Landforms CH 11
Have today's deserts always been deserts?
No, these landscapes used to be fields and forests but weathering, location, and temperature all played a role to turn it into a desert.
How can desertification in Africa affect the Caribbean?
Wind can blow particles from Africa into the Caribbean, some of them potentially toxic.
rain shadow desert
a dry area on the lee side of a mountain range
polar desert
a high-latitude region that receives very little precipitation
hogback
a narrow, sharp ridge formed on steeply inclined resistant rock
Bornhardts
a type of inselberg that has a loaf shape
dust storm
a windstorm that lifts up clouds of dust or sand. can be 100 km long and 1.5 km high
longitudinal dunes
abundant sand and a strong, steady wind, axis lies parallel to the wind direction
cuesta
asymmetric ridge that form in places where bedding dips at an angle
Why are playas found in almost all basins of the basin-and-range region?
because the depressions in the basins are ideal for the accumulation and evaporation of water
Why are alluvial fans and bajadas so common in the basin-and-range desert?
because there is a lot of canyons and flash floods occur periodically
What is a process that can change a mesa into a butte or pinnacle?
cliff retreat
coastal desert
cool dry air blows in from the ocean and evaporates occurs as it warms
barchan dune
crescent shaped dune, when sand is scarce and wind blows steadily in one direction
blowout
deflation on the land surface that scours a deep, bowl like shape
a lag deposit is also called a
desert pavement
What causes the process of desertification?
diversion of water, overpopulated arid areas, careless agricultural processes, overgrazing in arid areas, natural droughts
arid
dry
playa
dry, flat, exposed lake bed that come from desert lakes evaporating entirely
talus aprons
eroded bedrock form around cliff faces
suspended load
fine grain sediment such as dust and silt held in suspension
arches
formed when erosion along joints leave narrow walls of rock, having the lower part of the wall eroding while the upper part remains
Desertification
gradual transformation of temperate land to desert
ephemeral (intermittent) streams
have flowing water either episodically or during a portion of the year
cold deserts
high latitudes, high elevations, near cold ocean currents and stay below about 20 deg C for the year
subtropical desert
hot temperatures, extremely dry conditions, and sparse vegetation
Continental Desert
in continental interiors far from moisture sources
inselbergs
isolated, steep-sided erosion remnants that rise above desert plains
mesas
large, flat-topped hills
subtropical region
latitudes of 20-30
effects of desertification
loss of economic activity due to damage to agriculture, change of climate, reduction in species and biodiversity
buttes
medium-sized, flat-topped hills in an arid region.
which type of weathering is dominant in deserts
physical
sand dune
pile of sand deposited by a moving current
What two special conditions in deserts that tend to make fluvial erosion more likely when it does rain?
poor infiltration and lack of vegetation
deflation
process of lowering the land surface by wind erosion
water erosion in deserts
rainfall, sheetwash, and stream flow; causes more erosion than wind
how do you slow/stop the process of desertification
reduction in farming, cattle grazing and increase in vegetation
ventifacts
rocks shaped by wind blown sediments
what is the most important process of erosion and deposition in arid environments?
running water
chimneys
small sized, flat topped hills in arid regions
Desert characteristics
supports vegetation on no more than 15% of land, less than 25 cm of rainfall per year
hot deserts
temps exceed 35 deg C
desert varnish can reveal what about a desert?
that a desert surface has been exposed for quite some time as desert varnish takes a long time to form
lag deposit
the coarse sediment left behind in a desert after wind erosion removes the finer sediment
bajada
the elongated wedge shaped area between overlapping alluvial fans
alluvial fan
the network of distributaries that spread the sediment out into a broad fan, wedge or apron shaped pile of sediment
calcrete
when minerals that bind clasts together to form a new rock-like material
transverse dunes
when sand accumulates to bury the ground surface completely, and only moderate winds blow sand piles into simple, wave-like shapes
When do dunes form?
when sand becomes trapped on the windward side of an obstacle (rock or shrub)
parabolic dunes
when strong winds break through transverse dunes and change them into a parabolic shaped dune
When does Saltation begin?
when turbulence caused by wind shearing along the ground surface lifts sand grains
what creates smooth surfaces on rocks and boulders in the desert?
wind abrasion
star dune
wind shifts direction frequently, a group of crescents pointing in different directions overlap one another, constantly changing
desert varnish
A dark, rusty-brown coating of iron oxide and magnesium oxide that accumulates on the surface of the rock.
If the sand is relatively scarce, but the winds blow steadily in one direction the dunes that most likely will be formed are called___
Barchan Dunes
Why does the leeward side of a dune (the slip face) have a steeper slope than the windward side?
Because that is where sand "slips" down
types of deserts
Subtropical Continental Interior Rainshadow Coastal Desert Polar Desert
The Namib Desert lies to the north and west of the Kalahari Desert, in southern Africa. The reason that the former region is a desert is not the same as the reason that the latter is a desert. Explain this statement.
The Namib desert formed due to cold ocean currents which created dry air and decreased precipitation but the Kalahari formed due to its location's latitude and atmosphere
cliff retreat
The change in the position of a cliff face caused by erosion.
What factors determine which type of dune develops at a particular location?
The characteristic of wind and sand supply
saltation
The movement of sand or other sediments by short jumps, bounces, and rolls that is caused by wind. Saltating grins generally rise no more than 0.5m, but where sand bounces on bedrock, it may rise 2m.