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