Weathering

Weathering

Reason — Weathering is the process of breaking down rocks in situ (at their place of origin) without transporting them. The removal and transport of weathered material is called erosion.

It causes disintegration of soil

Reason — Weathering breaks down rocks to form soil; it does not cause the disintegration of soil.

Mechanical Weathering

Reason — Physical weathering, also known as mechanical weathering, involves rock disintegration without any change in the chemical constituents of the rock.

Exfoliation

Reason — Because rocks are poor conductors of heat, repeated heating and cooling cause the outer layers to expand, contract, and peel off, a process called exfoliation.

Chemical Weathering

Reason — Chemical weathering occurs in moist and cold climates as such climates have abundant water and oxygen, which are the main agents of chemical weathering.

Organic Weathering

Reason — Weathering caused by animals, insects, plants and man is called biological weathering, which is also known as organic weathering.

Hydration

Reason — In the process of hydration, the expansion of minerals occurs on their coming into contact with rainwater, causing the minerals to become heavy and start disintegrating.

Mechanical Weathering

Reason — Mechanical weathering is most rapid in hot deserts, where extreme temperature changes cause rocks to expand, contract, and break apart.

Chemical weathering

Reason — In chemical weathering, rocks decompose due to chemical reactions that alter their mineral composition, changing the chemical constituents of the rocks.

Constructive forces

Reason — Endogenic (internal) forces are called constructive forces because they create landforms on the Earth's surface.

Block Disintegration

Reason — Sudden temperature changes cause rocks to expand and contract, leading to block disintegration.

Polar climates

Reason — Frost action is most common in polar climates, where water in rock cracks repeatedly freezes and thaws, expands on freezing, and eventually breaks the rocks apart.

Both A and R are true and R is the correct explanation of A.

Explanation — A rock undergoes disintegration or decomposition only when exposed to natural weathering agents such as changes in temperature, moisture, and precipitation.

C

Reason — In dry (desert) climates, mechanical (physical) weathering is the dominant process due to extreme daily temperature variations and lack of moisture. Biological weathering is minimal because vegetation and other living organisms are scarce.

Chemical

Reason — The melting of ice provides more liquid water, which promotes chemical weathering. In polar regions, meltwater contains dissolved carbon dioxide, forming weak carbonic acid, which accelerates the chemical decomposition of rocks.

Weathering is the process of breaking down of rocks but not its removal. It is described as disintegration or decomposition of a rock in size by natural agents at or near the surface of the earth.

Three types of weathering are-

1. Physical weathering
2. Chemical weathering
3. Biological weathering

Exfoliation is the peeling off of a rock's outer layers due to repeated expansion and contraction caused by sudden temperature changes.

The four processes involved in chemical weathering are-

1. Oxidation
2. Carbonation
3. Hydration
4. Solution

Oxidation means reaction of minerals in rocks to atmospheric oxygen.

When the atmospheric oxygen comes in contact with iron-compounds in rocks, the iron starts rusting or crumbling. The colour of the rock changes to red, yellow or brown.

Weathering is the breaking down of rocks without their removal. It is the disintegration or decomposition of rocks by natural agents at or near the Earth's surface.

Chief characteristics of weathering:

1. It involves the disintegration or decomposition of rocks.
2. It depends on climate and the nature of rocks.
3. It occurs at or near the Earth's surface.
4. It leads to the formation of soil.
5. It involves several physical, chemical, and biological processes.
6. It changes hard rocks into finer materials.
7. It prepares rock material for transportation by agents of erosion.

(i) Physical weathering is also called mechanical weathering as it involves rock disintegration without any change in the chemical constituents of the rock.

(ii) Physical weathering is more rapid in desert climates because temperature changes are sharpest in a desert.

(iii) Chemical weathering occurs in moist and cold climates because such climate has abundant water and oxygen which are the main agents of chemical weathering.

Below diagram shows the process of physical weathering:

Chemical weathering is the process in which some or all of the minerals in rocks undergo decay or alteration due to the action of water, oxygen, carbon dioxide, and organic acids, forming new chemical compounds.

Four main processes involved in chemical weathering are-

1. Oxidation
2. Carbonation
3. Hydration
4. Solution

Biological weathering involves both physical disintegration and chemical decomposition as all biological matter is made up of oxygen and water.

The main agents of biological weathering are animals, insects, plants and man.

(i) Biological weathering is also known as organic weathering because it is caused by the action of living organisms such as plants, animals, and microorganisms.

(ii) Vegetation prevents the disintegration of rocks because its roots bind the soil and cover the rock surface, reducing the rocks' exposure to weathering agents.

(iii) Chemical and biological weathering are negligible in polar climates because water remains frozen for most of the year, limiting chemical reactions, and the extreme cold supports very little plant and animal life.

The chief characteristics of weathering in different climates are-

1. Equatorial climate – High temperature and humidity throughout the year make chemical weathering the dominant process.
2. Tropical climate – Alternate wet and dry seasons promote weathering. During the wet season, iron and aluminium oxides are leached and redeposited, leading to the formation of laterite soils.
3. Dry (desert) climate – Mechanical weathering is most dominant due to the high diurnal range of temperature.
4. Temperate climate – Frost action is an important agent of mechanical weathering, while solution (chemical weathering) is common in limestone regions.
5. Polar climate – Physical weathering due to frost action is most prevalent, whereas chemical and biological weathering are negligible.

Yes, I agree that weathering is a natural process, but human activities can accelerate it in the following ways:

1. Mining and quarrying expose fresh rock surfaces, making them more vulnerable to weathering.
2. Construction activities involve cutting and blasting rocks, increasing their exposure to weathering agents.
3. Deforestation removes the protective vegetation cover, exposing rocks and soil to wind, water, and temperature changes.
4. Industrial pollution can cause acid rain, which speeds up the chemical weathering of rocks, especially limestone and marble.

Thus, although weathering is a natural process, human activities can significantly increase its rate.

Weathering plays an important role in supporting biodiversity by creating conditions necessary for the growth and survival of living organisms.

1. Soil Formation — Weathering breaks down rocks to form soil, which supports the growth of plants. Different types of soil support different kinds of vegetation and, in turn, diverse animal life.
2. Nutrient Release – Chemical weathering releases essential minerals such as calcium, potassium, and phosphorus into the soil, making it fertile and suitable for plant growth.
3. Formation of Landforms – Weathering, along with erosion, creates mountains, valleys, plateaus, and other landforms that provide varied habitats for different plants and animals.
4. Support for Aquatic Life – Weathering supplies minerals and sediments to rivers and lakes, creating favourable conditions for aquatic organisms.

Thus, by forming soil, releasing nutrients, and creating diverse habitats, weathering plays a vital role in maintaining biodiversity on Earth.

On my way to the Rann of Kutch, I noticed mechanical (physical) weathering of rocks.

The Rann of Kutch has a hot desert climate, with very high daytime temperatures and cool nights. The large daily temperature range causes rocks to expand during the day and contract at night. Repeated expansion and contraction lead to block disintegration.

Since most rocks are poor conductors of heat, only their outer layers are affected. Repeated heating and cooling cause these layers to peel off, a process known as exfoliation.