UPSC CSE Prelims
Geomorphology Previous Year Questions (PYQs)

Detailed Explanation:

Explanation:

• Statement 1 is Correct: Rare Earth Elements (REEs) are essential for modern technologies such as Artificial Intelligence, robotics, electric vehicles, renewable energy systems, space exploration, and defense equipment.

• Statement 2 is Incorrect: China is the largest producer of REEs, but the United States is the second-largest producer. India is not the second-largest producer globally.

• Statement 3 is Correct: The Government of India launched the National Critical Mineral Mission (NCMM) in January 2025 to strengthen domestic production, secure supply chains, and reduce import dependence.

• Statement 4 is Incorrect: Rare Earth Elements consist of 17 elements—15 lanthanides along with scandium and yttrium—not 13 elements.

• Therefore, statements 1 and 3 are correct, making Option A the correct answer.

Rare Earth Elements (REEs) and Critical Minerals

• REEs are a group of 17 metallic elements used in high-tech industries, clean energy technologies, electronics, and defense systems.

• Critical minerals are minerals essential for economic security and strategic industries, with limited supply sources and high import dependence.

Detailed Explanation:

What is Tungurahua?

❌ Why Other Options Are Wrong

Revision Tip: All four countries share the Andes — the trap is assuming any Andean volcano could be in any of these countries. Always pin Tungurahua = Ecuador.

Detailed Explanation:

Correct Answer: ✅ Option 3

Chalk and clay differ mainly in permeability, not simply in porosity. Chalk contains many interconnected pores, allowing water to pass through easily. Clay also has pores, but they are extremely small and poorly connected, so water movement is very slow. Therefore, Statement II is correct and explains Statement I, while Statement III is incorrect.

✅ Statement I is Correct: Chalk is highly permeable, whereas clay is one of the least permeable rocks/soils.

✅ Statement II is Correct: Chalk is porous and can absorb and transmit water through its interconnected pore spaces.

❌ Statement III is Incorrect: Clay is not non-porous; it is porous but has very tiny pores that restrict water movement.

Short Notes: Porosity and Permeability

• Porosity is the percentage of pore spaces in a rock or soil.

• Permeability is the ability of water to move through those pore spaces.

• A rock can be porous but impermeable if pores are not well connected.

• Chalk is both porous and permeable.

• Clay is porous but largely impermeable due to tiny pore size.

• Groundwater is commonly stored in porous and permeable rocks called aquifers.

• Sandstone and chalk are common aquifer rocks.

Detailed Explanation:

All three statements are important geological evidences supporting Alfred Wegener’s Continental Drift Theory. Matching rock formations, similar mineral deposits, and identical sedimentary sequences across widely separated continents indicate that these landmasses were once part of a single supercontinent.

✅ Statement I is Correct: The ancient rock belts of Brazil and Western Africa match in age and structure, showing that the two continents were once connected.

✅ Statement II is Correct: Ghana's gold placer deposits are linked to gold-bearing source rocks found in Brazil, suggesting the continents were previously joined.

✅ Statement III is Correct: Gondwana sediments found in India have matching counterparts in Africa, South America, Antarctica, Australia, Madagascar, and the Falkland Islands.

Short Notes : Continental Drift Theory

• Proposed by Alfred Wegener in 1912.

• Continents were once part of Pangaea.

• Matching rock formations across continents support continental drift.

• Similar mineral deposits indicate former land connections.

• Gondwana sediments occur across several Southern Hemisphere continents.

• Geological evidence is one of the strongest proofs of continental drift.

Detailed Explanation:

Answer: Option 1 — Both Statement-II and Statement-III are correct and both of them explain Statement-I

Rainfall is a significant agent of weathering, particularly chemical weathering. Rainwater absorbs carbon dioxide from the atmosphere forming weak carbonic acid, and also dissolves atmospheric oxygen. Both these dissolved gases actively participate in breaking down rock minerals through chemical reactions.

✅ Statement I – Correct: Rainfall causes both physical and chemical weathering of rocks through impact and chemical reactions.
✅ Statement II – Correct: Rainwater dissolves atmospheric CO₂, forming carbonic acid (H₂CO₃) which chemically weathers rocks.
✅ Statement III – Correct: Rainwater contains dissolved atmospheric oxygen which causes oxidation of minerals, a form of chemical weathering.

📝 Short Notes: Chemical Weathering by Rainwater

• Carbonation: CO₂ in rainwater forms carbonic acid (H₂CO₃), which reacts with carbonate rocks (limestone, marble) and feldspars, dissolving them over time.
• Oxidation: Dissolved oxygen in rainwater reacts with iron-bearing minerals (like olivine, pyroxene) causing rust-like decomposition, weakening rock structure.
• Hydrolysis: Water molecules react with silicate minerals (feldspars, micas) to form clay minerals, contributing to rock breakdown.
• Solution: Rainwater can directly dissolve soluble minerals like halite and gypsum without additional chemical reactions.
• pH Factor: Natural rainwater has a pH of approximately 5.6 due to dissolved CO₂; acid rain (pH < 5.0) accelerates weathering rates significantly.
• Rate Factors: Weathering rate depends on rainfall intensity, temperature, rock composition, and vegetation cover which can either enhance or reduce weathering.
• Physical Impact: Besides chemical action, heavy rainfall causes mechanical weathering through raindrop impact and frost wedging in cold climates.

Detailed Explanation:

Answer: Option 4 — All four

All four items listed—pyroclastic debris, ash and dust, nitrogen compounds, and sulphur compounds—are products of volcanic eruptions. Volcanic eruptions release both solid materials (pyroclastic debris, ash) and various gases (nitrogen and sulphur compounds) that can have significant environmental impacts.

✅ Statement 1 – Correct: Pyroclastic debris includes fragmental materials like ash, pumice, cinders, and volcanic bombs ejected during eruptions.
✅ Statement 2 – Correct: Ash and dust are fine-grained particles of volcanic rock and glass produced during explosive volcanic activity.
✅ Statement 3 – Correct: Nitrogen compounds such as ammonia (NH₃) and nitrogen oxides (NOₓ) are released from volcanic gases.
✅ Statement 4 – Correct: Sulphur compounds, particularly sulphur dioxide (SO₂) and hydrogen sulphide (H₂S), are major volcanic gases.

📝 Short Notes: Products of Volcanic Eruptions

• Environmental Impact: Volcanic ash can disrupt air travel, damage crops, and contaminate water supplies; sulphur dioxide contributes to acid rain and can affect global climate by forming aerosols in the stratosphere.
• Tephra: General term for all pyroclastic material ejected during an eruption, regardless of size or composition.
• Volcanic Winter: Large eruptions releasing significant ash and SO₂ can block sunlight, temporarily cooling the Earth's surface.
• Health Hazards: Fine volcanic ash can cause respiratory problems; gases like SO₂ and H₂S are toxic in high concentrations.

Detailed Explanation:

Answer: Option 3 — Both 1 and 2

Both statements are correct regarding seismic waves. P waves (Primary waves) travel faster than S waves (Secondary waves) and are therefore recorded first by seismographs. The two wave types also differ fundamentally in their particle motion characteristics.

✅ Statement 1 – Correct: P waves are indeed recorded earlier than S waves on a seismograph because they are the fastest seismic waves, traveling at speeds of 5-8 km/s in the Earth's crust compared to S waves which travel at 3-4.5 km/s.

✅ Statement 2 – Correct: P waves are compressional/longitudinal waves where particles vibrate parallel to the direction of wave propagation (to and fro motion), while S waves are shear/transverse waves where particles vibrate perpendicular to the direction of wave propagation (up and down or side to side motion).

📝 Short Notes: Seismic Waves

Detailed Explanation:

Answer: Option 3 — Phosphorus Cycle

The Phosphorus Cycle is unique among biogeochemical cycles as it lacks a gaseous phase and primarily relies on the weathering of phosphate-rich rocks as its main source. Geological weathering processes break down these rocks over time, releasing phosphate ions (PO₄³⁻) into the soil and water, which are then absorbed by plants and move through the food chain.

Why other options are incorrect:
• Carbon Cycle: Primarily driven by atmospheric CO₂ from respiration, combustion, and volcanic activity, not rock weathering.
• Nitrogen Cycle: Relies on atmospheric nitrogen with fixation by bacteria as the key process, not weathering of rocks.
• Sulphur Cycle: Main sources include volcanic eruptions, decaying organic matter, and fossil fuel combustion, not primarily rock weathering.

📝 Short Notes: Biogeochemical Cycles

Detailed Explanation:

Answer: Option 4 — 2, 3 and 4 only

In India, major minerals are those specified in the First Schedule of the Mines and Minerals (Development and Regulation) Act, 1957. Bentonite is classified as a minor mineral, while Chromite, Kyanite, and Sillimanite are all major minerals.

1. Bentonite – Minor Mineral: Bentonite is a clay mineral used in drilling mud, foundry sand, and civil engineering applications. It is listed under minor minerals.

2. Chromite – Major Mineral ✅: Chromite is the only ore of chromium and is essential for manufacturing stainless steel and various alloys. It is a major mineral.

3. Kyanite – Major Mineral ✅: Kyanite is a refractory mineral used in ceramics and high-temperature industrial applications. It is classified as a major mineral.

4. Sillimanite – Major Mineral ✅: Sillimanite is another refractory mineral with applications in metallurgy and industrial furnaces. It is a major mineral.

📝 Short Notes: Major vs Minor Minerals in India

• Refractory Minerals: Kyanite and Sillimanite are aluminum silicate minerals with high heat resistance, crucial for refractory (heat-resistant) materials.
• Chromite in India: India has significant chromite reserves, mainly in Odisha (about 98% of national reserves).
• MMDR Amendment 2015: Provided greater transparency in mineral allocation through auction mechanism for major minerals.

Detailed Explanation:

✅ Statement 1 – Correct: Continental drift separated landmasses over millions of years, creating geographic barriers that isolated populations and led to allopatric speciation (e.g., unique species in Madagascar and Australia).

✅ Statement 2 – Correct: Glacial cycles caused repeated expansion and contraction of ice sheets, altered sea levels and habitats, and drove evolutionary adaptations, migrations, and extinctions (e.g., Ice Age megafauna evolution).

Detailed Explanation:

Electromagnetic radiation (solar energy) drives weather systems, ocean currents, and photosynthesis, creating dynamic surface changes.

Geothermal energy from Earth's interior fuels volcanism, hot springs, and geysers, altering landforms.

Gravitational force (Moon and Sun) generates ocean tides, causing coastal erosion and deposition.

Plate movements cause mountain building, earthquakes, volcanism, and continental drift, reshaping the Earth's surface.

Rotation of Earth creates Coriolis effect, influencing wind patterns, ocean currents, and cyclone formation.

Revolution of Earth around the Sun causes seasonal variations, affecting temperature, precipitation, and weathering rates.

All six forces work together to bring continuous dynamic changes to Earth's surface.