Q8
(a) Explain the concept of drainage basin morphometry. How do morphometric parameters influence the groundwater conditions of an area? (20 marks) (b) Discuss various modes of preservation of fossils. (15 marks) (c) Discuss the evolution of the Himalayas. Illustrate your answer with suitable labelled sketches. (15 marks)
हिंदी में प्रश्न पढ़ें
(a) अपवाह क्षेत्री आकृतिकी (मॉर्फोमीट्री) की अवधारणा की व्याख्या कीजिए। बताइए कि कैसे आकृतिकीय पैरामीटर किसी क्षेत्र की भूजल परिस्थिति को प्रभावित करते हैं। (20 अंक) (b) जीवाश्मों के संरक्षण की विभिन्न क्रियाविधियों पर प्रकाश डालिए। (15 अंक) (c) हिमालय के उद्भव का वर्णन कीजिए। उपयुक्त नामांकित चित्र सहित अपना उत्तर स्पष्ट कीजिए। (15 अंक)
Directive word: Explain
This question asks you to explain. 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 'explain' for part (a) demands conceptual clarity with cause-effect linkages, while 'discuss' in parts (b) and (c) requires balanced coverage with critical elaboration. Allocate approximately 40% of time/words to part (a) given its 20 marks, with ~30% each to parts (b) and (c). Structure with a brief integrated introduction, three distinct sections for each sub-part, and a concluding synthesis on geological processes and their applied significance.
Key points expected
- Part (a): Define drainage basin morphometry (linear, areal, relief parameters); explain Horton's laws and their hydrogeological significance; link bifurcation ratio, drainage density, and form factor to groundwater recharge potential and aquifer vulnerability
- Part (a): Correlate low drainage density with permeable lithologies favouring groundwater infiltration versus high density indicating surface runoff dominance; cite Indian examples like the Deccan Traps or Indo-Gangetic plains
- Part (b): Discuss unaltered preservation (original hard parts, mummification), permineralization and petrification, replacement and recrystallization, carbonization, and trace fossils; explain taphonomic controls and Lagerstätten significance
- Part (b): Distinguish between body fossils and ichnofossils; mention exceptional preservation sites like the Siwalik fossils or Vindhyan stromatolites
- Part (c): Trace the sequential evolution from Tethys geosyncline through collision phases (Trans-Himalayan, Greater, Lesser Himalayas); explain the duplex thrust model and inverted metamorphism
- Part (c): Illustrate with labelled cross-sections showing Main Central Thrust, Main Boundary Thrust, and Main Frontal Thrust; reference Argand's indenter-tectonic wedge model and critical taper mechanics
Evaluation rubric
| Dimension | Weight | Max marks | Excellent | Average | Poor |
|---|---|---|---|---|---|
| Concept correctness | 25% | 12.5 | Precisely defines morphometric parameters (Rb, Dd, Re, Rf, Cc) with correct formulae; accurately distinguishes permineralization from replacement; correctly sequences Himalayan orogeny from Eocene collision through Miocene uplift with proper terminology (MCT, MBT, STD) | Defines morphometry vaguely without formulae; conflates preservation modes; describes Himalayan evolution chronologically but without thrust mechanics or metamorphic gradients | Confuses morphometric parameters with drainage patterns; misidentifies preservation processes; presents incorrect collision timeline or omits major tectonic elements |
| Diagram / cross-section | 20% | 10 | Provides three distinct, accurately labelled diagrams: drainage basin morphometric parameters (Horton's laws), fossil preservation modes (comparative illustration), and detailed Himalayan cross-section showing duplex structure with thrust faults, metamorphic isograds, and lithotectonic units | Sketches basic drainage network and simple Himalayan section without isograds or duplex geometry; diagrams lack essential labels or scale | Omits diagrams for parts (b) and (c); provides only unlabelled schematic sketches; diagrams contradict textual explanation |
| Field evidence | 15% | 7.5 | Cites specific morphometric studies (Narmada, Kaveri basins); references Indian fossil Lagerstätten (Jaisalmer, Spiti, Siwaliks); integrates Himalayan field evidence from Zanskar, Sikkim or Garhwal transects with structural data | Mentions generic field examples without specificity; references 'Himalayan fossils' or 'Indian rivers' without named locations or studies | No field evidence cited; relies entirely on theoretical description; invents non-existent fossil sites or mislocates geological features |
| Quantitative reasoning | 20% | 10 | Applies Horton's laws quantitatively (bifurcation ratio 3-5, length-order relations); calculates drainage density and form factor implications for groundwater; uses metamorphic P-T data and convergence rates (cm/year) for Himalayan evolution | States morphometric formulae without calculation; mentions quantitative concepts qualitatively; provides approximate Himalayan uplift rates without context | No quantitative treatment; omits all numerical relationships; confuses dimensionless ratios with absolute measurements |
| Indian / economic relevance | 20% | 10 | Links morphometry to groundwater management in water-stressed regions (Rajasthan, Deccan); connects fossil preservation to hydrocarbon exploration (Cambay, Krishna-Godavari basins) and Himalayan evolution to seismic hazard assessment, GLOF risks, and infrastructure planning | Brief mention of Indian groundwater scarcity or Himalayan earthquakes without integrated analysis; generic economic significance stated | No Indian examples; ignores applied dimensions; fails to connect geological concepts to resource management or hazard mitigation |
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