Oceanography

Physical and chemical properties of the world’s oceans and their geographic significance.

Author

Geography Team

Official Syllabus

NEP-2020 Syllabus

Core I Paper XIII — Climatology and Oceanography (Oceanography Section)

Origin of ocean basins
Bottom relief of Indian, Atlantic, and Pacific Oceans
Ocean deposits
Coral reefs
Temperature and salinity of the oceans
Density of seawater
Tides and ocean currents
Sea-level changes

UGC NET Syllabus

Unit III — Oceanography

Origin of ocean basins
Bottom relief of Indian, Atlantic, and Pacific Oceans
Ocean deposits
Coral reefs
Temperature and salinity of the oceans
Density of seawater
Tides and ocean currents
Sea-level changes

Oceanography (Paper II / Advanced Topics)

Relief of Oceans
Composition: Temperature, Density and Salinity
Circulation: Warm and Cold Currents, Waves, Tides
Sea Level Changes
Hazards: Tsunami and Cyclone

NET Oceanography — Detailed Syllabus (Pulakesh Pradhan)

Syllabus Topics (10 Questions = 10 Marks)

Origin of Ocean Basin
Bottom Relief of Indian, Pacific and Atlantic Ocean
Ocean Deposits
Coral Reefs
Temperature and Salinity of Oceans
Density of Sea Water
Tides and Ocean Currents
Sea-Level Change

Key Books & Theories (NET Notes)

Concept	Scholar
Uniformitarianism	Charles Lyell / Hutton
Permanency of Ocean Basin	James D. Dana
Waves and Tides — Canal Theory	G.B. Airy
Progressive Wave Theory	William Whewell

Key Facts at a Glance (NET Notes)

Guyot → Flat-topped sea mountain (Table Mountain)
Sequence: Continent → Shelf → Slope → Rise → Abyssal Plain
Strait → Narrow strip of water joining two large sea bodies
Archipelago → A group of islands
Dead Sea → Called the *Salt Sea
Red Sea → Known as Erythraean Sea [Ocean Desert]; faulted structure
Submarine canyons form due to **turbidity currents*
Suez Canal connects Mediterranean Sea and Red Sea
Hypsographic curve explains ocean bottom topography
1 fathom = 2 metres = 6 feet = 1 nautical mile
Isobath = line joining same depth
71% of globe covered by hydrosphere
Ridge vs. Rise: Ridges have central rift valleys; Rises have gentler topography
Ocean size (ascending): Arctic → Indian → Atlantic → Pacific

NEP-2020 Programme Structure

UG Geography (Major) — Course Structure Under NEP-2020

Semester	Course Name	Credit	Marks
V	Climatology and Oceanography	4	100
V	Regional Planning and Development	4	100
V	Geography of Odisha	4	100

Multidisciplinary Courses: Oceanography (3 credits, 100 marks)

Welcome to the Oceanography module of Geography OpenCourseWare.

Part A: Common Topics (NEP-2020 & UGC NET)

These topics are covered in both the NEP-2020 undergraduate syllabus and the UGC NET syllabus.

Origin of Ocean Basins

📘 Syllabus Coverage

Syllabus	Topic Details
NEP-2020	Oceanography section — Origin of ocean basins
UGC NET	Unit III — Origin of ocean basins

Get the Presentation ↗ | Watch the Video ↗

Key Concepts

Continental Drift and Seafloor Spreading: Wegener’s theory and Hess’s seafloor spreading hypothesis explain ocean basin formation.
Plate Tectonics: Ocean basins form at divergent boundaries (mid-ocean ridges) and are consumed at convergent boundaries (subduction zones).
Wilson Cycle: Complete lifecycle of ocean basins — embryonic (rift valley), juvenile (Red Sea), mature (Atlantic), declining (Pacific), terminal (Mediterranean), suture (Himalayas).
Age of Ocean Floor: Youngest at mid-ocean ridges, oldest near continental margins — confirmed by magnetic anomalies.
Passive vs. Active Continental Margins: Atlantic-type (stable, wide shelves) vs. Pacific-type (subduction, narrow shelves, trenches).

Origin of Ocean Basins — Detailed (NET Notes — Pulakesh Pradhan)

Hypotheses

Hypothesis	Year	Scholar
Nebular Hypothesis	1755	Immanuel Kant; La Place
Planetesimal Hypothesis	1904	T.C. Chamberlain (geologist, USA)
Tetrahedral Hypothesis	1873/1875	Lowthian Green
Continental Drift (first proposed)	1910	F.B. Taylor
Drift Hypothesis	1911	H.B. Baker
Displacement Hypothesis	1912	Alfred Wegener

Carboniferous (298–358 Ma) — Pangaea started to break

Hemisphere Distribution of Water

Hemisphere	Area under Water	Share of Ocean Water
Northern	60.7%	43%
Southern	80.9%	57%

Depth of the Ocean (NET Notes)

Sonic Sounding Method — geographical method to measure depth
Fathoms — unit to measure ocean depth (1 fathom = 2 metres)
Hypsographic Curve: Kossinna (1921) first used; Sverdrup (1942) modified

Ocean Floor Zones

Zone	Depth	Key Statistics
Continental Shelf	Up to 200 m	7.6% of sea area; Atlantic 13.3%, Pacific 5.7%, Indian 4.2%
Continental Slope	200–2000 m	8.5% of total ocean area; Avg. slope 4°17’ (Shepard)
Deep Sea Plain	2000–6000 m	82.7% of total bottom
Deeps (Trenches)	Below 6000 m	1.2% of sea bottom; 57 total (Pacific 32, Atlantic 19, Indian 6)

Challenger Expedition (1872–76)

By Royal Society of London, vessel **HMS Challenger*
Prompted by **Charles Wyville Thomson*
Ocean deposits study by **Sir John Murray & Prof. Alphonse Renard*

Submarine Canyons (NET Notes)

Deep gorges on the ocean floor — restricted to continental shelf, slope, rise
Formed due to turbidity currents; also river origin and tectonic movement

Bottom Relief of the Oceans

📘 Syllabus Coverage

Syllabus	Topic Details
NEP-2020	Oceanography section — Bottom relief of Indian, Atlantic, and Pacific Oceans
UGC NET	Unit III / Relief of Oceans

Get the Presentation ↗ | Watch the Video ↗

Key Concepts

Continental Shelf: Shallow, gently sloping extension of continental landmass — up to 200m depth. Rich in marine resources.
Continental Slope: Steep descent from shelf edge to deep ocean floor. Submarine canyons.
Continental Rise: Gentle slope at base of continental slope — sediment accumulation from turbidity currents.
Abyssal Plains: Extensive flat areas of deep ocean floor — covered with fine sediments. Pelagic oozes cover about 50% of the world ocean floor area.
Mid-Ocean Ridges: Underwater mountain chains at divergent boundaries — Mid-Atlantic Ridge, East Pacific Rise, Indian Ocean Ridge system.
- Slow-spreading ridges are characterised by an axial graben with 1500–3000 m depth, faulted topography, and intermittent shield volcanoes.
- Ninety East Ridge (Indian Ocean): Formed by the Kerguelen Hotspot through the eruption of ocean island basalt. This hotspot is also linked to the formation of the Rajmahal Hills in India.
- Fracture Zones: Elevation differences across ocean floor fracture zones are explained by Age, Temperature, and Density differences (not material differences).
Deep Sea Trenches: Deepest parts of ocean — Mariana Trench (11,034m), Tonga Trench, Java Trench. Formed at subduction zones, they trace boundaries between tectonic plates, are almost parallel to the ‘Ring of Fire’, and are characterized by earthquakes. Deepest parts do not always lie away from the coast, as they are often near active continental margins.
- Submarine Canyons: e.g., Swatch of No Ground, extending offshore from the Ganga river delta. Pelagic oozes are quite uncommon in their occurrences within submarine canyons.
Isobath: A line connecting equal depths below a water surface.
Seamounts and Guyots: Submarine volcanic mountains — guyots are flat-topped (eroded by waves).
Calcareous Oozes: Found in lower latitudes and up to a depth of 4500 m because organisms with carbonate shells predominate in warm, shallow water, and calcium carbonate dissolves very slowly below this depth (Carbonate Compensation Depth).
Specific Ocean Features: Atlantic (S-shaped ridge), Pacific (Ring of Fire, trenches), Indian (triple junction, Ninety East Ridge).
- Marginal Sea: The Andaman Sea is considered a marginal sea, in true sense, in the Indian Ocean.

Bottom Relief — Atlantic Ocean (NET Notes — Pulakesh Pradhan)

Area: 82 million sq. km (S-shape); **1/6 of total world area*
25.7% area less than 2000 m depth

Continental Shelf

Newfoundland–British Islands → World’s widest continental shelf
Grand Bank, Dogger Bank, Bay of Biscay

Mid-Atlantic Ridge

‘Meteor’ — German Oceanographic Vessel (1920)
Pico Island of Azores → highest peak; Rocks of St. Paul → sharpest peak
Features: Telegraph Plateau, Dolphin Rise, Romanche Deep, Challenger Rise

Basins of the Atlantic Ocean (11 basins)

Basin	Notes
Labrador Basin	Between Greenland & Newfoundland
North-Western Atlantic Basin	Biggest
Brazilian Basin	~6000 m depth
North-East Atlantic (Iberian) Basin	~5000 m avg depth
Cape Verde, Guinea, Cape, Argentina, Agulhas Basins	Various locations

Bottom Relief — Indian Ocean (NET Notes)

Average Depth: 4000 m; 58.8% between 4000–6000 m
Continental Shelf: Bay of Bengal & Arabian Sea; width 400 miles
Andaman & Nicobar Islands — submerged folded mountain (Burma)
Laccadives, Maldives — submarine ridge location

Continental Ridges

Laccadive–Chagos Ridge, Chagos–Saint Paul Ridge, Kerguelen–Gaussberg Ridge, Seychelles–Mauritius Ridge

Basins (10): Oman, Arabian, Somali, Mauritius, Natal, Agulhas, Atlantic–Indian–Antarctic, Andaman, Cocos–Keeling, Eastern Indian–Antarctica

Bottom Relief — Pacific Ocean (NET Notes)

1/3 of total Earth area; E–W: 10,000 miles; N–S: 9,300 miles
Average Depth: 5000 m

Island Groups

Group	Islands
Melanesia	Solomons, New Hebrides, Fiji
Micronesia	Marshalls, Carolines, Gilbert Ellice
Polynesia	Society, Cook, Tuamotu
Volcanic	Hawaiian Islands
Coral	Fiji, Funafuti, Ellice

Ridges

Albatross Plateau / East-Pacific Ridge, Cocos Ridge, Hawaiian Swell, Marcus–Necker Rise, Tasmania Ridge

Major Deeps/Trenches (Pacific — 32 recorded)

Trench	Depth
Mariana / Challenger Deep	11,034 m (deepest)
Tonga / Aldrich Deep	10,882 m
Kuril–Kamchatka Deep	10,542 m
Philippine / Swire Deep	10,497 m
Kermadec Trench	10,047 m
Japan Trench	9,000 m
Aleutian Trench	7,679 m

Temperature, Salinity, and Density of Oceans

📘 Syllabus Coverage

Syllabus	Topic Details
NEP-2020	Oceanography section — Temperature, salinity, density
UGC NET	Unit III / Composition: Temperature, Density and Salinity

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Key Concepts

Ocean Temperature: Decreases with depth — three layers: mixed layer, thermocline, deep water. Average surface temperature ~17°C. Coasts are relatively warmer near onshore wind, but colder where wind blows from land towards sea because wind from land drives warm surface water away, causing cold bottom water to upwell.
Factors Affecting Temperature: Latitude, ocean currents, depth, season, proximity to landmass.
Salinity: Average 35‰ (parts per thousand). Highest in subtropics (high evaporation), lowest near equator and poles. Sea water is saline primarily because of the solution of salts derived from ocean floor rocks.
- Forchammer’s Principle (Rule of constant proportion): The ratio of major salts is constant. For example, Potassium constitutes 1.1% of dissolved salt in seawater.
Factors Affecting Salinity: Evaporation, precipitation, river discharge, ice formation/melting, ocean currents.
Density of Seawater: Function of temperature, salinity, and pressure. Cold, saline water is densest. Density does not decrease with decreasing depth (it decreases with increasing temperature and decreasing salinity).
- Pycnocline: A zone below the surface waters and above the deep waters where density changes rapidly. It is heavily influenced by the thermocline (temperature) and can also act as a halocline (salinity). Potential density of seawater is primarily dependent on Salinity and Temperature.
Thermohaline Circulation: Global conveyor belt driven primarily by differences in Heat and Density.
CaCO₃ Compensation Depth (CCD): The depth in the ocean below which the rate of supply of calcium carbonate lags behind the rate of solvation. It is related to the amount of carbonic acid present in sea water and generally occurs at depths greater than 2,000 m.
Heat and Salt Budget: Ocean as a heat reservoir — role in climate regulation.
Desalination Processes: Common methods include Reverse osmosis, Electrolysis, and Freeze separation.

Temperature of Oceans — Detailed (NET Notes — Pulakesh Pradhan)

M.F. Maury — Founder of ‘Scientific Marine Meteorology’
Pettersson–Nansen water bottle — for water sampling
Pyrheliometer — measurement of solar insolation

Processes of Heat Transfer

Convection, 2. Absorption, 3. Kinetic energy → heat, 4. Chemical processes, 5. Condensation of water vapour

Insolation at Different Latitudes (Blair)

Latitude	Insolation
Equator (0°)	100%
33°N/S	88%
50°N/S	68%
70°	47%
Poles	12%

Vertical Temperature Distribution

Depth	Temperature
100 fathoms	60.7°F
500 fathoms	40.1°F
1000 fathoms	36.5°F
2200 fathoms	35.2°F

Salinity of Oceans — Detailed (NET Notes)

Varies from **34 to 37.5‰*
Methods: Titration (constancy of composition), Hydrometer (sample)

Chemical Composition (Dittmar, 1884 — Challenger Expedition)

Salt	Amount (‰)	Percentage
Sodium Chloride	27.2	77.8%
Magnesium Chloride	3.80	10.9%
Magnesium Sulphate	1.65	4.7%
Calcium Sulphate	1.2	3.6%
Potassium Sulphate	0.86	2.5%

Controls of Salinity

Evaporation, Precipitation, River water, Atmospheric pressure, Movement of sea water, Periodic variation

Salinity by Ocean / Sea

Ocean / Sea	Salinity (‰)
Red Sea	37–41 (highest)
Mediterranean Sea	37–39
Atlantic Ocean	35.67
Baltic Sea	3–15 (lowest)
Hudson Bay	3–15

Density of Sea Water — Detailed (NET Notes)

Pure water has maximum density at **4°C*

Controlling Factors

Factor	Details
Temperature	Varies from −2°C to 30°C
Salinity	Average density at 35‰ = 1.028
Atmospheric Pressure	Measured in decibars

Holland–Hansen — T–S Diagram to delineate water masses

Water Masses

Water Mass	Type
Equatorial Water Mass	Surface
Antarctic Circumpolar	Surface
Sub-Antarctic / Sub-Arctic	Intermediate
Central Water Mass	Due to sub-tropical convergence
Antarctic Bottom Water	Bottom
North Atlantic Deep Bottom Water	Deep

Waves, Tides, and Ocean Currents

📘 Syllabus Coverage

Syllabus	Topic Details
NEP-2020	Oceanography section — Tides and ocean currents
UGC NET	Unit III / Circulation: Warm and Cold Currents, Waves, Tides

Get the Presentation ↗ | Watch the Video ↗

Key Concepts

Ocean Waves: Generated by wind — wave height, wavelength, period, fetch. Constructive vs. destructive waves. Water waves are termed ‘shallow’ when the water depth is less than 1/20th of the wavelength.
- Wave Transformation at Coast: As a wave approaches the coastline, wave height increases, celerity (speed) decreases, and wave length decreases.
- Wave Base: The depth where circular orbital motion of water molecules declines to zero, which is equivalent to 1/2 of the wavelength.
- Translatory Waves: Develop in the land-ward side after wave breaking.
- Breaker Types: Waves break as they approach the coast because water is pulled down by gravity as wave steepness exceeds a critical value.
  - Spilling Breaker: Gentle beach gradient, fine grain size, high energy dissipation.
  - Plunging Breaker: Steep beach gradient, coarse grain size, high energy dissipation.
  - Surging Breaker: Steep beach gradient, moderate grain size, moderate/low energy dissipation.
Tides: Periodic rise and fall of sea level caused by gravitational pull of Moon and Sun. Development of the earth’s tidal bulge on the opposite direction of the moon is best explained by Centrifugal force.
- Spring tides (syzygy), neap tides (quadrature)
- Perigean Spring Tides: These tides have the highest amplitude among various tidal types, occurring when the moon is at perigee (closest to Earth) during a full or new moon.
- Diurnal, semi-diurnal, and mixed tidal patterns
- Rotating Tide: The co-tidal line rotates in a clockwise direction, and tidal amplitude increases away from the amphidromic point, which is a position inside the ocean that experiences no fluctuation of water level due to tide.
- Tidal bore and tidal range
Ocean Currents: Large-scale movement of seawater driven by wind, temperature, salinity, and Coriolis force.
- Warm Currents: Gulf Stream, Kuroshio, North Atlantic Drift, Brazil Current
- Cold Currents: Labrador, Benguela, Peru (Humboldt), California Current, Kamchatka Current
- Gyres: Circular current systems in major ocean basins — North Atlantic, South Pacific, etc.
- Ekman Transport: In the southern hemisphere, it occurs 90° to the left of the wind direction.
Upwelling and Downwelling: Vertical water movements — upwelling brings nutrients to surface (productive fishing grounds).
**Coastal Circulation and Hazards:*
- Tsunami: Involves movement of water from surface to sea-floor. The shoaling effect can greatly increase wave-heights closer to the coast.
- Rip-cell circulations: Developed along the coasts by the combination of shore-normal and long-shore currents.

Tides & Tidal Waves — Detailed (NET Notes — Pulakesh Pradhan)

Pliny — tides developed due to combined action of sun and moon
Isaac Newton (1687) — first rational explanation: Gravitational attraction
Ratio of tidal forces: Moon : Sun = **11 : 5*

Key Tidal Concepts

Term	Description
Syzygy	Sun–Moon–Earth in line → Spring Tides
Quadrature	Moon at right angle → Neap Tides
Perigee	Moon nearest to Earth → tides 20% above average
Apogee	Moon farthest → tides 20% below average

Types of Tides

Type	Interval
Semi-diurnal	12½ hours — two high, two low per day
Diurnal	24¾ hours — one high, one low per day
Spring Tides	Once a fortnight (syzygy)
Neap Tides	Once a fortnight (quadrature)

Theories of Tides

Theory	Scholar	Year
Equilibrium Theory	Isaac Newton	1687
Progressive Wave Theory	William Whewell	1833
Dynamical Theory	Laplace	1755
Stationary Wave Theory	Dr. R.A. Harris	—

Ocean Currents — Detailed (NET Notes)

Alexander Von Humboldt (1816) — identified controls of ocean currents

Pacific Ocean Currents

Current	Type
Kuroshio / Japan Current	Warm
Peruvian (Humboldt) Current	Cold
California Current	Cold
Oyashio / Kuril Current	Cold
East Australian Current	Warm

Indian Ocean Currents

Current	Type
Monsoon Current	Warm
Mozambique & Agulhas Current	Warm
West Australian Current	Cold

Atlantic Ocean Currents

Current	Type
Gulf Stream	Warm
Brazil Current	Warm
Labrador Current	Cold
Benguela Current	Cold

Sea-Level Changes

📘 Syllabus Coverage

Syllabus	Topic Details
NEP-2020	Oceanography section — Sea-level changes
UGC NET	Unit III / Sea Level Changes

Get the Presentation ↗ | Watch the Video ↗

Key Concepts

Eustatic Changes: Global sea-level changes due to change in ocean water volume.
- Glacial periods → sea-level fall (water locked in ice sheets)
- Interglacial periods → sea-level rise (ice melting)
Isostatic Changes: Local changes due to crustal uplift or subsidence.
- Post-glacial rebound (Scandinavia, Canada). Some European coasts record sea-level fall due to isostatic rebound resulting from deglaciation.
- Tectonic subsidence
Current Sea-Level Rise: The average global rate of sea-level rise at present is about 3.3 mm/year. Past records of sea-level changes are best deciphered from Mangrove-fringed coasts.
Carbonate Compensation Depth (CCD): The depth in the ocean below which the rate of supply of calcium carbonate is exceeded by the rate of dissolution. In most oceans, the CCD is usually about 4,500 meters.
Impacts: Coastal flooding, erosion, saltwater intrusion, loss of wetlands, island submergence.
Emergent and Submergent Coastlines: Raised beaches, marine terraces (emergent); rias, fjords, drowned valleys (submergent).
Coral Reefs as Indicators: Reef growth tracks sea-level changes — Darwin’s subsidence theory.
**Maritime Law:*
- UNCLOS: Stands for United Nations Convention on the Law of the Sea.
- EEZ (Exclusive Economic Zone): In order of decreasing area of EEZs, the sequence is USA > France > Australia > Russia.

Sea Level Changes — Detailed (NET Notes — Pulakesh Pradhan)

Types of Sea Level Change

Type	Description
Eustatic	Change caused by change in volume of water in ocean store
Isostatic	Local change caused by change in level of land relative to sea
Emergence	Impact of a relative fall in sea level
Submergence	Impact of a rise in relative sea level

Causes of Sea Level Rise

Cause	Rate
Thermal expansion	1.2–1.6 mm/yr
Glacial / ice cap melting	0.4 mm/yr (1961–1990); 1.0 mm/yr since 2001

Effects

Coastal flooding, storm surge, coastal erosion (70% of worldwide beaches being eroded)
Current average: 3 mm/yr sea level rise

Coral Reefs and Ocean Deposits

📘 Syllabus Coverage

Syllabus	Topic Details
NEP-2020	Oceanography section — Coral reefs, Ocean deposits
UGC NET	Unit III — Coral reefs, Ocean deposits

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Key Concepts

Coral Reefs: Biogenic formations by coral polyps — require warm (>20°C), shallow, clear, saline water.
- Fringing Reefs: Grow directly from shore — most common type
- Barrier Reefs: Separated from shore by lagoon — Great Barrier Reef
- Atolls: Ring-shaped reefs enclosing lagoon — formed by subsidence of volcanic island (Darwin’s theory)
Coral Bleaching: Expulsion of symbiotic algae due to stress (warming, pollution) — widespread global threat.
Ocean Deposits: Materials deposited on the ocean floor.
- Terrigenous: Land-derived sediments (gravel, sand, silt, clay) — near coasts
- Pelagic: Deep-sea deposits — biogenic oozes (foraminiferal/calcareous, radiolarian/siliceous), red clay
- Authigenic: Formed in-situ — manganese nodules, phosphorite deposits

Ocean Deposits — Detailed (NET Notes — Pulakesh Pradhan)

1773 — Captain Phipps: 683 fathoms; found blue mud
1891 — Sir John Murray & Prof. Alphonse Renard: 1st world map of oceanic deposits

Classification by Source

**(A) Lithogenous / Terrigenous Material:* - Blue Mud — deeper ocean; 14.5 million sq. km - Red Mud — calcium carbonate 6–61%; off river mouths - Green Mud — glauconite; 100–900 fathoms

(B) Products of Volcanism: Sub-aerial and sub-marine

**(C) Organic Remains:* - Pelagic Calcareous: Pteropod Ooze, Globigerina Ooze - Pelagic Siliceous: Radiolarian Ooze, Diatom Ooze

(D) Inorganic Precipitates: Dolomite, iron, manganese oxide, phosphate

(E) Red Clay: Most widely spread pelagic deposit — hydrated silicate of aluminium

(F) Extra-Terrestrial: Meteoric dust, cosmic spherules

Coral Reefs — Detailed (NET Notes)

Masses of limestone and dolomite; confined between **25°N to 25°S*
Built by coral polyps; Zooxanthellae give colour
Western coast of continents — **no coral reefs*

Conditions for Growth

Condition	Requirement
Temperature	68–70°F (20°C)
Depth	Max 200–250 feet (60–70 m)
Water	Sediment-free
Salinity	27‰ to 40‰

Types

Type	Description	Example
Fringing Reef	Narrow belt along steep shores; boat channel	South Florida Reef
Barrier Reef	Largest type; 45° outward slope	Great Barrier Reef (Australia)
Atoll	Oval-shaped coral ring enclosing lagoon	Funafuti Atoll

Theories of Coral Reef Formation

Theory	Scholar	Year
Subsidence Theory	Charles Darwin	1837
Non-Subsidence / Stand Still Theory	Murray	1880
Glacial Control Theory	Daly	—

Part C: UGC NET Specific Topics

These topics are part of the UGC NET syllabus only.

Oceanic Hazards: Tsunami and Cyclone

📘 Syllabus Coverage

Syllabus	Topic Details
UGC NET	Hazards: Tsunami and Cyclone

Get the Presentation ↗ | Watch the Video ↗

Key Concepts

Tsunami: Series of ocean waves caused by underwater earthquakes, volcanic eruptions, or landslides.
- Characteristics: Long wavelength, short amplitude in deep water; amplified near coast
- 2004 Indian Ocean Tsunami: Magnitude 9.1 earthquake — devastated coastal regions of 14 countries
- Warning Systems: Pacific Tsunami Warning Centre, Indian Ocean Tsunami Warning System
Cyclones (Marine Perspective): Storm surge, coastal flooding, wave damage.
- Storm Surge: Abnormal rise in sea level during cyclone — most destructive component
- Coastal Vulnerability: Low-lying areas, deltaic regions, island nations
Rogue Waves: Unusually large, unexpected waves — hazard to shipping.
Marine Pollution: Oil spills, plastic pollution, chemical contamination — impact on marine ecosystems.
Law of the Sea (UNCLOS): Maritime zones — territorial sea, contiguous zone, EEZ, continental shelf, high seas.

Quick Reference

Oceanography Quick Reference

Key Books and Authors

Book	Author
The Oceans: Their Physics, Chemistry, and General Biology	Sverdrup, Johnson, & Fleming
Physical Geography of the Sea	Matthew Fontaine Maury (Father of Oceanography)
Oceanography	Paul R. Pinet

Theories and Models

Theory / Concept	Propounder	Description
Subsidence Theory of Coral Reefs	Charles Darwin (1842)	Fringing reef -> Barrier reef -> Atoll via island subsidence
Glacial Control Theory	R.A. Daly (1915)	Coral reef formation based on Pleistocene sea-level changes
Stand-still Theory	Murray (1880)	Reefs grow on submarine platforms that build up or are cut down
Equilibrium Theory of Tides	Isaac Newton (1687)	Tides caused by gravitational pull of Moon and Sun
Dynamical Theory of Tides	Pierre-Simon Laplace (1775)	Treats tides as long waves influenced by Coriolis force
Stationary Wave Theory	R.A. Harris (1904)	Tides caused by stationary waves in ocean basins
Progressive Wave Theory	William Whewell (1833)	Tidal wave originates in Southern Ocean and travels northwards

Key Oceanographic Terms

Thermocline: Layer where temperature decreases rapidly with depth.
Halocline: Layer of rapid salinity change.
Pycnocline: Layer of rapid density change.
Upwelling: Upward movement of cold, nutrient-rich deep water (e.g., Peru Current).
Gyre: Large system of circular ocean currents formed by global wind patterns.
Thermohaline Circulation: Deep-ocean currents driven by differences in water density (Global Conveyor Belt).

Notes compiled by Geography Team