Chemical and mechanical weathering are both irreversible processes that produce
ID: 120874 • Letter: C
Question
Chemical and mechanical weathering are both irreversible processes that produce sediments. However, there is a fundamental difference between the two processes in terms of compositional and mineralogical relationship between the parent rock and the sediment produced by the weathering process. Describe what the fundamental difference and the reasons behind it. Chemical and mechanical weathering are both irreversible processes that produce sediments. However, there is a fundamental difference between the two processes in terms of compositional and mineralogical relationship between the parent rock and the sediment produced by the weathering process. Describe what the fundamental difference and the reasons behind it.Explanation / Answer
Mechanical weathering is the physical breakdown of rock into smaller pieces. Chemical weathering is the breakdown of rock by chemical processes.
Chemical and mechanical weathering are both natural processes that will break down rocks. Their purpose may be the same but their processes are different. Chemical weathering demands chemical reactions with minerals inside the rock and causes changes in rock composition. Sometimes this process will produce a different kind of product due to the reaction. Mechanical weathering only involves the physical breakage of rocks to smaller pieces of fragments. Without changing the physical composition of the rocks, mechanical weathering disintegrates rocks with nature’s own physical pressures.
Climate is very important in the weathering process. Cold temperatures favor mechanical weathering while warm temperatures support chemical weathering. And once weathering is complete, residual materials will be eroded and transported by either wind or water.
Types of Physical Weathering
Wedging is caused by substances that get into holes and cracks in rock and expand outwards. This exerts pressure on the rock and may cause it to further crack and split apart. Water that freezes in cracks and forms ice, salt from evaporated seawater, and growing plant roots may all cause wedging.
Exfoliation occurs when rocks that formed in high pressure environments are brought to the Earth's surface. When the pressure on these rocks decreases, they expand and split apart into sheets.
Abrasion is caused when rocks rub together. For example, the rocks on a riverbed smooth each other because they collide in the current. Small particles of rock carried by the wind may cause abrasion as well.
Thermal expansion is caused by heating. When rocks are heated -- as by the sun -- they expand. If different portions of a rock expand at different rates, the heated parts will exert pressure on each other, and crack.
Types of Chemical Weathering
Oxidation is the reaction of oxygen with chemicals in a rock. For instance, oxygen reacts with iron to form iron oxide -- rust -- which is soft and vulnerable to physical weathering.
Hydrolysis is a process in which a rock absorbs water into its chemical structure. A rock with a higher water content is softer, and thus easier for physical weathering, or even just gravity, to decay.
Carbonation is caused by carbonic acid in water reacting with and degrading rock. This acid is especially effective at degrading limestone. Underground carbonation may form limestone caverns.
Acid rain is caused by sulfur and nitrogen compounds in the air reacting with water to form acids that then fall to the ground. These acids are particularly harmful to marble, chalk, and limestone, and cause damage to tombstones, statues, and other public monuments.
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