Desert Landforms

What % of land area is desert? About 30%

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 RegionsDesert 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

Southwest United States

Where is this? Colorado Plateau – Grand Canyon

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

Butte

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

Basins and Ranges A = Alluvial fan B = Playa C = Pediment D = Box Canyon

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

Role of Wind is Limited Wind erosion take two forms –Wind abrasion –Deflation

Wind Abrasion Wind is not as important as once thought in carving impressive arches and rocks Why? Most abrasion is limited to the first 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

Sand Dunes Depositional landforms Sand dunes are relatively rare - 10–25%

Barchan Dunes

Deflation – Blowouts