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ESS205H1 - FINAL 2022 > Reading Notes: CH 16 The Work of Wind and Deserts > Flashcards

Reading Notes: CH 16 The Work of Wind and Deserts Flashcards

1
Q

What is desertification?

A

The expansion of deserts into formerly productive land

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2
Q

What is a major contributor to desertification?

A

Human activity

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3
Q

What are the characteristics of wind

A

flows at a greater velocity than water, has a lower density and can carry only clay- and silt-size particles as suspended load.

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4
Q

What is bed load?

A

The part of a stream’s sediment load, mostly sand and gravel, transported along its bed

or heavy sediment particles moved via saltation or by rolling and sliding

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5
Q

Describe the saltation process

A

Sand grains are picked up by the wind and carried a short distance before falling back to the ground, where they usually hit other grains, causing them to bounce and move in the direction of the wind

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6
Q

What is suspended load

A

Consists of the smallest particles of silt and clay, which are kept suspended above the channel’s bed by fluid turbulence.

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7
Q

Why does wind move sand-sized particles first?

A

Larger sand grains, stick up into the turbulent air zone, where they can be moved.

Unless the stationary air layer is disrupted, the silt and clay particles remain undisturbed on the ground, providing a smooth surface

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8
Q

What are the two ways wind erodes materials?

A
  1. abrasion 2. deflation
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9
Q

What is abrasion?

A

involves the impact of saltating sand grains on an object and is analogous to sandblasting.

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10
Q

What odd form can wind abrasion produce?

A

hoodoos

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11
Q

What are ventifacts?

A

A stone with a surface polished, pitted, grooved, or faceted by wind abrasion

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12
Q

Characteristics of ventifacts

A

If the wind blows from different directions, or if the stone is moved, the ventifact will have multiple facets.
Most common in deserts, yet they can form wherever stones are exposed to saltating sand grains

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13
Q

How are ventifacts formed?

A

A ventifact forms when windborne particles (1) abrade the surface of a rock (2) forming a flat surface. If the rock is moved, (3) additional flat surfaces are formed.

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14
Q

What are Yardangs?

A

Larger features than ventifacts and also result from wind erosion. elongated, streamlined ridges. Found in clusters aligned parallel to the prevailing winds.

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15
Q

What is deflation?

A

The removal of sediment and soil by wind. it is an important mechanism of wind erosion.

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16
Q

What are deflation hollows or blowouts

A

Shallow depressions of variable dimensions resulting from differential erosion of surface materials.

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17
Q

What are desert pavements?

A

A surface mosaic of close-fitting pebbles, cobbles, and boulders found in many dry regions; results from wind erosion of sand and smaller particles.

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18
Q

What are the two main types of win deposits

A
  1. dunes 2. loess
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19
Q

What are dunes

A

A mound or ridge of wind-deposited sand.

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20
Q

Describe the dune formation process

A

Wind flows over and around an obstruction, resulting in the deposition of sand grains, which accumulate and build up a deposit of sand. As they grow, these sand deposits form self-generating wind barriers that further reduce the wind’s velocity, resulting in more sand deposition and dune growth

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21
Q

What are the characteristics of dunes?

A

Asymmetrical profile with a gentle windward slope and a steeper downwind or leeward slope that is inclined in the direction of the prevailing wind

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22
Q

How do dunes migrate?

A

Dunes migrate when sand moves up the windward side and slides down the leeward slope. Such movement of the sand grains produces a series of cross-beds that slope in the direction of wind movement

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23
Q

how do cross-beddings help geologists?

A

helps geologists determine the prevailing direction of the wind that formed these ancient sand dunes

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24
Q

What are the five major dune types?

A

barchan, longitudinal, transverse, parabolic, and star

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25
Q

What are barchan dunes?

A

Crescent-shaped dunes whose tips point downwind.

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26
Q

What conditions develop Barchan dunes?

A

areas that have a generally flat, dry surface with little vegetation, a limited supply of sand, and a nearly constant wind direction

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27
Q

What are Longitudinal dunes?

A

A long ridge of sand generally parallel to the direction of the prevailing wind. form in areas where the sand supply is somewhat limited.

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28
Q

What are Transverse dunes?

A

Long ridges perpendicular to the prevailing wind direction in areas that have abundant sand and little or no vegetation

29
Q

How are Transverse dunes similar to Barchan dunes?

A

Some transverse dunes develop a clearly distinguishable barchan form and may separate into individual barchan dunes. Such intermediate-form dunes are known as barchanoid dunes.

30
Q

What are parabolic dunes?

A

A crescent-shaped dune with its tips pointing upwind.

31
Q

What conditions develop parabolic dunes?

A

coastal areas with abundant sand, strong onshore winds, and a partial cover of vegetation

32
Q

What are Star dunes

A

Dunes that resemble a multipointed star.

33
Q

What conditions develop Star Dunes?

A

Star dunes develop where the wind direction is variable. tallest in the world. consist of pyramidal hills of sand, from which radiate several ridges of sand, and they develop where the wind direction is variable

34
Q

What are loess

A

Wind-blown silt and clay deposits composed of angular quartz grains, feldspars, micas, and calcite

35
Q

What three sources do loess derive from?

A

deserts, Pleistocene glacial outwash deposits, and the floodplains of rivers in semiarid regions

36
Q

How are loess characterized?

A

Because of its unconsolidated nature, loess is easily eroded, and as a result, loess areas are characterized by steep cliffs and rapid lateral and headward stream erosion

37
Q

What is air pressure?

A

the density of air exerted on its surroundings (i.e., its weight)

38
Q

What areas have low air pressure? and why?

A

areas of Earth’s surface that receive the most solar radiation, such as the equatorial regions

When air is heated, it expands and rises, reducing its mass for a given volume and causing a decrease in air pressure

39
Q

What areas have high air pressure? and why?

A

polar regions have high air pressure.

when air is cooled, it contracts and air pressure increases

40
Q

What is the Coriolis effect?

A

The deflection of air between latitudinal zones resulting from the Earth’s rotation.

Winds and oceanic currents are deflected clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere.

41
Q

Where are the majority of the world’s deserts located?

A

Dry climates of the low and middle latitudes where the potential loss of water by evaporation may exceed the yearly precipitation.

42
Q

What are Semiarid regions?

A

Receive more precipitation than arid regions, yet are moderately dry.

Their soils are usually well developed and fertile and support a natural grass cover.

43
Q

What are Arid regions?

A

generally described as deserts, are dry; they receive less than 25 cm of rain per year, have high evaporation rates, typically have poorly developed soils, and are mostly or completely devoid of vegetation.

44
Q

How are the dry climates divided?

A

into semiarid or arid regions

45
Q

Why are the dry climates in the middle and high latitudes and within the continental interiors in the Northern hemisphere dry?

A

their remoteness from moist maritime air and the presence of mountain ranges that produce a rain-shadow desert

46
Q

What is a rain-shadow dessert?

A

A desert found on the lee side of a mountain range because precipitation falls mostly on the windward side of the range.

47
Q

What is the process of rain-shadow dessert?

A

When moist marine air moving inland meets a mountain range, it is forced upward where it cools and forms clouds that produce rain. This rain falls on the windward side of the mountains

48
Q

The dryness of the low-latitude deserts is due to?

A

the year-round dominance of the subtropical high-pressure belt

49
Q

The dryness of the mid-latitude deserts is due to?

A

their isolation from moist marine winds and the rain-shadow effect created by mountain ranges

50
Q

How much rain on average do dessert receive annually?

A

less than 25 cm of rain

51
Q

What are the characteristics of dessert vegetation?

A

typically sparse, widely spaced, and characterized by slow growth rates.

stems and leaves are usually hard and waxy to minimize water loss by evaporation and for protection

widespread shallow root system to absorb morning dew and for anchoring

52
Q

What kind of weathering is dominant in desserts?

A

Mechanical weathering

53
Q

What is rock varnish?

A

A patina, or thin brown or black coating on a rock’s surface, and usually composed of iron and manganese oxides.

54
Q

What are petroglyphs?

A

The abraded, pecked, incised, or scratched marks made by humans on boulders, cliffs, and cave walls.

55
Q

What causes most desert erosion?

A

Running water / water erosion. Not wind.

56
Q

Describe water erosion in desserts

A

Dessert round cannot absorb all of rainwater. Runoff is rapid due to minimal hindering from sparse vegetation (especially on moderately to steeply sloping surfaces). This leads to flash floods and sheet flows.

Dry stream channels quickly fill with raging torrents of muddy water and mudflows, which carve out steep-sided gullies and overflow their banks. During this, a tremendous amount of sediment is rapidly transported and deposited far downstream.

57
Q

What is internal drainage

A

a stream’s load is deposited within the desert and is most common in arid regions

58
Q

Why are most desert streams poorly integrated and flow only intermittently?

A

Many of them never reach the sea because, as the water table is usually far deeper than the channels of most streams, they cannot draw upon groundwater to replace water lost to evaporation and absorption into the ground.

59
Q

What is wind effective at doing?

A

effective in transporting and depositing unconsolidated sand-, silt-, and dust-sized particles

60
Q

What are playa lakes?

A

After an infrequent and particularly intense rainstorm, excess water not absorbed by the ground may accumulate in low areas and form playa lakes

61
Q

What are the characteristics of playa lakes?

A

These lakes are temporary, lasting from a few hours to several months.

Most are shallow and have rapidly shifting boundaries as water flows in or leaves by evaporation and seepage into the ground

the waters are often very saline.

62
Q

What is a playa or salt pan?

A

A dry lakebed /evaporated playa lake found in deserts.

63
Q

What are alluvial fans / how are they formed?

A

Alluvial fans form when sediment-laden streams flowing out from the generally straight, steep mountain fronts deposit their load on the relatively flat desert floor.

64
Q

What are the characteristics of alluvial fans?

A

the sediment spreads out laterally, forming a gently sloping and poorly sorted fan-shaped sedimentary deposit.

they are formed entirely on land.

may coalesce to form a bajada

outer portions are typically composed of fine-grained sediments suitable for cultivation, and their gentle slopes allow good drainage of water.

65
Q

How are alluvial fans and bajadas important for agriculture?

A

Their outer portions are typically composed of fine-grained sediments suitable for cultivation, and their gentle slopes allow good drainage of water.

66
Q

What are pediments?

A

An erosion surface of low relief that is gently sloping away from the base of a mountain range.

67
Q

What are inselbergs?

A

An isolated steep-sided erosional remnant that rises conspicuously above the flat plains of many deserts.

68
Q

What is a mesa?

A

A broad, flat-topped erosional remnant bounded on all sides by steep slopes.

69
Q

what is a buttes?

A

An isolated, steep-sided, pillar-like hill formed when resistant cap rock is breached, allowing erosion of less resistant underlying rocks.

ESS205H1 - FINAL 2022 (8 decks)

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