TheGeoRoomHot Deserts

Definition of the Day
River Competence
The largest particle that can be carried by a river

Wind Erosion, Transportation & Landforms

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Types of Wind TransportationDeflation Hollows Desert Pavement Ventifact Yardangs Zeugens/ Mushroom rocks Mesas & Buttes Inselbergs

Perhaps the most powerful and effective phenomenon that occurs in deserts is wind, and is responsible for creating a wide range of desert features. Wind in deserts is able to erode and transport sand for considerable distances, locally, regionally or continentally. For example, sand from The Sahara desert can be transported into Europe and can reach as far as England causing "red rain."and some brilliant sunsets. Most landforms in deserts are carved and abraded by wind or sand blasted, the latter which erodes strata more quickly and effectively.

Definitions
Abrasion
The act of eroding and wearing down by wind
Deflation
The process whereby material is removed or scraped away from the surface.

Wind Transportation

Material in deserts is carried mainly by 3 processes, each depending on the size of material.

Suspension

Very fine material can be lifted and carried in the air by wind. These suspended materials are responsible for dust storms in deserts. Depending on the wind speed these dust storms can be torrential and devastating with larger sediments being also lifted covering everything e.g The Dust Bowl of 1939, Texas, USA.

Saltation

Fairly large materials such as corestones can be transported in a series of 'hops'. As these materials fall, they disturb the inertia of other lying materials causing them to also move or bounce.

Surface creep

Surface creep is the rolling of large stones that cannot be lifted along the surface. Sufficient strong winds are needed to roll these stops foward. As they roll, they can disturb other lying stones causing them to move

Animation showing creep, saltation & suspension

Wind produced features and landforms in deserts

Desert Pavements

Desert pavements are the surface of the desert occupied by coarse particles that are left when fine material is eroded away. These surfaces are durable and can resist future erosion. When insoluble material precipitate (removed from solution or water) under intense evaporation they cement together forming a hard layer called duricrust. Desert pavements have varying names in different locations; they're called "gibber" in Australia, sai in Asia and hamada by the Arabs.

Deflation Hollows

These are small to huge pits that are formed when wind gradually removes fine material from the surface (desert pavement). Erosion (deflation) stops when the material is large enough to be lifted or resistant to erosion.

Deflation hollow diagram
Deflation hollow

Ventifacts

Ventifacts are smoothened rocks that are polished and brushed by sand carrying wind.

Yardangs

Yardangs are ridges separated by troughs that are formed when wind erodes vertical bands of soft strata (troughs) leaving hard strata protruding as the ridges. Mega yardangs can be a kilometre long and can reach 100 m in height.

Yardangs source geol.umd.edu

Zuegen / Rock Pedestals

Zuegens are formed when soft and hard strata lies horizontally causing the soft strata to be eaten more than the hard strata. Zuegens can take the form of a mushroom shaped rock pedestal resulting from the intense wearing down of the lower soft strata by sand blasting wind.
View Animation

A zeugen/ mushroom rock

Mesas /Table Hills

Mesas are flat topped, steep sided hills rising abruptly from a plain. When the surrounding soft area is eroded away, hard stands of hills can be left untouched or slightly weathered. For example, in Monument Valley, Arizona USA the surrounding softer rocks have been eroded for millions of years living resistant sandstones standing as mesas. Mesas can form structural benches (staircases) which are also resistant rocks that protrudes below the main hard rock. Continued denudation can reduce the mesa into a butte.

Inselbergs

Several inselbergs such as bornhardts and whalebacks are also present in deserts. These are formed from the stripping and strapping of regolith by wind revealing deep seated basal surfaces as dome shaped bornhardts or or low lying bornhadts known as whalebacks.

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3 Comments

2019-03-14 03:21:12
Henry
Understandable!
2019-06-05 09:36:53
Asper
No
2019-06-06 10:39:22
Med
good for revision

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