Throughout the entire existence of the Earth, its surface has continuously changed. This process continues today. It proceeds extremely slowly and imperceptibly for a person and even for many generations. However, it is precisely these transformations that ultimately radically change the appearance of the Earth. Similar processes are divided into exogenous (external) and endogenous (internal).
Classification
Exogenous processes are the result of the interaction of the planet's shell with the hydrosphere, atmosphere, and biosphere. They are studied in order to accurately determine the dynamics of the geological evolution of the Earth. Without exogenous processes, the laws of planetary development would not have developed. They are studied by science of dynamic geology (or geomorphology).
Specialists adopted a universal classification of exogenous processes, divided into three groups. The first is weathering, which is a change in the properties of rocks and minerals under the influence of not only wind, but also carbon dioxide, oxygen, the life of organisms and water. The next type of exogenous processes is denudation. This is the destruction of rocks (and not a change in properties as in the case of weathering), their fragmentation by flowing waters and winds. The last type is accumulation. This is the formation of new sedimentary rocks due to precipitation accumulated in depressions of the earth's relief as a result of weathering and denudation. On the example of accumulation, we can note a clear interconnection of all exogenous processes.
Mechanical weathering
Physical weathering is also called mechanical. As a result of such exogenous processes, the rocks turn into boulders, sand and gravel, and also decay into fragments. The most important factor in physical weathering is insolation. Due to heating by the sun's rays and subsequent cooling, a periodic change in the volume of the rock occurs. It causes cracking and disruption of the bond between the minerals. The results of exogenous processes are obvious - the rock breaks into pieces. The larger the temperature amplitude, the faster this happens.
The rate of cracking depends on the properties of the rock, its schistosity, stratification, and cleavage of minerals. Mechanical failure can take several forms. Chunks that look like scales are broken off from a material with a massive structure, which is why this process is also called scales. And granite breaks up into blocks with a parallelepiped shape.
Chemical destruction
Among other things, the dissolution of rocks contributes to the chemical effects of water and air. Oxygen and carbon dioxide are the most active agents that are dangerous to the integrity of the surfaces. Water carries salt solutions, and therefore its role in the process of chemical weathering is especially great. Such destruction can be expressed in various forms: carbonation, oxidation and dissolution. In addition, chemical weathering leads to the formation of new minerals.
For thousands of years, water masses flow down the surfaces and seep through the pores formed in decaying rocks. The liquid tolerates a large number of elements, thereby leading to the decomposition of minerals. Therefore, we can say that in nature there are no absolutely insoluble substances. The whole question is just how long they retain their structure in spite of exogenous processes.
Oxidation
Oxidation mainly affects minerals, which include sulfur, iron, manganese, cobalt, nickel and some other elements. This chemical process is especially active in an environment saturated with air, oxygen and water. For example, in contact with moisture, metal oxides that make up the rocks become oxides, sulfides become sulfates, etc. All these processes directly affect the Earth's relief.
As a result of oxidation in the lower soil layers, precipitation of rough iron ore (ortzands) accumulate. There are other examples of its effect on the terrain. Thus, weathered rocks containing iron are covered with brown crusts of limonite.
Organic weathering
Organisms are also involved in the destruction of rocks. For example, lichens (simplest plants) can settle on almost any surface. They support life by extracting nutrients through the release of organic acids. After the simplest plants, woody vegetation settles in the rocks. In this case, the cracks become home to the roots.
The characterization of exogenous processes cannot do without mentioning worms, ants and termites. They make long and numerous underground passages and thereby contribute to the entry of atmospheric air under the soil, which contains destructive carbon dioxide and moisture.
The effect of ice
Ice is an important geological factor. It plays a significant role in the formation of the terrain. In mountainous areas, ice moving along river valleys changes the shape of drains and smooths surfaces. Geologists called this destruction an exarchation (plowing). Moving ice has another function. It carries debris that has broken away from rocks. Weathering products crumble from the slopes of the valleys and settle on the ice surface. Such destroyed geological material is called moraine.
No less important is ground ice, which is formed in the soil and fills the soil pores in the territories of perennial and permafrost. Here, climate also acts as a contributing factor. The lower the average temperature, the greater the freezing depth. Where ice melts in summer, pressure waters burst to the surface of the earth. They destroy the relief and change its shape. Such processes are cyclically repeated from year to year, for example, in the north of Russia.
Sea factor
The sea occupies about 70% of the surface of our planet and, without a doubt, has always been an important geological exogenous factor. Ocean water moves under the influence of wind, tidal currents. Significant destruction of the earth's crust is associated with this process. Waves that splash even with the weakest sea swell off the coast grind the surrounding rocks without stopping. During a storm, the strength of the surf can be several tons per square meter.
The process of demolition and physical destruction of coastal rocks by sea water is called abrasion. It proceeds unevenly. A blurred bay, cape or separate rocks may appear on the shore. In addition, the surf of the waves forms cliffs and ledges. The nature of the destruction depends on the structure and composition of coastal rocks.
At the bottom of the oceans and seas continuous processes of denudation take place. Intensive currents contribute to this. During a storm and other disasters, powerful deep waves form, which in their way stumble upon underwater slopes. In a collision, a hydraulic shock occurs , diluting the sludge and destroying the rock.
Wind work
Wind like nothing else changes the earth's surface. It destroys rocks, transfers small-sized clastic material and deposits it in an even layer. At a speed of 3 meters per second, the wind moves the leaves, at 10 meters it pumps thick branches, raises dust and sand, at 40 meters, tears out trees and demolishes houses. Particularly destructive work is done by dust vortices and tornadoes.
The process of blowing out rock particles by the wind is called deflation. In semi-deserts and deserts, it forms significant depressions on the surface composed of solonchaks. The wind acts more intensively if the earth is not protected by vegetation. Therefore, it deforms mountain depressions especially strongly.
Interaction
The interrelation of exogenous and endogenous geological processes plays a huge role in the formation of the Earth's relief . Nature is designed so that some give rise to others. For example, external exogenous processes over time lead to the appearance of cracks in the earth's crust. Through these holes magma enters from the bowels of the planet. It spreads in the form of integuments and forms new rocks.
Magmatism is not the only example of how the interaction of exogenous and endogenous processes works. Glaciers help level the terrain. This is an external exogenous process. As a result, peneplenite is formed (a plain with small hills). Then, as a result of endogenous processes (tectonic movement of plates), this surface rises. Thus, internal and external factors can contradict each other. The relationship between endogenous and exogenous processes is complex and multifaceted. Today it is studied in detail in the framework of geomorphology.