Post on 13-Jul-2020
transcript
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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
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Pressure Gradients Drive Wind
Coriolis Effect Deflects Flow Direction
Jet Stream
LLLL HHHH
LL
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Why Deserts?
• Rain Shadows• Global Circulation Patterns
Orographic Effects
Rain Shadow
Global Circulation
EquatorEquatorSun Hot Hot
ColdCold
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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
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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)
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Long
itudi
nal D
unes
, Aus
tralia
(G
eosc
ienc
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ustra
lia Im
age)
ht
tp://
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/edu
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Longitudinal Dunes, Arabian Peninsula (NASA Photo)
Saha
ra D
eser
t (Sk
ylab
Pho
to, N
ASA
)
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