Rocks, Landforms, Earthquakes, Volcanoes and Oceans
Rocks, Landforms, Earthquakes, Volcanoes and Oceans
The Earth's surface is built of rocks, shaped by internal forces (earthquakes, volcanoes, mountain building) and external agents (rivers, wind, glaciers), and mostly covered by oceans. NTPC asks rock types and examples, igneous intrusions, earthquake terms, volcano types and ocean features.
1. Rocks
| Type | How formed | Examples |
|---|---|---|
| Igneous | Cooling of magma | Granite (intrusive), basalt (extrusive) |
| Sedimentary | Layers of deposits | Sandstone, limestone, shale, coal |
| Metamorphic | Changed by heat and pressure | Marble (from limestone), slate (from shale), quartzite (from sandstone) |
| Intrusive igneous body | Shape |
|---|---|
| Batholith | Large, dome-shaped mass deep below |
| Laccolith | Dome-shaped with a level base |
| Lopolith | Saucer-shaped |
| Sill | Horizontal sheet |
| Dyke | Vertical wall |
2. Landforms
| Agent | Landforms |
|---|---|
| River | V-shaped valley, waterfall, meander, ox-bow lake, delta |
| Glacier | U-shaped valley, cirque, moraine |
| Wind | Sand dunes, barchans, mushroom rocks |
| Sea | Sea cliffs, sea arches, stacks, beaches |
3. Earthquakes and Volcanoes
| Item | Facts |
|---|---|
| Focus and epicentre | Focus is the point inside the Earth; epicentre is the point on the surface above it |
| Seismic waves | P-waves (fastest, pass through solids and liquids), S-waves (only solids), surface waves (most damage) |
| Measuring | Richter scale (magnitude), seismograph (instrument) |
| Volcano types | Active (Barren Island, India's only active volcano), dormant, extinct |
| Pacific Ring of Fire | Belt of volcanoes and earthquakes around the Pacific |
4. Oceans
| Item | Facts |
|---|---|
| Largest and deepest ocean | Pacific; Mariana Trench (Challenger Deep, about 11 km) |
| Ocean relief | Continental shelf, slope, deep-sea plain, trenches |
| Currents | Warm: Gulf Stream, Kuroshio; Cold: Labrador, Humboldt (Peru) |
| Salinity | Average about 35 parts per thousand; highest: Lake Van (Turkey, about 330), Dead Sea (about 238); among seas, the Red Sea |
✗ Marble is an igneous rock | ✓ Marble is metamorphic, formed from limestone
✗ S-waves travel through liquids | ✓ S-waves pass only through solids; P-waves pass through both
हिंदी नोट: आग्नेय चट्टान मैग्मा के ठंडा होने से बनती है (ग्रेनाइट, बेसाल्ट); अवसादी परतों से (बलुआ पत्थर, चूना पत्थर); कायांतरित ताप और दबाव से (संगमरमर, स्लेट)। लोपोलिथ तश्तरी के आकार का आग्नेय अंतर्वेधी पिंड है। भारत का एकमात्र सक्रिय ज्वालामुखी बैरन द्वीप है।
Exam Pointer: Verified NTPC pattern: the saucer-shaped intrusive igneous body (September 2025 UG CBT-1). Rock, landform, earthquake and ocean questions are tagged syllabus-based.
Pariksha Pattern: Every Way NTPC Asks This Topic
Pattern 1: Rock types and igneous bodies
[PYQ: NTPC UG CBT-1 2-Sep-2025 Shift-3]
EXAM LEVEL
Q. What is a saucer-shaped intrusive igneous body called?
A lopolith.
Answer: Lopolith
EXAMATLAS LEVEL
Q. Marble and slate are formed from which rocks, and to which rock group do they belong?
Marble forms from limestone and slate from shale; both are metamorphic rocks.
Answer: Limestone and shale; metamorphic
Pattern 2: Landforms by agent
[Pattern: syllabus-based, PYQ-style]
EXAM LEVEL
Q. Which landform is made by a glacier: V-shaped valley or U-shaped valley?
A U-shaped valley.
Answer: U-shaped valley
EXAMATLAS LEVEL
Q. Which river landform is a crescent-shaped lake cut off from a meander, and what are crescent-shaped sand dunes called?
An ox-bow lake; barchans.
Answer: Ox-bow lake; barchans
Pattern 3: Earthquakes and volcanoes
[Pattern: syllabus-based, PYQ-style]
EXAM LEVEL
Q. Which is India's only active volcano?
Barren Island, in the Andaman and Nicobar Islands.
Answer: Barren Island
EXAMATLAS LEVEL
Q. What is the point on the surface directly above the focus called, and which seismic waves cannot pass through liquids?
The epicentre; S-waves.
Answer: Epicentre; S-waves
Pattern 4: Oceans and currents
[Pattern: syllabus-based, PYQ-style]
EXAM LEVEL
Q. Which is the deepest point in the oceans?
The Challenger Deep in the Mariana Trench, Pacific Ocean.
Answer: Mariana Trench (Challenger Deep)
EXAMATLAS LEVEL
Q. Name one warm and one cold ocean current, and the average salinity of ocean water.
Warm: Gulf Stream (or Kuroshio). Cold: Labrador (or Humboldt). Average salinity is about 35 parts per thousand.
Answer: Gulf Stream; Labrador; about 35 per thousand
60-Second Revision
- Igneous (granite, basalt), sedimentary (sandstone, limestone), metamorphic (marble, slate).
- Lopolith saucer; laccolith dome; sill horizontal; dyke vertical.
- Focus vs epicentre; P-waves through all, S-waves only solids.
- Barren Island: India's only active volcano.
- Pacific deepest (Mariana); Gulf Stream warm, Labrador cold.