Wind Processes and Desert Wind Processes and Desert LandscapesLandscapes

OverviewOverview

Eolian (Aeolian) processesEolian (Aeolian) processes ErosionErosion

deflation and abrasiondeflation and abrasion TransportTransport

saltation and surface creepsaltation and surface creep DepositionDeposition

sand dunes and loesssand dunes and loess

Desert landscapesDesert landscapes

Eolian Eolian ErosionErosion

AbrasionAbrasion ““sandblasting”sandblasting”

ventifactsventifacts DeflationDeflation

Occurs where there Occurs where there is a mixture of is a mixture of cobbles and gravel cobbles and gravel with finer material with finer material (typically sand)(typically sand)

Wind removes finer Wind removes finer material, leaving material, leaving only the cobbles only the cobbles and gravel (desert and gravel (desert pavement)pavement)

Eolian TransportEolian Transport

SuspensioSuspensionn

SaltationSaltation CreepCreep

Eolian DepositionEolian Deposition Heavier material drops out of the wind Heavier material drops out of the wind

before lighter materialsbefore lighter materials Sand deposited before silt and clay Sand deposited before silt and clay

particlesparticles Deposition of sand forms sand dunesDeposition of sand forms sand dunes Deposition of clay and silt forms loessDeposition of clay and silt forms loess

Global Sandy AreasGlobal Sandy Areas

Global Loess DepositsGlobal Loess Deposits

Global Dry RegionsGlobal Dry Regions

Dune ProcessesDune Processes

Types of Sand DunesTypes of Sand Dunes

Several factors influence the formation of Several factors influence the formation of the various sand dune landformsthe various sand dune landforms Strength of the windStrength of the wind Prevailing wind vs. shifting windsPrevailing wind vs. shifting winds Presence of vegetationPresence of vegetation Amount of sand presentAmount of sand present

MovementMovement Free DunesFree Dunes Tied DunesTied Dunes

Crescentic Crescentic DunesDunes

BarchanBarchan Free dunesFree dunes Scarce sandScarce sand Consistent and Consistent and

effective wind from effective wind from one directionone direction

Single slipfaceSingle slipface Horns of crescent Horns of crescent

point downwindpoint downwind Barchanoid RidgeBarchanoid Ridge

merged barchansmerged barchans

Transverse dunesTransverse dunes Free dunesFree dunes Abundant sand Abundant sand

supplysupply Less effective windLess effective wind Consistent Consistent

direction of the direction of the windwind

Single slipfacesSingle slipfaces

ParabolicParabolic Tied duneTied dune Vegetation Vegetation

stabilizes stabilizes movementmovement

Consistent wind Consistent wind directiondirection

multiple slipfacesmultiple slipfaces crescents point crescents point

upwindupwind

Linear DunesLinear Dunes LongitudinalLongitudinal

Winds variable in Winds variable in one directionone direction

Ridge forms Ridge forms parallel to parallel to consistent wind consistent wind directiondirection

two slipfacestwo slipfaces 100 – 400 m tall, 100 – 400 m tall,

up to 100 km longup to 100 km long SeifSeif

Sharp crestSharp crest shorter in heightshorter in height

Star DunesStar Dunes

Star DunesStar Dunes Winds variable in all Winds variable in all

directionsdirections Multiple slipfacesMultiple slipfaces With effective winds, With effective winds,

form high moundsform high mounds With less effective With less effective

winds, form networks winds, form networks of connected sinuous of connected sinuous armsarms

Desert LandscapesDesert Landscapes Arid areas are the largest climatic Arid areas are the largest climatic

region on earth (35% of earth’s surface)region on earth (35% of earth’s surface) Fluvial featuresFluvial features

Flash floodingFlash flooding Washes, arroyos, wadisWashes, arroyos, wadis Bursts of vegetation growthBursts of vegetation growth

PlayasPlayas interior drainageinterior drainage salinizationsalinization

Alluvial fansAlluvial fans bajadasbajadas

Landscape featuresLandscape features Adapted vegetationAdapted vegetation Basin and Range ProvinceBasin and Range Province

Horst and Graben, interior drainage, playas, Horst and Graben, interior drainage, playas, alluvial fansalluvial fans

Colorado River IssuesColorado River Issues Headwaters originate in the Rocky MountainsHeadwaters originate in the Rocky Mountains

High levels of rainfallHigh levels of rainfall Snow meltSnow melt

Flows through an extremely arid area with Flows through an extremely arid area with few feeding tributariesfew feeding tributaries

High demand on water means that often no High demand on water means that often no water actually makes it to the seawater actually makes it to the sea

Flows through seven states, into MexicoFlows through seven states, into Mexico Beliefs on the river’s capacity based on a 400 Beliefs on the river’s capacity based on a 400

year high mark (greatly overestimated)year high mark (greatly overestimated) Subject to a variety of political treaties and Subject to a variety of political treaties and

agreements regulating its flowagreements regulating its flow In many cases, quotas are exceeded, esp. with In many cases, quotas are exceeded, esp. with

CaliforniaCalifornia

DesertificationDesertification Refers to the expansion of desert biomes Refers to the expansion of desert biomes

due to a combination of poor agricultural due to a combination of poor agricultural practices and climate changepractices and climate change grazing has been identified as a major causegrazing has been identified as a major cause

As a global phenomenon, this idea has As a global phenomenon, this idea has largely been falsifiedlargely been falsified Areas identified as “desertifying” were simply Areas identified as “desertifying” were simply

experiencing drought-like conditions, in experiencing drought-like conditions, in conjunction with ENSO cycles; many have conjunction with ENSO cycles; many have recoveredrecovered

There are some areas where There are some areas where desertification has occurred, but it is not desertification has occurred, but it is not a global phenomenona global phenomenon