FACTORS AFFECTING THE RATE AND NATURE OF WEATHERING

FACTORS AFFECTING THE RATE AND NATURE OF WEATHERING
The rate, speed and type of weathering are determined by several factors including the ones listed and explained below:

1. Nature of the rock: basing on nature of the rock consideration is made on the following character and constituent of the rock:

• Mineral composition of the rock: rocks are made up of different minerals sum of which are soluble when reacts with water while others are resistant. Where rocks contain minerals which are less resistant to water weathering particularly chemical weathering become rapid and dominant. Example salt rocks (NaCl) and (KCl) as well as Gypsum. Some rocks containing aluminum and iron when react with oxygen present in water undergoes rapid chemical weathering. Quartz has a very low solubility and thus resistance to chemical weathering hence undergoes slow mechanical weathering.
• Rock joints or rock fractures: where rocks consists of several cracks and joints, weathering both chemical and physical weathering is more likely to occur simply because, the lines of weakness allowing infiltration of water into the rock which creates room for reaction of oxygen, carbon dioxide or hydrogen with rock minerals hence decaying of the rock through oxidation, carbonation or hydrolysis respectively. On other hand rock joints create room for frost action to take place.
• Mineral colour. The colour of the rock is determined by the colour of minerals made up the rock. Mineral colour has an influence in the rate of expansion and contraction of rocks due to temperature change. Light coloured minerals has low degree of heat energy absorption hence less expanded due to temperature influence unlike dark coloured minerals where due to high  rate of heat absorption expands and shrinks rapidly which over time results into the formation of cracks hence disintegration of rocks.

• Exposure of the rock or relief factor: where the rock is exposed to weathering agents such as temperature (sun heat energy) or water weathering both physical and chemical becomes dominant. On a steep slope the rate of removal of weathered material is rapid hence the rocks becomes much exposed to weathering agent particularly heat. Likewise in lowland areas water collects and over time favors chemical weathering to occur such as oxidation in water lodging areas. Where the rock is exposed or unloaded after a long period of being compressed exfoliation may occur.

2. Organisms or biological factor: living organisms both plants and animals can in one way or the other results into weathering of rocks.

• Animals such as burrowing animals exposes rocks to the agents of weathering and also break down soft rocks resulting into disintegration of rocks(weathering of rocks).
• Likewise various human activities such as mining, quarrying and cultivation results into physical weathering of rocks. Also some chemicals introduced by man into the soil or water mix up with water to cause chemical weathering of rocks.
• On other hand plant roots penetrates into rock joints and as they continue to grow in size forces rock joints to expand causing physical weathering of rock. Also plant release humic acid through plant roots and also when some of the plant decompose, this humic acid react with rock minerals causing decaying of rocks.

3.Climate: climate (temperature and humidity) plays a greater role in determining the rate and type weathering.
Chemical weathering is enhanced by a combination of high temperatures and abundant precipitation.
Of these two factors, the moisture is usually more important than temperature in determining type and rate of chemical weathering. Example oxidation is the outcome of reaction of oxygen present in water and iron or aluminum mineral present in water. Hydration, hydrolysis, carbonation also operate under the presence of water.

Thus chemical weathering is much pronounced in hot and humid regions such as in equator and tropical areas where rainfall is abundant.

Most desert regions, because of a general lack of precipitation, mechanical weathering may be more dominant than chemical weathering where temperature acts as dominant factor through alternate heating and cooling.
Also salt crystallization is more pronounced in desert and semi-arid because of capillary action.

There are many variations in the connection between weathering and climate.
 Notice that, the depth of active weathering tends to be relatively shallow in regions of tundra and desert but relatively deep in regions of tropical rainforest.

SIGNIFICANCE OF WEATHERING
1. Weathering processes are responsible for breaking down the rocks into smaller fragments and preparing the way for soils erosion and mass movements.

2. Biomes and biodiversity is basically a result of forests (vegetation) and forests depend upon the depth of weathering mantles.

3. Weathering helps in modifying land forms and creation of new features. That means, weathering aids mass wasting, erosion and reduction of relief and changes in landforms.

4. Weathering of rocks and deposits helps in the enrichment and concentrations of certain valuable ores of iron, manganese, aluminium, copper etc., which are of great importance for the national economy.

5. Weathering is an important process in the formation of regolith and soils.

6. Weathering provides building materials such as stones, gravels for construction of buildings and roads.
7. Some newly modified and formed landforms attract tourism activities.

NOTE:
1. Two general kinds of weathering processes take place: mechanical (physical) and chemical. Mechanical weathering causes rock bodies to break into smaller rock fragments, whereas chemical weathering causes the rock to change chemical composition.
2.Although mechanical weathering and chemical weathering can occur anywhere, most mechanical weathering occurs in cold environments, whereas chemical weathering is more pervasive in warm/humid climates.
3.The three major kinds of mechanical weathering are frost wedging, salt-crystal growth, and exfoliation. Frost wedging involves water that expands and contracts upon freezing and thawing in joints and cracks in rock. Salt-crystal growth occurs when water seeps out of rock in arid environments. Exfoliation happens when rock expands because of unloading and temperature changes.
4. The three major kinds of chemical weathering are hydrolysis, oxidation, and carbonation. Hydrolysis occurs when water interacts with rocks, causing chemical reactions to occur. Oxidation occurs when oxygen combines with metals to form oxides. Carbonation takes place when carbonic acid in precipitation accumulates on rocks and causes them slowly to dissolve.
5. Humans have increased the amount of chemical weathering downwind of industrial cities through the process of acid rain. Most of these acids come in the form of sulfur dioxide and nitrogen oxides derived from coal-burning power plants.