Deck 14: The Work of Wind and Deserts

Question 1

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

Answer 1

Mechanical weathering is dominant because temperatures can fluctuate a great deal in a day and frost wedging is common in winter. Plant roots and salt crystal growth may also break down some rocks. Chemical weathering is almost slow to non-existent as the land is very arid because of scarcity of moisture and fewer plants mean fewer organic acids.

Question 2

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

Answer 2

Ventifacts are stones with polished, pitted, grooved, or faceted surfaces caused by wind abrasion. If the wind blows from different directions, the ventifacts will have multiple facets. Ventifacts are most common in deserts, but they can also form on beaches or outwash.

Question 3

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

Answer 3

Desertification is the expansion of deserts into formerly productive lands. Regions that are most susceptible to desertification are those on the margins of existing deserts. Natural changes in climate can cause deserts to expand or contract, but currently human activities are accelerating the rate of desertification. These activities include improper farming activities, farming marginal lands, and overgrazing livestock. In regions experiencing desertification, people are potentially displaced, and in extreme cases it results in deaths due to starvation.

Question 4

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

Question 5

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

Question 6

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 7

How do dunes build their characteristic asymmetrical profile?

Question 8

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

Question 9

Briefly explain how mesas and buttes form.

Question 10

Briefly explain how a pediment is formed.

Question 11

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

Question 12

Briefly explain how a rain-shadow desert forms.

Question 13

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 14

Describe sediment transport as bed load, including saltation.

Question 15

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

Question 16

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

Question 17

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

Question 18

What is desert pavement, and how does it form?

Question 19

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

Question 20

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

Question 21

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

Question 22

What are deflation hollows?

Question 23

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

Question 24

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

Question 25

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

Question 26

How do sand dunes migrate?

Question 27

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

Question 28

What are the four major dune types generally recognized?

Question 29

What are some of the characteristics of playas?

Question 30

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

Question 31

What can lithified or ancient sand dunes tell us?

Question 32

Besides deserts, where does wind play a role as a significant geologic agent?

Question 33

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

Question 34

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 35

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

Question 36

Why do most desert streams never reach the sea?

Question 37

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

Question 38

What factors enhance water erosion in deserts?

Question 39

What factors affect the type of dune that forms?

Question 40

How does saltation by wind differ from that in streams?

Question 41

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

Question 42

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

Question 43

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

Question 44

Wind travels at a _____ speed than water but has a _____ density which allows it to carry mainly clay- and silt-size particles.

Question 45

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

Question 46

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

Question 47

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

Question 48

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

Question 49

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 50

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

Question 51

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

Question 52

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

Question 53

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 54

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

Question 55

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 56

Air flows from ____________________ pressure regions to ____________________ pressure regions.

Question 57

A playa forms by ____________________ of a playa lake.

Question 58

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

Question 59

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

Question 60

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

Question 61

The most mobile dunes are:

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

Question 62

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 63

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 64

Desertification is a cause of concern as arable regions are lost as the deserts are expanding.

Question 65

Wind-blown deposits of silt and clay are called:

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

Question 66

All dunes originate in desert conditions.

Question 67

Deserts mostly occur at ____ latitudes.

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

Question 68

A common mode of mass wasting in deserts is:

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

Question 69

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

A) ventifact.
B) desert pavement.
C) longitudinal dune.
D) yardang.
E) barchan dune.

Question 70

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 71

Sandblasting in nature is caused by the process of saltation.

Question 72

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 73

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

Question 74

Wind erodes by:

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

Question 75

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

Question 76

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 77

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 78

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 79

The process of encroachment/invasion of deserts into regions that were once productive is termed as?

A) evaporation
B) expansion
C) desertification
D) desiccation
E) dehydration

Question 80

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.