GC Leong Test: Weathering, Mass Movement And Ground Water - 1 - BPSC (Bihar) MCQ

i. Weathering: the gradual disintegration rocks by atmospheric or weather forces; 

ii. Erosion: the active wearing away of the earth's surface by moving agents like running water, wind, ice and waves; 

iii. Transportation: the removal of the eroded debris to new positions; 

iv. Deposition: the dumping of the debris in certain parts of the earth, where it may accumulate to form new rocks.

• Chemical weathering is the basic process by which denudation proceeds. It is the extremely slow and gradual decomposition of rocks due to exposure to air and water. 

• Air and water contain chemical elements, which though they may be in small quantities, are sufficient to set up chemical reactions in exposed rocks' surface layers.

• When a rock's surface is weathered, some of the loosened material is removed by erosive agents such as wind or running water, thus exposing a fresh surface to weathering. Still, much of the weathered material or regolith (remains of the rock) may stay in position forming the basis of soil. 

• Regolith is simply the mineral remains of decomposed rocks. Still, the soil contains organic materials, such as plants, fallen leaves, and small animals such as worms, bacteria, etc.

• It is the soil's organic content, which makes it fertile and allows crops to be grown.

• When a soil cover exists, chemical weathering of the underlying rocks does not cease; on the contrary, it is usually enhanced. 

• This is because the soil absorbs rainwater and keeps the underlying rocks in contact with this moisture. 

• The rainwater absorbs organic acids from the soil and becomes a stronger weathering agent than pure rainwater acting on bare rock.

• Limestone, however, is by no means the only rock to suffer from solution. 

• All rocks are subject to the solution, though the process is much slower than with limestone. 

• The rate at which solution takes place is affected by the mineral composition of the rock and its structure; Sedimentary rocks often have pore-spaces between the grains in which air and water can lodge and thus attack the rock.

• Oxidation is the reaction of oxygen in air or water with minerals in the rock. 

• Most rocks contain a certain amount of iron when it comes in contact with air is changed to iron oxide, familiar brownish crust or rust. 

• Iron oxide crumbles easily and is fat more easily eroded than the original iron. 

• It is thus removed, loosening the overall structure of the rocks and weakening them.

Explanation:

Statement 1: In deserts, rocks are exposed to the blazing sun during the day and are intensely heated.

• Deserts are known for their extreme heat and lack of vegetation to provide shade.


• The rocks in deserts are exposed to direct sunlight, resulting in intense heating.


• Therefore, statement 1 is correct.

Statement 2: The outer layers expand much faster than the cooler interior of the rocks and tend to pull away from the rest.

• When rocks are heated by the sun, the outer layers expand due to the increase in temperature.


• The expansion of the outer layers is faster than the interior, leading to a pulling effect.


• Therefore, statement 2 is correct.

Statement 3: At nightfall, the temperature drops rapidly, and the outer layers contract more rapidly than the interior, setting up internal stresses.

• When the sun sets in the desert, the temperature drops rapidly.


• As the temperature decreases, the outer layers of the rocks contract faster than the interior.


• This differential contraction sets up internal stresses within the rocks.


• Therefore, statement 3 is correct.

Since all three statements are correct, the correct answer is option D: All of them.

• Rectangular blocks are thus gradually rounded by the splitting away of sharp corners. 

• When the surface layers of rounded boulders gradually split off the process is called onion peeling. 

• The various layers look like the layers of an onion, peeled off one after another. The technical term for this process is exfoliation.