This can occur due to either chemical decomposition or physical disintegration. It is important to note that for weathering rather than erosion to have occurred, the object being acted upon must remain stationary.
While there are many causes of weathering, there are four that are by far the most common. Frost weathering occurs in the presence of water, particularly in areas where the temperature is near the freezing point of water. Water freezes at 32 degrees Fahrenheit, or 0 degrees Celsius. This is particularly common in Alpine areas and around the edges of glaciers. When water freezes, it expands, so when liquid water seeps into a crevice in the rock or soil and freezes, its expansion can cause deeper cracks in the rock and eventually break pieces off.
Thermal stress occurs when heat absorbed from the surrounding air causes a rock to expand. Two other important agents of chemical weathering are carbon dioxide and oxygen. A water molecule has a very simple chemical formula, H 2 O, two hydrogen atoms bonded to one oxygen atom. But water is pretty remarkable in terms of all the things it can do. Water is a polar molecule; the positive side of the molecule attracts negative ions and the negative side attracts positive ions.
So water molecules separate the ions from their compounds and surround them. Water can completely dissolve some minerals, such as salt. Hydrolysis is the name of the chemical reaction between a chemical compound and water.
When this reaction takes place, water dissolves ions from the mineral and carries them away. These elements have undergone leaching. Through hydrolysis, a mineral such as potassium feldspar is leached of potassium and changed into a clay mineral. Carbon dioxide CO 2 combines with water as raindrops fall through the atmosphere. This makes a weak acid, called carbonic acid. Carbonic acid is a very common in nature where it works to dissolve rock. Pollutants, such as sulfur and nitrogen, from fossil fuel burning, create sulfuric and nitric acid.
Sulfuric and nitric acids are the two main components of acid rain, which accelerate chemical weathering. Oxidation is a chemical reaction that takes place when oxygen reacts with another element.
Oxygen is very strongly chemically reactive. The most familiar type of oxidation is when iron reacts with oxygen to create rust. Minerals that are rich in iron break down as the iron oxidizes and forms new compounds.
Iron oxide produces the red color in soils. Now that you know what chemical weathering is, can you think of some other ways chemical weathering might occur?
Erosion is a natural process , but human activities can cause it to happen faster. This could also be called man-made weathering. For example, trees and plants hold soil in place with their roots. When humans cut down forests or plow a prairie for agriculture, the soil is more likely to wash or blow away.
Landslides along slopes also become more common. Floods occur because the water is not able to soak into the soil. Lindsey is finishing her M. Environmental Conservation degree at the University of Wisconsin Madison.
She spent four summers communicating science in Denali National Park and has continued to search for ways to communicate science in and outside of work. In her free time, she enjoys hiking, backpacking, making music, and sitting around the campfire.
Related Articles Types of Weathering and Erosion. What Are the Agents of Weathering? Lava flows that are quickly buried by subsequent lava flows are less likely to be weathered than a flow which remains exposed to the elements for long periods of time.
Chemical weathering is a process where minerals in a rock may be converted into clays, oxidized or simply dissolved. Silicates comprise almost all minerals in igneous rocks and are also important components in metamorphic rocks. Not all silicates, however, survive weathering processes to become incorporated into sedimentary rocks. Figure 6. For example, interlocking silicate grains in fresh granite gradually decay along crystal boundaries due to conversion to clays.
Eventually cracks open around the boundaries, the rock weakens and easily disintegrates. Water dissolves some of the solid, leaving behind an altered material and producing a solution containing substances drawn from the original solid coffee grounds. The acid rainwater than reacts with minerals on the exposed rock face. Reaction of silicates with carbonic acid and water produces clays and also releases Si and certain cations into water as dissolved constituents:.
The dissolved cations are carried away by rain and river waters and ultimately transported to the oceans. In tropical regions, clays can further react with water to form Bauxite Al-hydroxide , an ore which is a major source of Al. Slightly acidic rainwater can also react with non-silicates in a rock or soil. For instance, carbonic acid can dissolve carbonates such as calcite so that all constinuents go into solution.
Oxidation involves the combining of certain metals Fe in particular with oxygen in the process of stealing electrons. During oxidation, metals like Fe lose one or more electrons to oxygen. Iron can also dissolve in water as cations. Table 6.
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