Geography [4 Mark Question Answer]

Colloids: Colloids are extremely tiny particles which are so small that they can not be seen by optical microscope ‘ and remain suspended indefinitely in water. They have the property of being electrically charged and can attract and hold ions of calcium, magnesium and potassium, known as bases. These bases are required by plants for their growth. – Soil colloids are also useful in holding water in the soil. When present in large quantities, they make the soil sticky and tough so that it is difficult to cultivate.

Erosion :

1. Erosion includes the work of weathering away of rocks of the earth.
2. It involves motion.
3. River, glacier, wind are its main agents.

Weathering :

1. Weathering is the breaking of rocks by elements of the atmosphere.
2. It involves no motion.
3. Temperature, frost, wind, plants and animals are its main agents.

Solution: It is the chemical process in which the soluble minerals are dissolved by water entering into rocks through crevices. The dissolved minerals are removed with the flow of water resulting in the break up of the rock. Rock-salt and gypsum weather away chemically because of this process. Since silica is highly soluble in water, and silica is found in so many rocks, this process is also known as Desilication.
Hydration: It is the process by which some minerals in crystalline form absorb water and become a powdery mass. Feldspar, a common rock-forming crystalline mineral absorbs water and becomes a mass of clay by the process of hydration. The other minerals present along with feldspar get separated into loose particles and the rock breaks up.

Granular Disintegration; The temperature changes during summer and winter lead to expansion, due to heating and contraction, due to cooling. Different minerals present in the rocks may have different rates of expansion and contraction. For example, dark coloured minerals will absorb more heat and expand to a greater extent than light coloured minerals. Such alternating expansion and contraction between day and night lead to a break up of the rock into different minerals. This type of weathering is called granular disintegration.
Block Disintegration: A rock may split along joints or fissures by the repeated freezing of water in cracks or other openings because water expands nearly one-tenth of its volume when it freezes. It is followed by melting during the daytime repeatedly. This type of weathering is called block disintegration because the rock is split into rectangular block along the joints.

 Physical weathering: It is also called Mechanical weathering. It includes the breaking up of rocks without changing their composition. It means the disintegration of rocks by mechanical means. This type of weathering results from the action of temperature changes, frost, wind, and rainfall. It is important in dry areas.
Chemical weathering: The decomposition of rocks by chemical processes is called chemical weathering. This type of weathering produces a chemical change in minerals of rocks. It results from the action of weak acids and atmospheric gases like oxygen, carbon dioxide, hydrogen. It involves the process of oxidation, carbonation, solution and hydration. It is important in hot humid areas.

The kinds of temperate zone soils may be classified as follows.
Name :

1. Podzol
2. Cheronozems region
3. Brown and Grey soils
4. Chestnut soils

Region :

1. Cool and cold coniferous forest
2. Grassy steppes and semi-arid lands
3. Deciduous forest region of high and middle latitudes
4. Arid margins of steppes.

Humus: Humus is a dark substance formed in soils. It is a dead organic matter formed by the decay of animals and plants. Trees, shrubs, grass, and bacteria help in the formation of humus. In warmer climates, humus is destroyed by countless bacteria. In colder areas, soils are rich in humus and it is collected in the soil. Tropical humid soils are poor in humus because it is consumed by bacteria.
Humus is vital to the fertility of soils. It provides nitrogen, phosphorus, and calcium to the soils. It sustains other forms of life. It helps the weathering of minerals to add to the fertility of soils. It increases the water-holding capacity of soils.

Mass movements are divided into slow and rapid movements. Slow movement includes Creep, movement of soil and debris and Solifluction or clay formation Rapid movement includes landslide, Earth Flow or a heavy thick paste of soil down the slope, Mud Flow in the areas without vegetation cover and Sheet Wash in the form of large sheet flow snatching thick rock strata uncovering the rocks below. It may also take place by human activities of settlement.
A mass movement has built many remarkable landforms as Himalayan lakes, Terraces, escarpment, etc

Chemical weathering takes place with the help of agents as water, wind, and various organic acids, reacting in the chemical composition of rocks which are then disintegrated. Four main processes are the solution by dissolving salts in the rocks with water, carbonation works with the reaction of carbon dioxide with rocks, oxidation takes place through atmospheric oxygen reacting with minerals present in rocks, hydration is evident by mixing of rainwater with minerals in rocks, which expand by this and become heavy.

Physical Weathering :

1. Rock disintegration without any change in chemical constituents of rocks takes place.
2. Factors such as temperature, moisture, pressure cause the physical break-up of rocks.
3. It takes place in hot dry and cold areas due to rapid temperature changes.
4. Rocks are affected to great depths.
5. Its agents are temperature and moisture.

Chemical Weathering :

1. Minerals in rocks are dissolved or altered.
2. Temperature, moisture, etc., cause minerals in rocks to dissolve in water or convert them into other minerals.
3. It takes place in hot and humid areas due to the chemical action of minerals in rocks.
4. It mostly takes place near the surface of the earth.
5. Its agents are solution, oxidation, carbonation, and hydration.

Weathering is the process of breaking down of rocks but not its removal. It is described as disintegration or decomposition of rock in size by natural agents at or near the surface of the earth.
Chief characteristics of weathering are :
The disintegration of rocks, chemical change in rocks, change in the surface of the land, the formation of soil, several processes involved in weathering like temperature and weather change and reactions, transportation of rock material from one place to another resulting in the formation of large plains like Northern plain of India.