A valley is defined as any extension of land that is flat and is surrounded by numerous mountains; This depression of the earth arises as a result of the fusion between two steep portions, for this reason the valleys are not totally flat but have slightly inclined directions. Normally from the steepest area (or slope) of a valley emerges a small stream of water known as rivers (fluvial), and if these mountains are very high from the surface they can be located even glaciers (glacier valleys). The formation of a valley is very varied: it can be the result of erosion, which is generated by water movements or by movements of the tectonic plates; its form will depend on its age in terms of its formation.
In this way you can differentiate the young valleys from the old ones; youngsters will always have a "V" -shaped appearance because erosion has not completed its effect; As erosion progresses, the valley is changing its shape to a flatter and wider space. On the other hand, the glacier valleys are characterized by having a “U” -shaped appearance, which is why a concave bottom can be seen and their walls are steep in an abrupt way; In turn, longitudinal valleys have been described whose orientation is directed parallel to the shape of the mountain range that surrounds it, as well as the example of transverse valleys that are perpendicular to the shape of the adjacent ridge.
However, valleys are not a unique and exclusive geographic form of planet Earth; The Moon that is characterized by having numerous craters, these merge with each other, then making what are lunar valleys (or also known as Lunar Fissure), the dimensions of the valleys on the Moon are varied and their formation is favored due to the action of heat, which significantly affected the most delicate areas of the satellite known as the Moon.
