Applied GeomorphologyApplied Geomorphology

Lecture 8: Arid (Eolian) LandformsLecture 8: Arid (Eolian) Landforms

Cycle of Landform DevelopmentCycle of Landform Development

• Initiated by tectonics: Normal Faulting resulting from lateral extension of lithosphere

• Alluvial Fans

• Playa Lakes

• Inselbergs• Bajada• Pediment

(Inselbergs)

(Bajada)

Arid Landform Stages of Arid Landform Stages of DevelopmentDevelopment

• Early– Alluvial Fans– Flat Divides

• Middle– Rounded Divides– Bajada– Playa Lakes

• Late– Inselbergs– Pediment

Alluvial Alluvial Fan Fan

ExampleExample(Early (Early Stage)Stage)

Middle Stage AridMiddle Stage Arid

Late Late Stage Stage AridArid

Wind (Eolian) LandformsWind (Eolian) Landforms

• Produced solely by wind action• Transported material:

– Bed Load: Sand (<= 2mm)– Suspended Load: Silt and Clay (<=.062mm)

• No dissolved load

Global Wind PatternsGlobal Wind Patterns

• Coriolis effect deflects wind direction• Driven by convection

Arid and SemiArid and Semi--Arid RegionsArid Regions

• Occur at 30 degrees latitude or in rainshadows

Wind VelocityWind Velocity

• A velocity of 50 kph is required to produce significant movement of sand by wind

Effects of Eolian TransportEffects of Eolian Transport

• Rounding of grains• Adds a “frosted” appearance to sand

grains

Wind Erosion ProductsWind Erosion Products

• Ventifacts: faceted pebbles

Wind Erosion LandformsWind Erosion Landforms

• Deflation: removal of topsoil by intense wind erosion lowers elevation of region

Wind Erosion LandformsWind Erosion Landforms

• Desert pavement: result of deflation

Wind Erosion LandformsWind Erosion Landforms

• Desert varnish: concentration of insoluble products on land surface

Wind Erosion LandformsWind Erosion Landforms

• Dry wash: stream channel of intermittent stream

Wind Erosion LandformsWind Erosion Landforms

• Hoodoos: erosional remnants that are spire-shaped

Wind Erosion LandformsWind Erosion Landforms

• Playa Lakes: due to rapid erosion and elevated base levels

Arid VegetationArid Vegetation

• Sparse concentration• Shallow roots• Not effective for erosion

control

Sand Dune FormationSand Dune Formation• Asymmetric cross section:

– Windward slope: low angle slope facing wind direction

– Lee slope: high angle slope facing opposite the wind direction

• Cross-bedding forms when lee slope fails

Dune TypesDune Types

• Barchan• Blowout• Transverse• Linear