WBBSE Class 9 Geography And Environment Chapter 5 Weathering Notes

WBBSE Chapter 5 Weathering Salient Points Introduction

The word weathering has been derived from the word weather.

The term weathering was first used by geologist G. K. Gilbert.

Weathering is a static process, i.e. disintegrated or decomposed rocks do not get removed from their original place.

Erosion is a process whereby weathered materials are transported and deposited elsewhere by various exogenetic forces.

WBBSE Class 9 Geography And Environment Chapter 5 Weathering Notes

Denudation is the process in which the lower layers of the rocks are exposed through the removal of the upper layers by weathering and erosion.

Without the effect of external or internal forces, the weathered debris of rocks moves downward along the slope due to the gravitational force and is transported and deposited elsewhere. This process is known as mass wasting.

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Mechanical weathering occurs in hot desert areas, polar regions, and high mountain regions.

Exfoliation occurs in homogeneous rocks like granite.

Block disintegration is seen more in basalt.

Granular disintegration is prevalent more in heterogeneous rocks, i.e. rocks formed of various minerals.

The formation of ice crystals is observed more along the foothills of the mountains in cold temperate climatic regions.

Chemical weathering is more active in equatorial and humid-tropical climatic regions.

Water and atmospheric oxygen react with the iron-containing rocks and lead to the formation of rust on them. This process is known as oxidation.

Weathering Notes For Class 9 WBBSE Geography

The process of solution is more active in rocks like chalk, limestone, dolomite, etc.

  • Biological weathering is caused by various plants and animals.
  • The fragmented rock waste creating a loose covering on the Earth’s surface due to weathering is called regolith.
  • The process of soil formation from rock debris is called pedogenesis.
  • The smallest particles in the process of soil formation are called the ped.
  • Minerals in the upper layers of the soil mix with rainwater and move downwards. This is called leaching and the process is called eluviation. The process of accumulation of these particles in the lower layers is called illuviation.

Humus is a deep black-colored complex matter, formed due to the decomposition of organic matter. Over a long period, soil develops as a result of the mixing of rock wastes, humus, and water.

Terrace farming, contour farming, and strip cropping prevent soil erosion on the slopes of the mountains.

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The process of preventing soil erosion by covering it with a layer of roots of crops, twigs, tendrils, and specks of dust is called mulching.

  • Due to changes in temperature and humidity, increase or decrease of pressure on rocks, etc., surface rocks get disintegrated by mechanical action. This process is called mechanical weathering.
  • Physical change or change of shape in the. rocks are seen in mechanical weathering but there is no change in the chemical composition or character of the rock-forming minerals.
  • The process of granular disintegration causes noises like gunshots.
  • Carbonic acid (H2CO3) plays an important role in the carbonation process,
  • The various methods of soil conservation maintain the quality of soil and prevent soil erosion.
  • Various natural causes of soil erosion are rainfall, winds, sea waves, glaciers, etc,. and human activities responsible for soil erosion are deforestation, unplanned urbanization, the extension of the transportation network, unscientific settlement, etc.

The processes of soil erosion due to stream action are sheet erosion, rill erosion, gully erosion, and ravine erosion.

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