Introduction:
The study of rocks and earthquakes
is an important part of Indian and world geography. Rocks form the basic crust
of the Earth, and earthquakes are sudden natural events caused by movements
inside the Earth. For exams like SSC, UPSC, and Railway, questions are
frequently asked about the types of rocks, the rock cycle, earthquake
causes, earthquake-prone areas in India, and safety measures.
This blog will explain these concepts in simple language, with examples, so
that you can understand and memorize them easily for your competitive exam
preparation.
Rocks
What are Rocks?
Rocks
are the solid material
that makes up the Earth’s crust. They are formed naturally and are made up of minerals.
Exam Tip:
Study of Rocks is Called Petrology.
Example: Granite
is a rock, but it contains minerals like quartz, feldspar, and mica.
Types of Rocks:
1. Igneous Rocks (Primary Rocks)
o Formed by cooling and solidification of molten magma.
o Called Primary rocks because they were the first to be formed.
o Two types:
§ Intrusive Igneous Rocks – Formed inside the Earth (e.g., Granite).
§ Extrusive Igneous Rocks – Formed on Earth’s surface after volcanic eruption (e.g., Basalt).
o Example: The Deccan Plateau in India is made of basalt rock.
2. Sedimentary Rocks
o Formed by deposition and compaction of sediments (sand, mud, etc.).
o Often contain fossils.
o Example: Sandstone (made of sand particles), Limestone (made of shells and remains).
o Example: Coal is a sedimentary rock used as fuel.
3. Metamorphic Rocks
o Formed when igneous or sedimentary rocks are subjected to heat and pressure.
o Example:
§ Limestone → Marble
§ Coal → Diamond
§ Shale → Slate
Exam
Tip: An upward fold is called an Anticline,
while a download fold is called an Syncline.
Earth's Internal Structure, Latitude & Longitude Explained.
The Rock Cycle
The continuous process of transformation between igneous, sedimentary, and metamorphic rocks is called the Rock Cycle.
Example: Magma cools to form igneous rocks → weathering produces sediments → forms sedimentary rocks → heat/pressure changes them into metamorphic rocks → melts back into magma.
Earthquakes
What is an Earthquake?
An earthquake is the sudden shaking of the Earth’s surface caused by the release of energy from inside the Earth’s crust.
Exam Tip: Study
of Earthquake is called Seismology.
Maximum Earthquake in Pacific Ocean (Pacific Ring of Fire).
Example: The 2001 Bhuj Earthquake
in Gujarat caused massive destruction and thousands of deaths.
Universe, galaxy & Earth Data. Geography notes.
Causes of Earthquakes
1. Tectonic Movements – Movement of plates (most common cause).
2. Volcanic Activity – Explosive eruptions can cause tremors.
3. Collapse of Caves – Minor local quakes.
4. Human Activities – Mining, dams, nuclear tests.
Important Terms in Earthquakes
· Focus: The point inside the Earth where the earthquake starts.
· Epicenter: The point directly above the focus on the surface.
· Seismograph: Instrument that records earthquake waves.
· Richter Scale: Measures the magnitude of an earthquake.
Example: The Nepal Earthquake 2015 had a magnitude of
7.8 on the Richter Scale.
Solar System: Notes & MCQ Quiz.
Earthquake Zones in India
India is divided into four seismic zones (II, III, IV, V).
Zone V: Very high risk (e.g., Kashmir, Northeast India).
Zone IV: High risk (e.g., Delhi, Gujarat).
Zone III: Moderate risk (e.g., Maharashtra, Odisha).
Zone II: Low risk (e.g., South India).
Effects of Earthquakes
· Positive: New landforms, underground resources exposed.
· Negative: Loss of life, property damage, tsunamis, landslides.
Example: The 2004 Indian Ocean Earthquake caused a massive tsunami affecting Tamil Nadu and Andaman Islands.
Earthquake Safety Measures
· Do not panic, take shelter under strong furniture.
· Avoid elevators, use stairs.
· Stay away from glass windows and weak buildings.
· After tremors, move to an open ground.
Example: In Japan, earthquake drills are
practiced regularly in schools and offices.
📜 Seismic Waves: 3 Types-
|
Quality |
P-Waves |
S-Waves |
L-Waves |
|
Other Name |
Primary waves |
Secondary waves |
Love wave or Surface waves |
|
Speed |
Maximum |
Less than P waves |
Minimum |
|
Medium |
Can travel in Solid>Liquid>Gas |
Only travel in Solid |
Near surface |
|
Nature |
Longitudinal waves |
Transverse waves |
Both |
|
Intensity |
Less intensity |
More than P waves |
More intensity |
📜 Articles Related to Disaster Management in India
While there is no direct Article in the Constitution about earthquakes, the Disaster Management Act, 2005 empowers government agencies to take preventive and relief measures.
· Article 355: Union can protect states against external aggression and internal disturbances (used during disasters).
· Article 51A(g): Fundamental duty of every citizen to protect and improve the natural environment.
📚 FAQs
Q1.
What are the three main types of rocks?
A: Igneous, Sedimentary, and Metamorphic.
Q2.
Which rock forms the Deccan Plateau?
A: Basalt (an igneous rock).
Q3.
What is the difference between focus and epicenter?
A: Focus is the origin point inside the Earth, epicenter is the surface point
above it.
Q4.
Which scale measures earthquakes?
A: The Richter Scale.
Q5.
Which are earthquake-prone areas in India?
A: Kashmir, Himachal Pradesh, Northeast India, Gujarat, and Andaman-Nicobar.
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