Q8
(a) Discuss the causes of various seismic discontinuities in the upper mantle. (20 marks) (b) Discuss the composition, source, types, environmental hazard and utility of fly ash. (15 marks) (c) Discuss the hazards in active volcanic terrain during and after eruption. (15 marks)
हिंदी में प्रश्न पढ़ें
(a) ऊपरी प्रावार (मेंटल) में विभिन्न भूकंपीय विच्छिन्नताओं (डिस्कन्टिन्यूटीज) के कारणों पर चर्चा कीजिए। (20 अंक) (b) उड़न राख (फ्लाई ऐश) के संयोजन, स्रोत, प्रकार, पर्यावरणीय दुष्परिणाम और उपयोग पर चर्चा कीजिए। (15 अंक) (c) सक्रिय ज्वालामुखी क्षेत्र में ज्वालामुखी विस्फोट के दौरान तथा उसके पश्चात् होने वाले खतरों पर चर्चा कीजिए। (15 अंक)
Directive word: Discuss
This question asks you to discuss. The directive word signals the depth of analysis expected, the structure of your answer, and the weight of evidence you must bring.
See our UPSC directive words guide for a full breakdown of how to respond to each command word.
How this answer will be evaluated
Approach
The directive 'discuss' demands a comprehensive, analytical treatment with balanced coverage across all three parts. Allocate approximately 40% of time/words to part (a) given its 20 marks, and 30% each to parts (b) and (c). Structure with a brief introduction, then three clearly demarcated sections addressing each sub-part with depth proportional to marks, and conclude with integrated insights on geohazard management. For (a), explain the 410 km and 660 km discontinuities with phase transitions; for (b), cover fly ash characteristics systematically; for (c), distinguish immediate versus long-term volcanic hazards.
Key points expected
- For (a): Explanation of the 410 km discontinuity (olivine to wadsleyite/ringwoodite transition) and 660 km discontinuity (ringwoodite to bridgmanite and periclase transition) as major upper mantle phase changes, plus minor discontinuities like the Lehmann and Gutenberg discontinuities
- For (a): Discussion of compositional layering (lithosphere-asthenosphere boundary, low velocity zone) and their seismic expression, with temperature-pressure conditions driving these transitions
- For (b): Chemical composition of fly ash (SiO₂, Al₂O₃, Fe₂O₃, CaO) from coal combustion, distinction between Class F and Class C types based on calcium content, and source from thermal power plants
- For (b): Environmental hazards including groundwater contamination, heavy metal leaching, air pollution, and land degradation; utility in cement manufacturing, mine filling, road construction, and agriculture
- For (c): Hazards during eruption: pyroclastic flows, lahars, lava flows, volcanic gases, tephra fall; hazards after eruption: secondary lahars, volcanic winter effects, acid rain, long-term landscape instability
- For (c): Distinction between effusive and explosive eruption styles and their differential hazard profiles, with reference to monitoring and mitigation strategies
Evaluation rubric
| Dimension | Weight | Max marks | Excellent | Average | Poor |
|---|---|---|---|---|---|
| Concept correctness | 25% | 12.5 | Demonstrates precise understanding of phase transition mineralogy at 410 km and 660 km depths (olivine-wadsleyite-ringwoodite-perovskite transformations), correctly identifies fly ash classification chemistry (ASTM C618), and accurately distinguishes primary from secondary volcanic hazards with correct terminology throughout | Identifies major discontinuities and fly ash components correctly but confuses phase transition mechanisms or misclassifies fly ash types; lists volcanic hazards without clear during/after distinction or uses imprecise terminology | Fundamental errors such as confusing crust-mantle boundary with upper mantle discontinuities, misidentifying fly ash source or composition, or conflating volcanic hazards with earthquake hazards |
| Diagram / cross-section | 20% | 10 | Includes a labeled cross-section of the upper mantle showing depth-marked discontinuities with P-wave velocity changes, a process diagram of fly ash generation and utilization pathways, and a volcanic hazard zonation diagram; all diagrams are neat, properly labeled, and directly support the narrative | Provides at least two relevant diagrams with basic labeling (e.g., mantle cross-section and simple fly ash schematic) but lacks detail on velocity profiles or hazard zonation; diagrams support but do not enhance the answer | Missing diagrams for the 20-mark seismic discontinuity section, or diagrams are unlabeled sketches that do not demonstrate understanding of depth-velocity relationships or material flows |
| Field evidence | 15% | 7.5 | Cites seismic tomography studies (e.g., from Indian seismological networks), references specific Indian thermal power plants and their ash pond failures (e.g., 2019 Singrauli dyke breach), and names documented volcanic hazard case studies (e.g., 1991 Pinatubo lahars, Vesuvius AD 79) with observed impacts | Mentions generic field observations without specific citations, or provides Indian examples for only one part (e.g., fly ash from NTPC plants but no seismic or volcanic case studies) | No field evidence cited; relies entirely on textbook descriptions without reference to actual seismic networks, industrial accidents, or historical eruptions |
| Quantitative reasoning | 20% | 10 | Provides depth values for discontinuities (410±2 km, 660±10 km), velocity jumps (~5% at 410 km, ~10% at 660 km), fly ash generation statistics (India produces ~200 million tonnes annually), and quantitative hazard metrics (VEI, pyroclastic flow velocities 80-700 km/h, lahar volumes) | States approximate depths for major discontinuities and rough fly ash quantities but lacks precision on velocity changes or volcanic explosivity indices; numbers mentioned but not integrated into analysis | No quantitative data provided; answer is purely qualitative despite the question lending itself to numerical treatment of depths, compositions, and hazard intensities |
| Indian / economic relevance | 20% | 10 | For (a): References Indian seismological contributions (NORSAR-India collaboration, Himalaya-Tibet velocity models); for (b): Detailed treatment of Indian coal sector fly ash utilization mandates (100% utilization target), NTPC and DVC experiences, and economic value in cement industry; for (c): Discusses volcanic hazard preparedness in Andaman-Nicobar and potential Barren Island implications, with cost-benefit framing of mitigation | Mentions Indian thermal power plants for fly ash but treats seismic discontinuities and volcanic hazards generically without Indian context; or provides superficial Indian references without economic analysis | Completely ignores Indian relevance despite abundant opportunities in all three parts; answer could apply to any country with no modification |
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