what is the most important agent of erosion in deserts?
running water, although it is infrequent.
inselberg
last stage of erosion. means "island mountains". large bedrock knob or mountain projecting above the surrounding sediment-filled basin
playa lake
pond that lasts only a short time before the water evaporates. caused when streams flow across the bajada to the center of the basin.
playa
dry, flat, often saline bed that remains a temporary water reservoir has dried up.
bajada
an apron of sediment along the base of desert mountains composed of coalesced alluvial fans.
alluvial fan
sporadic rains in the desert is heavily loaded with sediment. most of the load is deposited at the mouth of the stream. the coarsest material is dropped first therefore the head is the steepest.
how are sand grains transported by wind?
sand jumps by saltation in the lowest few meters above the land surface. sand moves by skipping & bouncing along the surface.
which of the following must be present for wind to be an effective agent of erosion?
dryness & scanty vegetation
deflation
lifting & removal of loose material over a large area, which progressively lowers the surface.
blowout
most noticeable result of deflation. a shallow depression in unconsolidated material. the factor that controls the depth of these basins is the water table.
desert pavement
in portions of many deserts the surface consists of a closely packed layer of coarse particles. a veneer of pebbles & cobbles only one or 2 stones thick.
ventifact
wind shaped rock with one or more sides that have been pitted & smoothed where they have been exposed to the prevailing wind.
yardang
streamlined, sculpted ridge, close tot he ground, oriented parallel to the prevailing wind. sometimes large features, also wind sculpted.
what is true about sand dunes
a dune migrates in the direction of inclination of the slope.
dunes have an asymmetrical profile where the leeward(sheltered) slope is steep while the windward slope is more gently inclined. sand moves up the windward slope by saltation. as more sand accu
star
these dunes exhibit a complex form, usually has 3 sharp crested ridges that diverge from a central high point. develop where wind directions are variable. plentiful sand.
parabolic
these dunes form along coasts where vegetation partially covers the sand and there are strong onshore winds & abundant sand. shape resembles barchan dunes except their tips point into the wind rather than downward.
longitudinal
these dunes form where the prevailing wind direction varies but remains in the same quadrant of the compass. they are long ridges of sand that form parallel to the prevailing wind where sand is moderate. varies from small to extremely large in size.
transverse
these dunes have steady prevailing winds, plentiful sand, & sparse or absent vegetation. dunes form a series of long ridges that are separated by troughs & oriented at right angles to the prevailing winds. coastal dunes.
barchan
these dunes for where sand is limited, the surface is free of vegetation & is relatively hard & flat. modest size. solitary sand dunes shaped like crescents.
near which major lines of latitude are low latitude deserts located?
Tropics of Cancer(23.5 degrees north) & the Tropics of Capricorn(23.5 degrees south). goes through places like north & south america, africa, & australia
much of the central US is covered by loess. what is loess & how did it pile up over much of the land?
silt that the wind blew over thousands of years dust storms deposited this material. in the US it was silt that blew in from the vast regions covered by glacial outwash during the ice age. there are 2 sources for this sediment: deserts & glacial deposits.
humans definitely impact the environment in derogatory ways. which inland water body has rapidly disappeared because of human intervention in a desert water system?
aral sea.
what is the definition of dry climate?
the annual precipitation is less than the potential loss of water by evaporation.
which combo best describes the production of mid-latitude deserts?
water-laden air evaporating from oceans rises over mountains & drops moisture on the windward side. dry air descends on leeward side of mountain, this area is referred to as a rainshadow desert. sierra nevada, cascades, & andes.
which combo best describes the results of disappearance of the Aral sea?
the climate changed to shorter growing seasons, hotter temps, & less precipitation
what best explains why there is a layer of fine silt underneath the desert pavement surface?
the layer of fine silt between the desert pavement & bedrock is the result of windborne sediments that land & wash into the soil faster than they are deflated & carried away by the wind.
what causes 2 belts of deserts that band the globe in low latitude?
dry air descends at subtropical high pressure belts.
the belts are the equatorial low (where heated air in the pressure belt rises to great heights & spreads out. air that rises through the atmosphere expands & cools which causes clouds & precipitation. e
which of the following is formed by abrasion of rocks by windblown sand?
ventifacts.
wind erodes with abrasion.
imagine that you live on the plains & you notice you are losing your soil because wind is blowing it to the neighbors field. which of the following might be yur first line of defense?
plant wind-resistant trees
what would most likely cause a significant dust cloud that might travel across the continent?
earth disturbance during a powerful earthquake
what instruments are the best for identifying & tracking clouds of dust & volcanic ash?
satellites
which of the following ares is experiencing the most desertification?
the Sahel in Africa
where's the worlds largest source of dust?
sahara desert
what name is applied to the great drought that occurred in north america during the 1930s
dust bowl
in which climate do rainfall & moisture content of the soil fall between those of true deserts & humid lands?
steppes
assume that the central slipface of a barchan dune slopes downhill toward the east. what is the direction of the prevailing wind?
west to east
ephemeral streams
carries water only in response to specific episodes of rainfall.
interior drainage
has a discontinuous pattern of intermittent streams that do not flow out of the desert to the ocean.
suspended load
unlike sand, finer dust particles can be swept high in the atmosphere by wind. both silt & clay can be in suspension but silt makes up the bulk. the dust must first be ejected.
wind
relatively unimportant in producing erosional landforms, but significant depositional landforms are created. 2 types of wind deposits: 1) mounds & ridges of sand from the winds bedload, dunes & 2) extensive blankets of silt called loess, that once were ca
cross beds
as sand is deposited at the slip face layers form that are inclined in the direction the wind is blowing.
factors that influence dunes
wind direction & velocity, availability of sand, & the amount of vegetation present.