Weathering

Weathering is breaks down and loosens the surface minerals of rock so they can be transported away by agents oferosion such as water, wind and ice. There are three types of weathering: mechanical chemical and biological  weathering .

Mechanical or Physical Weathering

Mechanical weathering
.....................................

Mechanical weathering is the physical breakdown of rocks into smaller and smaller pieces. One of the most common mechanical actions is frost shattering. It happens when water enters the pores and cracks of rocks, then freezes. Frost weathering, frost wedging, ice wedging or cryofracturing is the collective name for several processes where ice is present. These processes include frost shattering, frost-wedging and freeze-thaw weathering.

Organic or Biological Weathering
..........................................

It is the disintegration of rocks as a result of the action by living organisms. Trees and other plants can wear away rocks since as they penetrate into the soil and as their roots get bigger, they exert pressure on rocks and makes the cracks wider and deeper. Eventually, the plants break the rocks apart. Some plants also grow within the fissures in the rocks which lead to widening of the fissures and then eventual disintegration.

Microscopic organisms like algae, moss, lichens and bacteria can grow on the surface of the rocks and produce chemicals that have the potential of breaking down the outer layer of the rock. They eat away the surface of the rocks. These microscopic organisms also bring about moist chemical micro-environments which encourage the chemical and physical breakdown of the rock surfaces. The amount of biological activity depends upon how much life is in that area. Burrowing animals such as moles, squirrels and rabbits can speed up the development of fissures.

Chemical Weathering
..................................
It happens when rocks are worn away by chemical changes. The natural chemical reactions within the rocks change the composition of the rocks over time. Because the chemical processes are gradual and ongoing, the mineralogy of rocks changes over time thus making them wear away, dissolve, and disintegrate.

The chemical transformations occur when water and oxygen interacts with minerals within the rocks to create different chemical reactions and compounds through processes such as hydrolysis and oxidation. As a result, in the process of new material formations, pores and fissures are created in the rocks thus enhancing the disintegration forces.

Rainwater can also at times become acid when it mixes with acidic depositions in the atmosphere. Acid depositions are created in the atmosphere as a consequence of fossil fuel combustion that releases oxides of nitrogen, sulfur and carbon.

The resultant acid water from precipitation – (acid rain) reacts with the rock’s mineral particles producing new minerals and salts that can readily dissolve or wear away the rock grains. Chemical weathering mostly depends on the rock type and temperature. For instance, limestone is more prone to chemical erosion compared to granite. Higher temperatures increase the rate of chemical weathering.