Characteristics of Deserts Besides being dry few plants

Characteristics of Deserts Besides being dry > few plants > consist of nearly continuous rock and/or sand exposures > little soil development • Weathering, erosion, & deposition still operate, but more slowly. > in In a balance with the local climate

The Distribution of Deserts • Deserts form in two regions > areas of persistent high pressure - latitude effects related to Hadley Cell circulation > Areas on the lee side of Topographic Barriers (lee= downwind side) barriers - rainshadow effect > other things influence too - cold water ocean currents - extremely cold temperatures

Area of persistent arid conditions (subtropical desert)

Distribution of Arid and Semiarid Regions • Subtropical deserts occur at 20 -30° N-S latitude. Gobi Mojave Sonoran Chihuahuan Thar Sahara Atacama Arabian Kalahari Namib Australian Patagonian Antarctica

Rainshadow Deserts • Air that must cross coastal mountains loses much of its moisture, thus when it arrives over the inland areas it is drier.

Distribution of Arid and Semiarid Regions • Rainshadow deserts occur in places down wind of major mountain chains like the Himalayas, Sierra Nevadas, and Andes.

Weathering and Soils • Mechanical weathering dominates desert regions. • Chemical weathering is not effective > Rock varnish is a thin coating of iron and/or manganese oxides on many surface rocks in deserts.

Agents of Change • Water scarce >> scarce when it it rains, it it really rains hard! >> when erodes and deposits distinct landforms >> erodes -- no no plants to to slow erosion down • Wind common >> common lack of of plants facilitates effectiveness as as an an >> lack agent of of change. agent erodes and deposits distinct landforms >> erodes

Exotic & Local Streams • Local braided streams in deserts flow. infrequently- known as Arroyos • Arroyos usually exhibit braided channels coarse-grained sediments >> coarse-grained prone to to severe flash floods! >> prone • Exotic Streams Perennial rivers that begin outside the desert >> Perennial -- Nile River, Egypt. -- Colorado River, Southwest US. Can be be either Meandering or or Braided >> Can