DESERT DEPOSITIONAL FEATURES
Dune - a hill or ridge of wind-deposited sand; sand is trapped on a soft surface & a dune appears,
it migrates as wind erodes sand from its windward surface & deposits it on its leeward
surface. The leeward side has an angle of repose of ~30° while the windward side is more
gentle. Dune sand has a narrower range of grain sizes than beach or river sand. Wind
gathers dunes into vast dune fields. Dunes can be stabilized by plants.
Types of Dunes - depends on wind strength & direction, sand supply, & vegetation.
a) transverse or aklé - at right angles to the wind; occurs where vegetation is sparse & sand is
plentiful
b) barchan or crescentic - crescent-shaped with horns pointing downwind; occurs in dry
vegetation-free areas with limited sand
c) parabolic - similar in shape to barchan but facing opposite direction (i.e. horns point upwind);
occurs in moist areas with vegetation
d) longitudinal or seif - linear ridges aligned in direction of wind
e) star or rhourds - caused by winds from many directions, dune grows vertically
f) grid - caused by seasonal or long-term changes in wind direction
2) Drift - streamlined heaps of sand trapped in the wind shadows behind obstacles, they do not
move
3) Sand Ripples - trains of sand in straight & regular ripples caused by the wind with coarser
grains on the crests & smaller ones in troughs (opposite of those caused by water; by
observing ripples in ancient sandstone, it can be determined what type of environment
they were laid down in)
4) Loess - wind-deposited silt originating in glacial outwash plains or in desert regions
5) Alluvial Fans - caused by streams flowing from mountainous areas to flat areas & the
sediment builds up at the base of these mountains; poor sorting
6) Bajadas (Alluvial Aprons) - alluvial fans that join together laterally
DESERT EROSIONAL FEATURES
1) Desert Pavement - thin veneer of stones several stones thick, results as deflation
lowers the surface until only heavier particles remain
2) Desert Varnish - thin, shiny, bluish-black coating composed largely of Fe & Mn
oxides formed on stones & cliffs. Not sure how it forms
3) Ventifacts - wind-carved rocks; have concave surfaces (facet) that meet in sharp edges
& corners
4) Arroyo - steep-sided, flat-floored channel of an intermittent stream
5) Plateau - broad relatively flat or gently rolling region at high elevation exhibiting
“layer cake geology” (horizontal layers of sediment)
6) Mesa - large flat-topped remnant of a plateau that has been eroded down
7) Butte - similar to a mesa but smaller
8) Badlands - rough, steeply gullied terrain usually found in dry areas
9) Pediment - an erosional bedrock surface that slopes away from a desert mountain
range
10) Inselberg - isolated residual hill that rises abruptly above the surrounding plain in a
dry region (ex: Ayers Rock)
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Desert Lakes
Playa Lake - seasonal lake in the center of a desert basin, usually very shallow &
temporary
Playa - dried-up playa lake consisting of clay & silt or sand & soluble salt deposits