Arid and Semi-Arid Landscapes ESCI 307, Fall 2003, Lecture 14 About 10% of a non-polar desert is dune covered 1. Arid (Desert) has Precipitation (mm) < 10 x Temperature in oC 25o C Desert < 25 cm = 250 mm rain 2. UNESCO index Desert Precipitation/Potential Evaporation < 0.25 Desert Aridity Index = Potential Evaporation/ Precipitation < 4.0 Skip Lawson's Theory pp. 283-284

World's Deserts Types: subtropical, rain-shadow, ESCI 307, Fall 2003, Lecture 14 about 1/5th of land Types: subtropical, rain-shadow, coastal, interior, polar

Semi-Arid Semi-arid (Steppe, Savannah, dry grassland) has Precipitation (mm) > 10 x Temperature in oC but < than 20x (c) 2004-2009 Charles L. Smart. All rights reserved

Flash Floods Role of Desert Varnish, lack of plant cover Stream Flood ESCI 307, Fall 2003, Lecture 14 Flash Floods Role of Desert Varnish, lack of plant cover Stream Flood (c) 2004-2009 Charles L. Smart. All rights reserved

Desert Landforms Produced By Water ESCI 307, Fall 2003, Lecture 14 Desert Landforms Produced By Water bahada alluvial fan Inselberg playa arroyo pediment playa

Arroyo - Water-Carved Canyon ESCI 307, Fall 2003, Lecture 14 Usually dry

Playa, Salar, Sabkha A Playa in Death Valley, California ESCI 307, Fall 2003, Lecture 14 Playa, Salar, Sabkha A Playa in Death Valley, California Evaporite Pan of dried-up Playa

ESCI 307, Fall 2003, Lecture 14 Inselberg Uluru (Ayers Rock) Pediment

ESCI 307, Fall 2003, Lecture 14 Eolian Processes We have been studying the physics of wind generated landforms when we consider sand grains in wind tunnels Wind storm, Lothagam Hill dunes

Physics of Wind Transport ESCI 307, Fall 2003, Lecture 14 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

ESCI 307, Fall 2003, Lecture 14 Toadstools "Undercut, mushroom shaped pedestal rocks in desert areas are commonly attributed to wind erosion" Ignore Bloom's comments p291 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 ESCI 307, Fall 2003, Lecture 14 Wind-Borne Sediment causes deflation and abrasion Sahara to Caribbean Effect on Hurricanes Surface creep

Desert Pavements or Reg ESCI 307, Fall 2003, Lecture 14 Desert Pavements or Reg Note desert varnish, lack of sand, Iron Oxide over everything Infiltration is slow – Flash Floods, and most water leaves the area

Desert Pavements (cont'd) – ESCI 307, Fall 2003, Lecture 14 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 ESCI 307, Fall 2003, Lecture 14 Erosional Landform - Deflation Hollow Anecdote – How fast does this occur?

Abrasion Origin of Ventifacts ESCI 307, Fall 2003, Lecture 14 Abrasion Origin of Ventifacts

Erosional Landforms - Ventifacts ESCI 307, Fall 2003, Lecture 14 Wind eroded (sand blasted) surfaces

Erosional Landform - Yardangs ESCI 307, Fall 2003, Lecture 14 Sphinx? White Desert, Egypt

Deposition Landforms of Eolian Sands ESCI 307, Fall 2003, Lecture 14 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 Sand drift in Lee Of Mountains

Dunes form in a lee High velocity zone ESCI 307, Fall 2003, Lecture 14 Dunes form in a lee High velocity zone Dunes are accumulations in the lee of local obstructions, possibly an upwind dune

Dune Migration Windward slope Slip face (deposition) ESCI 307, Fall 2003, Lecture 14 Dune Migration Windward slope erosion and transport Slip face (deposition) Just like ripples in a stream

ESCI 307, Fall 2003, Lecture 14 Star Dunes

Star Dunes Variable Wind Direction Copyright © Frank Eckardt 2002

Longitudinal Dunes Constant wind direction, no vegetation ESCI 307, Fall 2003, Lecture 14 Longitudinal Dunes Constant wind direction, no vegetation

Longitudinal Dunes Constant wind direction, no vegetation ESCI 307, Fall 2003, Lecture 14 Longitudinal Dunes Constant wind direction, no vegetation

Transverse Dunes Massive volumes of sand, low consistent winds ESCI 307, Fall 2003, Lecture 14 Massive volumes of sand, low consistent winds

Transverse Dunes Massive volumes of sand, low consistent winds ESCI 307, Fall 2003, Lecture 14 Transverse Dunes Massive volumes of sand, low consistent winds

Barchan Dunes Isolated Dunes, low sand supply, migrating across rock ESCI 307, Fall 2003, Lecture 14 Isolated Dunes, low sand supply, migrating across rock

Barchan Dunes Isolated – low sand supply; migrating across rock ESCI 307, Fall 2003, Lecture 14 Barchan Dunes Isolated – low sand supply; migrating across rock

Parabolic Dunes Typical of coasts Horns pinned by plants ESCI 307, Fall 2003, Lecture 14 Horns pinned by plants Typical of coasts

Parabolic Dunes Stabilized “horns" point upwind ESCI 307, Fall 2003, Lecture 14 Parabolic Dunes Stabilized “horns" point upwind

Dunes in Victoria Crater - Mars ESCI 307, Fall 2003, Lecture 14 Dunes in Victoria Crater - Mars

Suspended Load Transport and Deposition ESCI 307, Fall 2003, Lecture 14 Suspended Load Transport and Deposition In dry areas very high winds can suspend fine sand particles

ESCI 307, Fall 2003, Lecture 14 Suspended Load Dust

Loess from the Columbia River Basin ESCI 307, Fall 2003, Lecture 14 Loess from the Columbia River Basin Loess deposits are (usually) of glacial outwash silt. These thin downwind.

Global loess Origins Desert Glacial ESCI 307, Fall 2003, Lecture 14 Global loess Origins Desert Glacial Layers of dust from Patagonia appear in Vostok cores just prior to interglacials

End Arid and semi-arid What type of dune? Wind ESCI 307, Fall 2003, Lecture 14 End Arid and semi-arid What type of dune? Wind