Valleys are depressions in the earth’s crust resulting from platonic movement of other natural factors. Depending on the formation and the shape of the depression, valleys are classified into different categories. Geological structures like ravines, canyons, gullies, kloofs and canyons may also be referred as a valley. Let us discuss about them one by one.
River valleys
Also known as V-shaped valleys, these valleys are formed by the erosion of flowing water. The nature of the stream determines the exact shape of these valleys. Steep slopes are formed when the river has a steep gradient. Shallow rivers may result in gentler slopes.
Examples:
• Grand Canyon, USA
• Black Canyon, Gunnison National Park, USA
• Inn Valley, Austria
• Napf region, Switzerland
• Rhine valley and Morsel valley, Germany
River valleys are the cradle of the earliest civilizations of the world.
Glacial valleys
As the name suggests, glacial valleys are those that have been carved by glacial activities. These valleys are generally U-shaped. The size of the flowing glaciers is responsible for the size of the valleys thus formed. In the ice-ages, continuous flowing glaciers formed large, deep and wide glacial valleys. The formation of glacial begins with a normal V-shaped one, as in the case of river valleys. Due to constant and severe aberration, the valleys become wider and become U-shaped. When the ice melts and recedes, the steep slopes and wide floors become evident.
Examples:
• Yosemite valley, USA
• Side valley, Austria
• St. Mary river valley, Montana, USA
• Scottish valleys
Hanging valleys
Hanging valleys are transition between the V-shaped and the U-shaped valleys. The formation of hanging valleys depends upon the rock type, topography and the climatic conditions. Violent erosion of the land results in wide valley shoulders. They are special features of the stress tectonic regions. The geological features that may be found are deep gorges and waterfalls. Hanging valleys may also result from flowing tributary glaciers. When a smaller U-shaped valley is formed by a tributary glacier on the floor of the main V-shaped valley, the structure looks to be hanging.
Examples:
• Tyrolean valley, Austria
• Valleys of Rockies and Alps
Rift valleys
Rift valleys are formed due to tectonic plate movement in the earth’s crust. Due to constant collision and moving away of the plates deep cracks (faults) may form. The land area between two cracks may be forced down exposing steep slopes. The folds which result when two continental plates strike against each other also give rise to valleys.
Examples:
• Great rift valley
• Himalayan valley
Hollows
A smaller valley formed by drying up of a stream is called a hollow.
Examples:
• Mansfield hollow
• Boston hollow
• Ice hollows, Austria
Geology tells us that earth was earlier a giant land mass known as ‘Pangaea’ which was a one supercontinent. Plate tectonic movements that are constantly happening (which occur still now) formed the various landforms. The asteroids that could enter the earth’s atmosphere without breaking apart created craters and changed several land features. Valleys have been formed with the combined effects of all these natural factors.
