Competitive Exams: Aeolian Landforms
Aeolian processes involve erosion of dry and loose material along with transportation and deposition of fine sediments mainly sands by action of wind. These occur mainly in arid and semi-arid regions of tropical and temperate environments.
Besides Aeolian process limited fluvial processes are also operative in arid and semi-arid regions characterised by inland drainage, ephemeral and intermittent streams. Wind erosion is largely controlled and determined by: 1. Wind velocity 2. Nature and amount of sands, dusts and pebbles 3. Composition of rocks 4. Nature of vegetation 5. Humidity, rainfall amount, and temperature
Wind Erosion Ways
Wind erosion occurs in three ways:
Deflation: Removal and blowing away of dry and loose particles of sands and dusts. Long and continuous deflation produces depressions or hollows known as ‘Blow Outs’
Abrasion or Sand Blasting: Wind armed with entrained sand grains as tools of erosion attacks the rocks and erodes them.
Attrition: Mechanical wear and tear of the particles.
- Deflation Basins-Depression created through deflation, also known as Deflation hollows e. g. Quattara depression (Egypt), Buffalo Hollow (American Great Plain) Big Hollow (Wyoming, USA), Pong Kiang Hollow (Mongolian Desert)
- Mushroom Rocks-Rocks having broad upper part and narrow base formed due to abrasion at base. Isenberg-Sharply rising residual hills.
- Demoiselles-Rock pillars having relatively resistant rocks at the top and soft rock below. These are formed due to differential erosion.
- Zeugens-Abrasive action of wind acting on exposed weakness of horizontally bedded rocks (hard above and soft below) thereby producing a tabular mass of resistant capping upon softer rocks beneath:
- Yardangs-Sinuous ridges and parallel depressions formed'due to differential abrasion of vertically arranged thin alterations of hard and soft strata. Typical of Turkistan Desert and also in Tibesti Massif (Sahara)
- Ventifacts-Faceted rock boulders, cobbles and pebbles formed due to prolonged wind abrasion (one abraded face-Einkanter, two abraded faces-Zweikanter, three abraded faces-Dreikanter).
- Stone lattice-Differential erosion of hard and soft portions of rocks through abrasion produces pitted and fluted surfaces called stone lattice.
Takes place through
Suspension-Materials kept in suspension by upward moving air (e. g. Dust, Haze, Smoke)
Saltation-Mechanism of bouncing, leaping or jumping of particles.
Surface creep-Transport of loosened materials on the ground surface.
- Ripples-Wave like features formed by saltation impact. They may be transverse or longitudinal
- Sand Dunes-Heaps or mounds of sands. They are mobile landforms and may be coastal dunes, riverine dunes, and lacustrine dunes. Formation of Sand dunes requires:
- Abundance of sand
- High velocity of wind
- Obstacles such as tree, bushes, rocks, forests etc.
- Suitable places for the accumulation of sands.
- Nebkhas-Dunes formed due to shrubs as obstacles
- Lunettes-Dunes that develop on the lee of desert depressions.
- Fore Dune-Those formed on the windward side of a hill.
- Depending upon shape they may be:
- Linear or Longitudinal (or Seif Dunes), Star, Dome, Reverse, Barachan, Transverse Loess-Thick deposits of non-stratified, non-indurated well-sorted fine grained sediments consisting of quartz silt. Sediments for the accumulation of loess are derived from desert areas, flood plains of river valleys, coastal areas etc (e. g. Chinese loess has been deposited from sediments from Gobi deserts. Hwang Ho flowing through loess plateau acquires enough sediments that makes it look yellowish in colour). Five Great Desert Provinces:
- Sahara-Central Asian Province (Sahara, Arabian, Indian, Karakum, Kizil Kum, Takla Makan, Gobi)
- Southern African province (Namib, Karroo, Kalahari)
- South American dry zone (Atacama, Patagonia) 4. North American (Mojave, Arizona, Sonoran) 5. Australian
- Desert having mobile sands are called Ergs.