AEOLIAN or WIND GEOMORPHOLOGY & LANDFORMS

1

GEOMORPHOLOGY 201 READER

PART III AEOLIAN or WIND GEOMORPHOLOGY amp LANDFORMS

While water is the most important landscape-forming agent in temperate and humid climates ice

fulfils this role in colder climates Coastal geomorphic processes (wave and tidal action) likewise are

the major processes where fluvial systems and oceans meet The landscaping effects of groundwater

action are limited to karst areas which is about 10 of the earths surface where limestone and

dolomite formations occur The remaining landscape creating work is done by wind in all areas where

water is in short supply As South Africa is considered a water scarce country aeolian or wind-driven

processes are therefore a key player in determining the form and function of our landscapes

Unique characteristics of arid regions include that chemical weathering occurs at a much slower rate

than where water is abundant Physical weathering is therefore the primary weathering agent and

results in rocks and talus being deposited on the land surface These materials are largely chemically

unchanged and are further characterised by a low content of organic material and water which in

turn is responsible for very slow rates of soil formation Dry regions are also characterised by sparse

vegetation which would normally protect and anchor soil and talus the conditions in arid regions are

therefore especially favourable for wind action to blow away dry talus and to be a major force in

landscape genesis

2 The distribution of Aeolian geomorphic action on earth

While wind occurs everywhere on the earthrsquos surface it is only where surface water is scarce that

wind action becomes a major landform- creating agent The main regulators determining if a

landscape will be prone to mainly water or wind erosion are therefore climate and more specifically

temperature and rainfall Hot deserts and semi-deserts (BSh amp BWh regions according to the Koppen

classification system) are the regions most prone to wind as landform creating agent While wind is the

more prevalent force in shaping desert landforms water is the more powerful Despite water being so

scarce in these environments it is the primary agent of erosion in the desert with many features owing

their formation to mass wasting and running water as sheet floods Even the driest deserts receive

occasional rainfall which then usually occurs as downpours which cause landform creation

processes over a large scale in a short time period

Mass action and fluvial action are therefore the main landscape-forming processes in deserts with

wind being only responsible for secondary localised and other minor landforms The wind action

however occurs over a persistent and ongoing basis and has an enduring presence and signature in

arid landscapes Due to climate changes over time the landscape bears evidence of former

landforms that were created when different climatic conditions controlled the prevailing landforms

such as the sandstone deposits in the Eastern Free State and Lesotho these date from times when

wind action and deposition by water were the chief landforming agents

In Africa there are many hot arid regions such as the Namib Sahel and Sahara deserts and also

many semi-arid regions including Namaqualand the Kalahari and parts of Ethiopia and Somalia

These regions are all have many features in their landscape that were created by the wind-cascade

system Other parts of Africa have long dry seasons and are subject to prolonged droughts even

though they are not classified as semi-arid regions In these regions as well as those where dryland

cultivation leaves large areas uncovered by vegetation or crops for part of the year large volumes of

surface material is lost annually and wind erosion plays a major role in forming the landscape

Furthermore landforms created by wind can also occur in dry river valleys along coasts and along

river floodplains where large quantities of talus are present

Wind is one of the three dominant agents in hot deserts after mass wasting and occasional water

action The desert floors get heated up rapidly as they are dry and consist of mainly mineral silicas

while being virtually devoid of organic matter and vegetation These heated floors heat the air

directly above them resulting in upward movements in the hot lighter air with turbulence and any

obstructions in its path sets up eddies whirlwinds updrafts and downdrafts Winds also move along

the desert floors with great speed and the obstructions in their path create turbulence while very

destructive storm winds also occur

Some fluvial processes and landforms found in deserts

Deserts are defined by their lack of water and while coastal deserts may experience one or two rainfalls a

year those further inland may get rain once or twice a decade only Although rain is scarce in deserts

(the Sahararsquos average annual rainfall is only 127mm) it usually comes down torrentially and lasts mere

minutes or a few hours This enhances rainsplash erosion on the bare unvegetated desert soil loosening

and spattering soil particles in all directions The desert rock material also undergoes accelerated

mechanical and chemical weathering processes due to drastic diurnal temperature changes

decaying fast with the torrential rains helping to remove the weathered materials speedily The

dislodged soil and talus is carried off with the flowing water which picks up and transports more sediment

as it rushes along Owing to a lack of organic-rich soil that can absorb the water and also the absence of

vegetation the desert landscape offers little resistance to water action and erodes rapidly Water

therefore accomplishes within a few days what would take desert winds a year to accomplish which

3 means that the weathered debris in deserts is moved by not only wind but also significantly by

rainsheet wash

Finding natural depressions such as gullies and canyons the sediment-laden water gains speed and

power as it is confined and flows downward Increased velocity allows the water to pick up more and

larger sediments and rock debris eroding them and the surface below as it rushes along Often clogged

with so much debris the water can resemble a mud-flow (a thick mixture of water mud and other surface

fragments) Arroyos the dry streambeds created by previous rains again fill with water When an arroyo

finally opens onto a flat broad plain the rushing water flows out and drops its load of sediments forming a

new alluvial fan In other areas basins or depressions in the desert floor fill with water forming playa lakes

that soon evaporate leaving a dry cracked salty lake bed that will remain until the next rain

Alluvial fan

Precipitation that falls in higher elevations in deserts flows rapidly down to flat areas through canyons

valleys and other narrow confined channels Because most desert soil lacks plants and their root systems

to help hold the soil together the flowing water easily picks up any loose material in its path The faster the

water flows the larger the pieces of material it is able to pick up and carry along

When the rushing water finally reaches a plain or flat area it loses power since gravity is no longer helping

it flow down a steep slope As it slows the water is unable to carry the sedimentmdashgravel clay sand and

siltmdashit picked up on its way downhill Large rocks and other heavy material are deposited first at the base

of the canyon followed by other material in decreasing size No longer confined to a narrow channel the

water spreads out the farther it moves away from the base of the canyon The finest material it carried is

deposited at the outer edge When the water evaporates the sediments remain behind Over time as

more water flows onto the plain more sediment is deposited and a wide fan-shaped pile known as an

alluvial fan forms When two or more alluvial fans merge on a plain to create a broad sloping surface

they form a bajada

Arroyo

An arroyo is a desert landform sculpted by the action of water Sudden heavy downpours cut channels in

the desert floor often in canyons or other low-lying areas These fast-moving but short-lived streams create

deeper channels or gullies with steep sides and an almost flat bed or bottom Just as quickly as the water

appears it disappears in the normally dry desert environment What remains is an arroyo a dry

watercourse with a floor that is often gravel-strewn

Stream channels in desert areas are broad smooth and indefinite and flow for a brief time after rains

Bajada

When two or more alluvial fans merge on a plain to create a broad sloping surface they form a bajada

THE WIND CASCADE SYSTEM

The work performed by aeolian systems is concentrated in desert regions and therefore desert is will

be used as model to describe this wind cascade system On the basis of its morphological

characteristics the desert landscape can be subdivided into the deflation-corrasion and the

aeolian-accumulation subsystems The processes of deflation and corrasion dominate in the

deflation-corrasion subsystem while the deposition of wind-transported talus is the major process in

the aeolian-accumulation subsystem

Deflation is the process of removing talus on the earth surface by wind while corrasion is the physical

weathering of rock by talus-carrying wind Corrasion processes include abrasion chipping and

polishing The deflation-corrasion subsystem consists of the Hamada and the serir The hamada has

4 exposed rock surfaces and products of mechanical weathering namely angular rock fragments

scattered about The serir is a stony desert with smaller rock fragments impacted mainly by corrosion

processes The size of the rock fragments decreases in the direction of the aeolian-accumulation

subsystem from boulders down to sand grains The aeolian-accumulation subsystem is therefore

characterised by fairly homogeneous sand-sized particles and landforms due to accumulation ndash such

as extensive sand sheets seif dunes transverse dunes and barchans dunes

The following are the major morphological regulators of the two subsystems

Morphological characteristics

Deflation-corrasion subsystem Aeolian-accumulation subsystem

Particle size Particle size

Rock composition Presence of obstructions [landforms

vegetation]

Rock structure Spacing of obstructions

Rock texture Slope of obstructions

Depth of soil-water table Height amp extent of obstructions

Depth of groundwater table

Regulators


Wind velocity Wind velocity

Talus present or absent Talus present or absent in air current

Size amp shape of talus particles Size amp shape of talus particles

Wind velocity is a threshold regulator in practice this means that wind needs to attain a velocity of

53 to 75 ms (19 kmh to 27 kmh) to be able to blow fine particles up into the air or to roll grains of

sand along the surface Velocities lower than these will not cause any movement of particles

Therefore if talus is available then its particle size will act as regulator of whether the threshold

velocity will cause deflation or corrosion ( if velocity gt 20 kmh) picking up or moving the talus

particle or whether it will remain stationary in the Aeolian-accumulation subsystem

EROSIONAL LANDFORMS

Overview

An overview of wind-driven processes and landforms in deserts

The wind moves like a fluid and has erosional ability only if it is strong enough More often it merely

transports material and very small particlesof less than 02 mm in diameter can be picked up easily and

carried aloft for hundreds or thousands of miles by desert winds Suspended on air currents dust from

Africas Sahara Desert sometimes crosses the Atlantic Ocean before landing in the west Atlantic and

Caribbean Sea while on the other hand sand particles of 02 to64 mm diameter can be carried only by

extremely strong winds Silt and other very small-sized particles fill the air during dust storms but these and

most other wind-borne grains are too small to cause erosion or sandblasting of major landforms that stand

high above the desert floor

Wind-blown sediment causes the most erosion at a height of no more than 250 mm above the surface

where the wind removes fine-grained particles which causes deflation - the lowering of the land surface

due to the removal of particles by the wind This continued action leads to blowouts and the formation of

desert pavements Another process is abrasion whereby sand and silt act as effective tools to abrade

5 (scour) the land surface while it is transported by wind Any stone or part of the bedrock that has been

abraded or shaped by the wind is known as a ventifact (artefact of the wind) A yardang is one large

desert landform that is sculpted by the wind though deflation and abrasion A third process caused by

wind action is impact which is simply the sheer force of momentum which occurs when sand is blown

into or against a rock surface similar to a sandblasting operation Wind action therefore creates a

number of interesting erosional and depositional features in the deserts

Sand storm Tunisia httpwwwnicholasdukeedueosgeo41win002gif

Wind storm Tunisia

httpwwwnicholasdukeedueosgeo41win003gif

Figure 31 Sandstorms in deserts

The wind transports larger-grained sediments particularly sand through the process called saltation

While light enough to be picked up by strong wind

sand is too heavy to remain suspended in the air As

a result it is moved along the Earths surface by the

wind through a series of short jumps and bounces

The majority of sand transported in this way travels

within 06 meter of the ground As saltating particles

crash to the ground they can dislodge and move

slightly larger particles such as small pebbles The

sliding and rolling movement of these particles is

called surface creep

Figure 32 Suspension saltation and creep

LANDFORMS

Pediments and pediplains

Landscape evolution in deserts is primarily concerned with the formation and extension of pediments

Gently inclined rocky floors close to the mountains at their foot with or without a thin cover of debris

are called pediments Such rocky floors form through the erosion of mountain fronts through a

combination of lateral erosion by streams and sheet flooding Erosion starts along the steep margins

of the landmass or the steep sides of the tectonically controlled steep incision features over the

landmass Once pediments are formed with a steep wash slope followed by a cliff or free face above

it the steep wash slope and free face retreat backwards This method of erosion is termed parallel

retreat of slopes through backwasting So through this process the pediments extend backwards at

the expense of the mountain front and gradually the mountain gets reduced leaving an inselberg

which is a remnant of the mountain This explains how the high relief in desert areas is reduced to low

featureless plains called pediplains

6 Playas

Plains are by far the most prominent landforms in the deserts In basins with mountains and hills around

and along the drainage is towards the centre of the basin and due to gradual deposition of

sediment from basin margins a nearly level plain forms at the centre of the basin When the water

falls on fairly flat areas it may collect in a basin or other slightly depressed area forming a small lake

that may last for a while before the water evaporates or is absorbed These shallow lakes are called

playas where water is retained only for short duration due to evaporation losses Evaporation causes

the gradual concentration of salts in the playa as only pure water evaporates leaving behind the

sediments mostly clay silt and various dissolved salts which form a level broad cracked surface

The playas therefore usually contain a good deposition of salt and such playa plains covered up by

salts are called alkali flats

When water is still present these bodies are called playa lakes Although they are very rare

permanent desert lakes do exist Two examples are the Great Salt Lake of Utah and the Dead Sea of

Israel and Jordan

Deflation Hollows and Caves

Following water wind is a major cause of erosion in the desert Without plants and their anchoring roots

loose desert soil is moved easily by near-constant blowing winds Blowouts also known as deflation basins

or hollows are depressions made in sand or light soil by strong wind action and may range in size from

metres to several kilometres in diameter As the name of the landform indicates they are formed by the

process of deflation These depressions may extend over several square kilometres Blowouts can form

around desert plants with hardy roots or around rock structures leaving them perched atop a column as

more and more sand or soil is blown away Deflation also creates numerous small pits or cavities over

rock surfaces The rock faces suffer impact and abrasion of wind-borne sand and first shallow

depressions called blow outs are created and some of the blow outs become deeper and wider to

the extent that they can be called caves

There are some examples of deflation hollows in the Richtersveld and in Bushmanland in the north-

western extreme of the Northern Cape Province and also near Velddrift in the Western Cape

Province Because the hollows or cavities that form trap surface water or at least store more water

than their immediate surroundings this promotes some chemical weathering of the underlying rock

which in turn causes further removal of talus by wind action The depth of the water table regulates

the depth to which a depression hollow can erode because as soon as the water table is

intersected an oasis swamp or pan is formed

This moistened landform is then not subject to further wind erosion Pan forms are abundant in the

Kalahari (in the Northern Cape Province ) and in Botswana with the extensive Makarikari depression

and Verneukpan as examples of large-scale landforms while there are thousands of much smaller

pans dotting this region as well Other examples of deflation hollows include the shallow salt lakes of

the Qattara Depression in Eqypt and the Etosha Pan in Namibia The Etosha Pan is situated on the

floor of a deflation hollow that developed on a structural basin and is one of the largest salt pans in

the world and an attraction for a spectacular diversity of wildlife

Desert pavements (also Reg Hamada or gibber plain)

The strength of the wind determines how much and what type of material will be removed from the desert

floor With increasing strength wind is able to move and transport more and larger particles Initially very

fine particles are removed but as more and more of these types of particles are removed the surface of

the land is lowered This action known as deflation continues until what remains on the desert floor is a

7 layer of closely packed pebbles and rocks too heavy for the wind to move Settled and wind-polished the

entire surface is called a desert pavement or reg The older the pavement the smoother and flatter it

appears like a highly worn cobblestone street

Desert pavements are gravel covered plains such as the serirs in Libya from which the landform of the

one main component of the deflation-corrasion subsystem derives its name These stony deserts with

small rock fragnments are referred to as lsquogibber plainsrsquo in Australia A similar landform is the Hamada

or reg (eg the Hamada el Homra in Libya and the Tanezrouft in Algeria) characterised by exposed

rock surfaces with scattered rock fragments In the Sahara an extensive stony desert plain is known as

Reg not to be confused with Erg which refers to a sandy desert area The term gibber plain is used in

Australia in parts of the Tirari-Sturt stony desert ecoregion where extensive areas are covered in

desert pavements (Aus pebble = gibber)

Deflation surface Desert pavement in the Mojave Desert California

The stony desert known as Reg delrsquoAdrar in Mauritania Tunisia pre-Sahara


Figure 33 Deflation surface and desert pavement

Oasis

Beneath the Earths surface water fills the pore spaces and openings between rocks The upper limit of the

groundwater is called the water table which is present even beneath desert regions Groundwater hardly

ever reaches the desert surface but when it does it can transform the stark landscape into a fertile haven

thriving with many species of plants and animals that otherwise would not exist in such a hot dry

environment This green area existing like an island in a sand sea is an oasis Many oases are artificial

ecosystems created by people living in the desert using large pipes to tap into the groundwater to bring it

to the surface A few are the result of natural forces and are centred on springs that have been exposed

because of blowouts and other erosive actions by the wind resulting in a lowering of the land surface

8 Abrasion acts on free-standing rock outcrops modifying them into interesting and unique landforms

Yardangs are the first of these landforms primary formed by abrasion The others are zeugen and

then collectively landfoms such as mushroom rocks rock pedestals and ventifacts

Yardangs and zeugen

Yardangs are extensively grooved fluted pitted and irregular rock ridges or reliefs of one to about

ten metres high running parallel to the prevailing winds They are caused by differential erosion when

the sand-laden wind corrades zones of softer or weaker rock between harder vertical ridges from old

lake sediment where soft poorly consolidated rock and bedrock surfaces are eroded into alternating

ridges and furrows Large- scale yardangs in Africa are to be found in Egypt (near Kom Ombo north

of Lake Aswan) Chad Libya and Algeria Local but smaller scale yardangs are to be seen near the

Umtamvuma River mouth in Kwazulu-Natal these are 4m high and were formed within a 60-year

period

Yardangs and allied ridge and furrow features are probably the only landforms in deserts that can

be ascribed to wind abrasion alone

Yardang Egypt copy H Kehl

Top Yardang Egypt copy Urs Moumlckli

9

Yardangs up to 180 m tall in the Lut Desert or Dasht-e Lut

(Desert of Emptiness) of Irans southeastern province of

Kerman This great sand and stone desert is among the

driest places on the planetrsquo

The Lut desert is extremely barren having the only region

devoid any life not even bacteria on Earth with annual

rainfall ranging from 0 to only 30 mm

Figure 34 Yardangs around the world

Zeugen Hoodoos - Mushroom Rocks - Pedestal Rocks

When differential erosion of horizontal rock layers take place we refer to the resulting landform as

zeugen Typically zeugen are mushroom-shaped rock that has been eroded by the abrasive action

of windblown sand The undercutting effect is concentrated near ground level where sand

movement is greatest and is enhanced in areas of near-horizontal strata when the lowest bed is

relatively weak and shows distinct signs of basal abrasion on the upwind side only A smoothly

rounded top (as opposed to a top with rough edges) is created by spheroidal weathering into a

form resembling a mushroom

The supporting column of a mushroom or pedestal rock is caused by etching differential weathering

and natural sandblasting of sedimentary deposits Often an erosion resistant layer will be deposited

above softer sediment layers and after burial and lithification joints and fractures form in the upper

layer allowing faster erosion of the soft strata below Abrasion near the ground by windblown sand

causes the lower portion of a rock mass to be undercut leaving the upper portion relatively

unaffected

Mushroom Table and Pedestal Rocks

More localised and on a smaller scale than the previous landforms many rock-outcrops in the deserts

are easily susceptible to wind deflation and abrasion Softer layers in these outcrops are worn out

easily leaving remnants of more resistant rocks in the shape of mushroom with a slender stalk and

capped by a broad and rounded pear shape above Mushroom rocks and similar landforms are

actually the products of mainly chemical weathering but wind abrasion also contributes in that the

chemically weakened (weathered) softer layers are easily abraded by wind The resulting landform is

the pedestal-shaped toadstool capped by a more resistant upper layer As wind-borne talus has

bigger-sized particles nearer the land surface compared to higher up free standing rock outcrops

are subject to more active or more concentrated abrasion at their bases relative to higher sections

resulting in the familiar stem or pedestal shape

10

The Mushroom Rock near Clarens Free State

Mukorob the ldquoFinger of Godrdquo near Mariental Namibia before

its collapse in 1988

Figure 35 Examples of Zeugen Hoodoos Mushroom Rocks or Pedestal Rocks

The Finger of God or Mukorob near Asab and Mariental in Namibia (which toppled in December

1988) was an excellent example of this landform (bottom rigt in Figure ) It consisted mostly of

sandstone and stood 12 m high and 45 m wide weighing some 450 tons but had a base of just 3 m

long and 15 m wide The Mushroom Rock near Clarens in the eastern Free State Province (top left) is

another local but much smaller example

11 Ventifacts

On a much smaller scale than the mega-landforms of yardangs and zeugen rock fragments and

stones are shaped into highly-polished conical shapes by wind-driven sand Typically larger rocks

too big to be pushed or moved along by the wind once they are polished display smooth faces or

facets and are then termed lsquoventifactsrsquo analogous to artefacts

The German term lsquoeinkantersrsquo is used for rocks with one face only polished but when such a one-

sided polished stone falls over it presents another face to the prevailing wind and after a second

toppling over three facets are smoothed and polished Such three-sided ventifacts are known as

lsquodreikantersrsquo The ergs of the Sahara and the stony northern Namib Desert have extensive sheets of

ventifacts

Ventifacts from all over

httpwwwnicholasdukeedueosgeo41win011gi

Ventifact showing facets


Figure 36 Ventifacts

12

DEPOSITIONAL LANDFORMS

Wind is a good sorting agent Depending upon the velocity of wind different sizes of grains are

moved along the floors by rolling or saltation and carried in suspension and in this process of

transportation itself the materials get sorted When the wind slows or begins to die down depending

upon sizes of grains and their critical velocities the grains will begin to settle Therefore good sorting of

grains can be found in depositional landforms made by wind More formally wind will deposit its talus

load when its supply of kinetic energy is too low to carry the talus mass Since a desert has an

abundant supply of sand and with nearly constant wind directions prevailing depositional features in

arid regions can develop anywhere

The three commonly distinguished landforms formed by wind deposition of talus are draas dunes and

ripples

Draas and ergs

Draas are huge sand accumulations and where these converge a landform termed erg is formed ndash

such as the star-shaped Great Continental Erg in Algeria There are approximately twenty ergs in the

Sahara which collectively cover about 15 of the Sahararsquos surface area

The Great Sand sea near Luderitz in the

Namib Desert

Ar Rub al Khali Sand Sea Arabian Peninsula

Figure 37 Sand seas or draas (ergs)

13 These lsquosand seasrsquo are extensive accumulations of sand up to 300 m thick and are essentially water

deposits while most of them occupy large depressions which are former (paleo) lakes or shallow

oceans which were subsequently filled with water-borne (ie fluvial) talus The surface of the draas

are shaped by wind ndash with dunes typically developing on the wind side On a smaller scale individual

ripples are formed on the surface of a draa or dune All three of these wind-shaped landforms draas

dunes and ripples are in essence waves ndash and can therefore be described in terms of their geometric

characteristics like wavelength and amplitude

The photograph on the top right (Figure 37) shows a part of The Ar Rub al Khali sand sea or erg - also

known as the Empty Quarter ndash in Oman In the western portion there is a large region of SW-NE oriented

transverse sand dunes (reddish brown) alternating with the blue-grey interdune salt flats known as sabkha

The dominant winds are Shamal winds which are northwesterly trade winds originating in Iraq The

formation of secondary barchan and star dunes on the parallel transverse dunes is due to southwesterly

Kharif winds that blow during the monsoon season The long l transverse dunes begin to break up into

isolated star dunes to the northeast and east (right) probably as a result of both wind pattern interactions

and changes in the sand supply to the dunes

The Great Sand Sea of the Namib extends northward for 400km from Luumlderitz Bay to Walvis Bay and as far

as 140km inland from the coast The sand consists of quartz grains mixed in a ratio of 91 with heavy

minerals like garnet ilmenite and magnetite as well as a little mica The colours darken from pale buff in

the west to deep red in the east as the iron oxide content of the sand increases

Sand Dunes

Dry hot deserts are good places for sand dune formation Obstacles to initiate dune formation are

equally important Dune form ie their shape and size is controlled or determined by three factors

namely the strength and direction of wind the amount of sand available and the amount (if any) of

vegetation present All dunes are mobile to some extent and can be classified into live dunes and

fixed dunes on the basis of their mobility

Figure 38 Sand dune form controls sand supply vegetation amp wind strength

14

Live dunes or free dunes have no fixed position but migrate downwind by erosion on the gently

inclined windward side and deposition on the leeward side (slip face) in the same way as described for

fixed dunes

The smallest free dunes are common

wind ripples that measure only a few

centimetres in height Large dunes are

found in extensive dune areas in

deserts in sand seas known as `ergs

Free dunes move frequently and their

shapes vary They are dependent on

the speed the wind is depositing or

removing sands and the size of the

materials being transported

Coastal dunes occur along beaches

or sand-flats that form part of a non-

erosional sandy or deltaic coast The

source areas of the sand will eventually

lose all sand silt and clay particles

some become wet (groundwater)

depressions whereas others acquire a

rocky or boulder-strewn surface known

as a `desert pavement

Figure 39 Four of the most common dune forms barchan transverse

longitudinal (or linear) and blowout (or parabolic)

Fixed dunes by contrast tend not to move and their shapes are relatively stable and static and they

are usually secured down by vegetation rocks and opposing winds They are formed when transported

sand settles in the lee of an obstacle such as a bush or a rock causing the obstruction to grow in size

capturing more sand The transport capacity of the wind decreases as it drives the sand grains to the top

of the dune causing an increasing part of the transported sand to settle before reaching the dune crest

This steepens the angle of the slope particularly near the crest Once the slope angle exceeds the angle

of repose of the deposited sand (typically 34˚ for dry sand) shearing sets in along a slightly less steep

plane Thus a slip face is formed on the leeward side of the dune Vegetation growing on especially the

lower part of dunes may eventually keep most of the sand in place Dunes along coasts are often fixed by

vegetation where shrub-coppice dunes and also parabolic dunes may develop by landward migration of

beach sand

During transport selection of particles (sorting and winnowing) occurs the momentary wind speed and

the size shape and density of minerals determine how far a particular grain will be transported Fine gravel

travels by creep and sand-sized particles by saltation Silt-sized particles can be carried over great

distances (Saharan `dust settles regularly in central Europe and in the past loess formations have formed

extensive blankets far from the source areas) Fine plate-shaped clay minerals and micas are blown out

and travel even farther (which explains why wind-borne sediments are normally poor in micas) This sorting

of grains results in deposits that consist of pure sand with a uniform particle size Many aeolian sand

deposits show characteristic large-scale cross bedding indicative of sand deposition on the slip faces of

dunes See Figure 310

Common to all dunes is the contrast between the gentle slope of the windward side (the side facing into

the wind) and the steep slope of the leeward side (the side facing away from the wind) The leeward side

is known as the slip face of the dune

15

Figure 310 Schematic dune structure

Longitudinal dunes also known as linear dunes form when the supply of sand is poor and the wind

direction is constant or where sand is more abundant and cross winds converge - often along coasts

where the winds from the sea and those from the land meet and push the sand into long lines They

appear as long ridges of considerable length but low in height The wind channels between existing

dunes and forms a vortex flow which then shapes and maintains the dune form In the central and

greater part of the Namib sand sea linear or longitudinal dunes lie parallel to one another and to the

southerly winds formations which in places are over 100km long and 120m high They are arranged in

nearly straight rows with valleys or so-called dune streets between them Their slipfaces change

position with the seasons Whereas they face north-east for much of the year when southerly winds

prevail they are turned around to face south-west in winter when the easterlies blow

Longitudinal dune [USGS]


Longitudinal dune Australia httpwwwnicholasdukeedueosgeo41win031gif

[NASA]

Longitudinal dunes Arabian peninsula


[NASA]

Figure 311 Longitudinal (Linear) dunes

16 Seif dunes a sinuous variety of longitudinal sand dunes or are usually found in very dry deserts They are

large compound forms where smaller secondary linear ridges coalesce and are superposed on the main

ridges of the underlying longitudinal dunes The secondary forms on seif dunes originate from barchan-

like forms but have only one wing or point due to shifting wind conditions disturbing the one point

The remaining lone wings of seifs can grow very long and high Seifs are the dominant dune form in

the Sahara and some of them are up to 100 m long and have a local relief of up to 100 m as well The

seifs in the central Namib Desert south of Walvis Bay reach heights between 50 m and 250 m reputed

to be of the highest dunes in the world These dunes have their origin as longitudinal dunes formed in

the prevailing south-westerly winds which have been changed into seifs as a result of sporadic

easterly winds

Figure 312 Seif dunes of the Namib desert wwwnationalgeographiccom

Barchan dunes are crescent shaped and have their points or wings directed downwind or away from

the wind direction

They form where the original surface over

which sand is moving is almost uniform

and where the wind direction is constant

and moderate Barchan dunes are a very

mobile dune type and are popularly called

wandering dunes

The rate of advancement of the sand is

roughly inversely proportional to the

height of the crest This causes the flanks

of a shifting dune to advance more

rapidly than the central part until the

flanks become sheltered by the main

mass of the dune Coalescing barchans

produce `transverse dunes

In the Namib Desert they grow to a height

of about 30m where strong south-westerly

winds blow mainly from coastal regions

with relatively little sand The barchans of

the Skeleton Coast and those near Walvis

Bay point to the north-east and also travel

in that direction ndash due to the south-

westerly winds shaping and driving them

Figure 313 The formation of barchan dunes Source Bagnold 1965

17

Barchan White sands New Mexico


Small barchans Tunisia


Figure 314 Barchan dunes

Transverse dunes

When the supply of sand is plentiful regular shaped dunes like barchans can coalesce and lose their

individual characteristics forming crescent-shaped (or barchanoid) ridges If the ridges become

fairly straight they are called transverse dunes The ideal conditions for their formation is when the

wind direction is constant and the source of sand is an elongated feature at right angles to the wind

direction In the Namib Desert transverse dunes are found a short distance inland from the barchans

reaching heights of two and a half times that of the barchans with their long axes similarly across the path

of the wind They may be very long and low in height

Transverse dunes USGS]


Figure 315 Transverse dunes

18

Star dunes

Mountainous piles of sand known as star dunes dominate the inland margin of the sand sea where high

winds blow from all directions They are reputed to be among the highest dunes in the world as high as

220 m or even higher when they rest on a raised surface Star dunes are named for their shape as seen

from above a lot of sharp ridges winding outwards and downwards from a central crest

Figure 316 Star dunes

Shrub-coppice dunes

Shrub-coppice dunes (also known as Nebkha dunes) usually only a metre or two high are common at the

sea-shore where clumps of grass or shrubs such as mesquite form obstructions to windblown sand The

sand starts to collect around the vegetation gradually forming a small mound As the mound grows the

roots lengthen to keep the plant above the surface thereby anchoring the dune while it also grows taller

These dunes are frequently found on sand sheets and on and around larger parabolic dunes

19

Figure 317 Coppice dune

Parabolic dunes (blowout dunes)

Parabolic dunes form when sandy surfaces are partially covered with vegetation They are also

crescent shaped but unlike the barchan dunes their points or wings (horns) point into the wind while

the arch is downwind They typically grow from the horns or trailing arms that are anchored around

an obstruction like vegetation or rock blocking the wind while its central part migrates with the wind

after a blowout or depression hollow has formed Parabolic dunes reach heights of up to 20 or 30 m

except at their crescent where more sand piles up as it is halted or slowed by surrounding

vegetation

20

Figure 318 Parabolic dunes

These dunes are usually less regularly shaped than barchans and in plan view can be either U-shaped

or V-shaped and are more elongated They consist of mounds of well-sorted very fine to medium

sand and usually occur on beaches downwind from blowouts in partially vegetated sand sheets

They also occur in semiarid areas ie where some precipitation is common and near-surface moisture

is available in the lower parts of the dune and underlying soils Parabolic dunes can also extend

inland into vegetated areas in coastal zones and on shores of large lakes

Most parabolic dunes do not grow to heights greater than a few tens of meters except at their

forward portions where sand piles up as its advance is halted or slowed by surrounding vegetation

There are two principal sub-types of parabolic dunes long walled and elliptical types

Loess

This is the lightest material carried by the winds which form a so-called blanket covering the existing

land This blanket is easily eroded and rain penetrates through them rapidly A large portion of the

worldrsquos loess has its origin from deserts

Loess is a predominantly silt-sized sediment originating from broken-down rock fragments which is

formed by the accumulation of wind-blown dust Loess is fairly even- sized sediment pale yellow or

buff in colour typically non-stratified and often calcerous ndash ie of calcium carbonate origin Loess

grains are angular with little polishing or rounding and composed of crystals of quartz feldspar mica

and other minerals Loess can be described as a rich very fertile dust-like soil which erodes very

easily

The word loess with connotations of origin by wind-deposited accumulation can probably be traced

back to Alemannic dialects of German

Parabolic dunes California copy 2012 Nature Education K Adelman

21

Loess profile in Vicksburg Mississippi

USA

Loess near Hunyuan in Chinarsquos Shanxi

province

A loess ioutcrop in Patagonia

Southern Argentina

Figure 319 Loess as found in different continents

Loess deposits may become very thick more than a hundred meters in areas of China and the

Midwestern United States It generally occurs as blanket deposit that covers areas of hundreds of

square kilometres and tens of metres thick Loess often stands in either steep or vertical faces

Because the grains are angular loess will often stand in banks for many years without slumping This

soil is easily excavated to form cave dwellings a popular method of making human habitations in

some parts of China

In several areas of the world loess ridges have formed that are aligned with the prevailing winbds

during the last glacial maximum These are called paha ridges in America and greda ridges in

Europe The form of these loess dunes has been explained by a combination of wind and tundra

conditions

Glacial or peri-glacial loess is derived from the floodplains of glacial braided rivers that carried large

volumes of glacial meltwater and sediments from the annual melting of continental ice sheets and

mountain icecaps during the summer while non-glacial loess can originate from deserts dune fields

playa lakes and volcanic ash The thick Chinese loess deposits are non-glacial loess having been

blown in from deserts in northern China The loess covering the Great Plains of Nebraska Kansas

and Colorado is non-glacial desert loess Non-glacial desert loess is also found in Africa and Australia

Sandy parent materials are also abundant in areas where sand accumulates after selective transportation

of weathering material by wind or water Aeolian (wind-borne) sands will be discussed in this paragraph

Dune and other desert features Words to Know

Abrasion

The erosion or wearing away of bedrock by continuous friction caused by sand or rock fragments in

water wind and ice

Aeolian

Formed or deposited by the action of the wind

Bajada

Several alluvial fans that have joined together

Basin

A hollow or depression in Earths surface with no outlet for water

Crescent

The sickle-moon shape of a barchan dune and also the shape of a parabolic dune

Crest

The highest point or level summit

Deflation

The lowering of the land surface due to the removal of fine-grained particles by the wind

22 Erg

A vast area deeply covered with sand and topped with dunes

Erosion

The gradual wearing away of Earth surfaces through the action of wind and water

Gully

A channel cut into the Earths surface by running water especially after a heavy rain

Leeward

On or toward the side facing away from the wind

Saltation

The jumping movement of sand caused by the wind

Silt

Fine earthy particles smaller than sand carried by moving water and deposited as a sediment

Slip face

The steeply sloped side of a dune that faces away from the wind

Surface creep

The rolling and pushing of sand and slightly larger particles by the wind

Ventifact

A stone or bedrock surface that has been shaped or eroded by the wind

Windward

On or toward the side facing into the wind

Bibliography

Books

Gallant Roy A Sand on the Move The Story of Dunes New York Franklin Watts 1997

Lancaster Nicholas The Geomorphology of Desert Dunes New York Routledge 1995

Websites

httpwww2agcarmymilresearchproductsdesert_guidelsmsheetlsparahtm dunes

httpwwwnpsgovgrsanaturesciencedune-typeshtm

httpgeog-leicsblogspotcom201208desert-depositional-featureshtml 13 april 2013

httpwwwindianaedu~geol116Week11wk11htm

httphrsbstaffednetnscamcallipDesertsdesert_deposit_featureshtm

httpwwwux1eiuedu~cfjps1300desertshtml

httpwwwgooglecozaurlsa=iampsource=imagesampcd=ampdocid=1Gk1J6g1KgticMamptbnid=5T83zLSc-

aKezMampved=0CAgQjRwwAAampurl=http3A2F2Fwwwhandsonthelandorg2Fgrsa2Fresources2Fc

urriculum2Fmid2Fdunes2Fphoto_files2Flongitudinalhtmampei=eQppUc_OBJSThgeE9IHYCQamppsig=AF

QjCNF6A1YoY3Cy3nbL8vAnK7FrILGpxwampust=1365924857233144

httpwwwscienceclarifiedcomlandformsBasins-to-DunesDune-and-Other-Desert-

Featureshtmlbixzz2QKPl4to5

httpwwwdesertusacommag99seppaprdesfeatureshtml

httppubsusgsgovgipdeserts

httpwwweosubccacourseseosc110fletcherslideshowdesertsdesertshtml

httpalicaridarizonaedusonoranPhysicalgeomorphologyhtml

httpwwwaqdnpsgovgrdtoursanddunehtml

httpwwwdesertusacomgeofactssanddunehtml

httpwwwfaoorgdocrep003Y1899Ey1899e06html

httpwwwscienceclarifiedcomlandformsBasins-to-DunesDune-and-Other-Desert-Featureshtmlb

23

APPLIED GEOMORPHOLOGY

Was the Sphinx Originally a Landform

In 2001 Farouk El-Baz Boston University professor and director of the universitys Center for Remote Sensing

published a paper in which he suggested that the pyramids and the Great Sphinx located on Egypts Giza

Plateau were based on natural landforms found in the eastern Sahara Desert El-Baz pointed out that the

landscape of the Nile River valley features coneshaped hills that have lasted many years because their

shape forces the strong winds in the area upward preventing the wind from eroding them or wearing

them down The pyramid builders El-Baz believes would have looked to these landforms in their quest to

build lasting structures

Extending his theory even further El-Baz asserted that the Great Sphinx the enormous sculpture with the

head of a man and the body of a reclining lion might even have been carved by ancient Egyptians in

2500 BCE from an existing desert landform He cited the works of early twentieth-century explorers and

geologists that described wind-eroded yardangs in northwestern China and southwestern Egypt as sphinx-

like or lionlike El-Baz believes the head of the sphinx was an existing yardang (a wind-sculpted ridge) the

Egyptians reshaped They then formed the body which sits in a hollow or depression by digging out the

naturally occurring limestone on the plateau around it due to compression caused by atmospheric

pressure (atmospheric pressure increases closer to the planets surface)

Great Sphinx Egypt Photograph reproduced by permission of the Corbis Corporation

During its descent the warming air pushes the air below it back toward the equator since air flows always

move toward areas of low pressure Passing over land on its way back to the equator the now heated dry

air evaporates any moisture in the air creating dry regions or deserts

These wind patterns explain the formation of many of the worlds deserts in the area between 15deg and 35deg

latitude north and south of the equator Although much weaker similar atmospheric circulation (with

heated dry air evaporating moisture as it moves over Earths surface) occurs over both poles creating

polar deserts While heated because of compression by the atmosphere the air over the polar regions is

not as warm as in equatorial regions simply because the Sun is farther away from Earth in these areas Polar

deserts however are similar to hot deserts because they have very low humidity and precipitation levels

The topography (physical features) of Earth in combination with atmospheric pressure creates other

deserts around the planet Rain-shadow deserts are those that lie on the leeward side of mountain ranges

located near coasts As moisture-laden air flows inland from an ocean and encounters a mountain range

it is pushed upward Cooling as it rises the air begins to lose its moisture on the windward side of the

mountain range through rainfall Once on the leeward side in the shadow of the mountain range the air

has little moisture left Heated by compression as it descends the warm dry air forms deserts in the slope of

the range All deserts in North America are formed by this action

2 The distribution of Aeolian geomorphic action on earth

While wind occurs everywhere on the earthrsquos surface it is only where surface water is scarce that

wind action becomes a major landform- creating agent The main regulators determining if a

landscape will be prone to mainly water or wind erosion are therefore climate and more specifically

temperature and rainfall Hot deserts and semi-deserts (BSh amp BWh regions according to the Koppen

classification system) are the regions most prone to wind as landform creating agent While wind is the

more prevalent force in shaping desert landforms water is the more powerful Despite water being so

scarce in these environments it is the primary agent of erosion in the desert with many features owing

their formation to mass wasting and running water as sheet floods Even the driest deserts receive

occasional rainfall which then usually occurs as downpours which cause landform creation

processes over a large scale in a short time period

Mass action and fluvial action are therefore the main landscape-forming processes in deserts with

wind being only responsible for secondary localised and other minor landforms The wind action

however occurs over a persistent and ongoing basis and has an enduring presence and signature in

arid landscapes Due to climate changes over time the landscape bears evidence of former

landforms that were created when different climatic conditions controlled the prevailing landforms

such as the sandstone deposits in the Eastern Free State and Lesotho these date from times when

wind action and deposition by water were the chief landforming agents

In Africa there are many hot arid regions such as the Namib Sahel and Sahara deserts and also

many semi-arid regions including Namaqualand the Kalahari and parts of Ethiopia and Somalia

These regions are all have many features in their landscape that were created by the wind-cascade

system Other parts of Africa have long dry seasons and are subject to prolonged droughts even

though they are not classified as semi-arid regions In these regions as well as those where dryland

cultivation leaves large areas uncovered by vegetation or crops for part of the year large volumes of

surface material is lost annually and wind erosion plays a major role in forming the landscape

Furthermore landforms created by wind can also occur in dry river valleys along coasts and along

river floodplains where large quantities of talus are present

Wind is one of the three dominant agents in hot deserts after mass wasting and occasional water

action The desert floors get heated up rapidly as they are dry and consist of mainly mineral silicas

while being virtually devoid of organic matter and vegetation These heated floors heat the air

directly above them resulting in upward movements in the hot lighter air with turbulence and any

obstructions in its path sets up eddies whirlwinds updrafts and downdrafts Winds also move along

the desert floors with great speed and the obstructions in their path create turbulence while very

destructive storm winds also occur

Some fluvial processes and landforms found in deserts

Deserts are defined by their lack of water and while coastal deserts may experience one or two rainfalls a

year those further inland may get rain once or twice a decade only Although rain is scarce in deserts

(the Sahararsquos average annual rainfall is only 127mm) it usually comes down torrentially and lasts mere

minutes or a few hours This enhances rainsplash erosion on the bare unvegetated desert soil loosening

and spattering soil particles in all directions The desert rock material also undergoes accelerated

mechanical and chemical weathering processes due to drastic diurnal temperature changes

decaying fast with the torrential rains helping to remove the weathered materials speedily The

dislodged soil and talus is carried off with the flowing water which picks up and transports more sediment

as it rushes along Owing to a lack of organic-rich soil that can absorb the water and also the absence of

vegetation the desert landscape offers little resistance to water action and erodes rapidly Water

therefore accomplishes within a few days what would take desert winds a year to accomplish which


rainsheet wash









Alluvial fan













they form a bajada

Arroyo







Bajada























vegetation]





Regulators











EROSIONAL LANDFORMS

Overview





















Wind storm Tunisia















LANDFORMS













6 Playas













Israel and Jordan














































Oasis












Yardangs and zeugen








period





9






















unaffected












10










11 Ventifacts









ventifacts






12











ripples

Draas and ergs





Namib Desert






















Sand Dunes







14



fixed dunes
































beach sand













15















[NASA]



[NASA]











easterly winds



the wind direction






wandering dunes


















17






Transverse dunes











18

Star dunes






Shrub-coppice dunes






19









vegetation

20











Loess









easily




21


USA


province


Southern Argentina







some parts of China




conditions










Abrasion


water wind and ice

Aeolian


Bajada


Basin


Crescent


Crest


Deflation


22 Erg


Erosion


Gully


Leeward


Saltation


Silt


Slip face


Surface creep


Ventifact


Windward


Bibliography

Books



Websites





















23




































rainsheet wash









Alluvial fan













they form a bajada

Arroyo







Bajada























vegetation]





Regulators











EROSIONAL LANDFORMS

Overview





















Wind storm Tunisia















LANDFORMS













6 Playas













Israel and Jordan














































Oasis












Yardangs and zeugen








period





9






















unaffected












10










11 Ventifacts









ventifacts






12











ripples

Draas and ergs





Namib Desert






















Sand Dunes







14



fixed dunes
































beach sand













15















[NASA]



[NASA]











easterly winds



the wind direction






wandering dunes


















17






Transverse dunes











18

Star dunes






Shrub-coppice dunes






19









vegetation

20











Loess









easily




21


USA


province


Southern Argentina







some parts of China




conditions










Abrasion


water wind and ice

Aeolian


Bajada


Basin


Crescent


Crest


Deflation


22 Erg


Erosion


Gully


Leeward


Saltation


Silt


Slip face


Surface creep


Ventifact


Windward


Bibliography

Books



Websites





















23














































vegetation]





Regulators











EROSIONAL LANDFORMS

Overview





















Wind storm Tunisia















LANDFORMS













6 Playas













Israel and Jordan














































Oasis












Yardangs and zeugen








period





9






















unaffected












10










11 Ventifacts









ventifacts






12











ripples

Draas and ergs





Namib Desert






















Sand Dunes







14



fixed dunes
































beach sand













15















[NASA]



[NASA]











easterly winds



the wind direction






wandering dunes


















17






Transverse dunes











18

Star dunes






Shrub-coppice dunes






19









vegetation

20











Loess









easily




21


USA


province


Southern Argentina







some parts of China




conditions










Abrasion


water wind and ice

Aeolian


Bajada


Basin


Crescent


Crest


Deflation


22 Erg


Erosion


Gully


Leeward


Saltation


Silt


Slip face


Surface creep


Ventifact


Windward


Bibliography

Books



Websites





















23










































Wind storm Tunisia















LANDFORMS













6 Playas













Israel and Jordan














































Oasis












Yardangs and zeugen








period





9






















unaffected












10










11 Ventifacts









ventifacts






12











ripples

Draas and ergs





Namib Desert






















Sand Dunes







14



fixed dunes
































beach sand













15















[NASA]



[NASA]











easterly winds



the wind direction






wandering dunes


















17






Transverse dunes











18

Star dunes






Shrub-coppice dunes






19









vegetation

20











Loess









easily




21


USA


province


Southern Argentina







some parts of China




conditions










Abrasion


water wind and ice

Aeolian


Bajada


Basin


Crescent


Crest


Deflation


22 Erg


Erosion


Gully


Leeward


Saltation


Silt


Slip face


Surface creep


Ventifact


Windward


Bibliography

Books



Websites





















23



































6 Playas













Israel and Jordan














































Oasis












Yardangs and zeugen








period





9






















unaffected












10










11 Ventifacts









ventifacts






12











ripples

Draas and ergs





Namib Desert






















Sand Dunes







14



fixed dunes
































beach sand













15















[NASA]



[NASA]











easterly winds



the wind direction






wandering dunes


















17






Transverse dunes











18

Star dunes






Shrub-coppice dunes






19









vegetation

20











Loess









easily




21


USA


province


Southern Argentina







some parts of China




conditions










Abrasion


water wind and ice

Aeolian


Bajada


Basin


Crescent


Crest


Deflation


22 Erg


Erosion


Gully


Leeward


Saltation


Silt


Slip face


Surface creep


Ventifact


Windward


Bibliography

Books



Websites





















23


















































Oasis












Yardangs and zeugen








period





9






















unaffected












10










11 Ventifacts









ventifacts






12











ripples

Draas and ergs





Namib Desert






















Sand Dunes







14



fixed dunes
































beach sand













15















[NASA]



[NASA]











easterly winds



the wind direction






wandering dunes


















17






Transverse dunes











18

Star dunes






Shrub-coppice dunes






19









vegetation

20











Loess









easily




21


USA


province


Southern Argentina







some parts of China




conditions










Abrasion


water wind and ice

Aeolian


Bajada


Basin


Crescent


Crest


Deflation


22 Erg


Erosion


Gully


Leeward


Saltation


Silt


Slip face


Surface creep


Ventifact


Windward


Bibliography

Books



Websites





















23






































Yardangs and zeugen








period





9






















unaffected












10










11 Ventifacts









ventifacts






12











ripples

Draas and ergs





Namib Desert






















Sand Dunes







14



fixed dunes
































beach sand













15















[NASA]



[NASA]











easterly winds



the wind direction






wandering dunes


















17






Transverse dunes











18

Star dunes






Shrub-coppice dunes






19









vegetation

20











Loess









easily




21


USA


province


Southern Argentina







some parts of China




conditions










Abrasion


water wind and ice

Aeolian


Bajada


Basin


Crescent


Crest


Deflation


22 Erg


Erosion


Gully


Leeward


Saltation


Silt


Slip face


Surface creep


Ventifact


Windward


Bibliography

Books



Websites





















23



































9






















unaffected












10










11 Ventifacts









ventifacts






12











ripples

Draas and ergs





Namib Desert






















Sand Dunes







14



fixed dunes
































beach sand













15















[NASA]



[NASA]











easterly winds



the wind direction






wandering dunes


















17






Transverse dunes











18

Star dunes






Shrub-coppice dunes






19









vegetation

20











Loess









easily




21


USA


province


Southern Argentina







some parts of China




conditions










Abrasion


water wind and ice

Aeolian


Bajada


Basin


Crescent


Crest


Deflation


22 Erg


Erosion


Gully


Leeward


Saltation


Silt


Slip face


Surface creep


Ventifact


Windward


Bibliography

Books



Websites





















23



































10










11 Ventifacts









ventifacts






12











ripples

Draas and ergs





Namib Desert






















Sand Dunes







14



fixed dunes
































beach sand













15















[NASA]



[NASA]











easterly winds



the wind direction






wandering dunes


















17






Transverse dunes











18

Star dunes






Shrub-coppice dunes






19









vegetation

20











Loess









easily




21


USA


province


Southern Argentina







some parts of China




conditions










Abrasion


water wind and ice

Aeolian


Bajada


Basin


Crescent


Crest


Deflation


22 Erg


Erosion


Gully


Leeward


Saltation


Silt


Slip face


Surface creep


Ventifact


Windward


Bibliography

Books



Websites





















23



































11 Ventifacts









ventifacts






12











ripples

Draas and ergs





Namib Desert






















Sand Dunes







14



fixed dunes
































beach sand













15















[NASA]



[NASA]











easterly winds



the wind direction






wandering dunes


















17






Transverse dunes











18

Star dunes






Shrub-coppice dunes






19









vegetation

20











Loess









easily




21


USA


province


Southern Argentina







some parts of China




conditions










Abrasion


water wind and ice

Aeolian


Bajada


Basin


Crescent


Crest


Deflation


22 Erg


Erosion


Gully


Leeward


Saltation


Silt


Slip face


Surface creep


Ventifact


Windward


Bibliography

Books



Websites





















23



































12











ripples

Draas and ergs





Namib Desert






















Sand Dunes







14



fixed dunes
































beach sand













15















[NASA]



[NASA]











easterly winds



the wind direction






wandering dunes


















17






Transverse dunes











18

Star dunes






Shrub-coppice dunes






19









vegetation

20











Loess









easily




21


USA


province


Southern Argentina







some parts of China




conditions










Abrasion


water wind and ice

Aeolian


Bajada


Basin


Crescent


Crest


Deflation


22 Erg


Erosion


Gully


Leeward


Saltation


Silt


Slip face


Surface creep


Ventifact


Windward


Bibliography

Books



Websites





















23






















































Sand Dunes







14



fixed dunes
































beach sand













15















[NASA]



[NASA]











easterly winds



the wind direction






wandering dunes


















17






Transverse dunes











18

Star dunes






Shrub-coppice dunes






19









vegetation

20











Loess









easily




21


USA


province


Southern Argentina







some parts of China




conditions










Abrasion


water wind and ice

Aeolian


Bajada


Basin


Crescent


Crest


Deflation


22 Erg


Erosion


Gully


Leeward


Saltation


Silt


Slip face


Surface creep


Ventifact


Windward


Bibliography

Books



Websites





















23



































14



fixed dunes
































beach sand













15















[NASA]



[NASA]











easterly winds



the wind direction






wandering dunes


















17






Transverse dunes











18

Star dunes






Shrub-coppice dunes






19









vegetation

20











Loess









easily




21


USA


province


Southern Argentina







some parts of China




conditions










Abrasion


water wind and ice

Aeolian


Bajada


Basin


Crescent


Crest


Deflation


22 Erg


Erosion


Gully


Leeward


Saltation


Silt


Slip face


Surface creep


Ventifact


Windward


Bibliography

Books



Websites





















23



































15















[NASA]



[NASA]











easterly winds



the wind direction






wandering dunes


















17






Transverse dunes











18

Star dunes






Shrub-coppice dunes






19









vegetation

20











Loess









easily




21


USA


province


Southern Argentina







some parts of China




conditions










Abrasion


water wind and ice

Aeolian


Bajada


Basin


Crescent


Crest


Deflation


22 Erg


Erosion


Gully


Leeward


Saltation


Silt


Slip face


Surface creep


Ventifact


Windward


Bibliography

Books



Websites





















23












































easterly winds



the wind direction






wandering dunes


















17






Transverse dunes











18

Star dunes






Shrub-coppice dunes






19









vegetation

20











Loess









easily




21


USA


province


Southern Argentina







some parts of China




conditions










Abrasion


water wind and ice

Aeolian


Bajada


Basin


Crescent


Crest


Deflation


22 Erg


Erosion


Gully


Leeward


Saltation


Silt


Slip face


Surface creep


Ventifact


Windward


Bibliography

Books



Websites





















23



































17






Transverse dunes











18

Star dunes






Shrub-coppice dunes






19









vegetation

20











Loess









easily




21


USA


province


Southern Argentina







some parts of China




conditions










Abrasion


water wind and ice

Aeolian


Bajada


Basin


Crescent


Crest


Deflation


22 Erg


Erosion


Gully


Leeward


Saltation


Silt


Slip face


Surface creep


Ventifact


Windward


Bibliography

Books



Websites





















23



































18

Star dunes






Shrub-coppice dunes






19









vegetation

20











Loess









easily




21


USA


province


Southern Argentina







some parts of China




conditions










Abrasion


water wind and ice

Aeolian


Bajada


Basin


Crescent


Crest


Deflation


22 Erg


Erosion


Gully


Leeward


Saltation


Silt


Slip face


Surface creep


Ventifact


Windward


Bibliography

Books



Websites





















23



































19









vegetation

20











Loess









easily




21


USA


province


Southern Argentina







some parts of China




conditions










Abrasion


water wind and ice

Aeolian


Bajada


Basin


Crescent


Crest


Deflation


22 Erg


Erosion


Gully


Leeward


Saltation


Silt


Slip face


Surface creep


Ventifact


Windward


Bibliography

Books



Websites





















23



































20











Loess









easily




21


USA


province


Southern Argentina







some parts of China




conditions










Abrasion


water wind and ice

Aeolian


Bajada


Basin


Crescent


Crest


Deflation


22 Erg


Erosion


Gully


Leeward


Saltation


Silt


Slip face


Surface creep


Ventifact


Windward


Bibliography

Books



Websites





















23



































21


USA


province


Southern Argentina







some parts of China




conditions










Abrasion


water wind and ice

Aeolian


Bajada


Basin


Crescent


Crest


Deflation


22 Erg


Erosion


Gully


Leeward


Saltation


Silt


Slip face


Surface creep


Ventifact


Windward


Bibliography

Books



Websites





















23



































22 Erg


Erosion


Gully


Leeward


Saltation


Silt


Slip face


Surface creep


Ventifact


Windward


Bibliography

Books



Websites





















23



































23



































AEOLIAN or WIND GEOMORPHOLOGY & LANDFORMS

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Transcript of AEOLIAN or WIND GEOMORPHOLOGY & LANDFORMS