|
A valley is a low area between hills, often with a river running through it. In geology, a valley or dale is a depression that is longer than it is wide. The terms U-shaped and V-shaped are descriptive terms of geography to characterize the form of valleys. Most valleys belong to one of these two main types or a mixture of them, (at least) with respect of the cross section of the slopes or hillsides. ==Valley terminology== A valley in its broadest geographic sense is also known as a ''dale''. A valley through which a river runs may also be referred to as a vale. A small, secluded, and often wooded valley is known as a dell or in Scotland as a glen. A wide, flat valley through which a river runs is known in Scotland as a strath. A mountain cove is a small valley, closed at one or both ends, in the central or southern Appalachian Mountains which sometimes results from the erosion of a geologic window. A small valley surrounded by mountains or ridges is sometimes known as a hollow. A deep, narrow valley is known as a cwm (also spelled ''combe'' or ''coombe''). Similar geological structures, such as canyons, ravines, gorges, gullies, and kloofs, are not usually referred to as valleys. See also: "chine". A valley formed by erosion is called an erosional valley; a valley formed by geologic events such as drop faults or the rise of highlands is called a structural valley. ==River valleys == :''For a comprehensive list of world wide river valleys see: '' A valley formed by flowing water, or ''river valley'', is usually V-shaped. The exact shape will depend on the characteristics of the stream flowing through it. Rivers with steep gradients, as in mountain ranges, produce steep walls and a bottom. Shallower slopes may produce broader and gentler valleys. However, in the lowest stretch of a river, where it approaches its base level, it begins to deposit sediment and the valley bottom becomes a floodplain. Some broad ''V'' examples are: * North America: Black Canyon of the Gunnison National Park, and others in Grand Canyon NP * Europe: * * Austria: narrow passages of upper Inn valley (Inntal), affluents of Enns * * Switzerland: Napf region, Zurich Oberland, Engadin * * Germany: affluents to the middle reaches of Rhine and Mosel Some of the first human complex societies originated in river valleys, such as that of the Nile, Tigris-Euphrates, Indus, Ganges, Yangtze, Huang He, Mississippi, and arguably Amazon. In prehistory, the rivers were used as a source of fresh water and food (fish and game), as well as a place to wash and a sewer. The proximity of water moderated temperature extremes and provided a source for irrigation, stimulating the development of agriculture. Most of the first civilizations developed from these river valley communities. Another word for river valley is River phenomenon. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Valley」の詳細全文を読む スポンサード リンク
|