Geology Cafe

Dust and Dunes: Wind-Dominated Processes and Environments

Dunes form in areas where loose sediments are exposed to the wind. They occur in desert environments where wind carries sand and dust off alluvial fans and dry lakebeds. Large dune fields accumulate where wind rises over mountain ranges, and sand is trapped. Dunes also form along shorelines where wind blows sand from beaches inland. California PrecipitationCalifornia's largest dunes occur in the southern arid regions of the Mojave Desert. Dunes fields formed in the past ~15,000 years after the last ice age, likely reworking sediments from lake beds and alluvial fans that dried up and lost vegetation when arid conditions replaced wetter environmental settings during the last ice age.
Click on thumbnail images for a larger view.
Dust devil in Death Valley. Dust devils are atmospheric current associated with rising air masses, sucking and pulling airstream entrained with dust-to-sand sized particles into the air. When atmospheric conditions are turbulent, material can be transported long distances, meters to many miles.
Sand ripples on Death Valley dunes.
A large dune in the center of the dune field is called a star dune. Star dunes are found typically near the center of a dune field that experiences. This star dune of the dune field near Stovepipe Wells in Death Valley.
This view is looking east from the top of the star dune in the dune field near Stovepipe Wells in Death Valley. The location of plants around the dune suggest that the dunes are in a fairly stable location. Wind changing between seasons moves sand back and forth in the dune field.  
Kelso Dunes in the Mojave National Preserve. This dune is a star dune. Wind and infrequent rains strip fine grained sediments off alluvial fans, creating surfaces covered with pebbles and cobbles. This type of surface is called a "desert pavement".
Aerial photograph of Death Valley near Stovepipe Wells. An alluvial fans form below the mouth of stream canyons draining from the Panamint Mountains. The alluvial fans provide sand to feed the dune field. During the last ice age, Lake Manly filled Death Valley. The dune field formed on the playa as the lake dried up. Rocks take on unusual shapes by being continuously sand blasted by desert winds. Rocks like these are called ventifacts.
Wind is a powerful force, strong enough to move large and heavy objects under the right conditions. This view shows a "sliding rock"on Racetrack Playa. Racetrack Playa is in a high mountain valley in Death Valley. Rocks slide on Racetrack Playa when the surface is wet. Rocks can move in strong winds across the slippery surface of the playa when it is wet, or possibly imbedded in ice sheets blown by the wind during the winter. Some of the trails left by rocks extend more than a kilometer.
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8/28/2012