Geol 202: Physical Geology Organization second lecture: deserts and wind action
Chapter 18 Deserts & the Work of Winds
ARID LANDS – CAUSES & TYPES
Deserts worldwide
Atmospheric convection cells
Rain shadow
Sonoran Desert vegetation, Tucson AZ
GROUND PROCESSES IN 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
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