Maharashtra Board Class 11 Geography Chapter 1 Earth Movements Solutions

Complete the Chain

 

Question 1.

A	B	C

🎯 Exam Tip: When completing three-column chain questions, always ensure there is a logical, sequential link connecting the concept in Column A to its process in Column B, and finally to its effect or example in Column C.

 

Question 1. Match the items in the following columns:

Column A	Column B	Column C
(1) Widespread volcanic eruption	(1) Zone V	(1) I to XII
(2) Andaman and Nicobar Islands	(2) Fissure eruption	(2) Block Mountain
(3) Mercalli scale	(3) Intensity	(3) Very high seismic vulnerability
(4) Slow movements	(4) Faulting	(4) Solid
(5) Philippines	(5) Volcanic bombs	(5) Deccan Trap
(6) Volcanic material	(6) Circum Pacific belt	(6) Mayon

Answer:

A	B	C
(1) Widespread volcanic eruption	(1) Fissure eruption	(1) Deccan Trap
(2) Andaman and Nicobar Islands	(2) Zone V	(2) Very high seismic vulnerability
(3) Mercalli scale	(3) Intensity	(3) I to XII
(4) Slow movements	(4) Faulting	(4) Block Mountain
(5) Philippines	(5) Circum Pacific belt	(5) Mayon
(6) Volcanic material	(6) Volcanic bombs	(6) Solid

In simple words: This table matches different geological features, scales, and locations with their correct characteristics and examples. For instance, the Mercalli scale measures earthquake intensity on a scale from I to XII.

🎯 Exam Tip: Double-check each row's correlation carefully, as matching one incorrect pair can lead to multiple errors in three-column matching questions.

 

2. Identify the Correct Correlation

A : Assertion R : Reasoning

 

Question 1. A – Faulting leads to development of fold mountains.
R – Faulting occurs when tensional forces move away from each other.
(a) Only A is correct.
(b) Only R is correct.
(c) Both A and R are correct and R is the correct explanation of A.
(d) Both A and R are correct but R is not the correct explanation of A.
Answer: (b) Only R is correct.
In simple words: Faulting is caused by tension pulling rocks apart, which creates block mountains, while folding is caused by compression. Thus, only statement R is correct.

🎯 Exam Tip: Remember that faulting is associated with tensional forces and block mountains, whereas folding is associated with compressional forces and fold mountains.

 

Question 2. A – Intensity of an earthquake is a measurement of the energy released during an earthquake.
R – Mercallis scale is used to measure intensity of an earthquake.
(a) Only A is correct.
(b) Only R is correct.
(c) Both A and R are correct and R is the correct explanation of A.
(d) Both A and R are correct but R is not the correct explanation of A.
Answer: (c) Both A and R are correct and R is the correct explanation of A.
In simple words: The Mercalli scale measures how strongly an earthquake is felt and the damage it causes at a specific location.

🎯 Exam Tip: Be careful with earthquake scales: the Richter scale measures magnitude (energy), while the Mercalli scale measures intensity (destruction/effects).

 

Question 3. A – South-East Asia, Japan and islands in the Pacific Ocean are most vulnerable to earthquakes and volcanic eruptions.
R – They are located in ‘Ring of Fire’.
(a) Only A is correct.
(b) Only R is correct.
(c) Both A and R are correct and R is the correct explanation of A.
(d) Both A and R are correct but R is not the correct explanation of A.
Answer: (c) Both A and R are correct and R is the correct explanation of A.
In simple words: The Pacific Ring of Fire is an area with high tectonic activity, making the regions along it highly prone to earthquakes and volcanic eruptions.

🎯 Exam Tip: Always link the high frequency of earthquakes and volcanoes in the Pacific region to its location on the active plate boundaries of the 'Ring of Fire'.

3. Identify the Correct Group

 

Question 1.

A	B	C	D

Question. Study the table below and identify the correct option:

(1) Symmetrical Fold	(1) Black Forest	(1) Narmada Valley	(1) Caldera
(2) Isoclinal Fold	(2) Vosges	(2) African Valley	(2) Crater Lake
(3) Overturned Fold	(3) Himalayas	(3) Tapi Valley	(3) Cinder Cone
(4) Recumbent Fault	(4) Satpuras	(4) Rhine Valley	(4) Lava Plateau

Answer: C
In simple words: The correct group of geological features is represented by column C.

🎯 Exam Tip: Pay close attention to the classification of landforms (folds, block mountains, rift valleys, and volcanic features) to match them correctly.

 

4. Give Geographical Reasons

 

Question 1. Extinct conical volcanoes often form crater lakes.
Answer: Extinct conical volcanoes often form crater lakes because:
1. An extinct volcano had no volcanic eruption for at least 10,000 years and is not expected to erupt again in future.
2. After the eruption, a large and deep depression remains in that area. Smaller depressions are called craters.
3. This crater eventually gets filled with water and crater lakes are formed.
4. The water may come from precipitation, ground water circulation or melted ice. This natural accumulation of water transforms the hollow volcanic summit into a scenic lake.
In simple words: When a volcano becomes completely inactive, the empty bowl-shaped opening at the top gets filled with rainwater or melted snow over time, creating a lake.

🎯 Exam Tip: Remember to mention that extinct volcanoes do not erupt anymore and explain how the depression (crater) collects water from rain or ice.

 

Question 2. People living in the Himalayas are more vulnerable to earthquakes.
Answer: People living in the Himalayas are more vulnerable to earthquakes because:
1. Himalayan mountain ranges are formed as a result of collision of Indo-Australian plate and Eurasian plate.
2. According to plate tectonic theory, Indo-Australian plate (on which India lies) is moving towards north and is subducting under Eurasian plate.
3. This movement obviously causes friction between two plates.
4. Thus, these regions are more prone to earthquakes. The continuous pressure build-up along these plate boundaries makes the entire region highly unstable.
In simple words: The Himalayas are built on two massive pieces of the Earth's crust that are constantly pushing against each other. This collision causes sudden movements and friction, leading to frequent earthquakes.

🎯 Exam Tip: Clearly state the names of the two colliding tectonic plates (Indo-Australian and Eurasian) to secure full marks.

 

Question 3. L-waves do not have a shadow zone.
Answer: L-waves do not have a shadow zone because-
1. The shadow zone is the area of the earth from angular distance of 105° to 140° from a given earthquake for both P-waves as well as S-waves.
2. Generally, seismographs located at any distance within 105° from epicentre record the arrival of S-waves and beyond 140° from epicentre record the arrival of P-waves.
3. L-waves are typically generated when the source of the earthquake is close to the earth’s surface. These surface waves travel along the outer crust of the Earth and do not pass through the deep interior layers where shadow zones are formed.
In simple words: L-waves travel only along the Earth's surface rather than going deep inside. Because they do not pass through the core, they do not get blocked or bent to create a shadow zone.

🎯 Exam Tip: Remember that shadow zones are created by waves passing through the Earth's interior. Since L-waves are surface waves, they do not have a shadow zone.

 

Question 4. Soft rocks form folds while hard rocks form faults.
Answer: Soft rocks form folds while hard rocks form faults because –
1. Soft and elastic rocks are affected by compressional forces.
2. Rocks that lie deep within the crust and are therefore under high pressure are generally ductile and particularly susceptible to folding without breaking.
3. Whereas rock layers that are near the earth’s surface are too rigid to bend into folds.
4. If the tectonic force is large enough, these rocks will break rather than bend and faulting on rupture occur. This difference in reaction to pressure determines the geological structures we see on the surface.
In simple words: Soft rocks are flexible and bend into folds when squeezed, like clay. Hard rocks are stiff and brittle, so they break and slip to form faults instead of bending.

🎯 Exam Tip: Clearly distinguish between the behavior of soft (ductile/elastic) and hard (rigid/brittle) rocks under pressure to secure full marks.

 

Question 5. Folds depend on the strength of rocks and intensity of forces.
Answer: Folds depend on the strength of rocks and intensity of forces because-
1. The elasticity of rocks largely affects the nature and magnitude of folding process.
2. The softer and more elastic rocks are subjected to intense folding while rigid and less elastic rocks are only moderately folded. The ultimate shape of the fold is a direct result of how strong the rock is and how hard the tectonic forces push against it.
In simple words: How much a rock bends depends on how soft it is and how hard it is being pushed. Soft rocks under strong pressure fold easily, while harder rocks or weaker forces result in very little bending.

🎯 Exam Tip: Mention both factors—rock elasticity (strength) and the pressure applied (intensity of force)—to explain the folding process completely.

Answer in Detail

 

Question 1. Explain different types of faults.
Answer: A fault is a fracture in the crustal rock, formed when the crustal rocks are displaced due to tensional movement caused by endogenic forces. The displacement of rock can occur in upward, downward or horizontal direction. The different types of faults determined by the direction of motion are:
Normal fault: It results when a portion of land slide down along the fault plane and when the exposed portion of the plane faces the sky.
Reverse fault: It results when a portion of the land is thrown upward relative to other side of the land. In such situation, the fault plane faces the ground.
Tear fault: At times, the rock strata on either side of the fault plane do not have vertical displacement. Instead, movement occurs along the plane in horizontal direction, causing lateral shifting of the blocks.
In simple words: A fault is a crack in the Earth's crust where rocks slide past each other. Depending on how the rocks move—up, down, or sideways—faults are classified as normal, reverse, or tear faults.

🎯 Exam Tip: Clearly define each type of fault and mention the direction of displacement (upward, downward, or horizontal) to secure maximum marks.

Thrust Fault: When the portion of the land on one side of the fault plane gets detached and moves over the land on the other side. The angle of fault plane is generally less than 45°.

 

Question 2. Explain with examples, different types of landforms produced by volcanic eruption.
Answer: A number of landforms are formed due to cooling and solidification of magma. These geological structures vary greatly in size and shape depending on the eruption style. Some important landforms are:

Lava domes:
1. Domes are developed when magma comes out and solidifies around its mouth.
2. The shape of the dome depends upon the fluidity of lava.
3. High dome with steep slopes is developed by acidic lava.
4. Due to basic lava, broad - based low domes are developed.

Lava plateaus:
1. Due to spread of lava in huge quantity from fissure volcano, it covers large areas and plateaus are formed.
2. The Deccan Trap in India has developed from volcanic eruptions millions of years ago.
In simple words: When volcanoes erupt, the hot liquid rock (magma) cools down and hardens into different shapes. This can create steep dome-like hills or flat, wide plains called plateaus.

🎯 Exam Tip: Clearly distinguish between lava domes and lava plateaus by mentioning how the acidity or fluidity of the lava affects their final shape.

Caldera

• At times, the eruption of volcano brings about large quantity of material and relieves lot of pressure.
• After the eruption, a large and deep depression remains in that area. This large depression is called caldera.
• These can be around 10 km wide and hundreds of metres deep.
• They may later turn into lakes. Smaller calderas are known as craters.

 

Crater Lake

When the funnel shaped crater of an extinct volcano gets filled with rain water, it forms a crater lake.

 

Volcanic Plug

• It is formed when the lava solidifies in the volcanic neck.
• The surrounding rock material is removed by different agents of erosion; the vent stands predominantly. It is called as volcanic plug.
• The diameter of a plug varies between 300 and 600 metres.
• The Devil’s Tower in Wyoming, United States of America is the best example.

 

Cinder Cone

• Solid material is ejected in large quantity.
• This material consists of ash, cinder and breccias.
• Cinders are half burnt pieces of solid material.
• The solid material is deposited around the mouth until a conical hill with steep slopes is formed.
• For example, cone of Mt. Nuovo in Italy.

 

Composite Cone

• Composite cones are built up of alternate layers of lave and cinder.
• This cone is composed of two materials and therefore it is called a composite cone.
• It is symmetrical in shape.
• For example, Mt. St. Helens, USA.

 

Question 3. Explain the concept of shadow zone.
Answer:
1. The waves which are caused by earthquake are called seismic waves. There are three types of waves: P-waves, S-waves and longitudinal waves.
2. P-waves can pass through all the mediums while S-wave can pass only through solid medium.
3. Even though P-waves pass through all mediums, they experience refraction as they pass from one medium to the other.
4. However, there exist some specific areas where the waves of that earthquake are not reported. Such zone is called ‘shadow zone’.
5. Generally, seismographs located at any distance within 105° from the epicentre, record both P-waves and S-wave. However, beyond 140° P-wave are recorded but not S-waves.
6. Thus, the zone between 105° and 140° is identified as the shadow zone for both types of waves.
7. The entire zone beyond 105° does not receive S-waves. The shadow zone of S-waves is much larger than that of P-waves.
8. The shadow zone of P-waves appears as a band round the earth between 105° and 140° away from the epicentre. This unique pattern helps scientists understand the internal structure and composition of the Earth's core.
In simple words: A shadow zone is an area on the Earth's surface where seismographs cannot detect earthquake waves. This happens because the waves bend or get blocked as they travel through different layers of the Earth.

🎯 Exam Tip: Remember the specific angles for the shadow zones: 105° to 140° is the shadow zone for both P and S waves, while the entire region beyond 105° is the shadow zone for S-waves.

 

Question 4. Write a note on volcanic materials.
Answer: There are three main types of material which come out in volcanic eruptions namely liquid, solid and gaseous form.
Liquid material:
1. It is the molten rock material. When the molten rock material is below the earth’s surface, it is called ‘Magma’.
2. When it appears on the surface it is called ‘lava’. On the basic of percentage of silica, it is classified as:
3. Acidic lava : (a) It contains higher percentage of silica, (b) It has high melting point, (c) It is thick, fluid and moves slowly. These materials provide valuable insights into the composition of the Earth's mantle.
In simple words: Volcanic materials are the substances released during an eruption, which can be liquid (like magma and lava), solid, or gas. Liquid lava is classified based on its silica content, which affects how thick it is and how fast it flows.

🎯 Exam Tip: Clearly distinguish between magma (below the surface) and lava (on the surface) to score full marks on volcanic materials.

Differentiate Between

 

Question 1. Folding and Faulting.
Answer: The primary difference lies in the type of force and the flexibility of the rocks involved.

Folding	Faulting
(i) Folds are bends in the rocks that are due to compressional forces.	(i) Faults are formed due to tensional forces along which displacement of rock takes place.
(ii) Folding occurs when compressional forces are applied to rocks that are ductile or flexible.	(ii) Faults occurs when force operating in opposite direction lead to tension and as a result rocks develops cracks on fissure.

In simple words: Folding happens when rocks bend and wrinkle due to being pushed together. Faulting happens when rocks crack and slide past each other because they are being pulled apart.

🎯 Exam Tip: Clearly highlight the key terms 'compressional forces' for folding and 'tensional forces' for faulting to secure maximum marks.

 

Question 2. Normal fault and Reverse fault.
Answer:

Normal fault	Reverse fault
(i) It results when a portion of landslides down along the fault plane.	(i) It results when a portion of land is thrown upward relative to other side of the land.
(ii) The exposed portion of plane faces the sky.	(ii) The fault plane faces the ground.

In simple words: A normal fault happens when rocks pull apart and one block slides downward, whereas a reverse fault happens when rocks are pushed together and one block is forced upward.

🎯 Exam Tip: Remember that normal faults are caused by tensional forces pulling the crust apart, while reverse faults are caused by compressional forces pushing it together.

 

Question 3. Syncline and Anticline.
Answer:

Syncline	Anticline
(i) As and when limbs slopes towards each other and the central part located at lower elevation forms synclines.	(i) As and when limbs slopes downward with central position getting raised up, it is called anticline.
(ii) They form valleys.	(ii) They form the top / peak of the mountain.
(iii) They have a greater depth.	(iii) They are of a greater height.

In simple words: A syncline is a downward fold in rock layers that forms a valley, while an anticline is an upward fold that forms a ridge or mountain peak.

🎯 Exam Tip: To easily remember the difference, think of the "A" in Anticline as pointing upward like a mountain peak, and the "S" in Syncline as sinking down into a valley.

Question 4. Asymmetrical fold and Symmetrical fold.
Answer:

Asymmetrical fold	Symmetrical fold
(i) The axial plane is inclined.	(i) The axial plane is vertical.
(ii) Limbs are inclined at different angles.	(ii) Limbs are inclined at same angles.
(iii) The height and shape of limbs is not same.	(iii) The height and shape of limbs is same.

These structural differences help geologists determine the direction and intensity of the tectonic forces that acted on the rock layers in the past.
In simple words: A symmetrical fold is perfectly balanced and looks the same on both sides, while an asymmetrical fold is tilted and uneven because of unequal pressure from the sides.

🎯 Exam Tip: Draw a simple line diagram showing a vertical axis for symmetrical folds and a tilted axis for asymmetrical folds to secure full marks.

 

Question 5. Mercalli scale and Richter scale.
Answer:

Mercalli scale	Richter scale
(i) It measures the intensity of earthquake.	(i) It measures the energy released during an earthquake.
(ii) The measurement is based on observed effects.	(ii) The measurement is done with the help of seismograph.
(iii) Quantified from observation of the effects on earth’s surface, human beings, objects and man-made structures.	(iii) Quantified from logarithmic scale obtained by calculating logarithm of the amplitude of waves.
(iv) Unit of measurement I (not felt) to XII (total destruction)	(iv) Unit of measurement from <2.0 to 10.0 + (never recorded) 3.0 earthquake releases 32 times more energy than a 2.0 earthquake.

Both scales are essential for seismologists to comprehensively evaluate both the physical strength and the real-world impact of seismic events.
In simple words: The Mercalli scale measures how much damage an earthquake causes to people and buildings, while the Richter scale measures the actual scientific energy released by the earthquake using instruments.

🎯 Exam Tip: Remember that Mercalli uses Roman numerals (I-XII) for observation, while Richter uses standard numbers (like 2.0, 7.0) for scientific energy measurement.

 

Question 6. Slow movements and Sudden movements.
Answer:

Slow movements	Sudden movements
(i) These movements occur continuously and very slowly over a long period of time.	(i) These movements occur suddenly and violently within a very short period of time.
(ii) They cause major structural changes in the Earth's crust like formation of mountains and plateaus.	(ii) They cause sudden disasters and rapid changes on the Earth's surface.
(iii) Examples: Orogenic (mountain-building) and Epeirogenic (continent-building) forces.	(iii) Examples: Earthquakes and volcanic eruptions.

These internal forces constantly reshape the Earth's topography over different timescales.
In simple words: Slow movements happen over thousands of years to build mountains, while sudden movements happen in seconds to cause earthquakes and volcanic eruptions.

🎯 Exam Tip: Clearly distinguish the time factor (millions of years vs. seconds) and give classic examples like fold mountains for slow movements and earthquakes for sudden movements.

Slow movements	Sudden movements
(i) Slow movement include both vertical and horizontal movement which are caused due to forces deep within the earth.	(i) Sudden movements are caused by sudden endogenic forces coming from deep within the earth.
(ii) These movements are occurring continuously.	(ii) These movement occurs in the form of events.
(iii) Slow movements include formation of mountains and continents.	(iii) Sudden movements include event such as earthquakes and volcanoes.

7. Draw a Neat and Labelled Diagram

 

Question 1. Types of folds
Answer: The different types of folds are:
• Symmetrical fold
• Recumbent fold
• Isoclinal fold
• Overturned fold
• Asymmetrical fold
These distinct folding patterns are primarily determined by the intensity and direction of the compressive forces acting on the rock layers.
In simple words: Folds are bends in the earth's crust caused by squeezing forces. Depending on how they bend and lean, they are classified into different types like symmetrical, recumbent, or overturned folds.

🎯 Exam Tip: Draw clear, wave-like lines to represent each fold type and label them accurately to secure full marks.

 

Question 2. Types of Faults
Answer: The main types of faults are:
• Normal Fault
• Reverse Fault
• Tear (Strike-slip) Fault
These fractures in the Earth's crust occur when rocks break and slide past each other due to intense tectonic stress.
In simple words: Faults are cracks in the earth's crust where blocks of rock have fractured and moved past each other. They can move up, down, or sideways depending on the force.

🎯 Exam Tip: Remember to use arrows in your fault diagrams to show the direction of movement of the rock blocks.

 

Question 2. Types of faults
Answer:
The major types of faults resulting from tectonic forces are:

• Normal fault: Formed due to tensional forces where the hanging wall moves downward relative to the footwall.
• Reverse fault: Formed due to compressional forces where the hanging wall moves upward relative to the footwall.
• Thrust fault: A type of reverse fault with a very low angle of fault plane.
• Tear fault: Formed when rock blocks slide horizontally past each other along the fault plane.

In simple words: Faults are cracks in the Earth's crust where blocks of rock slide past each other. They can move down (normal), up (reverse/thrust), or sideways (tear).

🎯 Exam Tip: When drawing fault diagrams, always use arrows to clearly show the direction of tensional or compressional forces acting on the rock strata.

 

Question 3. Shadow zone
Answer:
The shadow zone is a specific area of the Earth's surface where seismographs do not detect direct seismic waves from an earthquake. This occurs due to the refraction and absorption of waves as they pass through different layers of the Earth's interior:

• Epicenter: The point on the surface directly above the earthquake's focus where seismic waves originate.
• P-wave Shadow Zone: Located between \( 105^\circ \) and \( 140^\circ \) from the epicenter. P-waves are refracted (bent) by the liquid outer core, leaving this band blank.
• S-wave Shadow Zone: Extends beyond \( 105^\circ \) from the epicenter. Since S-waves cannot travel through liquids, they are completely blocked by the liquid outer core.
• Earth's Layers involved: Crust, Mantle, Liquid Outer Core, and Solid Inner Core.

In simple words: A shadow zone is like a blind spot on Earth where earthquake waves cannot be felt or recorded because the Earth's core bends or blocks them.

🎯 Exam Tip: Clearly mention the specific angles (\( 105^\circ \) to \( 140^\circ \) for P-waves and beyond \( 105^\circ \) for S-waves) as these are crucial for scoring full marks.

 

Question 4. Volcanic landforms
Answer: Volcanic landforms are created by the cooling and solidification of lava either on the surface (extrusive) or deep within the crust (intrusive). Extrusive landforms include volcanic cones, craters, calderas, and lava plateaus, while intrusive landforms include batholiths, dykes, sills, and laccoliths.
In simple words: Volcanic landforms are the shapes and structures made when hot molten lava cools down and turns into solid rock, both inside the ground and on the surface.

🎯 Exam Tip: Classify volcanic landforms into intrusive and extrusive categories to present a well-structured and complete answer.

Question. Identify and describe the different types of volcanic landforms shown in the diagrams.
Answer: The various volcanic landforms are:
• Lava Dome: A dome-shaped structure formed by highly viscous lava that piles up around the vent.
• Caldera: A large, basin-like depression formed when the summit of a volcano collapses.
• Crater Lake: A water-filled basin formed within a volcanic crater or caldera.
• Volcanic Plug: A column of solidified lava left standing after the surrounding softer volcanic cone has eroded away.
• Cinder Cone: A simple, steep-sided volcano built from particles and blobs of congealed lava ejected from a single vent.
• Composite Cone: A large, steep volcano built of alternating layers of ash, cinder, and lava flows. These landforms showcase the diverse ways eruptive materials shape our planet's surface.
In simple words: Volcanoes form different shapes on land, like steep hills, wide collapsed bowls, or lakes inside craters, depending on how the lava flows and cools.

🎯 Exam Tip: Memorize the key features of each volcanic cone type, especially the difference between a crater lake and a caldera, as these are frequently asked in exams.

 

Let’s Recall (Textbook Page No. 1)

Observe the Following Pictures in Fig 1.1 and Discuss the Questions

 

Question 1. What might be the reasons behind buildings collapsing in photo 1?
Answer: The major reason behind the buildings collapsing in photo 1 is the occurrence of earthquakes. These sudden movements of the earth's crust release massive energy that shakes the ground violently.
In simple words: Earthquakes shake the ground very hard, which makes weak buildings lose their balance and fall down.

🎯 Exam Tip: Mention 'earthquake' as the primary cause and briefly explain how ground shaking leads to structural failure to secure full marks.

 

Question 2. Which event in depicted in photo 2? What impact does it bring about in the surroundings?
Answer: The volcanic eruption and flowing of lava is depicted in photo 2. Heavy loss of life and property is experienced when the lava flows to the surrounding area, destroying everything in its path.
In simple words: This shows a volcano erupting with hot, melting rock called lava. It is very dangerous because it burns down forests, houses, and harms living things.

🎯 Exam Tip: Clearly state both parts of the answer: identify the event as a volcanic eruption and list its destructive impacts on life and property.

 

Question 3. In photo 3, what could be the reason behind the bend in the rock strata?
Answer: Due to compression of sediments within the earth’s interior and pressure from overlying layers the rock strata seems to be bended. This slow process of folding occurs over millions of years under immense heat and force.
In simple words: Deep inside the Earth, rocks get squeezed from the sides and pushed down by heavy layers above them, making them bend like folded paper.

🎯 Exam Tip: Use key terms like 'compression' and 'pressure' to explain how rock layers bend without breaking.

 

Question 4. What could be the reason behind the difference in altitudes of the land and the steepness of the slope in photo 4?
Answer: The reason could be displacement of rock due to vertical movement. It may form plateau on block mountains. These vertical movements are caused by internal forces deep within the Earth.
In simple words: When the Earth's crust moves up or down, it pushes rocks out of place. This can create flat-topped hills called plateaus or steep block mountains.

🎯 Exam Tip: Clearly mention 'vertical movement' and 'displacement of rock' as these are key geological terms that examiners look for.

 

Question 5. Classify the events in the photos into sudden and slow movements.
Answer: Sudden movements are earthquake and volcanoes in photo 1 and 2. Slow movements are formation of folds and formation of plateaus or block mountains in photo 3 and 4. Slow movements take thousands of years to show visible changes on the surface.
In simple words: Some Earth movements like earthquakes happen in seconds, while others like mountain building take millions of years.

🎯 Exam Tip: Create a clear distinction between sudden and slow movements by using examples from the photos provided in your textbook.

 

Question 6. Example of which of these movements is not likely to be found in the mainland of Indian sub- continent?
Answer: The volcanic eruptions are not found in mainland of India sub-continent. Active volcanoes are generally absent in this region, except for Barren Island in the Andaman Sea.
In simple words: You will not find active volcanoes on the mainland of India because the tectonic plates there are relatively stable.

🎯 Exam Tip: Remember to specify 'mainland' of India, as India does have an active volcano on Barren Island which is an offshore territory.

 

2. On 19th August, 2018, around 300 people died in Indonesia. Many buildings collapsed. Many roads broke apart. A tsunami was generated. (Textbook Page No. 6)

 

Question 1. What was the cause behind these events?
Answer: Collision of tectonic plates was the causes behind the events. This collision releases a massive amount of energy that shakes the ground above.
In simple words: The disaster happened because huge slabs of the Earth's crust crashed into each other deep underground.

🎯 Exam Tip: Always link tectonic plate movement or collision directly to the occurrence of earthquakes and tsunamis.

 

Question 2. What actually happened during this natural event?
Answer: A very high intensity earthquake struck north eastern parts of Indonesian coastline, where subsequent landslides into sea triggered tsunamis. The sudden displacement of water created massive waves that flooded the coast.
In simple words: A powerful earthquake shook the coast, causing underwater landslides that pushed the ocean water into giant, destructive waves.

🎯 Exam Tip: Explain the sequence of events clearly: first the earthquake, then the landslide, and finally the tsunami.

 

Question 3. Name the energy waves involved in this natural event.
Answer: Tsunamis were involved in this natural event where the tectonic plates moved horizontally. These seismic waves travel rapidly across the deep ocean before building into massive waves near the coast.
In simple words: The energy waves created by the sudden horizontal movement of tectonic plates under the ocean generate powerful tsunami waves.

🎯 Exam Tip: Clearly mention the horizontal movement of tectonic plates as the primary cause of these energy waves to score full marks.

 

Question 4. Observe the diagram in fig. 1.9 and label the boxes.
Answer: The labels for the boxes in the diagram are:
• Earth's surface (on the top left)
• Epicentre (on the top right)
• Focus (the point of origin inside the Earth)
• Primary waves (traveling outwards from the focus)
• Secondary waves (slower waves traveling from the focus)
• Surface waves (traveling along the surface)
In simple words: This diagram shows how an earthquake starts at the focus deep underground, sends out different types of waves, and affects the epicentre on the surface.

🎯 Exam Tip: Practice drawing and labeling the focus and epicentre, as examiners frequently ask to distinguish between these two points.

 

Think About It

 

Question 1. How will compressional forces affect brittle rocks? (Textbook Page No. 3)
Answer: Compressional forces acting on brittle rocks cause them to fracture or fault rather than fold. This leads to the displacement of rock strata along fault lines, often resulting in the formation of block mountains or rift valleys.
In simple words: When hard, brittle rocks are squeezed by strong forces, they do not bend; instead, they crack and break, creating faults.

🎯 Exam Tip: Remember that brittle rocks fracture under compression, whereas ductile rocks fold. Use the keyword 'faulting' to secure maximum marks.

Question 1. What is the effect of compressional forces on brittle rocks?
Answer: The compressional forces will break the brittle rocks into pieces. This happens because brittle rocks cannot withstand high pressure without fracturing.
In simple words: When you squeeze hard, easily breakable rocks, they will crack and break into smaller pieces instead of bending.

🎯 Exam Tip: Clearly state the relationship between the type of force (compressional) and the nature of the rock (brittle) to score full marks.

 

Question 2. 'A mountain never remains a mountain'. Can you relate this idiom with the mountain building process? (Textbook Page No. 4)
Answer: This happens because of continuous erosional activities taking place on the mountain sides. Running water, glaciers, wind, and volcanic activities keep on changing the surface of a mountain, gradually wearing it down over millions of years.
In simple words: Mountains are constantly being worn down by wind, rain, and ice, meaning their shape and height are always slowly changing.

🎯 Exam Tip: Mention external agents of erosion like wind, water, and glaciers as the primary reasons for the changing shape of mountains.

 

Question 3. When can faults form in fold mountains? (Textbook Page No. 6)
Answer: If compression takes place along the faults, folds can be formed. Additionally, when the pressure exceeds the bearing capacity of the folded rock layers, fractures or faults develop within them.
In simple words: When rocks are pushed together too hard, they first bend into folds, but if the pushing continues, they will crack and form faults.

🎯 Exam Tip: Remember that folding occurs due to compression, but extreme compression leads to faulting even in fold mountains.

 

Question 4. Can folds form into block mountains? Find the reason and discuss. (Textbook Page No. 6)
Answer: No, folds cannot form into block mountains because folding takes place due to compression of elastic rocks and block mountains are formed due to displacement of rocks owing to tension. These two processes are geologically distinct and occur under different stress conditions.
In simple words: No, because folding happens when rocks are pushed together, while block mountains are made when rocks are pulled apart and crack.

🎯 Exam Tip: Contrast the forces involved: folding is caused by compressional forces, whereas block mountains are caused by tensional forces.

 

Question 5. Look at fig.1.10 and answer following questions. During an earthquake, do you think the seismic waves reach entire portion of the earth. Is there any region on the earth’s surface where a given earthquake will not be reported? (Textbook Page No. 6)
Answer: It’s the shadow zone of P-waves and S-waves where the seismic waves do not reach. No, there is no region on the earth’s surface where a given earthquake is not reported, except for these specific shadow zones where seismographs do not record them.
In simple words: Seismic waves do not reach every single part of the Earth because some areas, called shadow zones, block or bend these waves.

🎯 Exam Tip: Use the term "shadow zone" and specify that it applies to both P-waves and S-waves to get maximum marks.

 

Question 6. Why has the shadow zone for L-waves not been shown in fig 1.10? (Textbook Page No. 6)
Answer: L-waves are surface waves that travel only along the earth's crust and do not pass through the deep interior of the earth. Since they do not travel through the core, they do not produce a deep interior shadow zone like P-waves and S-waves.
In simple words: L-waves only travel along the surface of the Earth, so they don't go deep inside to create a shadow zone.

🎯 Exam Tip: Explain that L-waves are surface waves, which distinguishes them from body waves (P and S waves) that travel through the Earth's interior.

Question 7. Why do L-waves not form a shadow zone?
Answer: L-waves travel through the circumference of the earth. Thus, they do not form a shadow zone.
In simple words: L-waves travel along the Earth's surface rather than through its deep interior, so they do not get blocked or bent by the core to create a shadow zone.

🎯 Exam Tip: Remember that surface waves (L-waves) ripple along the crust, which is why they don't have a shadow zone like body waves (P and S-waves) do.

Try This

 

Question 1. Observe the diagrams in fig. 1.5. Try to understand the different types of fold shown in the diagram. Write the name of the fold. (Textbook Page No. 4)
Answer:
1. Symmetrical fold
2. Isoclinal fold
3. Asymmetrical fold
4. Recumbent fold
5. Overturned fold
In simple words: Folds are bends in the Earth's crust caused by compression, and they are classified into different types like symmetrical or overturned based on how tilted or compressed their sides are.

🎯 Exam Tip: Clearly label each fold type with its corresponding number from the diagram to ensure you get full marks. Key terms like 'symmetrical' and 'recumbent' are highly looked for by examiners.

 

Question 2. Observe the diagram in fig. 1.6 and read the explanation regarding the characteristics of various faults given. Identify the faults and match each of them.
Answer:
1. Normal Fault: Occurs when rocks pull apart due to tension, causing one block to slide down.
2. Reverse Fault: Occurs when rocks are compressed together, pushing one block upward over the other.
3. Strike-slip (Tear) Fault: Occurs when rock blocks slide horizontally past each other with little vertical movement.
4. Thrust Fault: A specific type of reverse fault where the angle of the fault plane is very low.
In simple words: Faults are fractures in the Earth's crust where movement occurs, and they are classified as normal, reverse, strike-slip, or thrust depending on the direction the rocks move.

🎯 Exam Tip: Always associate 'tension' with normal faults and 'compression' with reverse faults, as these are the primary forces driving fault development.

Question 1. Identify the types of faults shown in the diagram (A, B, C, and D) with their characteristics.
Answer: The faults shown in the diagram are classified as follows:
A – Normal fault
B – Reverse fault
C – Thrust fault
D – Tear fault. These distinct fault lines represent different ways in which the Earth's crust fractures and moves under tectonic stress.
In simple words: This diagram shows four different ways rocks can break and slide past each other when tectonic forces push or pull the Earth's crust.

🎯 Exam Tip: Clearly label each fault type with its corresponding letter and draw simple arrows to show the direction of displacement to secure full marks.

 

Can You Tell? (Textbook Page No. 7)

 

Question 2. In fig 1.10 textbook page 6 A, B, C are three points on the earth’s surface. Analyse their location with respect to epicentre and shadow zones.
Answer: A, B, C are the points on the surface of the earth.
(i) ‘A’ point is located with 105° from the epicentre, therefore P waves and S waves reach at ‘A’ point. The seismograph at ‘A’ point records both waves, therefore ‘A’ point is not in shadow zone.
(ii) ‘B’ point is in shadow zone because both the waves do not reach there. P waves pass through all mediums, they experience refraction as they pass on one medium to another, which prevents them from reaching this specific zone.
In simple words: Point A receives both types of earthquake waves because it is close to the epicenter, while Point B is in a shadow zone where waves cannot reach because they get bent or blocked as they travel through the Earth.

🎯 Exam Tip: Remember that the shadow zone for S-waves is larger than that for P-waves because S-waves cannot travel through the liquid outer core.

 

Question 1. On the basis of the intensity of damage risk, India is classified into five risk zone. Use the given weblink http://www.bmtpc.org/DataFiles/CMS/file/map%20of%20india/eq-india.pdf and complete the table given. (Textbook Page No. 9)
Answer:

Zone	Degree of Risk	States / UTs
I	Least	–
II	Low	–
III	Moderate	–
IV	High	Jammu & Kashmir. Himachal Pradesh, Uttarakhand, Sikkim, Parts of Indo Gangetic plains (North Punjab, Chandigarh, Western Uttar Pradesh) Delhi, Maharashtra, Bihar.
V	Very High	Region of Kashmir, Andaman and Nicobar island.

In simple words: This table groups different regions of India into five zones based on how likely they are to experience earthquake damage, ranging from Zone I with the lowest risk to Zone V with the highest risk.

🎯 Exam Tip: Memorize the states that fall under high-risk zones (Zone IV and V) as these are frequently asked in map-pointing and short-answer questions.

Read the Following Passage About Krakatoa Volcanic Eruption and Answer the Following Questions (Textbook Page No. 10)

There is an island known as Krakatoa between the islands of Java and Sumatra in Indonesia. There were frequent volcanic eruptions here. From May 1883, massive explosions began. The eruption that took place at about 10 in the morning on 28 August 1883 was the largest ever recorded explosion. As a result of this explosion,

The entire island disappeared. During this eruption, rock particles and dust thrown up in the atmosphere was about \( 25 \text{ km}^3 \). The column of this dust-ash rose as high as \( 80 \text{ km} \).

The discharge of Krakatoa threw into the air nearly \( 21 \text{ km}^3 \) of rock fragments, and large quantities of ash fell over an area of some \( 800,000 \text{ km}^2 \). Near the volcano, masses of floating pumice, were so thick that ships had to halt. The surrounding region was plunged into darkness for two and a half days because of ash in the air. For some years after this, cloud kept moving round the earth. About 36,000 people died in these eruptions and the tsunami waves created by it.

In 1927, volcanic eruptions began at the same place and a new island rose in place of the Krakatoa island that had vanished. It was named 'Anak Krakatoa' or 'Child Krakatoa'. The volcano here constantly emits ash and steam. This new island has now become a laboratory for geologists and biologists.

 

Question 1. Make a list of materials that came out during eruptions.
Answer: Rock, particles, dust, ash, floating pumice, steam were the materials that came out during eruption. These substances are ejected with great force from deep within the Earth.
In simple words: The materials that come out of a volcano during an eruption include rocks, dust, ash, floating pumice, and steam.

🎯 Exam Tip: Mention all the materials listed in the text, such as ash, pumice, and steam, to ensure you get full marks.

 

Question 2. Classify them into liquid, solid and gaseous forms.
Answer: The classification of the erupted materials based on their physical state is shown in the table below:

Liquid	Solid	Gaseous
Pumice	Rock particles	Steam
	Dust
	Ash

In simple words: We can group volcanic materials into solids like dust and ash, liquids like pumice, and gases like steam.

🎯 Exam Tip: Draw a neat table with clear headings for liquid, solid, and gaseous states to present your classification clearly.

 

Find Out! (Textbook Page No. 9)

 

Question. Find out examples of active, dormant and extinct volcanoes.
Answer: Examples of active volcanoes are – Mt. Etna (Italy), Stromboli (Italy), Mt. Merapi (Indonesia). These active volcanoes erupt frequently and release lava, gases, and ash into the environment.
In simple words: Active volcanoes are those that erupt regularly, and some famous examples include Mt. Etna and Stromboli in Italy, and Mt. Merapi.

🎯 Exam Tip: Always write the country name in brackets next to the volcano's name to show precise geographical knowledge.

Volcano Examples

Active Volcanoes: (Indonesia), Erta Ale (Ethiopia), Mt. Erebus (Antarctica)
Examples of dormant volcanoes – Mt. Kilimanjaro (Africa), Mt. Katmai (Alaska)
Examples of extinct volcanoes – Mt. Egmont (New Zealand), Chimborazo (Ecuador), Mt. Kulal (Kenya)

 

Give It A Try (Textbook Page No. 8)

 

Question. Take the given hypothetical data in the table. The data shows the time of arrival of P-waves and S-waves at 3 seismograph stations. Assume the scale of the map as \( 1\text{ cm} : 18\text{ km} \). See fig. 1.11.

Recording Station	P-wave arrival time (IST)	S-wave arrival time
Jalana	11 : 06 : 06	11 : 06 : 19
Washim	11 : 06 : 46	11 : 07 : 03
Aurangabad	11 : 07 : 06	11 : 07 : 24

Answer:
Speed of waves = 08 kms per second
Scale of the map = \( 1\text{ cm} = 18\text{ kms} \)
First step: Find out the difference in time for waves at Jalana recording centre.
Difference in time of waves = Time of S-wave – Time of P-wave
11 : 06 : 19 (Time of S-wave)
11 : 06 : 06 (Time of P-wave)
= (Time of S-wave) – (Time of P-wave)
= 11 : 06 : 19 – 11 : 06 : 06
= 00 : 00 : 13
Therefore difference in time for waves at Jalana recording centre is 13 seconds. This calculation helps us determine the exact time lag between the primary and secondary seismic waves.
Second Step: Find out distance on land between Jalana and Epicentre
Distance on land = Difference in time of waves \(\times\) speed of waves per second
= \( 13 \times 8 \)
= 104
Therefore distance on land between Jalana and Epicentre is 104 km.
In simple words: To find how far the earthquake's center is, we first calculate the time gap between the fast P-waves and slower S-waves. By multiplying this time difference by the speed of the waves, we get the actual distance on land.

🎯 Exam Tip: Always write down the formula for calculating the time difference and distance clearly before substituting the values to ensure you get step-wise marks.

Third Step: Find Out Radius for Jalana Station

Jalana – Radius of circle = \( \frac{\text{Distance on land}}{\text{Scale of the map}} \)
\( = \frac{104}{18} \)
\( = 5.7 \text{ cm} \)

Therefore radius of circle around Jalana station is 5.7 cm.

Now find out radium for remaing stations.

Jalana – 5.7 cm, Washim – 7.5 cm, Aurangabad – 8 cm.

Fouth Step: Now Draw Circles Around Jalana, Washim and Aurangad with the Help of Radius Calculated

All arcs of circle will intersect one another at a particular point. That point is the location of Epicentre.

In the map given below Epicentre is to the south of Mudgal.

Map Locations Shown:

• Washim
• Jafrabad
• Khultabad
• Jalana
• Lonar
• Aurangabad
• Hingoli
• Gangapur
• Jintur
• Ambad
• Nevasa
• Paithan
• Ghansawangi
• Takli Ambad
• Parbhani
• Shevgaon
• Gevrai
• Pathri
• Mudgal
• Beed

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