Plate Tectonics and Continental Drift for UPSC Prelims
1. Introduction to Plate Tectonics
Plate tectonics is the scientific theory that Earth's lithosphere is divided into large, rigid plates that move relative to one another. This movement explains continental drift, earthquakes, volcanic activity, and the formation of mountain ranges and ocean basins.
Key Facts
- Number of Major Plates: 7 (Pacific, North American, Eurasian, African, Antarctic, Indo-Australian, South American)
- Speed of Movement: 1-10 cm per year (about as fast as fingernails grow)
- Theory Developed: 1960s, building on continental drift theory
- Significance: Explains Earth's topography, seismic zones, and volcanic belts
Important Facts for UPSC
- The lithosphere (crust + upper mantle) is divided into tectonic plates.
- Plate movements are driven by mantle convection currents.
- The theory unified earlier concepts of continental drift and seafloor spreading.
2. Continental Drift Theory
Alfred Wegener's Theory (1912)
Proposed that continents were once joined in a supercontinent called Pangaea (meaning "all Earth"), which began breaking apart about 200 million years ago.
| Era |
Supercontinent |
Description |
| Late Paleozoic to Early Mesozoic |
Pangaea |
Single supercontinent surrounded by Panthalassa ocean |
| Jurassic Period |
Laurasia (North) and Gondwana (South) |
Pangaea split into two major landmasses |
| Cretaceous to Present |
Modern continents |
Further breakup into current continental configuration |
Important Facts for UPSC
- Wegener couldn't explain the mechanism of drift, leading to initial rejection.
- The theory was later supported by seafloor spreading evidence in the 1960s.
- India was part of Gondwana before drifting north to collide with Eurasia.
3. Evidence Supporting Continental Drift
Key Evidence
- Jigsaw Fit: Coastlines of continents (especially Africa and South America) match like puzzle pieces.
- Fossil Evidence: Identical fossils found on now-separated continents (e.g., Mesosaurus).
- Rock Formations: Matching mountain ranges and rock types across oceans.
- Paleoclimatic Evidence: Glacial deposits in now-tropical regions.
- Paleomagnetism: Magnetic minerals in rocks show past pole positions that only make sense if continents moved.
Important Facts for UPSC
- The Glossopteris flora (fossil plant) is found across southern continents.
- The Appalachian Mountains (USA) align with mountains in Scotland and Scandinavia.
- Coal deposits in Antarctica indicate it was once in warmer latitudes.
4. Types of Plate Boundaries
| Boundary Type |
Description |
Geological Features |
Examples |
| Divergent |
Plates move apart |
Mid-ocean ridges, rift valleys |
Mid-Atlantic Ridge, East African Rift |
| Convergent |
Plates move toward each other |
Mountains, trenches, volcanoes |
Himalayas, Andes, Mariana Trench |
| Transform |
Plates slide past each other |
Earthquakes, fault lines |
San Andreas Fault (California) |
Convergent Boundary Subtypes
- Oceanic-Continental: Denser oceanic plate subducts (e.g., Nazca Plate under South America)
- Oceanic-Oceanic: One plate subducts, forming island arcs (e.g., Japan)
- Continental-Continental: Collision forms mountains (e.g., India-Eurasia forming Himalayas)
Important Facts for UPSC
- The "Ring of Fire" around the Pacific is a convergent boundary zone.
- Divergent boundaries create new crust; convergent boundaries destroy it.
- Transform boundaries often cause shallow but powerful earthquakes.
5. Forces Behind Plate Movements
Driving Mechanisms
- Mantle Convection: Heat from Earth's core creates slow-moving convection currents in the mantle.
- Ridge Push: Elevated mid-ocean ridges push plates away.
- Slab Pull: Subducting plates pull the rest of the plate behind them.
Important Facts for UPSC
- Slab pull is considered the dominant driving force.
- Convection currents move at about 1-20 cm/year.
- Hotspots (like Hawaii) show absolute plate motion over stationary mantle plumes.
6. Major and Minor Tectonic Plates
| Plate Name |
Type |
Area (million km²) |
Notable Features |
| Pacific Plate |
Major (Oceanic) |
103.3 |
Ring of Fire, Hawaii hotspot |
| Eurasian Plate |
Major (Continental) |
67.8 |
Contains Europe and most of Asia |
| Indo-Australian Plate |
Major |
58.9 |
Colliding with Eurasian Plate (Himalayas) |
| Nazca Plate |
Minor (Oceanic) |
15.6 |
Subducting under South America (Andes) |
Important Facts for UPSC
- The Indo-Australian Plate is breaking into Indian and Australian plates.
- The Philippine Sea Plate is a notable minor plate with complex boundaries.
- Turkey sits on the Anatolian Plate, a microplate causing frequent earthquakes.
7. The Indian Plate and Its Movement
Key Features
- Originally part of Gondwana, broke away ~120 million years ago.
- Moved north at ~15 cm/year (fast for a plate), collided with Eurasia ~50 million years ago.
- Continues to move north at ~5 cm/year, causing Himalayan uplift.
Effects of Indian Plate Movement
- Formation of the Himalayas (still rising ~1 cm/year).
- Creation of the Tibetan Plateau (world's highest and largest plateau).
- Seismic activity along the plate boundary (e.g., 2005 Kashmir earthquake).
Important Facts for UPSC
- The collision is responsible for the formation of the Himalayas, Karakoram, and Hindu Kush ranges.
- Deccan Traps (volcanic province) formed as India passed over the Réunion hotspot.
- India's northward push causes frequent earthquakes in the Himalayan region.
| Landform |
Plate Boundary |
Formation Process |
Examples |
| Fold Mountains |
Convergent (C-C) |
Continental collision compresses crust upward |
Himalayas, Alps, Appalachians |
| Ocean Trenches |
Convergent (O-O or O-C) |
Subduction creates deep troughs |
Mariana Trench, Peru-Chile Trench |
| Mid-Ocean Ridges |
Divergent |
Seafloor spreading creates underwater mountain chains |
Mid-Atlantic Ridge, East Pacific Rise |
| Rift Valleys |
Divergent (Continental) |
Crust stretches and fractures |
East African Rift, Rhine Valley |
Important Facts for UPSC
- The East African Rift may eventually split Africa, creating a new ocean.
- The Himalayas contain the world's highest peaks, including Everest.
- Island arcs like Japan form where two oceanic plates converge.
9. Associated Natural Hazards
Earthquakes
Most occur along plate boundaries, especially convergent and transform boundaries. The circum-Pacific belt ("Ring of Fire") is particularly active.
Volcanoes
Common at convergent boundaries (subduction zones) and divergent boundaries. Hotspots like Hawaii can occur within plates.
Tsunamis
Often generated by undersea earthquakes at subduction zones (e.g., 2004 Indian Ocean tsunami).
Important Facts for UPSC
- India's earthquake zones: Himalayan (high risk), Indo-Gangetic (moderate), Peninsula (low).
- Barren Island (Andamans) is India's only active volcano.
- The 2001 Bhuj earthquake occurred on an intraplate fault, showing risk beyond boundaries.
10. UPSC Relevance and Preparation Tips
Why Important for UPSC?
- Foundation for physical geography questions in Prelims.
- Explains India's seismic zones, Himalayan formation, and Deccan Traps.
- Linked to disaster management (earthquakes, tsunamis).
Preparation Tips
- Memorize the 7 major plates and their movements.
- Understand the three boundary types and associated landforms.
- Focus on the Indian Plate's history and current effects.
- Relate plate tectonics to earthquake and volcano distribution.
- Practice map-based questions on plate boundaries and seismic zones.
- Revise key terms: subduction, seafloor spreading, paleomagnetism.
Important Facts for UPSC
- Previous UPSC questions have asked about the Ring of Fire, Himalayan formation, and evidence for continental drift.
- Understand the difference between continental drift (Wegener) and plate tectonics (modern theory).
- Note that the theory explains mineral and fossil fuel distribution patterns.