The surface of the globe is forty percent occupied by mountains. This is a landform, which is a sharp rise among the rest of the territory, with significant elevations - up to several kilometers. Sometimes the mountains have a fairly clear line of the sole at the slope, but more often - the foothills.
Finding folded mountains on the map is very simple, because mountains as such are everywhere, on absolutely all continents and even on every island. Somewhere there are more, somewhere less - as, for example, in Australia. In Antarctica, they are hidden by an ice layer. The highest (and youngest) mountain system is the Himalayas, the longest is the Andes, which stretch across all of South America for seven and a half thousand kilometers.
How old are the mountains
Mountains are like people, they can also be young, mature and old. But if people are younger, the smoother, then the mountains are the opposite: a sharp relief and high altitudes indicate a young age.
The old mountains and the relief is worn out, flattened, and the heights are not with such large differences. For example, the Pamirs are young mountains, and the Ural mountains are old, any map will show this.
Landform
Folded mountains have an integral structure, but for the most detailed inspection you need to know the principles by which the general characteristic of the relief is compiled. This applies not only to high mountains, but also literally meter deviations from the state of flat lands - this is the so-called mountain microrelief. The ability to correctly classify and depends on the exact knowledge of what mountains are.
Here it is necessary to consider such elements as foots, valleys, slopes, moraines, passes, ridges, peaks, glaciers, and many others, because on the earth there are very different, including folded mountains.
Mountain classification by height
The height can be classified very simply - only three groups:
- Low mountains with a height of not more than a kilometer. Most often these are old mountains, destroyed by time, or very young, gradually growing. They have rounded peaks, gentle slopes on which trees grow. Such mountains are on every continent.
- Midlands in height from a thousand to three thousand meters. Here is another, changing landscape, depending on the height - the so-called altitudinal zonation. Such mountains are in Siberia and the Far East, on the Apennine, on the Iberian Peninsulas, Scandinavian, Appalachian mountains and many others.
- Highlands - more than three thousand meters. These are always young mountains, subject to weathering, the effects of temperature changes and the growth of glaciers. Characteristic features: troughs - troughs of valleys, carlings - sharp peaks, glacial circuses - bowl-like depressions on the slopes. Here, the altitude is marked by belts - a forest at the foot, icy deserts closer to the peaks. The term summarizing these characteristic features is “alpine landscape”. The Alps are a very young mountain system, as are the Himalayas, Karakoram, Andes, Rocky and other folded mountains.
Classification of mountains by geographical location
The geographical position divides the relief into mountain ranges, mountain systems, mountain groups, mountain ranges and solitary mountains. Of the largest formations - mountain belts: Alpine-Himalayan - across Eurasia, Andean-Cordillera - in both Americas.
A little smaller is a mountainous country, that is, many integrated mountain systems. In turn, the mountain system consists of groups of mountains and ranges of the same age, most often folded mountains. Examples: Appalachian Mountains, Sangre de Cristo.
The group of mountains differs from the ridge in that it does not build its peaks with a narrow long strip. Solitary mountains are most often of volcanic origin. In appearance, the peaks are divided into peak-shaped, plate-shaped, dome-shaped and some others. Seamounts can form islands with their peaks.
Mountain formation
Orogenesis is the most complicated of the processes, as a result of which the rocks are crumpled into folds. What are folded mountains, scientists know for sure, but how they appeared, only hypotheses are considered.
- Hypothesis One - Oceanic Depressions. The map clearly shows that all mountain systems are located on the outskirts of the continents. This means that the mainland rocks are lighter than the bottom rocks of the ocean. The movements inside the Earth seem to squeeze the mainland out of their gut, and the folded mountains are the bottom surfaces that have come out to land. This theory has many opponents. For example, folded mountains are the Himalayas, which are clearly not bottom, as they are located on the mainland itself. And according to this hypothesis, it is impossible to explain the existence of depressions - geosynclinal troughs.
- The hypothesis of Leopold Kober, who studied the geological structure of his native Alps. These young mountains have not yet undergone destructive processes. It turned out that large tectonic thrusts were formed by huge strata of sedimentary rocks. The Alpine mountains clarified their origin, but this path is completely different from the emergence of other mountains, and this theory has not been applied anywhere else.
- The continental drift is a very popular theory, which is also criticized for not explaining the whole process of orogenesis.
- Subcortical currents in the bowels of the Earth cause surface deformation and form mountains. However, this hypothesis has not been proved. On the contrary, mankind does not even know such parameters as the temperature of the earth's interior, and even more so - the viscosity, fluidity and crystalline structure of deep rocks, compressive strength, and so on.
- The compression hypothesis of the Earth - with its own advantages and disadvantages. We do not know whether the planet accumulates heat or loses it, if it loses, this theory is consistent, if it accumulates, no.
What are the mountains
In the troughs of the earth's crust, all kinds of sedimentary rocks accumulated, which were then crushed and folded mountains were formed with the help of volcanic activity. Examples: Appalachian Mountains on the east coast of North America, Zagros Mountains in Turkey.
Block mountains appeared due to tectonic uplifts along faults in the earth's crust. As, for example, California - Sierra Levada. But sometimes the folded folds suddenly begin to rise along the fault. Thus, folded-block mountains are formed. The most typical are the Appalachians.
Those mountains that formed as folded strata of rocks, but were broken by young faults into blocks and climbed to different heights, also folded-block. Tien Shan mountains, for example, as well as Altai.
Vaulted mountains are a vaulted tectonic uplift plus erosion processes over a small area. These are the Lake District mountains in England, as well as the Black Hills in South Dakota.
Volcanic formed under the influence of lava. There are two types: volcanic cones (Fujiyama and others like that) and shield volcanoes (less high and not so symmetrical).
Mountain climate
The mountain climate is radically different from the climate of any other territories. Temperatures drop by more than half a degree, for every one hundred meters of height. The wind is also usually very cold, due to cloud cover. Frequent hurricanes.
With climb and atmospheric pressure decreases. On Everest, for example, up to 250 millimeters of mercury. Water boils at eighty-six degrees.
The higher, the less vegetation cover, to its complete absence, and life is almost completely absent in glaciers and on snow caps.
Line zones
Thanks to fault-tectonic analysis, it was possible to determine what folded mountains are, as a result of which they formed and how much they are dependent on deep planetary faults. All - ancient and modern - mountainous regions are included in certain linear zones, which were formed in only two directions - northwest and northeast, repeating the direction of deep faults.
These belts are bordered by platforms. There is a dependence: the platform changes its position and shape, both the external forms and the orientation in the space of folded belts change. During the formation of mountains, fault tectonics (blocks) of the crystalline base decide everything. The vertical movements of the foundation blocks form folded mountains.
Examples of the Carpathians or the Verkhoyansk-Chukotka region show various types of tectonic movements during the formation of mountain folds. The mountains of Zagros also arose in a characteristic way.
Geological structure
Everything in the mountains is diverse - from structure to structure. Rocks, for example, of the same Rocky Mountains change throughout their entire length. In the northern part - Paleozoic schists and limestones, further - closer to Colorado - granites, igneous rocks with Mesozoic sediments. Even further - in the central part - volcanic rocks, which in the northern areas do not exist. The same picture will appear if we consider the geological structure of many other mountain ranges.
They say that there are no two identical mountains, but volcanic origin massifs, for example, often have rows of similar features. The correctness of the outlines of the cone of Japanese and Philippine volcanoes, for example. But we begin now a detailed geological analysis, we will see that the saying is quite right. Many volcanoes in Japan are composed of andesites (magma), and the Philippine rocks are basaltic, much heavier due to the high iron content. And the Oregon Cascade Mountains stacked their volcanoes with rhyolite (silica).
The formation of folded mountains
The formation of mountains throughout the process was due to the development of geosynclines in various geological periods, even during the folding era before the Cambrian. But only young (comparatively, of course) - Cenozoic uplifts belong to the modern mountains. More ancient mountains were leveled a long time ago and were again raised by new tectonic movements in the form of blocks and arches.
Arch-block mountains are most often revived. They are just as common as younger, folded ones. The present relief of the Earth is neotectonics. You can study the folding that formed the tectonic structures, if we consider the difference in the age of the mountains, and not the relief created by it. If Cenozoic is recent, it is difficult to think about the age of the very first mountain formations.
And only volcanic mountains can grow right before our eyes - during the entire eruption. Eruptions most often occur in the same place, so each portion of lava builds up the mountain. In the center of the mainland, a volcano is a rarity. They usually form entire underwater islands, often forming arcs several thousand kilometers long.
How mountains die
Mountains could stand forever. But they are being killed, albeit slowly, when compared with human life. These are, first of all, frosts, splitting the rock into small pieces. Thus, screes are formed, which are then blown down by snow or ice, building moraine ridges. This water - rain, snow, hail - breaking its way even through such indestructible walls. Water is collected in the rivers, which suit themselves for winding between the mountain spurs of the valley. The history of the destruction of the unshakable mountains, of course, is long, but inevitable. And the glaciers! Entire spurs, sometimes, are completely cut off by them.
Such erosion gradually reduces the mountains, turning them into a plain: somewhere green, with full-flowing rivers, somewhere desert, sanding all the remaining hills with sand. Such a surface of the Earth is called "foam" - almost a plain. And, I must say, such a stage occurs extremely rarely. Mountains are reborn! The crust begins to move again, the terrain rises, starting a new phase of relief development.