Desert Landforms. What % of land area is desert? About 30%

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 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

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 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

Sand Dunes

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

Barchan Dunes

Deflation – Blowouts