Geology 2021 Paper I 50 marks Discuss

Q2

(a) What are lithospheric plates? Discuss the theory of plate tectonics. Which plates were involved when a major earthquake caused tsunami in Indian Ocean in 2004? (20 marks) (b) Discuss the geomorphic processes. Cite any four aggradational and four degradational land forms associated with fluvial processes. (15 marks) (c) What does attitude of a bed mean? Define strike, dip direction and dip amount of a bed and explain how these are represented on a map for vertical, horizontal and inclined strata. (15 marks)

हिंदी में प्रश्न पढ़ें

(a) स्थलमंडलीय प्लेटें क्या हैं ? प्लेट विवर्तनिक के सिद्धांत पर चर्चा कीजिए । हिंदमहासागर में 2004 के महाभूकंप के कारण आई भूकंपीसिंधु तरंग (सुनामी) में कौन सी स्थलमंडलीय प्लेटें शामिल थीं ? (20 अंक) (b) भूआकृतिक प्रक्रियाओं पर चर्चा कीजिए । जलीय प्रक्रियाओं से संबंधित कोई चार तलोच्चन और चार तलावचन स्थलरूपों को उद्धृत करें । (15 अंक) (c) एक संस्तर की अभिवृत्ति का क्या अर्थ है ? एक संस्तर की नतिलंब, नतिदिशा और नतिसंख्या (डिप अमाउंट) को परिभाषित कीजिए और स्पष्ट कीजिए कैसे इनके ऊर्ध्वाधर क्षैतिज एवं आनत स्तरों को मानचित्र पर दर्शाया जाता है ? (15 अंक)

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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 logical flow. Allocate approximately 40% of effort to part (a) given its 20 marks weightage—cover lithospheric plate definition, comprehensive plate tectonics theory, and specific 2004 tsunami plate boundaries; devote ~30% each to parts (b) and (c). Structure with a brief integrated introduction, then tackle each sub-part sequentially with clear sub-headings, ensuring diagrams for (a) and (c), and conclude with synthesis on geological dynamism.

Key points expected

  • Part (a): Definition of lithospheric plates (crust + upper mantle, 50-150 km thick, rigid); comprehensive plate tectonics theory including seafloor spreading, continental drift, subduction zones, mantle convection; identification of Indian Plate, Burma Microplate, and Indo-Australian Plate involvement in 2004 Sumatra-Andaman earthquake (Mw 9.1-9.3) with thrust fault mechanism at Sunda Trench
  • Part (b): Classification of geomorphic processes (endogenic—tectonic, volcanic, diastrophic; exogenic—weathering, erosion, transportation, deposition); four aggradational fluvial landforms (alluvial fans, point bars, natural levees, deltas—preferably Indian examples like Ganga-Brahmaputra delta); four degradational fluvial landforms (river valleys—V-shaped, gorges, canyons, waterfalls—e.g., Jog Falls, Grand Canyon)
  • Part (c): Definition of attitude (orientation of bedding plane in 3D space); precise definitions of strike (line of intersection with horizontal plane, compass direction), dip direction (perpendicular to strike, downslope), dip amount (angle from horizontal); map representation symbols for horizontal (H with tick marks), vertical (V or straight line with arrows), inclined (strike line with dip angle and direction arrow)
  • Integration of Wilson cycle or triple junction concepts for plate tectonics depth; mention of Himalayan orogeny as ongoing Indian Plate collision
  • Specific Indian examples: Chambal badlands for degradational, Kosi fan for aggradational; geological map symbols as per GSI conventions

Evaluation rubric

DimensionWeightMax marksExcellentAveragePoor
Concept correctness25%12.5Precise definitions across all parts: for (a) correctly identifies asthenosphere as decoupling layer, distinguishes divergent/convergent/transform boundaries, and accurately names Burma Microplate with thrust mechanism; for (b) correctly classifies endogenic vs exogenic processes and distinguishes aggradation from degradation; for (c) mathematically correct strike-dip relationships with proper angular conventionsGenerally correct definitions with minor errors—e.g., confuses crust with lithosphere in (a), mixes some landform processes in (b), or shows strike-dip perpendicularity errors in (c); lacks precision in 2004 tsunami plate identificationFundamental conceptual errors—e.g., describes plates as crust-only, confuses weathering with erosion throughout, or completely misrepresents strike-dip geometry; fails to identify correct plates for 2004 event
Diagram / cross-section20%10High-quality, labeled diagrams for (a) showing plate boundaries with 2004 tsunami focal mechanism (beach ball diagram), cross-section of Sunda subduction; for (c) clear block diagrams showing strike-dip measurement, and map symbols for all three attitudes with proper GSI conventions; neat, scaled, with essential annotationsBasic diagrams present but incomplete—e.g., plate boundary sketch without subduction zone detail, or attitude diagrams missing one of the three cases; labels present but sparse or occasionally incorrectMissing critical diagrams (especially for part c), or sketches too rough to interpret; no attempt at 2004 tsunami mechanism illustration; map symbols incorrectly drawn or confused
Field evidence15%7.5Cites specific field evidence: for (a) paleomagnetic stripes, GPS data showing Indian Plate movement (~50 mm/yr NE), seismic gap analysis; for (b) field indicators of aggradation (sedimentary structures, terrace sequences) and degradation (incised meanders, knickpoints); for (c) compass-clinometer measurement technique in fieldMentions general field evidence types without specificity—e.g., 'seismic activity' without GPS data, or 'river deposits' without sedimentary structures; limited quantitative field supportNo field evidence cited; purely theoretical treatment; confuses laboratory with field observations
Quantitative reasoning20%10Precise quantitative elements: for (a) 2004 earthquake magnitude (Mw 9.1-9.3), rupture length (~1300 km), slip amount (~20 m), depth (~30 km), Indian Plate velocity (~50 mm/yr); for (c) correct dip angle calculations, strike notation (e.g., N45°E/45°SE), understanding of apparent vs true dip; for (b) gradient calculations or discharge-sediment relationshipsSome quantitative data present but imprecise—e.g., 'magnitude 9' without specification, approximate dip angles without notation system, or general slope mentions without valuesNo quantitative treatment; avoids all numerical aspects; incorrect magnitude or completely wrong angular relationships
Indian / economic relevance20%10Strong Indian contextualization: for (a) Himalayan seismic hazard, Andaman-Nicobar tectonics, Indian Ocean Tsunami Warning System (IOTWS) post-2004; for (b) specific Indian landforms (Ganga delta, Western Ghats escarpments, Chambal ravines) with economic implications—agriculture, dam sedimentation, navigation; for (c) GSI mapping conventions, hydrocarbon exploration relevance in KG BasinSome Indian examples mentioned but superficial—e.g., 'Himalayas' without specific reference, generic 'river deltas' without naming Ganga-Brahmaputra; limited economic connectionNo Indian examples; relies entirely on foreign case studies (San Andreas, Grand Canyon only); misses economic significance entirely

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