Relief refers to the shape of the surface of our planet, which is considered in relation to a certain level. In other words, these are all the irregularities of the land, sea and ocean bottom. Different types of relief differ in their size, age, and history of development.
It is especially important to take this into account at the design stage and in the construction of automobile, railway and other networks. The characteristics of the relief (mountainous, hilly, flat, etc.) will significantly affect the volume of work and their cost.
A variety of forms of the earth's surface
All sushi bumps are divided into:
1. The mountains. This is a cone-shaped relief that rises above the surrounding area. The highest point of the mountain is called the peak, which can be either sharp or in the form of a platform (plateau). The lateral surfaces of such hills are composed of slopes. That line, which indicates the confluence of the mountains with the surrounding area, is the base, or sole.
2. Pits. This form of relief is opposite to the mountain and is a closed depression. The lowest point of the pit is called the bottom. The lateral surfaces of this form of relief are slopes, and the line of their confluence with the surrounding territory is the edge.
3. The ridges. This is nothing more than a hill extended in any direction and constantly decreasing in its height. All ranges have two slopes, which, merging at the top, form a watershed line.
4. The hollows. Such landforms are opposite to the ridges. They are elongated, constantly lowering recesses that are open from one end. The hollow has two slopes connecting to a watershed line running along the bottom of a similar formation. An example of this form is the valley and ravine. In the first case, one can speak of a wide hollow having gently sloping, soddy ramps. The ravine is fundamentally different from such a formation. This is a narrow hollow, the slopes of which are steep and do not have turf.
5. Saddles. These are places starting in the confluence zones of slopes and located between two neighboring mountains. Sometimes the saddle is located at the confluence of the watersheds of the ranges. On its territory, as a rule, people lay hiking trails or roads, calling them passes. Hazel trees depart from the saddle in opposite directions.
All of the above relief types are basic.
Ways of education
The surface relief is individual convex or concave irregularities that can be observed on the surface of the earth. Its forms vary in size and origin. So, all the irregularities of the terrain existing on our planet are referred to as mega-, micro-, meso- or nanorelief. Moreover, their formation could be caused by water-erosive or volcanic, karst or glacial, tectonic or aeolian processes. Each of the above paths means a certain type of movement of energy and matter in the depths or on the surface of the earth's crust.
Varieties of relief-forming processes
All factors affecting the formation of the surface of our planet are divided into endogenous and exogenous. Despite the existing differences, they always act together. However, the characteristics of the terrain in a particular area depend on the predominant role of one of them.
As for
exogenous factors, they always occur on the surface of the Earth. The zone of action of such processes is the highest parts of the soil. These are such factors as relief formation, such as erosion and weathering, abrasion and denudation, the impact of glaciers, etc. This causes the vital activity of organisms, gravity, the influence of solar radiation and energy. Exogenous factors, acting on the upper layer of the earth's crust, form, as a rule, meso- and microforms of the surface. This is due to their insignificant effect on the geological structures of our planet.
Large relief forms are formed as a result of exposure to endogenous factors. These are processes that occur in the bowels of the Earth, which are caused by gravity and internal energy. Large relief forms also arise due to certain factors arising from the rotation of our planet. How are endogenous processes manifested? The presence of mud volcanoes, magmatism, tectonic movements, etc., tells us about their presence. Moreover, all these manifestations are caused by the influence of the thermal energy of the planet, resulting from radioactive decay occurring in the mantle. It is worth saying that endogenous processes divided the crust into two types - oceanic and continental.
The influence of internal thermal energy causes the movement of the lithosphere. In this case, the relief map changes significantly. Faults and folds, mountains and troughs of the upper layer of the earth's crust are formed.
What are some examples of topography resulting from endogenous processes? First of all, these are faults of the Earth's crust. They differ in their size and shape, as well as in the time of formation. The deepest of these faults are the largest blocks experiencing horizontal and vertical displacements. Often they are defined by the outlines of the continents. Large blocks of the Earth's crust are literally pierced by small faults. Most often these are river valleys, highlands, and also lowlands. Moreover, all these forms, as a rule, make modern vertical movements in one direction or another. So, the Central Russian Upland, where the Kursk, Voronezh and Belgorod regions are located, has a constant ascent rate from 4 to 6 millimeters per year. But the Oka-Don Lowland, on the contrary, is falling. The speed of this process is 2 mm per year. It should be said that the relief and geological structure of the earth's crust are closely interconnected. The ancient movements of the blocks of our planet are reflected in the nature of the occurrence of rocks located in them.
Today, one of the factors influencing the change in relief is human economic activity. There is a direct impact on the earth's crust during mining, during construction, as well as in the development of fields for growing agricultural products.
Wind work
The impact of air mass flows on the environment can be observed everywhere. The work of the wind is also a relief-forming factor, which has a particularly great influence on the territory of sand deserts. Various irregularities of the earth's surface in this case take place in connection with the action of the deflation process. This is blowing sand masses.
Their transfer and further deposition (accumulation) also occur. Those landforms that were formed as a result of the work of the wind are called aeolian. And this is not accidental, because Aeolus is the name of the ancient Greek god of the wind. What is the origin of the relief of this kind? It is formed under the influence of the following processes:
- deflation - blowing loose soil;
- corrosion - grinding and grinding of hard rocks;
- soil transfer by air currents;
- accumulation of materials.
Wind speed is directly related to the transport of particles of soil located on the surface of the Earth. So, when the flow of air masses moves for one second at a distance of 4.5-6.7 meters, grains of sand up to 0.25 mm can move. At higher speeds (11.4-13 m / s), their value can be up to 1.5 mm.
Shapes of deflation relief
The processes of blowing loose soil often occur on arable land given for agricultural land. What caused the formation of aeolian landforms in this case? The deflation process occurs due to the loss of the structure of the humus horizon as a result of plowing the land for a long period. The soil begins to be easily blown out, and the scale of this phenomenon reaches up to 125 tons per hectare. Deflationary processes are taking place in the Russian Central Black Earth Region. For example, in 1967, in the south of the Voronezh region, a raging dust storm blew about 60 tons per hectare of soil.
The description of the relief of territories in which there is partially fixed vegetation is an alternation of blowing basins and partitions between them. This is the so-called landscape of cellular sands, formed during the uneven spreading of soil particles by air masses of a variable direction. With steady winds, the basins acquire the shape of a crescent and have a certain orientation. They are called so: hole aeolian sands. The largest such forms are up to seventy meters deep. They are often found in Arabia, where they are called fuljs.
Forms of corrosion relief
Sand masses transported by the wind often grind and grind the surface layers of those rocks that are found along the path of their movement. In this case, the formation of:
- corrosion niches;
- "stone pillars";
- eolian “stone mushrooms”.
As for corrosion niches, their formation occurs, as a rule, in easily destructible rocks. They, for example, are marls and sandstones. If loose rocks are covered with more dense, then the formation of "stone mushrooms" or "stone pillars" occurs. These are amazingly beautiful landforms. They may resemble pillars, towers, or mushrooms.
How is this miracle of nature formed? The air masses carry away the smallest weathering products along with their flow, as well as flutter accumulations of loose material. Large in mass sand masses come into contact with rock formations. In this case, soil particles act as abrasive material. They grind and grind the surface of the rock. The result of such exposure and become a kind of aeolian forms in the form of pillars and mushrooms.
Sometimes the wind blows whole cavities in the loose material. These are oval or rounded shapes, ranging from several tens to several hundred meters across. Sometimes the hollows of blowing look like furrows. Then they are called yards. Such furrows are often formed along roads or other formations with elongated dimensions.
Accumulative forms
Any of the streams of air masses has its own capacity, power and saturation. The first indicator characterizes the amount of sand that a given wind force can move. Power is determined by the actual amount of transported soil particles. But what is wind saturation? This is the ratio of the power of the air flow and its capacity. At small values of this indicator, deflationary processes occur, and at large values, accumulative ones. Consider the effect of the latter.
What causes the formation of aeolian landforms of the accumulative type? All the same work of the wind carrying particles of sand. When there is a bush or any other obstacle in the way of such a mass, a winding hill is formed. Accumulating, sand completely covers the plant.
There are various examples of relief formed by accumulative processes. But all its forms are divided into two types:
- longitudinal;
- transverse.
To the longitudinal forms include sand ridges, which are also called ridge sands. Their formation occurs due to the action of winds of a constant direction. Such a process causes sand to be blown out of the lowlands with its simultaneous ejection onto the elevations or ridges formed in this process. At the same time, soil particles move in the direction of wind movement along the ridge, which contributes to the constant lengthening of this form.
Among the transverse accumulative aeolian formations are dunes, dune chains and dunes. Let's consider them in more detail.
Dunes
In deserts, one can often find crescent-shaped hills, the peaks of which are pointed and face the prevailing action of air masses. This is the dunes. What caused the formation of eolian relief forms of this kind? All the same work of the wind. Dunes have asymmetric slopes. With their gentle side, they face the windward side, and the steep side - towards the leeward side. Dunes are moving forms of sandy terrain. Their movement is slow but constant. During the year it is 50-60 meters. In Karakum, this speed is much higher. She is 12 meters in a month.
What caused the formation of eolian relief forms of this kind? Of course, the work of frequent and strong winds. However, there are some other factors under the influence of which dunes arise. These include:
- a small amount of precipitation;
- active physical weathering of land rocks;
- a small amount or complete absence of vegetation.
In what conditions is such a relief formed? The climate of the deserts of the tropics and temperate latitudes is very favorable for the emergence of dunes. The height of such sand formations, as a rule, is no more than eight meters. But some of the widest of them can rise up to 40 m.
Dune chains
These are aeolian landforms that rise above the earth's surface in separate ridges. They represent several merged dunes. The description of the relief of this kind often contains an indication of the presence of ripple signs located on the windward slopes. These are small, parallelly directed rollers made of sand, the height of which is within 2-5 cm. The appearance of signs of ripples is caused by fluctuations in air masses.
Dunes
In extratropical deserts, transverse eolian formations can often be observed. These are the dunes. Under the influence of wind, such formations can also take a longitudinal form. Sometimes the dunes resemble dunes in their appearance. However, in contrast to them, the "horns" of such formations are directed towards the wind. According to the contours of the contours, such dunes are called parabolic.
What else are aeolian landforms? These include those dunes that are leaning and pyramidal. Similar formations are the largest of the aeolian. You can see them in Central Asia and in the Sahara. Pyramidal dunes form when winds blow in different directions. Sometimes these forms reach a height of 150 meters. Leaned dunes form near mountain ranges. This is a kind of sand trail, inspired by the air masses on the slope. The leaning dunes are often 200 m high.
Other aeolian formations
Often the mobility of soil particles limits the vegetation located in the territory of their distribution. So, in the presence of rare layers of fauna, the formation of hilly sand occurs. In the sandy valleys and on the seashores there are Kuchugurs. These are the so-called cumulus sands.
On the territory of arid countries, not only sandy, but also rocky, as well as clay deserts are widespread. Here you can observe the formation of a variety of deflationary forms. So, the ledges of rocks in rocky deserts are often covered with the so-called desert tan. It is a shiny crust formed by capillary drawing of salt solutions from a stone. Most likely, microorganisms that concentrate hydroxides and oxides of iron, manganese, and other chemical elements also participate in this process.
On the surface of clay deserts there are loesslike rocks. That is why the relief in such an area is composed of closed shallow depressions with a flat bottom. Such formations are called takyrs. Their surface is covered with a clay crust, which is broken by a network of cracks. During rare rains, water accumulates in the takyrs, which compacts the upper layer.
The relief of arid regions is also characterized by drainage depressions. The rainwater accumulated in them has no way out. Such depressions can stretch for hundreds of kilometers, reaching a depth of 200 m. Such formations can be seen in the Libyan desert. This is the depression of Qattara, the absolute mark of which is minus 134 m. Not only the wind takes part in the formation of such forms. A large role is assigned to lithological and structural-geological conditions. In some places, such depressions are buried under a layer of sand.
It is interesting that takyrs are constantly deepening. This is due to the fact that the wind destroys and blows clay cake on their surface. Similar deflationary processes lead to the formation of clay dunes. Such forms can be found in Mexico.
The landscape of the subtropical and tropical zones adorn the remnant or island zones, as well as the denudation plains. These forms also form under other climatic conditions, but nevertheless they are most typical for deserts.
In the relief of Central Asia, denudation stratum plains are present, complicated by cantilevered outlying elevations.These are island ridges with flat peaks and steep steep slopes. Similar forms in Central Asia are called Turtkuli. Perhaps their formation was first facilitated by erosion of unstable watercourses, and after that the deflation processes caused by the work of the wind were assigned the main role.