Geol 202:Physical Geology

Organizationsecond lecture: deserts and wind action

Chapter 18Deserts &

the Work of Winds

ARID LANDS – CAUSES & TYPES

Deserts worldwide

Atmospheric convection cells

Rain shadow

Sonoran Desert vegetation, Tucson AZ

GROUND PROCESSESIN ARID LANDS

Desert varnish, Panamint Valley CA

Rock varnish, Utah

Desert varnish, Death Valley

Desert pavement, Panamint Valley

Desert pavement pebbles, Death Valley

WORK OF WATER IN DESERTS

Desert landscape features

Arroyo, flash flood, NE Arizona

Playa

Stages in pediment formation

Ayers Rock, Australia – inselberg

WORK OF WINDS

Aeolus

Greek god of winds

Ventifacts – Lake Vide, Victoria Valley, Antarctica

Ventifacts

Yardang in Roman Playa, Egypt

Yardang

compact

lake

sediment

Rogers

Lake

Playa

Southern

California

Desert and wind abrasion

Erosion (Pillar of God) sandstone butte on pyramid of shale

Colorado Plateau landforms

Monument Valley

Butte in Monument Valley, Arizona

EOLIAN DEPOSITION

Particle size is used to distinguish among various clastic rock types

Erosion of soil – Texas

Erosion – St Park field, 1 m deflation since 1977

Grand Mar

Eolian

sand ripples,

Monument

Valley,

Arizona

Ripple marks

Death Valley

Modern eolian ripple marks

Wind dunes

Great Sand Dunes, Colorado (200m, some of tallest in world)

Great Sand Dunes N Pk, Colorado

Great Sand Dunes N Pk, Colorado

Dra dunes, Africa’s Namib Desert

Dune types

Transverse dunes

Sand dunes, Tsangpo River

Transverse and barchans – Takla Makan Desert, China

Longitudinal dunes

Simpson Desert,

Australia

Longitudinal dunes

Dune types

Barchan dunes

west of the Salton

Sea, CA

Barchan dunes

Transverse dunes; crescent shaped barchan dunes

Parabolic dune, Michigan

Star dunes

Sand Hills of Nebraska – North America’s largest dune field

Loess in U.S.

Boulder, Colorado dust storm

Loess blowing from deflation of floodplain downstream from Tasman Glacier, NZ

Loess cliff

Yellow River

Xian, China

Loess cliff, Miss.

Loess house

in loess cave

Xian, China

Loess paleosol in Peoria Loess, Vicksburg (east 2 miles on I-20)

Loess

paleosol

below Adam’s hand

Vicksburg

(east 2 miles on I-20)

Loess

Yellow River

loess plateaus

Paleosols developed on loess

DESERTIFICATION

Encroachment on pasture – sand dune in Niger

Barchan dunes – Danakil depression (Ethiopia) irrigated field

next: Chapter 17 – Glaciers