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45 Cards in this Set
- Front
- Back
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Desert
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~Region w/ low precipitation
~Usually less than 25 cm of rain per yer |
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descending air
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Deserts distribution is related most to
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Desert distribution
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~Belts at 30 degrees North and South latitude
-Polar desserts -Not on Equator |
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oceans
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Deserts occur great distances from
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cold ocean currents
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Deserts occur in tropical coast next to
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Characteristic of desert
(Sparse Vegitation) |
- Drought tolerant
- Deep Rooted - Thick cuticled leaves or no leaves |
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Characteristic of desert
(Lack of through-flowing streams) |
-Internal Drainage
-Local base levels |
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Characteristic of desert
(Dessert Thunderstorms) |
- Paralled cliff retreat- running water in a dessert: where the greatest amount of erosion occurs (even more than wind)
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Charactertic of desert
(Flash floods) |
-mudflows
-dangers in slot canyons |
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Characteristic of desert
(Resistance of rocks to weathering) |
-desert topography typically steep and angular
-plateaus held up by resistant rocks -erode 2 mesas and buttes |
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Characteristic of desert
(Stream channels normally dry:arroys) |
-covered w/ sand and gravel
-narrow, slot canyons w/ vertical walls |
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Examples of parallel cliff retreat in u.s. dessert
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plateaus, mesas, buttes
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Colorado plateau
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-mostly flat lying sedimentary beds
-most erosion occurs during infrequent rains |
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2 major dessert regions of the U.s. Southwest
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-Colorado plateau
-Basin and Range Providence |
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Basin and Range province ( nearly all Neveda)
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-Alluvial fans at slope breaks coalesce to form a bajada
-playa lake |
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playa lake
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an internal drained lake
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playa
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the deposit/mud and evaporate minerals
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Death Valley
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-A fault-bounded valley in southern California (Basin and Range)
-More than 250 below sea level -Mudcracks, salt and other evaporate deposits |
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Dust storms
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moves "fines" out of source area
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sand stays close to
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source area
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saltation
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sand moves along ground by
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Ventifact
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rocks 2 large 2 move
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Deflation
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-Blowout
-Controlled by water table |
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one meter
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Sandblasting above ground up to
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Strong wind action
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100 km/h
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reasons for strong wind action in the desert
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-low humidity
-great temperature ranges -more effective b/c of lack of vegitation |
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reasons for effective erosion in deserts
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-sediment is dry (no surface tension)
-sand is more easily eroded than silt or clay sized particles -Fines are carried much farther |
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Loess
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deposits of wind blown "fines"
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Desert pavement
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the gravel that the wind cannot move
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sand
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loess is harder to erode than
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Loess travels by
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suspension farther (may go 100's of miles from source)
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Desert Varnish
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Very fine, wind-blown material may form as
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Desert Varnish on rock surfaces
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Iron and Manganese oxide coatings on wet rock surfaces
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Barchan dunes
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- formed where sand supply is limited
- horns point in down-wind direction |
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Transverse dunes
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-more sand and elongate form
-wave perpendicular to wind pattern |
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Parabolic dunes
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-Requires abudant sand-beaches
-horns point in up-wind direction -Commonly form around a blowout |
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longitudinal or sief dunes
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-large: to 650 high and 75 miles long
-Parallel to wind |
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fines but settles first
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sand erodes easier than
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A ventifact
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not a depositional feature
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slip face
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Dunes migrate in the direction of their
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The lower limit of a "blowout"
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the water table
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sand dunes sand
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-well sorted,well rounded, frosted sand grains
-saltation movement over the gentle slope to the slip face |
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steep beds (cross beds)
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sand is deposited in
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slip face
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-angle of repose
-this surface "faces" down wind |
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the gentle surface
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in sand dunes wind ripples may occur on
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