Deck 14: The Work of Wind and Deserts

Question 1

Briefly explain how a rain-shadow desert forms.

Answer 1

Air masses are forced to rise over mountains.As they do,they cool,and moisture condenses and falls as precipitation.Upon descending the leeward side of the mountain range,this air mass is dry.It heats,and its aridity causes increased evaporation.

Question 2

How do dunes build their characteristic asymmetrical profile?

Answer 2

Most dunes have an asymmetrical profile with a gentle windward slope and a steeper leeward slope that is included in the direction of the prevailing wind.Sand grains move up the gentle windward slop by saltation and accumulate on the leeward side,forming an angle of 30 to 34 degrees from the horizontal,which is the angle of repose of dry sand.When the angle is exceeded by accumulating sand,the slope collapses,and the sand slides down the leeward slope,coming to rest at its base.As sand moves from the dune's windward side and then slides down the leeward slope,the dune migrates in the direction of the prevailing wind.

Question 3

What is desert pavement,and how does it form?

Answer 3

Desert pavement is a mosaic of close-fitting rocks found in the desert.Winds remove sand-sized particles by deflation,leaving a surface of pebbles,cobbles,and boulders.Once desert pavement forms,it protects the underlying material from further deflation.

Question 4

What is desertification? Which regions are most susceptible to desertification? What causes desertification,and what are its effects?

Question 5

Briefly explain how a pediment is formed.

Question 6

Describe sediment transport as bed load,including saltation.

Question 7

How does air flow with regard to air pressure? How would air flow on Earth if the planet didn't rotate? How does air flow since it does rotate?

Question 8

What are alluvial fans,and why are they common in desert mountain ranges?

Question 9

What produces the worldwide pattern of east-west-oriented wind belts?

Question 10

Briefly explain why sand is moved by wind before clay and silt during wind erosion.

Question 11

What are ventifacts? How are multiple facets formed on ventifacts? Where are they found?

Question 12

What is air pressure,and how does it vary with temperature?

Question 13

What are deserts,and where are they located on Earth?

Question 14

Define the Coriolis effect.Which direction does Coriolis deflect winds? What does the word "apparent" mean in the definition?

Question 15

Why do dunes form? How are they self-generating?

Question 16

Briefly describe the four main dune types and how they differ from each other?

Question 17

Think about what you learned about sedimentary rocks.Why would ancient cross-bedded sandstone beds,as seen in Zion National Park,Utah,be useful to geologists?

Question 18

Why are flash floods and sheet flows common in deserts? What do these events have to do with erosion in the desert?

Question 19

Briefly explain how mesas and buttes form.

Question 20

What type of weathering is dominant in deserts and why? What about other types of weathering?

Question 21

Explain how wind can be a significant intercontinental agent of erosion and deposition.

Question 22

What factors enhance water erosion in deserts?

Question 23

What factors affect the type of dune that forms?

Question 24

What are the three main sources from which loess is derived?

Question 25

What are the four major dune types generally recognized?

Question 26

Besides deserts,where is the wind a significant geologic agent?

Question 27

Briefly explain why loess can originate in,but is not deposited in,deserts.

Question 28

What can lithified or ancient sand dunes tell us?

Question 29

Explain the ways in which alluvial fans and deltas are similar.

Question 30

Why is wind unable to transport sediment with the same grain size competency as water?

Question 31

How do sand dunes migrate?

Question 32

What are deflation hollows?

Question 33

Why do most desert streams never reach the sea?

Question 34

What are some of the characteristics of playas?

Question 35

Since most deserts have internal drainage,why are there through-flowing streams,such as the Nile,Niger,Indus,and Colorado Rivers in some deserts?

Question 36

What are some of the ways in which desert plants have adapted to the conditions in which they live?

Question 37

How does saltation by wind differ from that in streams?

Question 38

Briefly explain how the geological conditions that produced and deposited loess have determined the sites of the world's major grain belts.

Question 39

Equatorial regions receive the most heat,while polar regions receive the least.Therefore,what air pressures would you expect to be characteristic of these regions?

Question 40

Briefly explain why most deserts develop in the mid-latitude dry climate zone.

Question 41

High pressure troughs exist where cooler,denser air begins to descend at about ____________________ to ____________________ degrees latitude,N and S.

Question 42

Stones whose polished,pitted,faceted surfaces have been produced by wind erosion are called ____________________.

Question 43

Deserts receive less than ____________________ centimeters of rain per year,on average.

Question 44

____________________ involves the impact of saltating sand grains on an object.

Question 45

The Coriolis effect causes winds to be deflected to the ____________________ of their direction of motion in the Northern Hemisphere and to the ____________________ of their direction of motion in the Southern Hemisphere.

Question 46

Regions that receive more precipitation than arid regions but are moderately dry are ____________________ regions.

Question 47

A playa forms by ____________________ of a playa lake.

Question 48

Wind deposits composed of sand-sized particles that are deposited near their source are called ____________________.

Question 49

The drainage characteristic of most deserts in which streams dry up and do not have enough water to become integrated and reach outside their drainage areas is called ____________________ drainage.

Question 50

The most effective agent of erosion in the deserts is ____________________.

Question 51

Air flows from ____________________ pressure regions to ____________________ pressure regions.

Question 52

Dunes that form long ridges perpendicular to the prevailing wind direction in areas with abundant sand and little vegetation are ____________________ dunes.

Question 53

Although loess forms in only a few environments,it covers approximately ____________________% of Earth's land surface.

Question 54

The deflection of a moving mass from a straight line is known as the ____________________.

Question 55

The two types of sediment load transported by wind are ____________________ and ____________________ load.

Question 56

Alluvial fans are composed of sediment that is ____________________-sorted and ____________________ stratified.

Question 57

Dunes that form long-parallel ridges of sand aligned generally parallel to the direction of the prevailing winds where sand supply is somewhat limited are ____________________ dunes.

Question 58

The transformation of formerly productive lands into deserts is called ____________________.

Question 59

A saline,temporary lake in a desert is known as a(n)____________________ lake.

Question 60

The size of material that is frequently carried as suspended load by wind is ____________________ and ____________________.

Question 61

The most mobile dunes are:

A)longitudinal.
B)transverse.
C)barchan.
D)parabolic.
E)none of the above

Question 62

Desertification is taking place in the Sahara but not in the developed world.

Question 63

The size of particles that are usually the first to be set in motion by wind is(are):

A)silt.
B)clay.
C)sand.
D)pebbles.
E)boulders.

Question 64

Deserts mostly occur at ____ latitudes.

A)low
B)middle
C)high
D)low and middle
E)middle and high

Question 65

If a surface,like a road,only has silt- and clay-sized particles,the particles will only be picked up by wind if a car or other disturbance disturbs the road surface.

Question 66

Wind-blown deposits of silt and clay are called:

A)dunes.
B)loess.
C)ventifacts.
D)yardangs.
E)till.

Question 67

A common mode of mass wasting in deserts is:

A)mudflows.
B)rock fall.
C)creep.
D)slumps.
E)slides.

Question 68

An erosional bedrock surface of low relief that slopes gently away from a mountain base is a(n):

A)alluvium.
B)bajada.
C)playa.
D)plain.
E)pediment.

Question 69

Loess is important because it:

A)is an important source of building material.
B)is rich in important ore deposits.
C)sometimes contains petroleum.
D)makes fertile soil.
E)is an important source of groundwater.

Question 70

Sandblasting in nature is caused by the process of saltation.

Question 71

Wind erodes by:

A)saltation.
B)abrasion.
C)deflation.
D)saltation and abrasion.
E)abrasion and deflation.

Question 72

All dunes originate in desert conditions.

Question 73

The Coriolis effect is caused by:

A)wind shear between water and the atmosphere.
B)the axial tilt of the Earth.
C)the rotation of the Earth.
D)differences in air pressure in different regions.
E)Milankovitch cycles.

Question 74

How much land area is converted to deserts globally each year?

A)10,000 square kilometers
B)25,000 square kilometers
C)40,000 square kilometers
D)55,000 square kilometers
E)70,000 square kilometers

Question 75

Landforms that are made of relatively easily weathered sedimentary rocks capped by nearly horizontal more resistant rocks include

A)mesas.
B)ventifacts.
C)playas.
D)pediments.

Question 76

Long,parallel ridges of sand aligned perpendicular to the wind direction are:

A)longitudinal.
B)transverse.
C)barchan.
D)parabolic.
E)none of the above

Question 77

Dunes that form when vegetation cover is broken by deflation and the dune tips point upwind are:

A)longitudinal.
B)transverse.
C)barchan.
D)parabolic.
E)none of the above

Question 78

In the desert,wind is a more effective agent of erosion and deposition than water.

Question 79

Long,parallel ridges of sand aligned parallel to the wind direction are:

A)longitudinal.
B)transverse.
C)barchan.
D)parabolic.
E)none of the above

Question 80

The close-fitting mosaic of pebbles,cobbles,and boulders covering the floor of many deserts and semiarid regions is called:

A)ventifacts.
B)desert pavement.
C)longitudinal dunes.
D)yardangs.
E)barchan dunes.