Eolian system

In general, the dominant erosional landforms in desert regions are developed by

running water

The migration of sand dunes results from

erosion of sand on the windward side and deposition on the slip-face

formation of dunes

originate where an obstacle creates a zone of quieter air behind it -as sand is blown up or around the obstruction, its velocity decreases and deposition occurs -once a small dune is formed, it acts as a dune -commonly originate in wind shadows

Sand dunes on the shores of oceans and lakes are likely to be

parabolic (blowout)

ripples

-saltating grains form ripples that are perpendicular to the wind direction -regularly spaced intervals -can be found on surface of dunes and sand sheets

abrasion

-sandblasting action of wind-blown sand -Kinetic energy from the wind -sand particles driven by the wind impacting rock surfaces -knock off small pieces -polishes and shapes the rock

Barchan dunes

-supply of sand is limited -winds of moderate velocity blow in a constant direction -crescent-shaped dunes -tips (horns) point downwind (direction the wind is blowing toward) -isolated

slip face

-the opposite side of the wind face -aka lee slope

Dune types

-transverse dunes - barchan dunes - longitudinal/linear dunes -star dunes -parabolic dunes

wind face

-where the wind is hitting the dune

sand sheets

-where wind velocity decreases, moving sand grains may be deposited -deposits of gently undulating but nearly flat layers of eolian sand formed of grains that are too big to saltate and form dunes -may grade into higher sand dunes

sand deposits

-wind blown sand accumulates to form: -sand sheets -ripples -dunes

desert pavements

-wind can move only sand and dust-sized particles -deflation leaves concentrations of coarse materials

Eolian systems

-wind is not an effective agent in eroding the landscape -major result: transportation of loose, unconsolidated fragments of sand and dust -wind transports sand by saltation and surface creep -dust is transported in suspension and can remain high in the atmosphere for long periods -sand dunes migrate -source of loess is desert dust -desertification can be caused by human activity or by slight climatic fluctuations -dynamic open system driven by HEAT FROM SUN -most obvious in deserts -erodes, transports , and deposits fine sediment

transportation of sediment by wind

-wind transports by saltation and surface creep -silt and dust-sized particles are carried in suspension -grain can only be lifted when it overcomes the forces resisting movement -main force=weigth of grains

deserts and latitudes

-world's greatest deserts are in low-latitude belts -dry air

A limited supply of sand in a region of strong, unidirectional wind would likely produce

barchan dunes

transverse dunes

-large supply of sand -constant wind direction -cover large areas -develop wavelike forms perpendicular to wind -dunes become aligned and "march" downwind

Changes to farming practices

-less invasion -use less water -return to rangeland rather than farmland

deflation

-lifting and removal of loose sand and dust particles from Earth's surface -semiarid regions (deserts or semi-arid regions) -only where unconsolidated material is exposed at the surface -limited to areas like deserts, beaches, and barren fields

Ventifact creation

-pebbles that are shaped and polished by the wind -2 or more well polished sides formed by sandblasting

deflation basins

-result of deflation -shallow depression formed by wind erosion -produced where solution activity in the layers of the horizontal bedrock dissolves the cement that binds the sand grains

saltation

-results from impact and bounce -leaping -medium grains move by skipping or bouncing

creep

-rolling and sliding -coarse grains move by impact from other grains

True facts about deserts

-Desert and near-desert areas cover one third of the land surface of Earth. -Major desert areas lie between 10 and 30 degrees north or south of the equator -They are characterized by high atmospheric pressure and low humidity. -False: All deserts develop in rain shadows.

1930's

-Dust bowl -drought -bad farming practices -no wind breaks -fallow fields without vegetative protection -water intensive crops failed without water -dust bowl was in many regions -more than 75% of topsoil was eroded

Parabolic dunes

-aka blowout dunes -develop along coastlines where vegetation partly covers a ridge of wind-blown sand -transported landward from the beach -U or V shaped dune with long arms -abundant sand -prevailing ocean winds blowing onshore -migrate landward -arms pointed upwind (opposite of barchan dunes)

Loess is deposited

-as a comparatively uniform blanket over hundreds of square kilometers -by the wind -tens of meters thick -as dust

rain shadows

-as air is forced to rise over mountain range, it cools and precipitates its moisture -on the other side of the range, dry air is heated

suspension

-carried into the air -fine silt and clay

lift

-caused by air flowing over grain -changes in pressure over and under the particle

wind erosion

-deflation -abrasion -wind can't do much to erode solid rock exposed at a surface, but it can transport loose material -dry climate is best

Loess

-deposit of wind-blown dust that accumulates slowly and blankets large areas -composed of qartz, feldspars, and clay -mostly silt-sized particles -transported long distances -widespread beyond desert areas -not widespread in major desert regions because dust is swept out of the deserts and deposited -common in glaciated areas -covers 10% of Earth's present land surface -derived from nearby glaciers or rock flour -highly erodible -especially if: plants are removed, plowed, or overgrazed -ex: dust in Beijing from Mongolia

cross bedding

-deposition of sediment on the slip face creates cross beds -layer upon layer of older buried slip faces -when the sand grains exceed the angle of repose, they slip down the slip face

Dunes

-deposits of sand -migrate downwind -as sand dunes migrate, they produce a series of layers (cross-beds) inclined in a downhill direction -quartz is most common mineral in wind-blown sand

sand dunes

-different kinds of sand dunes result from variation in -sand supply -wind speed -direction

Yardangs

-distinctive linear ridges -elongated ridges formed by wind erosion of relatively soft material -analogs to drumlins -restricted to the most arid parts of deserts -formed parallel to wind direction -most easily formed in weakly cemented sediment

Dust in the wind

-dust particles remain suspended until: -wind velocities drop -dust particles collide and stick together -larger particles are heavier -rain washes dust

deserts

-form because of rain shadows -latitudinal

asymmetry

-gives direction of prevailing wind

Drag

-impact of air molecules on the grain's surface

star dunes

-isolated sand hill -mounds of sand having a high central point -wind blowing in 3+ direction (no single prevailing wind direction) -moderate amounts of sand

Desertification

-land degradation -occurs naturally or from people -exploitation and overgrazing of sensitive lands can cause deserts to expand -poor cultivation practices, overgrazing, and deforestation are the major causes

Linear/seif dunes

-long, parallel ridges of sand -elongated in a parallel direction -long, evenly spaced ridges -limited sand -strong, bi-directional wind (2 slightly different wind directions)

Ventifacts are a product of

abrasion

A yardang is

an erosional landform caused by wind

Desert pavement or a lag deposit is a concentration of

gravel-size particles left behind as wind selectively removes sand and dust from the surface.

The bouncing movement of sand grains by the wind is called

saltation