Exogenic processes part-1 - class-VIII

An estuary is the area where a river meets the sea or ocean, where fresh water from the river meets salt water from the sea.

Gradation is the process of leveling the land surface by the combined action of degradation (wearing down) and aggradation (building up).

• Weathering is the breakdown of rocks and materials attached to the earth's surface.
• Erosion is the removal of material from their original place on earth's surface after it has been weathered.
• Transportation is the movement of the eroded materials to long distances by the actions of various agents like water, wind etc.
• Hence the sequence will be weathering, erosion and transportation

The moving ice mass downslope under the impact of gravity is called a glacier. About 10% of the earth's surface is now covered by the glacier. Glaciers are generally divided into two broad categories viz.

Weathering refers to the breakdown or disintegration and decomposition of rocks in situ through mechanical and chemical changes in the rocks. Weathering by itself is a static process and does not involve removal of the material. The products of weathering tend to accumulate in a soft surface layer.

Quartz is the second most abundant mineral in the earth’s crust. This is used in making jewelry and hard stone carvings. It is the hardest material and is least susceptible to chemical weathering.

• Glaciers, winds and rainwater are the agents of wethering which imply they are the forces that carry out the breakdown of materials over the earth's surface
  
• Soil is the material which is formed as the result of wethering hence it is not the agent of wethering and this is the right answer.

The Intertropical Convergence Zone (ITCZ), known by sailors as the doldrums, is the area encircling the earth near the equator where the northeast and southeast trade winds come together.

The repeated heating and cooling exerts stress on the outer layers of rocks, which can cause their outer layers to peel off in thin sheets. The process of peeling off is also called exfoliation and it is a mechanical process. Over time, sheets of rock break away from the exposed rocks along the fractures, a process known as exfoliation. Exfoliation due to pressure release is also known as "sheeting". Retreat of an overlying glacier can also lead to exfoliation due to pressure release.

Solution is obtained when some substances present in the rocks are directly soluble in water. The soluble substances are removed by the continuous action of water and the rock no longer remains solid and form holes, rills or rough surface and ultimately falls into pieces or decomposes. The action is considerably increased when the water is acidified by the dissolution of organic and inorganic acids.

Biological weathering also means organic weathering. It is the disintegration of rocks as a result of the action by living organisms. Plant and animals have a significant effect on the rocks as they penetrate or burrow into the soil respectively. Biological weathering can work hand in hand with physical weathering by weakening rock or exposing it to the forces of physical or chemical weathering.

Weathering is the breaking down of rocks, soil, and minerals as well as wood and artificial materials through contact with the Earth's atmosphere, waters, and biological organisms. Weathering occurs in situ, that is, in the same place, with little or no movement, and thus should not be confused with erosion, which involves the movement of rocks and minerals by agents such as water, ice, snow, wind, waves and gravity and then being transported and deposited in other locations.

Temperature, rain, and wind are physical or mechanical agents of weathering because they cause the physical breakdown of rocks without changing their chemical composition.

Breaking or weakening of rocks is a natural phenomenon. It is called weathering. Weathering can be of three type:-

• Mechanical
• Chemical
• Biological

Mechanical weathering mainly occurs because of the following reasons:-

• Temperature
• Frost
• Crystal growth
• Release of pressure
• Water

Water plays an important role in chemical weathering. Rock is a mixture of many minerals and water is a universal solvent. Chemical weathering takes place in the areas which receives heavy rainfall. Chemical weathering occurs in the following ways: Carbonation, Solution and Oxidation.

The iron in the rock comes in contact with water and chemical reaction takes place between iron and oxygen. Hence,a reddish coloured layer forms on the rocks. This is called rust.

When water penetrates through sandstone rocks, the particles get loose and separate from the main rock. This is called granular weathering.

Ants make large anthills. Rats, mice, rabbits and other worms and insects make burrows in the ground. These animals are called burrowing animals.

Lime stone is formed due to chemical precipitation between water and alkalis. At Wadgaon Darya in Ahmadnagar district, limestones gets precipitated chemically i.e. undergoes chemical weathering. Similarly, because of solution, alkalis in the rock dissolve and make them brittle.

Chemical weathering occurs in following ways:-

• By carbonation
• By solution
• By oxidation

The arid or hot desert areas dominated by mechanical weathering. Due to the high diurnal range of temperature in the arid areas, repeated expansion and contraction of the outer layer of the rock takes place. The rocks then disintegrate along these joints and big blocks of rocks are dislodged from the main rock mass and fall down the slope under the impact of gravity.

Weathering refers to the breakdown or disintegration and decomposition of rocks in situ through mechanical and chemical changes in rock. The nature and magnitude of weathering differs from place to place and region to region. 

Weathering is a process used to explain the breakdown of the rocks due to exposure to the atmosphere. Weathering down of the rock into small pieces is called disintegration. It is in granular weathering, when water penetrates through the rocks, the particles get loose and separate from the main rock. It is a process where a rock disintegrates due to frost action. The water in the rocks freezes as well as liquify at the same time. The rock disintegrates because of heating and cooling at the same time, which result in the expansion and contraction of minerals in the rock breaking it into small pieces.

Decomposition and disintegration and decomposition of rocks due to chemical reaction is called chemical weathering. Chemical weathering takes place through the process of solution, oxidation and carbonation. Solution refers to the dissolution of soluble particles and minerals from the rocks with the help of water in motion. The atmospheric oxygen in rain water when meet with mineral like iron, rusting takes place and the colour of the rock changes. The process is called oxidation. When the carbon dioxide present in water reacts with rocks new chemical substances like calcium carbonation and iron carbonate are formed. This process is called carbonation. 

Exfoliation is type of mechanical weathering, it is also known as onion weathering. The exfoliation refers to peeling off concentric shells of rocks due to combined actions of heat and wind in hot arid and semi-arid regions and monsoon lands. Exfoliation is more common over crystalline rocks.  

Carbonation is the reaction of carbonate or bicarbonate ions with minerals. The process of carbonation is also known as solution wherein atmospheric carbon dioxide after mixing with water forms carbonic acid which after reacting with carbonate rocks like limestoe forms calcium bicarbonate which is easily dissolved in water.

The exogenetic forces or processes are originated from the atmosphere. These forces are continuously engaged in the destruction of the relief features created by the endogenertic forces through their weathering, erosion, mass movement. 

Biological weathering refers to decomposition and disintegration of rocks due to organic material of both flora and fauna. Production of different kinds of organic acids such as humic acids, baterial acids, microfaunal acids etc produced by organic materials help in the decomposition and disintegration of rocks and soils.

Decomposition and disintegration of rocks due to chemical reaction is called chemical weathering. The chief agents of chemical weathering are air and water. By the action of this two agents, the minerals in rock undergo chemical change and form a new chemical substance. Chemical weathering is more dominant in the area of humid climate. 

The oxidation simply means a reaction of atmospheric oxygen to form oxides. The atmospheric oxygen after reacting with the rocks produces several types of oxides, iron oxide being the most important, which weaken the rocks to disintegrate.

Weathering describes the breaking down or dissolving of rocks and minerals on the surface of the Earth. Water, ice, acids, salts, plants, animals, and changes in weather conditions like temperature, moisture, precipitation, are all agents of weathering.

• The correct sequence of events of the soil erosion process is weathering, erosion, transportation.
  
• Weathering: It is a process by which small rocks are broken down into further smaller pieces.
  
• Erosion: The small fragments of rocks or dust formed by weathering process is moved by wind or water.
  
• Transportation: This is the process by which the sand or rock fragments are carried on to the other places.