Our planet continues to be influenced by geological processes which help make the way look it is today, some of these account for weathering. Weathering is essentially the breakdown of rocks, soils and minerals in water and land through interaction with the Earth’s atmosphere. Weathering occurs by means of two processes, physical and chemical. Chemical weathering involves atmospheric chemicals in breakdown of rocks and solids. Physical weathering occurs more frequently than chemical and it also involves breakdown of rocks and solids but this is more direct and less chemicals involved. To understand how weathering really works we have to take an example of Rocky Mountain.
Weathering has had a major impact on this region for the past years. Rocky Mountains are a major mountain region which stretches from British Columbia, Canada to South-western United States. This paper investigates the different types of weathering reaction in the rocky mountain regions, how it affects the region, what features are formed as a result of weathering reactions. The dissolved minerals present in some of the water bodies around the Rocky Mountains. Anthropogenic effect due to weathering rates and many more interesting topics are discussed in detail.
Through the course of geological history, the Earth has witnessed many major events which have transformed it into the present Earth we see today. At the start of the geological time scale earth was known to be molten because of frequently occurring volcanic activities and collisions within the Earth’s crust. Surfaces continued to reshape themselves over periods of hundreds to millions of years through geological processes some of which are weathering, and this helped shape up continents which would at times break apart and form together. Weathering is essentially the breakdown of rocks, soils and minerals in water and land through interaction with the Earth’s atmosphere. Weathering occurs by means of two processes, physical and chemical. Physical weathering occurs more frequently than chemical weathering.
Physical weathering involves the breakdown of rocks and soils through direct interaction with the atmosphere, such as ice, pressure, water and heat. Chemical weathering is the effect caused by atmospheric chemicals involved in the breakdown of rocks and other solids. In weathering, the process occurs inside; this means that there is no movement which is involved during this process. (Paradise, 2002). In an attempt to understand the concepts of weathering we have to first consider a living geological module which has been affected by weathering. A common example of this is Rocky Mountains, it a major mountain range in western North America which stretches to about 3000 miles from British Columbia, Canada to south-western United States (Richards 2007). In this paper we will try to better understand the different weathering reaction from a chemical and geological standpoint.
First let’s take a look at the types of weathering and their subtypes.
Physical weathering or mechanical weathering is a process in which the rocks are reduced in size due to disintegration. The main process in physical weathering is abrasion. Abrasion means that the large rocks are reduced in size due to various processes such as frost action, pressure, and also due to temperature changes (Calvaruso, 2002).
Types of Physical Weathering Processes
* Thermal stress: – In thermal stress it is a process in which the expansion and contraction causes the rocks which are in the earth’s crust to expand and contract and thus disintegrate. The repetitive process of expansion and contraction will make the rock to develop cracks which will then lead to the cracks developing and then, the rock will break to smaller pieces (Uroz, 2002). * Frost weathering: – In frost weathering, the ice wedges itself in the cracks that were formed in the rocks. These cracks will then be expanded by the wedging of the ice and therefore, it will cause the rock to disintegrate and therefore lead to weathering. * Pressure Release: – In this process the overlying materials which were protecting the rocks from the physical activities are removed by other processes such as erosion. The exposed rock now starts to expand and contract and this will mean that the weathering process will occur (Smith, 2012). A point to note is that in the physical processes, thermal changes play a key role in the disintegration of the rocks.
In chemical weathering the process occurs as a result of the changes which occur in the rock. The chemical composition of the rock is altered and thus weathering occurs. The main processes that occur in this type of weathering are dissolution, carbonation, oxidation and hydrolysis.
Dissolution and Carbonation
In this process, the rock is disintegrated because it is exposed to acid rain. Acid rain occurs when the normal rain absorbs gases such as Carbon dioxide and Sulphur dioxide. These gases can lower the pH of the rain to reach levels of up to 3 to 4. These values tell us that the rain water that comes into contact with the rocks is very capable of disintegrating it.
Rocks which contain Calcium Carbonate are largely affected by acid rain especially the one which contains dissolved Carbon dioxide. This is because; rocks which contain Calcium Carbonate will be dissolved leading to the weathering process (Robinson D.A., 1994).
The reaction which occurs is as follows:
CO2 + H2O = H2CO3
H2CO3 + CaCO3 = Ca (HCO3)2
This will lead to weathering.
In this type of chemical weathering process, it is whereby the rocks take up H+ and OH- ions. The rocks then take up water and this leads to the physical stress which will be experienced by the rocks and this will cause it to disintegrate.
Oxidation is a process whereby the ions that are in the rock are changed through the process. This leads to a change in the chemical process of the rock. The process mainly occurs in rocks that contain Iron compounds. The Fe2+ is converted to the Fe3+, this is as a result of the ion combining with the water and oxygen. The process can be summarised in the following equation: Fe2+ + H2O +O2= Fe3+
Fe2+ + OH- = Fe3+
Weathering through the Oxidation Process
In the oxidation process an ion looses one electron as a result of combining with Oxygen. Metals that contain Iron (Fe2+) are oxidized and theyform Iron III ( Fe3+). Iron II is known as Ferrite while Iron III is known as Ferrous. Ferrous is the one that is also known as rust. When a rock rusts it will disintegrate and thus the weathering process will have occurred. This process occurs as represented in the following equation: 4Fe + 3O2 = 2Fe2O3
The iron looses one electron as a result of the oxidation process and therefore forms the rust. Rocks which contain Iron compounds are in most cases coloured brown or red and thus are mostly found in the deserts or areas which have red soils and are humid.
Chemical weathering also involves the disintegration of rocks to convert them to soils or small rocks. In chemical weathering, rocks can be converted to clays, the minerals may be oxidized or in some cases the minerals will be dissolved.
Examples of Chemical Weathering
* The Silicate components that are in the rock can be converted to clay. * Some minerals due to various chemical reactions can be dissolved. * Some rock components are oxidized and, thus weathering takes place.
Conversion of Silicates to Clay
Rocks such as Igneous and Metamorphic rocks mainly consist different varieties of Silicates. When these rocks are exposed to weathering agents such as water, these Silicates are then converted to Clay. The process is shown below: Silicate + Water = Dissolved SiO2 + Clay + dissolved cations ( Na+, K+). This is a chemical weathering process, whereby Silicates which are in a rock such as the Granite, the Silicates are converted to Clay. As a result the crystal boundaries start to decay. This leads to the formation of cracks. As the decay process continues, the cracks widen and eventually the rock will disintegrate. This conversion of Silicates to clay is often enhanced in the event that the water which is involved in this weathering process is slightly acidic. In such a case, the acidic rain mainly comprised of acidic rain that is formed in the following process: H2O + CO2 = H2CO3.
This acid will then react with the Silicates leading to the formation of the clay. The equation can be represented below as follows:
Carbonic acid + Silicates+ water = Clay
Dissolving of Minerals
Some rocks contain minerals which can easily dissolve when they are exposed to the weathering agents. One such mineral is the Calcite which can also be represented as CaCO3. The Calcite when it is exposed to Carbonic rain it will be dissolved as it is shown in the equation below: CaCO3 + H2CO3 = Ca2+ 2HCO3-
Other minerals which can be dissolved when they are exposed to acid rain include Halites. Halites dissolve to form the ions which are represented in the equation below: NaCl = Na+ + Cl-
Diagram showing weathering processes
A rock in Abisko, Sweden fractured along existing joints possibly by frost weathering or thermal stress. Weathering Reactions in Rocky Mountains
Rocky Mountains exist in North America. As these mountains age there are different changes which occur in these mountains. We can start by looking at the size of the mountains. Mountains that are old i.e. they are over a hundred million years old, have been known to undergo various changes which have affected their height. Due to natural processes such as weathering, these mountains have been seen to reduce in size over the years (Ritter, 2003).
Different agents such as plants, glaciers, wind, water and even the chemical processes have been known to affect the size of the rocks that are in the mountain and therefore, reducing their size. Plants such as trees have roots which penetrate the rocks. This will result to the formation of cracks which will be widened by these cracks. Therefore over a certain period of time, the rocks will disintegrate into smaller rock particles.
Looking at other agents such as water, we can see that they also have an effect on the rocks which are in the mountain. Running water makes the rocks to be smooth and round. This shows that weathering has occurred on such rocks.
There are also Glaciers, these also have an impact on the rocks. Glaciers offer various effects on the rocks. When you look at the glaciers, they offer a lot of pressure on the underlying rocks. The second thing that they do is that they lead to temperature changes on these rocks. This eventually leads to the rocks to disintegrate over time (Kayar, 2011). a picture showing Rocky mountains as it is seen in Colorado. This is a photo showing weathering process and how it has affected the Rocky’s mountain.
How does Weathering Affect the Mountains?
Weathering is a very slow process. It occurs over a very long period of time. However, weathering is termed as the first process in the denudation process. The denudation process is a process which involves two things: The first process is the breakdown of the rocks to smaller pieces. The second process involves the disintegrated rocks are transported from other areas. As we have stated earlier, there are factors which have been known to promote on the weathering processes. These factors include things like water, wind and other factors which will eventually lead to the weathering process.
There are various ways, in which weathering affects the mountains. These are: * Weathering will eventually lead to the change in the elevation of the mountain. One can ask the question how? Mountains are basically made up of large rocks. These rocks are then exposed to both the physical and the chemical processes which will eventually lead to the weathering process occurring in these mountains. The disintegration of the rocks will then eventually lead to the mountain size reducing and, therefore this will have a negative effect on the elevation of the mountain. This is due to the reduced size of the rocks that make up the mountain.
* Shaping the mountains: Most of the mountains were developed using the same processes i.e. via volcanic activities or the plate movements which led to block mountains. Whichever the case most mountains were developed using the same processes. However, many mountains are of different shapes. Some of the mountains are tall, rocky and even have pointy peaks. These are mountains such as the Rockies Mountain. Other mountains can be described as short and rounded. Examples of such mountains are the Appalachians and the Great Dividing Range. This can be described as a result of weathering actions on these mountains. Mountains which have pointy peaks are not as old as those which have round peaks and, therefore they have not been exposed to the weathering processes.
Features Formed as a Result of Weathering
This land feature starts out as a narrow bridge between two mountains. The weathering processes occur on this feature and this means that there will be a portion on this arch where the interior of the ridge will be withered away. However, the large part of this arch will not be weathered away as it will be resistive to the weathering process. The result of this is the formation of the Natural Arch. There are regions in the Rockies Mountains where there are natural arches. There are arches in the Arch national park called delicate arch.
The stream lines are a result of cracks which were developed on the various rocks and they expanded to form these stream lines. Eventually they become big enough to form rivers.
Catchment Areas in Rocky Mountains
Mountains are catchment areas for waters. The source of most of the rivers is in the mountains. The source of a large water body such as a river, lake or even an ocean in most cases is the mountain. Water from small sources such as: the rainfall, melting snow, converge on the mountain and forms streams which join up to Form Rivers which go and drain their waters in large water bodies such as rivers and lakes.
Latorita river is an example of a river which starts on a mountain, the catchment area is the mountain. How then do mountains become water catchment areas? We all know that rainfall usually rains in areas where there are forests. Winds transport the clouds (nimbus clouds which carry the rain). As the winds pass by a mountain, the resistive force from the trees and the height of the mountain ensures that there is rainfall in that area. When it rains, the water flows down the slope and it basically forms a water body.
Other things such as leaves of trees ensure that the water is channelled to a stream or a river and thus the water catchment area is formed. In mountainous areas the rainfall in that region is higher and therefore it becomes the source of water. Rivers such as the Himalayan river have their source from the Himalaya mountain. Other rivers such as the Colarado also have their sources from Rocky Mountains (Rocky mountain cordilleras). The Gila River has its source from the Mogollon Mountains in the New Mexico (Ritter, 2003). There are two catchment areas in the Rocky mountains i.e. Northern Rocky Mountain stretch and Souhern Rocky Mountain stretch.
Typical Concentrations of Specific ions in the Rocky Mountain Waters
In most Rocky mountain waters, they have the following ions in its waters. These ions are: Mg2+, Ca2+, Na+ and K +. These ions have been known to elevate the ph of the water due to the presence of the H+ ions. These ions will make the water to be more acidic than in the cases where the waters do not have these ions.
There are also other acidic ions such as NO3-, SO4²-, and Cl-. There are also carbonates and bicarbonates. These carbonates when they combine with the H+ ions, will make the water to be more acidic. The equation can be represented as follows: H+ + HCO3 = HCOOH.
HCOOH is a weak acid but it will make the water to be more acidic in this region than in the areas where this acidic solution is not present. In a case study which was conducted in the Rocky Mountains of 2003, the researchers were looking for the ions which are present in the snow. This was crucial because the snow precipitate leads to the water that is found in these Rocky Mountains. The research was conducted from New Mexico to Montana whereby there were a total of seventy three sites from where the data samples were collected from these sites. The results of the study showed us that the ions which are mostly found in these waters are: Al3+, Ca2+, Mg2+, NH4, Cl-, NO3, and DOC (Uroz, 2002).
Weathering Hot Spots
Weathering occurs mostly in areas where there are deserts. In deserts the temperatures keep changing i.e. during the day the temperatures are high due to the heat that is brought about by the sun. During the night, because there are no clouds heat is lost at a high rate and therefore during the night temperatures are very low. In the deserts during the night the temperatures will be lower.
During the nights the area is very cold.
This change in the weather pattern contributes to weathering in that the rocks are exposed to constant expansion and contraction. This change will result to the rocks to develop cracks. The constant expansion and contraction of the rocks will lead to the cracks developing further to be bigger cracks. These thermal changes will lead to the rocks to be disintegrated and therefore contribute to weathering.
Another area where weathering is higher than in other regions is, in places where there are glaciers. Glaciers make the rocks to be exposed to low temperatures. These low temperatures will make the rock to contract. If the rock is exposed to high temperatures from the sun it will lead to it contracting and expanding and therefore, this will lead to the weathering of the rocks, as they will disintegrate and become smaller and this will contribute to the weathering process (Paradise, 2002).
Also glaciers will bring pressure to the underlying rocks. As they lay on the rocks they will weigh down on the rocks that are underlying them. As the glacier melts, it will release the pressure it was offering to the rocks that are beneath it. This release of pressure will lead to the rocks to be exposed to other weathering agents such as the; heat from the sun, chemical components and other factors and this will lead to the weathering of the rocks that are in that region.
The glaciers also lead to the frost wedging. In this set up it is whereby the ice or the frost attaches itself to the cracks that have been formed in the rocks. As they join themselves or wedge themselves to these cracks, the cracks will expand and this will eventually contribute to the weathering of the rocks. In these areas weathering is more pronounced than in the other regions (Smith, 2012). Chemical weathering in the Loch Vale Watershed in Rocky Mountain Colorado
There have been various studies which have been conducted to see the effects of chemical weathering in the Rocky mountain area of Colorado. In this area it has been exposed to various chemical elements that have had an effect on the rocks. The rainfall has been studied and there were traces of the following chemicals: ANC, NO3, SO4, Cl and SiO2. These chemicals have played a negative role on the rocks because; they have combined with the rain and thus have created the acid rain that has had a drastic effect on the rocks.
The rocks which are found in this area are mainly comprised of Granite and Gneiss. These two rocks are comprised of the same chemical elements and this ensures that the chemical weathering has the same effect on both rocks. A point to note is that the chemical Chlorine has little effect on these rocks. The table below shows how the chemicals affect weathering in the area.
In this region the area has a lot of cations which have contributed to the weathering process. The table below shows us how the distribution of the cations in the region.
Anthropogenic effects on weathering rates
Human activities have been known to contribute to the weathering process in that they increase the weathering process in that area. Activities which have increased the pollution have played a key role in increasing the weathering in an area. Looking at things like acid rain, it has increased because of pollution, whereby you find an area has a lot of carbon dioxide in the air. When it rains, this Carbon dioxide interacts with the rain and form the acid rain. This acid rain when it comes into contact with the rocks it will react on them and thus increase the weathering processes in an area.
There is also the issue of paving of land. When the land has been paved it means that the water will not be able to use its normal route as the rain falls it will not have its correct path and, thus it will look for an alternative route whereby it will use so as to drain. This will lead it to come into contact with rocks and thus contribute to the weathering process of these rocks.
Mining also contributes to weathering and it can do so in a large scale. Mining involves the digging and removing the top soil that is in the earth’s surface. When one mines, it involves drilling and in some cases even blowing up the rocks. This will lead to weathering process.
Also in the mining process the rocks are exposed to chemical processes which will contribute to the weathering process. When there are drilling activities the outer layers of the rocks will be removed and the inner layers will be exposed and thus the weathering process will occur.
In the mining process, there are shafts and tunnels which are dug so as to mine different minerals. The digging in the rocks will contribute to the weathering process to occur at a faster process than in the areas where the mining process has not occurred.
Effects of Mining
Mining requires the clearing of large tracts of land. When the land is being cleared, there is deforestation as the vegetation cover has to be removed so as to allow the land to be mined. Deforestation has a negative impact on the environment. Forest cover are the main source of Oxygen and they take up the Carbon dioxide that has been released to the atmosphere. If the environment is rid off trees there will be the accumulation of the Carbon dioxide and then there will also be less Oxygen. This means that the pollution levels will increase and this will affect the area.
Also, in such areas when mining occurs, it will lead to large areas being dug. The top soil will be removed. This will then mean that; there will be no area where vegetation can be planted. This will be a degradation of the land because once the mining has stopped, there will be no use of this land.
Mining also leads to creation of gullies which if they are not filled up with soil and stones, water will fill that deep hole. What does this mean? It will create a breeding ground for various pests and diseases. If the water is infested with diseases and pests it will mean that the area surrounding these regions; the people will be affected in terms of their wealth. This will mean that there will be health deterioration and therefore it will affect both the environment and the people who live in this region.
In the Rocky mountain, people mainly mine Coal. This has accelerated weathering in the region due to physical and chemical weathering: * Physical weathering due to mining: involves open cast mining. In the open cast mining the strata will be exposed. The rocks will be exposed and therefore it will speed up the weathering process in the area. Also there is strip mining in the area. This type of mining process involves people blasting and removing the soils. This will also expose the rocks and therefore increase the weathering process. * Chemical weathering due to mining is because carbon is introduced in the area. It will lead to the area to start receiving acid rain. Acid rain will contribute to increase the weathering process.
Mining will also affect the surrounding water bodies. The water bodies will be exposed to various chemicals which will pollute the water bodies. Chemicals such as Mercury, Cyanides, and nitrates are the ones which are introduced to the water. The chemicals will affect the aquatic life in an area. It will lead to the death of the aquatic life due to pollution. Sediments that are found in Lakes and other water bodies
Sediments that are found in water bodies are as a result of weathering. Weathering occurs on these rocks which may be igneous, sedimentary or metamorphic. These rocks then disintegrate and become smaller particles. These smaller particles are then carried by various water bodies and are deposited as sediments.
Most of the sediments that are found in the lakes or the water bodies which are involved are in relation to the rocks, which surround the lake or where the water body originates from. The rock that are near the water bodies after weathering process, the small particles or the sediments will be deposited in the lakes and other water bodies.
The lakes and rivers that have been affected by the weathering process in the Rocky’s mountain are the following: Abraham Lake, Crimson Lake, Fish Lake, Bighorn River, and Cline River. These lakes have sediments that have been received from the weathering process. The walls of the lakes and rivers have also been exposed by the weathering process.
Weathering process occurs through two processes i.e. physical and chemical weathering. Weathering also leads to formation of soil. Weathering is the first process of denudation. After the weathering process has occurred, erosion will occur. Weathering is a very slow process. It occurs over a very long period of time. However, weathering is termed as the first process in the denudation process. The denudation process is a process which involves two things: The first process is the breakdown of the rocks to smaller pieces. The second process involves the disintegrated rocks being transported from other areas. As we have stated earlier, there are factors which have been known to promote the weathering processes. These factors include things like water, wind and other factors which will eventually lead to the weathering process.
How has Weathering affected the Rockies
Weathering has affected the Rockies mountains in various ways. The mechanical process of weathering has reduced the size of these mountains. Abrasion has reduced the size of the Talus at the base of Rocky mountains in Canada. The exfoliation process that has taken place in Georgia has meant that the igneous rocks, which were once beneath have been exposed and thus cracked.
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