Desert Landforms

Notes

Deserts receive less than about 25 cm of rain a year. Causes: location under subtropical high-pressure belts (trade wind deserts), rain shadow (Patagonia), cold ocean currents (Atacama by the Humboldt current, Namib by the Benguela current) and continentality (Gobi). Examples: Sahara (the largest hot desert), Arabian, Thar, Kalahari, Atacama (the driest), Great Australian, Mojave; the Gobi is a cold desert.

Wind (aeolian) processes: deflation (lifting of fine material), abrasion and attrition; transport by suspension, saltation (the major mode) and surface creep.

Erosional landforms

Deflation hollows and blowouts (Qattara Depression, Egypt).
Mushroom (pedestal) rocks, zeugen, yardangs, ventifacts (wind-polished stones).
Inselbergs (isolated residual hills such as Uluru, also called bornhardts) and mesas and buttes.
Desert pavement (reg, a stony surface); hamada (rocky desert); erg (sand sea).

Water-formed features in deserts

Wadi (dry river channel that flows after rain), playa (a dry lake bed, salt flat; Sambhar, Didwana in Rajasthan are salt lakes), pediments, bajada (a coalesced alluvial fans), alluvial fans, bolson basins.

Depositional landforms: sand dunes

Barchan: crescent-shaped, horns point downwind; forms under a single wind direction.
Seif (longitudinal) dunes: long ridges parallel to the wind (two wind directions).
Transverse, parabolic and star dunes.
Loess: wind-blown silt deposited beyond the deserts (China).

Thar Desert (India): western Rajasthan, the Luni is the only large river; dunes, mostly barchans, with salt lakes and a Great Indian Desert extension into Pakistan.

Key Points

Deserts: under 25 cm rain; causes include subtropical highs, rain shadow, cold currents.
Erosional: mushroom rocks, zeugen, yardangs, inselbergs, deflation hollows.
Barchan: crescent-shaped; seif: longitudinal.
Wadi: dry channel; playa: dry lake bed.
Atacama is the driest; Sahara is the largest hot desert.

MCQs

Q1. A crescent-shaped sand dune formed by a unidirectional wind is a:

(a) Seif
(b) Barchan
(c) Star dune
(d) Parabolic dune
Ans: (b).

Q2. A dry river channel in a desert that flows after rain is a:

(a) Wadi
(b) Playa
(c) Erg
(d) Hamada
Ans:
(a).

Q3. The driest desert of the world is the:

(a) Sahara
(b) Atacama
(c) Kalahari
(d) Gobi
Ans: (b).