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Dust Storm, Tunisia, (D. Heron Photo)

Many of The Images Used in This Presentation Were

Obtained From a Web Site Constructed by Duncan Heron,

Duke University

Http://www.Geo.Duke.Edu/geo41/win.Htm

Aeolian Processes

What Causes Wind?Pressure Gradients

What Causes Differences in Air Pressure?

Temperature, Moisture

2

Pressure Gradients Drive Wind

Coriolis Effect Deflects Flow Direction

Jet Stream

LLLL HHHH

LL

3

Why Deserts?

• Rain Shadows• Global Circulation Patterns

Orographic Effects

Rain Shadow

Global Circulation

EquatorEquatorSun Hot Hot

ColdCold

4

Hadley’s Model

EquatorEquatorSun

Hot Air Rises

Cold AirSinks

Hadley’s Model

EquatorEquatorSun

Hot Air Rises

Cold AirSinks

Simple Convection Cell in Each Hemisphere

Better Model

EquatorEquatorSunHot Air Rises

3 Convection Cellsin Each Hemisphere

2020--3030oo

5050--6060oo

5

Gas LawsPV = nRT

Better Model

EquatorEquatorSun Hot, Wet Air

Cold, Dry Air

3 Convection Cellsin Each Hemisphere

2020--3030oo

5050--6060oo

Cool, Wet Air

Warm, Dry Air

Better Model

Wet HotWet HotSun

3 Convection Cellsin Each Hemisphere

Dry, HotDry, Hot

Wet, CoolWet, Cool

Dry, ColdDry, Cold

Dry, Hot Dry, Hot

Dry, Cold Dry, Cold

Wet, Cool Wet, Cool

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Better Model

EquatorEquatorSun

3 Convection Cellsin Each Hemisphere

Easterlies

Westerlies

Easterlies

Summer Model

Thermal EquatorThermal EquatorSun

Easterlies

Westerlies

Easterlies

““RealReal”” EquatorEquator

WinterModel

Sun

Easterlies

Westerlies

Easterlies

““RealReal”” EquatorEquator

Thermal EquatorThermal Equator

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Global Circulation

http://pubs.usgs.gov/gip/deserts/what/world.html

Distribution of Deserts

Aeolian Sediments

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Aeolian SedimentsTractive Load:

Surface Creep (Larger Clasts)

Saltation: Mostly Msd-Fsd,Can Be Crs Silt to Pebble (Rare)

Ripples (D. Heron Photo)

Topsail Beach, NC (D. Heron Photo)

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Suspension Load (Silt + Clay = Dust)

Gravity Settling (Fallout!)

Condensation Nucleii in Precip.

Aeolian Depositional Systems

Most Aeolian Landscapes Begin as Fluvial Landscapes

Lag

GravelVentifacts

Source: Old Floodplains

Barren RockSurface

Site of Deposition

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Cover sands

(often glacio-eolian)

Deflation Hollows -

RegSurface ArmorRock Varnish

HammadaYardangs =Streamlined Erosional Forms

Erg = Dune FieldRipples, DunesDraa

Reg, Pre-Sahara Desert (D. Heron Photo)

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Desert Pavement

Antarctica: Ventifacts & Desert Pavement

Yardangs

John StimacEastern Illinois

Universityhttp://www.ux1.eiu.edu

/~cfjps/1300/deserts.html

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http://www.qantasvacations.com/images/pg33ayqsunset.jpg

Uluru (= Ayers Rock) a Yardang

Yardang?

http://www.hermes-group.com/Photos/Cairo/Sphinx.jpg

Dune Field, Victoria Valley, AntarcticaGlacier

Transverse Dunes

Dune in Later Slide

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Cross-Bedding in Dunes

Grain Flow Down Slip FaceStoss, Lee

Wind Direction

Sand Dune, Victoria Valley, Antarctica

Windward Face of Dune, Victoria Valley

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Lee Slip-Face of Dune, Victoria Valley

Longitudinal: Stripes of ErgSeparated By Reg Low Sand Supply, High Wind Velocity (“Unidirectional”)

Longitudinal Dunes, Australia (NASA photo)

15

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unes

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Longitudinal Dunes, Arabian Peninsula (NASA Photo)

Saha

ra D

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http://pubs.usgs.gov/gip/deserts/types/

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Transverse Dunes:High sand supply, low wind velocity

Stopped Here 30 March

Algodones Sand Sea, SE Calif. (Photo by P. Kresan, U. of AZ, USGS)

Transverse Dunes, Bogue Bank, NC (D. Heron Photo)

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Barchan Dunes: Transitional between.Longitudinal & Transverse

BarchanDune

John StimacEastern IllinoisUniversityhttp://www.ux1.eiu.edu/~cfjps/1300/deserts.html

“Megabarchan” John Stimac, Eastern Illinois U.

http://www.ux1.eiu.edu/~cfjps/1300/deserts.html

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Star Dunes: Multi-Directional Winds

Star Dune, Namib Desert(G. Gerster photo, NASA)

http://pubs.usgs.gov/gip/deserts/types/

Star Dune, Namib Desert, G. Gersterphoto, http://pubs.usgs.gov/gip/deserts/dunes/)

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Star Dunes

John StimacEastern Illinois

Universityhttp://www.ux1.eiu.edu/~cfjps/1300/deserts.html

Ripples on Dune in

GranDesierto, Sonora, Mexico

(P. Kresnanphoto, U of AZ, USGS)

http://pubs.usgs.

gov/gip/deserts/what/

Other Dune Types

Parabolic w/ blow-out zone, vegetationCoppice w/ vegetation core

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Parabolic Dunes

Sechura Desert, Peru http://www.tec.army.mil/terrain/desert/lifsheet/lipara.htm

Parabolic Dunes

Rajasthan (Thar) Desert India and Pakistan

Coppice Dune = Windshadow (D. Heron Photo)

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Coppice Dunes, Assateaque Island, VA

S. Kite Photo, 19 March 2005

Matanuska Valley Loess, W. Huff Photo

http://tvl1.geo.uc.edu/ice/Image/propro/32.html

Loess: silt mantle

"typical" Missouri River bluff• 10s of m at bluff, • 1-2 m 50 mi East

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Illinois Loess

Thickness

Illinois State Museumhttp://www.museum.state.il.us/exhibits/larson/loess_map.html

Missouri-Mississippi

River System Loess

Maximum Extent of Late Wisconsin

Laurentide Ice Sheet~14,000-20,000

C-14 Years B.P.

Loess

Loess on Outwash Terrace, New Zealand

S. Kite Photo, Jan 1977

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Loess Hills, Iowa

Loess Bluff, Wildwood, Missouri

http://www.medulogic.com/Caulks/loess.GIFphoto by C.M. Woodruff