1. Wind as an Agent of Change
Earth Science 11

2. Abrasion
Mainly by sand grains (Windblown silt and clay particles are too small and too soft to wear away rock)
Affects below 1 meter – formation of toadstool rocks

3. Wind as an Agent of Change
Agent of erosion
Most effective in dry areas (deserts) where sands, silts, and clays lie loose and dry
Act in two ways:
1. Pick up and move sediment
2. Drive sediment against rocks and other materials

4. Wind as an Agent of Change
Dust storm:
When strong, steady winds lift great amounts of silt and clay from top soil

5. Wind as an Agent of Change
Materials eroded:
Fine grained materials (silt, clay, some sand)
Materials usually moved close to ground
Most wind erosion occurs in dry climates

6. Ventifact Sand blasted boulder
The side of the ventifact that faces the steady wind direction wears into a smooth, flat surface or “facet”

7. Erosion
Suspension: Clay and silt
Saltation: Sand

8. Desert Pavement
Pebbles and boulders left in a desert when the sand and silt are blown away
80% of the Sahara Desert
Makes up the surface surrounding the ventifact
Protects the materials beneath from further deflation

9. Deflation
Removal of loose particles by wind

10. Blowout Small, shallow depressions formed by deflation
Can be many thousands of meters long and a hundred meters deep

11. Wind Deposits
1. Loess:
Made of unlayered, yellowish particles that are size of silt
Common in China, N. Europe, and N. US
Unlike ordinary silt, particles are angular in shape

12. Wind Deposits 2. Sand Dunes Hill of sand
Form when sand piles up against shrubs, boulders, or other obstructions
Require loose sand and strong winds
Migrate downwind up to 30 m/yr burying oases, towns, farms
Movement controlled with vegetation and fences

13. Types of Dunes

14. Assignment
Read pages
Questions #1-6 on page 194