SS3 Second Term Geography Lesson Note – Weathering

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WEEK:  1           

TOPIC: WEATHERING

CONTENT: MAJOR CONCEPT

1. Rock disintegration (expansion and decomposition)
2. Rock decomposition (oxidation and carbonation)
3. Weathered debris and regolith etc.

TYPES OF WEATHERING

Physical (mechanical) weathering; temperature change, wetting and drying, frost action

SUB-TOPIC 1: MAJOR CONCEPT OF WEATHERING

The major concepts of weathering include:

ROCK DISINTEGRATION (EXPANSION AND CONTRACTION): In desert regions, during the day, rock surfaces receive heat from the sun. This heat causes expansion to the rock surface. In the night, the rock surface becomes cool which leads to contraction. This continuous process daily, weekly and yearly leads to breaking down of the rock ‘disintegration.

ROCK DECOMPOSITION (OXIDATION AND CARBONATION): This is the process whereby oxidation reactions weaken the stability of rocks. It is the reaction of both oxygen content in water and the carbon dioxide in the atmosphere on the rock surface. This process leads to quick decomposition of the rock.

EVALUATION:

1. Differentiate between rock disintegration and rock decomposition.

SUB – TOPIC 2: TYPES OF WEATHERING.

There are three types of weathering; i. Physical (Mechanical) weathering. ii. Chemical weathering. iii. Biological weathering.

PHYSICAL (MECHANICAL) WEATHERING.

This is a type of weathering that takes place in rock which the chemical composition of the rock does not change. In physical weathering, disintegration of rock boulders, regolith and pebbles take place. This disintegration takes place in four ways.

1. TEMPERATURE CHANGE: When changes occur in temperature, a rock that is subjected to heat undergoes physical disintegration. In desert areas, during the day the rock surface is exposed to the direct rays of the sun. The elements or the minerals in the rock receive the heat and expand. During the night the temperature falls and the mineral elements that make up the rock contract. The expansion and contraction of the rock lead to disintegration of rock. In desert region, exfoliation results in which there is an onion peeling of the surface of the rock.

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