global environment chapter 15: eolian processes and arid landscapes
largest dunes
star dunes
The motion of _________ _______ slides and rolls particles too large for saltation.
surface creep
eolian processes transport dust, silt, and sand by ___________
suspension, saltation, and surface creep.
In the U.S. interior west, the _________ is known for its north-and-south-trending basins and mountains
the Basin and Range Province
badlands are another example of _________
the erosive work of water in arid and semiarid regions
only_________ travel significant distances
the finest dust particles
deflation
the process by which wind removes surface materials
barchan dunes form ___________
usually in areas with limited sand supply and little or no vegetation
Rocks that bear evidence of eolian abrasion
ventifacts
How are ventifacts and yardangs formed by wind processes?
ventifacts: -pitted, fluted, grooved, polished from erosion -direction determined by consistent flow of airborne particles in winds yardangs: -larger scale -deflation + abrasion -abrasion on windward, deflation on leeward
List some landforms unique to arid regions and explain their formation.
*alluvial fans *bajada *playa *badlands *basin and range province *mesa *butte *inselberg
Discuss eolian erosion and the resultant landforms.
*deflation -deflation hallows -blowouts *abrasion *ventifacts *yardangs *desert pavement
Discuss the causes and consequences of desertification.
*desertification
Explain the formation of sand dunes and describe loess deposits and their origins.
*dunes *erg -sand sea -slipface -crescentic -linear -star *barchan dunes *star dunes *loess
Describe eolian transport of dust and sand.
*eolian *surface creep
What processes are involved in the formation of an alluvial fan?
-flowing water (like flash flood) loses velocity as it leaves a canyon -stream drops sediment layers on base of mountain block -water flows over surface of fan -> braided channel
What is the arrangement, or sorting, of alluvial material on the fan?
-naturally sorted by size -coarsest materials: near mouth of canyon/apex of fan -finest clays carried in suspension + solution all the way to valley floor
Explain the concept of surface creep.
-particles larger than 0.5mm (too large for saltation) slide along ground -can collide w/saltating particles, knocking them loose -mechanism for wind transport
an example of aligned pairs of normal faults and a distinctive horst-and-graben landscape
Basin and Range Province region
desertification
Degradation of land, especially in semiarid areas, primarily because of human actions like excessive crop planting, animal grazing, and tree cutting.
__________ crash into other particles, knocking them both loose and forward.
Saltating particles
surface creep
Sediment transport in which the wind causes particles to roll along the ground.
abrasion
The grinding away of rock by other rock particles carried in water, ice, or wind
badlands
Wasteland that has been carved into unusual shapes by wind and water
As the height of the sand pile increases above 30 cm (12 in.) _____________
a steeply sloping *slipface* on the lee side and characteristic dune features are formed
yardang
a streamlined rock structure formed by deflation and abrasion; appears elongated and aligned with the most effective wind direction
ventifact
any rock that is pitted, grooved, or polished by wind abrasion
rugged terrain of slopes dissected by rills and gullies
badlands
A ______ may form where individual alluvial fans coalesce along a mountain block.
bajada
form with their tips pointing downwind
barchan dunes
low-elevation areas that dip downward toward the center
basins
smaller, steep-sided landforms that form from the weathering and mass wasting of mesas
buttes
Wind, or _________, processes transport dust, silt, and sand by supension, saltation, and surface creep.
eolian
What is the difference between eolian saltation and fluvial saltation?
eolian saltation: -fine grain sand bounces + skips -wind transport -only works for dry surface material fluvial saltation: -river/water transport
An extensive area of dunes, such as that found in North Africa
erg or sand sea
What is the role of chemical weathering processes in arid environments?
ex] desert varnish/rock varnish -thin, dark coating of clay + iron + manganese -> metabolized by microbes -> oxide minerals ex] cave/side of cave drawings
erg
extensive area of sand and dunes
mesa
flat-topped landforms with steep slopes on all sides, elevated above surrounding landscape
What is the origin of loess in the Palouse?
glacial sources
star dunes are formed __________
in areas with shifting wind directions
an isolated remnant formed of resistant rock, a product of weathering and erosion
inselberg
With water diversions for agriculture and development ___________
lakes are shrinking
The finer material suspended in a dust storm is __________ than are the coarser particles of a sandstorm
lifted much higher
Windblown ________ consists of fine-grained clays and silts that are moved long distances by wind and are redeposited as an unstratified, homogeneous blanket of material
loess
Together, these features form the ____________ ________ seen in parts of Arizona and Utah
mesa-and-butte topography
flat landforms with steep slopes on all sides that are elevated above the surrounding landscape
mesas
Differential erosion can produce ________ and _____
mesas, buttes
Describe two landforms associated with basin and range topography.
mountains + valleys ex] Death Valley, CA
In other regions, _____ ______ resources has combined with ________ to cause desertification
overexploitation of water, drought
In some drylands, ___________ is a primary cause of desertification, often in combination with socioeconomic factors.
overgrazing
Runoff may flow all the way to the valley floor where it forms a _________
playa
a low, intermittently wet area in a region of internal drainage
playa
interconnected mountains of varying elevations above the basins
ranges
lakes are shrinking, leaving _________ and ________ that is moved by ______ across the landscape.
salt and dust, wind
deflation hollows, or blowouts ranging in size from _________
small indentations less than a meter wide up to areas hundreds of meters wide and many meters deep.
overgrazing is a primary cause of desertification often in combination with ___________
socioeconomic factors.
desertification currently affects ___________
some 1.5 billion people
Describe and explain the recent changes at Lake Urmia in Iran.
-vanishing lake -> worsening desertification -decreased 88% since 1970s -shrinking even during times of enough rain -water withdrawals for agri + development = main cause -shallow water -> shoreline covered in salt deposits -increased salinity -> not safe for brine shrimp -> no food for migratory birds
basin and range province
A broad, Cenozoic continental rift that has affected a portion of the western United States in Nevada, Utah, and Arizona; in this province, tilted fault blocks form ranges, and alluvium-filled valleys are basins.
butte
A flat topped rock or hill formation with steep sides. related: mesa
dune
A hill or ridge of sand piled up by the wind
desert pavement
A layer of coarse pebbles and gravel created when wind removed the finer material. related: deflation, sheetflow
barchan dune
A solitary sand dune shaped like a crescent with its tips pointing downwind.
alluvial fan
A wide, sloping deposit of sediment formed where a stream leaves a mountain range related: bajada
loess
A wind-formed deposit made of fine particles of clay and silt
bajada
An apron of sediment along a mountain front created by the coalescence of alluvial fans. related: alluvial fan
star dune
An isolated hill of sand that exhibits a complex form and develops where wind directions are variable.
the "sandblasting" of rock surfaces with particles captured in the air
abrasion
Along mountain fronts in drylands, _______ ______ develop where ephemeral stream channels exit from canyons into the valley below.
alluvial fans
What world regions are affected by desertification?
along margins of semiarid + arid lands -worldwide -covers 1.9 billion hectares + affect 1.5 billion people -more land each year
inselberg
an isolated mountain
playa
area of salt crust left behind by evaporation on desert floor
What are the main causes and consequences of desertification?
causes: -poor agricultural practices (overgrazing, abusing soil structure + fertility) -improper soil-moisture management -salinization + nutrient depletion -deforestation -climate change consequences: -expansion of deserts -less rainfall -deterioration of vegetation + soils -Loss of biodiversity -Food insecurity due to crop failure or reduced yields -loss of vegetation cover and therefore of food for livestock and humans -Increased risk of zoonotic diseases, such as COVID-19
Dune forms are broadly classified as_________
crescentic, linear, and star
Erosion of the ground surface from the lifting and removal of particles by wind
deflation
Wherever wind encounters loose sediment, deflation may remove enough material to form depressions
deflation hollows, or blowouts
eolian
deposited by wind
name for the hard, stony surface that forms in some deserts and protects underlying sediment from erosion.
desert pavement
The ongoing degradation of drylands caused by human activities and climate change
desertification
When saltating sand grains encounter small patches of sand, kinetic energy is _________, and the grains start to _____________
dissipated, build into a dune
Wind exerts a __________ on surface particles until they become airborne
drag or frictional pull
wind-sculpted accumulations of sand that form in arid and semiarid climates and along some coastlines where sand is available
dunes
What is deflation and what role does it have in the formation of desert pavement?
what is it: erosion of ground surface from lifting + removal of individual particles by wind desert pavement: hard stony surface (not usual sand) role: wind removes fine particles -> leaving larger pebbles, gravels, + rocks -> consolidated desert pavement
Where does the sediment that forms the loess deposits of China come from?
windblown desert sediment
These windblown deposits occur _______ and can develop into _____ ______ ______
worldwide, good agricultural soils
deflation and abrasion are capable of streamlining rock structures, leaving behind distinctive rock formations or elongated ridges
yardangs