Side valleys and tributary valleys are valleys whose brooks or

river A river is a natural stream of fresh water that flows on land or inside Subterranean river, caves towards another body of water at a lower elevation, such as an ocean, lake, or another river. A river may run dry before reaching the end of ...

s flow into greater ones. Upstream, the valleys can be

classified Classified may refer to: General *Classified information, material that a government body deems to be sensitive *Classified advertising or "classifieds" Music *Classified (rapper) (born 1977), Canadian rapper * The Classified, a 1980s American ro ...

in an increasing order which is equivalent to the usual orographic order: the tributaries are ordered from those nearest to the source of the river to those nearest to the mouth of the river. A

confluence In geography, a confluence (also ''conflux'') occurs where two or more watercourses join to form a single channel (geography), channel. A confluence can occur in several configurations: at the point where a tributary joins a larger river (main ...

is where two or more tributaries or rivers flow together.

Orographic order (e.g. Humber)

In the

orographic Orography is the study of the topographic relief of mountains, and can more broadly include hills, and any part of a region's elevated terrain. Orography (also known as ''oreography'', ''orology,'' or ''oreology'') falls within the broader disc ...

classification (order of rivers) the

tributary A tributary, or an ''affluent'', is a stream or river that flows into a larger stream (''main stem'' or ''"parent"''), river, or a lake. A tributary does not flow directly into a sea or ocean. Tributaries, and the main stem river into which they ...

river has order ''n+1'', if ''n'' describes the primary (or main) river. A river which flows directly into the

ocean The ocean is the body of salt water that covers approximately 70.8% of Earth. The ocean is conventionally divided into large bodies of water, which are also referred to as ''oceans'' (the Pacific, Atlantic, Indian Ocean, Indian, Southern Ocean ...

(e.g. the English rivers

Thames The River Thames ( ), known alternatively in parts as the River Isis, is a river that flows through southern England including London. At , it is the longest river entirely in England and the second-longest in the United Kingdom, after th ...

Humber The Humber is a large tidal estuary on the east coast of Northern England. It is formed at Trent Falls, Faxfleet, by the confluence of the tidal rivers River Ouse, Yorkshire, Ouse and River Trent, Trent. From there to the North Sea, it forms ...

) has the orographic order n=1, the River Ouse n=2, the Wharfe n=3 and so on.

Geomorphology

The term "side valley" is used for ''higher order valleys'' near mountains (example above: the

Pennines The Pennines (), also known as the Pennine Chain or Pennine Hills, are a range of highland, uplands mainly located in Northern England. Commonly described as the "Vertebral column, backbone of England" because of its length and position, the ra ...

), as opposed to lower valleys that do not have a strong relief. This is because the " main stem river" (into which the secondary river flows) passes much more water than its tributaries and therefore * has a lower current. * has finer

sediment Sediment is a solid material that is transported to a new location where it is deposited. It occurs naturally and, through the processes of weathering and erosion, is broken down and subsequently sediment transport, transported by the action of ...

s that are deposited in a more flat manner. The higher the order of a valley, the steeper the

hill A hill is a landform that extends above the surrounding terrain. It often has a distinct summit, and is usually applied to peaks which are above elevation compared to the relative landmass, though not as prominent as Mountain, mountains. Hills ...

sides. Looking upstream, the steepest slopes are normally near the source of a brook (with the exception of very hard rocks in downstream direction).

Hanging valleys

The

estuary An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime enviro ...

of broad rivers lies in flat regions (river flats) rather than in regions with higher elevation. Therefore, the

stream gradient Stream gradient (or stream slope) is the grade (or slope) of a stream. It is measured by the ratio of drop in elevation and horizontal distance. It is a dimensionless quantity, usually expressed in units of meters per kilometer (m/km) or feet pe ...

of the tributary near its

mouth A mouth also referred to as the oral is the body orifice through which many animals ingest food and animal communication#Auditory, vocalize. The body cavity immediately behind the mouth opening, known as the oral cavity (or in Latin), is also t ...

is small (e.g. 1 m per km), but much more at waters of higher order (in the

Alps The Alps () are some of the highest and most extensive mountain ranges in Europe, stretching approximately across eight Alpine countries (from west to east): Monaco, France, Switzerland, Italy, Liechtenstein, Germany, Austria and Slovenia. ...

up to 100 m per km). This is one reason for the large number of

hanging valley A valley is an elongated low area often running between hills or mountains and typically containing a river or stream running from one end to the other. Most valleys are formed by erosion of the land surface by rivers or streams over a ve ...

s in some mountain ranges (e.g.

Salzburg Salzburg is the List of cities and towns in Austria, fourth-largest city in Austria. In 2020 its population was 156,852. The city lies on the Salzach, Salzach River, near the border with Germany and at the foot of the Austrian Alps, Alps moun ...

or Graubünden). Glaciologic or geologic reasons: * The

glacier A glacier (; or ) is a persistent body of dense ice, a form of rock, that is constantly moving downhill under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires ...

s of the

ice age An ice age is a long period of reduction in the temperature of Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers. Earth's climate alternates between ice ages, and g ...

caused major

erosion Erosion is the action of surface processes (such as Surface runoff, water flow or wind) that removes soil, Rock (geology), rock, or dissolved material from one location on the Earth's crust#Crust, Earth's crust and then sediment transport, tran ...

that resulted in many

U-shaped Many shapes have metaphorical names, i.e., their names are metaphors: these shape A shape is a graphics, graphical representation of an object's form or its external boundary, outline, or external Surface (mathematics), surface. It is distinc ...

"glacial valleys", especially at an altitude of 400–800 m which is typical for alpine main valleys. * A valley shoulder appears at the place where the tributary flowed into the river before the glacial period. The side valley loses its height and develops into a hanging valley. * In permeable rock like

limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...

) a side-valley becomes a

gorge A canyon (; archaic British English spelling: ''cañon''), gorge or chasm, is a deep cleft between escarpments or cliffs resulting from weathering and the erosion, erosive activity of a river over geologic time scales. Rivers have a natural tend ...

. * In

granite Granite ( ) is a coarse-grained (phanerite, phaneritic) intrusive rock, intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly coo ...

or other crystalline areas a

waterfall A waterfall is any point in a river or stream where water flows over a vertical drop or a series of steep drops. Waterfalls also occur where meltwater drops over the edge of a tabular iceberg or ice shelf. Waterfalls can be formed in seve ...

may result. These stages of valley genesis can be seen in higher mountain ranges - e.g. in the "young"

Rocky Mountains The Rocky Mountains, also known as the Rockies, are a major mountain range and the largest mountain system in North America. The Rocky Mountains stretch in great-circle distance, straight-line distance from the northernmost part of Western Can ...

, in the "old" ranges and

fjord In physical geography, a fjord (also spelled fiord in New Zealand English; ) is a long, narrow sea inlet with steep sides or cliffs, created by a glacier. Fjords exist on the coasts of Antarctica, the Arctic, and surrounding landmasses of the n ...

s of

Scandinavia Scandinavia is a subregion#Europe, subregion of northern Europe, with strong historical, cultural, and linguistic ties between its constituent peoples. ''Scandinavia'' most commonly refers to Denmark, Norway, and Sweden. It can sometimes also ...

, or in the Eastern Alps (

Salzach The Salzach (Austrian: �saltsax ) is a river in Austria and Germany. It is in length and is a right tributary of the Inn (river), Inn, which eventually joins the Danube. Its drainage basin of comprises large parts of the Northern Limeston ...

or Inn valley). Sandbanks often occur at reaches with slow current, especially near river banks. Studying the various

gravel Gravel () is a loose aggregation of rock fragments. Gravel occurs naturally on Earth as a result of sedimentation, sedimentary and erosion, erosive geological processes; it is also produced in large quantities commercially as crushed stone. Gr ...

rock types is an excellent and cheap survey for a summarized

geology Geology (). is a branch of natural science concerned with the Earth and other astronomical objects, the rocks of which they are composed, and the processes by which they change over time. Modern geology significantly overlaps all other Earth ...

of the rivers watershed (catchment area). Generally the main river and tributary are easily identified, as one stream is both longer and carries more water than the other. Occasionally one stream is longer, but the other carries more water. This case offers no fixed rules, but the longer valley is usually chosen as the main valley. In

Switzerland Switzerland, officially the Swiss Confederation, is a landlocked country located in west-central Europe. It is bordered by Italy to the south, France to the west, Germany to the north, and Austria and Liechtenstein to the east. Switzerland ...

the long Alpine

Rhine The Rhine ( ) is one of the List of rivers of Europe, major rivers in Europe. The river begins in the Swiss canton of Graubünden in the southeastern Swiss Alps. It forms part of the Swiss-Liechtenstein border, then part of the Austria–Swit ...

is chosen as the main stream, although the

Aar The Aare () or Aar () is the main tributary of the High Rhine (its discharge even exceeds that of the latter at their confluence) and the longest river that both rises and ends entirely within Switzerland. Its total length from its source to i ...

carries more water. The

Mississippi River The Mississippi River is the main stem, primary river of the largest drainage basin in the United States. It is the second-longest river in the United States, behind only the Missouri River, Missouri. From its traditional source of Lake Ita ...

carries more water while the

Missouri River The Missouri River is a river in the Central United States, Central and Mountain states, Mountain West regions of the United States. The nation's longest, it rises in the eastern Centennial Mountains of the Bitterroot Range of the Rocky Moun ...

is much longer, but is still rated the tributary.

Shape

Whereas the valleys near river flats don't have special forms, the shape of alpine valleys depends much more from the former glaciology and of the rock type. Side- or secondary valleys can be V-shaped or U-shaped. Valley floors vary - from just a few meters up to some 100 m (e.g. Bad Gastein or

St. Moritz St. Moritz ( , , ; ; ; ; ) is a high Alpine resort town in the Engadine in Switzerland, at an elevation of about above sea level. It is Upper Engadine's major town and a municipality in the administrative region of Maloja in the Swiss ...

, where small towns have been developed instead of 1000 or 1500 m altitude). Some valleys are stepped in longitudinal direction (German "Talstufe") which means that these zones show a quicker current than average. The brook digs its own canal and the eroded sediments are deposed at the end of each clammy, forming a series of local

plain In geography, a plain, commonly known as flatland, is a flat expanse of land that generally does not change much in elevation, and is primarily treeless. Plains occur as lowlands along valleys or at the base of mountains, as coastal plains, and ...

s. They are an excellent sites for alpine

agriculture Agriculture encompasses crop and livestock production, aquaculture, and forestry for food and non-food products. Agriculture was a key factor in the rise of sedentary human civilization, whereby farming of domesticated species created ...

pasture Pasture (from the Latin ''pastus'', past participle of ''pascere'', "to feed") is land used for grazing. Types of pasture Pasture lands in the narrow sense are enclosed tracts of farmland, grazed by domesticated livestock, such as horses, c ...

Orographic order (e.g. Humber)

Geomorphology

Hanging valleys

Shape

References

See also