Throughout the existence of the Earth, its surface has been continuously changing. This process continues today. It proceeds extremely slowly and imperceptibly for a person and even for many generations. However, it is these transformations that ultimately radically change the appearance of the Earth. Such 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 patterns of the planet's development would not have developed. They are studied by the science of dynamic geology (or geomorphology).
Specialists have adopted a general 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 vital activity of organisms and water. next typeexogenous processes - 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, one can note a clear interconnection of all exogenous processes.
Mechanical weathering
Physical weathering is also called mechanical weathering. As a result of such exogenous processes, rocks turn into blocks, sand and gruss, and also break up into fragments. The most important factor of physical weathering is insolation. As a result of heating by sunlight and subsequent cooling, a periodic change in the volume of the rock occurs. It causes cracking and disruption of the bond between minerals. The results of exogenous processes are obvious - the rock is split into pieces. The larger the temperature amplitude, the faster this happens.
The rate of formation of cracks depends on the properties of the rock, its schistosity, layering, cleavage of minerals. Mechanical failure can take several forms. Pieces that look like scales break off from a material with a massive structure, which is why this process is also called scales. And granite breaks up into blocks with the shape of a parallelepiped.
Chemical destruction
Among other things, the chemical action of water and air contributes to the dissolution of rocks. Oxygen and carbon dioxideare the most active agents hazardous to the integrity of surfaces. Water carries s alt solutions, and therefore its role in the process of chemical weathering is especially great. Such destruction can be expressed in various forms: carbonatization, oxidation and dissolution. In addition, chemical weathering leads to the formation of new minerals.
Water masses have been flowing down surfaces every day for thousands of years and seeping through the pores formed in decaying rocks. The liquid carries out 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 only question is how long they retain their structure despite exogenous processes.
Oxidation
Oxidation affects mainly minerals, which include sulfur, iron, manganese, cob alt, 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, the oxides of metals that are part of the rocks become oxides, sulfides - sulfates, etc. All these processes directly affect the Earth's topography.
As a result of oxidation, deposits of brown iron ore (ortsand) accumulate in the lower layers of the soil. There are other examples of its influence on relief. So, 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 (the simplest plants) can settle on almost any surface. They support life by extracting nutrients with the help of secreted organic acids. After the simplest plants, woody vegetation settles on the rocks. In this case, the cracks become a home for the roots.
Characterization of exogenous processes cannot do without mentioning worms, ants and termites. They make long and numerous underground passages and thereby contribute to the penetration of atmospheric air into the soil, which contains destructive carbon dioxide and moisture.
Influence of ice
Ice is an important geological factor. It plays a significant role in the formation of the earth's relief. In mountainous areas, ice, moving along river valleys, changes the shape of runoff and smoothes the surface. Geologists called such destruction exaration (ploughing). Moving ice performs another function. It carries clastic material that has broken away from rocks. Weathering products fall off the slopes of the valleys and settle on the surface of the ice. This destroyed geological material is called moraine.
No less important is ground ice, which forms in the soil and fills the ground pores in permafrost and permafrost areas. The climate is also a contributing factor. The lower the average temperature, the greater the depth of freezing. Where the ice melts in summer, pressure waters break out to the surface of the earth. They destroy the relief and change its shape. Similar processes are repeated cyclically from year to year, for example, in the north of Russia.
The Sea Factor
The sea occupies about 70% of the surface of our planet and, no doubt, has always been an important geological exogenous factor. Ocean water moves under the influence of wind, tidal and tidal currents. Significant destruction of the earth's crust is associated with this process. Waves that splash even with the weakest sea waves off the coast, undermine the surrounding rocks without stopping. During a storm, the force 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 flows unevenly. A eroded bay, a cape, or individual rocks may appear on the shore. In addition, the surf of the waves forms cliffs and ledges. The nature of destruction depends on the structure and composition of coastal rocks.
At the bottom of the oceans and seas there are continuous processes of denudation. This is facilitated by strong currents. During a storm and other cataclysms, powerful deep waves are formed, which on their way stumble upon underwater slopes. In the event of a collision, water hammer occurs, liquefying the silt and destroying the rock.
Wind work
Wind like nothing else changes the earth's surface. It destroys rocks, transfersclastic material is small in size and deposits it in an even layer. At a speed of 3 meters per second, the wind moves the leaves, at 10 meters it shakes thick branches, raises dust and sand, at 40 meters it uproots trees and demolishes houses. Especially destructive work is done by dust whirlwinds and tornadoes.
The process of wind blowing rock particles 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 ground is not protected by vegetation. Therefore, it deforms mountain hollows especially strongly.
Interaction
In the formation of the Earth's relief, the interconnection of exogenous and endogenous geological processes plays a huge role. Nature is arranged in such a way that some give rise to others. For example, external exogenous processes eventually lead to the appearance of cracks in the earth's crust. Through these openings, magma enters from the bowels of the planet. It spreads in the form of sheets and forms new rocks.
Magmatism is not the only example of how the interaction of exogenous and endogenous processes works. Glaciers contribute to the leveling of the relief. This is an external exogenous process. As a result, a peneplain (plain with small hills) is formed. Then, as a result of endogenous processes (tectonic movement of plates), this surface rises. Thus, internal and external factors may contradict each other. The relationship between endogenous and exogenous processes is complex and multifaceted. Today it is being studied in detail.within geomorphology.
