Wind processes shape desert landscapes through erosion, transportation, and deposition of materials. Erosion occurs through abrasion and deflation. Transportation is primarily through saltation and surface creep. Deposition forms sand dunes and loess. Different types of dunes like barchan and transverse form depending on factors like wind strength and direction and sand supply. Desert landscapes cover 35% of Earth's surface and include features like washes, playas, and alluvial fans adapted to arid conditions. The Colorado River flows through arid lands and seven states facing issues of overuse and political agreements regulating its flow. While grazing has been identified as a cause of desertification in some local areas, the idea of it as a global

1. Wind Processes and Desert Landscapes

2. Overview Eolian (Aeolian) processes Erosion deflation and abrasion Transport saltation and surface creep Deposition sand dunes and loess Desert landscapes

3. Eolian Erosion Abrasion “ sandblasting” ventifacts Deflation Occurs where there is a mixture of cobbles and gravel with finer material (typically sand) Wind removes finer material, leaving only the cobbles and gravel (desert pavement)

6. Eolian Transport Suspension Saltation Creep

7. Eolian Deposition Heavier material drops out of the wind before lighter materials Sand deposited before silt and clay particles Deposition of sand forms sand dunes Deposition of clay and silt forms loess

8. Global Sandy Areas

9. Global Loess Deposits

10. Global Dry Regions

11. Dune Processes

12. Types of Sand Dunes Several factors influence the formation of the various sand dune landforms Strength of the wind Prevailing wind vs. shifting winds Presence of vegetation Amount of sand present Movement Free Dunes Tied Dunes

15. Crescentic Dunes Barchan Free dunes Scarce sand Consistent and effective wind from one direction Single slipface Horns of crescent point downwind Barchanoid Ridge merged barchans

20. Transverse dunes Free dunes Abundant sand supply Less effective wind Consistent direction of the wind Single slipfaces

22. Parabolic Tied dune Vegetation stabilizes movement Consistent wind direction multiple slipfaces crescents point upwind

24. Linear Dunes Longitudinal Winds variable in one direction Ridge forms parallel to consistent wind direction two slipfaces 100 – 400 m tall, up to 100 km long Seif Sharp crest shorter in height

28. Star Dunes Star Dunes Winds variable in all directions Multiple slipfaces With effective winds, form high mounds With less effective winds, form networks of connected sinuous arms

32. Desert Landscapes Arid areas are the largest climatic region on earth (35% of earth’s surface) Fluvial features Flash flooding Washes, arroyos, wadis Bursts of vegetation growth Playas interior drainage salinization Alluvial fans bajadas Landscape features Adapted vegetation Basin and Range Province Horst and Graben, interior drainage, playas, alluvial fans

37. Colorado River Issues Headwaters originate in the Rocky Mountains High levels of rainfall Snow melt Flows through an extremely arid area with few feeding tributaries High demand on water means that often no water actually makes it to the sea Flows through seven states, into Mexico Beliefs on the river’s capacity based on a 400 year high mark (greatly overestimated) Subject to a variety of political treaties and agreements regulating its flow In many cases, quotas are exceeded, esp. with California

38. Desertification Refers to the expansion of desert biomes due to a combination of poor agricultural practices and climate change grazing has been identified as a major cause As a global phenomenon, this idea has largely been falsified Areas identified as “desertifying” were simply experiencing drought-like conditions, in conjunction with ENSO cycles; many have recovered There are some areas where desertification has occurred, but it is not a global phenomenon