What is Mechanical Weathering?

Mechanical weathering done by tree roots is pictured here.
Mechanical weathering done by tree roots is pictured here.

From a human perspective, rocks seem not to change at all. However, in geological timelines, rocks are acted upon by different forces of nature which ultimately lead to their degeneration into smaller fragments in a process known as weathering. Weathering of rocks occurs either through chemical weathering or mechanical weathering. Mechanical weathering is the process of breaking down of rocks into smaller particles without the involvement of any chemical reaction. Mechanical weathering is a continuous process occurring in nature and it usually occurs in a significant geological time frame and not easily noticeable in ordinary human observation.

How Does Temperature Cause Mechanical Weathering?

Mechanical weathering occurs in various forms. One type of mechanical weathering is one which occurs through thermal fracture which is also known as insolation weathering. Thermal fracturing is the process where differences in temperature affect the stability of a rock through expansion and contraction and ultimately lead to the degeneration of the rock into small fragments in a process known as thermal pressure. Thermal pressure can also be seen in rocks with a varied composition where their layers expand and contract at different rates leading to the rocks to break apart. Thermal fracturing can also occur through shock where a rock is exposed to frequent drastic changes in the temperature resulting in the degradation of the rock. Such forms of thermal weathering are evident in deserts where temperatures during the day soar to scorching levels while during the night the temperatures plunge to near freezing.

How Does Ice Cause Mechanical Weathering?

Mechanical weathering can also occur in the form of frost weathering. Frost weathering is the process which involves the action of ice on a rock and is also known as frost wedging or cryofracture. Frost weathering is common in mountain peaks where extremely low temperatures allow for the freezing of water covering the rocks and in any cracks found on the rocks. When frozen the icy water expand causing a significant amount of stress on the rock which in the long-run degenerates. When frozen to ice, water expands by up to 10% in size and the entire size is confined inside the crevices of rock which lead to the exertion of high amount of pressure. Estimates put the pressure placed on the rock by the freezing water with a temperature of (negative) -7.6 degrees Fahrenheit at about 30,000 pounds per square inch. Ice is also a medium of mechanical weathering while on transit through moving ice in avalanches. These powerful forces of nature carry with them millions of tons of debris, snow, and ice down a mountain slope and any loose rock on their path quickly erodes away. The debris in avalanches also features rocks which are further disintegrated by the powerful pressure and force created by the rapidly moving ice and snow.

How Do Plants Cause Mechanical Weathering?

Plants are also attributed to mechanical weathering of rocks. One of the best examples of this form of mechanical weathering is the root system of trees. Trees which grow on rocky surfaces are among the best mediums of weathering as their root systems infiltrate any fractures on the rocks and as the roots grow in size, they exert a tremendous amount of pressure on the rocks leading to their fragmentation. Other species of trees such as the giant sequoia grow to become so large that their sheer weight causes any underlying rocks to undergo extreme amount of stress and finally disintegrate. However, size is not the only factor considered in plant-based mechanical weathering. Some of the most effective plants in the weathering of rocks are also some of the smallest; lichens and algae. These plants which grow on moist rocks ultimately cause a rock to break away.

How Does Salt Cause Mechanical Weathering?

Salt can be more closely linked with chemical weathering than mechanical weathering considering the composition of the compound, and its dissolving ability in the water. However, salt is another primary cause of mechanical weathering in rocks. After being inside rock crevices primarily located along the shorelines of salt lakes or seas, increased heat causes the water to evaporate, leaving the salt inside the rock’s crevices. These salt crystals are some of the leading mechanical weathering causes whereby these crystals expand upon the increase in temperature and hence exerting tremendous pressure on the rock.

What Is Abrasion In Mechanical Weathering?

Abrasion is the process where rocks are eroded by continuous friction acting on the rock surfaces. Such friction is brought about by rapidly moving particles colliding with the rock while such particles are being carried by water, wind or glaciers. The velocity and size of the moving particles are responsible for the intensity of the mechanical weathering process. Abrasion is also present in the formation of coastal geography through ocean waves. These waves which consistently hit the shore carry with them fragments which ultimately lead to the erosion of rocks. Winds are also leading causes of mechanical weathering through abrasion as strong winds moving particles of sand and rock fragments collide with a rock and with time cause such rock to display denudation. Such forms of mechanical weathering is usually present in desert landscapes where massive sand storms which carry with them millions upon millions of dust particles which have eroded away the desert rocks.

How Are Animals Involved In Mechanical Weathering?

Animals are also responsible for mechanical weathering albeit to a relatively small extent. The rare mechanical weathering linked to animals is predominantly caused by burrowing animals who dig burrows beneath the earth’s surface, and these burrows cause the surface above them to weaken and susceptible to collapse. However, there are instances where marine invertebrates are known to cause mechanical weathering. Piddocks, also known as angel wings are mollusks which use their sharp teeth-like structures to burrow into the rock where they then reside in for their lifespan. Each piddock leaves behind a hole in the rock after it dies which caused such a rock to be susceptible to breaking down.

How Do Human Beings Cause Mechanical Weathering?

Humans are another agent of mechanical weathering. People have innovated massive machines which break up rocks into finer materials used in building and construction. Humans also break up big lumps of earth into finer particles when preparing land for farming which is another form of mechanical weathering.


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