Question 1

Multiple choice questions.

(i) Which one of the following earthquake waves is more destructive?

(a) P-waves
(c) Surface waves
(b) S-waves
(d) None of the above

(ii) Which one of the following is a direct source of information about the interior of the earth?

(a) Earthquake waves
(c) Gravitational force
(b) Volcanoes
(d) Earth magnetism

(iii) Which type of volcanic eruptions have caused Deccan Trap formations?

(a) Shield
(c) Composite
(b) Flood
(d) Caldera

(iv) Which one of the following describes the lithosphere:

(a) upper and lower mantle
(c) crust and core
(b) crust and upper mantle
(d) mantle and core

Accepted Answer

1.(i) (c) Surface waves are more destructive because they travel along the Earth's surface causing the most damage during earthquakes.

(ii) (a) Earthquake waves are a direct source of information about the Earth's interior as their propagation reveals internal structure.

(iii) (b) Flood volcanic eruptions have caused the Deccan Trap formations, characterized by extensive lava flows.

(iv) (b) Lithosphere comprises the crust and upper mantle, forming the rigid outer layer of the Earth. — Surface waves cause the most ground shaking and damage during earthquakes. Earthquake waves (seismic waves) provide direct data about Earth's interior by their travel times and paths. Deccan Traps were formed by flood basalt eruptions, which are large-scale lava flows. The lithosphere includes the crust and uppermost mantle, making it rigid compared to the underlying asthenosphere.

Question 2

Answer the following questions in about 30 words.

(i) What are body waves?
(ii) Name the direct sources of information about the interior of the earth.
(iii) Why do earthquake waves develop shadow zone?
(iv) Briefly explain the indirect sources of information of the interior of the earth other than those of seismic activity.

Accepted Answer

(i) Body waves are seismic waves that travel through the Earth's interior. They include P-waves (primary) and S-waves (secondary).

(ii) Direct sources of information about the Earth's interior include earthquake (seismic) waves.

(iii) Earthquake waves develop shadow zones because S-waves cannot travel through the liquid outer core and P-waves are refracted, creating areas where no waves are detected.

(iv) Indirect sources include studies of meteorites, Earth's magnetic field, gravitational studies, and volcanic activity which provide clues about Earth's internal composition and structure. — Body waves penetrate Earth's interior and are classified as P and S waves. Seismic waves provide direct evidence of Earth's layers. Shadow zones occur due to wave behavior at core boundaries. Indirect methods complement seismic data by analyzing related geophysical phenomena.

Question 3

Answer the following questions in about 150 words.

(i) What are the effects of propagation of earthquake waves on the rock mass through which they travel?
(ii) What do you understand by intrusive forms? Briefly describe various intrusive forms.

Accepted Answer

(i) The propagation of earthquake waves causes vibrations in the rock mass through which they travel. These vibrations can lead to fracturing, displacement, and deformation of rocks. The intensity of damage depends on the wave type, rock properties, and distance from the epicenter. Surface waves cause the most destruction near the surface, while body waves affect deeper layers.

(ii) Intrusive forms are igneous rock bodies formed when magma cools and solidifies beneath the Earth's surface. Various intrusive forms include:
- Dykes: vertical or steeply inclined sheets cutting across rock layers.
- Sills: horizontal or gently inclined sheets parallel to rock layers.
- Laccoliths: dome-shaped intrusions causing uplift of overlying strata.
- Batholiths: large, irregular masses of intrusive rock forming the core of mountains.
- Stocks: smaller irregular intrusive bodies. — Earthquake waves cause mechanical effects on rocks, leading to structural changes. Intrusive forms represent different shapes and orientations of magma solidified underground, classified based on their geometry and relation to surrounding rocks.

Question 4

Which of the following is the main source of magma that finds its way to the surface during volcanic eruptions?

Accepted Answer

Asthenosphere — The asthenosphere is the upper portion of the mantle, extending up to about 400 km depth, characterized by weak and ductile rock that acts as the main source of magma during volcanic eruptions.

Question 5

Identify the type of earthquake caused by the collapse of roofs in underground mines.

Accepted Answer

Collapse earthquake — Collapse earthquakes occur due to the collapse of roofs in underground mines and are minor tremors associated with intense mining activity.

Question 6

Which of the following statements about P-waves is correct?

Accepted Answer

P-waves vibrate parallel to the direction of wave propagation — P-waves, or primary waves, travel fastest among seismic waves and vibrate parallel to the direction of wave propagation, similar to sound waves. They can travel through solids, liquids, and gases.

Question 7

Fill in the blank: The point on the earth's surface directly above the focus of an earthquake is called the _____.

Accepted Answer

epicentre — The epicentre is the point on the earth's surface directly above the focus (hypocentre) where the energy of an earthquake is first felt and recorded.

Question 8

Explain the difference between the lithosphere and asthenosphere in terms of their physical properties and depth range.

Accepted Answer

— The lithosphere is the rigid outer layer of the earth extending up to 10-200 km depth, including the crust and uppermost mantle. It is brittle and solid. The asthenosphere lies beneath the lithosphere, extending up to about 400 km depth, and is semi-fluid or weak, allowing plastic flow. The asthenosphere is the source of magma for volcanic eruptions.

Question 9

Describe the characteristics of Himalayan rivers and explain why they are prone to flooding during monsoons.

Accepted Answer

— Himalayan rivers originate from glaciers and snowfields, making them perennial with large drainage basins. They have steep gradients causing rapid flow and deep valleys. Due to young and fragile geology, they carry heavy sediment loads. During monsoons, heavy rainfall and sediment deposition reduce channel capacity, causing floods. Examples include the Indus, Ganga, and Brahmaputra.

Question 10

Match the following types of volcanoes with their characteristics:

1. Shield Volcano
2. Composite Volcano
3. Caldera
4. Flood Basalt Province

A. Most explosive, collapse depressions
B. Large, gentle slopes, fluid basalt lava
C. Layers of lava and pyroclastic material, explosive eruptions
D. Extensive lava flows covering large areas

Accepted Answer

— 1-B: Shield volcanoes have large, gentle slopes formed by fluid basalt lava.
2-C: Composite volcanoes have layered lava and pyroclastic deposits with explosive eruptions.
3-A: Calderas are highly explosive volcanoes with collapsed depressions.
4-D: Flood basalt provinces consist of extensive lava flows covering large areas.

Question 11

Using the diagram description: A curve recorded on a seismograph shows three distinct sections representing P-waves, S-waves, and surface waves. Which wave type arrives first at the surface during an earthquake?

Accepted Answer

P-waves — P-waves, also called primary waves, travel fastest and arrive first at the surface. They are followed by S-waves and then surface waves, which are the slowest and most destructive.

Question 12

Explain why S-waves do not travel through the outer core of the Earth.

Accepted Answer

— S-waves are shear waves that can only travel through solid materials. The outer core of the Earth is in a liquid state, so S-waves cannot propagate through it. This property helps scientists identify the liquid nature of the outer core.

Question 13

Describe the shadow zone of earthquake waves and explain its significance in understanding Earth's interior.

Accepted Answer

— (a) The shadow zone is an area on Earth's surface where seismic waves from an earthquake are not detected by seismographs.

(b) For P-waves, the shadow zone lies between 105° and 145° from the epicentre, where waves are refracted by the liquid outer core.

(c) For S-waves, the shadow zone is larger, beyond 105°, because S-waves cannot travel through the liquid outer core.

(d) The existence of shadow zones provides evidence for the liquid state of the outer core and helps map the layered structure of the Earth.

(e) Thus, shadow zones are crucial for understanding Earth's internal composition and structure.

Question 14

What is a batholith and how does it form? Provide an example from India.

Accepted Answer

— A batholith is a large body of magmatic material that cools and solidifies deep within the Earth's crust, forming large dome-shaped granitic masses. They appear on the surface only after erosion removes overlying rocks. An example of batholiths in India is found in the Karnataka plateau, where granitic domal hills are exposed.

Question 15

Which of the following is NOT an effect of an earthquake?

Accepted Answer

Tornado formation — Tornado formation is not an effect of earthquakes. Earthquake effects include ground shaking, soil liquefaction, tsunamis (if epicentre is under ocean), landslides, and structural collapse.

DRAINAGE SYSTEM

DRAINAGE SYSTEM — Study Notes

Introduction

Drainage Systems of India

Himalayan Rivers

Practice Questions — DRAINAGE SYSTEM

All 6 Chapters in India - Physical Environment