Arid and desert landforms

Desert

A desert is essentially a dry, barren land where rainfall is extremely low—generally less than 250 mm a year. Vegetation is sparse or completely absent, and temperatures can be extreme, swinging from scorching hot during the day to freezing cold at night.

But here’s the twist: deserts aren’t always about endless sand dunes. Some are rocky, some are cold, and many are shaped by the fascinating and relentless forces of wind and water.

Types of Deserts (Based on Surface Features)

Not all deserts are just seas of sand. In fact, many deserts are more rocky or stony than sandy. Based on surface composition, deserts are classified into five major types:

1. Hamada (Rocky Desert)

• A barren, hard, and flat expanse of exposed rock surfaces—often rugged and dissected.
• Wind removes the loose particles (deflation), leaving behind solid rock platforms.
• Key feature: Almost no sand or vegetation.
• Example: Hamada el-Hamra in Libya.
  

2. Reg (Stony Desert)

• A desert surface covered with pebbles, gravel, and angular stones.
• Wind deflation clears finer particles, leaving behind a desert pavement.
• Key feature: Regs are widespread and can appear polished due to abrasion.
• Example: Large parts of the Sahara are actually regs.

3. Erg (Sandy Desert)

• This is the classic image of a desert—vast seas of sand dunes.
• Loose sand is transported and deposited by wind, building up into dunes of various shapes.
• Key feature: Shifting dunes, barchans, and star dunes are common.
• Example: The Grand Erg Oriental in Algeria.
  

4. Badlands

• A maze-like landscape of deep gullies, ravines, and steep ridges, often dry and cracked.
• Occasional rainstorms cause rapid erosion in areas with soft, easily erodible rocks.
• Key feature: Highly dissected and rugged terrain; unsuitable for agriculture or travel.
• Example: Badlands of South Dakota (USA), Chambal Valley (India).
  

5. Mountain Deserts

• Desert areas where rugged mountains rise amidst arid surroundings.
• Typically found in highlands or intermontane basins where rain shadow effect or continentality causes dryness.
• Key feature: Combination of rocky slopes, snow in higher altitudes, and dry valleys.
• Example: Gobi Desert in Mongolia and China.

The Mechanism of Arid Erosion

In deserts, wind is the main agent of erosion, far more dominant than water. Here’s how it works:

• The wind deflates the surface by lifting and removing loose particles.
• It abrades rock surfaces using sand particles, wearing them down like sandpaper.
• Over time, this erodes softer rocks and leaves behind bizarre and striking landforms.

It’s nature’s own sculptor, working slowly but powerfully across centuries.

Landforms of Wind Erosion in Deserts

Wind erosion gives rise to some unique features. Let’s walk through them:

1. Deflation Hollows (Blowouts)
   These are shallow depressions formed when the wind scoops out loose materials from the surface. If the hollow gets deep enough, it might even hit the water table and turn into a temporary salt lake.
2. Mushroom Rocks (Rock Pedestals)
   These odd-shaped rocks look like mushrooms – narrow at the bottom, wide at the top – formed as wind-driven sand erodes the lower portion more than the upper.
3. Zeugen
   These are long, narrow ridges of hard rock that stand above softer surrounding material. Horizontal layers get eroded by wind and occasional water flow, leaving behind these flat-topped features.
4. Yardangs
   These are streamlined ridges aligned with the wind direction, carved by wind abrasion and deflation. Unlike zeugens, yardangs have vertical layers and often look like inverted boat hulls.

Landforms Due to Wind Deposition in Deserts

Wind doesn’t just erode—it also deposits materials, forming:

1. Sand Dunes
   These are mounds or hills of sand built by wind deposition. Based on shape and wind pattern, they can be:
   • Barchans – crescent-shaped with tips pointing downwind.
   • Seifs – long and narrow, running parallel to the prevailing wind.
   • Transverse dunes – wave-like dunes perpendicular to the wind.
   • Star dunes – with arms radiating out from a center, formed by multidirectional winds.
2. Loess
   When fine silt is blown far from deserts and deposited in thick layers, it forms loess. These are extremely fertile soils, like those found in northern China.

Landforms Due to Water Action in Deserts

Though deserts are dry, occasional rains can be powerful. Water in deserts usually flows in short, intense bursts, causing flash floods that shape the terrain dramatically:

1. Wadis
   These are dry riverbeds or stream channels that fill up rapidly after heavy rainfall. Most of the time, they remain dry.
2. Alluvial Fans
   As floodwaters rush out of the mountains, they slow down and deposit sediments in a fan shape at the base of the slope.
3. Playas (Salinas)
   These are flat, low-lying areas that temporarily fill with water during rains and then dry up, leaving behind salt flats or clay pans.
4. Badlands
   In regions with soft rocks, the action of occasional rain leads to intricate patterns of deep gullies and steep ridges. The terrain looks rugged and “broken”—hence the name.