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🏜️ How do deserts turn into dunes?

Loose dry sand saltates, avalanches on the lee, and piles into forms that migrate with the wind.

lessons

~10 min

to learn

🔬 Science

subject

Adults

level

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What you’ll learn

Sand, wind, and a dry stageState the sand-supply and wind-threshold conditions that allow dunes to form.Dunes need free dry sand and winds strong enough to move it. Aridity helps, but sand budget and open ground decide whether piles grow.
Saltation, ripples, and the avalanche faceExplain saltation, nested bedforms, and windward/lee asymmetry that drive migration.Grains hop, ripples organize, and slip-face avalanches rebuild the lee. Climb and collapse move dunes downwind.
Shapes that name the wind climateLink dune morphologies and human/climate factors to long-term wind and sand budgets.Barchans, stars, and ridges encode wind patterns. Coasts and cold drylands can host dunes too; people and plants alter mobility.

Questions this course answers

What combination most directly builds classic desert dunes?

Dunes need a sand budget, winds capable of saltation, and depositional conditions — aridity helps free grains, but empty heat alone is not enough.

Put these steps of dune migration in order

Erosion on the windward ramp feeds deposition and avalanche on the lee; repeated, the body of the dune advances downwind.

Why do different dune shapes appear in different deserts?

Wind rose complexity and sand supply control whether crescents, ridges, or multi-armed stars dominate the field.

Grounded in trusted sources

USGS / National Park Service education pages on sand dunes and eolian processes
Bagnold — The Physics of Blown Sand and Desert Dunes (classic eolian transport foundation)
NASA Earth Observatory features on dune fields and desert geomorphology
Open university / geoscience textbooks on bedforms, saltation, and dune classification

Every Wunder lesson is built from real, reputable sources — never invented.

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