2.1: Himalayan Orogeny & Deccan Volcanism
Indian Geography → Indian Geography → PHYSICAL FOUNDATIONS → PHYSICAL FOUNDATIONS → Geological Structure | Author: admin | Feb 11, 2026
TYPE 1: DETAILED NOTES
1. Introduction & Significance Unit 2.1 (Himalayan Orogeny & Deccan Volcanism) is core to UPSC Prelims (MCQs on formation, age, plate tectonics) and Mains (analytical on earthquakes, biodiversity, climate impact). SSC/RRB/State PSC ask factuals (young vs old mountains, basalt flows). High weightage in 2026 due to Himalayan disasters (landslides, floods) and Deccan resources (soil, minerals). Links to current (e.g., NDMA hazard mapping, GFRA 2025 forest rankings in Himalayan biosphere). This is a 10–15 mark area in Mains — master linkages for geomorphology answers.
2. Chronological/Geological Timeline
- ~200 million years ago: Pangea breakup; Indian plate drifts from Gondwana.
- ~180–140 million years ago: Tethys Sea forms between India and Eurasia.
- ~65–55 million years ago: Deccan volcanism peaks (Reunion hotspot; massive basalt flows).
- ~50–40 million years ago: Indian-Eurasian plate collision starts Himalayan orogeny.
- ~35–10 million years ago: Multiple phases of Himalayan uplift (folding, thrusting).
- Present–2026: Himalayas still rising (~5 mm/year); Deccan stable plateau; recent studies (e.g., tomographic images 2024–2025) show subduction cessation.
3. Concept Deep Dive Himalayan Orogeny: Step 1 – Indian plate drifts north (~15 cm/year initially). Step 2 – Collides with Eurasian plate, closing Tethys Sea. Step 3 – Compression forms fold mountains (young, unstable, seismic). Deccan Volcanism: Step 1 – Reunion hotspot under India. Step 2 – Massive lava eruptions (~65 Ma, end-Cretaceous). Step 3 – Forms basalt layers (traps) over ~500,000 sq km plateau. Both from plate tectonics; Himalayas convergent, Deccan hotspot. (Ref: Savindra Singh Ch. 4 "Plate Tectonics & Mountain Building"; Goh Cheng Leong Ch. on Volcanism & Earth Movements; NCERT Class 11 Fundamentals of Physical Geography Ch. 6 "Geomorphic Processes"; Majid Husain Ch. 2 for Indian context).
4. Key Terminology Box
- Orogeny: Mountain-building process (e.g., Himalayan fold orogeny).
- Plate Tectonics: Theory of crustal plates moving (Indian-Eurasian collision).
- Tethys Sea: Ancient ocean closed by plate convergence.
- Volcanism: Magma eruption (Deccan flood basalts).
- Deccan Traps: Layered basalt flows from volcanic eruptions.
- Hotspot: Volcanic plume under plate (Reunion for Deccan).
- Fold Mountains: Compressed, uplifted ranges (young Himalayas).
- Subduction: Plate sinking under another (Indian under Eurasian).
5. Important Factual Details
| Feature | Himalayan Orogeny | Deccan Volcanism |
|---|---|---|
| Age | ~50–10 Ma (ongoing) | ~65 Ma (Cretaceous-Paleogene) |
| Cause | Indian-Eurasian convergence | Reunion hotspot |
| Area/Height | ~2,500 km long; ~8,848 m (Everest) | ~500,000 sq km; ~1,500 m elevation |
| Rock Type | Sedimentary/metamorphic folds | Basalt layers (traps) |
| Phases | Three (Alpine orogeny) | Flood basalt eruptions |
| Current Impact | Earthquakes, rising ~5 mm/year | Black cotton soil, stable plateau |
6. Frequently Asked Exam Facts
- Himalayan orogeny: Indian plate collides with Eurasian ~50 Ma.
- Deccan volcanism: ~65 Ma, Reunion hotspot, basalt traps.
- Himalayas: Young fold mountains, still rising.
- Deccan: Volcanic plateau, ~500,000 sq km.
- Tethys Sea: Closed during Himalayan formation.
- Deccan Traps: Layered basalt from flood eruptions.
- Himalayas: Convergent boundary product.
- Deccan: Intraplate volcanism.
- Everest: Highest due to orogeny.
- Black soil: From Deccan basalt weathering.
7. Comparison Charts/Tables
| Aspect | Himalayan Orogeny | Deccan Volcanism |
|---|---|---|
| Type | Tectonic convergence (fold mountains) | Hotspot volcanism (plateau) |
| Location | Northern India (arc shape) | Peninsular south-central |
| Age/Process | Young, ongoing uplift | Ancient, extinct eruptions |
| Features | High peaks, seismic zones | Flat basalt layers, fertile soil |
| Impact | Glaciers, rivers origin | Minerals, agriculture (cotton) |
8. Spatial Context
- Himalayas: Northern arc from J&K (west) to Arunachal (east); sites like Everest (Nepal/India border), Siachen Glacier.
- Deccan: Central-south peninsula (Maharashtra, MP, Karnataka, TN, AP); sites like Western Ghats edges, Mahabaleshwar plateau.
- Salem/TN relevance: Salem in Deccan Plateau; basalt rocks influence local soil/agriculture (cotton, minerals); Eastern Ghats nearby.
Image credit: EurekAlert via search, showing tomographic diagram of Himalayan orogeny stages with plate subduction. Image credit: Wikipedia via search, showing Deccan Traps map with basalt flow extent in India.
9. Flowchart Summary Pangea Breakup (~200 Ma) ? Indian Plate Drift ? Tethys Closure + Collision (~50 Ma) ? Himalayan Orogeny (folds, uplift) ? Ongoing Earthquakes. Parallel: Reunion Hotspot (~65 Ma) ? Deccan Volcanism (basalt floods) ? Plateau Formation ? Stable Landscape. Image credit: Wikipedia via search, showing diagram of Indian plate collision with Eurasia for Himalayan formation.
10. Ultra-Short Exam Capsule
- Himalayan orogeny: ~50 Ma, Indian-Eurasian collision.
- Deccan volcanism: ~65 Ma, Reunion hotspot.
- Himalayas: Young folds, rising.
- Deccan: Basalt traps, plateau.
- Tethys: Closed sea.
- Black soil: Deccan weathering.
- Everest: Orogeny product.
TYPE 2: QUICK REVISION & EXAM TRICKS
1. Highlights & Tricky Points
- Key: Himalayas convergent orogeny; Deccan hotspot volcanism.
- Trap: "Age of Himalayas" — young (50 Ma), not ancient.
- Trap: "Deccan cause" — hotspot, not orogeny.
- Trap: Confuse with Western Ghats (Deccan edge, but Ghats uplift separate).
2. Memory Aids/Mnemonics
- Himalayan formation: "India Eurasia Crash ~50 Ma" ? "IEC-50" (Indian Eurasian Collision 50).
- Deccan: "Reunion Hotspot ~65 Ma Basalt" ? "RH-65B".
- Phases: "Tethys Closed ? Collision ? Folds" (TCF for Himalayas).
3. Confusing Concepts
- Orogeny vs Volcanism: Orogeny = mountain building (Himalayas folds); Volcanism = lava eruptions (Deccan basalt).
- Himalayas: Tectonic; Deccan: Intraplate.
- Young vs Old: Himalayas young (unstable, quakes); Deccan old (stable plateau).
TYPE 3: PYQs & EXPECTED QUESTIONS
1. PYQ Vault
- UPSC Prelims 2013: The Himalayas are formed of parallel fold ranges of which the oldest range is? ? Great Himalayas.
- SSC CGL 2016: The Himalayas are a result of which type of plate movement? ? Convergent.
- UPSC Prelims 2018: The Deccan Trap is a large? ? Volcanic plateau.
- RRB NTPC 2019: Himalayan mountains are an example of? ? Fold mountains.
- SSC CGL 2021: Deccan Traps are formed due to? ? Volcanic activity.
- State PSC (MPPSC 2020): The Tethys Sea was closed due to? ? Indian plate collision.
- SSC CGL 2019: The age of Himalayan orogeny is? ? Tertiary.
- RRB JE 2022: Deccan volcanism is associated with? ? Reunion hotspot.
- BPSC 2021: Himalayas are? ? Young fold mountains.
- TNPSC 2022: Deccan Traps are made of? ? Basalt rocks.
2. 2026 Expected Questions
- Explain the process of Himalayan orogeny due to plate tectonics.
- What is the geological origin of the Deccan Traps?
- How old is the Himalayan mountain system?
- Which ancient sea was closed during the formation of the Himalayas?
- What type of volcanism formed the Deccan Plateau?
- Describe the role of the Reunion hotspot in Indian geology.