Maharashtra Board Class 9 Geography Chapter 3 Exogenetic Movements Part 1 Solutions

Exogenetic Movements Part 1 Class 9 Questions And Answers Maharashtra Board

Class 9 Geography Chapter 3 Exogenetic Movements Part 1 Questions And Answers Maharashtra Board

Geography Class 9 Chapter 3 Question Answer Maharashtra Board

1. Answer in brief.

Question 1. (a) What is mechanical weathering?
Answer:
1. The disintegration of rocks without any change in their chemical composition is called mechanical weathering.
2. The minerals in the rocks expand because of heat and contract when the temperature decreases. Due to such continuous contracting and expansion, tension develops in the rock particles.
3. Each mineral reacts differently to the temperature; some minerals expand more, while others do not expand as much. Consequently, the tension formed in the rocks also increases and decreases. As a result, cracks develop in the rocks and they break.
4. In areas where the temperatures drop below 0°C for quite some time, the water accumulated in the cracks and crevices in the rocks freezes. Its volume increases which leads to tension in the rocks and they shatter.
5. When the alkaline water of the sea fills in the cracks of the rocks, the soluble minerals in the rock get dissolved leading to the formation of small holes in the rocks.
6. Because of the heat, this water turns into water vapour and only crystals of alkaline materials remain in the rocks. Crystals occupy more space which causes tension in the rock.
7. Sometimes the outer layers of the rocks exert pressure on the inner or lower layers. When this pressure ceases to exist, the lower or inner layers get freed from the pressure. This also leads to weathering.
8. In areas of heavy rainfall soaking of rock water also causes weathering of some rocks like sandstone and conglomerate. When water penetrates such rocks, the particles get loose and separate from the main rock.
In simple words: Mechanical weathering breaks down rocks physically without changing their chemical makeup. This happens due to temperature changes causing expansion and contraction, freezing water in cracks, crystal growth, and pressure release, leading to cracks and shattering.

🎯 Exam Tip: Focus on the different physical processes like thermal expansion, frost wedging, and salt crystal growth as key mechanisms for mechanical weathering.

 

Question 1. (b) What are the main types of chemical weathering?
Answer:
The process of decomposition of rocks due to changes in their chemical composition is called chemical weathering.
Its main types are:
(i) Carbonation
• When the rain water mixes with the carbon dioxide in the atmosphere it leads to the formation of dilute carbonic acid.
• Many rocks like limestone get easily dissolved in such acids.
(ii) Solution
• Some minerals in the rock get dissolved in water.
• Because of this solution, alkalis in the rock dissolve and make them brittle.
(iii) Oxidation
• This process occurs in rocks which have iron present in them. The iron in the rock comes in contact with water and a chemical reaction takes place between iron and oxygen.
• Hence, a reddish coloured layer forms on the rocks. This is called rust.
• It occurs in rocks in areas with high rainfall.
In simple words: Chemical weathering involves the breakdown of rocks through chemical reactions, changing their composition. Key types include carbonation (acid rain dissolving rocks), solution (minerals dissolving in water), and oxidation (iron in rocks reacting with oxygen and water, causing rust).

🎯 Exam Tip: Understand the role of water, carbon dioxide, and oxygen in chemical reactions that alter rock composition. Examples like rusting for oxidation are important.

 

Question 1. (c) How does biological weathering occur?
Answer:
• It is the process by which rocks are broken into small fragments and fine particles due to the action of plants, animals and human beings.
• The roots of the plants enter the points and cracks of the rocks in search of moisture.
• As the roots grow bigger, they create tension in the rocks and start breaking them.
• Animals such as mice, rabbits and rats dig holes, anthills etc. and weaken the rock, which makes them loose and break into pieces.
• Besides these, algae, moss1, lichen2, other flora grow in the rocks. They also help in weathering.
• Thus, the weathering caused by living organisms is called biological weathering,
In simple words: Biological weathering is the breakdown of rocks by living organisms like plants, animals, and microbes. Plant roots grow into cracks, animals burrow, and organisms like algae weaken rock structures, causing them to break apart.

🎯 Exam Tip: Remember that biological weathering involves both physical (roots, burrowing) and sometimes chemical (microbial secretions) actions of living things on rocks.

 

Question 1. (d) Distinguish between weathering and mass wasting.
Answer:

Weathering	Mass Wasting
(i) Breaking or weakening of rocks is called as weathering.	(i) When weathered rock material moves down the slopes due to gravity and accumulate near the foothills or gentle slopes, it is mass wasting.
(ii) Weathering is of three types - Mechanical, Chemical and Biological.	(ii) Mass wasting is of two types - Rapid and Slow.

In simple words: Weathering is the process where rocks break down or weaken in place. Mass wasting, on the other hand, is the movement of these weathered materials down a slope due to gravity, accumulating at the base.

🎯 Exam Tip: Distinguish between the 'in-situ' breakdown (weathering) and the 'movement' of material (mass wasting). Understanding their causes and types is crucial.

 

2. Write whether the statements are true or false. Correct the incorrect ones.

Question 2. (a) Climate affects earthquakes.
Answer:
False - Internal movements affect (leads to) earthquakes.
In simple words: This statement is false because earthquakes are caused by internal forces and movements within the Earth's crust, not by climate. Climate influences surface processes like weathering, but not seismic activity.

🎯 Exam Tip: Remember that earthquakes are endogenetic processes (from within the Earth), while climate influences exogenetic processes (on the Earth's surface).

 

Question 2. (b) Mechanical weathering is less effective in humid climates.
Answer:
True
In simple words: This statement is true because humid climates typically have less extreme temperature fluctuations and less freeze-thaw action, making mechanical weathering, which relies heavily on these, less dominant compared to chemical weathering.

🎯 Exam Tip: Associate mechanical weathering with arid and cold regions (large diurnal temperature range, freeze-thaw cycles) and chemical weathering with hot and humid regions.

 

Question 2. (c) Mechanical weathering happens on a large scale in dry climates.
Answer:
True
In simple words: This statement is true because dry climates often experience significant daily temperature swings, leading to repeated expansion and contraction of rocks, which is a major driver of mechanical weathering.

🎯 Exam Tip: Arid (dry) regions are prime locations for mechanical weathering due to intense heating and cooling cycles that stress rock structures.

 

Question 2. (d) The breaking down of rocks into smaller particles is called weathering.
Answer:
True
In simple words: This statement is true as weathering is precisely the process by which rocks and minerals are broken down into smaller pieces or altered on the Earth's surface.

🎯 Exam Tip: This is a fundamental definition. Ensure you understand that weathering is about breaking down rocks 'in situ' (in place).

 

Question 2. (e) Lateritic rocks are formed through exfoliation.
Answer:
False - Lateritic rocks are formed due to oxidation.
In simple words: This statement is false. Lateritic rocks, rich in iron and aluminum oxides, are formed through intense chemical weathering (specifically oxidation and leaching) in hot, humid climates, while exfoliation is a mechanical weathering process.

🎯 Exam Tip: Differentiate between the formation of rock types (like laterite from oxidation) and the processes of rock breakdown (like exfoliation for mechanical weathering).

 

3. Complete the flowchart below.

ℹ️ चित्र व्याख्या (Diagram Explanation): यह प्रवाहचार्ट (flowchart) 'अपक्षय प्रक्रिया' (Weathering process) के विभिन्न प्रकारों को दर्शाता है। यह यांत्रिक अपक्षय (Mechanical Weathering), रासायनिक अपक्षय (Chemical Weathering) और जैविक अपक्षय (Biological Weathering) को उनके संबंधित उप-प्रक्रियाओं के साथ वर्गीकृत करता है, जैसे कि ब्लॉक विघटन, अपपर्णन, कार्बोनेशन, घोल, ऑक्सीकरण, जानवरों द्वारा बिल बनाना और पेड़ों की जड़ें।

Answer:

Weathering Process
Mechanical Weathering	Chemical Weathering	Biological Weathering
Block Disintegration	Carbonation	Burrowing by animals
Exfoliation	Solution	Roots of the trees
	Oxidation

In simple words: This flowchart illustrates the three main types of weathering: Mechanical (physical breakdown), Chemical (alteration of rock composition), and Biological (action of living organisms), along with their specific sub-processes.

🎯 Exam Tip: Practice drawing and labeling flowcharts for weathering processes. Understanding the categories and examples for each type is crucial for comprehensive answers.

 

4. Identify the type of weathering from the given description.

Question 4. (a) Some animals live inside the grounds by making burrows.
Answer:
(a) Biological weathering
In simple words: When animals create burrows in the ground, they physically break apart rock and soil, which is a form of biological weathering.

🎯 Exam Tip: Any action by living organisms (plants, animals, microbes) that breaks down rocks falls under biological weathering.

 

Question 4. (b) The rock rusts.
Answer:
(b) Chemical weathering
In simple words: Rusting occurs when iron in rocks reacts with oxygen and water, changing its chemical composition, thus it is a type of chemical weathering.

🎯 Exam Tip: Rust is a classic example of oxidation, which is a key process within chemical weathering.

 

Question 4. (c) Water which has accumulated in the crevices of the rocks freezes. Consequently, the rock breaks.
Answer:
(c) Mechanical weathering
In simple words: When water freezes in rock cracks, it expands and exerts pressure, physically breaking the rock without changing its chemical makeup, which is mechanical weathering (specifically frost wedging).

🎯 Exam Tip: Frost wedging, where freezing water expands and breaks rocks, is a prime example of mechanical weathering, especially in cold regions.

 

Question 4. (d) The pipes supplying water in colder regions break.
Answer:
(d) Mechanical weathering
In simple words: The breaking of pipes due to water freezing and expanding inside them is an analogy for the physical process of frost wedging, a type of mechanical weathering.

🎯 Exam Tip: Understand the principle of water expansion upon freezing; this physical process, whether in rocks or pipes, is mechanical.

 

Question 4. (e) Sand formation occurs in deserts
Answer:
(e) Mechanical weathering
In simple words: Sand formation in deserts often results from physical breakdown of rocks due to extreme temperature changes and wind abrasion, both being forms of mechanical weathering.

🎯 Exam Tip: Desert environments with large diurnal temperature ranges and strong winds are conducive to mechanical weathering processes that break rocks into sand grains.

 

Class 9 Geography Chapter 3 Exogenetic Movements Part 1 Intext Questions and Answers

Can You Tell?

Question 1. (1) See the given pictures. Observe the physical appearance of the rocks in each picture. You can see that rocks are broken, fractured and have holes in them. In a picture you can also see that the statue has been deformed. Why are the rocks in such a condition? Think about them and briefly tell the reasons you can think of. Discuss the reasons. Check with the teachers if your reasons are relevant.

ℹ️ चित्र व्याख्या (Diagram Explanation): यह प्रश्न छात्रों को काल्पनिक चित्रों का अवलोकन करने के लिए प्रेरित करता है जो चट्टानों को टूटा हुआ, फ्रैक्चर वाला और उनमें छेद दिखाते हैं, साथ ही एक विकृत मूर्ति भी। इसका उद्देश्य छात्रों को इन दृश्यों के पीछे के कारणों पर विचार करने और अपक्षय प्रक्रियाओं (यांत्रिक, रासायनिक, जैविक) से संबंधित उनके ज्ञान का उपयोग करके इन भूगर्भीय परिवर्तनों की व्याख्या करने के लिए प्रोत्साहित करना है।

Answer:
• At some places the day temperatures are very high and the night temperatures are very low. In the given pictures the rocks may have broken due to temperature variation during day time and night time.
• In coastal areas when the sea waves hit the rocks, the rocks fracture and break down.
• Due to the roots of trees, and activities of burrowing animals like ant, rats etc. in the soft rocks, the rocks break down.
• The statues might be deformed due to heat and humidity.
In simple words: The rocks and statues show damage like breaks, fractures, holes, and deformation due to various weathering processes. These include thermal stress from day-night temperature changes, physical force from sea waves, biological action by plant roots and burrowing animals, and chemical changes from heat and humidity.

🎯 Exam Tip: When analyzing visual evidence of weathering, consider the climate, local environment (e.g., coast, forest), and the potential for mechanical, chemical, and biological agents to cause the observed changes.

 

Lets Recall

Question 1. Have you seen the process of biological weathering3 around you?
Answer:
I have seen process of biological weathering3 around me. Many plants and trees have grown in an old dilapidated building which is located near my house. The roots of the trees have broken the walls and slabs of the building at many places.
In simple words: Yes, biological weathering is visible when plants grow on old buildings, as their expanding roots can crack and break the walls and slabs.

🎯 Exam Tip: Practical examples from your surroundings, like plants growing on walls, help illustrate geological concepts like biological weathering clearly.

 

Class 9 Geography Chapter 3 Exogenetic Movements Part 1 Additional Important Questions and Answers

Complete the statements choosing the correct option from the bracket:

Question 1. _________ is formed due to chemical precipitation between water and alkalis.
(a) Limestone
(b) Sandstone
(c) Coal
(d) Iron
Answer: (a) Limestone
In simple words: Limestone is formed when minerals, often in the presence of water and alkalis, chemically precipitate and settle out of solution.

🎯 Exam Tip: Remember that chemical precipitation is a key process for the formation of certain sedimentary rocks like limestone.

 

Question 2. _________ process occurs in rocks which have iron present in them.
(a) Shattering
(b) Oxidation
(c) Carbonation
(d) Granular
Answer: (b) Oxidation
In simple words: Oxidation is the chemical process where iron-containing rocks react with oxygen, often in the presence of water, leading to the formation of rust.

🎯 Exam Tip: Oxidation is a common chemical weathering process, easily identified by the reddish-brown coloration (rust) it imparts to rocks containing iron.

 

Question 3. Sometimes the weathered materials do not move downward but sink 'in situ'. This is called _________
(a) carbonation
(b) exfoliation
(c) precipitation
(d) slumping
Answer: (d) slumping
In simple words: Slumping refers to a type of mass movement where a mass of weathered material moves downslope as a coherent block, often rotating on a concave slip surface, without disintegrating completely.

🎯 Exam Tip: Slumping is a specific type of mass wasting characterized by a rotational movement of a coherent mass of material on a slope.

 

Question 4. In periglacial regions along the slopes, small layers of soil accumulate because of the movement of soil. This is called _________
(a) soil erosion
(b) solifluction
(c) shattering
(d) block disintegration
Answer: (b) solifluction
In simple words: Solifluction is a slow flowage of saturated soil and regolith down a slope, especially in periglacial environments where freezing and thawing occur.

🎯 Exam Tip: Solifluction is a distinct type of slow mass movement linked to periglacial environments and the saturation of soil above permafrost.

 

Question 5. Biological weathering occurs because of _________
(a) high temperatures
(b) frost
(c) crystal growth
(d) living organisms
Answer: (d) living organisms
In simple words: Biological weathering is exclusively caused by the actions of living organisms, such as plants, animals, or microorganisms.

🎯 Exam Tip: Biological weathering is unique because it involves organic activity, unlike mechanical (physical forces) or chemical (chemical reactions) weathering driven by inanimate factors.

 

Question 6. Some minerals in the rock get dissolved in water and undergo chemical weathering. This process is called _________
(a) solution
(b) carbonation
(c) exfoliation
(d) precipitation
Answer: (a) solution
In simple words: When minerals in a rock dissolve in water, forming a solution that alters the rock's composition, this process is known as solution weathering.

🎯 Exam Tip: Solution is a direct form of chemical weathering where soluble minerals are removed from the rock by water.

 

Question 7. When dilute carbonic acids reacts with the minerals in the rocks the process is called as _________
(a) carbonation
(b) exfoliation
(c) precipitation
(d) slumping
Answer: (a) carbonation
In simple words: Carbonation is a chemical weathering process where carbonic acid, formed from CO2 and water, reacts with rock minerals, particularly calcium carbonate, leading to their dissolution.

🎯 Exam Tip: Carbonation is a chemical weathering process specifically involving carbonic acid, which is key to dissolving carbonate rocks like limestone.

 

Question 8. When the outer layers of the rock fall apart from the main rock due to difference in temperatures, the process is called _________
(a) shattering
(b) oxidation
(c) exfoliation
(d) carbonation
Answer: (c) exfoliation
In simple words: Exfoliation is a mechanical weathering process where outer layers of rock peel off like an onion skin due to pressure release or thermal expansion and contraction.

🎯 Exam Tip: Exfoliation, often forming rounded rock surfaces, is a clear sign of mechanical weathering related to temperature changes or pressure unloading.

 

Question 9. _________ is a universal solvent1.
(a) Soil
(b) Water
(c) Carbon
(d) Oxygen
Answer: (b) Water
In simple words: Water is known as a universal solvent because of its ability to dissolve more substances than any other liquid, playing a crucial role in chemical weathering.

🎯 Exam Tip: Water's property as a universal solvent makes it central to many chemical weathering processes, facilitating reactions and dissolving minerals.

 

Question 10. Alkalis in the rock dissolve because of the solution and make them _________
(a) even
(b) sturdy
(c) brittle
(d) crusty
Answer: (c) brittle
In simple words: When alkalis in rocks dissolve through the process of solution, it weakens the rock's structure, causing it to become brittle and prone to breakage.

🎯 Exam Tip: The dissolution of minerals, including alkalis, through chemical weathering ultimately weakens the rock, making it brittle and susceptible to further breakdown.

 

Match the Column:

Question 1. I.
Answer:

Column 'A'	Column 'B'
(1) Mechanical weathering	(b) frost
(2) Chemical weathering	(c) carbonation
(3) Biological weathering	(a) burrowing

In simple words: Mechanical weathering is associated with frost action, chemical weathering with carbonation, and biological weathering with animal burrowing.

🎯 Exam Tip: Clearly link each weathering type with its characteristic process or agent (e.g., mechanical-frost, chemical-carbonation, biological-burrowing).

 

Question 1. II.
Answer:

Column 'A'	Column 'B'
(1) Oxidation	(c) Chemical reaction between iron and oxygen
(2) Slumping	(d) Weathered material which sink in situ
(3) Solifluction	(a) Mass movement occurring slowly

In simple words: Oxidation is a chemical reaction of iron with oxygen, slumping is the sinking of weathered material in place, and solifluction is a slow mass movement.

🎯 Exam Tip: Precisely match geological terms with their definitions to score full marks in 'match the column' questions.

 

Answer in one sentence each;

Question 1. What are the Exogenetic processes?
Answer:
Exogenetic processes are external processes 1 that occur on or above the earth's surface, E.g. weathering, erosion, transportation, deposition etc.
In simple words: Exogenetic processes are external forces acting on the Earth's surface that cause breakdown, movement, and deposition of materials, like weathering and erosion.

🎯 Exam Tip: Remember that exogenetic processes are external, surface-level processes, contrasted with endogenetic processes which originate from within the Earth.

 

Question 2. Explain the Process of weathering
Answer:
Breaking or weakening of rocks is called as weathering.
In simple words: Weathering is the natural process where rocks break down or weaken into smaller fragments or altered forms while remaining in their original place.

🎯 Exam Tip: A concise definition of weathering emphasizing 'in-situ' breakdown is crucial.

 

Question 3. What is Mechanical Weathering?
Answer:
The disintegration of rocks without any change in their chemical composition is called mechanical weathering.
In simple words: Mechanical weathering is the physical breakdown of rocks into smaller pieces without any change in their chemical makeup.

🎯 Exam Tip: The key differentiator for mechanical weathering is the *absence* of chemical change in the rock's composition.

 

Question 4. What is Chemical Weathering (Salt Weathering)?
Answer:
The process of decomposition of rocks due to changes in their chemical composition is called chemical weathering.
In simple words: Chemical weathering is the decomposition of rocks where their internal chemical composition is altered, often through reactions with water, oxygen, or acids.

🎯 Exam Tip: For chemical weathering, focus on the *change in chemical composition* as the defining characteristic.

 

Question 5. What do you mean by Biological Weathering?
Answer:
The weathering process caused by human beings, animals and plants is called biological weathering.
In simple words: Biological weathering is the breakdown of rocks caused by the activities of living organisms, including plants, animals, and humans.

🎯 Exam Tip: Clearly state that biological weathering involves *living organisms* as the agents of rock breakdown.

 

Question 6. What is Slumping?
Answer:
Sometimes the weathered materials do not move downward but sink 'in situ' (where they are). This is called slumping.
In simple words: Slumping is a type of mass movement where a block of weathered material moves down a slope with a rotational motion, often leaving a distinct curved slip surface.

🎯 Exam Tip: Emphasize the 'rotational movement' and the 'in-situ sinking' aspect when defining slumping.

 

Question 7. What is Solifluction?
Answer:
In periglacial regions along the slopes, small layers of soil accumulate because of the movement of soil. This is called solifluction.
In simple words: Solifluction is the slow flow of water-saturated soil and regolith over frozen ground (permafrost or seasonally frozen ground) in periglacial regions.

🎯 Exam Tip: Connect solifluction specifically with periglacial environments and the movement of saturated soil layers over frozen subsoil.

 

Question 8. Explain Granular Weathering.
Answer:
When water penetrates in rocks like sandstones and conglomerates1, the particles get loose and separate from the main rock. This is called granular weathering.
In simple words: Granular weathering occurs when individual mineral grains within a rock become loose and separate, often due to water penetration and subsequent expansion or dissolution, leading to the disintegration of the rock.

🎯 Exam Tip: Highlight that granular weathering involves the breakdown into *individual grains*, often seen in coarse-grained rocks like sandstone.

 

Question 9. What is Block Disintegration?
Answer:
When water accumulates in wide points and big blocks of rocks separate from each other, this is called block disintegration.
In simple words: Block disintegration is a form of mechanical weathering where rocks break into large, angular blocks along existing joints and cracks, often due to temperature fluctuations or frost action.

🎯 Exam Tip: Focus on the separation of rocks into *large, angular blocks* along pre-existing weaknesses like joints when describing block disintegration.

 

Question 10. What is Exfoliation?
Answer:
When the outer layer of the racks fall apart from the main rock due to temperature, the process is called exfoliation.
In simple words: Exfoliation is a mechanical weathering process where successive layers of rock peel off from the surface, resembling an onion, due to changes in temperature or release of pressure.

🎯 Exam Tip: Use the analogy of an 'onion peeling' to describe exfoliation, which is caused by differential expansion/contraction or pressure release.

 

Question 11. What does the term 'diurnal Range' mean
Answer:
The difference between the daily maximum and minimum temperature is diurnal Range.
In simple words: Diurnal range refers to the difference between the highest and lowest temperatures recorded within a single 24-hour period.

🎯 Exam Tip: Diurnal range is a meteorological term important for understanding temperature-driven mechanical weathering processes, especially in deserts.

 

Question 12. What is Solution?
Answer:
The minerals in rocks which dissolve in water leads to the formation of solutions.
In simple words: Solution is a type of chemical weathering where soluble minerals within a rock dissolve directly into water, forming a dissolved substance.

🎯 Exam Tip: Solution is a straightforward chemical weathering process; identify it by the direct dissolving of minerals in water.

 

Question 13. Name the two types of mass movements.
Answer:
The two types of mass movements are:
(a) Rapid Mass Movement and
(b) Show Mass movement.
In simple words: The two primary categories of mass movements are rapid mass movements, which involve quick downhill transport, and slow mass movements, characterized by gradual, almost imperceptible downhill creep.

🎯 Exam Tip: Classify mass movements based on their speed and mechanism: 'rapid' for events like landslides and 'slow' for creep or solifluction.

 

Question 14. What are the types of Mechanical weathering?
Answer:
The types of Mechanical weathering are
(a) Temperatures
(b) Frost
(c) Crystal growth
(d) Release of pressure and
(c) water
In simple words: Mechanical weathering can occur due to extreme temperature changes (thermal stress), frost wedging (freezing water), crystal growth (salts), and pressure release from overlying rock removal.

🎯 Exam Tip: Remember the main agents causing mechanical weathering: temperature variations, water (freezing/expanding), and pressure release.

 

Question 15. Types of chemical weathering.
Answer:
The types of chemical weathering are:
(a) Carbonation
(b) Solution and
(c) Oxidation
In simple words: The main types of chemical weathering are carbonation (reaction with carbonic acid), solution (dissolving minerals in water), and oxidation (reaction of minerals, especially iron, with oxygen).

🎯 Exam Tip: Memorize the three main types of chemical weathering (carbonation, solution, oxidation) and their basic mechanisms.

 

Question 16. Where does Mechanical weathering occur?
Answer:
Mechanical weathering occurs mainly in the arid climates.
In simple words: Mechanical weathering is most prevalent in arid (dry) climates due to significant daily temperature fluctuations, and also in cold regions due to intense freeze-thaw cycles.

🎯 Exam Tip: Connect mechanical weathering primarily with arid and cold regions, where the conditions favor physical breakdown over chemical alteration.

 

Question 17. Chemical weathering can be seen in which climates?
Answer:
In humid conditions, one can see chemical weathering.
In simple words: Chemical weathering is most prominent in hot and humid climates because water and high temperatures accelerate chemical reactions that alter rock composition.

🎯 Exam Tip: Remember that chemical weathering thrives in hot and humid environments where water is abundant and temperatures promote chemical reactions.

 

Write whether the statements are TRUE or FALSE. Correct the incorrect statements.

Question 1. Soil creep is uncommon in areas with dry climates and gentle slopes.
Answer:
False - It is a common phenomenon in such areas.
In simple words: This statement is false because soil creep, a slow form of mass movement, is actually very common in dry climates with gentle slopes where gradual movement of soil occurs over time.

🎯 Exam Tip: Soil creep is a subtle, slow process prevalent in various climates, not uncommon in dry areas with gentle slopes.

 

Question 2. Shattering is a type of mechanical weathering
Answer:
True.
In simple words: This statement is true as shattering is a mechanical weathering process where rocks break into sharp, angular fragments due to stress, often from rapid temperature changes or frost wedging.

🎯 Exam Tip: Shattering is a direct consequence of physical stress on rocks, classifying it as mechanical weathering.

 

Question 3. Granular weathering occurs in areas of heavy rainfall.
Answer:
True.
In simple words: This statement is true because heavy rainfall can facilitate water penetration into porous rocks, leading to the loosening and separation of individual grains, which is granular weathering.

🎯 Exam Tip: While often associated with arid regions, granular weathering can also occur in heavy rainfall areas where water aids in grain separation.

 

Distinguish Between:

Question 1. Mechanical Weathering and Chemical Weathering.
Answer:

Mechanical Weathering	Chemical Weathering
(i) In this type of weathering, rocks get disintegrated but the chemical composition of the rocks does not change.	(i) It is a process where rocks get disintegrated and the chemical composition of the rocks change.
(ii) It is caused due to differences in the day and night temperature.	(ii) It is caused due to the reaction of oxygen, carbon dioxide and water with certain rock minerals.
(iii) It is more common in an extremely cold climates and hot dry desert climates.	(iii) It is more common in hot and humid climates.

In simple words: Mechanical weathering physically breaks down rocks without changing their chemical makeup, driven by temperature fluctuations or frost, common in arid/cold climates. Chemical weathering alters rock's chemical composition through reactions with water, gases, or acids, predominant in hot and humid climates.

🎯 Exam Tip: The fundamental distinction lies in whether the rock's chemical composition changes. Mechanical weathering is physical, chemical weathering is compositional.

 

Fill the map with the given information and make a legend.

Question 1. (1) Area affected by a landslide (mudslide) in Maharashtra.
Question 1. (2) Wadgaon Darya

ℹ️ चित्र व्याख्या (Diagram Explanation): यह भारत का एक राजनीतिक मानचित्र है जो राज्यों की सीमाओं को दर्शाता है। मानचित्र पर कुछ स्थानों को 'मालीन गाँव' और 'वडगाँव दरिया' के रूप में एक किंवदंती के साथ चिन्हित किया गया है। यह प्रश्न छात्रों को महाराष्ट्र में भूस्खलन (mudslide) से प्रभावित क्षेत्रों और विशेष रूप से 'वडगाँव दरिया' स्थान को मानचित्र पर भरने के लिए निर्देशित करता है, जिससे वे भूगर्भीय घटनाओं के भौगोलिक वितरण को समझ सकें।

Answer: (The task here is to explain the instruction to fill the map, not to literally fill it. The answer would involve locating these places on a map of Maharashtra. For textual output, we state the intended action.)
The areas affected by landslides in Maharashtra, such as Malin Village and Wadgaon Darya (likely Wadgaon Darya in Ahmadnagar district), need to be marked on a political map of India, specifically within the state of Maharashtra. A legend should then be created to identify these marked locations.
In simple words: This task requires identifying and marking specific landslide-affected locations like Malin Village and Wadgaon Darya on a map of Maharashtra, then creating a legend to indicate these points.

🎯 Exam Tip: When given a map-filling task, accurately locate the specified geographical features and create a clear, descriptive legend to identify them.

 

Give Geographical Reasons:

Question 1. Oxidation process occurs in heavy rainfall areas.
Answer:
• The oxidation process occurs in rocks which have iron present in them.
• The iron in the rock comes in contact with water and a chemical reaction takes place between iron and oxygen.
• A reddish coloured layer forms on the rocks.
• Thus, the oxidation process occurs in heavy rainfall areas.
In simple words: Oxidation, a chemical weathering process, is prevalent in heavy rainfall areas because it requires water to facilitate the reaction between iron present in rocks and atmospheric oxygen, resulting in the formation of reddish rust.

🎯 Exam Tip: For oxidation, remember the key ingredients: iron in the rock, oxygen, and crucially, water, which is abundant in heavy rainfall areas.

Question 3. Mechanical weathering3 takes place in the cold regions.
Answer:

• In the cold regions, the temperature drops below 0°C for a period of time.
• The water that has percolated through the cracks in the rocks freezes and turns into ice.
• Ice requires greater space than water. Tension is developed when the ice tries to acquire greater space.
• The continuous process of freezing and melting finally leads to the breaking of the rock mass.

In simple words: Mechanical weathering in cold regions happens because water seeps into rock cracks, freezes, expands, and creates tension that eventually breaks the rock apart. This freeze-thaw cycle repeatedly weakens the rock structure.

🎯 Exam Tip: Focus on understanding the role of ice expansion as the primary mechanism for mechanical weathering in cold climates.

Question 4. Rapid mass movements occurs along the steep slopes.
Answer:

• A thick layer of weathered material forms on the steep slopes.
• When it rains in such areas, the rainwater penetrates the weathered materials and their weight increases.

In simple words: Rapid mass movements occur on steep slopes when weathered material becomes heavy with rainwater, causing it to quickly slide or flow downhill due to gravity.

🎯 Exam Tip: Remember that increased weight from water saturation is a key factor in triggering rapid mass movements on steep slopes.

Question 5. Mechanical weathering is seen in areas where the diurnal range of temperature is high. OR Change in temperature leads to Mechanical weathering.
Answer:

• The minerals in the rocks expand because of heat and contract when the temperature decreases.
• Due to such continuous contracting and expanding, tension develops in the rock particles.
• Each mineral reacts differently to the temperature. Some minerals expand more, while others do not expand as much.
• Consequently, the tension formed in the rocks also increases and decreases. As a result, cracks develop in the rocks and they break.
• Thus in areas, where the diurnal range of temperature is higher, mechanical weathering is seen.

In simple words: Mechanical weathering is common in areas with large daily temperature changes because rocks, and their varying minerals, expand and contract unevenly with heat fluctuations, causing stress that leads to cracks and eventual breakage.

🎯 Exam Tip: Highlight the differential expansion and contraction of minerals within a rock as the core mechanism of temperature-induced mechanical weathering.

Question 6. Water plays an important role in chemical weathering.
Answer:

• Rock is a mixture of many minerals.
• Since many things get dissolved easily in water, it is considered a universal solvent.
• The solubility1 of the solution increases because the matter gets dissolved in water.
• Water speeds up the process of carbonation, solution and oxidation. These processes lead to the weathering of rocks.
• Thus water plays an important role in chemical weathering.

In simple words: Water is crucial for chemical weathering because it acts as a universal solvent, dissolving minerals and accelerating processes like carbonation and oxidation, which chemically break down rocks.

🎯 Exam Tip: Emphasize water's role as a "universal solvent" and its acceleration of key chemical reactions (carbonation, oxidation, solution) for a complete answer.

Question 7. Frost leads to mechanical weathering.
Answer:

• In areas where the temperatures drop below 0°C for quite some time, the water accumulated in the cracks and crevices in the rocks freezes.
• The volume of water increases on freezing.
• This leads to tension in the rocks and they shatter.
• In this way frost leads to mechanical weathering.

In simple words: Frost causes mechanical weathering because water trapped in rock cracks expands when it freezes, exerting pressure that eventually causes the rock to fracture and break apart.

🎯 Exam Tip: The key concept here is the expansion of water upon freezing, which directly creates tension and breaks rocks.

Answer In Brief:

Question 1. What is a mass movement? What are the types of mass movements?
Answer:The weathered rock materials move along the slopes due to gravity and accumulate near the foothills or the gentler slopes. When the weathered particles move down due to gravity alone, the process is called mass movements. Types of Mass movements:
(i) Rapid mass movements:

• A thick layer of weathered material forms on the slope. When it rains in such areas, the rain water penetrates the weathered materials and their weight increases.
• The weathered materials move very rapidly and come down the slope.
• Sometimes the weathered materials sink in situ. (Where they are)
• Rockfalls, landslides, land subsidence are ; termed as rapid mass movements.

(ii) Slower mass movements:

• Soil creep is the most common phenomenon in areas with dry climate and gentler slopes.
• In periglacial regions along the soil. This is called as solifluction.

In simple words: Mass movement is the downslope movement of weathered rock material primarily due to gravity. It's categorized into rapid movements like landslides and slower ones like soil creep, depending on speed and triggering factors.

🎯 Exam Tip: Clearly define mass movement and differentiate between rapid and slow types with specific examples for higher scores.

Question 2. How does external processes occur?
Answer:

• External processes occur because of the forces working on the earth's surface.
• They are mainly solar energy, gravitational force and kinetic energy associated with the moving objects on the earth's surface.

In simple words: External processes on Earth's surface are driven by forces like solar energy, gravity, and the kinetic energy of moving elements, shaping the landscape through weathering, erosion, and deposition.

🎯 Exam Tip: When explaining external processes, always link them back to the primary energy sources that drive them, such as solar energy and gravity.

Question 3. What is exfoliation?
Answer:

• In regions of high temperatures, the exposed part of the rock heats more while the inner part is comparatively cooler.
• As a result, the outer layers of the rocks fall apart from the main rock.
• This is called the exfoliation of the rock.

In simple words: Exfoliation is a type of mechanical weathering where the outer layers of rocks peel off, much like an onion skin, due to differential heating and cooling between the surface and inner parts of the rock.

🎯 Exam Tip: To describe exfoliation accurately, mention both the temperature difference within the rock and the peeling-off of outer layers.

Question 4. Explain the process of oxidation.
Answer:

• The oxidation process occurs in rocks which have iron present in them.
• The iron in the rock comes in contact with water and a chemical reaction takes place between iron and oxygen.
• Hence, a reddish coloured layer forms on the rocks. This is called rust.

In simple words: Oxidation in rocks is a chemical weathering process where iron-containing minerals react with oxygen and water, causing the formation of a reddish rust layer that weakens the rock.

🎯 Exam Tip: Clearly state the reactants (iron, oxygen, water) and the product (rust/reddish layer) to fully explain oxidation in rocks.

Explain:

Question 1. Block Disintegration
Answer:

• Sometimes both temperature and water are responsible for weathering.
• The difference in temperature cause contraction and expansion of minerals in the rocks. This leads to widening theoints or cracks in the rocks.
• Water accumulates in such wideouts and big blocks of rocks separate from each other.
• This is called Block Disintegration.

In simple words: Block disintegration is a type of weathering where temperature changes and water cause cracks in rocks to widen, eventually leading to large blocks separating from the main rock mass.

🎯 Exam Tip: Emphasize the combined effect of temperature fluctuations and water penetration in creating and widening cracks, leading to the separation of rock blocks.

Question 2. Carbonation
Answer:

• Carbonation is a type of chemical weathering.
• The rainwater travels through the atmosphere before reaching the ground.
• Carbon dioxide in the air gets mixed in the water in this process and dilute carbonic acid gets formed.
• For e.g Water + Carbon Dioxide = Carbonic Acid \((\text{H}_2\text{O} +\text{CO}_2 = \text{H}_2\text{CO}_3)\)
• Materials like limestone get easily dissolved in such acids.

In simple words: Carbonation is a chemical weathering process where atmospheric carbon dioxide dissolves in rainwater to form carbonic acid, which then reacts with and dissolves minerals in rocks like limestone.

🎯 Exam Tip: Remember the specific chemical reaction: rainwater + carbon dioxide = carbonic acid, and its effect on calcium-rich rocks.

Question 3. Solution
Answer:

• Some minerals in the rock get dissolved in water.
• Limestone is formed due to chemical precipitation between water and alkalis.
• At Wadgaon Darya in Ahmadnagar district, limestone gets precipitated chemically i.e. undergoes chemical weathering again.
• Similarly, because of solution, alkalis in the rock dissolve and make them brittle.

In simple words: Solution weathering occurs when certain minerals within a rock, particularly alkalis, dissolve directly in water, weakening the rock structure and making it brittle.

🎯 Exam Tip: Differentiate solution from carbonation by focusing on the direct dissolving of minerals in water, without the prior formation of carbonic acid.

Question 4. Make a record of few landslides that have occured in India and write about them briefly.
Answer:Landslide is a rapid mass movement which is caused majorly due to heavy rains, floods, earthquakes etc. The following are some fatal landsides in India. 1. Guwahati landslide, Assam:- The landslide took place in the year 1948 due to heavy rains & over 500 people died in this landslide. 2. Darjeeling landslide, West Negal:- This landslide happened in the year of 1968. It was triggered by floods and thousands of people died due to this landslide. 3. Malpa landslide, Uttarkhand:- Consecutive landslides occured in August 1998 in village of Mapla due to which 380 people died as an entire village was destroyed in the landslide. 4. Kedarnath landslide, Uttarakhand:- This landslide took place onune 16, 2013 & was the result of Uttar Khand floods. Over 5700 people were reported dead and over 4200 villages were affected by floods and post-flood landslide. 5. Malin landslide, Maharashtra:- This landslide occured onuly 30, 2014, in a village in Malin. The landslide occured due to heavy rainfall and around 151 people died and 100 people went missing after the disaster.In simple words: Landslides are rapid mass movements triggered by events like heavy rains or earthquakes. Notable examples in India include the Guwahati (1948), Darjeeling (1968), Malpa (1998), Kedarnath (2013), and Malin (2014) landslides, which caused significant loss of life and destruction.

🎯 Exam Tip: When listing specific events, include the location, year, and a brief mention of the cause or impact to demonstrate comprehensive knowledge.