Reinforcing Walls With Carbon Fiber Strips

Natural processes removing soil and rock

For other uses, see Erosion (disambiguation).

 

Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust and then transports it to another location where it is deposited. Erosion is distinct from weathering which involves no movement.^[1][2] Removal of rock or soil as clastic sediment is referred to as physical or mechanical erosion; this contrasts with chemical erosion, where soil or rock material is removed from an area by dissolution.^[3] Eroded sediment or solutes may be transported just a few millimetres, or for thousands of kilometres.

Agents of erosion include rainfall;^[4] bedrock wear in rivers; coastal erosion by the sea and waves; glacial plucking, abrasion, and scour; areal flooding; wind abrasion; groundwater processes; and mass movement processes in steep landscapes like landslides and debris flows. The rates at which such processes act control how fast a surface is eroded. Typically, physical erosion proceeds the fastest on steeply sloping surfaces, and rates may also be sensitive to some climatically controlled properties including amounts of water supplied (e.g., by rain), storminess, wind speed, wave fetch, or atmospheric temperature (especially for some ice-related processes). Feedbacks are also possible between rates of erosion and the amount of eroded material that is already carried by, for example, a river or glacier.^[5][6] The transport of eroded materials from their original location is followed by deposition, which is arrival and emplacement of material at a new location.^[1]

While erosion is a natural process, human activities have increased by 10–40 times the rate at which soil erosion is occurring globally.^[7] At agriculture sites in the Appalachian Mountains, intensive farming practices have caused erosion at up to 100 times the natural rate of erosion in the region.^[8] Excessive (or accelerated) erosion causes both "on-site" and "off-site" problems. On-site impacts include decreases in agricultural productivity and (on natural landscapes) ecological collapse, both because of loss of the nutrient-rich upper soil layers. In some cases, this leads to desertification. Off-site effects include sedimentation of waterways and eutrophication of water bodies, as well as sediment-related damage to roads and houses. Water and wind erosion are the two primary causes of land degradation; combined, they are responsible for about 84% of the global extent of degraded land, making excessive erosion one of the most significant environmental problems worldwide.^{[9]: 2 [10]: 1 [11]}

Intensive agriculture, deforestation, roads, anthropogenic climate change and urban sprawl are amongst the most significant human activities in regard to their effect on stimulating erosion.^[12] However, there are many prevention and remediation practices that can curtail or limit erosion of vulnerable soils.

Physical processes

[edit]

Rainfall and surface runoff

[edit]

Rainfall, and the surface runoff which may result from rainfall, produces four main types of soil erosion: splash erosion, sheet erosion, rill erosion, and gully erosion. Splash erosion is generally seen as the first and least severe stage in the soil erosion process, which is followed by sheet erosion, then rill erosion and finally gully erosion (the most severe of the four).^{[10]: 60–61 [13]}

In splash erosion, the impact of a falling raindrop creates a small crater in the soil,^[14] ejecting soil particles.^[4] The distance these soil particles travel can be as much as 0.6 m (2.0 ft) vertically and 1.5 m (4.9 ft) horizontally on level ground.

If the soil is saturated, or if the rainfall rate is greater than the rate at which water can infiltrate into the soil, surface runoff occurs. If the runoff has sufficient flow energy, it will transport loosened soil particles (sediment) down the slope.^[15] Sheet erosion is the transport of loosened soil particles by overland flow.^[15]

Rill erosion refers to the development of small, ephemeral concentrated flow paths which function as both sediment source and sediment delivery systems for erosion on hillslopes. Generally, where water erosion rates on disturbed upland areas are greatest, rills are active. Flow depths in rills are typically of the order of a few centimetres (about an inch) or less and along-channel slopes may be quite steep. This means that rills exhibit hydraulic physics very different from water flowing through the deeper, wider channels of streams and rivers.^[16]

Gully erosion occurs when runoff water accumulates and rapidly flows in narrow channels during or immediately after heavy rains or melting snow, removing soil to a considerable depth.^[17][18][19] A gully is distinguished from a rill based on a critical cross-sectional area of at least one square foot, i.e. the size of a channel that can no longer be erased via normal tillage operations.^[20]

Extreme gully erosion can progress to formation of badlands. These form under conditions of high relief on easily eroded bedrock in climates favorable to erosion. Conditions or disturbances that limit the growth of protective vegetation (rhexistasy) are a key element of badland formation.^[21]

Rivers and streams

[edit]

Valley or stream erosion occurs with continued water flow along a linear feature. The erosion is both downward, deepening the valley, and headward, extending the valley into the hillside, creating head cuts and steep banks. In the earliest stage of stream erosion, the erosive activity is dominantly vertical, the valleys have a typical V-shaped cross-section and the stream gradient is relatively steep. When some base level is reached, the erosive activity switches to lateral erosion, which widens the valley floor and creates a narrow floodplain. The stream gradient becomes nearly flat, and lateral deposition of sediments becomes important as the stream meanders across the valley floor. In all stages of stream erosion, by far the most erosion occurs during times of flood when more and faster-moving water is available to carry a larger sediment load. In such processes, it is not the water alone that erodes: suspended abrasive particles, pebbles, and boulders can also act erosively as they traverse a surface, in a process known as traction.^[22]

Bank erosion is the wearing away of the banks of a stream or river. This is distinguished from changes on the bed of the watercourse, which is referred to as scour. Erosion and changes in the form of river banks may be measured by inserting metal rods into the bank and marking the position of the bank surface along the rods at different times.^[23]

Thermal erosion is the result of melting and weakening permafrost due to moving water.^[24] It can occur both along rivers and at the coast. Rapid river channel migration observed in the Lena River of Siberia is due to thermal erosion, as these portions of the banks are composed of permafrost-cemented non-cohesive materials.^[25] Much of this erosion occurs as the weakened banks fail in large slumps. Thermal erosion also affects the Arctic coast, where wave action and near-shore temperatures combine to undercut permafrost bluffs along the shoreline and cause them to fail. Annual erosion rates along a 100-kilometre (62-mile) segment of the Beaufort Sea shoreline averaged 5.6 metres (18 feet) per year from 1955 to 2002.^[26]

Most river erosion happens nearer to the mouth of a river. On a river bend, the longest least sharp side has slower moving water. Here deposits build up. On the narrowest sharpest side of the bend, there is faster moving water so this side tends to erode away mostly.

Rapid erosion by a large river can remove enough sediments to produce a river anticline,^[27] as isostatic rebound raises rock beds unburdened by erosion of overlying beds.

Shoreline erosion, which occurs on both exposed and sheltered coasts, primarily occurs through the action of currents and waves but sea level (tidal) change can also play a role.

Hydraulic action takes place when the air in a joint is suddenly compressed by a wave closing the entrance of the joint. This then cracks it. Wave pounding is when the sheer energy of the wave hitting the cliff or rock breaks pieces off. Abrasion or corrasion is caused by waves launching sea load at the cliff. It is the most effective and rapid form of shoreline erosion (not to be confused with corrosion). Corrosion is the dissolving of rock by carbonic acid in sea water.^[28] Limestone cliffs are particularly vulnerable to this kind of erosion. Attrition is where particles/sea load carried by the waves are worn down as they hit each other and the cliffs. This then makes the material easier to wash away. The material ends up as shingle and sand. Another significant source of erosion, particularly on carbonate coastlines, is boring, scraping and grinding of organisms, a process termed bioerosion.^[29]

Sediment is transported along the coast in the direction of the prevailing current (longshore drift). When the upcurrent supply of sediment is less than the amount being carried away, erosion occurs. When the upcurrent amount of sediment is greater, sand or gravel banks will tend to form as a result of deposition. These banks may slowly migrate along the coast in the direction of the longshore drift, alternately protecting and exposing parts of the coastline. Where there is a bend in the coastline, quite often a buildup of eroded material occurs forming a long narrow bank (a spit). Armoured beaches and submerged offshore sandbanks may also protect parts of a coastline from erosion. Over the years, as the shoals gradually shift, the erosion may be redirected to attack different parts of the shore.^[30]

Erosion of a coastal surface, followed by a fall in sea level, can produce a distinctive landform called a raised beach.^[31]

Chemical erosion is the loss of matter in a landscape in the form of solutes. Chemical erosion is usually calculated from the solutes found in streams. Anders Rapp pioneered the study of chemical erosion in his work about Kärkevagge published in 1960.^[32]

Formation of sinkholes and other features of karst topography is an example of extreme chemical erosion.^[33]

Glaciers erode predominantly by three different processes: abrasion/scouring, plucking, and ice thrusting. In an abrasion process, debris in the basal ice scrapes along the bed, polishing and gouging the underlying rocks, similar to sandpaper on wood. Scientists have shown that, in addition to the role of temperature played in valley-deepening, other glaciological processes, such as erosion also control cross-valley variations. In a homogeneous bedrock erosion pattern, curved channel cross-section beneath the ice is created. Though the glacier continues to incise vertically, the shape of the channel beneath the ice eventually remain constant, reaching a U-shaped parabolic steady-state shape as we now see in glaciated valleys. Scientists also provide a numerical estimate of the time required for the ultimate formation of a steady-shaped U-shaped valley—approximately 100,000 years. In a weak bedrock (containing material more erodible than the surrounding rocks) erosion pattern, on the contrary, the amount of over deepening is limited because ice velocities and erosion rates are reduced.^[35]

Glaciers can also cause pieces of bedrock to crack off in the process of plucking. In ice thrusting, the glacier freezes to its bed, then as it surges forward, it moves large sheets of frozen sediment at the base along with the glacier. This method produced some of the many thousands of lake basins that dot the edge of the Canadian Shield. Differences in the height of mountain ranges are not only being the result tectonic forces, such as rock uplift, but also local climate variations. Scientists use global analysis of topography to show that glacial erosion controls the maximum height of mountains, as the relief between mountain peaks and the snow line are generally confined to altitudes less than 1500 m.^[36] The erosion caused by glaciers worldwide erodes mountains so effectively that the term glacial buzzsaw has become widely used, which describes the limiting effect of glaciers on the height of mountain ranges.^[37] As mountains grow higher, they generally allow for more glacial activity (especially in the accumulation zone above the glacial equilibrium line altitude),^[38] which causes increased rates of erosion of the mountain, decreasing mass faster than isostatic rebound can add to the mountain.^[39] This provides a good example of a negative feedback loop. Ongoing research is showing that while glaciers tend to decrease mountain size, in some areas, glaciers can actually reduce the rate of erosion, acting as a glacial armor.^[37] Ice can not only erode mountains but also protect them from erosion. Depending on glacier regime, even steep alpine lands can be preserved through time with the help of ice. Scientists have proved this theory by sampling eight summits of northwestern Svalbard using Be10 and Al26, showing that northwestern Svalbard transformed from a glacier-erosion state under relatively mild glacial maxima temperature, to a glacier-armor state occupied by cold-based, protective ice during much colder glacial maxima temperatures as the Quaternary ice age progressed.^[40]

These processes, combined with erosion and transport by the water network beneath the glacier, leave behind glacial landforms such as moraines, drumlins, ground moraine (till), glaciokarst, kames, kame deltas, moulins, and glacial erratics in their wake, typically at the terminus or during glacier retreat.^[41]

The best-developed glacial valley morphology appears to be restricted to landscapes with low rock uplift rates (less than or equal to 2mm per year) and high relief, leading to long-turnover times. Where rock uplift rates exceed 2mm per year, glacial valley morphology has generally been significantly modified in postglacial time. Interplay of glacial erosion and tectonic forcing governs the morphologic impact of glaciations on active orogens, by both influencing their height, and by altering the patterns of erosion during subsequent glacial periods via a link between rock uplift and valley cross-sectional shape.^[42]

At extremely high flows, kolks, or vortices are formed by large volumes of rapidly rushing water. Kolks cause extreme local erosion, plucking bedrock and creating pothole-type geographical features called rock-cut basins. Examples can be seen in the flood regions result from glacial Lake Missoula, which created the channeled scablands in the Columbia Basin region of eastern Washington.^[43]

Wind erosion is a major geomorphological force, especially in arid and semi-arid regions. It is also a major source of land degradation, evaporation, desertification, harmful airborne dust, and crop damage—especially after being increased far above natural rates by human activities such as deforestation, urbanization, and agriculture.^[44][45]

Wind erosion is of two primary varieties: deflation, where the wind picks up and carries away loose particles; and abrasion, where surfaces are worn down as they are struck by airborne particles carried by wind. Deflation is divided into three categories: (1) surface creep, where larger, heavier particles slide or roll along the ground; (2) saltation, where particles are lifted a short height into the air, and bounce and saltate across the surface of the soil; and (3) suspension, where very small and light particles are lifted into the air by the wind, and are often carried for long distances. Saltation is responsible for the majority (50–70%) of wind erosion, followed by suspension (30–40%), and then surface creep (5–25%).^{[46]: 57 [47]}

Wind erosion is much more severe in arid areas and during times of drought. For example, in the Great Plains, it is estimated that soil loss due to wind erosion can be as much as 6100 times greater in drought years than in wet years.^[48]

Mass wasting or mass movement is the downward and outward movement of rock and sediments on a sloped surface, mainly due to the force of gravity.^[49][50]

Mass wasting is an important part of the erosional process and is often the first stage in the breakdown and transport of weathered materials in mountainous areas.^{[51]: 93â€Å}  It moves material from higher elevations to lower elevations where other eroding agents such as streams and glaciers can then pick up the material and move it to even lower elevations. Mass-wasting processes are always occurring continuously on all slopes; some mass-wasting processes act very slowly; others occur very suddenly, often with disastrous results. Any perceptible down-slope movement of rock or sediment is often referred to in general terms as a landslide. However, landslides can be classified in a much more detailed way that reflects the mechanisms responsible for the movement and the velocity at which the movement occurs. One of the visible topographical manifestations of a very slow form of such activity is a scree slope.^{[citation needed]}

Slumping happens on steep hillsides, occurring along distinct fracture zones, often within materials like clay that, once released, may move quite rapidly downhill. They will often show a spoon-shaped isostatic depression, in which the material has begun to slide downhill. In some cases, the slump is caused by water beneath the slope weakening it. In many cases it is simply the result of poor engineering along highways where it is a regular occurrence.^[52]

Surface creep is the slow movement of soil and rock debris by gravity which is usually not perceptible except through extended observation. However, the term can also describe the rolling of dislodged soil particles 0.5 to 1.0 mm (0.02 to 0.04 in) in diameter by wind along the soil surface.^[53]

On the continental slope, erosion of the ocean floor to create channels and submarine canyons can result from the rapid downslope flow of sediment gravity flows, bodies of sediment-laden water that move rapidly downslope as turbidity currents. Where erosion by turbidity currents creates oversteepened slopes it can also trigger underwater landslides and debris flows. Turbidity currents can erode channels and canyons into substrates ranging from recently deposited unconsolidated sediments to hard crystalline bedrock.^[54][55][56] Almost all continental slopes and deep ocean basins display such channels and canyons resulting from sediment gravity flows and submarine canyons act as conduits for the transfer of sediment from the continents and shallow marine environments to the deep sea.^[57][58][59] Turbidites, which are the sedimentary deposits resulting from turbidity currents, comprise some of the thickest and largest sedimentary sequences on Earth, indicating that the associated erosional processes must also have played a prominent role in Earth's history.

Part of a series on
Geology
Science of the solid Earth
Index Outline Category Glossary History (Timeline)
Key components Minerals Rock (Igneous Sedimentary Metamorphic) Sediment Plate tectonics Strata Weathering Erosion Geologic time scale
Laws, principles, theories Stratigraphic principles Principle of original horizontality Law of superposition Principle of lateral continuity Principle of cross-cutting relationships Principle of faunal succession Principle of inclusions and components Walther's law
Topics Composition Geochemistry Mineralogy Sedimentology Petrology Structure of Earth Landform structures Geomorphology Glaciology Structural Geology Volcanology Geologic history Geological history of Earth
Research Branches of geology Geologist (List) Methods Geological survey
Applications Engineering Mining Forensics Military
Planetary geology Lists of geological features of the Solar System Geology of solar terrestrial planets By planet and body Mercury Venus Moon Mars Vesta Ceres Io Titan Triton Pluto Charon
Geology portal

The amount and intensity of precipitation is the main climatic factor governing soil erosion by water. The relationship is particularly strong if heavy rainfall occurs at times when, or in locations where, the soil's surface is not well protected by vegetation. This might be during periods when agricultural activities leave the soil bare, or in semi-arid regions where vegetation is naturally sparse. Wind erosion requires strong winds, particularly during times of drought when vegetation is sparse and soil is dry (and so is more erodible). Other climatic factors such as average temperature and temperature range may also affect erosion, via their effects on vegetation and soil properties. In general, given similar vegetation and ecosystems, areas with more precipitation (especially high-intensity rainfall), more wind, or more storms are expected to have more erosion.

In some areas of the world (e.g. the mid-western US), rainfall intensity is the primary determinant of erosivity (for a definition of erosivity check,^[60]) with higher intensity rainfall generally resulting in more soil erosion by water. The size and velocity of rain drops is also an important factor. Larger and higher-velocity rain drops have greater kinetic energy, and thus their impact will displace soil particles by larger distances than smaller, slower-moving rain drops.^[61]

In other regions of the world (e.g. western Europe), runoff and erosion result from relatively low intensities of stratiform rainfall falling onto the previously saturated soil. In such situations, rainfall amount rather than intensity is the main factor determining the severity of soil erosion by water.^[17] According to the climate change projections, erosivity will increase significantly in Europe and soil erosion may increase by 13–22.5% by 2050 ^[62]

In Taiwan, where typhoon frequency increased significantly in the 21st century, a strong link has been drawn between the increase in storm frequency with an increase in sediment load in rivers and reservoirs, highlighting the impacts climate change can have on erosion.^[63]

Vegetation acts as an interface between the atmosphere and the soil. It increases the permeability of the soil to rainwater, thus decreasing runoff. It shelters the soil from winds, which results in decreased wind erosion, as well as advantageous changes in microclimate. The roots of the plants bind the soil together, and interweave with other roots, forming a more solid mass that is less susceptible to both water^[64] and wind erosion. The removal of vegetation increases the rate of surface erosion.^[65]

The topography of the land determines the velocity at which surface runoff will flow, which in turn determines the erosivity of the runoff. Longer, steeper slopes (especially those without adequate vegetative cover) are more susceptible to very high rates of erosion during heavy rains than shorter, less steep slopes. Steeper terrain is also more prone to mudslides, landslides, and other forms of gravitational erosion processes.^{[61]: 28–30 [66][67]}

Tectonic processes control rates and distributions of erosion at the Earth's surface. If the tectonic action causes part of the Earth's surface (e.g., a mountain range) to be raised or lowered relative to surrounding areas, this must necessarily change the gradient of the land surface. Because erosion rates are almost always sensitive to the local slope (see above), this will change the rates of erosion in the uplifted area. Active tectonics also brings fresh, unweathered rock towards the surface, where it is exposed to the action of erosion.

However, erosion can also affect tectonic processes. The removal by erosion of large amounts of rock from a particular region, and its deposition elsewhere, can result in a lightening of the load on the lower crust and mantle. Because tectonic processes are driven by gradients in the stress field developed in the crust, this unloading can in turn cause tectonic or isostatic uplift in the region.^{[51]: 99 [68]} In some cases, it has been hypothesised that these twin feedbacks can act to localize and enhance zones of very rapid exhumation of deep crustal rocks beneath places on the Earth's surface with extremely high erosion rates, for example, beneath the extremely steep terrain of Nanga Parbat in the western Himalayas. Such a place has been called a "tectonic aneurysm".^[69]

Human land development, in forms including agricultural and urban development, is considered a significant factor in erosion and sediment transport, which aggravate food insecurity.^[70] In Taiwan, increases in sediment load in the northern, central, and southern regions of the island can be tracked with the timeline of development for each region throughout the 20th century.^[63] The intentional removal of soil and rock by humans is a form of erosion that has been named lisasion.^[71]

Mountain ranges take millions of years to erode to the degree they effectively cease to exist. Scholars Pitman and Golovchenko estimate that it takes probably more than 450 million years to erode a mountain mass similar to the Himalaya into an almost-flat peneplain if there are no significant sea-level changes.^[72] Erosion of mountains massifs can create a pattern of equally high summits called summit accordance.^[73] It has been argued that extension during post-orogenic collapse is a more effective mechanism of lowering the height of orogenic mountains than erosion.^[74]

Examples of heavily eroded mountain ranges include the Timanides of Northern Russia. Erosion of this orogen has produced sediments that are now found in the East European Platform, including the Cambrian Sablya Formation near Lake Ladoga. Studies of these sediments indicate that it is likely that the erosion of the orogen began in the Cambrian and then intensified in the Ordovician.^[75]

If the erosion rate exceeds soil formation, erosion destroys the soil.^[76] Lower rates of erosion can prevent the formation of soil features that take time to develop. Inceptisols develop on eroded landscapes that, if stable, would have supported the formation of more developed Alfisols.^[77]

While erosion of soils is a natural process, human activities have increased by 10-40 times the rate at which erosion occurs globally. Excessive (or accelerated) erosion causes both "on-site" and "off-site" problems. On-site impacts include decreases in agricultural productivity and (on natural landscapes) ecological collapse, both because of loss of the nutrient-rich upper soil layers. In some cases, the eventual result is desertification. Off-site effects include sedimentation of waterways and eutrophication of water bodies, as well as sediment-related damage to roads and houses. Water and wind erosion are the two primary causes of land degradation; combined, they are responsible for about 84% of the global extent of degraded land, making excessive erosion one of the most significant environmental problems.^[10][78]

Often in the United States, farmers cultivating highly erodible land must comply with a conservation plan to be eligible for agricultural assistance.^[79]

• The Soil Erosion Site
• International Erosion Control Association
• Soil Erosion Data in the European Soil Portal
• USDA National Soil Erosion Laboratory
• The Soil and Water Conservation Society

Vertical structure, usually solid, that defines and sometimes protects an area

For other uses, see Wall (disambiguation).

 

The article's lead section may need to be rewritten. Please help improve the lead and read the lead layout guide. (December 2017) (Learn how and when to remove this message)

Great Wall of China - Western Wall
Hadrian's Wall - Walls of Ston

A wall is a structure and a surface that defines an area; carries a load; provides security, shelter, or soundproofing; or, is decorative. There are many kinds of walls, including:

• Border barriers between countries
• Brick walls
• Defensive walls in fortifications
• Permanent, solid fences
• Retaining walls, which hold back dirt, stone, water, or noise sound
• Stone walls
• Walls in buildings that form a fundamental part of the superstructure or separate interior rooms, sometimes for fire safety
• Glass walls in which the primary structure is made of glass; does not include openings within walls that have glass coverings as these are windows
• Walls that protect from oceans (seawalls) or rivers (levees)

Etymology

[edit]

The term wall comes from the Latin vallum meaning "an earthen wall or rampart set with palisades, a row or line of stakes, a wall, a rampart, fortification", while the Latin word murus means a defensive stone wall.^[1] English uses the same word to mean an external wall and the internal sides of a room, but this is not universal. Many languages distinguish between the two. In German, some of this distinction can be seen between Wand and Mauer, in Spanish between pared and muro.

Defensive wall

[edit]

The word wall originally referred to defensive walls and ramparts.

The purposes of walls in buildings are to support roofs, floors and ceilings; to enclose a space as part of the building envelope along with a roof to give buildings form; and to provide shelter and security. In addition, the wall may house various types of utilities such as electrical wiring or plumbing. Wall construction falls into two basic categories: framed walls or mass-walls. In framed walls the load is transferred to the foundation through posts, columns or studs. Framed walls most often have three or more separate components: the structural elements (such as 2×4 studs in a house wall), insulation, and finish elements or surfaces (such as drywall or panelling). Mass-walls are of a solid material including masonry, concrete including slipform stonemasonry, log building, cordwood construction, adobe, rammed earth, cob, earthbag construction, bottles, tin cans, straw-bale construction, and ice. Walls may or may not be leadbearing. Walls are required to conform to the local building and/or fire codes.

There are three basic methods walls control water intrusion: moisture storage, drained cladding, or face-sealed cladding.^[2] Moisture storage is typical of stone and brick mass-wall buildings where moisture is absorbed and released by the walls of the structure itself. Drained cladding also known as screened walls^[3] acknowledges moisture will penetrate the cladding so a moisture barrier such as housewrap or felt paper inside the cladding provides a second line of defense and sometimes a drainage plane or air gap allows a path for the moisture to drain down through and exit the wall. Sometimes ventilation is provided in addition to the drainage plane such as in rainscreen construction. Face-sealed also called barrier wall or perfect barrier^[3] cladding relies on maintaining a leak-free surface of the cladding. Examples of face sealed cladding are the early exterior insulation finishing systems, structural glazing, metal clad panels, and corrugated metal.

Building walls frequently become works of art, externally and internally, such as when featuring mosaic work or when murals are painted on them; or as design foci when they exhibit textures or painted finishes for effect.

In architecture and civil engineering, curtain wall refers to a building facade that is not load-bearing but provides decoration, finish, front, face, or historical preservation.

Precast walls are walls which have been manufactured in a factory and then shipped to where it is needed, ready to install. It is faster to install compared to brick and other walls and may have a lower cost compared to other types of wall. Precast walls are cost effective compare to Brick Wall compound wall.

Mullion walls are a structural system that carries the load of the floor slab on prefabricated panels around the perimeter.

A partition wall is a usually thin wall that is used to separate or divide a room, primarily a pre-existing one. Partition walls are usually not load-bearing, and can be constructed out of many materials, including steel panels, bricks, cloth, plastic, plasterboard, wood, blocks of clay, terracotta, concrete, and glass.

Some partition walls are made of sheet glass. Glass partition walls are a series of individual toughened glass panels mounted in wood or metal framing. They may be suspended from or slide along a robust aluminium ceiling track.^[5] The system does not require the use of a floor guide, which allows easy operation and an uninterrupted threshold.

A timber partition consists of a wooden framework, supported on the floor or by side walls. Metal lath and plaster, properly laid, forms a reinforced partition wall. Partition walls constructed from fibre cement backer board are popular as bases for tiling in kitchens or in wet areas like bathrooms. Galvanized sheet fixed to wooden or steel members are mostly adopted in works of temporary character. Plain or reinforced partition walls may also be constructed from concrete, including pre-cast concrete blocks. Metal framed partitioning is also available. This partition consists of track (used primarily at the base and head of the partition) and studs (vertical sections fixed into the track typically spaced at 24", 16", or at 12").

Internal wall partitions, also known as office partitioning, are usually made of plasterboard (drywall) or varieties of glass. Toughened glass is a common option, as low-iron glass (better known as opti-white glass) increases light and solar heat transmission.

Wall partitions are constructed using beads and tracking that is either hung from the ceiling or fixed into the ground.^[6] The panels are inserted into the tracking and fixed. Some wall partition variations specify their fire resistance and acoustic performance rating.

Movable partitions

Movable partitions are walls that open to join two or more rooms into one large floor area. These include:

• Sliding—a series of panels that slide in tracks fixed to the floor and ceiling, similar sliding doors
• Sliding and folding doors —similar to sliding folding doors, these are good for smaller spans
• Folding partition walls - a series of interlocking panels suspended from an overhead track that when extended provide an acoustical separation, and when retracted stack against a wall, ceiling, closet, or ceiling pocket.
• Screens—usually constructed of a metal or timber frame fixed with plywood and chipboard and supported with legs for free standing and easy movement
• Pipe and drape—fixed or telescopic uprights and horizontals provide a ground supported drape system with removable panels.

Party walls are walls that separate buildings or units within a building. They provide fire resistance and sound resistance between occupants in a building. The minimum fire resistance and sound resistance required for the party wall is determined by a building code and may be modified to suit a variety of situations. Ownership of such walls can become a legal issue. It is not a load-bearing wall and may be owned by different people.

An infill wall is the supported wall that closes the perimeter of a building constructed with a three-dimensional framework structure.

Fire walls resist spread of fire within or sometimes between structures to provide passive fire protection. A delay in the spread of fire gives occupants more time to escape and fire fighters more time to extinguish the fire. Some fire walls allow fire resistive window assemblies,^[7] and are made of non-combustible material such as concrete, cement block, brick, or fire rated drywall. Wall penetrations are sealed with fire resistive materials. A doorway in a firewall must have a rated fire door. Fire walls provide varying resistance to the spread of fire, (e.g., one, two, three or four hours). Firewalls can also act as smoke barriers when constructed vertically from slab to roof deck and horizontally from an exterior wall to exterior wall subdividing a building into sections.

Shear walls resist lateral forces such as in an earthquake or severe wind. There are different kinds of shear walls such as the steel plate shear wall.

Knee walls are short walls that either support rafters or add height in the top floor rooms of houses. In a 1+1⁄2-story house, the knee wall supports the half story.

Cavity walls are walls made with a space between two "skins" to inhibit heat transfer.

Pony wall (or dwarf wall) is a general term for short walls, such as:

• A half wall that only extends partway from floor to ceiling, without supporting anything
• A stem wall—a concrete wall that extends from the foundation slab to the cripple wall or floor joists
• A cripple wall—a framed wall from the stem wall or foundation slab to the floor joists

Demountable walls fall into 3 different main types:

• Glass walls (unitesed panels or butt joint),
• Laminated particle board walls (this may also include other finishes, such as whiteboards, cork board, magnetic, etc., typically all on purpose-made wall studs)
• Drywall

A trombe wall in passive solar building design acts as a heat sink.

On a ship, a wall that separates major compartments is called a bulkhead. A thinner wall between cabins is called a partition.

Boundary walls include privacy walls, boundary-marking walls on property, and town walls. These intergrade into fences. The conventional differentiation is that a fence is of minimal thickness and often open in nature, while a wall is usually more than a nominal thickness and is completely closed, or opaque. More to the point, an exterior structure of wood or wire is generally called a fence—but one of masonry is a wall. A common term for both is barrier, which is convenient for structures that are partly wall and partly fence—for example the Berlin Wall. Another kind of wall-fence ambiguity is the ha-ha—which is set below ground level to protect a view, yet acts as a barrier (to cattle, for example).

Before the invention of artillery, many of the world's cities and towns, particularly in Europe and Asia, had defensive or protective walls (also called town walls or city walls). In fact, the English word "wall" derives from Latin vallum—a type of fortification wall. These walls are no longer relevant for defense, so such cities have grown beyond their walls, and many fortification walls, or portions of them, have been torn down—for example in Rome, Italy and Beijing, China. Examples of protective walls on a much larger scale include the Great Wall of China and Hadrian's Wall.

Some walls formally mark the border between one population and another. A border wall is constructed to limit the movement of people across a certain line or border. These structures vary in placement with regard to international borders and topography. The most famous example of border barrier in history is probably the Great Wall of China, a series of walls that separated the Empire of China from nomadic powers to the north. The most prominent recent example is the Berlin Wall, which surrounded the enclave of West Berlin and separated it from East Germany for most of the Cold War era. The US-Mexico border wall, separating the United States and Mexico, is another recent example.

In areas of rocky soils around the world, farmers have often pulled large quantities of stone out of their fields to make farming easier and have stacked those stones to make walls that either mark the field boundary, or the property boundary, or both.

Retaining walls resist movement of earth, stone, or water. They may be part of a building or external. The ground surface or water on one side of a retaining wall is typically higher than on the other side. A dike is a retaining wall, as is a levee, a load-bearing foundation wall, and a sea wall.

Special laws often govern walls that neighbouring properties share. Typically, one neighbour cannot alter the common wall if it is likely to affect the building or property on the other side. A wall may also separate apartment or hotel rooms from each other. Each wall has two sides and breaking a wall on one side will break the wall on the other side.

Portable walls, such as room dividers or portable partitions divide a larger open space into smaller rooms. Portable walls can be static, such as cubicle walls, or can be wall panels mounted on casters to provide an easy way to reconfigure assembly space. They are often found inside schools, churches, convention centers, hotels, and corporate facilities.

A temporary wall is constructed for easy removal or demolition. A typical temporary wall can be constructed with 1⁄2" (6 mm) to 5⁄8" (16 mm) sheet rock (plasterboard), metal 2 × 3s (approx. 5 × 7 cm), or 2 × 4s, or taped, plastered and compounded. Most installation companies use lattice (strips of wood) to cover the joints of the temporary wall with the ceiling. These are sometimes known as pressurized walls or temporary pressurized walls.

Walls are often seen in popular culture, oftentimes representing barriers preventing progress or entry. For example:

Fictional and symbolic walls

The progressive/psychedelic rock band Pink Floyd used a metaphorical wall to represent the isolation felt by the protagonist of their 1979 concept album The Wall.

The American poet laureate Robert Frost describes a pointless rock wall as a metaphor for the myopia of the culture-bound in his poem "Mending Wall", published in 1914.

Walls are a recurring symbol in Ursula K. Le Guin's 1974 novel The Dispossessed'.

In some cases, a wall may refer to an individual's debilitating mental or physical condition, seen as an impassable barrier.^{[citation needed]}

In George R. R. Martin's A Song of Ice and Fire series and its television adaptation, Game of Thrones, The Wall plays multiple important roles: as a colossal fortification, made of ice and fortified with magic spells; as a cultural barrier; and as a codification of assumptions. Breaches of the wall, who is allowed to cross it and who is not, and its destruction have important symbolic, logistical, and socio-political implications in the storyline. Reportedly over 700 feet high and 100 leagues (300 miles) wide, it divides the northern border of the Seven Kingdoms realm from the domain of the wildlings and several categories of undead who live beyond it.^[8][9][10]

Historical walls

In a real-life example, the Berlin Wall, constructed by the Soviet Union to divide Berlin into NATO and Warsaw Pact zones of occupation, became a worldwide symbol of oppression and isolation.^[11]

Social media walls

Another common usage is as a communal surface to write upon. For instance the social networking site Facebook previously used an electronic "wall" to log the scrawls of friends until it was replaced by the "timeline" feature.

Wikiquote has quotations related to Wall.

Wikisource has the text of the 1911 Encyclopædia Britannica article "Wall".

Look up wall in Wiktionary, the free dictionary.

Wikimedia Commons has media related to Walls.