UPSC Prelims 2018
Indian Geography Previous Year Questions (PYQs)

Detailed Explanation:

The correct answer is 1, 2, 3 and 4 (Option 4). Birds, dust, rain, and wind all help spread plant diseases by carrying fungi, bacteria, viruses, or other pathogens from infected plants to healthy ones.

📗 Concept 

Plant disease transmission occurs through different agents called vectors or dispersal agents. Wind and rain spread fungal spores and bacteria, while birds and other animals carry pathogens through their feathers, feet, or droppings.

Detailed Explanation:

Answer: Option 4 — 1 only

Only Statement 1 is correct. Barren Island is indeed India's only active volcano, located in the Andaman Sea within Indian territory. Statement 2 is incorrect because Barren Island lies approximately 135-140 km east of Port Blair, not Great Nicobar, which is much further south. Statement 3 is also incorrect as the volcano has erupted multiple times after 1991, including in 1994-95, 2005-07, and most recently in 2017, proving it has not remained inactive.

✅ Statement 1 – Correct: Barren Island is the only confirmed active volcano in India, located in the Andaman Sea, part of the Union Territory of Andaman and Nicobar Islands.
❌ Statement 2 – Incorrect: Barren Island is located approximately 135-140 km east of Port Blair, not Great Nicobar; Great Nicobar is the southernmost island located much further south (around 7°N) while Barren Island is at approximately 12.2°N.
❌ Statement 3 – Incorrect: The volcano has not remained inactive since 1991; it has erupted several times including in 1994-95, 2005-07, and as recently as 2017.

📝 Short Notes: Barren Island Volcano

• Location: Barren Island is located in the Andaman Sea, approximately 135-140 km east of Port Blair in the Andaman and Nicobar Islands.
• Only Active Volcano: It is the only confirmed active volcano in South Asia and India.
• Part of Volcanic Arc: Barren Island is part of the volcanic arc chain extending from Sumatra to Myanmar, formed due to the subduction of the Indian Plate beneath the Burmese Plate.
• Eruption History: After lying dormant for nearly 150 years, it erupted in 1991, and has since shown activity in 1994-95, 2005-07, and 2017.
• Uninhabited: The island is uninhabited due to volcanic activity and is restricted for tourism, though diving expeditions are sometimes permitted.
• Geographical Coordinates: Approximately 12.2°N latitude and 93.9°E longitude.

Detailed Explanation:

Answer: Option 1 — Kodaikanal Tamil Nadu

Kodaikanal Lake, also known as Kodai Lake, is a man-made lake located in Kodaikanal city in Dindigul district, Tamil Nadu. It was created in 1863 by Sir Vere Henry Levinge, the then Collector of Madurai, and is a popular tourist attraction. The other three lakes mentioned—Kolleru (Andhra Pradesh), Nainital (Uttarakhand), and Renuka (Himachal Pradesh)—are all natural lakes.

📝 Short Notes: Important Artificial and Natural Lakes of India

Detailed Explanation:

Answer: Option 2 — 3 only

Among the three statements about agricultural soils, only statement 3 is correct. Statement 1 incorrectly claims that organic matter reduces water-holding capacity, when it actually increases it. Statement 2 incorrectly suggests soil plays no role in the sulphur cycle, when in fact soil is crucial for sulphur transformations and storage.

❌ Statement 1 – Incorrect: High organic matter content actually increases water-holding capacity of soil, not reduces it. Organic matter acts like a sponge, creating pore spaces that retain moisture effectively.

❌ Statement 2 – Incorrect: Soil plays a vital role in the sulphur cycle through microbial transformations (mineralization, immobilization) and storage of sulphur compounds like sulfates that are essential plant nutrients.

✅ Statement 3 – Correct: Prolonged irrigation, especially with poor drainage and high-salt water, causes accumulation of salts in the soil profile, leading to salinization that adversely affects crop productivity.

📝 Short Notes: Soil Properties and Agricultural Impacts

• Organic Matter Benefits: Increases water retention, improves soil structure, enhances nutrient availability, promotes microbial activity, and increases cation exchange capacity (CEC).
• Soil in Nutrient Cycles: Soil is integral to carbon, nitrogen, phosphorus, and sulphur cycles through microbial decomposition, mineralization, and nutrient transformation processes.
• Salinization Process: Occurs when irrigation water brings dissolved salts that accumulate in root zones due to evaporation and inadequate drainage, particularly in arid and semi-arid regions.
• Prevention of Salinization: Proper drainage systems, use of quality irrigation water, crop rotation with salt-tolerant species, and leaching of accumulated salts.
• Indicators of Salinization: White salt crusts on soil surface, reduced crop growth, increased soil pH, and presence of salt-tolerant weeds.