In modern science, they talk about the relief and its main components: appearance, historical origin, gradual development, dynamics in modern conditions and special distribution patterns from the point of view of geography, and also often mention endogenous and exogenous processes. It is a part of geography as a community and as a complex science that geomorphology can be considered, for which, in fact, the definition mentioned above is characteristic. This intra-geographic scientific branch today is dominated by the idea of relief as the end product of the mutual influence of exogenous and endogenous geological processes.
Exogenous processes
Under exogenous processes are understood such geological processes, which are caused by sources of energy external to the globe, combined with gravity. The predominant source of energy is solar radiation. Exogenous processes take place in the near-surface zone and directly on the surface of the earth's crust. They areare presented in the form of physicochemical and mechanical interaction of the earth's crust with water and air layers. Exogenous processes are responsible in nature for destructive work in order to smooth out surface irregularities, which, in turn, are formed by endogenous processes, namely, cutting off protrusions and filling relief depressions with destruction products.
Endogenous processes
The globe is constantly changing. Endogenous and exogenous geological processes are antagonistic. They are able to cancel the impact on the Earth of their opponent. Endogenous processes are such geological processes that are directly related to the energy generated in the deep bowels of the solid earth's surface (lithosphere). The property of endogeneity is characteristic of many fundamental phenomena in the formation of the earth's surface. Endogenous include metamorphism of rocks, magmatism, seismic activity. An example of endogenous processes is the tectonic movements of the earth's crust. The main sources of energy for this type of processes are thermal, as well as material redistribution in the depths in accordance with the density of certain materials (scientifically called gravitational differentiation). Endogenous processes are fed (as the name implies) by the internal energy of the Earth and manifest themselves primarily in multidirectional movements of huge masses of rocks of the Earth's crust, and with them the molten substance of the earth's mantle. As a result of endogenous processes, large irregularities are created on the earthsurfaces. It is these processes that are responsible for the formation of mountains and mountain ranges, intermountain troughs, and ocean depressions.
In the mutual influence of exogenous and endogenous variants of processes, the earth's crust and its surface develop. We will consider the process-constructors, that is, endogenous geological processes, which, in fact, create the largest parts of the earth's relief.
Endogenous groups
Among the endogenous, there are 3 groups of tightly interconnected, but at the same time independent processes:
- magmatism;
- earthquakes;
- tectonic influences.
Let's take a closer look at each process.
Magmatism
Volcanic phenomena belong to endogenous processes. They should be understood as processes based on the movement of magma to the surface of the earth's crust and to its upper layers. Volcanism demonstrates to man the matter that is in the bowels of the Earth, scientists have the opportunity to get acquainted with its chemical composition and physical state. Volcanic phenomena do not appear everywhere, but only in the so-called seismically active regions, to which, in fact, the possibility of such phenomena is confined. Territories with active or dormant volcanoes often underwent geological changes in the course of the historical process. Magma, penetrating into the internal endogenous processes of the Earth, may not reach the surface, in which case it solidifies somewhere in the bowels of the earth and forms special intrusive (deep) rocks (they includegabbro, granite and many others). Phenomena, the result of which is the penetration of magma into the earth's crust, received the name of Platonism, otherwise - deep volcanism.
Earthquakes
Earthquakes, which are also among the main endogenous processes, manifest themselves in certain parts of the Earth's surface, expressed in short-term tremors. Everyone understands that earthquakes, like natural disasters, along with volcanism, have always been close to human society, and as a result, they struck the imagination of people. Earthquakes did not pass without a trace for a person, causing enormous damage to his economy (and sometimes even he alth and life) in the form of destruction of buildings, violation of the integrity of agricultural crops, severe injuries or even death.
Tectonic influences
Besides earthquakes, which are short-term and powerful vibrations, the earth's surface experiences influences in which some of its parts rise, while others fall. Such crustal movements are unimaginably slow (in relation to the pace of our everyday life): their speed is equivalent to changes at the level of several centimeters or even millimeters per century. So they are, of course, inaccessible to the observations of the human eye, measurements are requested only with the use of special measuring instruments. However, paradoxically, these changes are very significant for the appearance of our planet, and even on a historical scale.their speed is not so small. Since such movements occur constantly and everywhere for many hundreds or even millions of years, their final results are impressive. Under the influence of tectonic movements (and they are called that way), many land areas turned into a deep ocean floor, on the contrary, with the same success, some parts of the surface that now rise hundreds, thousands of meters above sea level were once hidden under a dense water cover. Like everything in nature, the intensity of oscillatory movements is different: in some areas, tectonic processes are more rapid and have a greater impact, while in other places they are much slower and less significant.
In this article, we will focus on tectonic processes, as they are of decisive importance in the formation of the relief, and hence the external appearance of our planet. So, tectonics determines the nature and plan of the future outlines of the Earth's relief forms for many centuries.
Tectonic blocks
Let us once again denote that tectonic changes are understood as endogenous processes of formation of a relief image. Tectonics is directly related to the movements of special monolithic blocks, which are separate fragmentary parts of the earth's crust. It is important to understand that these blocks are different from each other:
- in thickness (minimum from single meters and tens of meters, and maximum up to kilometers, counted in tens);
- by area (the smallest are tens and hundreds of kilometers squared, and the largest reach acrossarea to millionths);
- according to the nature of the deformation of the rocks that make up the earth's crust (again, we distinguish two types of changes: discontinuous and folded);
- in the direction of movement (there are two types of multidirectional movements: horizontal and vertical tectonic movements).
History of the development of the teachings of tectonics
Until the middle of the 20th century, the concept of fixism was in the leading positions in geomorphology and geology. It was based on the idea that the main, dominant type of oscillatory movements should be considered vertical, while the horizontal type of movements is secondary. Thus, geologists believed that all the major forms of the earth's relief (namely, oceanic depressions and even entire continents) were created solely due to vertical movements of the crust. The continents were listed as areas of surface uplift, and the oceans were perceived as areas of its subsidence. The same theory explained, and it must be admitted quite clearly and reasonably, the formation of smaller relief irregularities in terms of size ratio, namely, separate mountains, mountain ranges and depressions separating these same ranges.
However, as you know, ideas tend to change over time, and any truth can easily turn from an absolute status into a relative one. A geoscientist named Alfred Wegener focused the attention of the scientific community on the fact that the outlines and shapes of different continents geometrically fit quite well together. At the same time beganactive work on the collection of geological and paleontological data from various continents available for study at that time. These studies showed an interesting thing: on the continents, currently located at distances equal to many thousands of kilometers from each other, absolutely identical creatures lived in the distant past, moreover, due to structural features, many types of creatures had absolutely no opportunity to cross incredibly large water spaces.
All the same Wegener did an invaluable job of analyzing a huge amount of paleontological and geological data. He compared them with the outlines of the current continents, and based on the results of his research, he put forward the theory that in a past life the continents on the surface of the Earth were located completely differently than they are now. In addition to this, the scientist tried to make a unique reconstruction of the general appearance of the land of past geological eras. Let's talk about Wenger's theory in more detail.
In his opinion, in the Permian period of the Paleozoic, there actually existed on Earth one supercontinent of enormous size, which was called Pangea. By the middle of the Jurassic period of the Mesozoic, it was divided into two independent parts - the continents of Gondwana and Laurasia. Further, the number of continents steadily increased: Laurasia broke up into modern North America and Eurasia, and Gondwana, in turn, was divided into Africa, South America, Antarctica, Australia and Hindustan (later Hindustan became Eurasia). In fact, this is how the concept of fixism fell. Reasonablyit became impossible to explain changes in the outlines of the continents of such a plan and further movements of the continents on the surface of the Earth within the framework of this theory.
Wegener didn't stop there. He consolidated the collapse of fixism by the assumption that the continents, having taken the form of huge lithospheric blocks, move not at all in a vertical, but in a horizontal direction. Moreover, it is the horizontal movements, from his point of view, that are the main tectonic oscillations that had a decisive influence on the appearance of our planet. The theory of Alfred Wegener was called the theory of continental drift, and its adherents became known as mobilists (as opposed to fixists). Perhaps Wegener could have contributed to the study of other endogenous and exogenous geological processes, but he stopped at this stage.
Be that as it may, apart from the incompletely substantiated conclusions of Wegener himself and paleontological data, there was no confirmation of the reality of the continental drift series. In order to obtain data to confirm or refute the new theory and, finally, to understand the reason for the movement of the continents, it was necessary to study the structure of the earth's crust more carefully. However, the second aspect of the work was more important: it was necessary to study as fully as possible the structure of the bottom of the oceans, which had not been studied at all until then. Just imagine: according to the opinion that existed at that time among the vast majority of scientists, the ocean floor was a completely flat surface!
Continental and oceanic crust
Datastudies were carried out and gave completely unexpected results. To the surprise of scientists, the relief of the Earth under the ocean layer and under the continents turned out to be arranged differently.
The continental crust is thick and consists of three layers:
- upper (formed by sedimentary rocks of the sedimentary layer that forms on the earth's surface);
- granite (next to top);
- bas altic (the two lower layers are formed by rocks born in the earth's interior due to cooling and further crystallization of the mantle substance).
The crust at the bottom of the oceans is very different. It is thinner and consists of only two layers:
- upper (formed by sedimentary rocks);
- bas alt (missing granite layer).
A real revolution has taken place: it has become possible and, moreover, the existence of two different types of the earth's crust has been proven: oceanic and continental.
Mantle layer
Below the earth's crust is the mantle, the substance of which is presented in a molten state. Asthenosphere - the mantle layer, located at a depth of 30-40 kilometers under the oceans and 100-120 kilometers under the continents. It, judging by the data of the speed qualities of seismic waves, is endowed with high plasticity, and even such a property as fluidity. It should be understood that absolutely all layers above the asthenosphere are the lithosphere. That is, the Earth's crust and the mantle layer above the asthenosphere are included in a kind of lithospheric formula.
Bottom reliefocean
The relief of the ocean floor also turned out to be much more complex than previously thought. Its main components are:
- shelf (a surface conditionally continuing the slope of the mainland from the water line to 200-500 meters deep);
- mainland slope (from the end of the shelf zone up to 2.5-4 thousand meters, and possibly more);
- marginal sea basin (somewhat uneven (hilly) flat surface into which the continental slope flows through the continental foot, otherwise called the concave inflection);
- island arc (a chain of volcanoes or volcanic islands underwater, this bottom component separates the marginal sea from the open sea zone);
- deep-sea trench (the deepest part of the ocean floor, which is parallel to the island arc along the outer edge of the bottom, it is a rather narrow and deep fissure);
- ocean bed (outwardly resembles a marginal sea basin, but much wider: several thousand kilometers, the bed is divided into two parts by an uplift, which connects into a whole system with the concepts of other oceans (mid-ocean ridges are created);
- rift valley (in elevated parts of mid-ocean ridges, narrow and deep).
New theory of tectonic movements
The new theory, which quite clearly and reasonably substantiates the movements of the continents, was born by comparing information about the structure of the earth's interior under the continents and oceans. It also shows the true role of horizont altectonic movements, proving the connection between endogenous processes and relief.
The basis of this concept was the theory that the lithosphere is composed of several independent monolithic blocks capable of moving in different directions relative to each other. This happens along the surface of the asthenosphere. The asthenosphere and its plastics act as, in some way, a lubricant to facilitate the movement of monoliths.
The mantle substance systematically moves in the bowels of the earth. On some parts of the surface, the mantle material moves in an upward direction, this is exactly how magma flows to the surface. In these areas of the Earth, the asthenosphere becomes thinner and slightly arches upwards, due to the fact that it experiences pressure from below, the lithosphere also slightly arches upwards. Thus, the mid-ocean ridge originates as a linearly elongated uplift. Further, if everything is preserved in this form and nothing supernatural happens, a crack appears on the uplift axis (this is the rift valley). The mantle substance, due to approaching the earth's surface or outpouring on this surface, begins to act on the connected lithospheric blocks, forcing them to move in different directions. And in parallel with this, the mantle substance solidifies in the near-surface layer and directly on the surface itself, thus forming a renewed earth's crust. The process during which the monolithic blocks of the lithosphere move apart and which accompanies the formation of a new earth's crustin the mid-ocean ridges, they decided to call it spreading.
Lithospheric plates that slide along the asthenosphere away from the axis of the mid-ocean ridge and, accordingly, towards the neighboring continents, will certainly collide (this cannot be avoided) with continental blocks of the lithosphere of much higher density. A process occurs in which the less powerful and lighter oceanic crust often sinks under the continental one, and then penetrates into the zone of high temperatures in the upper mantle and, unable to withstand them, melts, thus adding new matter to the mantle. The material that is added to the mantle replaces that which was poured out earlier in the mid-ocean ridge. The process of formation of a continental plate over an oceanic one is called subduction. The deep sea trough, in turn, is formed by a sharp decrease in temperatures above the zone, where the oceanic plate is subducting under a section of the continental crust.
Actually, the described theory determines the division of the lithosphere of our planet into monoliths of different areas, which move in different directions. Everything is simple, you only need to figure out once what will interest you in the field of endogenous and exogenous processes!
