UPSC CSE Prelims
Earthquakes and Volcanoes Previous Year Questions (PYQs)
Practice solved questions for Earthquakes and Volcanoes with detailed step-by-step solutions, key insights, and trend analysis for UPSC CSE PRELIMS.
Solved Previous Year Questions
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Tungurahua Volcano, which was declared a Global Geopark by UNESCO in 2025, is situated in which one among the following countries ?
Detailed Explanation:
What is Tungurahua?
| Feature | Detail |
|---|---|
| Meaning | "Throat of Fire" (Quichua language) |
| Type | Highly active Stratovolcano |
| Location | Cordillera Oriental, Central Andes, Ecuador |
| UNESCO Status | Global Geopark — April 2025 |
| Area | 2,300+ sq km across Tungurahua & Chimborazo provinces |
| Geological History | 417 million years preserved |
| National Park | Within Sangay National Park |
| Nearby Town | Baños de Agua Santa |
❌ Why Other Options Are Wrong
| Country | Their Notable Volcano | Why Wrong |
|---|---|---|
| Peru | Ubinas | Shares Andes but Tungurahua is NOT here |
| Bolivia | — | No connection to Tungurahua |
| Colombia | Nevado del Ruiz | Also Andean but different country |
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.
Consider the following:
- Pyroclastic debris
- Ash and dust
- Nitrogen compounds
- Sulphur compounds
How many of the above are products of volcanic eruptions?
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
| Product Type | Examples | Characteristics |
|---|---|---|
| Pyroclastic Materials | Volcanic bombs, lapilli, ash, pumice, scoria | Solid fragments ejected during eruptions; size ranges from fine ash to large bombs |
| Volcanic Gases | Water vapor (H₂O), CO₂, SO₂, H₂S, HCl, HF | Water vapor constitutes 60-90% of volcanic gases; SO₂ contributes to acid rain |
| Nitrogen Compounds | N₂, NH₃, nitrogen oxides (NOₓ) | Released in smaller quantities; can react in atmosphere to form various compounds |
| Sulphur Compounds | SO₂, H₂S, elemental sulphur | SO₂ is a major volcanic gas causing respiratory issues and environmental impacts |
- 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.
Consider the following statements:
- In a seismograph, P waves are recorded earlier than S waves.
- In P waves, the individual particles vibrate to and fro in the direction of wave propagation whereas in S waves, the particles vibrate up and down at right angles to the direction of wave propagation.
Which of the statements given above is/are correct?
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
| Feature | P Waves (Primary) | S Waves (Secondary) |
|---|---|---|
| Speed | Fastest (5-8 km/s in crust) | Slower (3-4.5 km/s in crust) |
| Arrival Time | First to arrive | Second to arrive |
| Wave Type | Longitudinal/Compressional | Transverse/Shear |
| Particle Motion | Parallel to wave direction (push-pull) | Perpendicular to wave direction (up-down/side-side) |
| Medium | Travel through solids, liquids, and gases | Travel only through solids |
| Destructive Power | Less destructive | More destructive |
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