Geomorphic Processes — Practice

Question 1

Classify each process as endogenic or exogenic and identify the specific type:
(a) The Himalayan range being pushed upward at ~5mm per year by Indian Plate collision
(b) A river cutting a V-shaped valley in the mountains
(c) Magma erupting from a volcano and building a cone
(d) Freeze-thaw action breaking apart rock in the Himalayas in winter

Accepted Answer

(a) **Endogenic — Diastrophism (folding)**: The Indian Plate colliding with Eurasian Plate creates compressional forces that fold the crust upward. This is tectonic movement driven by Earth's internal heat.

(b) **Exogenic — Fluvial erosion**: River water flowing downslope under gravity cuts into bedrock, creating the V-shaped valley. Energy source: solar energy (drives hydrological cycle that creates rivers) + gravity.

(c) **Endogenic — Volcanism**: Magma from Earth's interior erupting through a vent builds a volcanic cone. Energy source: Earth's internal heat from radioactive decay and original accretion.

(d) **Exogenic — Physical (Mechanical) Weathering (Freeze-Thaw/Frost Action)**: Water enters rock cracks, freezes, expands by 9%, exerting pressure of ~2,000 kg/cm² — shatters rock. This is in-situ breakdown (no movement), so weathering not erosion.

Question 2

Compare physical (mechanical), chemical, and biological weathering. For each: give the dominant process, the environment where it is most active, and one Indian example.

Accepted Answer

**Physical (Mechanical) Weathering**:
- Process: Rock breaks into smaller pieces WITHOUT changing mineral composition. Common types: exfoliation (onion peeling due to temperature change), freeze-thaw (water freezes in cracks, expands, shatters), salt crystallisation (salt deposits grow in rock pores).
- Environment: Most active in deserts (extreme temperature fluctuations) and cold mountain regions (freeze-thaw).
- Indian example: Rock exfoliation in Rajasthan desert (day temperature 50°C, night 10°C → sheets peel off granite boulders).

**Chemical Weathering**:
- Process: Rock minerals react with water, oxygen, CO₂, or acids — CHANGING mineral composition. Types: hydration (minerals absorb water, swell, weaken), oxidation (iron minerals rust = red laterite soils), carbonation (CO₂ + water → carbonic acid dissolves limestone).
- Environment: Most active in warm, humid tropical regions (high temperature + moisture = fast reactions).
- Indian example: Laterisation in Kerala and Western Ghats — iron-rich rock oxidises, forming red laterite soil. Limestone caves in Meghalaya (Mawsmai Cave) = carbonation of limestone.

**Biological Weathering**:
- Process: Plants and organisms break down rock. Plant roots penetrate cracks, exert wedging pressure; lichens secrete acids that dissolve minerals; burrowing animals loosen soil and expose rock.
- Environment: Active in all vegetated areas; most effective in tropical rainforests where root systems are dense.
- Indian example: Fig trees (Ficus) growing through granite temple walls in Hampi — root expansion shatters the stone.

Question 3

The Kedarnath disaster of June 2013 involved a combination of heavy rainfall, glacial lake outburst, and debris flow that killed over 5,700 people. Using the concept of mass movements, explain what happened and what geographical factors made the Kedarnath valley particularly vulnerable.

Accepted Answer

**Type of Mass Movement**: The Kedarnath event was primarily a **debris flow** — a fast-moving mixture of rock fragments, soil, and water that moves like a fluid on steep slopes. It was triggered by a combination of:
(i) Unusual monsoon rainfall (3× normal in 3 days)
(ii) Glacial Lake Outburst Flood (GLOF) from Chorabari Glacier, releasing ~9 million cubic metres of water
(iii) Saturated soil and debris on steep valley walls

**Geographical Vulnerability Factors**:

1. **Young, geologically unstable terrain**: The Himalayas are the world's youngest fold mountains (still rising at ~5mm/year). Young rocks are poorly consolidated — fractured, jointed, and easily mobilised by water.

2. **Steep slopes**: The Mandakini valley has slopes exceeding 45°. As slope angle increases, shear stress (driving force for movement) increases while friction (resisting force) decreases. Above a critical angle, any trigger causes movement.

3. **Glacially deposited material**: Moraines (glacial deposits) and glaciofluvial sediments are unconsolidated — they behave like loose gravel when saturated. The valley is filled with such deposits from retreating glaciers.

4. **Permafrost thawing**: Climate change is thawing permafrost, which previously locked slope material in place. Liquid water replaces ice, lubricating rock-soil interfaces and triggering slides.

5. **Human factors compounding natural vulnerability**: Construction of roads, hotels, and pilgrimage infrastructure on slopes removed vegetation (biological weathering protection removed), cut into hillsides (removed toe support), and paved surfaces increased surface runoff.

**Lesson**: Geomorphic processes are natural — their consequences become disasters when human settlements occupy vulnerable zones. The Char Dham project now uses slope stability analysis before construction — an application of geomorphic process knowledge.

Practice — Geomorphic Processes

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