UPSC loves to slip one Himalayan fact into a list of Peninsular ones. Deep, V-shaped valleys belong to young rivers, not the ancient, worn-down Peninsular Block.
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Indian Geography · IndGeo0122
Ancient and stable, but not silent.
6.3
magnitude, Koyna, 1967
Largest known reservoir-triggered earthquake anywhere, on the Peninsular Block’s western fault-edge.
Coastline eroding
34%
NCCR Shoreline Change Atlas, 2022
West coast erosion
~2.5 m/yr
On top of older tectonic submergence
Koyna Dam built
1962
Reservoir filling triggered quakes since
Peninsular vs Himalayan Block
Mountain type
Residual
River valleys
Broad, shallow
Tectonic state
Mostly stable
River flow
Mature, seasonal
Residual mountain ranges
Aravalli RangeOldest in India
Veliconda hillsAndhra Pradesh
Mahendragiri hillsOdisha-AP border
Javadi hillsTamil Nadu
🌍 An Ancient, Worn-Down Landmass
1. A Piece of Gondwanaland
- Origin The Peninsular Block is a fragment of Gondwanaland, the ancient supercontinent that also included Africa, South America, and Australia.
- Age It is one of the oldest and most stable landmasses on Earth, largely untouched by the folding that built the Himalayas.
- Erosion Millions of years of erosion wore down its original highlands. What remains are residual mountains, not active fold mountains.
- Examples The Aravalli Range, the Veliconda hills, and the Mahendragiri hills are all residual mountains of the Peninsular Block.
2. A Coast of Submergence
- Western Coast The Konkan and Malabar coasts show clear submergence. Faulting and tectonic subsidence drowned the lower reaches of west-flowing rivers.
- Result This drowning created natural harbours, like Mumbai, and estuaries, rather than deltas.
- Contrast Parts of the east coast instead show features of emergence, where land has risen or sea level has fallen, exposing former sea floor.
🏔️ Peninsular vs Himalayan Drainage
1. Why Peninsular Rivers Don't Cut V-Shaped Valleys
- Peninsular Rivers Peninsular rivers are old and mature. They flow over a stable, worn-down landmass, and form broad, shallow valleys.
- Himalayan Rivers Deep, V-shaped valleys are a Himalayan feature instead. Young, fast-flowing, snow-fed rivers cut them into the still-rising fold mountains.
- The Common Trap UPSC often mixes one Himalayan fact into a list of Peninsular features. V-shaped valleys are the classic example.
2. Himalayan and Peninsular Blocks, Compared
- Age The Himalayas are young fold mountains, still rising. The Peninsular Block is an ancient, largely stable Gondwanaland remnant.
- Tectonic Activity The Himalayan belt is highly active, with frequent earthquakes. The Peninsular Block is stable overall, except along its western fault-edge.
- Mountains Himalayan ranges are rising fold mountains. Peninsular ranges, like the Aravallis, are residual mountains, worn down rather than uplifted.
- River Flow Himalayan rivers are fast-flowing and snow-fed, perennial year-round. Peninsular rivers are mature, slower, and largely rain-fed, so many run seasonal.
Test Yourself
⚠️ The Western Edge Is Not Fully Quiet
1. The Koyna Seismic Zone
- Location The Koyna-Warna zone sits in Maharashtra's Western Ghats, near the western fault-edge of the Peninsular Block.
- Cause It is a textbook case of reservoir-triggered seismicity. Filling the Koyna Dam's reservoir, completed in 1962, raised pore pressure on nearby faults and set off earthquakes.
- Scale A magnitude 6.3 quake struck on 10 December 1967, the largest known reservoir-induced earthquake anywhere. Thousands of smaller quakes have followed since.
- Why It Matters Koyna shows that even a largely stable landmass can have locally active zones, especially near its fault-bound western edge.
2. A Coastline Under Erosion
- NCCR Findings The National Centre for Coastal Research's 2022 Shoreline Change Assessment Atlas found about 34% of India's coastline eroding.
- West Coast Rate Parts of the west coast are eroding at roughly 2.5 metres a year, on top of the older, natural submergence that shaped this coast.
- Response NCCR's shoreline-change mapping feeds into coastal-zone planning, helping states identify and manage the most vulnerable stretches.
Previous Year Question
Asked as: “Which of the following geographical features or phenomena is/are associated with the Peninsular Block of India?” (UPSC CSP 2026, GS Paper I, Q34).
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