Weathering Class 6 ICSE — Geography Chapter 9

Weathering class 6 ICSE introduces how rocks break down without being carried away. This Geography chapter 9 of the ICSE Class 6 book explains the three types of weathering — physical, chemical, and biological — and the processes behind each. You will learn why deserts weather fastest, how frost splits rocks, and how climate decides which type dominates. The chapter PDF is available for revision.

ICSE Class 6 Geography Chapter 9 Weathering PDF

What is inside Chapter 9

5 pages · 3 sections

1 TYPES OF WEATHERING

Weathering is a static process. Rocks break down, but nothing carries the fragments away. The chapter names three types: physical, chemical, and biological weathering. The removal of broken material belongs to denudation, explained in Chapter 10: Denudation.

Physical weathering, also called mechanical weathering, disintegrates rocks without changing their chemical constituents. The main factors are temperature changes, moisture, frost action, and wind. Temperature-driven weathering works fastest in hot deserts, because temperature swings there are the sharpest on Earth.

Four processes sit under physical weathering. Block disintegration happens when sudden temperature changes make rocks expand and contract, building tension that splits them. Granular disintegration reduces rocks to pieces and fragments, even in cold places and high altitudes.

Frost action fills cracks with water during the day. At night the water freezes and ruptures the rock. Exfoliation peels off the outer layer, because most rocks conduct heat poorly.

Worked example: a desert where daytime temperature reaches 48^\circ\text{C} and night falls to 4^\circ\text{C} gives a swing of 44^\circ\text{C} each day. Every day the rock surface expands; every night it contracts. Repeated over years, the tension splits the rock into blocks — the block disintegration described above.

2 Chemical Weathering

Chemical weathering decomposes rocks. Some or all minerals suffer decay or alteration through water, oxygen, carbon, or organic acids. Chemical reactions transform minerals into new chemical combinations. This is decomposition, not mere break-up. It works alongside the physical processes covered in the rest of the Class 6 Geography book.

Four processes carry out chemical weathering.

• Oxidation: minerals react with atmospheric oxygen, also present in rainwater. Iron compounds rust and crumble, and the rock turns red, yellow, or brown.
• Carbonation: carbon dioxide in rainwater produces an acidic effect. It dissolves calcareous rocks such as gypsum, marble, and limestone. Rainwater converts calcium carbonate into soluble calcium bicarbonate, which groundwater carries away.
• Hydration: minerals expand on contact with rainwater, become heavy, and disintegrate. Feldspar converts into kaolin.
• Solution: minerals dissolve in water. Rock-salt and gypsum are highly soluble. Sedimentary rocks are attacked faster, because pore spaces between grains let air and water lodge inside.

Common mistake: students confuse carbonation with solution. In carbonation, the mineral first changes chemical form — calcium carbonate becomes calcium bicarbonate — and only then dissolves. In solution, the mineral dissolves directly, with no change of form.

3 Biological Weathering

Biological weathering, also called organic weathering, uses living agents: humans, plants, animals, and insects. Both physical disintegration and chemical decomposition occur, because all living matter contains water and oxygen — the two substances that set off reactions in minerals. You can verify how these agents fit the syllabus on the official CISCE website.

• Humans: mining, excavations, and the construction of roads and buildings cause physical disintegration. Agriculture, and the dumping of chemicals and waste underground, promote both physical and chemical weathering.
• Plants: roots of large trees press deep into rocks and cause physical disintegration. Most vegetation, however, binds the surface layer and shields rocks from the elements, so it prevents disintegration.
• Animals and insects: burrowing animals such as rabbits, worms, and moles loosen surface material around rocks. When they die, their decaying bodies add chemicals and acids that help break rocks down.

Mechanical versus chemical weathering — five differences:

Climate is the most important factor in weathering. Different regions favour different types:

• Equatorial climates: humidity and temperature stay constantly high, so chemical weathering is more active.
• Tropical climates: a marked dry and wet season drives high evaporation. In the wet season, precipitation of iron and aluminium oxides from rocks promotes laterite soils.
• Dry deserts: mechanical weathering dominates, because the diurnal temperature range is high.
• Temperate climates: frost action is the most powerful agent. In limestone areas, solution operates on a large scale.
• Polar climates: frost action prevails, and chemical and biological weathering are negligible. Recent studies found more carbonic acid in melting water, because carbon dioxide dissolves better at low temperatures. Chemical weathering is therefore more active than once thought.

What to practise from this chapter

The chapter closes with five exercise blocks. Practise them in order to test your understanding.

• I. Short Answer Questions — 6 questions
• II. Give a technical term — 3 questions
• III. Distinguish between — 2 questions
• IV. Structured Questions — 2 questions
• V. Practical Work — 2 tasks

Structured Questions IV.1(d) and IV.2(d) ask for labelled diagrams and climate-based reasons. Practise drawing the physical weathering diagram. Be ready to explain why physical weathering is rapid in deserts, why vegetation prevents disintegration, and why chemical and biological weathering are negligible in polar climates. For more practice across subjects, browse all Class 6 books.

Frequently asked questions

What is weathering in class 6 ICSE geography?

Weathering is the breaking down of rocks without their removal. It is a static process. The three types are physical, chemical, and biological weathering.

What is the difference between weathering and erosion?

Weathering breaks rocks down in place; nothing carries the material away. Erosion, part of denudation, moves the broken material to a new location. Weathering prepares the material; erosion transports it.

Why is physical weathering more rapid in deserts?

Desert temperature swings are the sharpest on Earth. Rocks expand in the day and contract at night, and the repeated action splits them. This drives block disintegration and exfoliation.

What is exfoliation in weathering?

Exfoliation is the peeling off of the outer layer of a rock. It happens because most rocks conduct heat poorly, so sudden contraction and expansion breaks the surface layer free.

Which processes come under chemical weathering?

The four processes are oxidation, carbonation, hydration, and solution. They decompose rock minerals through water, oxygen, carbon, and organic acids.

Reference: ICSE Class 6 Geography textbook material, chapter 9: Weathering — CISCE-aligned.

More from this book

• Chapter 1: Earth As a Planet
• Chapter 2: Geographic Grid Laitudes and Longitufes
• Chapter 3: Rotation and Revolution
• Chapter 5: Landforms of the Earth
• Chapter 6: Rocks
• Chapter 7: Volcanoes
• Chapter 8: Earthquakes
• Chapter 10: Denudation
• Chapter 12: Composition and Structure of Atmosphere