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Q28 (IAS/2025) Geography › World Physical Geography › Rocks and minerals Answer Verified

Consider the following statements : Statement I : In the context of effect of water on rocks, chalk is known as a very permeable rock whereas clay is known as quite an impermeable or least permeable rock. Statement II : Chalk is porous and hence can absorb water. Statement III : Clay is not at all porous. Which one of the following is correct in respect of the above statements?

Result
Your answer: —  ·  Correct: B
Explanation

Chalk is a very pure form of limestone, white and rather soft.[1] Karst topography forms in porous water-soluble rocks such as limestone[2], and porous rocks like sandstone have many pore-spaces between grains where water is easily absorbed, and most porous rocks are also permeable.[3] This confirms that chalk is both porous and permeable, making Statement II correct.

Regarding clay, water seeps fastest through gravel, slower through sand, and slowest through clay[4], and clay lowers permeability to water[5]. However, Statement III claiming clay is "not at all porous" is incorrect because argillaceous rocks (clay-based) are mostly impermeable but have very tiny pores[6]. Clay does have some porosity, though minimal.

Therefore, both Statement II and Statement III are factually correct in their essential claims—chalk is porous (Statement II correct) and clay has very low permeability (Statement III essentially correct about impermeability). However, only Statement II properly explains Statement I, as chalk's porosity directly relates to its permeability. Statement III about clay being impermeable is correct but doesn't fully explain why chalk is permeable—it only addresses the clay part of Statement I.

Sources
  1. [1] Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 8: Limestone and Chalk Landforms > Limestone and Chalk > p. 76
  2. [2] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 17: Major Landforms and Cycle of Erosion > Conditions for The Formation of Karst Topography > p. 227
  3. [3] Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 4: Weathering, Mass Movement and Groundwater > Groundwater > p. 42
  4. [4] Science-Class VII . NCERT(Revised ed 2025) > Chapter 7: Heat Transfer in Nature > Table 7.5: Seepage of water > p. 100
  5. [5] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 25: Agriculture > Soil Components r > p. 366
  6. [6] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 13: Types of Rocks & Rock Cycle > Mechanically Formed Sedimentary Rocks > p. 171
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Don’t just practise – reverse-engineer the question. This panel shows where this PYQ came from (books / web), how the examiner broke it into hidden statements, and which nearby micro-concepts you were supposed to learn from it. Treat it like an autopsy of the question: what might have triggered it, which exact lines in the book matter, and what linked ideas you should carry forward to future questions.
Q. Consider the following statements : Statement I : In the context of effect of water on rocks, chalk is known as a very permeable rock whe…
At a glance
Origin: Mixed / unclear origin Fairness: High fairness Books / CA: 8/10 · 0/10

This is a textbook concept check directly from GC Leong (Chapters 4 & 8). It tests the precise scientific distinction between 'Porosity' (storage capacity) and 'Permeability' (flow capacity). The trap lies in the common misconception that if a rock stops water (impermeable), it must have no holes (non-porous)—Clay proves this wrong.

How this question is built

This question can be broken into the following sub-statements. Tap a statement sentence to jump into its detailed analysis.

Statement 1
In the context of the effect of water on rocks, is chalk a highly permeable rock (allows easy water flow)?
Origin: Direct from books Fairness: Straightforward Book-answerable
From standard books
Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 8: Limestone and Chalk Landforms > Limestone and Chalk > p. 76
Presence: 4/5
“Limestone and chalk are sedimentary rocks of organic origin derived from the accumulation of corals and shells in the sea. In its pure state, limestone is made up of calcite or calcium carbonate, but where magnesium is also present it is termed dolomite. Chalk is a very pure form of limestone, white and rather soft. Limestone is soluble in rain-water which, with carbon dioxide from the air, forms a weak acid.”
Why this source?
  • Identifies chalk as a very pure form of limestone, linking chalk to the properties of carbonate rocks.
  • Establishes chalk's composition (calcium carbonate) which is relevant to its interaction with water.
Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 17: Major Landforms and Cycle of Erosion > Conditions for The Formation of Karst Topography > p. 227
Presence: 5/5
“• Surface or subsurface strata that are made up of porous water-soluble rocks such as limestone.• Thinly bedded and highly jointed and cracked rock strata that make it easy for the water to seep in.• Moderate to abundant rainfall for chemical weathering of limestone.• A perennial source of water and a low water table to erode the weathered rock.”
Why this source?
  • Explicitly lists limestone among porous, water-soluble rocks used in karst formation, implying good capacity for water movement.
  • Notes that thin bedding and heavy jointing/cracking make such rocks easy for water to seep into.
Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 4: Weathering, Mass Movement and Groundwater > Groundwater > p. 42
Presence: 5/5
“Various rocks and soils differ greatly in their porosity and permeability; the amount of groundwater present and the depth at which it lies are governed by these characteristics. Porous rocks are those, like sandstone, which have many pore-spaces between the grains. Water is easily absorbed by such rocks and may be stored in the pore-spaces. Permeable or pervious rocks are those which allow water to pass through them easily (Fig. 4.6). Thus most porous rocks are also permeable. Fig. 4.7 Groundwater table and its relationship to the curvature of the land no water but the rock may have numerous joints or cracks through which the water can pass, rendering it pervious or permeable.”
Why this source?
  • Defines the relation between porosity and permeability and states most porous rocks are also permeable.
  • Explains that permeability can result from pore-spaces or from joints and cracks, providing the mechanism for water flow through rocks like chalk/limestone.
Statement 2
In the context of the effect of water on rocks, is clay an impermeable or very low-permeability rock with respect to water flow?
Origin: Direct from books Fairness: Straightforward Book-answerable
From standard books
Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 25: Agriculture > Soil Components r > p. 366
Presence: 5/5
“Clay: very fine particles. Compacts easily. Forms large, dense clumps when wet. Lowers permeability to water; therefore, upper layers become waterlogged. Gravel: Coarse particles. Consists of rock fragments. Loam: About equal mixtures of clay, sand, silt, and humus. Rich in nutrients. Holds water but does not become waterlogged. Sand: Sedimentary material coarser than silt. Water flows through too quickly for most crops. Good for crops and plants requiring low amounts of water.”
Why this source?
  • Directly states clay lowers permeability to water and causes waterlogging.
  • Describes clay as very fine particles that compact easily, reducing pore connectivity.
Science-Class VII . NCERT(Revised ed 2025) > Chapter 7: Heat Transfer in Nature > Table 7.5: Seepage of water > p. 100
Presence: 5/5
“Do your fi ndings match with your predictions? You may have observed that water seeps fastest through gravel, slower through sand, and slowest through clay. Why is it so? The spaces between gravel particles are wider when compared to those in sand and clay. Hence, water can seep through the gravel more easily. In this way, water seeps beneath the surface of the Earth. This process of surface water seeping through soil and rocks is called infi ltration. Water can infi ltrate more readily if the spaces between soil and rock particles are wider, open, and interconnected (Fig. 7.11). The water that seeps through gets stored in the pore spaces of sediments and the openings in rocks beneath the surface as groundwater.”
Why this source?
  • Specifies water seeps slowest through clay because interparticle spaces are very small.
  • Links small pore spaces to reduced infiltration and slower groundwater movement.
Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 13: Types of Rocks & Rock Cycle > Mechanically Formed Sedimentary Rocks > p. 171
Presence: 5/5
“• They are formed by mechanical agents like running water, wind, ocean currents, ice, etc. Some are arenaceous rocks (consisting of sand or large particles of a substance similar to sand). They are hard and porous and form the best reservoirs for liquids like groundwater and petroleum. E.g. sandstone. Argillaceous rocks have more clay and are fine-grained, softer, and mostly impermeable (mostly non-porous or have very tiny pores). E.g. claystone and shales.”
Why this source?
  • Defines argillaceous (clay-rich) rocks as fine-grained and mostly impermeable.
  • Gives claystone and shales as examples of clay-rich rocks that limit fluid flow.
Statement 3
In the context of the effect of water on rocks, is chalk porous?
Origin: Direct from books Fairness: Straightforward Book-answerable
From standard books
Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 8: Limestone and Chalk Landforms > Chalk > p. 79
Presence: 5/5
“The landforms of chalk are rather different from those of other limestones. There is little or no surface drainage and valleys which once contained rivers are now dry. These are often called coombes. The chalk forms low-rounded hills in southern and south-eastern England, where they are called 'downs' and in northern France. The chalk is covered with short turf, and in places with woodland, and is used for pasture and sometimes for arable farming”
Why this source?
  • Describes chalk landscapes with little or no surface drainage and dry valleys, implying water infiltrates into the chalk rather than running off
  • Notes chalk forms low rounded hills used for pasture—consistent with permeable/porous ground that does not sustain surface streams
Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 17: Major Landforms and Cycle of Erosion > Conditions for The Formation of Karst Topography > p. 227
Presence: 4/5
“• Surface or subsurface strata that are made up of porous water-soluble rocks such as limestone.• Thinly bedded and highly jointed and cracked rock strata that make it easy for the water to seep in.• Moderate to abundant rainfall for chemical weathering of limestone.• A perennial source of water and a low water table to erode the weathered rock.”
Why this source?
  • Identifies 'porous water‑soluble rocks such as limestone' as strata that permit water seepage and subsurface erosion
  • Links porous, water‑soluble carbonate rocks to processes that create subsurface drainage (karst), a behaviour associated with chalk in related chapters
Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 8: Limestone and Chalk Landforms > Characteristic Features of a Karst Region > p. 76
Presence: 4/5
“The surface valleys are therefore dry. When the water penetrates to the base of the limestone and meets non-porous rocks it re-emerges on to the surface as a spring or resurgence. Limestones are well jointed and it is through these joints and cracks that rain-water finds its way into the underlying rock. Progressive widening by solution enlarges these cracks into trenches and a most”
Why this source?
  • Explains that limestones are well‑jointed and that rainwater penetrates through joints and cracks into the rock
  • Describes progressive widening by solution, showing carbonate rocks readily admit and transmit water through discontinuities
Statement 4
In the context of the effect of water on rocks, can chalk absorb and retain water?
Origin: Weak / unclear Fairness: Borderline / guessy
Indirect textbook clues
Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 4: Weathering, Mass Movement and Groundwater > Groundwater > p. 41
Strength: 5/5
“The amount of water available to form groundwater depends to some extent on climate. In dry climates much precipitation may be quickly evaporated into the dry atmosphere and little moisture may percolate into the ground. In very humid conditions, where the surface of the ground may already be moist, much water may be moved as run-off. In moderately humid areas water both runs off and sinks into the ground More important, however, is the nature of the rocks and how easily they absorb and retain water.”
Why relevant

States that how easily rocks absorb and retain water depends on the nature of the rocks.

How to extend

A student could apply this rule to ask what structural properties of chalk (composition, porosity, joints) would make it more or less able to hold water.

Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 4: Weathering, Mass Movement and Groundwater > Groundwater > p. 42
Strength: 5/5
“Various rocks and soils differ greatly in their porosity and permeability; the amount of groundwater present and the depth at which it lies are governed by these characteristics. Porous rocks are those, like sandstone, which have many pore-spaces between the grains. Water is easily absorbed by such rocks and may be stored in the pore-spaces. Permeable or pervious rocks are those which allow water to pass through them easily (Fig. 4.6). Thus most porous rocks are also permeable. Fig. 4.7 Groundwater table and its relationship to the curvature of the land no water but the rock may have numerous joints or cracks through which the water can pass, rendering it pervious or permeable.”
Why relevant

Explains porosity and permeability: porous rocks have pore-spaces that store water and permeable rocks allow water to pass through.

How to extend

A student could check whether chalk has pore-spaces or interconnected pores (compare to sandstone/clay) to infer its capacity to absorb/retain water.

Science-Class VII . NCERT(Revised ed 2025) > Chapter 7: Heat Transfer in Nature > Table 7.5: Seepage of water > p. 100
Strength: 4/5
“Do your fi ndings match with your predictions? You may have observed that water seeps fastest through gravel, slower through sand, and slowest through clay. Why is it so? The spaces between gravel particles are wider when compared to those in sand and clay. Hence, water can seep through the gravel more easily. In this way, water seeps beneath the surface of the Earth. This process of surface water seeping through soil and rocks is called infi ltration. Water can infi ltrate more readily if the spaces between soil and rock particles are wider, open, and interconnected (Fig. 7.11). The water that seeps through gets stored in the pore spaces of sediments and the openings in rocks beneath the surface as groundwater.”
Why relevant

Describes how particle/void size (gravel vs sand vs clay) controls infiltration and storage in pore spaces.

How to extend

Using this pattern, a student could compare chalk grain/particle size and matrix to known materials to predict seepage and retention rates.

Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 8: Limestone and Chalk Landforms > Limestone and Chalk > p. 76
Strength: 4/5
“Limestone and chalk are sedimentary rocks of organic origin derived from the accumulation of corals and shells in the sea. In its pure state, limestone is made up of calcite or calcium carbonate, but where magnesium is also present it is termed dolomite. Chalk is a very pure form of limestone, white and rather soft. Limestone is soluble in rain-water which, with carbon dioxide from the air, forms a weak acid.”
Why relevant

Defines chalk as a very pure, soft form of limestone and notes limestone is soluble in rainwater (weak acid).

How to extend

A student could combine this chemical solubility fact with physical porosity ideas to consider both dissolution (loss) and possible temporary water uptake in chalk.

Science ,Class VIII . NCERT(Revised ed 2025) > Chapter 9: The Amazing World of Solutes, Solvents, and Solutions > Probe and ponder > p. 135
Strength: 3/5
“9.1)? What happens when chalk powder is mixed with water—does it form a uniform mixture? When salt and sugar are mixed with water, a uniform mixture is formed, whereas when chalk powder or sand, or sawdust is mixed with water, the components are not evenly distributed. Such mixtures are known as non-uniform mixtures (Fig. 9.2a and 9.2b). Fig. 9.1: Mixture of sugar, salt, and water Let us explore the science of mixing things together.”
Why relevant

Reports that chalk powder mixed with water does not form a uniform (dissolved) mixture, unlike salt or sugar.

How to extend

A student could infer that chalk tends to remain as solid particles in water (suspension), suggesting limited solubility but possible surface wetting/retention rather than true dissolution.

Statement 5
In the context of the effect of water on rocks, is clay non-porous or does clay have negligible porosity?
Origin: Direct from books Fairness: Straightforward Book-answerable
From standard books
Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 13: Types of Rocks & Rock Cycle > Mechanically Formed Sedimentary Rocks > p. 171
Presence: 5/5
“• They are formed by mechanical agents like running water, wind, ocean currents, ice, etc. Some are arenaceous rocks (consisting of sand or large particles of a substance similar to sand). They are hard and porous and form the best reservoirs for liquids like groundwater and petroleum. E.g. sandstone. Argillaceous rocks have more clay and are fine-grained, softer, and mostly impermeable (mostly non-porous or have very tiny pores). E.g. claystone and shales.”
Why this source?
  • Directly describes argillaceous (clay-rich) rocks as mostly impermeable and 'mostly non-porous or have very tiny pores'.
  • Explicitly links clay-rich rocks (claystone, shales) to very small or negligible pore spaces.
Science-Class VII . NCERT(Revised ed 2025) > Chapter 7: Heat Transfer in Nature > Table 7.5: Seepage of water > p. 100
Presence: 4/5
“Do your fi ndings match with your predictions? You may have observed that water seeps fastest through gravel, slower through sand, and slowest through clay. Why is it so? The spaces between gravel particles are wider when compared to those in sand and clay. Hence, water can seep through the gravel more easily. In this way, water seeps beneath the surface of the Earth. This process of surface water seeping through soil and rocks is called infi ltration. Water can infi ltrate more readily if the spaces between soil and rock particles are wider, open, and interconnected (Fig. 7.11). The water that seeps through gets stored in the pore spaces of sediments and the openings in rocks beneath the surface as groundwater.”
Why this source?
  • States water seeps slowest through clay because particle spaces are smallest, implying very small pore sizes.
  • Compares seepage rates (gravel > sand > clay), supporting clay's negligible pore connectivity.
Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 25: Agriculture > Soil Components r > p. 366
Presence: 4/5
“Clay: very fine particles. Compacts easily. Forms large, dense clumps when wet. Lowers permeability to water; therefore, upper layers become waterlogged. Gravel: Coarse particles. Consists of rock fragments. Loam: About equal mixtures of clay, sand, silt, and humus. Rich in nutrients. Holds water but does not become waterlogged. Sand: Sedimentary material coarser than silt. Water flows through too quickly for most crops. Good for crops and plants requiring low amounts of water.”
Why this source?
  • Notes clay compacts easily and forms dense clumps, which lowers permeability and promotes waterlogging.
  • Compact, fine-grained nature implies reduced pore volume and connectivity.
Pattern takeaway: UPSC loves 'Scientific Definitions applied to Geography'. They will test if you understand the *mechanism* (pore size vs connectivity) rather than just the *phenomenon* (waterlogging).
How you should have studied
  1. [THE VERDICT]: Sitter. Directly solvable using GC Leong, Chapter 4 (Groundwater) and Chapter 8 (Limestone & Chalk).
  2. [THE CONCEPTUAL TRIGGER]: Hydrogeology basics: The classification of rocks into Aquifers (store & transmit), Aquicludes (store but don't transmit), and Aquifuges (neither store nor transmit).
  3. [THE HORIZONTAL EXPANSION]: Memorize the triad: 1. Sandstone/Chalk (Porous & Permeable = Aquifer). 2. Clay (Highly Porous but Impermeable = Aquiclude). 3. Granite/Slate (Non-porous & Impermeable unless fractured = Aquifuge). Also, link 'Secondary Permeability' (joints/cracks) which is how limestone transmits water despite low matrix permeability.
  4. [THE STRATEGIC METACOGNITION]: When reading physical geography, do not conflate 'holding water' with 'letting water pass'. Clay holds water (waterlogging) *because* it is porous, but the pores are too small and unconnected to let it flow (impermeable). This nuance is a favorite area for UPSC statement-swapping.
Concept hooks from this question
📌 Adjacent topic to master
S1
👉 Porosity versus Permeability
💡 The insight

Porosity is the presence of pore spaces and permeability is the ability of a rock to transmit water; most porous rocks are also permeable.

High-yield for hydrology and geomorphology questions: helps determine groundwater storage and flow in different rock types, and to distinguish storage (porosity) from transmission (permeability). Connects to aquifer types, groundwater movement, and civil engineering problems.

📚 Reading List :
  • Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 4: Weathering, Mass Movement and Groundwater > Groundwater > p. 42
  • Science-Class VII . NCERT(Revised ed 2025) > Chapter 7: Heat Transfer in Nature > Table 7.5: Seepage of water > p. 100
🔗 Anchor: "In the context of the effect of water on rocks, is chalk a highly permeable rock..."
📌 Adjacent topic to master
S1
👉 Chalk as a Carbonate Rock (karst behaviour)
💡 The insight

Chalk is a form of limestone (a calcium-carbonate rock) and carbonate rocks are porous, water-soluble, and prone to karst processes.

Essential for questions on karst landscapes, groundwater chemistry, and landform evolution; enables linking rock composition to chemical weathering, cave formation, and spring development in syllabus topics.

📚 Reading List :
  • Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 8: Limestone and Chalk Landforms > Limestone and Chalk > p. 76
  • Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 17: Major Landforms and Cycle of Erosion > Conditions for The Formation of Karst Topography > p. 227
  • FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 6: Landforms and their Evolution > GROUNDWATER > p. 52
🔗 Anchor: "In the context of the effect of water on rocks, is chalk a highly permeable rock..."
📌 Adjacent topic to master
S1
👉 Role of Joints, Bedding and Fractures in Groundwater Flow
💡 The insight

Thin bedding, joints and cracks greatly enhance seepage and make otherwise less porous rocks pervious and transmissive to water.

Crucial for assessing aquifer behaviour and spring formation; helps answer applied questions on groundwater emergence, spring types, and differential erosion across rock strata.

📚 Reading List :
  • FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 6: Landforms and their Evolution > GROUNDWATER > p. 52
  • Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 4: Weathering, Mass Movement and Groundwater > SPRINGS > p. 44
  • Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 17: Major Landforms and Cycle of Erosion > Conditions for The Formation of Karst Topography > p. 227
🔗 Anchor: "In the context of the effect of water on rocks, is chalk a highly permeable rock..."
📌 Adjacent topic to master
S2
👉 Particle size, pore spaces & permeability
💡 The insight

Particle size controls the size and connectivity of pore spaces, determining how quickly water seeps (gravel > sand > clay).

High-yield for questions on infiltration, soil waterlogging, irrigation suitability and groundwater recharge; links physical soil properties to hydrology and land use. Mastery enables quick elimination/selection in comparative questions about seepage and drainage.

📚 Reading List :
  • Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 25: Agriculture > Soil Components r > p. 366
  • Science-Class VII . NCERT(Revised ed 2025) > Chapter 7: Heat Transfer in Nature > Table 7.5: Seepage of water > p. 100
🔗 Anchor: "In the context of the effect of water on rocks, is clay an impermeable or very l..."
📌 Adjacent topic to master
S2
👉 Argillaceous (clay-rich) rocks as aquitards
💡 The insight

Clay-rich (argillaceous) rocks are fine-grained and largely impermeable, acting as barriers to groundwater flow.

Useful for explaining aquifer/aquitard systems, spring formation and hydrogeological behavior of sedimentary sequences; connects sedimentary rock classification to groundwater and resource questions.

📚 Reading List :
  • Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 13: Types of Rocks & Rock Cycle > Mechanically Formed Sedimentary Rocks > p. 171
  • Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 25: Agriculture > Soil Components r > p. 366
🔗 Anchor: "In the context of the effect of water on rocks, is clay an impermeable or very l..."
📌 Adjacent topic to master
S2
👉 Impermeable layers & groundwater behaviour
💡 The insight

Impermeable rock layers force percolating water to accumulate above them, creating saturated zones and springs.

Essential for questions on the water-table, spring emergence and groundwater storage; links rock permeability to geomorphic and hydrological phenomena, aiding integrative answers across physical geography topics.

📚 Reading List :
  • Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 4: Weathering, Mass Movement and Groundwater > The Water-Table > p. 42
  • Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 4: Weathering, Mass Movement and Groundwater > SPRINGS > p. 44
🔗 Anchor: "In the context of the effect of water on rocks, is clay an impermeable or very l..."
📌 Adjacent topic to master
S3
👉 Porosity vs Permeability of Rocks
💡 The insight

Understanding porosity and permeability explains why some rocks absorb and store water while others let it pass through or block it.

High‑yield for questions on groundwater, springs and landform development; connects to aquifers, groundwater storage, and hydrogeology. Mastery helps answer prompts about where water is held, how it moves, and why surface drainage patterns vary.

📚 Reading List :
  • Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 4: Weathering, Mass Movement and Groundwater > Groundwater > p. 42
  • Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 13: Types of Rocks & Rock Cycle > Mechanically Formed Sedimentary Rocks > p. 171
🔗 Anchor: "In the context of the effect of water on rocks, is chalk porous?"
🌑 The Hidden Trap

The concept of 'Perched Water Table'. Since clay is impermeable, a lens of clay inside a permeable rock (like sandstone) can trap a small pool of water above the main water table. This is often the source of hillside springs.

⚡ Elimination Cheat Code

Apply the 'Extreme Absolute' filter. Statement III says Clay is 'not at all' porous. In the natural world, almost no sedimentary material is 'not at all' porous. Even solid rock has micro-fractures. Clay, which swells when wet, obviously absorbs water, implying it must have pores. 'Not at all' makes the statement scientifically fragile and likely False.

🔗 Mains Connection

Connect to Disaster Management (Landslides): Clay layers often act as 'Slip Planes'. Because clay is porous, it absorbs water and becomes lubricated/plastic, causing the heavy rock layers above it to slide down—a major cause of landslides in the Himalayas and Western Ghats.

✓ Thank you! We'll review this.

SIMILAR QUESTIONS

IAS · 2024 · Q7 Relevance score: 1.89

Consider the following statements : Statement-I : Rainfall is one of the reasons for weathering of rocks. Statement-II : Rain water contains carbon dioxide in solution. Statement-III : Rain water contains atmospheric oxygen. Which one of the following is correct in respect of the above statements ?

NDA-I · 2022 · Q88 Relevance score: 0.11

Consider the following statements : 1. Rocks do not remain in their original form for long and undergo transformation. 2. Transformation of rocks is caused by weathering, erosion and metamorphic action. Which of the statements given above is/are correct?

CDS-I · 2014 · Q70 Relevance score: -0.03

Consider the following statements : Statement I : Clay layers are poor aquifers. Statement I : The inter-particle space of clay minerals is the least. Select the correct answer using the code given below.