The chemical weathering is a reaction of the water molecules in an atmosphere with aqueous molecules of minerals to produce secondary chemicals. ]
Chemical weathering has been demonstrated on Earth since Precambrian times and is known to occur when the surface layer of an igneous rock becomes in contact with rain or snow.
This process happens very slowly and results in the dissolution, transport, and redeposition of significant quantities of ions that yield nitrate salts and sulfuric acid from rocks over long periods
of time.
Chemical weathering produces soil-reactive substances that act as nutrients for plants.
The erosion of silicate minerals in rocks, forest soils, and the upper layer of the soil by chemical weathering is responsible for supplying more than half of atmospheric oxygen (see O2 photosynthesis ).
The last geoscientist to complete a PhD thesis on the nature and control of chemical weathering was Sigurd H. Zandee in 1967.
The modern study of chemical weathering owes much to Charles W. Knauss (1905-1963), a USGS research chemist who had studied the rate at which minerals are eroded from igneous rock formations by aqueous solutions, especially water-saturated steam, during investigations of pegmatite deposits in South Dakota in 1937.
Which climate contains the optimum environment for chemical weathering?
1. Tropical climate –
The erosion rate is slow due to the continuous rainfall and high humidity. Most of the surface water from rain and snow is retained in the soil, and does not get much time to interact with minerals.
2. Temperate climate –
The erosion rate is moderate due to the rainfall mainly in winter months.
The temperature remains moderate throughout the year, but this climate still has a slightly higher erosion rate than tropical climate.
3. Polar climate –
The erosion rate is low due to the short and cool summers, but unlike Tropical climates, Arctic soil can be frozen for over 6 months of a year.
This greatly reduces chemical weathering because water-saturated steam cannot contact minerals as easily during freezing periods when it would cause a more pronounced chemical reaction.
4. Desert climate –
The erosion rate is very low due to the low rainfall and high temperature.
Chemical weathering is only caused by the rain, but due to its low amount, chemical weathering does not affect rock or soil as much as in other climates.
5. Forests –
The forests result in a very low erosion rate due to the thick layer of base saturation minerals. This slows down chemical weathering.
The soil of the forest is more dense than the soil in other climate types.
6. Rainforests –
Rainforests slow down chemical weathering because they have large amounts of base saturation minerals on their surface layer in comparison to forest soil and rock.
Soils are thin and porous, with a thin surface layer that locks out the water molecules, limiting chemical weathering to lead to a low erosion rate.
7. Tundra –
Because the tundra has a low pollen productivity, chemical weathering is very slow due to the low amount of water-saturated steam.
8. Mountains –
Mountains produce very little water-saturated steam during cold winters and a strong base saturation minerals in the top layer.
Although the erosion rate is low due to the flat surfaces of the mountains, it is still significant.
However, chemical weathering is still limited because water-saturated steam cannot get through the rock layers easily and cause a fast chemical reaction on mineral surfaces.
9. Shallow soils –
Shallow soils with little soil depth cause fast chemical reactions on mineral surfaces due to high amounts of rain and snowfall that quickly evaporate into steam.
10. Deep soils –
Deep soils are very thick, and have slow chemical reactions on mineral surfaces due to the low amounts of rain and snowfall usually present.
Soil is constantly locked out by the surface layer of minerals, causing a low erosion rate.
From the above climates, it can be concluded that chemical weathering is quicker in a tropical climate than in a polar climate, and quicker in an arid climate than in an arctic or temperate climate. The most harmful weathering agents are quick to react with the surface of rocks, so they are more active under tropical conditions. Rocks and minerals weather fastest in hot, wet climates, although this fact is only useful under conditions found in climates such as tropical or arid ones.
This is different because chemical weathering takes place on rocks found on the Earth’s surface, which are made up of silicate minerals.
Weathering can also occur underground when minerals come in contact with water-saturated steam.
Chemical weathering is not significantly affected by the seasons unlike physical weathering. It depends on other factors such as humidity, rainfall rate and temperature to determine how fast chemical weathering will occur.
Chemical weathering usually occurs at a much slower rate than physical processes unless the chemical reactions cause rapid decomposition of rocks .
