Physical Geography Questions for NDA

Structure of the Earth

The Earth has three main layers. The outermost is the Crust (also called Lithosphere when combined with upper mantle). Below it is the Mantle, which is semi-molten rock called Magma. The innermost part is the Core — the Outer Core is liquid iron-nickel and the Inner Core is solid iron-nickel. The boundary between Crust and Mantle is called the Mohorovicic Discontinuity (Moho). The boundary between Mantle and Core is called the Gutenberg Discontinuity.

• Crust thickness: Continental crust 30-50 km, Oceanic crust 5-10 km
• Mantle extends from Moho down to about 2900 km depth
• Outer Core (liquid) from 2900 km to 5100 km; Inner Core (solid) from 5100 km to 6371 km (centre)
• Moho Discontinuity separates Crust from Mantle
• Gutenberg Discontinuity separates Mantle from Core
• Seismic waves (P and S waves) are used to study Earth interior — S waves cannot pass through liquid, which proved Outer Core is liquid

Plate Tectonics and Landform Building

Earth's crust is broken into large pieces called Tectonic Plates. These plates float on the semi-molten Asthenosphere (upper Mantle) and move slowly. Where plates meet, major landforms are created. Convergent boundaries (plates collide) create fold mountains and trenches. Divergent boundaries (plates move apart) create rift valleys and mid-ocean ridges. Transform boundaries (plates slide past each other) cause earthquakes like the San Andreas Fault.

• Himalayas formed by collision of Indian Plate and Eurasian Plate — classic convergent boundary example
• Mid-Atlantic Ridge is the longest mountain range on Earth — formed at divergent boundary under ocean
• Mariana Trench (Pacific Ocean) is the deepest point on Earth — about 11,000 m deep, at convergent boundary
• Volcanoes are common at convergent and divergent boundaries — Ring of Fire in Pacific is most volcano-dense zone
• Deccan Traps in India formed by hot-spot volcanic activity, not plate boundary

Types of Rocks

Rocks are classified into three types based on how they form. Igneous rocks form from cooled magma. Sedimentary rocks form by deposition of sediments in layers. Metamorphic rocks form when existing rocks are changed by heat and pressure. The Rock Cycle shows how each type can convert into another over geological time.

• Igneous: Granite (intrusive, cools slowly underground), Basalt (extrusive, cools fast on surface)
• Sedimentary: Sandstone, Limestone, Shale — fossils are found only in sedimentary rocks
• Metamorphic: Marble (from Limestone), Slate (from Shale), Quartzite (from Sandstone)
• Coal and petroleum are found in sedimentary rock layers
• Most of Indian Peninsula (Deccan Plateau) is made of Basalt (igneous)

Landforms — Erosion and Deposition

Landforms are created by agents like rivers, wind, glaciers, and sea waves through erosion (wearing away) and deposition (building up). Rivers create V-shaped valleys in mountains and deposit deltas at their mouths. Glaciers create U-shaped valleys, cirques, moraines, and fjords. Wind in deserts creates sand dunes, mushroom rocks, and deflation hollows. Waves along coasts create cliffs, caves, sea arches, and beaches.

• River: V-valley (upper course), meanders and ox-bow lakes (middle course), delta and estuary (lower course)
• Glacier: U-valley, cirque (bowl-shaped hollow), arête (sharp ridge), horn peak (e.g. Matterhorn)
• Wind (Aeolian): Barchan dune (crescent shaped), inselberg (isolated hill), mushroom rock
• Karst landforms from limestone dissolution: sinkholes, stalactites (hang from ceiling), stalagmites (rise from floor)
• Delta vs Estuary: Delta forms when river deposits sediment at mouth; Estuary forms when tides keep mouth open and clear

Climate Zones and Factors

Climate is the long-term average weather of a region. The main factors affecting climate are latitude, altitude, distance from sea, ocean currents, and winds. Koppen Classification divides world climates into 5 major types. In NDA, questions focus on monsoon, tropical, desert, and polar climates most frequently. The Indian Monsoon is caused by differential heating of land and sea — land heats faster in summer creating low pressure that pulls moisture-laden winds from the Indian Ocean.

• Tropical Rainforest (near equator): Amazon, Congo, parts of Southeast Asia — heavy rain, no dry season
• Desert Climate: 20-30 degrees latitude (Horse Latitudes) — Sahara, Arabian, Thar Desert
• Mediterranean Climate: 30-40 degrees, west coasts — dry summer, wet winter (opposite of monsoon)
• Tundra and Polar: high latitude, permafrost, very short summers
• Monsoon Climate: seasonal wind reversal — SW Monsoon (June-September) brings rain to India
• Altitude lowers temperature at rate of about 6.5 degrees Celsius per 1000 m rise (Normal Lapse Rate)

Ocean Currents

Ocean currents are like rivers within the sea. Warm currents flow from equator towards poles and make coastal areas warmer. Cold currents flow from poles towards equator and make coastal areas cooler and drier — they cause deserts on west coasts. The Gulf Stream is the most famous warm current, keeping Western Europe mild. Currents in Northern Hemisphere move clockwise; in Southern Hemisphere they move anticlockwise (Coriolis Effect).

• Warm Currents: Gulf Stream (Atlantic), Kuroshio (Pacific), North Atlantic Drift
• Cold Currents: Labrador, Canaries, Benguela, California, Humboldt (Peru) Current
• Humboldt/Peru Cold Current causes Atacama Desert on South America west coast
• Canary Cold Current causes Sahara Desert on Africa west coast
• El Nino: warming of Pacific Ocean surface waters near Peru — disrupts monsoon worldwide
• La Nina: opposite of El Nino — cooling of same region — can cause excess rain in India

Earthquakes and Volcanoes

Earthquakes are vibrations caused by sudden movement of tectonic plates. The point of origin underground is called Focus (Hypocentre). The point on surface directly above is called Epicentre — maximum destruction happens here. Richter Scale measures earthquake energy (logarithmic — each point is 10 times stronger). Volcanoes are openings in Earth's crust through which magma erupts. Active volcanoes erupt regularly; Dormant ones are resting; Extinct ones have not erupted in recorded history.

• Richter Scale: 1-9+ scale, each unit = 10 times more energy release
• Seismograph is the instrument used to measure earthquakes
• Tsunami is a giant sea wave caused by undersea earthquake or volcanic eruption
• Barren Island (Andaman) is India's only active volcano
• Narcondam Island (Andaman) is a dormant volcano in India
• Ring of Fire: belt around Pacific Ocean with 75 percent of world's volcanoes and 90 percent of earthquakes

• Confusing Stalactite and Stalagmite — remember: stalaCTite has C for Ceiling, stalagMite has M for ground (Mound)
• Mixing up Convergent and Divergent boundaries — Convergent means plates COME together (mountains and trenches), Divergent means plates DRIFT apart (rift valleys and mid-ocean ridges)
• Thinking all deserts are hot — Thar is hot but Gobi and Ladakh are cold deserts; NDA sometimes asks about cold deserts
• Confusing El Nino effect on India — El Nino typically weakens Indian monsoon (drought risk); La Nina strengthens it
• Saying Himalayas are oldest mountains — they are youngest fold mountains (formed 50 million years ago). Aravalli is oldest in India

• Earth layers from outside in: Can My Giant Oven Cook — Crust, Mantle, Outer Core, Inner Core (solid)
• Stalactite vs Stalagmite: tIGHT holds to ceiling (stalactite), mIGHT grow from floor (stalagmite) — both hang and rise TIGHT and MIGHT
• Rock cycle mnemonic: I See Mountains — Igneous becomes Sedimentary becomes Metamorphic (under pressure and heat)
• Ocean current rule: West coasts of continents get COLD currents (which cause deserts) — think Sahara on Africa west coast, Atacama on South America west coast
• Warm vs Cold current effect: Warm currents bring rain and warmth, Cold currents bring dry and foggy conditions — Gulf Stream keeps UK warm despite high latitude

• NDA typically asks 2-4 questions on Indian physical features — know locations of major passes (Khyber, Bolan, Nathu La, Rohtang), peaks (K2, Kangchenjunga, Nanda Devi), and rivers (Ganga, Brahmaputra, Krishna systems)
• Map-based questions often ask which river joins which — focus on tributaries of Ganga (Yamuna, Ghaghra, Son, Kosi) and Deccan rivers (Godavari, Krishna, Cauvery direction of flow — west to east into Bay of Bengal)
• Climate questions often use indirect clues like crop names or vegetation — if question mentions mangroves, think coastal/tidal areas; if cork trees or olives, think Mediterranean climate
• Earthquake and volcano questions are short and factual — just memorize Barren Island (active), Narcondam (dormant), Ring of Fire statistics, and Richter Scale basics
• Time yourself on map questions — they look easy but aspirants waste time visualizing. Practice with blank India and World maps before exam. Each geography question in NDA should take under 45 seconds