Aeolian processes, also spelled eolian or æolian, pertain to wind activity in the study of geology and weather and specifically to the wind's ability to shape the surface of the Earth (or other planets). Winds may erode, transport, and deposit materials and are effective agents in regions with sparse vegetation, a lack of soil moisture and a large supply of unconsolidated sediments. Although water is a much more powerful eroding force than wind, aeolian processes are important in arid environments such as deserts.
Wind erodes the Earth's surface by deflation (the removal of loose, fine-grained particles by the turbulent action of the wind) and by abrasion (the wearing down of surfaces by the grinding action and sandblasting by windborne particles).
Regions which experience intense and sustained erosion are called deflation zones. Most aeolian deflation zones are composed of desert pavement, a sheet-like surface of rock fragments that remains after wind and water have removed the fine particles. Almost half of Earth's desert surfaces are stony deflation zones. The rock mantle in desert pavements protects the underlying material from deflation.
A dark, shiny stain, called desert varnish or rock varnish, is often found on the surfaces of some desert rocks that have been exposed at the surface for a long period of time. Manganese, iron oxides, hydroxides, and clay minerals form most varnishes and provide the shine.
Deflation basins, called blowouts, are hollows formed by the removal of particles by wind. Blowouts are generally small, but may be up to several kilometers in diameter.
Wind-driven grains abrade landforms. In parts of Antarctica wind-blown snowflakes that are technically sediments have also caused abrasion of exposed rocks. Grinding by particles carried in the wind creates grooves or small depressions. Ventifacts are rocks which have been cut, and sometimes polished, by the abrasive action of wind.
Sculpted landforms, called yardangs, are up to tens of meters high and kilometers long and are forms that have been streamlined by desert winds. The famous Great Sphinx of Giza in Egypt may be a modified yardang.
Major global aeolian dust movements thought to influence and/or be influenced by weather and climate variation:
Particles are transported by winds through suspension, saltation (skipping or bouncing) and creeping (rolling or sliding) along the ground.
Small particles may be held in the atmosphere in suspension. Upward currents of air support the weight of suspended particles and hold them indefinitely in the surrounding air. Typical winds near Earth's surface suspend particles less than 0.2 millimeters in diameter and scatter them aloft as dust or haze.
Saltation is downwind movement of particles in a series of jumps or skips. Saltation normally lifts sand-size particles no more than one centimeter above the ground and proceeds at one-half to one-third the speed of the wind. A saltating grain may hit other grains that jump up to continue the saltation. The grain may also hit larger grains that are too heavy to hop, but that slowly creep forward as they are pushed by saltating grains. Surface creep accounts for as much as 25 percent of grain movement in a desert.
Aeolian turbidity currents are better known as dust storms. Air over deserts is cooled significantly when rain passes through it. This cooler and denser air sinks toward the desert surface. When it reaches the ground, the air is deflected forward and sweeps up surface debris in its turbulence as a dust storm.
Crops, people, villages, and possibly even climates are affected by dust storms. Some dust storms are intercontinental, a few may circle the globe, and occasionally they may engulf entire planets. When the Mariner 9 spacecraft entered its orbit around Mars in 1971, a dust storm lasting one month covered the entire planet, thus delaying the task of photo-mapping the planet's surface.
Most of the dust carried by dust storms is in the form of silt-size particles. Deposits of this windblown silt are known as loess. The thickest known deposit of loess, 335 meters, is on the Loess Plateau in China. This very same Asian dust is blown for thousands of miles, forming deep beds in places as far away as Hawaii. In Europe and in the Americas, accumulations of loess are generally from 20 to 30 meters thick. The soils developed on loess are generally highly productive for agriculture.
Aeolian transport from deserts plays an important role in ecosystems globally, e.g. by transport of minerals from the Sahara to the Amazon basin. Saharan dust is also responsible for forming red clay soils in southern Europe. Aeolian processes are affected by human activity, such as the use of 4x4 vehicles.
Small whirlwinds, called dust devils, are common in arid lands and are thought to be related to very intense local heating of the air that results in instabilities of the air mass. Dust devils may be as much as one kilometer high.
Wind-deposited materials hold clues to past as well as to present wind directions and intensities. These features help us understand the present climate and the forces that molded it. Wind-deposited sand bodies occur as sand sheets, ripples, and dunes.
Sand sheets are flat, gently undulating sandy plots of sand surfaced by grains that may be too large for saltation. They form approximately 40 percent of aeolian depositional surfaces. The Selima Sand Sheet in the eastern Sahara Desert, which occupies 60,000 square kilometers in southern Egypt and northern Sudan, is one of the Earth's largest sand sheets. The Selima is absolutely flat in a few places; in others, active dunes move over its surface.
Wind blowing on a sand surface ripples the surface into crests and troughs whose long axes are perpendicular to the wind direction. The average length of jumps during saltation corresponds to the wavelength, or distance between adjacent crests, of the ripples. In ripples, the coarsest materials collect at the crests causing inverse grading. This distinguishes small ripples from dunes, where the coarsest materials are generally in the troughs. This is also a distinguishing feature between water laid ripples and aeolian ripples.
Accumulations of sediment blown by the wind into a mound or ridge, dunes have gentle upwind slopes on the windward side. The downwind portion of the dune, the lee slope, is commonly a steep avalanche slope referred to as a slipface. Dunes may have more than one slipface. The minimum height of a slipface is about 30 centimeters.
Wind-blown sand moves up the gentle upwind side of the dune by saltation or creep. Sand accumulates at the brink, the top of the slipface. When the buildup of sand at the brink exceeds the angle of repose, a small avalanche of grains slides down the slipface. Grain by grain, the dune moves downwind.
Some of the most significant experimental measurements on aeolian sand movement were performed by Ralph Alger Bagnold, a British army engineer who worked in Egypt prior to World War II. Bagnold investigated the physics of particles moving through the atmosphere and deposited by wind. He recognized two basic dune types, the crescentic dune, which he called "barchan," and the linear dune, which he called longitudinal or "seif" (Arabic for "sword").
A 2011 study published in Catena examined the effect of vegetation on aeolian dust accumulation in the semiarid steppe of northern China. Using a series of trays with different vegetation coverage and a control model with none, the authors found that an increase in vegetation coverage improves the efficiency of dust accumulation and adds more nutrients to the environment, particularly organic carbon. Two critical point were revealed by their data: 1. the efficiency of trapping dust increases slowly above 15% coverage, and decreases rapidly below 15% coverage. 2. at around 55%-75% coverage, dust accumulation reaches a maximum capacity.
In Europe, the European Commission requested the Joint Research Centre to develop the first pan-European wind erosion map. In a first step, a group of scientists have used the LUCAS topsoil dataset to develop the wind erosion susceptibility of European soils. Then, they have developed an index to land susceptibility  for making a qualitative assessment of wind erosion. Finally, they modified the RWEQ model to estimate the soil Loss Due to Wind Erosion in European Agricultural Soils.
A three-year quantitative study on the effects of vegetation removal on wind erosion found that the removal of grasses in an aeolian environment increased the rate of soil deposition. In the same study, a relationship was shown between decreasing plant density with decreasing soil nutrients. Similarly, horizontal soil flux across the test site was shown to increase with increasing vegetation removal.
A 1998 study published in Earth Surfaces Processes and Landforms investigated the relationship between vegetative cover on sand surfaces with the rate of sand transport. It was found that sand flux decreased exponentially with vegetation cover. This was done by measuring plots of land with varying degrees of vegetation against rates of sand transport. The authors contend that this relationship can be utilized to manipulate rates of sediment flux by introducing vegetation in an area or to quantify human impact by recognizing vegetation loss's effect on sandy landscapes.
Ablation zone or ablation area refers to the low-altitude area of a glacier or ice sheet below firn with a net loss in ice mass due to melting, sublimation, evaporation, ice calving, aeolian processes like blowing snow, avalanche, and any other ablation. The equilibrium line altitude (ELA) or snow line separates the ablation zone from the higher-altitude accumulation zone. The ablation zone often contains meltwater features such as supraglacial lakes, englacial streams, and subglacial lakes. Sediments dropped in the ablation zone forming small mounds or hillocks are called kames. Kame and kettle hole topography is useful in identifying an ablation zone of a glacier. The seasonally melting glacier deposits much sediment at its fringes in the ablation area. Ablation constitutes a key part of the glacier mass balance.
The amount of snow and ice gained in the accumulation zone and the amount of snow and ice lost in the ablation zone determine glacier mass balance. Often mass balance measurements are made in the ablation zone using snow stakes.Abrasion (geology)
Abrasion is a process of erosion which occurs when material being transported wears away at a surface over time. It is the process of friction caused by scuffing, scratching, wearing down, marring, and rubbing away of materials. The intensity of abrasion depends on the hardness, concentration, velocity and mass of the moving particles. Abrasion generally occurs four ways. Glaciation slowly grinds rocks picked up by ice against rock surfaces. Solid objects transported in river channels make abrasive surface contact with the bed and walls. Objects transported in waves breaking on coastlines cause abrasion. And, finally, abrasion can be caused by wind transporting sand or small stones against surface rocks.
Abrasion, under its strictest definition, is commonly confused with attrition. Both abrasion and attrition refer to the wearing down of an object. Abrasion occurs as a result of two surfaces rubbing against each other resulting in the wearing down of one or both of the surfaces. However, attrition refers to the breaking off of particles (erosion) which occurs as a result of objects hitting against each other. Abrasion leads to surface-level destruction over time, whereas attrition results in more change at a faster rate. Today, the geomorphology community uses the term "abrasion" in a looser way, often interchangeably with the term "wear".Aeolian
Aeolian or Eolian refers to things related to Aeolus, the Greek God of wind and patriarch of the Greeks of Aeolia. Specific items include:
Aeolian Islands, islands in the Tyrrhenian Sea
Aeolian or Aeolic order, an early order of Classical architecture
Aeolian processes, wind-generated geologic processes
Aeolian dust, atmospheric or wind-borne dust
Aeolians, an ancient Greek tribe allegedly descended from Aeolus, son of Hellen
Eolian, a volume of poetry by David Bates (poet)
Eolian (Solar car), a solar car designed at the University of Chile
Eolianite, a sandstone formed from wind-transported sedimentIn music:
Aeolian (album), an album by German post-metal band The Ocean Collective
Aeolian Company (1887–1985), a maker of organs, pianos, sheet music, and phonographs
Aeolian Hall (disambiguation), any one of a number of concert halls of that name
Aeolian harp, a harp that is played by the wind
Aeolian mode, a musical mode, the natural minor key
Aeolian Quartet (1952–1981), a string quartet based in London
Aeolian-Skinner (1932–1972), pipe organ builderAeolian landform
Aeolian landforms are features of the Earth's surface produced by either the erosive or constructive action of the wind. This process is not unique to the Earth, and it has been observed and studied on other planets, including Mars.Denning (Martian crater)
Denning Crater is a large Noachian-age impact crater in the southwestern Terra Sabaea region of the southern Martian highlands, within the Sinus Sabaeus quadrangle. It is located to the northwest of the Hellas impact basin within the furthest outskirts of the Hellas debris apron. The crater is 165 km in diameter and likely formed during the Late Heavy Bombardment, a period of intense bolide impacts affecting the entirety of the Solar System; during the Hesperian period, aeolian processes caused significant degradation of the crater's rim features and infilled the crater's floor (which is nearly at the same elevation as the surrounding plains terrain). Similar to other large craters in this region of Mars, wind-eroded features are sporadically found on the basin floor. The presence of wrinkle ridges of varying orientations within and around the Denning basin has been correlated to regional tectonic events, including the formation of the Hellas basin itself. The crater was named for British astronomer William Frederick Denning.Eolianite
Eolianite or aeolianite is any rock formed by the lithification of sediment deposited by aeolian processes; that is, the wind. In common use, however, the term refers specifically to the most common form of eolianite: coastal limestone consisting of carbonate sediment of shallow marine biogenic origin, formed into coastal dunes by the wind, and subsequently lithified. It is also known as kurkar in the Middle East, miliolite in India and Arabia, and grès dunaire in the eastern Mediterranean.
Sayles coined the term in 1931, when he described the dune-shaped hills of Bermuda, consisting of bioclastic grainstones. Thus, Bermuda is considered the type locality for carbonate eolianite facies, with clearly defined cross-bedding, foresets, and topsets. Deposition is controlled by glacio-eustatic changes, with eolianites forming during interglaciations. Eolianites occur along the margins of the global carbonate belt, on the carbonate islands along northeastern Yucatan, and Rottnest Island.Eolianite occurs in many parts of the world. It occurs most extensively between the latitudes of 20° and 40° in both hemispheres, with little nearer the equator, and virtually no deposits nearer the poles. There is no apparent difference in distribution between the hemispheres, but if the extent and thickness of deposits are taken into account, the Southern Hemisphere has the bulk of eolianite.
Conditions favourable for formation of eolianite are:
a warm climate, favourable to the production of carbonate by shallow marine animals; for example, the production of seashells by marine molluscs;
onshore winds to form beached sediment into dunes;
a relatively low onshore topography, rather than onshore cliffs, to allow the formation of dune systems;
relatively low onshore rainfall, to promote rapid lithification;
tectonic stability;The most extensive deposits of eolianite in the world are located on the southern and western coasts of Australia. On the west coast, there are over 800 kilometres (500 mi) of eolianite cliffs, which are over 150 metres thick in some places. These cliffs, locally known as the Tamala Limestone Formation, contain layers of dune origin interspersed with layers of shallow-marine origin. Other substantial deposits occur in Bermuda, the Bahamas, the southern and eastern coasts of South Africa, the Mediterranean, India, and oceanic islands of the Pacific, Atlantic, and Indian Oceans.Geomorphology
Geomorphology (from Ancient Greek: γῆ, gê, "earth"; μορφή, morphḗ, "form"; and λόγος, lógos, "study") is the scientific study of the origin and evolution of topographic and bathymetric features created by physical, chemical or biological processes operating at or near the Earth's surface. Geomorphologists seek to understand why landscapes look the way they do, to understand landform history and dynamics and to predict changes through a combination of field observations, physical experiments and numerical modeling. Geomorphologists work within disciplines such as physical geography, geology, geodesy, engineering geology, archaeology, climatology and geotechnical engineering. This broad base of interests contributes to many research styles and interests within the field.Graded bedding
In geology, a graded bed is one characterized by a systematic change in grain or clast size from one side of the bed to the other. Most commonly this takes the form of normal grading, with coarser sediments at the base, which grade upward into progressively finer ones. Normally graded beds generally represent depositional environments which decrease in transport energy (rate of flow) as time passes, but these beds can also form during rapid depositional events. They are perhaps best represented in turbidite strata, where they indicate a sudden strong current that deposits heavy, coarse sediments first, with finer ones following as the current weakens. They can also form in terrestrial stream deposits.
In reverse or inverse grading the bed coarsens upwards. This type of grading is relatively uncommon but is characteristic of sediments deposited by grain flow and debris flow. It is also observed in Aeolian processes. These deposition processes are examples of granular convection.Lag deposit
A lag deposit is the deposition of material winnowed by physical action. Aeolian processes, fluvial processes, and tidal processes can remove the finer portion of a sedimentary deposit leaving the coarser material behind.
Lag deposits are found in processes such as central island formation in streams and rivers. One theory of desert pavement formation is that they are an aeolian lag deposit. Armored beaches and inlets can be composed in part by lag deposits of shells or cobbles created when tidal forces strip away the finer sand and silt.Matti Seppälä
Matti Kullervo Seppälä (born 5 September 1941 in Vaasa) is a Finnish geomorphologist specialized in cold climate aeolian processes. Seppälä is arguably the foremost expert on palsas. Seppälä obtained a Ph.D. at the University of Turku in 1971 and moved after to work at the University of Oulu until in 1978 he moved to the University of Helsinki.
He served at that university as professor from 1978 to 2009 and is currently a retired professor of physical geography at that university.Matti Seppälä has also been a research fellow at Uppsala University, Heidelberg University, Université de Montréal, University of Cambridge and Durham University.Olando kepurė
Olando kepurė or Dutchman's Cap is a hill with a 24.4 m high bluff, which is in Lithuania's Seaside Regional Park, near Karklė and 2 km north of Giruliai on the Baltic Sea coast. It was created 12000–15000 years ago during the last Baltic glaciation.The hill is a parabolic dune created by Aeolian processes on a moraine ridge. The location is now subject to strong erosion by the Baltic Sea, which is exposing various-sized boulders from the moraine. As a consequence, boulder rubble has accumulated on the so-called beach. As the bluff's base is destroyed, earth slips down the bluff's entire face, in an example of mass wasting.
Olando kepurė has long been a navigational guide for sailors and fishermen and so in the early 19th century, markers were erected here and have been shown on charts ever since. A view of the sea with a steep shoreline and stony beaches opens up here. The top of the bluff is a good place to watch birds flying above the sea.Orcus Patera
Orcus Patera is a region on the surface of the planet Mars first imaged by Mariner 4. It is a depression about 380 km long, 140 km wide, and about 0.5 km (500 meters) deep but with a relatively smooth floor. It has a rim up to 1.8 km high. Orcus Patera is west of Olympus Mons and east of Elysium Mons. It is about halfway between those two volcanoes, and east and north of Gale crater.
It has experienced aeolian processes, and has some small craters and graben structures. However, it is not known how the patera originally formed. Theories include volcanic, tectonic, or cratering events. A study in 2000 that incorporated new results from Mars Global Surveyor along with older Viking data, did not come out clearly in favor of either volcanic or cratering processes.Mars Express observed this region in 2005, yielding a digital terrain model and color pictures.Planetary geology
Planetary geology, alternatively known as astrogeology or exogeology, is a planetary science discipline concerned with the geology of the celestial bodies such as the planets and their moons, asteroids, comets, and meteorites. Although the geo- prefix typically indicates topics of or relating to Earth, planetary geology is named as such for historical and convenience reasons; due to the types of investigations involved, it is closely linked with Earth-based geology.
Planetary geology includes such topics as determining the internal structure of the terrestrial planets, and also looks at planetary volcanism and surface processes such as impact craters, fluvial and aeolian processes. The structures of the giant planets and their moons are also examined, as is the make-up of the minor bodies of the Solar System, such as asteroids, the Kuiper Belt, and comets.Quartz arenite
A quartz arenite or quartzarenite is a sandstone composed of greater than 90% detrital quartz, with limited amounts of other framework grains (feldspar, lithic fragments, etc.) and matrix. It can have higher-than-average amounts of resistant grains, like chert and minerals in the ZTR index.
The term 'quartz arenite' is derived from the main component (quartz) and arenite, a Latin term for a rock with sand-sized grains. In some literature, these can be called orthoquartzites, a confusing term which usually refers to the metamorphic rock quartzite, though most metamorphic quartzites are diagentically fused from quartz arenites. The term "quartzose sandstone" can also be used for a quartz arenite.
Quartz arenites are the most mature sedimentary rocks possible, and are often referred to as ultra- or super-mature, and are usually cemented by silica. They often exhibit both textural and compositional maturity. The two primary sedimentary depositional environments that produce quartz arenites are beaches/upper shoreface and aeolian processes, due to their high residence time, high transport distance, and/or high energy of the environment. Most of the time, these sediments are reworked over and over, even being eroded out of a lithified rock and becoming a brand new sediment and rock. This is known as a multicycle sand.Ripple marks
In geology, ripple marks are sedimentary structures (i.e., bedforms of the lower flow regime) and indicate agitation by water (current or waves) or wind.Río Cuarto craters
The Río Cuarto craters are a purported group of impact craters located in Córdoba Province, Argentina. Research published in 2002 indicates that they are more likely a result of Aeolian processes.Sediment
Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand and silt can be carried in suspension in river water and on reaching the sea bed deposited by sedimentation and if buried, may eventually become sandstone and siltstone (sedimentary rocks).
Sediments are most often transported by water (fluvial processes), but also wind (aeolian processes) and glaciers. Beach sands and river channel deposits are examples of fluvial transport and deposition, though sediment also often settles out of slow-moving or standing water in lakes and oceans. Desert sand dunes and loess are examples of aeolian transport and deposition. Glacial moraine deposits and till are ice-transported sediments.Terrain softening
The landscape polewards of around 30 degrees latitude on Mars has a distinctively different appearance to that nearer the equator, and is said to have undergone terrain softening. Softened terrain lacks the sharp ridge crests seen near the equator, and is instead smoothly rounded. This rounding is thought to be caused by high concentrations of water ice in soils. The term was coined in 1986 by Steve Squyres and Michael Carr from examining imagery from the Viking missions to Mars.
Below 30 degrees of latitude, impact craters have steep walls; well-defined, sharp rims; and flat or smoothly bowl-shaped floors. Ridges on intercrater plains come to similarly well-defined, pointed crests. However, above this latitude, these same features appear very different. The crests seen on ridges and crater rims appear strongly rounded and much more poorly defined. The relief (height) of features is somewhat reduced. Small craters are noticeably less common. In other words, terrain which elsewhere looked sharp here looks "soft". This texture has also been described as "smooth", or "rolling". Softened craters are also commonly infilled with concentric patterns on their floors.On Earth, diffusive creep of soils is associated with rounded hillslopes. Squyres and Carr thus attributed the softened texture to accelerated viscous creep in shallow soils near the surface, and went on to associate this accelerated creep with the presence of ground ice at these latitudes. This conclusion has been largely borne out by subsequent research. In the late 1980s some attempts were made to link terrain softening with dust and aeolian processes, though this hypothesis has largely been superseded by more recent observations.Terrain softening is one of a suite of features seen in the midlatitudes of Mars—also including lobate debris aprons, lineated valley fill, concentric crater fill, latitude dependent mantle, patterned ground, viscous flow features, arcuate ridges, recurring slope lineae, and gullies—whose form and distribution strongly suggest the abundance of ice at the surface.Trumao
Trumao is the name of a soil of the Andosol order found in southern and central Chile. Trumaos are formed from young volcanic ash, by volcanic ash redeposited by aeolian processes or by volcanic ash mobilized as alluvium. Trumaos are characterized by containing the following minerals: allophane, imogolite plus a series of paracrystalline and non-crystalline clays. These soils have high porosity and low bulk density. A more dry and a more humid variety of trumaos exists. The dry variety is known simply as trumao while the humid variety is known as trumao húmedo.In terms of latitude trumaos can be found in the Andes from 33° S to 43° S, in the Central Valley from 38° S to 43° S and in the eastern slopes of the Chilean Coast Range from 39° S to 43° S.
Geologic principles and processes