The longitudinal valleys They are valleys that run parallel to mountain ranges or mountain ranges, while their geomorphological counterpart, the transverse valleys, are arranged at right angles to them..
Valleys are depressions located between two mountains or mountain alignments, produced by the erosion of water currents, excavation of glaciers or, less frequently, as a product of tectonic forces.
Valleys are classified according to their origin as: glacial and fluvial; erosion and tectonics; and longitudinal or transverse (according to your disposition).
Longitudinal and transverse valleys can be fluvial and glacial. For example, if a transversal valley was formed by the passage of a river, it is a transversal valley, of fluvial origin. The categories are not exclusive, they are all descriptors of the same formation, that is, of the valleys.
While glacial and river valleys have been shaped mainly by erosive processes, tectonic valleys arise as a consequence of faults or ruptures in the earth's crust. These are then filed or filled in by erosive and / or sedimentary action..
Valleys are one of the most common geographical features on the planet's surface and can be found on all continents, as well as on the seabed and even on other planets (such as on Mars).
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The longitudinal valleys are elongated and run parallel to mountain ranges, specifically between the two. These valleys are formed in geologically young systems, of little evolution, such as those of the Andes mountain range and the Himalayas mountain range..
The use of the term longitudinal makes sense when there are also valleys that cross the same mountain ranges or mountain ranges, but perpendicular to them. The latter are usually called transversal valleys and are, therefore, the geomorphological counterpart of the longitudinal valley.
An example of a longitudinal valley is the Assam valley in the Brahmaputra river basin (see figure 3), which is located between the Himalayas and the Shillong and Karbi Anglong plains..
The valleys register extreme temperatures in summer and winter. The deeper a valley, the greater the fluctuation in temperature. This means that valleys that are surrounded by very high mountains can have large changes in temperature..
Experienced mountaineers know that the temperature at the bottom of a valley can be much lower than on the side cliffs. This is because a change in pressure can displace cold air masses, pushing them to the bottom of the valley..
When we refer to the flora and fauna of the valleys, we must consider that they are the most common geographical features on planet Earth, and also, the relationship of the valleys with the mountain ranges makes them located in all latitudes.
The flora and fauna that exist in the valleys depend on their geographical location, their climatic conditions, the amount of available water, among other factors. In general, in the valleys there are rivers, which allow the presence of aquatic and terrestrial life forms.
For example, the valleys that accompany the Andes mountain range, ranging from Venezuela to Argentina and Chile, passing through Colombia, Ecuador, Peru and Bolivia, which represents the presence of valleys in practically the entire South American continent (around 7000 km ).
Throughout the extension of this mountain range there are valleys at different heights (meters above sea level), from valleys with cloudy forests to glacial valleys.
Another important example is the valleys of the Himalayas, where their fauna and flora vary widely depending on the climate, precipitation, height and specific characteristics of the soil, of the valley under consideration..
In general terms, in the valleys of the Himalayas it is found that the tropical climate prevails in the valleys at the foot of the mountain, becoming colder and colder as one advances in height. The influence of the monsoon causes the rains to have a gradient from west to east (from higher to lower rainfall).
For all the above, we can relate the fauna and flora of the valleys to environments that range from extreme cold such as subglacial and cold alpine regions, glaciers and polar deserts, to environments of extreme heat (for example, the famous Death Valley in California), or more benign climates such as alpine, semi-tropical and tropical.
The polar dry valleys are famous for their climatic severity, such as the Macmurdo valleys, where the only place on earth where no life has been recorded has been found (Valle Universidad or University valley).
The fauna associated with underwater valleys and hydrothermal vents can be reviewed in the articles:
The most common classification of glacial or river valleys focuses mainly on their shape, considering the following three main ones:
2. Flat floor valley.
3. U-shaped valley or glacier valley.
The "V" shaped valleys are the valleys typically formed by rivers. Its name refers directly to its “V” -shaped cross section and very pronounced sides..
These valleys are common near the source of the rivers, due to the presence of a steeper bank, however, they can also form downstream..
The "V" shaped valleys are the product of erosion. The river carries stones and rocks in its waters, which together with the force of the water itself, carve the bed and give shape to the valley.
When a river valley becomes particularly deep, it is often referred to as a canyon, gorge, ravine, ravine, or gorge. In the case of ravines, the watercourse is not permanent.
The passage of time causes the cross section of these valleys to deepen and widen, eventually producing a flat-bottomed valley..
The valleys in the shape of a "U" or troughs, are those that, having been initially formed by rivers, were deepened and carved out by a glacier. The glacier erodes the typical valley in the shape of a "V", widening it, scraping the sides and bottom, until it ends with a contour similar to a "U".
These valleys are generally wider and flattened, since the glacier is much heavier and wider than a river.
Glacial valleys were formed during the last ice age (Pleistocene) and continue to form even today, in places where glaciers exist.
The third type of valley, the most common in the world, is the flat-bottomed valley. Like the "V" shaped valleys, they were formed by streams, but in general they are older or more developed than these.
As the slope of a stream channel becomes gentle, and the steep "V", or "U" shaped valley begins to smooth out, the valley floor widens and flattens..
Over time, the stream continues to erode the valley floor, widening it further. During this process, the shape of the valley changes from a “V” or “U” shaped valley to one with a wide flat bottom. An example of a flat-bottomed valley is the Nile River Valley.
In addition to the valleys previously described, those that arise from tectonic processes, such as the so-called fault or Rift valleys, should be considered..
These are valleys that form where the Earth's crust spreads or spreads (diverges). This type of valley is often narrow, with steep sides and a flat floor..
Rift valleys can be found even in places where you would expect a river or glacial one (see figure 3, for an example of this type of valley).
Many valleys have been found underwater in the oceans, along the ridges of the seafloor. An example of these valleys is the so-called mid-Atlantic ridge.
The valleys of the seabed are completely different, from an ecological point of view, to the valleys of the earth's crust..
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