Weathering Sample Paper 2020


What is weathering?

It is the breaking down of earth surface rocks due to extreme temperatures, rainfall, plants, animals and biological activities. Weathering aids to loosen and breakdown rock minerals to enable transportation by erosion agents such as ice, wind, and water.

Distinguish between the two main categories of weathering and give examples of how each type operates to create sediments?

Physical and chemical weathering are the main categories of weathering. Better known as mechanical weathering, physical weathering is the disintegration of rocks after weakening due to mechanical forces without alteration of their chemical structure. Physical weathering occurs constantly through the influence of natural forces such as temperature, water, and wind. Wind acts on loose rocks often leaving them denudated. The forces of wind sweep away light rock particles colliding them with other rocks causing wearing down. Wind action is a common weathering agent in deserts through sandstorms.

As an agent slides to spaces between rocks and freezes. Once frozen, it expands causing it to crack and widens cracks to the ones previously cracked. Eventually, big boulders are broken to smaller fragments. Fluctuations in temperature are a key contributor to thermal stress. This is the expansion and contraction of rocks due to changes in temperatures. The rocks experience uneven contraction and expansion causing them to disintegrate to smaller fragments. There are several forms of physical weathering such as thermal pressure, freeze-thaw, exfoliation, salt weathering, plant and animal action, and abrasion.

On the other hand, chemical weathering alters the original composition of a substance giving it new physical characteristics as well as different chemical composition. The new structure becomes softer and prone to erosion agents compared to the original one. For the occurrence of chemical weathering, moisture and temperature play an important role. Chemical weathering is determined through several agents such as acid rain, storm water, rock uplift or mountain movement, and bio-chemical processes. Storm water plays a vital role in the oxidation and hydrolysis process occurring within the rocks. The water tends to be slightly acidic due to the carbon iv oxide absorbed in the atmosphere. The acidity in turn activates chemical processes within the rock giving rise to chemical compounds like minerals and salts which aid in dissolving the rock.

Acidic rain occurs when acidic particles mix with water droplets in the atmosphere. Gasoline, combustion of fossil fuel, gas releases such as oxides of nitrogen, carbon, and sulphur in the atmosphere reacts with moisture forms acidic rainwater. The water reacts with rock particles producing salts and minerals which wear rock grains away. Bio-chemical processes due to excretion of acidic compounds by various animals and plants. When growing on rocky surfaces, microorganisms such as lichens, moss, algae, and bacteria aid quicken the weathering process. These organisms release acidifying molecules and chelating compounds. On their own the compounds can breakdown aluminum and iron minerals found in the rocks. Eventually, they are dissolved in water resulting to chemical weathering. Furthermore, rock uplifts exposes underlying rocks to atmospheric conditions giving room for chemical weathering to take place. There are several forms of chemical weathering such as dissolution, carbonation, hydrolysis, and oxidation.

Give your opinion on which type of weathering works the most rapidly to wear down rock and create sediments.

Both types of weathering take years and at times centuries to happen though physical weathering happens more rapidly compared to chemical weathering. This is because for mechanical weathering to occur, agents such as plant growth, animal movement or abrasion happen quickly since movements of these agents occur day by day. On the contrary, chemical weathering is a gradual process since it entails the changing of the entire chemical composition of an element before it is prone to weathering.