Weathering often leads to erosion, breaking down the rock into small pieces that are easier for wind and water to carry away. There are two distinct types of weathering, which alter and degrade rock in different ways.
Another form of physical weathering occurs when wind or water causes rocks to rub against each other, smoothing their surfaces. For example, iron in a rock might react with oxygen to form easily degradable rust, or acids in rainwater may remove calcium from limestone and marble.
Different types of erosion are usually differentiated by the force that carries rocks, stone or soil away from its location. Similar erosion occurs in the ocean, where moving water and waves degrade and carry away particles of coastline rock.
Wind erosion can only occur on smaller particles of ash, dust and rock, but it can still move large quantities of these particles from their original locations and create impressive formations, such as sand dunes. It occurs when soil or rocks are carried away, not by wind or water, but by falling or sliding downwards.
A rock slide or landslide is a common example of mass wasting, as a large quantity of loose rock or soil rolls or slides down a slope. Differentiating between weathering and erosion can be confusing if one does not understand the technical details leading to the two processes.
Erosion, on the other hand, involves processes like wind, water flow, and ice movement, resulting in a change from one location to another. During solidification, water increases in volume and widens the crack, repeatedly, this breaks the rock.
In erosion, natural forces sweep away broken rock pieces and settle them in another location. Erosion transports pieces of rocks and usually settles them in lower altitude areas, near river mouths or by the seas.
Entrainment, where the rock sediments mix with water, air or melting ice. Weathering is unstoppable, but humans have since found ways to reduce erosion through mitigation by building gab ions or planting trees.
Both weathering and erosion lead to the formation of new geological features through surface reshaping. If weathering did not exist, the earth would consist of bare rocks unable to support flora and fauna.
Weathering is a leading cause of breaking down of human-made structures like roads, bridges, and houses. Weathering and erosion may cause natural disasters through mass wasting like rock slides and mudslides that kill hundreds of people annually.
Weathering refers to the breaking up of the rocks into smaller fragments that ultimately changes the size and structure of the rocks. Forces of nature are for the most part responsible for this process.
Washes away the soil, the pollutants, and the harmful sediments into the water bodies Physical weathering depicts a change that influences the structure of a rock, however not its composition.
Physical weathering doesn't change the chemical composition of rocks. While physical weathering separates rocks without altering their composition, chemical weathering alters the chemicals that form the rocks.
Depending upon the chemicals that are used, the rock may break down completely, or may essentially become gentler and increasingly vulnerable to different forms of weathering. This section introduces you to weathering and erosion, both important parts of the rock cycle.
Identify the ways mechanical weathering alters materials on Earth. Identify the ways chemical weathering alters materials on Earth.
Weathering is the process that changes solid rock into sediments. The four forces of erosion are water, wind, glaciers, and gravity.
Water can move most sizes of sediments, depending on the strength of the force. Wind moves sand-sized and smaller pieces of rock through the air.
Glaciers move all sizes of sediments, from extremely large boulders to the tiniest fragments. Gravity moves broken pieces of rock, large or small, down slope.
A once smooth road surface has cracks and fractures, plus a large pothole. Together with erosion, tall mountains turn into hills and even plains.
Ice wedging is the main form of mechanical weathering in any climate that regularly cycles above and below the freezing point (figure 2). Ice wedging works quickly, breaking apart rocks in areas with temperatures that cycle above and below freezing in the day and night, and also that cycle above and below freezing with the seasons.
Ice wedging is common in Earth’s polar regions and mid latitudes, and also at higher elevations, such as in the mountains. Rocks on a beach are worn down by abrasion as passing waves cause them to strike each other.
Strong winds carrying pieces of sand can sandblast surfaces. Abrasion makes rocks with sharp or jagged edges smooth and round.
If you have ever collected beach glass or cobbles from a stream, you have witnessed the work of abrasion (figure 3). Burrowing animals can also break apart rock as they dig for food or to make living spaces for themselves.
(a) Human activities are responsible for enormous amounts of mechanical weathering, by digging or blasting into rock to build homes, roads, subways, or to quarry stone. (b) Salt weathering of building stone on the island of Goo, Malta.
When these rocks reach the Earth’s surface, they are now at very low temperatures and pressures. The minerals that form at the highest temperatures and pressures are the least stable at the surface.
Two other important agents of chemical weathering are carbon dioxide and oxygen. Remember from the Earth’s Minerals chapter that water is a polar molecule.
Follow this link to check out this animation of how water dissolves salt. When this reaction takes place, water dissolves ions from the mineral and carries them away.
Carbon dioxide (CO 2) combines with water as raindrops fall through the atmosphere. Carbonic acid is a very common in nature where it works to dissolve rock.
Acid rain is discussed in the Human Actions and the Atmosphere chapter. When iron rich minerals oxidize, they produce the familiar red color found in rust.
Oxidation is a chemical reaction that takes place when oxygen reacts with another element. The most familiar type of oxidation is when iron reacts with oxygen to create rust (figure 8).
As plant roots take in soluble ions as nutrients, certain elements are exchanged. Plant roots and bacterial decay use carbon dioxide in the process of respiration.
Devil’s Tower is the central plug of resistant lava from which the surrounding rock weathered and eroded away. Other types of rock, such as limestone, are easily weathered because they dissolve in weak acids.
Rocks that resist weathering remain at the surface and form ridges or hills. Devil’s Tower in Wyoming is an igneous rock from beneath a volcano (figure 9).
Climate is determined by the temperature of a region plus the amount of precipitation it receives. For each 10 o C increase in average temperature, the rate of chemical reactions doubles.
A cold, dry climate will produce the lowest rate of weathering. A warm, wet climate will produce the highest rate of weathering.
The warmer a climate is, the more types of vegetation it will have and the greater the rate of biological weathering (figure 10). This happens because plants and bacteria grow and multiply faster in warmer temperatures.
Answer the question(s) below to see how well you understand the topics covered in the previous section. This short quiz does not count toward your grade in the class, and you can retake it an unlimited number of times.