Lecture Notes: Dune Classification in Geomorphology

Introduction

• Discussion on dune formation in Aeolian environments.
• Key factors for dune formation:
  • Wind speed
  • Sand supply
  • Vegetation cover
  • Minimum sand body size (critical size: 4-6 meters spread)

Characteristics of Dunes

• Formed due to wind's shearing action on sand.
• Gentle slope on the windward side; steep slope on the lee side.
• Dunes can migrate but maintain internal structures.

Dune Classification

1. Star Dunes

• Radiates from a central point with sharp ridges.
• Formed by wind from multiple directions.
• Little to no migration; growth is vertical.
• Slip faces change seasonally.

2. Longitudinal Dunes

• Elongated, parallel to wind direction.
• Huge landforms extending over kilometers.
• Common in trade wind deserts.
• Form in areas with persistent wind and little vegetation.
• Origin theories by Bagnold (1941), Livingstone (1986), and Tsoar (1989).

3. Transverse Dunes

• Perpendicular to wind direction.
• Form in areas with massive sand supply and relatively ineffective wind.
• Common in coastal regions and erodible sandy bedrock zones.

4. Barchan Dunes

• Classic crescent-shaped Aeolian landforms.
• Gentle windward slope, steep lee side.
• Migrate across deserted plains with constant sand mass.

5. Parabolic Dunes

• Opposite orientation to Barchan dunes.
• Formed in partially stabilized terrains with blowouts.
• Associated with vegetation and coastal areas.
• Can elongate into hairpin shapes and transform into longitudinal forms.

Special Dune Forms

Whalebacks and Zibar Dunes

• Formed by the migration of longitudinal dunes.
• Low, rolling ridges of coarse sand.
• Common in semi-arid steppe and prairie regions.

Influences on Dune Formation

• Wind and sand supply are critical.
• Vegetation plays a role in stabilizing dunes.
• Coastal dunes often include biogenetic calcareous material.

Conclusion

• Dunes form due to the interaction of wind, sand, and vegetation.
• Different types of dunes result from varying conditions, but the internal structure remains constant.
• Dune formation triangle: balance between wind, sand supply, and vegetation.