Physical Geography (India & World)

1Plate boundaries and the Himalayas

Earth's lithosphere is divided into major and minor plates. Convergent, divergent and transform boundaries explain where earthquakes, volcanoes and fold mountains concentrate.

The Himalayas are young fold mountains at the convergent boundary of the Indian and Eurasian plates, formed as the Tethys Sea closed. Mid-oceanic ridges mark divergent spreading; transform faults slide plates past each other without creating or destroying crust in the same way.

Figure. Plate margins come in three mechanical types: convergent (Indian–Eurasian → Himalaya), divergent (mid-ocean ridges) and transform (slide-past faults). Schematic classes, not a world map.

2Rock cycle

Igneous, sedimentary and metamorphic rocks continuously transform. Igneous rocks cool from magma; sedimentary rocks form by deposition and lithification; metamorphic rocks recrystallise under heat and pressure.

Any of the three can feed any of the others through melting, weathering and burial — the cycle is a closed transformation set, not a one-way ladder from magma to sediment.

Figure. The rock cycle is a closed transformation among igneous, sedimentary and metamorphic families via weathering, heat and pressure, melting and cooling — a cycle graph, not a table of names.

3Atmospheric layers and lapse rate

Bottom to top: troposphere, stratosphere, mesosphere, thermosphere and exosphere. Weather lives in the troposphere, where temperature normally falls with height. The stratosphere holds the ozone layer; the thermosphere includes the ionosphere and is where auroras appear.

Normal lapse rate in the troposphere is about 6.5°C temperature fall per 1000 m rise. Insolation, latitude and albedo set the planetary heat budget that this layered structure sits inside.

Figure. Atmosphere as a vertical stack: weather lives in the troposphere; ozone peaks in the stratosphere; mesosphere, thermosphere and exosphere continue upward. Order is the exam point.

4Pressure belts, Coriolis and planetary winds

Global pressure belts — Equatorial Low (doldrums), Sub-tropical High (horse latitudes), Sub-polar Low and Polar High — drive the planetary winds: trades, westerlies and polar easterlies.

Coriolis force deflects moving air to the right in the Northern Hemisphere and to the left in the Southern (Ferrel's Law). It is zero at the equator and maximum at the poles, and it increases with the speed of the moving body.

Figure. Global pressure belts stacked by latitude from pole to equator drive planetary winds; Coriolis deflects them. Schematic latitude bands — not a globe outline.

How deflection sorts options

1. Name the beltEquatorial Low, Sub-tropical High, Sub-polar Low, Polar High — each anchors a wind family.
2. Apply CoriolisNorthern Hemisphere: deflect right. Southern Hemisphere: deflect left. Equator: no Coriolis.
3. Reject false claimsAny option that puts maximum Coriolis at the equator, or reverses hemisphere deflection, is out.

5Types of rainfall

Three textbook mechanisms produce rainfall: convectional, orographic and cyclonic (frontal).

Convectional rain is typical of equatorial heating; orographic rain falls on windward slopes such as the Western Ghats; cyclonic or frontal rain belongs to temperate convergence of air masses.

Figure. Orographic rain falls on the windward slope; the leeward side is the rain-shadow. Convectional and cyclonic/frontal rain are the other two textbook mechanisms (shown as a separate class box).

6Indian Southwest monsoon

The Southwest monsoon (June–September) brings about 75% of India's rainfall. Differential heating, the seasonal shift of the ITCZ, the Tibetan Plateau and the Tropical Easterly Jet frame the dynamics.

El Niño (warming of the central-east Pacific) is linked to a weak or deficient Indian monsoon; La Niña to a good monsoon. A positive Indian Ocean Dipole (warmer western Indian Ocean) and a strong Tropical Easterly Jet also favour stronger monsoon activity.

Figure. Southwest monsoon chain: differential heating, ITCZ shift north, moisture-laden southwest inflow, about three-quarters of India's annual rain — El Niño/La Niña modulate reliability, not this spine.

Boosters versus dampeners

1. Season windowJune–September Southwest monsoon delivers roughly three-quarters of annual rain.
2. Core driversDifferential heating, ITCZ shift, Tibetan Plateau and Tropical Easterly Jet structure the flow.
3. Pacific and Indian OceanLa Niña, positive IOD and strong TEJ favour a strong monsoon; El Niño and negative IOD dampen it.

7Indian physiographic divisions

India's physiography is divided into the Himalayas, the Northern (Indo-Gangetic) Plains, the Peninsular Plateau, the Coastal Plains and the Islands.

The Peninsular Plateau includes the Deccan Traps and is treated as the oldest large landmass among these divisions. Andaman–Nicobar islands are volcanic in origin; Lakshadweep is coral.

Figure. Physiographic stack north to south: Himalayas, Northern Plains, Peninsular Plateau, coastal plains (west and east) and islands. Institutional boxes standing in for a national outline.

8Ocean currents, reefs and tides

Warm currents such as the Gulf Stream and cold currents such as the Labrador Current reshape coastal climates. The Indian Ocean shows a seasonal reversal of currents tied to the monsoon winds.

Salinity, coral reefs and upwelling (which supports rich fisheries) are standard oceanography pegs. Tides arise from the gravitational pull of the Moon and the Sun.

Figure. Ocean exam pegs without a world map: warm versus cold currents reshape coasts; reefs need warm shallow seas; tides follow Sun–Moon gravitational pull. Indian Ocean monsoon reversal is a seasonal special case of currents.