Module 21Module 21

Eolian SystemEolian System

Deserts and Wind ActionDeserts and Wind Action

Photo Credit: Jon Sullivan; 2003

Desert VegetationDesert Vegetation

Less than 25 cm rain per yearLess than 25 cm rain per year

Deserts and Winds TopicsDeserts and Winds Topics

• Global Distribution of DesertsGlobal Distribution of Deserts– 10-15° latitude bands close to 30°N/S10-15° latitude bands close to 30°N/S– Great distance from oceanGreat distance from ocean– Rain shadowsRain shadows

• Characteristics of DesertsCharacteristics of Deserts– Lack of through-flowing streams - Internal Lack of through-flowing streams - Internal

drainagedrainage– Flash floodsFlash floods– <25 cm of annual rainfall; few plants<25 cm of annual rainfall; few plants

• Desert Features in the Southwestern United Desert Features in the Southwestern United StatesStates– Basin & Range topographyBasin & Range topography

Global Wind SystematicsGlobal Wind Systematics

Important Controls:-Solar Heating-Atmospheric Convection-Coriolis Force (rotation)

Global Wind ZonesGlobal Wind Zones

Image source: http://www.newmediastudio.org

Global Distribution of Deserts and RainfallGlobal Distribution of Deserts and Rainfall

Global Loess DepositsGlobal Loess Deposits

Development of Rain ShadowsDevelopment of Rain Shadows

Desert Stream ChannelDesert Stream Channel

Western US Tectonic ProvincesWestern US Tectonic Provinces

Plateaus, Mesas, and ButtesPlateaus, Mesas, and Buttes

Plateau: Broad, flat-topped elevated areas bounded by cliffsMesa: Flat-topped hill bounded by cliffs and capped by resistant rockButte: Narrow hill with steep cliffs

Monument Valley, UTMonument Valley, UT

Formation of Hogbacks & CuestasFormation of Hogbacks & Cuestas

Monocline - Big Horn Mtns., WYMonocline - Big Horn Mtns., WY

Death Valley - Basin & RangeDeath Valley - Basin & Range

3 km of relief

Models of Graben FormationModels of Graben Formation

Desert LandformsDesert Landforms

Wind ActionWind Action

• Wind Erosion and Transportation– Dust storms and Sandstorms– Blowouts– Deflation: removal of fine particles from land

surface by wind action

• Wind Deposition– Development of loess: deposits of wind-blown silt

and clay composed of unweathered angular grains of quartz, feldspar, etc. weakly cemeted by calcite. High porosity (~60%).

Agricultural Haze - Wind ErosionAgricultural Haze - Wind Erosion

Dust StormDust Storm

Effects of Wind ErosionEffects of Wind Erosion

Wind Erosion and DesertificationWind Erosion and Desertification

VentifactsVentifacts

Blowout and Pillar FormationBlowout and Pillar Formation

Desert VegetationDesert Vegetation

Less than 25 cm rain per year

Sand PillarSand Pillar

Petroglyphs and Desert VarnishPetroglyphs and Desert Varnish

Dune FormationDune Formation

Monument Valley Wind RipplesMonument Valley Wind Ripples

Image source: George Oxford Miller

Ripples on Dune FaceRipples on Dune Face

Dune Morphology Dune Morphology vsvs Wind Strength/OrientationWind Strength/Orientation

Barchan Dunes form when there is limited sand.Parabolic Dunes require abundant sand and strong wind!

Barchan Dune Field - MarsBarchan Dune Field - Mars

Longitudinal Dune Field - AlgeriaLongitudinal Dune Field - Algeria

Dunes up to 200 m high