Elongate depression of the Earth's surface. Valleys are commonly drained by rivers and may be in a relatively flat plain or between ranges of hills or mountains. Valleys formed by rivers and slope denudation are typically V-shaped; those formerly occupied by glaciers are characteristically U-shaped. Valley evolution is controlled mainly by climate and rock type. Very narrow, deep valleys cut in resistant rock and having steep, almost vertical sides are called canyons. Smaller valleys of similar appearance are called gorges.
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Elongated trough formed by the subsidence of a segment of the Earth's crust between dip-slip, or normal, faults. Rift valleys are usually narrow and long and have a relatively flat floor. The sides drop away steeply in steps and terraces. Rift valleys are found on the continents and along the crests of oceanic ridges. They occur where two plates that make up the Earth's surface are separating (see plate tectonics). Submarine rift valleys are usually centres of seafloor spreading, where magma wells up from the mantle. The most extensive continental rift valleys are those of the East African Rift System; other notable examples include Russia's Baikal Rift Valley and Germany's Rhine Rift Valley.
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Lily of the valley (Convallaria majalis)
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U.S. government agency established in 1933 to control floods, improve navigation, and generate electrical power along the Tennessee River and its tributaries. The TVA is a public corporation governed by a board of directors. It has jurisdiction over the entire basin of the river, which covers parts of seven states: Alabama, Georgia, Kentucky, Mississippi, North Carolina, Tennessee, and Virginia. Created by Congress as one of the major public-works projects of the New Deal, the TVA built a system of dams to control the region's chronic flooding, deepened the channel to improve navigation, and encouraged the development of port facilities along the river. The projects greatly increased traffic on the river and provided cheap electricity, spurring the industrial development of what had been a chronically depressed regional economy. Seealso Public Works Administration.
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Volcanic region, southern Alaska, U.S. Located in Katmai National Park and Preserve, the valley covers 56 sq mi (145 sq km). It was created in 1912 when the eruption of the Novarupta and Mount Katmai volcanoes covered the valley in a flow of lava. When an expedition visited the site in 1916, it discovered tens of thousands of fissures known as fumaroles spouting smoke, gas, and steam in the valley floor. The largest was 150 ft (46 m) in diameter; some had temperatures as high as 1,200 °F (649 °C). About 60 years later there were fewer than 12 fumaroles left. In the 1960s U.S. astronauts used the scarred region to train for Moon landings.
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Valley, eastern California, U.S. Squaw Valley is located in the Sierra Nevada range on the eastern slope of Squaw Peak, northwest of Lake Tahoe. A world-famous winter sports area, it has ice-skating facilities, ski lifts, and trails, and it was the site of the 1960 Winter Olympic Games.
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Industrial region, west-central California. Roughly bounded by San Francisco Bay on the north, the Santa Cruz Mountains on the west, and the Diablo Range on the east, it takes its (unofficial) name from the extensive use of silicon in the region's electronics industries. The U.S. government invested heavily in the region's industry following World War II. A second economic surge occurred with the proliferation of personal computers in the 1980s, and a third surge followed the growth of the Internet in the 1990s.
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National park, northwestern Alaska, U.S. Located north of the Arctic Circle, it was made a national monument in 1978 and a national park in 1980. Occupying an area of 1,750,421 acres (708,370 hectares), it preserves the Kobuk River valley, including the Kobuk and Salmon rivers, forest lands, and the Great Kobuk Sand Dunes. Archaeological sites reveal more than 10,000 years of human habitation. It protects caribou migration routes; other wildlife include grizzly and black bears, foxes, moose, and wolves.
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(circa 2500–circa 1700 BC) Earliest known urban culture of the Indian subcontinent and the most extensive of the world's three earliest civilizations. It stretched from near the present-day Iran-Pakistan border on the Arabian Sea in the west to near Delhi in the east, and 500 mi (800 km) to the south and 1,000 mi (1,600 km) to the northeast. It is known to have included two large cities, Harappa and Mohenjo Daro (in what is now Pakistan), whose large size suggests centralization in two large states or one state with two capitals. Alternatively, Harappa may have succeeded Mohenjo Daro. It was a literate civilization; the language has been tentatively identified as Dravidian. Wheat and barley were grown, many animals (including cats, dogs, and cattle) were domesticated, and cotton was cultivated. The best-known artifacts are seals depicting real and imaginary animals. How and when the civilization came to an end is unclear; Mohenjo Daro was attacked and destroyed in the mid-2nd millennium BC, but in the south there was continuity between the Indus civilization and the Copper Age civilizations of central and western India.
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Valley extending from southeastern California, U.S., to Mexico. It forms part of the Colorado Desert. Intensive irrigation began in 1901 with the opening of the Imperial Canal, which diverted water from the Colorado River. Floodwaters in 1905–07 destroyed the irrigation channels and created the Salton Sea. The valley is now watered by the Hoover Dam and the All-American Canal. With 3,000 mi (4,800 km) of irrigation canals, it contains 500,000 acres (200,000 hectares) of cultivated land.
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Valley, south-central Norway. It extends about 140 mi (225 km) above Lake Mjøsa and Lillehammer. It was the scene of severe fighting in World War II in which the Norwegians and British attempted to hold off a German invasion. It is the setting for Henrik Ibsen's play Peer Gynt.
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Large valley, western Central Asia. It is mainly in eastern Uzbekistan and partly in Tajikistan and Kyrgyzstan and is situated between the Tien Shan system and the smaller Gissar and Alay ranges. It has an area of 8,500 sq mi (22,000 sq km). One of the most densely populated areas of Central Asia, it is a major producer of cotton, fruit, and raw silk. Among the mineral deposits exploited are coal, petroleum, and mercury. It was conquered by the Arabs (8th century AD), Genghis Khan (13th century), and Timur (14th century). The khans of Kokand (see
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Valley, southeastern California, U.S. The lowest, hottest, driest portion of North America, it is about 140 mi (225 km) long and 5–15 mi (8–24 km) wide. The Amargosa River flows into it from the south and contains a small pool, Badwater, near which is the lowest point in North America at 282 ft (86 m) below sea level. Death Valley was formerly an obstacle to pioneer settlers (hence its name); it later was a centre of borax mining. Declared a national monument in 1933, it was made a national park in 1994; the park covers 5,269 sq mi (13,648 sq km) and extends into Nevada.
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Valley, southern California, U.S. Part of the Colorado Desert, the 15-mi- (24-km-) wide valley stretches 45 mi (72 km) between the Little San Bernardino Mountains and the San Jacinto and Santa Rosa mountains. A productive agricultural region, it also has popular desert resorts, including Palm Springs.
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Valley, Chile. Located in central Chile between the Western Cordillera of the Andes Mountains and the coastal range, it extends about 400 mi (650 km) from the Chacabuco Range in the north to the Bío-Bío River in the south. The agricultural heartland of Chile, it was the original centre of European colonization beginning in the mid-1500s, and it continues to be home to most Chileans. Santiago is at its northern end.
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In geology, a valley (also called a vale, dale, glen or strath and near or in Appalachia, a draw) is a depression with predominant extent in one direction. A very deep river valley may be called a canyon or gorge.
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.
A V-shaped valley is formed by downcutting when the flowing stream erodes its channel at a higher rate than the sides are eroded. The resulting landform is a narrow canyon with fast water and little bank (floodplain) on the river sides.
Some broad V examples are:
A valley carved by glaciers, or glacial valley, is normally U-shaped. The 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.
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 are the
|Depending on the topography, the rock types and the climate, a lot of transition forms between V-, U- and plain valleys exist. Their bottoms can be broad or narrow, but characteristic is also the type of valley shoulder. The broader a mountain valley, the lower its shoulders are located in most cases. An important exception are canyons where the shoulder almost is near the top of the valley's slope. In the Alps - e.g. the Tyrolean Inn valley - the shoulders are quite low (100-200 meters above the bottom). Many villages are located here (esp. at the sunny side) because the climate is very mild: even in winter when the valley's floor is completely filled with fog, these villages are in sunshine.|
In some stress-tectonic regions of the Rockies or the Alps (e.g. Salzburg) the side valleys are parallel to each other, and additionally they are hanging. The brooks flow into the river in form of deep gorges or waterfalls. Usually this fact is the result of a violent erosion of the former valley shoulders. A special genesis we find also at arêtes and glacial cirques, at every Scottish glen, or a northern fjord.
A hanging valley is a tributary valley with the floor at a higher relief than the main channel into which it flows. They are most commonly associated with U-shaped valleys when a tributary glacier flows into a glacier of larger volume. The main glacier erodes a deep U-shaped valley with nearly vertical sides while the tributary glacier, with a smaller volume of ice, makes a shallower U-shaped valley. Since the surfaces of the glaciers were originally at the same elevation, the shallower valley appears to be ‘hanging’ above the main valley. Often, waterfalls form at or near the outlet of the upper valley.
Usually the bottom of a main valley is broad - independent of the U or x shape. It typically ranges from about one to ten kilometers in width and is commonly filled with mountain sediments. The shape of the floor can be rather horizontal, similar to a flat cylinder, or terraced.
Side valleys are rather V than U-shaped; near the mouth clammies are possible if it is a hanging valley. The location of the villages depends on the across-valley profile, on climate and local traditions, and on the danger of avalanches or landslides. Predominant are places on terraces or alluvial fans if they exist.
A hollow is a small valley or dry stream bed. This term is commonly used in New England, Arkansas, Missouri and Pennsylvania to describe such geographic features. The term is also used in Southern Appalachia, but pronounced "holler." Hollows may be formed by river valleys such as Mansfield Hollow or they may be relatively dry clefts with a notch-like characteristic in that they have a height of land and consequent water divide in their bases. A hollow such as this is Boston Hollow. Tourists in Europe can further visit a lot of karst, stalactite and ice hollows (e.g. in Slovenia and Austria).
The other terrestrial planets and the moons of our Solar System can also have valley-like features. Lunar valleys can be formed from a linked chain of impact craters. Smaller valleys, known as rilles, may have originated from lava flows or from the contractions of cooling lava sheets.
Besides the lunar craters, the details of lunar mountain ranges have been well known for more than 300 years (e.g. J.H. Schröter's Selenotopographische Fragmente of 1791). A lot of linear phenomena like Rheita or Schröter valley and the famous Vallis Alpes (see also below) were observed with details less than 1 km (which corresponds to a coin seen from 5-10 km distance)—but the geological genesis was debated until the Apollo 11 mission in 1969. Astronomers have long been able to observe some highlands and mountains on Mars, and therefore guessed that there may be valleys, as well. In the 1970s this interpretation was proven correct by results from space probes. Valleys have also been found on Mercury and on the volcanic surfaces of Venus and Io.
The largest valley in our solar system is the Valles Marineris formation on Mars. The Valles (which were first detected in 1877 by Schiaparelli) are a huge canyon system spanning 4,500 x 600 km in area and having a depth up to 8 km. These enormous dimensions are 4-8 times greater than those of the American Grand Canyon. The Valles is currently understood to have been created by tectonic forces like the main grabens on Earth, rather than by running water. Later, though, it may have been expanded considerably by erosion, possibly including the action of surface water.
Icy moons of the gas planets Jupiter, Saturn and Neptune were also photographed by the two Voyagers as well as by other space probes. Some linear ruptures in the ice or apparent low areas between hills have been interpreted by astrogeologists as tectonic structures or valleys similar to grabens or active geologic rifts on Earth.