Arid Regions

• Rainfall < 25 cm annually
• High evaporation
• Sparse vegetation
• Dominant processes → Wind (Aeolian) + Flash floods

I.  WATER ERODED ARID LANDFORMS

 Rill

• Small, shallow channels
• First stage of fluvial erosion
• Formed by runoff after sudden rain

 Gully

• Larger & deeper than rill
• Cannot be removed by normal ploughing
• Advanced erosion stage

 Ravine

• Larger than gully
• Narrower than canyon
• Example: Chambal region

 Badland Topography

• Network of rills, gullies, ravines
• Formed in weak sedimentary rocks
• Highly dissected terrain

 Bolsons

• Intermontane basins in arid areas
• Closed drainage system

 Playas

• Temporary lakes in bolsons
• After evaporation → Salina (salt crust)

 Pediment

• Gently sloping rock-cut surface
• Located at mountain foot
• Erosional landform
• NOT depositional (common Prelims trap)

 Bajada

• Formed by merging of alluvial fans
• Depositional
• Located between pediment & playa

II.  WIND ERODED ARID LANDFORMS

Aeolian Processes:

• Deflation → Removal of loose particles
• Abrasion → Sand blasting
• Attrition → Particle collision

 Deflation Basin (Blowout)

• Hollow formed due to removal of particles
• May reach several km diameter

 Mushroom Rock (Rock Pedestal)

• Narrow base, broad top
• Due to greater abrasion near ground
• Different from yardang

 Inselberg (Monadnock)

• Isolated hill rising abruptly from the plain
• Residual landform

Demoiselles

• Rock pillars
• Hard rock protects softer rock below
• Differential erosion

 Zeugen

• Table-shaped rock mass
• Resistant cap rock
• Undercutting of softer rock

Yardang

• Streamlined ridge
• Parallel to prevailing wind

 Wind Windows & Bridges

• Holes created by abrasion
• If widened → arch (bridge)

III. WIND DEPOSITIONAL LANDFORMS

Ripple Marks

• Small-scale ridges
• Formed by saltation

SAND DUNES

 Longitudinal Dunes

• Parallel to wind
• Also called Seif dunes

 Transverse Dunes

• Perpendicular to wind
• Form when sand supply abundant

Barchans

• Crescent-shaped
• Horns point downwind
• Form in limited sand areas

 Parabolic Dunes

• U-shaped
• Horns point upwind
• Often vegetation anchored

 Star Dunes

• Central peak
• Multi-directional winds

 Loess

• Wind-blown fine silt
• Very fertile soil
• Major deposits → China (Yellow River), USA (Missouri Basin)