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Aeolian (wind) Landscapes
Mt Etna & the Aeolian Islands
Aeolus, king of the Aeolian Islands, rules the winds in Greek Mythology
Wind Landscapes
1. Dust (Loess)
2. Dunes (sand)
3. Ventifacts (erosion)
1. Dust (loess)Dust collects on margins of deserts and glaciers
Breck P. Kent
Deflation Hollow
DeflationThe process of removing all of the
small (easily moved) particles by wind.
Deflation lowering surface
Old Palm surface
Medium Palm surface
Young Palm surface
Dust Deflation
1500 m dust storm, 300 km/hr windsSan Joaquin Valley, California, 1977
drought
Dust storm across Red Sea
Dust storm Kaho’olawe Island, Hawai’i
The Dustbowl, America, 1930’s
• Period of severe droughts • Wind erosion of soil • Organic matter, clay, and silt removed
– carried great distances by wind– darkened sky on Atlantic coast
• Abandoned farms worsened problem
Classroom ResourceMovie of dust blow era deflation
Loess Source: Negev Desert
Loess Accumulation: Wetter Margin of the Negev Desert
Loess Source: Peru DesertLoess Source: Atacama Desert
Loess Accumulation: Wetter Margin of the Atacama Desert
Loess Plateau, China
2. Dunes (sand)
Tallest Dunes Found in Namibia (980 ft)
Dunes are less dominant than many thinkDeserts cover about 1/5th of the land
Only 10% of that is dune covered (1/50th)
Transport of Wind-Borne Sediment
Classroom ResourceSlowed down process of saltation
(bouncing)
Ripples form on surface of Sand Dunes
Some dunes “anchored”Falling dunes, Sinai, Egypt (depend on mtn)
Coppice dunes, depending on vegetation
Beach Sand Dunes
Parabolic (blow-out) Dunes
Horns pinned by plants
Parabolic (blow-out) Dune
Parabolic (blow-out) Dune
True Dunes Migrate
Stoss (backslope) Lee (slip) face
Animation that will play in the powerpoint file, showing howolder “slip faces” create the cross bedding
Ripples on
Stoss Side
Stoss (backslope)
Slip Faceon LeeSide
Steep side of dune
Sand Surfing
Dune Jumping
Cross Beddingcharacteristic of dunes
Slip faces
Slip faces
Slip faces
Classroom Resources
Crossbedding.swf – Animation of how crossbedding forms
Transverse Dunes
Transverse Dunes
Slip face tells you the wind direction
Longitudinal (linear, seif) Dunes
Longitudinal (Linear or Seif) Dunes• Elongate parallel to wind
direction
Slip faces change from one side to the other side, as wind changes directions
Longitudinal Dunes
Barchan Dunes
Barchan Dune
Slip face tells you the wind direction
Transverse Dunes turn into Barchan when sand supply drops
Star Dunes
Erg (Sand Sea)
LargestSand Seas
JurassicToday
Great Sand Dunessmall erg
Great Sand Dunes
Classroom Resource: Animation of how build up by wind reversing
Tremendous Variety Exists inside an Erg(Rub Al Khali, Arabia)
3. Ventifacts (wind erosion)
Look at surfaces: Polished Smooth (with grooves) by sand
and dust abrasion
If boulders, grooved
Wind flow
If small enough (pebbles,cobbles), rock is rotated so that polishing
occurs on several sides
Ventifacts very common on Mars
How do you know it’s a true ventifact?
Rub with your hand. If wind-abraded the surface is smooth
Iceland Mojave Desert (Greeley et al., ASU)
NOT FROM Wind AbrasionNo evidence of sand blasting.Only evidence of water erosion (rainsplash and rill)
NOT FROM Wind AbrasionNo evidence of sand blasting.Only evidence of weathering, splitting apart the individual mineral grains – roughening surface
No!
Salt weathering
Not from wind abrasion!
Wind can help blow out weathered products (clays, silt) from tafoni. But form is made by weathering (salt, chemical)
Erosion by the wind:
Abrasion smooths surfaces
Ventifacts
Erosion by wind polishes rental cars
Claims of Yardangs in Iran
• See mostly evidence of water flow, not wind
I am very skeptical about claims of hills eroded by wind – when you look carefully, you don’t see evidence of wind abrasion, only evidence of water erosion
Notch where saltating sand grainserode
Yardangs , White Desert, EgyptRight scale & Good Evidence
Wrong
Correct
Weathering only
Online Animations
Dunes: Process and Form Visualizations http://serc.carleton.edu/NAGTWorkshops/visualization/collections/dunes.html
Visualizations for Soil Erosion (wind)
http://serc.carleton.edu/NAGTWorkshops/visualization/collections/soil_erosion.html
Imagery seen in this presentation is courtesy of Ron Dorn and other ASU colleagues, students and colleagues in other academic departments, individual illustrations in scholarly journals such as Science and Nature, scholarly societies such as the Association of American Geographers, city,state governments, other countries government websites and U.S. government agencies such as NASA, USGS, NRCS, Library of Congress, U.S. Fish and Wildlife Service USAID and NOAA.c