Earth Sciences 1022A/B Lecture 18: Earth Science Lecture March 17 2016

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MARCH 17 2016 LECTURE
DESERTS AND WINDS
Deserts are dry places where there is low precipitation and little vegetation.
Geologic Processes
In spite of lack of water and vegetation processes still occur
Weathering
oAlmost entirely mechanical and very slow due to low precipitation
However, clays and thin soils form by oxidation of ferromagnesian silicate
minerals
Water
oEphemeral streams and flash floods from short, intense rainstorms do most of
the erosion of desert surfaces, especially sediment not anchored by vegetation
Transportation of Sediment by Wind
Wind can move faster than water and carries sediment farther and higher than streams
because flow is not confined to channels
Bedload
oSand moves by saltation and by rolling over the ground
Grain collisions
Suspended load
oDust particles are pushed into the air by saltating sand grains
The grains are then swept up by the wind in dense clouds and carried
high into the air
Wind Erosion
Occurs by deflation and abrasion
oDeflation
Blowing away fine sediment to create blowouts while leaving coarser
particles behind that cover the desert floor as desert pavements
oAbrasion
Mainly by saltation as particles sandblast things
Wind polishes, pits and facets stones sitting on desert floor and
streamlines ridges
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