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How do desert landscapes differ from humid landscapes?
Great
Basin – Fault block mountains
Colorado Plateau
Humid Landscape
How do desert landscapes differ from humid regions?
• Rounded hills• V shaped valleys• Soil and vegetation
mask geology• Mass wasting • Streams reach ocean
• Angular landforms• Box-shaped canyons• Naked landscape reveals
geology• Very little mass wasting• Most streams are short and
short-lived• End up in internal drainage
basins• Exception: exotic rivers
Humid Regions Desert Regions
What is the dominant process shaping the desert landscape?
• Running water or wind?
• Running water is most important
Why is running water important in deserts?
• Landscape has little vegetation to absorb water so it quickly runs off
• Rain comes in torrential downpours• A sudden flashflood can move tons of loose
rocks in minutes
United States Deserts
• Most U.S. deserts are rocky deserts
• Colorado Plateau– Horizontal sedimentary rock
• Basin and Range– Fault block Mountains
Colorado Plateau
• Alternating hard and soft rock layers
• Hard rocks form cliffs
• Soft rocks form shelves
• Grand Canyon has a stair-step appearance
• Isolated hard rocks – mesas and buttes
Fault Block Mountains of Great Basin
• Note the fault block mountains and ranges
• Ranges are eroded by flash floods that cut box canyons
• Alluvial fans form at the mouth of canyons
Alluvial fans and Playas
• Fine sands and salts accumulate in playa lakes• Playa lakes evaporate into saltflats• Erosion lowers the mountains until the landscape
forms a surface of low relief called a pediplain
Wind Abrasion
• Wind is not as important as once thought in carving impressive arches and rocks
• Why?• Most abrasion is limited to the first 18-24
inches above the ground• Abrasion and deflation form desert
pavement • A layer of coarse rocks and pebbles
Duststorm
Deflation – the removal of fine sand and dust by the wind
Leaves behind blow-outs or deflation hollows