About 10 of a non polar desert is

About 10% of a non -polar desert is dune covered Arid and Semi-Arid Landscapes 1. Arid (Desert) has Precipitation (mm) < 10 x Temperature in o. C 25 o C Desert < 25 cm = 250 mm rain 2. UNESCO index Desert Precipitation/Potential Evaporation < 0. 25 Aridity Index = Potential Evaporation/ Precipitation > 4. 0 Skip Lawson's Theory pp. 283 -284

World's Deserts about 1/5 th of land Types: subtropical, rain-shadow, coastal, interior, polar

Semi-Arid Semi-arid (Steppe, Savannah, dry grassland) has Precipitation (mm) > 10 x Temperature in

Flash Floods Role of Desert Varnish, lack of plant cover Stream Flood (c) 2004

Desert Landforms Produced By ba Water ja da alluvial fan Insel berg o arroy pla ya pedim ent pla ya

Arroyo - Water-Carved Canyon Usually dry

Playa, Salar, Sabkha A Playa in Death Valley, California Evaporite Pan of dried-up Playa

Inselberg, Monadnock, Kopje Uluru (Ayers Rock) Pediment

Eolian Processes The physics of wind generated landforms is studied using sand grains in wind tunnels Wind storm, Lothagam Hill dunes

Physics of Wind Transport Sandstorm • Air has low density, so wind is a relatively minor agent of geomorphic change • Rock density 2000 times density same volume of air so rock fragments are difficult to lift with air. • A one meter per second (1 m/sec) flow of water lifts the same particle as about 30 m/sec flow of air

Toadstools • "Undercut, mushroom shaped pedestal rocks in desert areas are commonly attributed to wind erosion" • Ignore Bloom's comments p 291 right 1 following the line above. • This area is frequently hit with high sandstorms. These remove the paint from our trucks. Water and wind formed erosional features such as this toadstool

Wind-Borne Sediment causes deflation and abrasion Sahara to Caribbean Effect on Hurricanes Surface creep

Desert Pavements or Reg Note desert varnish, lack of sand, Iron and Manganese oxides over everything Infiltration is slow – Flash Floods, and most water leaves the area

Desert Pavements (cont'd) – Hammada (Hamada) = barren rock Makes a great runway for supply aircraft Just clear away a few big rocks We tow makeshift rakes behind our Land Rovers Desert Pavement Source: Martin Miller

Erosional Landform - Deflation Hollow Anecdote – How fast does this occur?

Abrasion Origin of Ventifacts

Erosional Landforms - Ventifacts Wind eroded (sand blasted) surfaces

Erosional Landform - Yardangs Sphinx? White Desert, Egypt

Deposition Landforms of Eolian Sands • Reduced wind velocity results in sediments deposition • Dunes are hills of loose wind-born sand • Size, shape, and orientation of dunes are determined by available sand, vegetation, and wind Only 10% of desert surface Sand drift in Lee Of Mountains