Forty percent of the surface of the globe is occupied by mountains. This is a relief form, which is a sharp rise among the rest of the territory, with significant elevation changes - up to several kilometers. Sometimes the mountains have a fairly clear line of soles near the slope, but more often they are foothills.
Finding folded mountains on the map is very easy, because mountains as such are everywhere, on absolutely all continents and even on every island. Somewhere there are more of them, 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 South America for seven and a half thousand kilometers.
How old are the mountains
Mountains are like people, they too can 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.
At the old mountains, the relief is worn out, smoothed, and the heights are not with such large differences. For example, the Pamirs are young mountains, and the Urals are old, any map will show this.
Relief characteristics
Folded mountains have an integral structure, but for the most detailed examination you need to know the principles by which the general characteristics of the relief are 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 depends on the exact knowledge of what mountains are.
Here you need to consider such elements as foothills, valleys, slopes, moraines, passes, ridges, peaks, glaciers and many others, since there are a variety of different ones on earth, including folded mountains.
Classification of mountains by height
Height can be classified very simply - there are only three groups:
- Low mountains with a height of no more than a kilometer. Most often these are old mountains, destroyed by time, or very young, gradually growing. They have rounded tops, gentle slopes on which trees grow. There are such mountains on every continent.
- Middle mountains 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 Peninsula, Scandinavian, Appalachian and many others.
- Highlands - more than three thousand meters. These are always young mountains,exposed to weathering, temperature fluctuations and glacier growth. Characteristic features: troughs - trough-shaped valleys, carlings - sharp peaks, glacial cirques - bowl-like depressions on the slopes. Here, the altitude is marked by belts - the forest is at the foot, the icy deserts are closer to the peaks. The term generalizing these characteristic features is "alpine landscape". The Alps are a very young mountain system, as are the Himalayas, the Karakoram, the Andes, the Rocky Mountains 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 single mountains. Of the largest formations - mountain belts: Alpine-Himalayan - through the whole of Eurasia, Andean-Cordillera - in both Americas.
Slightly smaller - a mountainous country, that is, many united mountain systems. In turn, the mountain system consists of groups of mountains and ridges of the same age, most often these are folded mountains. Examples: Appalachians, Sangre de Cristo.
A group of mountains differs from a ridge in that it does not line up its peaks in a narrow long strip. Single mountains are most often of volcanic origin. By appearance, the peaks are divided into peak-shaped, plateau-shaped, domed and some others. Seamounts can form islands with their peaks.
Mountain formation
Orogenesis is the most complex of processes, as a result of which rocks are crushed into folds. Whatfolded mountains, scientists know for certain, but how they appeared - only hypotheses are considered.
- The first hypothesis is oceanic depressions. The map clearly shows that all mountain systems are located on the outskirts of the continents. This means that continental rocks are lighter than ocean bottom rocks. Movements inside the Earth seem to squeeze the mainland out of its interior, and folded mountains are bottom surfaces that have come out on land. This theory has many opponents. For example, folded mountains are also the Himalayas, which are clearly not bottom ones, since 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 have clarified their origin, but this path is absolutely different from the emergence of other mountains, it was not possible to apply this theory anywhere else.
- Continental drift is a very popular theory, which is also criticized as not explaining the entire process of orogeny.
- Subcrustal currents in the bowels of the Earth cause deformation of the surface and form mountains. However, this hypothesis has not been proven. On the contrary, humanity does not yet know even such parameters as the temperature of the earth's interior, and even more so - the viscosity, fluidity and crystal structure of deep rocks, compressive strength, and so on.
- Earth compression hypothesis - with its advantages and disadvantages. We don'tit is known whether the planet accumulates heat or loses it, if it loses - this theory is consistent, if it accumulates - no.
What are the mountains
All sorts of sedimentary rocks accumulated in the troughs of the earth's crust, which were then crushed and folded mountains formed with the help of volcanic activity. Examples: Appalachians on the east coast of North America, the Zagros Mountains in Turkey.
The blocky mountains appeared due to tectonic uplifts along faults in the earth's crust. As, for example, Californian - Sierra Levada. But sometimes already formed folds suddenly begin to rise along the fault. This is how folded-block mountains are formed. The most typical are the Appalachians.
Those mountains that were formed as folded strata of rocks, but were broken by young faults into blocks and rose to different heights, are also folded-block. The Tien Shan mountains, for example, as well as the Altai.
Arched mountains are arched tectonic uplift plus erosion processes over a small area. These are the mountains of the Lake District in England, as well as the Black Hills, located in South Dakota.
Volcanic was formed under the influence of lava. There are two types: volcanic cones (Fujiyama and others) and shield volcanoes (smaller and less symmetrical).
Mountain climate
The mountain climate is fundamentally different from the climate of any other territories. Temperatures drop by more than half a degree for every hundred meters of altitude. The wind is also usually very cold,which contributes to cloudiness. Frequent hurricanes.
As you climb, the 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 snow caps.
Linear zones
Thanks to fault-tectonic analysis, it was possible to make a definition of what folded mountains are, as a result of which they were formed and how dependent on deep planetary faults. All - both ancient and modern - mountainous areas are included in certain linear zones, which were formed only in two directions - northwest and northeast, repeating the direction of deep faults.
These belts are lined with platforms. There is a dependence: the position and shape of the platform changes, both the external forms and the orientation in space of the folded belts change. During the formation of mountains, everything is decided by the fault tectonics (blocks) of the crystalline base. The vertical movements of the foundation blocks form folded mountains.
Examples of the Carpathians or the Verkhoyansk-Chukotka region show different types of tectonic movements during the formation of mountain folds. The Zagros Mountains also characteristically arose.
Geological structure
Everything is diverse in the mountains - from structure to structure. Rocks, for example, of the same Rocky Mountains change throughout their length. In the northernparts - Paleozoic shales and limestones, then - closer to Colorado - granites, igneous rocks with Mesozoic sediments. Even further - in the central part - volcanic rocks, which are absent in the northern areas at all. The same picture emerges when we consider the geological structure of many other mountain ranges.
They say that no two mountains are the same, but massifs of volcanic origin, for example, often have a number of similar features. The correctness of the outlines of the cone of Japanese and Philippine volcanoes, for example. But if we now begin a detailed geological analysis, we will see that the saying is quite right. Many volcanoes in Japan are composed of andesites (magma), while the Philippine rocks are bas alt, much heavier due to the high iron content. And the Cascades of Oregon built their volcanoes with rhyolite (silica).
The time of formation of folded mountains
The formation of mountains throughout the process was due to the development of geosynclines in various geological periods, even in the epoch of folding before the Cambrian. But modern mountains include only young (comparatively, of course) - Cenozoic uplifts. More ancient mountains were leveled a long time ago and were again raised by new tectonic shifts in the form of blocks and vaults.
Arched-block mountains - most often revived. They are as common as the younger, folded ones. Today's relief of the Earth is neotectonics. It is possible to study the folding that formed tectonic structures, if we consider the difference in the age of the mountains, and not the topography created by it. If aCenozoic is recent, it is difficult to think about the age of the very first rock formations.
And only volcanic mountains can grow right in front of our eyes - all the time of the eruption. Eruptions most often occur in the same place, so each portion of lava builds up a mountain. In the center of the mainland, a volcano is a rarity. They tend to 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 compared to human life. These are, first of all, frosts, splitting the rock into small pieces. This is how screes are formed, which then carry snow or ice down, building moraine ridges. This is water - rain, snow, hail - breaking its way even through such indestructible walls. Water is collected in rivers, which arrange themselves winding valleys between mountain spurs. The history of the destruction of immutable mountains, of course, is long, but inevitable. And the glaciers! Whole spurs are sometimes cut clean by them.
Such erosion gradually reduces the mountains, turning them into a plain: somewhere green, with full-flowing rivers, somewhere deserted, grinding all the remaining hills with sand. Such a surface of the Earth is called "peneplain" - almost a plain. And, I must say, this stage occurs extremely rarely. The mountains are reborn! The earth's crust begins to move again, the terrain rises, starting a new phase of landform development.
