A valley is a low area between hills or mountains typically 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 to the cross section of the slopes or hillsides.[1]
Valley terminology
A valley in its broadest geographic sense is also known as a dale. Other terms used for valleys are:
- Vale: A valley through which a river runs.
- Dell: A small, secluded and often wooded valley.
- Glen: A long valley bounded by gently sloped concave sides.
- Strath: A wide, flat valley through which a river runs.
- Mountain cove: 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.
- Hollow: A term used sometimes for a small valley surrounded by mountains or ridges.
- cwm (also spelled combe or coombe): A deep, narrow valley.
- A steephead valley is a deep, narrow, flat bottomed valley with an abrupt ending.
- Erosional valley: A valley formed by erosion.
- Structural valley: A valley formed by geologic events such as drop faults or the rise of highlands.[2]
- Dry valley: A valley not created by sustained surface water flow.
- Longitudinal valley: An elongated valley found between two almost parallel mountain chains.
Similar geological structures, such as canyons, ravines, gorges, gullies, chines and kloofs, are not usually referred to as valleys.
River valleys
A valley formed by flowing water, called fluvial valley 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.[3]
Some broad V examples are:
- North America: Black Canyon of the Gunnison National Park, and others in Grand Canyon NP
- Europe:
Some of the first human complex societies originated in river valleys, such as that of the Nile, Tigris-Euphrates, Indus, Ganges, Yangtze, Yellow River, 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.
Vales
In geography, a vale is a wide river valley, usually with a particularly wide flood plain or flat valley bottom.
In Southern England, vales commonly occur between the escarpment slopes of pairs of chalk formations, where the chalk dome has been eroded, exposing less resistant underlying rock, usually claystone. An example is the Vale of White Horse in Oxfordshire.
Rift valleys
Rift valleys, such as the Albertine Rift and Gregory Rift are formed by the expansion of the Earth's crust due to tectonic activity beneath the Earth's surface.
Glacial valleys
A valley in its broadest geographic sense is also known as a dale. Other terms used for valleys are:
- Vale: A valley through which a river runs.
- Dell: A small, secluded and often wooded valley.
- Glen: A long valley bounded by gently sloped concave sides.
- Strath: A wide, flat valley through which a river runs.
- Mountain cove: 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.
- Hollow: A term used sometimes for a small valley surrounded by mountains or ridges.
- cwm (also spelled combe or coombe): A deep, narrow valley.
- A steephead valley is a deep, narrow, flat bottomed valley with an abrupt ending.
- Erosional valley: A valley formed by erosion.
- Structural valley: A valley formed by geologic events such as drop faults or the rise of highlands.[2]
- Dry valley: A valley not created by sustained surface water flow.
- Longitudinal valley: An elongated valley found between two almost parallel mountain chains.
Similar geological structures, such as canyons, ravines, gorges, gullies, chines and kloofs, are not usually referred to as valleys.
River valleys
A valley formed by flowing water, called fluvial valley 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.[3]
Some broad V examples are:
- ravines, gorges, gullies, chines and kloofs, are not usually referred to as valleys.
River valleys
A valley formed by flowing water, called fluvial valley or river valley, is usually V-shaped. The exact shape will depend on the characteristics of the stream flowing through it. Rive
A valley formed by flowing water, called fluvial valley 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.[3]
Some broad V examples are:
- North America: Black Canyon of the Gunnison National Park, and others in Grand Canyon NP
- Europe:
Some of the first human complex societies originated in river valleys, such as that of the Nile, Tigris-Euphrates, Indus, Ganges, Yangtze, Yellow RiverSome broad V examples are:
Some of the first human complex societies originated in river valleys, such as that of the Nile, Tigris-Euphrates, Indus, Ganges, Yangtze, Yellow River, 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.
Vales
In geography, a vale is a wide river valley, usually with a particularly wide flood plain or flat valley bottom.
In Southern England, vales commonly occur between the escarpment slopes of pairs of chalk formations, where the chalk dome has been eroded, exposing less In geography, a vale is a wide river valley, usually with a particularly wide flood plain or flat valley bottom.
In Southern England, vales commonly occur between the escarpment slopes of pairs of chalk formations, where the chalk dome has been In Southern England, vales commonly occur between the escarpment slopes of pairs of chalk formations, where the chalk dome has been eroded, exposing less resistant underlying rock, usually claystone. An example is the Vale of White Horse in Oxfordshire.
Rift valleys, such as the Albertine Rift and Gregory Rift are formed by the expansion of the Earth's crust due to tectonic activity beneath the Earth's surface.
Glacial valleys
U-shaped or trough valleyA valley carved by glaciers is normally U-shaped and resembles a trough. This trough valley becomes visible upon the recession of the glacier that forms it. When the ice recedes or thaws, the valley remains, often littered with small boulders that were transported within the ice. Floor gradient does not affect the valley's shape, it is the glacier's size that does. Continuously flowing glaciers – especially in the ice age – and large-sized glaciers carve wide, deep incised valleys, sometimes with valley steps that reflect differing erosion rates.
Examples of U-shaped valleys are found in every mountainous region that has experienced glaciation, usually during the Pleistocene ice ages. Most present U-shaped valleys started as V-shaped before glaciation. The glaciers carved it out wider and deeper, simultaneously changing the shape. This proceeds through the glacial erosion processes of glaciation and abrasion, which results in large rocky material (glacial till) being carried in the glacier. A material called boulder clay is deposited on the floor of the valley. As the ice melts and retreats, the valley is left with very steep sides and a wide, flat floor. A river or A valley carved by glaciers is normally U-shaped and resembles a trough. This trough valley becomes visible upon the recession of the glacier that forms it. When the ice recedes or thaws, the valley remains, often littered with small boulders that were transported within the ice. Floor gradient does not affect the valley's shape, it is the glacier's size that does. Continuously flowing glaciers – especially in the ice age – and large-sized glaciers carve wide, deep incised valleys, sometimes with valley steps that reflect differing erosion rates.
Examples of U-shaped valleys are found in every mountainous region that has experienced glaciation, usually during the Pleistocene ice ages. Most present U-shaped valleys started as V-shaped before glaciation. The glaciers carved it out wider and deeper, simultaneously changing the shape. This proceeds through the glacial erosion processes of glaciation and abrasion, which results in large rocky material (glacial till) being carried in the glacier. A material called boulder clay is deposited on the floor of the valley. As the ice melts and retreats, the valley is left with very steep sides and a wide, flat floor. A river or stream may remain in the valley. This replaces the original stream or river and is known as a misfit stream because it is smaller than one would expect given the size of its valley.
Other interesting glacially carved valleys include:
- Yosemite Valley (United States)
- Side valleys of the Austrian river Salzach for their parallel di
Examples of U-shaped valleys are found in every mountainous region that has experienced glaciation, usually during the Pleistocene ice ages. Most present U-shaped valleys started as V-shaped before glaciation. The glaciers carved it out wider and deeper, simultaneously changing the shape. This proceeds through the glacial erosion processes of glaciation and abrasion, which results in large rocky material (glacial till) being carried in the glacier. A material called boulder clay is deposited on the floor of the valley. As the ice melts and retreats, the valley is left with very steep sides and a wide, flat floor. A river or stream may remain in the valley. This replaces the original stream or river and is known as a misfit stream because it is smaller than one would expect given the size of its valley.
Other interesting glacially carved valleys include:
A tunnel valley is a large, long, U-shaped valley originally cut under the glacial ice near the margin of continental ice sheets such as that now covering Antarctica and formerly covering portions of all continents during past glacial ages.[4]
A tunnel valley can be up to 100 km (62 mi), 4 km (2.5 mi) wide, and 400 m (1,300 ft) deep (its depth may vary along its length).
Tunnel valleys were formed by subglacial erosion by water. They served as subglacial drainage pathways carrying large volumes of melt water. Their cross-sections exhibit steep-sided flanks similar to fjord walls, and their flat bottoms are typical of subglacial glacial erosion.
Meltwater valley
In northern Central Europe, the Scandinavian ice sheet during the various ice ages advanced slightly uphill against the lie of the land. As a result, its meltwaters flowed parallel to the ice margin to reach the North Sea basin, forming huge, flat valleys known as A tunnel valley can be up to 100 km (62 mi), 4 km (2.5 mi) wide, and 400 m (1,300 ft) deep (its depth may vary along its length).
Tunnel valleys were formed by subglacial erosion by water. They served as subglacial drainage pathways carrying large volumes of melt water. Their cross-sections exhibit steep-sided flanks similar to fjord walls, and their flat bottoms are typical of subglacial glacial erosion.
In northern Central Europe, the Scandinavian ice sheet during the various ice ages advanced slightly uphill against the lie of the land. As a result, its meltwaters flowed parallel to the ice margin to reach the North Sea basin, forming huge, flat valleys known as Urstromtäler. Unlike the other forms of glacial valley, these were formed by glacial meltwaters.
