displacements along faults (seismic waves). #### Major Concepts That Tried to Explain the Tectonic Processes - **Continental Drift Theory (CDT):** Movement of continents relative to each other. - **Polar wandering:** Relative movement of crust/upper mantle with respect to rotational poles. - **Seafloor Spreading Theory (SST):** Movement of oceanic plates relative to one another. - **Plate Tectonics (PT):** Movement of lithospheric plates relative to each other. - **Convection Current Theory (CCT):** Explains force behind plate movements (basis for SST & PT). #### Continental Drift Theory - Alfred Wegener (1912): One supercontinent **Pangaea** (covered by **Panthalassa** ocean). - Tethys Sea divided Pangaea into **Laurentia (Laurasia)** (north) and **Gondwanaland** (south). - Drift began ~200 million years ago (Mesozoic Era). ##### Forces Behind The Drifting Of Continents (According to Wegener) 1. **Equatorwards:** Gravity, pole-fleeing force (centrifugal force from Earth's rotation), buoyancy. 2. **Westwards:** Tidal currents (from Earth's west-to-east rotation). - Believed these forces acted over millions of years. ##### Evidence in Support of Continental Drift - **Apparent Affinity of Physical Features:** "Jigsaw fit" of continents (e.g., Brazil bulge into Gulf of Guinea). Criticism: Coastlines temporary, other combinations possible, geological affinity not always present. - **Botanical Evidence:** Glossopteris vegetation in Gondwana regions. Criticism: Similar vegetation in unrelated areas. - **Distribution of Fossils:** Mesosaurus fossils in South Africa/Brazil. Lemur occurrence in India/Madagascar/Africa (led to "Lemuria" concept). Criticism: Similar fossils in unrelated areas. - **Polar wandering (Shifting of Poles):** Past pole positions constantly drifted. Criticism: Poles may have shifted, not necessarily continents. - **Rocks of Same Age Across the Oceans:** 2-billion-year-old rocks in Brazil match western Africa. Criticism: Similar rocks elsewhere. - **Tillite deposits:** Glacial sedimentary rocks (Gondwana system) in India, Africa, etc., show similar history. - **Placer Deposits:** Gold deposits in Ghana (West Africa) from source veins in Brazil. ##### Drawbacks of Continental Drift Theory - Failed to explain why drift began only in Mesozoic. - Didn't consider oceans. - Proofs based on generalistic assumptions. - Proposed forces (gravity, buoyancy, tidal currents) too weak to cause such magnitude of drift. - Modern theories (Plate Tectonics) explain drift differently. - Despite flaws, a significant milestone for later theories. #### Seafloor Spreading - Harry Hess (1960): Explains continental drift within plate tectonics. - Oceanic plates diverge, tensional stress causes lithospheric fractures. - Basaltic magma rises, cools, forms new seafloor. - New seafloor moves away from ridge, replaced by newer seafloor. Older rocks move farther from spreading zone. - Underpinned by **Convection Current Theory** and **Palaeomagnetism**. ##### Convection Current Theory (CCT) - Arthur Holmes (1930s): Mantle convection currents (from radioactive elements) drive lithospheric plate movement. - **Falling limbs:** Create negative pressure (pulling force), causing plate convergence (trenches, volcanic arcs, fold mountains). - **Rising limbs:** Create positive pressure (pushing force), causing plate divergence (oceanic ridges, rift valleys/lakes). - Some internal heat reaches surface via volcanoes/springs/geysers (negligible compared to solar), but crucial for deep ocean life (chemosynthesis). ##### Palaeomagnetism - Study of Earth's past magnetic field recorded in rocks. - Magnetic minerals in solidifying basalt align with Earth's magnetic field, recording its orientation. - Paleomagnetic studies show frequent **geomagnetic reversals** over geologic time. - **Strong evidence for SST & PT:** - **Magnetic Striping:** Along mid-ocean ridges, alternate magnetic rock stripes show flipped polarity. Rising magma assumes current polarity, then moves away as new magma forms (series of narrow parallel bands with alternating polarity). - **Nature of Oceanic Rocks:** Rocks equidistant from ridge crest have similar composition, age, magnetic orientation. Rocks closer to ridge are youngest, age increases away from crest. Oceanic crust rocks much younger than continental crust. - **Distribution of Earthquakes and Volcanoes:** Higher temperature gradient near ridges (magmatic upwelling). Earthquakes shallow at mid-ocean ridges, deep-seated in subduction zones (Alpine-Himalayan, Pacific Rim). #### Plate Tectonics - McKenzie & Parker (1967), Morgan (1968). - Earth's lithosphere broken into rigid plates floating on ductile asthenosphere. - Plates move horizontally as rigid units. - Lithosphere: Crust + top mantle. Thickness: 5-100 km (oceanic), ~200 km (continental). - **Oceanic plates:** Simatic (silica, magnesium), thinner, heavier. - **Continental plates:** Sialic (silica, alumina), thicker. - Plates vary: minor/major, continental/oceanic, or combined (e.g., Indo-Australian). - Movement driven by mantle convection currents. - Rates: Arctic Ridge (slowest, 15 cm/yr). ##### Major Tectonic Plates 1. Antarctica and surrounding oceanic plate 2. North American plate 3. South American plate 4. Pacific plate 5. India-Australia-New Zealand plate 6. Africa with eastern Atlantic floor plate 7. Eurasia and adjacent oceanic plate ##### The Indo-Australian Plate - Includes Peninsular India, Australian continental portions. - **Northern boundary:** Subduction zone along Himalayas (continent-continent convergence). - **East:** Rakinyoma Mountains (Myanmar) to Java Trench island arc. - **Southeastern:** Oceanic ridge in SW Pacific. - **Boundary with Antarctic plate:** Oceanic ridge (divergent) south of New Zealand. - **Western boundary:** Kirthar Mountain (Pakistan), Makrana coast (Pakistan/Iran), Red Sea rift (divergence of Somali & Arabian plates), Chagos Archipelago (hotspot volcanism). ##### Minor Tectonic Plates - Cocos, Nazca, Arabian, Philippine, Caroline, Fuji, Turkish, Aegean, Caribbean, Juan de Fuca, Iranian. - Many microplates (e.g., Macquarie, Capricorn) identified in updated maps. ##### Interaction of Tectonic Plates - Forms major geomorphological features (fold/block mountains, mid-ocean ridges, trenches, volcanism, earthquakes). - Three types of interaction: ###### Divergence Forming the Divergent Edge (Constructive Edge) - Plates move apart. - Shallow focus earthquakes, volcanic landforms common. - **Oceans:** Mid-ocean ridges (e.g., Mid-Atlantic Ridge) formed by basaltic magma eruption, seafloor spreading (crust formation). - **Continents:** Rift valleys (e.g., East African Rift Valley). ###### Convergence Forming the Convergent Edge (Destructive Edge) - Plates collide. - **Orogenic collision:** Crumpling/folding, forming fold mountains (e.g., Himalayas). - Crust destroyed (compensated by crust formation at divergent edges). - **Oceanic plate subducts:** Trenches formed (subduction zone), subducted material melts, forms volcanic island arcs/continental arcs. Dynamic equilibrium. ###### Transcurrent Edge (Conservative Edge or Transform Edge) - Plates slide past each other. - No creation/destruction of landform, only deformation. - **Oceans:** Transform faults (perpendicular to mid-ocean ridges). - **Continents:** San Andreas Fault (USA). ##### Evidence in Support of Plate Tectonics - **Paleomagnetism:** Iron grain orientation in old rocks (polar wandering). - **Older Rocks Form the Continents While Younger Rocks are Present on the Ocean Floor:** Continental rocks up to 3.5 billion yrs old; oceanic floor rocks ### Convergent Boundary - Subtypes of convergence: 1. Ocean-Ocean (O-O) Convergence: Volcanic island arcs. 2. Continent-Ocean (C-O) Convergence: Continental arcs, fold mountains. 3. Continent-Continent (C-C) Convergence: Fold mountains. 4. Continent-Arc Convergence. - Denser plate subducts; less dense plate upthrust or folded. #### Ocean-Ocean Convergence (O-O Convergence) or The Island-Arc Convergence - Denser oceanic plate subducts below less dense oceanic plate, forming a trench. - **Formation of Island Arcs:** - Subducting oceanic plate (with sediments) metamorphoses under high P/T. - At ~100 km depth, plates melt, magma (lower density, high P) rises due to buoyancy. - Magma flows out, creating constant volcanic eruptions. - Continuous volcanism builds layers, forming volcanic landforms (island arcs) above sea level (e.g., Indonesian, Philippine, Japanese Island Arcs). - Orogenesis builds continental crust by replacing oceanic crust over millions of years. ##### Formation of The Philippine Island Arc System - Philippine Sea plate subducts under Sunda Plate (Eurasian plate). Forms Philippine Trench. ##### Formation of The Indonesian Archipelago - Indo-Australian plate subducts below Sunda Plate (Eurasian Plate). Forms Sunda Trench (Java Trench). ##### Formation of The Caribbean Islands - Caribbean Plate moves east, North American Plate moves west (transform/strike-slip boundary with small subduction component). Forms Greater Antilles, Puerto Rico Trench. - Lesser Antilles subduction zone: Oceanic crust of South American Plate subducts under Caribbean Plate (active volcanoes like Mount Pelée). ##### Formation of The Isthmus of Panama - Pacific-Farallon Plate subducts beneath Caribbean/South American plates, forming volcanic Panama arc. - N/S American plates move past Caribbean Plate (strike-slip/transform motion). - N-S convergence component leads to Panama Arc colliding with South America, causing uplift (Northern Andes, Panama Arc), forming Isthmus of Panama. ##### Formation of The Japanese Island Arc - Japan's volcanoes are part of three arcs. - Northern arc: Pacific Plate subducts under Eurasian Plate (Japan Trench). - Central arc: Pacific Plate subducts under Philippine Plate (Izu Trench). - Southern arc: Philippine Plate subducts under Eurasian Plate (Ryukyu Trench). - Arc tilted eastward by Pacific/Philippine plates, forming Sea of Japan. ##### The Mariana Trench or Marianas Trench - Deepest trench (Pacific Ocean), formed by Pacific Plate subducting below Mariana Plate. - Challenger Deep: >11 km deep. - Not closest to Earth's center (Earth's geoid shape makes Arctic Ocean seabed closer). #### Continent-Ocean (C-O) Convergence or The Cordilleran Convergence - Oceanic plate (denser) subducts below continental plate (less dense), forming a trench (shallower than O-O trenches). - **Formation of Continental Arcs:** - Subducting oceanic plate melts, magma rises, forms chain of volcanic mountains on continental plate (continental arc, e.g., Cascade Range, Western Chile range). - Accretionary wedge: Sediments accumulate in trench, compressed into continental margin (crustal shortening). - **Formation of Fold Mountains (Orogeny):** - Continental crust overrides oceanic crust. - Advancing oceanic plate compresses deformed continental margin, forming fold mountain system (orogenic belt). - Resistance builds, stopping convergence; subduction zone moves seaward. - Erosion, then isostatic adjustment, exposes mountain roots. (e.g., Rockies, Andes). - Andes: Nazca Plate subducts under South American Plate. Peru-Chile Trench. Continental arc volcanism. Accretionary wedge folds volcanic mountains. - Rockies: Juan de Fuca/Pacific plates move east, North American plate moves west. Less steep subduction, less conspicuous trench, many fault zones. #### Continent-Continent Convergence or The Himalayan Convergence - Both continental crustal plates too buoyant to subduct deep (>40-50 km). - Plates converge, buckle up (suture zone), fold, and fault. - Sedimentary basin (geoclinal/geosynclinal) squeezed between plates. - Huge rock slivers thrust over each other, forming towering mountain range. - Resistance builds, convergence ends. Mountain belt erodes, followed by isostatic adjustment. - Examples: Himalayas, Alps, Urals, Appalachians, Atlas Mountains. ##### Formation of The Himalayans and The Tibetan Plateau - Himalayas: Youngest mountain chain. Formed from Tethys Sea geosyncline. - India (Gondwanaland) separated from Eurasia (Laurasia) ~200 mya, moved north. - Sediments deposited in Tethys Sea (e.g., Everest summit is marine limestone). - India collided with Asia ~40-50 mya, causing folding and rapid uplift. - Indian plate movement (5-6 cm/yr) and Himalayan uplift continue (frequent earthquakes). - Indo-Gangetic plain formed by alluvium from Himalayan rivers. - Tibetan plateau: Formed by upthrusting of southern Eurasian Plate. - Curved shape of Himalayas attributed to maximum push at Indian Peninsula ends. - **Phases of Formation:** Great Himalayas (50-40 mya), Middle Himalayas (25-30 mya), Shiwaliks (2-20 mya). - **Evidence for Rising Himalayas:** Satellite measurements (5-10 cm/yr uplift), desiccated lakes in Tibet, rejuvenated rivers, frequent earthquakes. ##### Formation of Alps, Urals, Appalachians and the Atlas Mountains - **Alps, Atlas:** Young fold mountains (African Plate colliding with Eurasian Plate). Atlas still forming. - **Urals, Appalachians:** Very old fold mountains (formed before Pangaea breakup). Urals (Europe-Asia collision), Appalachians (N. America-Europe collision). ##### Volcanism and Earthquakes in Continent-Continent Convergence - No volcanoes: Continental crust (50-70 km thick) too thick for magma to penetrate. Magma stays in crust. - Metamorphic rocks common (stress on crust). - Numerous, large earthquakes: Enormous slabs of crust smashing together (e.g., Himalayas, North Indian Region, Kachchh). #### Continent-Arc Convergence or New Guinea Convergence - New Guinea formed ~20 mya by continent-arc collision. - Australian continental plate pushed New Guinea island arc towards oceanic crust. Caroline oceanic plate plunged under New Guinea island arc. - New Guinea trench formed, continental margin welded against island arc. ### Divergent Boundary - Responsible for evolution/creation of new seas and oceans. - Process begins with divergent boundary formation. #### Formation and Evolution of Rift Valleys, Rift Lakes, Seas, and Oceans - **Upwarp:** Broad elevated area. - **Plume:** Column of magma rising by convection. - **Rift Valley:** Linear lowland (graben) between highlands (horst) from geological rift/fault. ##### Stage 1: Upwarping and Fault Zones - Rising limbs of convection currents create plume, upwarping lithosphere. - Series of normal/thrust faults created during upwarping. Plates begin to diverge. ##### Stage 2: Rift Valley Formation - Faulting from divergence creates extensive rift system. - Lithosphere stretches, thins, eventually ruptures, forming rift valley. - Accompanied by volcanism and seismic activity. - Initial stage of continental breakup (e.g., South Atlantic Ocean from S. America-Africa breakup). - East African Rift (EAR): Active rift, large mantle plume doming lithosphere. Rifting began ~30 mya, propagating southwards. - Flood basalt volcanism (plateaus, highlands) follows rifting (e.g., Ethiopian Highlands). - Narmada/Tapti Rift Valleys: Formed by bending of Indian plate during Himalayas formation (different mechanism). ##### Stage 3: Formation of Linear Sea or Rift Lakes - Rift valley deepens (further divergence), oceanic crust replaces continental crust. - Ocean waters enter, forming linear seas (e.g., Red Sea). - Rift valleys evolve into volcanic vents, block mountains into oceanic ridges. - Successive volcanism/seafloor spreading create spreading sites (new crust formed: constructive edge). - **Rift Lakes:** If rift valleys form deeper within continents, rainwater accumulates (e.g., Lake Baikal, Lake Tanganyika). ##### Stage 4: Linear Sea Transforms Into Ocean - Intense basaltic magma outpouring accentuates seafloor spreading/oceanic crust formation. - Oceanic crust replaces continental crust, forming a mighty ocean. - Crust formation at mid-oceanic ridge (divergent) compensated by crust destruction at convergent boundary (destructive edge). - Continents and oceans transform. #### The Great Rift Valley - Runs ~6,400 km from Syria to Mozambique. - Northern part: Beqaa Valley (Lebanon), Jordan River, Dead Sea, Gulf of Aqaba, Red Sea. - Afar Triangle (Ethiopia/Eritrea): Triple junction. Gulf of Aden (eastward continuation), East African Rift (south-eastward). - East African Rift: Divides into Eastern Rift (Gregory Rift) and Western Rift (Albertine Rift, with deep lakes). - Before rifting: Continental flood basalts, uplift of Ethiopian/Somalian/East African plateaus. - Africa Splitting: EAR is active continental rift zone (~22-25 mya). African Plate splitting into Somali Plate and Nubian Plate (6-7 mm/yr). Lithospheric rupture in 10 mya, new ocean basin. ##### Volcanism & Seismicity Along East African Rift Valley - EAR zone has active/dormant volcanoes (e.g., Mount Kilimanjaro - dormant stratovolcano, Mount Kenya - extinct stratovolcano). - Most earthquakes near Afar Depression. ##### Mains Practise: Despite extensive volcanism, there is no island formation along the divergent boundary (mid-ocean ridge) - Basaltic magma (less viscous, low silica) flows out quietly, spreads widely, causing seafloor spreading, not conical volcanic islands. - Convergent boundaries have andesitic/acidic magma (more viscous, high silica), which builds stratovolcanoes. ##### Mains Practise: How is it that Mount Kilimanjaro and Mount Kenya that formed close to the divergent boundary are stratovolcanoes when the magma that flows out at the divergent boundary is basaltic? - Stratovolcanoes (andesitic magma) vs. Shield volcanoes (basaltic magma) depends on silica content (viscosity), not just location. - Mt. Kilimanjaro/Kenya (stratovolcanoes) formed from melting of subsurface crustal layers (andesitic magma) due to faulting stress during EAR formation. - Ethiopian Highlands formed from basaltic magma (shield volcanism) due to EAR divergence and Afar Hotspot. ### Types of Mountains #### Classification of Mountains based on The Period Of Origin - Nine orogenic movements. Three most recent: Caledonian, Hercynian, Alpine. - **Precambrian Mountains:** >541 mya. Remnants of old mountains (upheaval, denudation, metamorphosis). E.g., Laurentian, Algoman. - **Caledonian Mountains:** ~430-380 mya (late Silurian, early Devonian). E.g., Appalachians, Aravallis, Mahadeo. - **Hercynian Mountains:** ~340-225 mya (upper Carboniferous to Permian). E.g., Vosges, Black Forest, Altai, Tien Shan, Ural Mountains. - **Alpine Mountain System:** Tertiary Period (65-7 mya). Youngest, loftiest, rugged (e.g., Rockies, Alps, Atlas, Himalayas). #### Classification of Mountains based on Mode Of Origin - **Original or Tectonic Mountains:** 1. **Fold mountains:** Himalayas, Rockies, Andes. 2. **Block mountains:** Vosges, Black Forest, Vindhya, Satpura. 3. **Volcanic mountains (mountains of accumulation):** Cascade Range, Mount Aconcagua, Mount Kenya, Mount Kilimanjaro, Mount Mauna Kea, Mount Fujiyama. - **Circum-Erosional or Relict or Residual Mountains:** Remnants of old fold mountains due to denudation (e.g., Aravallis, Urals). Also from dissected plateaus (e.g., Scottish Highlands, Deccan Plateau). #### Classification of Mountains Based on Location - **Continental Mountains:** - **Coastal Mountains:** Rockies, Appalachians, Alpine chain, Western/Eastern Ghats. - **Inland Mountains:** Vosges, Black Forest, Kunlun, Tienshan, Altai, Urals, Aravallis, Himalayas, Satpura, Maikal. - **Oceanic Mountains:** On continental shelves/ocean floors. Mauna Kea (Hawaii) is tallest from ocean floor. #### Fold Mountains - Formed when sedimentary rock strata in geosynclines are subjected to compressive forces. - Loftiest, concentrated along continental margins. - **Geosyncline:** Large depression with thick sediment deposits (e.g., Tethys geosyncline). ##### ‘Fold’ In Geology - Undulating (wave-like) structure from bending of rocks/crust under compression. - **Anticlines:** Upwardly convex. Older strata in core, progressively younger outwards. - **Synclines:** Downwardly convex. Younger strata in core, progressively older outwards. - **Types of Folds:** Symmetrical, asymmetrical, isoclinal, overturned, recumbent. ##### Classification of Fold Mountains - **On the Basis of Period of Origin:** 1. **Very Old Fold Mountains:** >500 mya. Rounded features, low elevation (denudation). E.g., Appalachians, Urals. 2. **Old Fold Mountains:** Caledonian/Hercynian periods (>66 mya). Thickening relict, slightly rounded, medium elevation. E.g., Aravalli Range (oldest in India). 3. **Alpine or Young Fold Mountains:** Tertiary period (66 mya-present). Rugged relief, conical peaks (e.g., Rockies, Andes, Alps, Himalayas). - **On The Basis of The Nature of Folds:** 1. **Simple fold mountains:** Well-developed synclines/anticlines, wavy patterns. 2. **Complex fold mountains:** Intensely compressed strata, complex folds. Overfolds/recumbent folds detached from roots (nappe). ##### Characteristics of Fold Mountains - Youngest mountains. - Sedimentary rocks contain fossils (formed from marine silt/sediments). - Great length, small width. - Concave slope on one side, convex on other. - Mostly along continental margins facing oceans (C-O Convergence). - Granite intrusions common. - Recurrent seismicity. - High heat flow, often volcanic activity (Himalayas an exception). - Most widespread, important (influence climate), rich in minerals (tin, copper, gold). #### Block Mountains or Fault-Block Mountains - Formed by large-scale faulting (blocks broken, displaced vertically/horizontally). - **Horsts:** Uplifted blocks. - **Graben:** Lowered blocks (rift valley). - Examples: Great African Rift Valley (graben), Rhine Valley (graben), Vosges mountain (horst). - Two types: 1. **Tilted block mountains:** One steep side, one gentle slope. 2. **Lifted block mountains:** Flat top, extremely steep slopes. ##### ‘Fault’ in Geology - Crack in crust with significant displacement of block(s). - Faulted edges usually very steep. - Result from plate tectonic forces (subduction zones, transform faults). - Energy release from rapid movement on active faults causes most earthquakes. - **Active fault:** Pieces move over time. - **Inactive fault:** No longer move. ##### Types of Faults - **Strike-Slip Fault (Transcurrent fault):** Plane near vertical, blocks move laterally (left/right) with little vertical motion. - **Transform Fault (Transform boundary):** Special strike-slip fault forming plate boundary. Ends abruptly, connected to another transform, spreading ridge, or subduction zone. Most in deep ocean, offset divergent boundaries. - **Dip-Slip Faults:** - **Normal fault:** Hanging wall moves downward (crust extended, divergent boundary). - **Reverse fault (Thrust fault):** Hanging wall moves upward (crust shortened, convergent boundary). - **Graben:** Downthrown block between two normal faults (rift valley). - **Horst:** Upthrown block between two normal faults (block mountain). - **Rift Valley system:** Tension causes central portion to drop between fault blocks (graben/rift valley). Large-scale block mountains/rift valleys from tension, not compression. - **Block Mountains:** Middle block moves down (rift valley), surrounding blocks stand higher. - **Plateaus:** Surrounding blocks subside, middle block stationary. - **Oblique-Slip Faults:** Component of both dip-slip and strike-slip. Most faults have both. Cause many disastrous earthquakes. ### Volcanism - **Volcano:** Vent/fissure in Earth's crust erupting lava, ash, gases, rock fragments from magma chamber. - **Volcanism:** Phenomenon of pyroclastics eruption. #### What Causes Volcanism? - **Mantle convection currents:** Create convergent/divergent boundaries. - **Divergent boundary:** Volcanism through fault zones. - **Convergent boundary:** Denser plate subducts, magma forms at high pressure, escapes violently. - **Mantle plumes:** Hotspot volcanism (unusual locations, far from plate margins, e.g., Hawaii, Yellowstone). #### Lava Types - **Magma:** Molten rock stored in crust. - **Lava:** Magma reaching surface. ##### Andesitic Or Acidic Or Composite Or Stratovolcanic Lava - Mostly at destructive (convergent) boundaries. - From melting subducting plate/sediments. - **High silica content:** Highly viscous, high melting point, light-colored, low density. - Flows slowly, solidifies quickly. Forms stratified, steep-sided composite/stratovolcanoes. - Rapid solidification in vent obstructs flow, causes explosions (volcanic bombs/pyroclasts). - Viscous lava can form volcanic plug at crater (e.g., Mt. Pelée). ##### Basic Or Basaltic Or Shield Lava - Mostly at constructive (divergent) boundaries, volcanic hotspots. - From mantle (less silica than crust). - **Hottest lavas** (~1,000 °C). - Rich in iron/magnesium (dark), poor in silica (less viscous, highly fluid). - Flows quietly, not explosive. - Flows readily (10-30 mph), spreads as thin sheets. Forms gently sloping, wide shield volcanoes. #### Types of Volcanoes - **Composite Type Volcano (Stratovolcano):** Large, steep conical volcano from layers of hardened andesitic lava, pyroclastic/mudflow deposits, tephra. Steep profile, summit crater, explosive/effusive eruptions, sometimes calderas. E.g., Stromboli, Vesuvius, Krakatoa, Fuji. - **Shield Type Volcano:** From basaltic lava (very fluid). Not steep, less common. Explosive if water enters vent, otherwise less explosive. E.g., Mauna Loa, Mauna Kea (Hawaii). - **Fissure Type or Flood Basalt Volcano (Lava Plateaus):** Thin magma escapes through cracks/fissures, flows for long periods, spreads over vast areas, forms layered, undulating flat surface. E.g., Siberian Traps, Deccan Traps. #### Types of Volcanoes Based on Frequency of Eruption - **Active Volcanoes:** Erupt fairly frequently (e.g., Barren Island, Anak Krakatoa). - **Dormant Volcanoes:** Not erupted regularly recently, long repose intervals. May become active/extinct (e.g., Mount Kilimanjaro). - **Extinct or Ancient Volcanoes:** Eruptions recorded historically but dormant for hundreds of years (e.g., Mount Kenya). - Waning stage: Steam/hot gases exhaled (fumaroles/solfataras). Indicates extinction. #### Volcanism Types 1. **Exhalative (Vapour Or Fumes):** Discharge of gases (steam, HCl, SO2, CO2, etc.). Through hot springs, geysers, fumaroles (emit steam/gases), solfataras (sulfur gases dominant). Indicates waning stage. Forms sinter mounds, precipitated mineral cones, mud volcanoes. 2. **Effusive (Lava Outpouring):** Abundant outpourings/solidification of basaltic lava from vent/fissure. Columnar structure in fine-grained plateau basalts (e.g., Deccan Traps). 3. **Explosive (Violent Ejection Of Solid Material):** Fragmentation/ejection of volcanic ejecta. - **Tephra:** All fragmented ejecta. - **Ash:** Finest sand-sized tephra. - **Lapilli:** Gravel-sized particles (molten/solid). - **Blocks:** Boulder-sized solid ejecta. - **Bombs:** Lump of lava thrown out, solidifies while falling. - **Tuff:** Layers of volcanic dust/ashes. 4. **Subaqueous Volcanism:** Below water surface. Lava forms pillow-like structures. Related product: hyaloclastite (e.g., Iceland). #### Eruptive Volcanism Types 1. **Hawaiian Eruption:** Calmest, effusive basaltic lavas from craters/lava lakes/fissures, little ejected material. Single flow spreads wide, builds large shield volcano. 2. **Icelandic Eruption:** Effusions of molten basaltic lava from long, parallel fissures. Builds lava plateaus. E.g., Deccan Traps. 3. **Strombolian Eruption:** Episodic explosive eruptions (fountain-like) from gas bubbles in magma. Burst with loud pop, throw magma in air. E.g., Stromboli. - Anak Krakatau: 1883 Krakatau eruption (Plinian) caused tsunamis. Anak Krakatau emerged later, active with Strombolian eruptions (2018 tsunami). 4. **Vulcanian Eruption:** Intermediate viscous magma, gas buildup, explosive eruption. Volcano dormant for decades/centuries after. More explosive than Strombolian, columns 5-10 km high. Molten lava ejected as cauliflower cloud of tephra. 5. **Plinian Eruption:** Dissolved volatile gases channeled through narrow conduit, erupt into massive gas plume (up to 45 km into atmosphere). Plume expands, driven by winds. - Mount Vesuvius: Famous for AD 79 Plinian eruption (destroyed Pompeii). Very dangerous due to population. - Mount St. Helens: 1980 Plinian eruption. - Mount Tambora: 1815 Plinian eruption (VEI 7), lowered global temperatures ("Year Without a Summer"). - Nevado del Ruiz: Vulcanian to Plinian eruptions, destructive lahars (1985 eruption). - **Lahar:** Violent mudflow/debris flow of pyroclastic material/water, flows down volcano. - Mount Pinatubo: 1991 Plinian eruption, cooled global temps, increased ozone depletion. 6. **Pelean Eruption:** Sudden burst of lava dome, collapse of cinder cone, large amount of viscous, ash-rich acidic lava/fragments blown out laterally. Hot gases spread downslope as nuée ardente (dense cloud of hot gases/ashes/lava fragments). E.g., Mount Pelée (1902 eruption, destroyed Saint-Pierre). #### Volcanic Landforms - **Extrusive:** From material thrown out to surface (lava flows, pyroclastic debris, bombs, ash, dust, gases). - **Volcanic Vents:** - **Fissure Vent:** Narrow, linear vent, effusive basaltic lava eruptions (shield-type). - **Conical Vent:** Narrow cylindrical vent, violent magma outflow (andesitic, composite/stratovolcano). - **Crater:** Inverted cone-shaped vent. Bowl-shaped depression when inactive. Crater lake if water accumulates. - **Caldera:** Large cauldron-like hollow from collapse of volcanic material into empty magma chamber after eruptions. Caldera lake if water accumulates (e.g., Lake Toba). - **Difference (Crater vs. Caldera):** Caldera lakes larger, longer-lasting. - **Pseudo Volcanic Features:** Resemble volcanic forms but non-volcanic (meteorite craters, salt plugs, mud volcanoes). - **Meteorite Craters:** Impact craters. - **Salt Plug (Salt Dome):** Underground salt pierces overlying sediments, creates diapir (dome-like intrusion). - **Mud-Volcano:** Eruption of mud, water, gases. Near subduction zones/hot springs. Also near oil fields (non-volcanic). - **Cinder Cone:** Steep circular/oval hill of loose pyroclastic fragments around vent. Bowl-shaped crater. - **Lava Dome (Volcanic Dome):** Mound-shaped protrusion from slow extrusion of viscous magma. Magma doesn't escape, pressure builds, may erupt explosively. - **Mid-Ocean Ridges:** System of two mountain chains separated by depression (divergent boundary). Frequent basaltic eruptions, seafloor spreading. - **Intrusive (Plutonic):** Magma cools within crust. - **Batholiths:** Large granitic rock bodies from magma solidification deep inside. Form mountain cores, exposed by denudation. - **Laccoliths:** Dome-shaped intrusive bodies connected by pipe-like conduit. Intrusive counterparts of exposed batholiths (e.g., Karnataka plateau). - **Lopolith:** Saucer-shaped depression from horizontal magma movement. - **Phacolith:** Lens-shaped plutons at base of synclines or top of anticlines in folded igneous strata. - **Sills:** Near-horizontal bodies of intrusive igneous rocks. Thinner ones are sheets. - **Dykes:** Lava makes way through cracks/fissures, solidifies perpendicular to ground, forms wall-like structure. Feeders for eruptions (e.g., Deccan Traps). #### Distribution of Earthquakes and Volcanoes across the World - Most along converging plate margins and mid-oceanic ridges. - **Circum-Pacific belt ("Pacific Ring of Fire"):** ~70% of earthquakes, greatest concentration of active volcanoes. (Aleutian-Kurile, Japan, Philippines, Indonesia, Solomon, New Hebrides, Tonga, New Zealand, Andes, Central America, Mexico, Alaska). - **Alpine Belt (Mediterranean-Himalayan belt):** ~20% of earthquakes. Asia Minor, Himalayas, parts of NW China. - Other regions: Atlantic coasts (few active volcanoes, many dormant/extinct), East African Rift Valley (Mt. Kilimanjaro, Mt. Kenya). - West Indian Islands (Lesser Antilles): Volcanic islands. - Mediterranean region: Alpine folds (Vesuvius, Stromboli), Aegean islands (Eurasian-African plate convergence). - **Volcanoes in India:** No volcanoes in Himalayan region/Indian peninsula. Barren Island (active), Narcondam (extinct) in Andaman & Nicobar. #### Geysers and Hot Springs - Water percolates, heated by hot magma, converts to high-pressure steam. - **Geyser:** Steam/water bursts out through narrow vents (accumulated in reservoirs, then pressure exceeds limit). Near active volcanic areas (Iceland, New Zealand, Yellowstone). - **Hot water spring:** Steam/water flows smoothly to surface, condenses. Some colorful due to cyanobacteria. #### Destructive Effects of Volcanoes - Cinders/bombs damage life (e.g., Vesuvius AD 79). - Tsunamis from violent eruptions (e.g., Krakatoa 1883) or collapse of volcanic landforms (e.g., Anak Krakatoa 2018). - Ash from large eruption lowers regional/global temps, causes famines (e.g., Tambora 1815). - Lava flows engulf cities (Hawaiian type). - Lahars bury cities (e.g., Nevado del Ruiz 1985). - Lava dome collapse causes violent flows (e.g., Mount Pelée 1902). - Gas plumes disrupt air travel (e.g., Iceland 2010). - Super-eruptions cause small-scale extinction (e.g., Toba 74,000 yrs ago). - **Acid Rain/Ozone Destruction:** Volcanic gases (SO2, CO2, HF) cause acid rain, large explosive eruptions inject sulfur aerosols into stratosphere (lower temps, ozone depletion). #### Positive Effects of Volcanoes - Creates new fertile landforms (islands, plateaus, volcanic mountains, e.g., Deccan Traps). - Volcanic ash/dust fertile for farms/orchards. - Mineral resources (metallic ores, diamonds in Kimberlite rock) brought to surface. - Geothermal electricity from Earth's interior heat (USA, Russia, Japan, Italy, NZ, Mexico; Puga Valley, Manikaran in India). - Scenic beauty, tourism (Yellowstone NP). - Lava rock used as crushed rock for construction. ### Hotspot Volcanism - Occurs in interior parts of lithospheric plates, not plate margins (exceptions: Iceland, Afar Hotspot at divergent boundary). - Caused by **mantle plumes** (abnormally hot centers in mantle). - Explains anomalous volcanism (far from plate margins, e.g., Hawaii, Yellowstone) or excessive volcanism at mid-ocean ridges (e.g., Iceland). #### Mantle Plumes - Convection of abnormally hot magma within Earth's mantle. - Form at core-mantle boundary, accumulate, rise as mushroom-shaped plume (long conduit, bulbous head). - Plume is relatively fixed in position (unlike larger mantle convection cells). - Rises, becomes diapir in upper mantle, flattens at lithosphere base. #### Mantle Plumes and Flood Basalt Volcanism (Large Igneous Provinces) - Plume head encounters lithosphere base, widespread decompression melting forms large basalt magma volumes. - Basaltic magma erupts through fissures, forming **large igneous provinces (LIPs)** (extensive flood basalts). E.g., Iceland, Siberian Traps, Deccan Traps. - **Flood Basalt Events and Extinctions:** Large LIPs cause long-lasting climate change (e.g., Siberian Traps ~250 mya coincided with Permian–Triassic extinction). Réunion hotspot (Deccan Traps ~66 mya) coincided with Cretaceous–Paleogene extinction. #### Mantle Plumes and Volcanic Hotspots - Mantle plume provides continuous supply of hot magma to fixed hotspot. - High heat melts rock at lithosphere base. Magma pushes through cracks, forms hotspot volcanoes (e.g., Mount Mauna Kea). - **Hotspot Volcano Chain:** Volcano moves with tectonic plate, cut off from hotspot, becomes extinct. New volcano forms over hotspot. Creates volcanic arc parallel to plate motion. E.g., Hawaiian Islands chain (age progression, youngest near Hawaii). Other examples: Réunion, Chagos-Laccadive Ridge, Louisville Ridge, Yellowstone. ##### Reunion Hotspot - Under Island of Reunion (Indian Ocean). - Huge eruption ~66 mya formed Deccan Traps, separated India from Seychelles Plateau. - As Indian plate drifted north, hotspot punched through, creating volcanic islands/plateaus (Chagos-Laccadive Ridge, southern Mascarene Plateau). - Laccadive, Maldives, Chagos Archipelago: Atolls on former volcanoes. - Hotspot passed under African Plate, activity resumed, created Mascarene Islands. ##### Mantle Plumes And Divergence (Plate Tectonics) - Plume diverges below lithosphere, exerts extensional stress, stretches/ruptures plate, forms rift. - Afar hotspot ruptured, creating Afar triple junction (Arabian, African, Somali plates diverging). #### Mantle Plumes and Uplifted Landforms (Epeirogenic Movements) - Plume spreads laterally at crust, doming zones (e.g., Ethiopian Highlands). - Uplifted ancient rocks, then flood basalt plateau (Ethiopian Highlands). - Great Rift Valley split dome into three parts. #### Mantle Plumes and Thinning of The Continental Crust - Yellowstone hotspot: Beneath continent, plume thinning crust (extensional stress), may lead to eruption of underlying supervolcano. #### Mantle Plumes and Supervolcanoes - **Supervolcano:** Large volcano, >1,000 km³ magma erupted. Magma accumulates under lithosphere, unable to break through. Pressure builds, plate erupts. - Occurs at hotspots (Yellowstone Caldera) or subduction zones (Toba Caldera Lake). - **Supervolcano Eruptions:** >40 in Earth's history. Most recent: Lake Taupo (NZ) ~26,000 yrs ago (VEI 8). Toba eruption (Indonesia) ~74,000 yrs ago caused global winter. - **Disaster Potential:** Small-scale/regional extinction. Ash blankets continent, gases/dust cause severe climate change (global winter). ### Types of Rocks & Rock Cycle - **Rocks:** Aggregates of one or more minerals held by chemical bonds. Feldspar and quartz are common. - **Petrology:** Scientific study of rocks. - Three major groups based on formation: 1. Igneous Rocks (from magma/lava). 2. Sedimentary Rocks (from sediment deposition). 3. Metamorphic Rocks (from existing rocks recrystallizing). #### Igneous Rocks or Primary rocks - Formed from solidification of magma (below surface) or lava (above surface). - High temperatures, unfossiliferous. E.g., Granite, gabbro, basalt. - Types based on cooling: plutonic, volcanic, intermediate. - Types based on silica: acidic, basic. ##### Intrusive Igneous Rocks (Plutonic Rocks) - Magma cools slowly at great depths. Large mineral grains. E.g., Granite. - Exposed by uplift and denudation. ##### Extrusive Igneous Rocks (Lava Or Volcanic Rocks) - Sudden cooling of magma just below surface or lava above. Small/smooth grains, fine-grained. E.g., Basalt. - Deccan Traps are basaltic. Basic rocks (iron, aluminum, magnesium) denser, darker. ##### Hypabyssal or Dyke Rocks or Intermediate rocks - Intermediate position between deep plutonic bodies and surface lava flows. Semi-crystalline. ##### Acid Rocks - High silica content (up to 80%, quartz, feldspar). Lesser heavy minerals (Fe, Mg), so less dense, lighter color. - Hard, compact, massive, resistant to weathering. Constitute sial. E.g., Granite, quartz, feldspar. - Acidic magma cools fast, doesn't flow far, forms high mountains. ##### Basic Rocks - Low silica content (~40%). High magnesia (~40%). Dark color (heavy elements). - Not very hard, weather easily. E.g., Basalt, gabbro, dolerite. - Basaltic magma cools slowly, flows far, forms plateaus. ##### Economic Significance of Igneous Rocks - Magma is chief source of metal ores (iron, nickel, copper, lead, zinc, chromite, manganese, gold, diamond, platinum). - Amygdales: Bubbles in basalt filled with minerals. - Used as building materials (granite). #### Sedimentary Rocks or Detrital Rocks - Formed by **lithification** (consolidation/compaction) of sediments (from weathering/erosion of other rocks). - Layered/stratified, varying thicknesses. E.g., Sandstone, shale. - Tillite: Ice-deposited. - Loess: Wind-deposited. - Cover 75% of Earth's crust (by area), but only 5% by volume (upper crust). - Classified by formation mode: 1. **Mechanically formed:** Running water, wind, ocean currents, ice. - **Arenaceous:** Sand/large particles (hard, porous, good reservoirs for groundwater/petroleum, e.g., sandstone). - **Argillaceous:** More clay, fine-grained, softer, impermeable (e.g., claystone, shales). 2. **Chemically formed:** Water with minerals evaporates (stalactites, stalagmites). E.g., Limestone, halite, potash. 3. **Organically formed:** Remains of plants/animals buried, change composition under heat/pressure. E.g., Coal, limestone. - **Calcareous:** Predominant calcium (limestone, chalk, dolomite). - **Carbonaceous:** Predominant carbon (coal). ##### Chief Characteristics of Sedimentary Rocks - Stratified (many layers). - Generally porous, allow water percolation. - Fossiliferous (contain fossils), hold geological records. ##### The Spread of Sedimentary Rocks in India - Alluvial deposits in Indo-Gangetic plain/coastal plains (loam, clay). - Sandstone: Madhya Pradesh, eastern Rajasthan, Himalayas, Andhra Pradesh, Bihar, Orissa. - Vindhyan highland: Sandstones, shales, limestones. - Coal deposits: Damodar, Mahanadi, Godavari basins (Gondwana sedimentary deposits). ##### Economic Significance of Sedimentary Rocks - Less rich in economic minerals than igneous rocks. - Important minerals: Hematite iron ore, phosphates, building stones, coals, petroleum, cement industry materials. - Bauxite, manganese, tin: Derived from other rocks, found in gravels/sands. - Yield rich soils. #### Metamorphic Rocks - "Change of form." Recrystallization and reorganization of minerals within a rock. - Due to pressure, volume, temperature changes. - Formed when rocks forced to lower levels (tectonics) or magma contacts crustal rocks. - E.g., Gneissoid, slate, schist, marble, quartzite. - **Foliation/Lineation:** Grains/minerals arranged in layers/lines. - **Banding:** Minerals/materials arranged in alternating thin/thick layers. ##### Causes of Metamorphism - **Orogenic (Mountain Building) Movements:** Folding, warping, high temperatures give rocks new appearance. - **Lava Inflow:** Molten magma heats surrounding rocks, causing changes. - **Geodynamic Forces:** Plate tectonics play important role. ##### Thermal Metamorphism - Recrystallization from high temperatures. - Sandstone to quartzite, limestone to marble. - Magmatic intrusion causes Mt. Everest's metamorphosed limestone peak. ##### Dynamic Metamorphism - Formation under high pressure (sometimes with high T and chemically charged water). - Granite to gneiss; clay/shale to schist. - **Dynamo thermal metamorphism:** Combined directed pressure and heat cause complete recrystallization, new structures. ##### Metamorphic Rocks in India - Gneisses/schists: Himalayas, Assam, West Bengal, Bihar, Orissa, Madhya Pradesh, Rajasthan. - Quartzite: Rajasthan, Bihar, Madhya Pradesh, Tamil Nadu, Delhi. - Marble: Alwar, Ajmer, Jaipur, Jodhpur (Rajasthan), Narmada Valley (MP). - Slate: Rewari (Haryana), Kangra (HP), Bihar. - Graphite: Orissa, Andhra Pradesh. #### Rock Cycle - Continuous process: Old rocks transformed into new ones. - Igneous rocks are primary. - Igneous/Metamorphic fragments form sedimentary rocks. - Sedimentary/Igneous rocks can become metamorphic. - Crustal rocks (igneous, metamorphic, sedimentary) subducted into mantle, melt to magma (source for igneous rocks). #### Some Rock-Forming Minerals - **Feldspar:** Half of crust. Light color, Si, O, Na, K, Ca, Al. Used for ceramics, glass. - **Quartz:** Si, O. Hexagonal crystalline, uncleaved, white/colorless. In sand, granite. Used in radio/radar. - **Bauxite:** Hydrous Al oxide. Ore of Al. Non-crystalline, small pellets. - **Cinnabar:** Mercury sulfide. Brownish. Source of Hg. - **Dolomite:** Double carbonate of Ca, Mg. Used in cement, iron/steel. - **Gypsum:** Hydrous Ca sulfate. Used in cement, fertilizer, chemical industries. - **Haematite:** Red iron ore. - **Magnetite:** Black iron ore (iron oxide). - **Amphibole:** 7% of crust. Al, Ca, Si, Fe, Mg. Used in asbestos. Hornblende is a form. - **Mica:** K, Al, Mg, Fe, Si. 4% of crust. In igneous/metamorphic rocks. Used in electrical instruments. - **Olivine:** Mg, Fe, Si. Greenish crystal, in basaltic rocks. Used in jewelry. - **Pyroxene:** Ca, Al, Mg, Fe, Si. In meteorites. Green/black. - Other minerals: Chlorite, calcite, bauxite, barite. ### Earthquakes - Shaking/trembling of Earth's surface from seismic waves. - Caused by sudden movement/release of energy in crust (shallow-focus) or upper mantle (intermediate/deep-focus). #### Terms - **Seismograph/Seismometer:** Detects and records earthquakes. - **Focus (Hypocentre):** Point where energy is released. - **Epicentre:** Point on surface directly above focus (first to experience waves). - **Isoseismic line:** Connects points on surface with same intensity. - **Aftershocks:** Smaller earthquakes following a major one. - **Foreshock:** Mild earthquake preceding a major one. - **Earthquake swarms:** Large numbers of small earthquakes for months without a major one (e.g., volcanic activity). #### Causes of Earthquakes - **Fault Zones:** Sudden release of stress along crustal fault rupture (due to volume/density changes). Longer/wider fault = larger magnitude. - Thrust faults (convergent): Ruptures ~1,000 km. - Strike-slip faults (transform): Ruptures ~1/2 to 1/3 of thrust. - Normal faults (divergent): Shorter ruptures. - **Plate Tectonics:** Slipping of land along faultline at plate boundaries. - Normal faults (divergent): 70 km. Occur in **Benioff zones** (subducting slab). Also called intraplate EQs. Huge quakes (M6-8), but energy dissipates over wide area (less surface destruction). Strongest: Okhotsk Sea M8.3 (609 km). Deepest: Vanuatu M4.2 (735.8 km). - **Wadati–Benioff Zone:** Zone of subduction along which earthquakes are common (most powerful EQs here). Differential motion produces EQs up to ~700 km deep. Slipping along subduction thrust fault (C-C) or faults within downgoing plate (O-O, C-O). #### Distribution of Earthquakes - Mainly in belts coinciding with tectonic plate margins. - **Circum-Pacific Belt ("Pacific Ring of Fire"):** ~68% of EQs. Many populated coastal regions (NZ, New Guinea, Japan, Aleutian, Alaska, W. N/S America). Associated with volcanic activity. - **Alpine Belt:** ~15% of world's energy. Mexico across Atlantic, Mediterranean, Alpine-Caucasus, Caspian, Himalayas. - **Oceanic Ridges:** Arctic, Atlantic, W. Indian Ocean. - **Rift valleys:** East Africa. #### Richter Magnitude Scale - Charles F. Richter (1930s) developed ML scale for strength. Now Moment Magnitude Scale (Mw) used, commonly called Richter Scale. - Logarithmic scale. Increase of 1 step = ~32x energy release. - **Magnitude:** - Micro (1.0-1.9): Not felt. Millions/year. - Minor (2.0-2.9): Felt slightly. Million+/year. - (3.0-3.9): Often felt, rarely damage. 100,000+/year. - Light (4.0-4.9): Noticeable shaking, minimal damage. 10,000-15,000/year. - Moderate (5.0-5.9): Damage to poorly built. 1,000-1,500/year. - Strong (6.0-6.9): Damage to well-built. 100-150/year. E.g., Christchurch 2011. - Major (7.0-7.9): Damage to most buildings. 10-20/year. E.g., Gujarat 2001. - Great (8.0-8.9): Major damage/destruction. 1/year. E.g., Assam-Tibet 1950. - (9.0+): Near total destruction, permanent ground changes. 1/10-50 years. E.g., Valdivia 1960, Indian Ocean 2004. #### Most Powerful Earthquakes Ever Recorded 1. Valdivia (Chile) 1960: Mw 9.4-9.6. Undersea megathrust, most powerful. Tsunami affected Pacific Rim. 2. Alaska 1964: Mw 9.2. Collapsing structures, tsunamis. 3. Indian Ocean 2004: Mw 9.1-9.3. Undersea megathrust (Burma-Indian Plate rupture). Large tsunamis (up to 30m). 6th deadliest natural disaster. Altered Earth's rotation. 4. Tōhoku (Japan) 2011: Mw 9.1. Undersea megathrust, most powerful in Japan. Triggered tsunamis, Fukushima disaster. #### Notable Earthquakes - Shaanxi 1556 (M8.0): Deadliest (>800,000 fatalities), mostly from cave collapse. - Tōhoku 2011 (M9.1): Costliest ($250 billion damage). - Rann of Kutch 1819 (M7.7-8.2): Triggered tsunami. Caused subsidence (Sindri Lake) and uplift (Allah Bund). - Gujarat 2001 (M7.7): 13,000-20,000 deaths. Caused by reactivation of old rift faults from Indian-Eurasian plate collision. #### Earthquake Zones of India - 59% of India's land prone to moderate/severe EQs. - **Zone 5:** North-East, J&K, Uttarakhand, parts of Himachal Pradesh. - **Zone 4:** Delhi. - **Zone 3:** Central India. - **Zone 2:** Most of South India. - **Delhi NCR:** Low-intensity EQs, near multiple tectonic faults (Mahendragarh-Dehradun, Sohna, Mathura). 500 km "Central Himalayan seismic gap" with accumulated strain. - **North East:** Highly fragile/EQ-prone. Complex tectonic juxtaposition (Himalayas, Arakan Yoma belt), major faults (Po Chu, Kopili, Jiali). - **Kopili Fault Zone:** 300 km long, 50 km wide faultline (Manipur to Bhutan/Arunachal/Assam). Tectonic depression filled by Kopili river alluvium. Close to Himalayan Frontal Thrust (seismically active, Zone V). #### Effects of Earthquakes - **Shaking and Ground Rupture:** Damage to structures, major risk for dams/bridges/nuclear plants. - **Landslides and Avalanches:** EQs cause slope instability. - **Fires:** Damage to electrical/gas lines (e.g., San Francisco 1906). - **Soil Liquefaction:** Water-saturated soil temporarily loses strength, becomes liquid. Rigid structures tilt/sink. - **Tsunami:** Megathrust EQs cause long-wavelength sea waves from abrupt water displacement. - **Floods:** Secondary effect if dams damaged, or if landslips dam rivers. ### Tsunami - Japanese for "Harbour wave." Series of very long-wavelength waves in large water bodies. - Caused by major disturbance above/below water surface or large water volume displacement. - Not tidal waves (Moon/Sun not involved). - Generated by: Earthquakes (e.g., 2004 Indian Ocean), volcanic eruptions (Krakatoa 1883), landslides (Anak Krakatoa 2018), underwater explosions, meteorite impacts. - Pacific Ocean has most tsunamis. #### Mechanism of Tsunami Waves - **Disturbance:** Megathrust EQs cause sudden seabed displacement, raising large water body (e.g., 2004 Sumatra). Subducting plate gives way, upthrusts oceanic crust, displaces water. - Marine volcanic eruption/submarine landslide can also generate. - **Propagation of The Waves:** Gravity returns sea surface to original shape, ripples race outward. - As tsunami enters shallow water: Speed reduces, height (amplitude) grows ("shoaling" effect). - Can grow to many meters high in closed harbors/inlets ("funneling" effect). - Often preceded by extraordinary water recession from shore. #### Properties of Tsunami Waves - **Basics:** Wave crest/trough, height, amplitude, period, wavelength, frequency. - **Normal Waves:** Wind-generated, water moves in circles, wave trains move. Seldom affect deep water. Break/die near shore. - **Normal Waves vs Tsunami Waves:** - **Wavelength/Period:** Tsunamis have very long wavelengths (>500 km), periods (10 min-2 hrs). Wind waves: few meters, 5-20 sec. - **Energy Loss:** Tsunamis lose little energy (large wavelength), travel far. Wind waves die out. - **Wavespeed:** Tsunamis travel fast in deep water (850 kmph at 6000m), slow in shallow water. - **Shoaling Effect:** Imperceptible in deep water, amplitude increases in shallow water (conservation of energy). #### 2004 Indian Ocean Tsunami - Dec 26, 2004. Megathrust EQ (M9.0) off Sumatra. - **Plate Tectonics:** Indian plate went under Burma plate, sudden seafloor movement. Ocean floor displaced, tilted downward. Water flowed in, then rushed back as tsunami. - **Tsunami Waves:** Travelled ~800 kmph. Submerged Indira Point (Andaman & Nicobar). Wavelength decreased, speed declined closer to land. Travelled up to 3 km inland. Worst affected: Andhra Pradesh, Tamil Nadu, Kerala, Pondicherry, Andaman & Nicobar. - **Shifts in Geography:** Shifted North Pole by 2.5 cm, reduced day length by 2.68 microseconds. Andaman & Nicobar islands moved ~1.25m. #### Tsunami Warning Systems - EQs cannot be predicted, but tsunamis can be (3-hour notice). - Pacific Ocean systems (NOAA DART gauge). Indian Ocean systems post-2004. - DART gauge: Sensitive pressure recorder on seafloor, transmits data to buoy, relayed by satellite to Pacific Tsunami Warning Centre (Hawaii). - **India's Preparedness:** Deep Ocean Assessment and Reporting System (DOARS) in Indian Ocean. National Tsunami Early Warning Centre (INCOIS, Hyderabad) detects >M6 EQs, issues warnings in 10-30 min. Regional Tsunami Service Provider (RTSP) for Indian Ocean Rim. - **'Tsunami Ready' Tag:** UNESCO program to facilitate preparedness, implemented by INCOIS in India. ### Fluvial Landforms and Cycle of Erosion - **Soil erosion:** Loosening/displacement of topsoil by wind/water. Slow (geological) or fast (human activity). - Weathering/erosion lead to **degradation** and **aggradation**. - **Erosion:** Mobile process. **Weathering:** Static process (no motion of disintegrated material except gravity). - **Fluvial landforms:** Created by degradational (erosion, transportation) or aggradational (deposition) work of running water. #### Fluvial Erosional Landforms - Created by erosional activity of rivers. - **Fluvial erosive action:** - **Hydration:** Force of running water wearing down rocks. - **Corrosion:** Chemical weathering. - **Attrition:** River load particles striking/colliding. - **Abrasion:** Solid river load striking rocks. - **Downcutting (vertical erosion):** Erosion of stream base (valley deepening). - **Lateral erosion:** Erosion of stream walls (valley widening). - **Headward erosion:** Erosion at stream origin, lengthens channel. - **Braiding:** Main channel splits into multiple, narrower channels (braid bars). In low slopes/large sediment loads. ##### River Valley - Extended depression where stream flows. Different profiles at different erosional stages. - **Young stage:** Deep, narrow, steep sides, convex slope. Predominantly vertical downcutting. V-shaped valley. Tributary valleys hang above main valley. - **Gorge:** Deep, narrow V-shaped valley (downcutting, waterfall recession). E.g., Himalayan gorges. - **Canyon:** Extended gorge. E.g., Grand Canyon (Colorado River). - **Maturity:** Lateral erosion prominent, valley floor flattens (V to U shape). Broad base, concave slope. ##### River Course - **Youth:** Fast-flowing, high-energy, rapid headward erosion. V-shaped valleys, waterfalls, rapids. E.g., Himalayan rivers. - **Maturity:** Lower-energy. Erosion on outside bends (meanders), deposition on inside bends/bed. E.g., Indo-Gangetic-Brahmaputra plain rivers. - **Old Age:** Sediment deposited at river mouth (velocity slows). Shallower, more deposition. Forms temporary islands (Majuli), braiding. Actual mouth moves into sea/lake, forming delta. E.g., Ganga-Brahmaputra delta. ##### Meanders - Pronounced curve/loop in river channel. Wavy, horse-shoe, or oxbow. - **Outer bend:** Intense erosion, vertical cliffs (cliff-slope side, concave slope). - **Inner bend:** Deposition, gentle convex slope (slip-off side). - Common on floodplains/delta plains (gentle gradients). - **Incised/entrenched meanders:** Very deep/wide meanders cut in hard rocks. ##### Point Bars - Also meander bars. Sediments deposited linearly on convex side of large river meanders. Uniform profile/width, mixed sediments. ##### Oxbow Lake - Intense erosion accentuates outer curve, inner ends disconnect from main channel. Independent water bodies. Convert to swamps. E.g., north of Ganga's present course. ##### Waterfalls - Enormous water fall from great height. Mostly in youth stage. - Causes: Relative resistance of rocks, topographic relief, sea level fall (rejuvenation), earth movements. - E.g., Kunchikal Falls (highest in India), Nohkalikai Falls (tallest plunge), Jog Falls (2nd highest plunge), Angel Falls (world's highest). ##### Potholes - Small cylindrical depressions in rocky river beds. - **Potholing/pothole-drilling:** Rock fragments caught in water eddies grind/drill beds. - **Plunge pools:** Large, deep holes at base of waterfalls. ##### Terraces - Stepped benches along river course in floodplain. Represent former valley floors/floodplains. ##### Gulleys/Rills - **Rill:** Narrow, shallow channel cut by flowing water. - **Gulley:** Larger than rill, between ditches/small valleys. Formed when overland flow concentrates, enlarges rills. E.g., Chambal Valley ravines, Chos of Hoshiarpur. ##### Peneplane (Peneplain) - Undulating, featureless plain with low residual hills of resistant rocks. End product of erosional cycle. - Fluvial erosion reduces land to base level, little gradient, no more erosion. E.g., Uluru (Ayers) Rock on peneplane. #### Fluvial Depositional Landforms - Created by depositional activity of rivers. - Influenced by stream velocity, river load volume. Decreased velocity reduces transporting power, forcing deposition. ##### Alluvial Fans and Cones - Stream leaves mountains, velocity decreases (lower gradient), sheds material at foothills. - Deposited material forms conical shape, series of continuous fans. E.g., Himalayan foothills. - Streams shift across fan, forming distributaries. - Humid areas: Low cones, gentle slope. Arid/semi-arid: High cones, steep slope. ##### Floodplains - Generally flat land next to river/stream, from banks to outer valley edges. - **Active floodplain:** Riverbed of deposits. - **Inactive floodplain:** Above bank. - In plains, channels shift laterally, leave cut-off courses filled gradually (coarse deposits). Flood deposits (spilled waters) carry finer materials (silt, clay). ##### Natural Levees - Along banks of large rivers. Low, linear, parallel ridges of coarse deposits. - Formed by deposition, act as natural embankments. Breach causes sudden floods (e.g., Hwang Ho River). ##### Delta - Tract of alluvium at river mouth, deposits more material than can be carried away. - River divides into distributaries. - Formed by: Reduced load-bearing capacity (velocity check), clay particles coagulate in salt water. - **Bottom-set beds:** Finest particles carried farthest. - **Types:** - **Arcuate/Fan-Shaped (Curved):** Light depositions, shallow shifting distributaries, fan-shaped profile. E.g., Nile, Ganga, Indus. - **Bird’s Foot Delta (Elongated):** Limestone sediments prevent downward seepage. Distributaries flow over projections, appear as bird's foot. Weak currents/tides, fewer distributaries. E.g., Mississippi River. - **Cuspate Delta:** Pointed delta, along strong coasts, strong wave action. Few/no distributaries. E.g., Tiber River, Ebro River. - **High-Constructive Deltas (Elongate, Lobate):** Fluvial/depositional processes dominate. Large sediment supply. Elongate (bird-foot) - Mississippi. Lobate - Godavari. - Lobate: River water as dense as seawater, immediate precipitation/coagulation. - Bird-foot: River water lighter than seawater, precipitation/coagulation occurs farther from shore. - **High-Destructive Deltas:** High shoreline energy, sediment reworked by waves/currents. Deposited as arcuate sand barriers near mouth. E.g., Nile, Rhône (wave-dominated). ##### Estuaries - Submerged river mouth (drowned valley from sea level rise). Fresh/saline water mix. - Mud bars, marshes, plains develop. Ideal for fisheries, ports, industries (deep water access, protected from currents/tides). E.g., Hudson Estuary. #### Drainage Basin or River Basin - Also drainage area, river basin, water basin. Land area that drains to a water body. - Acts as funnel, collects water, channels to single point. - **Closed (endorheic) drainage basins:** Water converges to sink within basin (permanent lake, dry lake, sinkhole). E.g., Lake Aral, Dead Sea. ##### Drainage Divide - Separates adjacent drainage basins. Ridge or high platform. - Conspicuous in youthful topography (Himalayas), less marked in plains/senile topography. ##### Difference between a River Basin, Watershed and Catchment Area - **River Basin:** All water drains into a large river. - **Watershed:** Smaller area, drains to smaller stream/lake/wetland. Many watersheds in a basin. - **Catchment area:** Area from which water flows into river (rainfall, snowmelt, springs). #### Drainage Systems (Drainage Patterns) - Patterns formed by streams/rivers/lakes in a basin. - Governed by tectonic irregularity, rock strata, land gradient. - **Concordant drainage:** Correlates to topology/geology. Path dependent on slope/topography. Most common. - **Consequent Rivers:** Follow general slope direction. E.g., Godavari, Krishna, Cauvery (Peninsular India). - **Subsequent Rivers:** Tributary forms by headward erosion along underlying rock after main pattern established. E.g., Chambal, Sind, Ken, Betwa, Tons, Son (meet Yamuna/Ganga at right angles). - **Obsequent Rivers:** Form at right angles to subsequent, flow opposite to original consequent. - **Resequent Rivers:** Flow in same direction as initial consequent, but form later. - **Discordant or Insequent Drainage Patterns:** Does not correlate to topology/geology. River follows initial path regardless of topography changes. Flows through highly sloping surface. - **Antecedent Drainage (Inconsequent):** River maintains original slope, cuts through uplifted portion (vertical erosion), forms deep gorges. E.g., Indus, Sutlej, Brahmaputra (older than Himalayas). - **Superimposed or Epigenetic (Discordant)/Superinduced Drainage:** River flowing over softer rock reaches harder basal rocks, continues initial slope. No relation with hard rock bed. Pattern inherited from former cover rocks, now eroded. E.g., Damodar, Subarnarekha, Chambal, Banas (Rewa Plateau). - **Other Drainage Patterns:** - **Dendritic or Pinnate:** Irregular tree branch shape. In uniform lithology, insignificant faulting/jointing. E.g., Indus, Godavari, Mahanadi, Cauvery, Krishna. - **Trellis:** Short subsequent streams meet main stream at right angles. Differential erosion through soft rocks. E.g., Singhbhum (Chotanagpur), Seine tributaries (Paris basin). - **Angular:** Tributaries join main stream at acute angles. Common in Himalayan foothills. - **Rectangular:** Main stream bends at right angles, tributaries join at right angles. Subsequent origin. E.g., Colorado River, Vindhyan Mountains. - **Radial:** Tributaries from summit follow downslope in all directions. E.g., Saurashtra, Amarkantak Mountain, Central French Plateau, Mt. Kilimanjaro. - **Annular:** Upland has soft outer stratum, radial streams develop circular drainage around summit. E.g., Black Hill streams (South Dakota). - **Parallel:** Tributaries run parallel in uniformly sloping region. E.g., Lesser Himalayas, Western Ghats rivers to Arabian Sea. - **Centripetal:** Streams converge from all sides into low-lying basin. E.g., Ladakh, Tibet, Baghmati tributaries (Nepal). - **Deranged:** Uncoordinated pattern, characteristic of recently glaciated regions (numerous watercourses, lakes, marshes). E.g., Karakoram glaciated valleys. - **Barbed:** Confluence of tributary with main river is discordant. Tributary seems to flow upstream. Result of main river capture, reversing flow direction. E.g., Arun River (Kosi tributary). ### Major Landforms and Cycle of Erosion #### Marine Landforms and Cycle of Erosion - Sea waves, winds, currents, tides, storms cause erosional/depositional processes. - Erosive work depends on wave size/strength, slope, shore height, coast shape, rock composition, water depth, human activity. - Wave pressure compresses air in rock fissures, causing expansion/rupture. - Waves use rock debris as erosion instruments. - Chemical action (solvent) in soluble rocks (limestone, chalk). ##### Marine Erosional Landforms - **Chasms:** Narrow, deep indentations carved by headward erosion through rock planes of weakness. Lateral erosion widens mouth to form bay. - **Wave-Cut Platform:** Sea waves erode cliff, it retreats. Waves level shore, carving horizontal platform. Notch appears at cliff base (intensive erosion). - **Sea Cliff:** Steep bank/escarpment shoreline. - **Sea Caves:** Differential erosion by waves through rock of varying resistance. - **Sea Arches:** Waves from opposite directions strike narrow rock wall, differential erosion leaves bridge-like structure. - **Stacks/Skarries/Chimney Rock:** Portion of sea arch collapses, remaining column-like structure. - **Hanging Valleys:** Fluvial erosion of stream at shore doesn't match sea retreat, rivers hang over sea. - **Blow Holes or Spouting Horns:** Burst of water through small hole in sea cave (compressed air by strong waves). - **Plain of Marine Erosion/Peneplain:** Eroded plain left by marine action. If level difference with sea not much, becomes peneplain. ##### Marine Depositional Landforms - **Beach:** Temporary covering of rock debris/sand on/along wave-cut platform. - **Bar:** Currents/tidal currents deposit rock debris/sand along coast, submerged. Enclosed water body is lagoon. - **Barrier:** Overwater counterpart of bar. - **Tombolos:** Islands connected by a bar. - **Shoal:** Submerged ridge/bank/bar of unconsolidated material, rises near surface. Dangerous for navigation. - **Spit and Hook:** - **Spit:** Projected deposition joined to headland at one end, free in sea at other. - **Hook:** Shorter spit with one end curved towards land. - **Reef:** Shoal of rock/coral material at/near ocean surface. Coral reefs (consolidated coral skeletons). E.g., Great Barrier Reef. Dangerous for navigation if above surface. ##### Coral Reefs - Formed by accumulation of calcareous skeletons of dead coral polyps. - Polyps: Shallow warm water organisms (phylum cnidaria), soft body, calcareous skeleton. Extract calcium salts from seawater. - Live in colonies on rocky seafloor. Skeletons grow as cemented calcareous rocky mass. - Dead polyps shed skeletons, new polyps grow. Cycle repeats, forms layers of corals (coral reefs). - Transform into coral islands (e.g., Lakshadweep). ##### Coral Reef Relief Features - **Fringing reef:** Most common. Grows directly from shore. Very narrow (1-2 km). Shallow lagoon between beach and reef. Seaward side slopes steeply. E.g., New Hebrides, Florida. - **Barrier reef:** Extensive linear reefs parallel to shore, separated by lagoon. Broken, irregular ring. Largest (hundreds of km long, several km wide). E.g., Great Barrier Reef (Australia). - **Atolls:** Roughly circular oceanic reef system surrounding large central lagoon (80-150m deep). May be joined to seawater by channels. Form on submarine features. More common in Pacific (Fiji, French Polynesia, Caroline/Marshall/Cook Islands). Lakshadweep, Maldives, Chagos are atolls. ##### Development of Major Coral Reef Types (Darwin's Theory) 1. **Fringing reef:** Forms in shallow water near tropical island. 2. **Barrier reef:** Island subsides, reef grows outwards, distance increases. Fringing reef develops into barrier reef. 3. **Atoll:** Island completely subsides, only reef left. Reef retains island shape, forms ring enclosing lagoon. ##### Coastlines - Boundary between coast (land adjoining sea) and shore (land along sea edge). - Modified by sea level rise/fall, land uplift/subsidence. - **Coastline of Emergence:** Formed by land uplift or sea level lowering. Bars, spits, lagoons, salt marshes, beaches, sea cliffs, arches. E.g., East coast of India, Kerala coast. - **Coastlines of Submergence:** Formed by land subsidence or sea level rise. Ria, fjord, Dalmatian, drowned lowlands. - **Ria:** Irregular shoreline from submergence of dissected valley system. E.g., SW Ireland. - **Fjord:** Glacially eroded valley glacier troughs excavated below sea level, then glaciers disappear. Long, narrow inlets with steep sides. E.g., Norway. - **Dalmatian:** Submergence of mountain ridges (crests/troughs parallel to coast). E.g., Dalmatian coast (Yugoslavia). - **Drowned Valley (Lowland):** Low, indentation-free, formed by submergence of low-lying area. Series of bars parallel to coast, enclosing lagoons. E.g., Baltic coast (Germany). - **Indented Coastline:** Irregular, with creeks/inland waterways. Ideal for natural harbors (e.g., Europe). - **Neutral Coastlines:** New materials built out into water. No relative change between sea/land level. Alluvial fan-shaped, delta, volcano, coral reef coastlines. - **Compound Coastlines:** Combination of previous classes (e.g., submergence then emergence). E.g., Norway, Sweden. - **Fault Coastlines:** Unusual, from submergence of downthrown block along fault. Uplifted block's steep side/faultline against sea. #### Karst Landforms and Cycle of Erosion - Named after Karst province (Yugoslavia). - Characterized by underground drainage systems (sinkholes, fissures, caves) from dissolution/erosion of soluble rocks (limestone, dolomite). - General absence of surface drainage (water flow mostly subsurface). ##### Chemistry Behind Karst Landforms - Limestone: Calcium carbonate. Dolomite: Also magnesium. - Limestone soluble in rainwater. Carbonic acid (rain + atmospheric CO2, or soil CO2) dissolves limestone, forms calcium bicarbonate. ##### Conditions for The Formation of Karst Topography - Porous water-soluble rocks (limestone). - Thinly bedded, highly jointed/cracked strata. - Moderate to abundant rainfall. - Perennial water source, low water table. ##### Karst Landforms - **Sinkhole/Swallow Hole:** Funnel-shaped depressions from enlarged cracks in porous soluble rocks (solvent action of rainwater). Surface streams disappear underground. - **Karst Window:** Adjoining sinkholes collapse, form open aquifer/broad area directly exposed to surface. - **Polje/Blind Valley:** - **Dolines:** Small depressions. - **Uvala:** Adjoining dolines form long, narrow trench. - **Polje:** Uvalas coalesce to form U-shaped valley. - **Blind valleys:** Streams lose themselves in these valleys. - **Cavern:** Underground cave formed by water action (mechanical/solution) in limestone. E.g., Bastar, Dehradun, Shillong. - **Arch/Natural Bridge:** Part of cavern collapses, remaining portion forms arch. - **Sinking Creeks/Bogas:** Water in karst valley lost through cracks/fissures. If tops open, called bogas. - **Stalactite and Stalagmite:** - **Stalactite:** Lean inverted cone growing downwards from roof (limestone-bearing water seeps, evaporates). - **Stalagmite:** Thicker, flatter cone rising upwards from floor (remaining drops fall, evaporate). - **Column:** Stalactite and stalagmite join. - **Dry Valley/Hanging Valley/Bourne:** Stream erodes deep, water table lowered. Tributaries serve subterranean drainage, dry up. Dry valleys/bournes. Hang at height from main valley (hanging valleys). ##### The Karst Cycle of Erosion - **Youth:** Surface drainage on limestone. Upper impervious layer erodes. Dolines, sinkholes, swallow holes form. No large caverns. - **Maturity:** Maximum underground drainage. Limited surface drainage. Cavern networks. Late maturity: Decline of karst features. Karst windows expose cavern streams. Expand to large uvalas. Hums (detached uplands). - **Old Age:** Large-scale limestone removal leaves karst plain. Surface drainage reappears, few isolated hums. #### Glacial Landforms and Cycle of Erosion - **Glacier:** Moving mass of ice (few meters/day), charged with rock debris (erosional activity). - Types: Continental, ice caps, piedmont, valley (alpine). - **Continental:** Antarctica, Greenland (biggest ice sheet in Iceland). - **Ice caps:** Covers of snow/ice on mountains (origin for valley/mountain glaciers). - **Piedmont:** Continuous ice sheet at mountain base (e.g., S. Alaska). - **Valley (Alpine):** In higher Himalayas, other high mountain ranges. ##### Glacial Erosional Landforms - **Cirque/Corrie:** Hollow basin cut into mountain ridge (steep sides, open end, flat bottom). Tarn lake if ice melts. - **Glacial Trough:** Stream-cut steep-sided U-shaped valley, modified by glacial action. Uniform erosion (heavy, slow-moving ice). - **Hanging Valley:** Smaller glacial tributaries unable to cut as deep as bigger ones, remain "hanging" at higher levels. - **Arete:** Steep-sided, sharp-tipped summit (glacial activity from two sides). - **Horn:** Ridge with "horn" shape (glacial activity from >two sides). E.g., Matterhorn (Alps), Everest (Himalayas). - **D-Fjord:** Steep-sided, narrow entrance at coast where stream meets. Common in Norway, Greenland, New Zealand. ##### Glacial Depositional Landforms - **Outwash Plain:** Glacier melts, leaves stratified depositional material (rock debris, clay, sand, gravel). Layered surface (till plain). - **Moraine:** General term for rock fragments, gravel, sand carried by glacier. - Types: Ground, lateral (along sides of glacial valleys), recessional (from temporary standstill), medial (in glacial valley, flanked by lateral), end (terminal) (at edge where glacier retreats). - **Esker:** Winding ridge of un-assorted depositions (rock, gravel, clay) along glacier in till plain. Resembles embankment, used for roads. - **Kame Terraces:** Sediment accumulates in ponds/lakes trapped between glacier lobes or glacier/valley side. - **Kame:** Irregularly shaped hill/mound of sand/gravel, accumulates in depression on retreating glacier. - **Drumlin:** Inverted boat-shaped deposition in till plain. Indicates glacier movement direction. - **Kettle Holes:** Depressed material in till plain forms basin. ##### Glacial Cycle of Erosion - **Youth:** Inward cutting of ice in cirque. Aretes/horns emerge. Hanging valleys not prominent. - **Maturity:** Hanging valleys emerge. Opposite cirques closer. Glacial trough has stepped profile. - **Old Age:** U-shaped valley emerges. Outwash plain with eskers, kame terraces, drumlins, kettle holes. #### Arid Landforms and Cycle of Erosion - Arid regions: Scanty rainfall (deserts, semi-arid). ##### Water Eroded Arid Landforms - **Rill:** Narrow, shallow channel cut by flowing water. - **Gully:** Landform created by running water. Larger than rill. - **Ravine:** Narrower than canyon, product of stream-cutting erosion. Larger than gully, smaller than valley. - **Canyon:** Deep, narrow valley with steep sides. Gorge similar but steeper/narrower. - **Badland Topography:** Occasional rainstorms produce rills/channels, extensively erode weak sedimentary formations. Ravines/gullies develop by linear fluvial erosion. E.g., Chambal Ravines. - **Bolsons:** Intermontane basins in dry regions. - **Playas:** Small streams flow into bolsons, water accumulates. Temporary lakes. Salt-covered playas are salinas. - **Pediments:** Erosional landform (rock-cut surface at mountain foot). - **Bajadas:** Moderately sloping depositional plains between pediments and playa. Coalesced alluvial fans. ##### Wind Eroded Arid Landforms - **Aeolian erosion:** Deflation, abrasion, attrition. - **Deflation:** Removing, lifting, carrying dry, unsorted dust particles by winds. Causes depressions (blowouts). - **Abrasion:** Wind with sand grains erodes rock by grinding ("sandblasting"). - **Attrition:** Wear and tear of sand particles during transport. - **Deflation Basins (Blowouts):** Hollows from particle removal by wind. - **Mushroom Rocks (Rock Pedestal/Pedestal Rock):** Naturally occurring rock resembling mushroom (erosion, weathering, glacial action, disturbance). - **Inselbergs (Monadnock):** Isolated hill/knob/ridge rising abruptly from gently sloping plain. - **Demoiselles:** Rock pillars (resistant) standing above soft rocks (differential erosion). - **Zeugen:** Table-shaped rock area in arid/semi-arid regions (more resistant rock reduces slower than softer). - **Yardangs:** Ridges of rock formed by wind, usually parallel to wind direction. - **Wind Bridges and Windows:** Powerful wind abrades stone lattices, creating holes. Widened holes form window, further widening forms arch-like bridge. ##### Arid Depositional Landforms - **Ripple Marks:** Small-scale depositional features formed by saltation (transport of hard particles in turbulent flow). - **Sand Dunes:** Heaps/mounds of sand in deserts. - **Longitudinal Dunes:** Parallel to wind movement. Gentle windward slope, steep leeward side. In trade-wind deserts (Sahara, Australian, Thar). - **Transverse Dunes:** Perpendicular to prevailing wind. - **Barchans:** Crescent-shaped. Convex windward, concave/steep leeward. - **Parabolic Dunes:** U-shaped, longer/narrower than barchans. - **Star Dunes:** High central peak, 3+ radically extending arms. - **Loess:** Windblown dust/silt blankets land. Fine, mineral-rich material. In northern China, Great Plains (N. America), central Europe, Russia/Kazakhstan. Thickest near Missouri River, Yellow River. - Accumulates at desert edges. - Extremely fertile agricultural soil (minerals, good drainage, easily tilled). Erodes slowly.