Wind (Aeolian) Erosional Landforms: Pediments, Pediplains, Playas, Deflation Hollows, Mushroom Rocks
Geography › Geomorphic Processes and Landform Evolution · Topic 3.17
Wind erodes land in deserts and dry coasts by deflation, the lifting and removal of loose sand and dust, and by abrasion, the sandblasting of rock surfaces by wind-borne grains. Its erosional landforms include deflation hollows and blowouts, mushroom rocks and yardangs, and, with occasional water, pediments, pediplains and playas. Deserts are shaped by wind and also by rare, sudden rains, so water's role is as important as wind's in many landforms.
6 min read · UPSC Prelims · Geography · Geomorphic Processes and Landform Evolution
At a Glance
- Deflation Wind lifts loose material
- Abrasion Wind-borne sand cuts rock
- Mushroom rock Pedestal shaped by abrasion at the base
- Pediment Gently sloping rock surface at a mountain foot
- Playa Dry desert lake bed
- Exam link UPSC Prelims, Geography: Geomorphic Processes and Landform Evolution
Where Does It Fit?
This topic begins the group of topics on landforms made by each geomorphic agent, starting with wind. It follows the topics on weathering and mass movement, which supply the loose material that wind and water carry away in deserts. Previous topic: Mass Movements: Heave, Flow, Slide; Slow, Rapid and Landslide Categories. Next topic: Wind Depositional Landforms: Barchans, Seif, Parabolic, Transverse and Longitudinal Dunes.
How Does Wind Shape Deserts?
In short: in deserts, wind lifts and carries sand and dust, and builds dunes and carves rocks.
Deserts are regions with very little rainfall, usually less than about 250 mm a year, sparse vegetation and a great range of temperature. Hot deserts lie mostly in the subtropical belts between about 15 and 30 degrees north and south, where descending dry air dominates, as in the Sahara, Arabian, Thar, Kalahari and Australian deserts, and are linked to the pressure belts described in General Circulation of the Atmosphere: Hadley Cell, Ferrel Cell, Polar Cell. Dry soil and bare ground leave particles exposed, so wind is a powerful agent. It acts through deflation, the lifting and removal of loose particles, which lowers the surface, and abrasion, the sandblasting of rock by wind-borne grains, as explained in Soil Erosion and Conservation. Though wind is the typical agent, desert landforms also result from rare but violent rains and flash floods, and so many desert landscapes are partly the work of water.
What Are the Erosional Aeolian Landforms?
| Landform | Description |
|---|---|
| Deflation hollow (blowout) | A shallow depression where wind has removed loose material; may reach the water table and form an oasis |
| Desert pavement (reg, serir) | A surface of closely packed pebbles left when the finer sand and dust has been blown away |
| Ventifact | A stone polished or faceted by wind-blown sand |
| Mushroom rock (pedestal rock, gara) | A rock with a narrow base and a wider top, eroded more at the base where the sand-laden wind is strongest |
| Yardang | A streamlined ridge of soft rock carved parallel to the direction of the prevailing wind |
| Zeugen | Table-like ridges of hard rock capping softer rock |
What Are Pediments, Pediplains and Playas?
| Landform | Description | How it forms |
|---|---|---|
| Pediment | Gently sloping, rock-cut surface at the foot of a desert mountain, covered by a thin layer of debris | Sheet floods and streams wash away material, and the mountain front retreats |
| Pediplain | Wide, nearly flat rock plain with isolated hills (inselbergs); formed when pediments join | Retreat of mountains by repeated pediment growth; the idea of pediplanation is credited to L. C. King |
| Playa | Flat bed of a shallow desert lake that is dry for most of the year | Water collects after rain, evaporates, and leaves salt and clay; the large ones are salt flats |
| Bajada | Slope of merged alluvial fans below a pediment | Sediment from mountain streams |
| Wadi | Dry valley of a stream that flows only after rain | Sudden flash floods cut channels |
In India, the Rann of Kachchh is a salt flat of the playa type, and Sambhar Lake in Rajasthan is a salt lake that dries for part of the year. The Thar is described in Wind Depositional Landforms: Barchans, Seif, Parabolic, Transverse and Longitudinal Dunes.
What Other Erosional Forms Does Wind Make?
- Deflation hollows and blowouts: shallow basins scooped out where wind has removed loose sand and silt. Large ones such as the Qattara Depression in Egypt lie below sea level, and the wind may stop deepening them when it reaches the water table.
- Desert pavement: after the wind removes fine material, a surface of closely packed pebbles remains, which protects the ground below.
- Mushroom rocks (pedestal rocks): sand grains move mainly close to the ground, so the base of a rock outcrop is worn away more than the top, which leaves a mushroom shape. The Gol Pahari and other rock outcrops in the Thar show this.
- Yardangs and zeugen: streamlined ridges aligned with the wind, and tabular ridges with deep grooves cut in soft rock beneath hard caps.
- Ventifacts: pebbles with smooth faces, polished by wind-blown sand.
As an analytical point, wind erosion alone cannot explain most desert relief. Occasional heavy rain and flash floods do a large share of the work, and the wind then removes the loosened debris, which links this topic with the water-made forms in Running Water Erosional Landforms: V-Shaped Valleys, Gorges, Canyons, Potholes, Incised Meanders, River Terraces. The material removed from one place is laid down elsewhere, as explained in the next topic.
Why Is This Topic Important?
- Terms Pediment and playa are asked
- India Thar and Rann of Kachchh
- Concept Water also shapes deserts
What Came Next?
The next topic describes the depositional landforms of wind, namely the dunes and loess. Next topic: Wind Depositional Landforms: Barchans, Seif, Parabolic, Transverse and Longitudinal Dunes.
Key People and Terms
- Deflation Lifting of loose material by wind
- Abrasion Sandblasting of rock
- Pediment Rock slope at mountain foot
- Pediplain Plain formed by joined pediments
- Playa Dry desert lake bed
- Yardang Streamlined wind-cut ridge
Exam Corner
Points to Remember
- Deflation removes loose grains; abrasion cuts rock.
- Mushroom rocks form where abrasion is strongest near the ground.
- A playa is a dry desert lake.
- Pediplains form when pediments join.
- Qattara Depression is a deflation hollow.
Do Not Confuse With
- Deflation and abrasion Lifting of loose grains versus cutting rock
- Pediment and bajada Rock slope versus fan-shaped deposit slope
- Playa and oasis Dry salt basin versus watered spot
Memory Hook
Wind lifts, sand cuts; pediment slopes, playa shuts.
Mains Angle
Questions ask for desert landforms and the role of water. These points add depth.
- Processes Deflation and abrasion
- Water Flash floods shape deserts
- India Thar and Kachchh
A Question You May Face
An original practice question, not a past paper question.
“Describe the erosional landforms of hot deserts and discuss the role of wind and water in their formation.”
How to Answer
- Wind Deflation and abrasion.
- Forms Hollows and mushroom rocks.
- Water Pediments and playas.
- India Thar.
GS Relevance
Frequently Asked Questions
What are aeolian landforms?
Aeolian landforms are those shaped by wind. Wind erosion makes deflation hollows, desert pavements, mushroom rocks and yardangs, and wind deposition builds sand dunes of various types and spreads fine dust as loess, mainly in deserts and dry regions.
What are deflation and abrasion?
Deflation is the removal of loose, fine particles from a surface by wind, which lowers the ground and may form hollows. Abrasion is the wearing down of rock by sand grains carried by the wind, which polishes and shapes rocks like sandpaper.
What is a pediment?
A pediment is a gently sloping, rock-cut surface at the foot of a mountain in a desert, usually covered by a thin layer of debris. It forms as sheet floods and streams remove material and the mountain front retreats. When many pediments join, they make a wide plain called a pediplain.
What is a playa?
A playa is the flat bed of a shallow desert lake that is dry for most of the year. After rain it fills with water, which then evaporates and leaves behind layers of clay and salt. Large playas form salt flats, such as the Rann of Kachchh in India.
How does a mushroom rock form?
A mushroom rock, or pedestal rock, forms when wind-blown sand cuts the base of a rock outcrop more than the upper part, because the grains are carried mostly near the ground. The base becomes narrow while the top stays wide, leaving a mushroom shape.
PYQ Practice — Statement Analysis
1 A playa is a dry desert lake bed.
It often has a salt crust.
2 Deflation is the sandblasting of rocks by wind-borne sand.
That is abrasion; deflation is the lifting of loose particles.
3 Mushroom rocks are formed by wind abrasion near the ground.
Sand is carried close to the ground.
4 Pediplains are formed by the joining of dunes.
They are formed by joining pediments.
Past Mains Questions on This Topic
This topic comes under Geomorphic Processes and Landform Evolution. UPSC Mains questions asked on the matching syllabus topic, year-wise with marks:
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