Deck 15: The Work of Wind and Deserts

Question 1

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

Answer 1

Because loess derived soils are some of the most fertile in the world,the locations where large loess deposits have occurred have developed into some of the most productive farmland.

Question 2

What are deflation hollows?

Answer 2

Deflation hollows are shallow depressions created by differential wind erosion of surface materials.

Question 3

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

Answer 3

Wind is significant anyplace where exposure of sediment and soil is widespread,such as on shorelines and plains.

Question 4

What are the four major dune types generally recognized?

Question 5

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

Question 6

Briefly explain how mesas and buttes form.

Question 7

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 8

Explain how air masses are set into motion.

Question 9

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

Question 10

What factors enhance water erosion in deserts?

Question 11

How is rock/desert varnish produced?

Question 12

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

Question 13

What can lithified sand dunes tell us?

Question 14

What are some of the human-caused factors that may be initiators of desertification?

Question 15

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

Question 16

Briefly explain why there are extensive deposits of loess in China,Mississippi Valley,and north-central states of the United States.

Question 17

What type of weathering is dominant in deserts,and why?

Question 18

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

Question 19

Briefly explain how a rain-shadow desert forms.

Question 20

What factors affect the type of dune that forms?

Question 21

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

Question 22

Air flows from ____________________ pressure regions to ____________________ pressure regions.

Question 23

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

Question 24

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

Question 25

A playa forms by ____________________ of a playa lake.

Question 26

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

Question 27

Why are large alluvial fan deposits of importance to human residents of deserts?

Question 28

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

Question 29

Crescent shaped dunes whose tips point downward are _______ dunes.

Question 30

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

Question 31

Briefly explain how a pediment is formed.

Question 32

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

Question 33

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

Question 34

How does the topography of the water table in deserts with through-flowing streams result in the restriction of much of the vegetation to the stream banks?

Question 35

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

Question 36

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 37

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 38

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

Question 39

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

Question 40

Why are flash floods and sheet flows common in deserts?

Question 41

During sandstorms,how high can sand be lifted into the air?

A) a few inches
B) about one foot
C) about three feet
D) about 10 feet
E) hundreds of feet.

Question 42

What are elongated,streamlined rock ridges in wind-dominated erosional areas called?

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

Question 43

What is a common mode of mass wasting in deserts?

A) mud flows
B) rock fall
C) creep
D) slumps
E) slides

Question 44

The close-fitting mosaic of pebbles,cobbles,and boulders covering the floor of many deserts and semi-arid regions is called what?

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

Question 45

Deserts mostly occur at ____ latitudes.

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

Question 46

What is an isolated mountain that rises from the flat plain of a desert called?

A) mesa
B) butte
C) inselberg
D) drumlin
E) yardang

Question 47

Fan-shaped landforms that develop in deserts adjacent to highlands are known as ____ fans.

A) alluvial
B) bajada
C) playa
D) plain
E) pediment

Question 48

Although loess may originate in deserts,it is not deposited in them.

Question 49

All dunes have crests oriented perpendicular to the direction of wind movement.

Question 50

What does wind erode by?

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

Question 51

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 these

Question 52

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 53

Which are the most mobile dunes?

A) longitudinal
B) transverse
C) barchan
D) parabolic
E) none of these

Question 54

What are windblown deposits of silt and clay called?

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

Question 55

What is the size of particles that are usually the first to be set in motion by wind?

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

Question 56

What is Coriolis effect 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 57

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 58

Loess

A) must be stabilized by moisture and vegetation.
B) is most common in desert regions.
C) is very fine-grained and bad for crops.
D) all of these.

Question 59

All dunes originate in desert conditions.

Question 60

A broad alluvial apron formed by the coalescence of alluvial fans is called a(n)____.

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

Question 61

The same geological agents work in all deserts,so landforms of various deserts are similar.

Question 62

The finest-grained material in an alluvial fan is found along its margins.

Question 63

Surface creep is a common type of mass wasting in deserts.

Question 64

Sand covers approximately 75 percent of the world's deserts.

Question 65

The major topographic features of western United States deserts formed in the last 8,000 years.

Question 66

Deserts are the one environment where wind erosion is more important than water erosion.

Question 67

Alluvial fan sediment is deposited by flashflood,sheetflow,mudflow,and debris flow.

Question 68

Wind is as effective an agent of landform creation,as is water.

Question 69

The water table in deserts with through-flowing streams slopes toward the streams.