Desert
any region with an arid climate that receives less than 25 cm (10 inches) of precipitation per year
running water
the predominant force shaping most desert landscapes
Most deserts are associated with areas where
air is descending
rainshadow
A region on the downwind side of mountains that has little or no rain because of the loss of moisture on the upwind side.
shale/mudstone
the least resistant rock in a desert
plateaus
broad, flat-topped areas elevated above the surrounding land
mesa
a broad, flat-topped hill bounded by cliffs and capped by a resistant rock layer
Butte
a narrow hill of resistant rock with a flat top and very steep sides
monocline
a step-like fold in rock layers
Hogback
Steeply tilted resistant layer, Sharp-topped ridges formed by the erosion of steeply dipping beds
Cuesta
Gently tilted resistant layer with one steep side
desert washes/arroyos
commonly steep-sided, with flat floors covered by loose sediments - a result of rare but highly erosive flash flood events
bajadas
coalesced fans
playa
a very flat surface underlain by hard, mud-cracked clay, a dry lakebed
Pediment
A gently sloping erosional surface cut into the solid rock of an eroding mountain range; usually covered with a thin veneer of sediment
Pediment development
As the mountain front erodes, it retreats uphill, maintaining a constant slope on the mountain front and the pediment.
wind
is an important agent of erosion and transportation of fine sediments in desert regions
wind differs from water in 2 different ways
Air is less dense than water and can erode only fine sediment
Wind is not confined to channels and wind can have widespread effects over vast areas.
deflation
The removal of clay, silt and sand particles from the land surface. A blowout is a depression on the land surface caused by wind
ventifacts
rocks with wind-abraded surfaces
Desert pavement
: A thin, surface layer of closely packed pebbles.
Two possible causes: as lag deposits, left behind as strong winds blow away the fine grains or by cycles of wet and dry periods causing the soil to swell and shrink...raising the pebbles to the surface.
Loess
a deposit of wind-blown silt and clay composed of unweathered, angular grains of quartz, feldspar and other minerals (glacial rock flour) weakly cemented by calcite.
sand dunes
mounds of loose sand piled up by the wind. Generally develop in areas with large sand supply and winds that generally blow in the same direction
Asymmetrical in cross section
Gentle slope facing the wind
slip face
Steep slope on downwind side
different types of sand dunes form depending on:
the amount of sand available
wind's velocity and direction (that is, whether constant or shifting)
and arrangement of any existing vegetation cover
Barchans
crescent-shaped, with horns that point downwind and a steep slip face on the concave side
Sand supply is limited
Transverse Dunes
Relatively straight, elongate dunes oriented perpendicular to the wind direction
Where more sand is available
Parabolic Dunes
Form around blowouts in areas with abundant sand, and have horns that point upwind which are typically anchored by vegetation
Deeply curved, look similar to barchans, but are convex in the downwind direction
Longitudinal
Form in areas with large sand supply, parallel to the prevailing wind direction - the largest type of dune