Chapter 13-Wind and Deserts

                  Physical Geology Illustrated Vocabulary
Cochise College                                                     
Geology Home Page  
Wind and Deserts
Roger Weller, geology instructor
wellerr@cochise.edu 
copyright 2018-Roger Weller    3/24/18


desert in Southern Nevada    

Vocabulary

aeolian

-refers to a wind-blown environment which might include sand dunes
or desert pavement.
An alternative spelling is eolian.

 

alluvial fan

-is a deposit of sediment deposited at the base of a mountain where a stream
coming off the mountain dumps its load. 
The sediments usually form a fan-like cone shape that gives this
structure its name.
-collection of alluvial fan views from Google Earth

-alluvial fan-1     

-alluvial fan-2 

-alluvial fan-3   
-alluvial fan-Opal's Pals 

 

badlands topography

-is an area almost devoid of plants that has eroded into a complex array of jagged pinnacles and
many narrow ravines.

-badlands in Bryce Canyon, Utah 

           

bajada

-consists of overlapping alluvial fans.

-bajada             

 

barchan

-is a sand dune with a crescent shape.
-barchans in Africa
-barchan sand dune-Opal's Pals

 

butte

-is a hill or small mountain, usually with steep sides, that stands apart from surrounding hills or
mountains.

-butte-1             

-butte-2             

 

caliche

-is soil cemented by lime (calcite) and may closely resemble concrete.  Caliche is very common
in the Southwest U.S.A.
-caliche-Opal's Pals

 

coalesced alluvial fans

-occurs where several alluvial fans overlap each other.

-coalesced alluvial fans             

 

cross bedding

-is a primary sedimentary structure in which one set of inclined sedimentary layers is beveled off
by an erosional process and a new set of sedimentary layers is deposited on top of the truncated
original layers; common in
stream sediments and sand dunes.

-cross bedding pattern             

-cross bedding-formed by stream flow             

 

desertification

-is the process by which a fertile area slowly becomes a desert.

 

desert pavement

-occurs when a desert surface is completely covered with a layer of wind polished interlocked
pebbles.  Desert pavement is appropriately named because it does resemble a paved surface.

-desert pavement             

 

desert varnish

-Rocks in a hot desert area, such as around the Phoenix, Arizona area, acquire a dark coating made
of iron and manganese oxides along with polymerized organic compounds.

-desert varnish-1            

-desert varnish-2             

 

Dust Bowl

-Dry, windy conditions during the 1930s subjected the Great Plains of the United States to great dust
storms that stripped away soil.

 

eolian

-is an adjective indicating a windblown, desert environment. An alternative spelling is aeolian.

 

exfoliation

-is a weathering process, common in semiarid regions, in which the weathered outer portion of a
granite boulder peels off in slabs parallel to the surface of the boulder.  Exfoliation is often
compared to the peeling away of layers of an onion.

-exfoliation             

-exfoliation, close up view 

           

flash flood

-occurs when a dry wash (stream channel) suddenly fills with water.  The water level in the
channel quickly raises, surge after surge.  Often the source of the water may be a rainstorm in the
mountains many miles away.

 

lee slope

-is the steep side of a sand dune that faces away from the wind
-saltation of sand-Opal's Pals

 

loess

-is a loose, silty soil, perhaps derived from rock flour (rocks ground up by glaciers) that has been
deposited by the wind.

 

mesa

-is a flat-topped mountain or plateau bounded at least on one side by a cliff; the term comes from
Spanish and means table.

 

pedocal

-is a soil found in semiarid regions. Pedocals are rich in the mineral calcite.

 

playa

-is a dry lake bed.

ripple marks
-can be created by wind blowing sand into a series of small ridges.
-sand ripple marks, Kihei beach, Maui, Hawaii
-close up view of sand ripple marks, Kihei beach, Maui, Hawaii

 

salinization of soils

-is the buildup of salt in the soil thereby decreasing the useful of the soil for agriculture. 
Salinization of soils is a serious growing problem in the western part of the United States.

 

saltation

-is a form of transportation of materials by rolling, bouncing, and skipping.
The term is often applied to wind-blown sand grains moving over the surface of sand dunes.
-saltation of sand-Opal's Pals

 

salt buildup

-If there is insufficient drainage of agricultural watering of crops, then salt, which is produced by
the breakdown of soil minerals, is not washed out of the system.  Consequently, the concentration
of salt slowly builds up until plants cannot live in the soil.

 

sandblasting

-is a form of physical weathering in which wind slams hard sand grains into softer substances

 

sand dune

-is a large pile of sand shaped by wind action.
-sand dunes in Africa

 

sandstorm

-is a violent storm, very windy, that picks up sand grains and causes sandblasting

stoss slope
-is the upwind side of a sand dune
-saltation of sand-Opal's Pals

 

thermal expansion

-occurs when most materials are heated.  Similarly, most materials contract in size when cooled. 
Repeated heat-cold cycles loosen grains within rocks and may cause the rock to eventually
crumble.

 

ventifact

-is a rock shaped by sandblasting.

 

White Sands, New Mexico

-is a national park near Alamogordo, New Mexico noted for large white sand dunes made of
gypsum.
-White Sands, New Mexico


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