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Geography > 1B - Hot environments > Flashcards

1B - Hot environments Flashcards

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1
Q

What is a desert?

A

A place receiving less than 250mm of rainfall a year

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2
Q

5 inputs of desert systems

A

insolation, weathering, climate change, Water energy, wind energy

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3
Q

3 processes of desert systems

A

mass movement, processes of water erosion, processes of wind erosion

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4
Q

What comes after the processes of desert systems that leads to the outputs?

A

transport

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5
Q

3 outputs of desert systems

A

landforms of deposition, landforms of erosion, water and sediment losses

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6
Q

Locations of hot deserts

A

Not distributed evenly across the world – however, there is a clear pattern to where they are located

This pattern is closely related to the causes of aridity

Generally lie between the Tropic of Cancer and Capricorn – not on the Equator itself

Quite often on the Western edge of large continents

Can also be located far into continents

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7
Q

Climate Characteristics of deserts:

Temperature ranges

A

Annual - hottest and coolest months

Diurnal - between day and night

Days are hot = no clouds to block incoming short wave radiation (INSOLATION)

Nights are cold = no clouds to keep long wave radiation so it can all escape back to space (RE-RADIATION)

Close to sea = lower diurnal temp (cold off shore currents)

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8
Q

Climate Characteristics of deserts:

Wind

A

Can often be very strong as little to provide shelter

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9
Q

Climate Characteristics of deserts:

Rainfall

A

Generally low and unreliable - but can have extreme and sudden events

If this happens, low infiltration and high potential evaporation (due to temperature) so very little available to plants

Rapid surface runoff + low infiltration + high evaporation= poor vegetation

Extreme flash floods

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10
Q

What is water balance?

A

The balance between inputs (precipitation) and outputs (run-off, evapotranspiration, soil and groundwater storage) is known as the water balance (or budget)

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11
Q

Water Balance Equation

A

P = Q + E +/- S

P = precipitation

Q= streamflow (which is a result of run off and release of stores)

E = evapotranspiration

S = storage

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12
Q

Key points in the water balance equation

A

The two most important parts of this relationship are precipitation and ‘potential’ evapotranspiration

Potential evaporation (PE) is the maximum evaporation which could occur if water was always readily available to plants.

All deserts will have a negative water balance where evapotranspiration > precipitation

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13
Q

What is the aridity index?

A

The relationship between precipitation and potential evapotranspiration

This will usually be less than 1 in an arid area as PotentialEvapoTranspiration is much greater than Precipitaion

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14
Q

What is soil composed of?

A

· Biota

· Regolith

· Humus

· Air

· Water

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15
Q

Desert soil characteristics

A

Poor in quality and organic content - unproductive

Thin

Highly saline (salty) – alkaline

Formation inhibited by lack of water which impedes breakdown of bedrock

When moisture is available, can be drawn to the surface bringing mineral salts up adding to alkalinity

Main type – aridosol

There are two ‘sub-types’ of soil within this umbrella that are formed by specific conditions in an area – Solonetzs and solonchaks

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16
Q

4 types of vegetation in deserts

A

Ephemerals

Halophytes

Xerophytes

Phreatophytes

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17
Q

What are ephemerals? (vegetation)

A

Vegetation that only lasts a short amount of time

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18
Q

What are halophytes? (vegetation)

A

Plants that thrive in saline soil

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19
Q

What are xerophytes? (vegetation)

A

Plants that are adapted for growth under dry conditions

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20
Q

What are phreatophytes? (vegetation)

A

Long-rooted plants that absorbs water from the water table or soil above it

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21
Q

Key characteristics of almost all types of desert vegetation

A

· Fleshy stems

· Swollen leaves

· Thick, waxy cuticles

· Thick, protective bark

· Small, spikey / waxy leaves

· Bulbous roots

· Salt tolerance

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22
Q

Causes of aridity

A

Global Atmospheric Circulation

The Continentality Effect

The Rain Shadow Effect

The Cold Current Effect

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23
Q

How does global atmospheric circulation work?

A
  1. Air is heated in equatorial zone / surplus of energy here (high angle, concentrated insolation)
  2. Humid air at ground level rises creating low pressure over the equatorial latitudes
  3. Water vapour condenses and clouds form
  4. Releases large amounts of latent heat energy (latent heat of evaporation) producing further uplift and further cooling hence more cloud formation
  5. Results in larger, thick layers of cloud cover in many equatorial regions which is responsible for heavy rainfalls that equatorial regions experience
  6. Rising air reaches the tropopause and moves polewards in both directions - i.e. North and South of the equator
  7. As the air cools, it sinks towards the surface of the planet (around 20-30 degrees) as it is more dense and ‘heavier’.
  8. Also less space in the atmosphere as the tropopause becomes lower with increasing latitude (16 km over the equator and 8km over the poles) so helping to force the air back to the ground).
  9. Where the air sinks, these are called the subtropical regions.
  10. This sinking air produces high pressure at the sub-tropical latitudes at ground level.
  11. A pressure gradient has occurred - Air has risen at the equator and sunk at the subtropics…as a vacuum cannot exist, air moves back to the equator to replace the air that has risen from the sub-tropical high pressure area to the equatorial low pressure area.
  12. This movement from high to low pressure causes movement of air (wind!) along the surface (esp. seas) are called the trade winds. In effect, winds serve to cancel out pressure differences across the Earth’s surface. The steeper the pressure gradients, the stronger the winds.
  13. Near the equator, these trade winds converge from both Hadley cells in both hemispheres at what is called the Inter-tropical Convergence Zone (ITCZ)
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24
Q

How does global atmospheric circulation affect aridity?

A

The sinking air produces a high pressure (Anticyclone) - Warm air, stable cloudless skies.

Dry air, because any water vapour was dropped as convection rainfall near to the equator,

No clouds due to air warming so no condensation: so heat builds up in the day, but radiates back at night = a high diurnal temperature range

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25
Q

How does the Continentality Effect work and affect aridity?

A

Maritime places have higher rainfall than those inland.

As air masses move over a continent, they will lose moisture - this causes the air to become very dry

Central parts of the Sahara Desert are the parts of Africa that are furthest from the sea: 2000km away, and even further in central Australia

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26
Q

How does the Rain Shadow Effect work and affect aridity?

A

Prevailing winds across oceans gather moisture.

As they reach land, the air is forced to rise over the mountains, leading to condensation and precipitation on the windward side.

As the air descends on the leeward side, it warms and is high pressure

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27
Q

How does the Cold Current Effect work and affect aridity?

A

When winds blow towards shore their lower layers are cooled by contact with the water.

This causes mist or fog to form offshore. This mist may roll inland, but it quickly evaporates again in contact with the warm surface.

The air has lost some moisture and it becomes drier as it warms making rain even less likely

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28
Q

What is the sediment budget?

A

The difference between the amount of sediment that enters the system and the amount that leaves

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29
Q

3 sediment inputs

A

Weathering of underlying rock, Fluvial (water) sources, Aeolian (wind) sources

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30
Q

2 sediment stores

A

Deposits, Landforms

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31
Q

2 sediment outputs

A

Erosion (wind and water), Transportation (wind and water)

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32
Q

What is weathering?

A

The breaking down of rocks, soils and minerals as well as artificial materials through contact with the Earth’s atmosphere, biota and waters.

Weathering occurs in situ, or “with no movement”, and thus should not be confused with erosion, which involves the movement of rocks and minerals by agents such as water, ice, snow, wind and gravity.

It occurs over a long period of time.

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33
Q

Types of weathering

A

mechanical and chemical

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34
Q

3 Types of mechanical weathering

A

Exfoliation, Granular disintegration, Shattering,

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35
Q

Types of mechanical weathering:

Exfoliation

A

Heat doesn’t penetrate easily into rock, so the surface is heated higher than the interior.

This means that stresses are set up in the rock, leading to cracking that runs parallel to the surface, layering then peeling off.

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36
Q

Types of mechanical weathering:

Granular disintegration

A

Changes in temp can cause different minerals within a rock to expand and contract at different rates.

This is common and granites and eventually leads to the breakdown of the rock.

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37
Q

Types of mechanical weathering:

Shattering

A

Some rocks, such as basalt, which have a homogenous structure may shatter as a result of constant expansion and contraction

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38
Q

4 Types of chemical weathering

A

Crystal growth, oxidation, hydrolysis, hydration

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39
Q

Types of chemical weathering:

Crystal Growth

A

Dissolved salts in water in cracks or joints form geometric shapes as the water evaporates. (Further heating causes the crystals to expand, resulting in rocks being prized apart, eventually falling off.)

40
Q

Types of chemical weathering:

Oxidation

A

Rocks containing iron are oxidised in air at the presence of salt and water, this causes them to turn a red/brown colour and they are weakened. (This colour is called desert varnish)

41
Q

Types of chemical weathering:

Hydration

A

Certain rocks capable of absorbing water will become vulnerable to future breakdown as they swell and break

42
Q

Types of chemical weathering:

Hydrolysis

A

Rainwater is slightly acidic so when it falls on rocks containing clays and dissolvable salts, it can dissolve the rock

43
Q

Why is wind common in the desert?

A

The creation of the high-pressure cell that generates strong winds blowing out of the desert

The absence of vegetation and surface features to create friction and reduce wind speed, and provide shelter

44
Q

What is deflation?

A

the process by which wind removes surface materials (sand, soil etc.)

45
Q

Features created by deflation

A

Desert Pavements, Deflation Hollows

46
Q

How are desert pavements formed?

A

Wind strips away fine grain particles from the surface of the desert floor.

Large particles are too heavy to be transported by the wind and as such are left behind, creating a pebble strewn surface.

47
Q

How are deflation hollows formed?

A

DEFLATION lowers the surface, creating a hollow, the best-known example is the Qattara Depression

Cold air sinks into hollows at night forming dew

Dew speeds up rock weathering making particles available for removal by the wind.

This process repeats and the deflation hollow increases in size

Depressions range from several metres to over 100m (Egypt).

Oases have probably formed where deflation hollows reach the water table. Vegetation binds the sand and creates soil so preventing further erosion. Oases are settled and cultivated so the vegetation is no longer natural.

48
Q

What is Abrasion?

A

Sand carried in the wind, principally by saltation

Sandblasts the rock, mostly close to the surface (up to about 1.5m) carving rocks with narrow bases, often sitting in hollows created as the sand is removed by winds swirling around the base (deflation).

49
Q

What do rates of abrasion depend on?

A 
Velocity of wind
Frequency of wind
Wind direction
Rock lithology 
Size of loose particles on the desert floor
50
Q

When is aeolian transport the most effective?

A

Sediment size is small

Wind is strong (high-pressure gradient) and blows for a long period of time

There is an absence of natural and man-made shelter e.g vegetation

There is a lot of weathering and/or erosion to provide lose material that is dry and unconsolidated

51
Q

4 Landforms caused by abrasion?

A

Rock pedestals, Ventifacts, Yardangs, Zeugens

52
Q

How are rock pedestals formed?

A

Caused by abrasion of the sand against the bottom of the rock

53
Q

How are ventifacts formed?

A

Fin-shaped rocks lying on the desert surface.

Shaped by wind-driven sand (abrasion)

They have a smooth, flat windward side, and
sharp narrow edges

54
Q

How are yardangs formed?

A

Formed when ridges of hard and soft rock run parallel to the direction of the prevailing wind.

Wind erodes the softer rock (by abrasion) and leaves the ridges standing up as yardangs.

May be broken down over time to become discontinuous features, but will still leave scars on the landscape

A ridge and furrow landscape.

Wind abrasion concentrates on weak strata; leaving harder material upstanding.

55
Q

How are zeugens formed?

A

Zeugens are similar in appearance to yardang but formed on horizontal bedded structures rather than vertical beds.

Often form where the surface has developed a duricrust (a brittle layer of mineral salts on the surface)

If this surface gets broken, the softer rock beneath loses its protection so Aeolian erosion quickly strips away the underlying rock

56
Q

When does aeolian deposition occur?

A

Deposition occurs when wind velocity decreases such that sediment can no longer be transported

57
Q

Landforms created by aeolian deposition

A

Dunes

58
Q

What are sand dunes?

A

Sand dunes are large deposits of sand characteristic of many arid environments

The formation depends mainly on wind direction and sand supply

Some types of dune can be highly mobile, constantly moving and changing shape whereas others are stable and constant

They can vary greatly in size from a few m’s high to several 00m high and many km’s long

59
Q

Two main types of dune

A

Barchan, Seif

60
Q

What are the 3 main roles of water in deserts?

A

Contributes to weathering processes

The action of rivers

Flash floods and erosion

61
Q

What are Exogenous Rivers?

A

They are perennial (flow all year round)

Have their source in mountains outside deserts and flow through them and out the other side

Arid land contains some of the world’s largest rivers e.g Nile (Africa), Colorado (USA), Tigris and Euphrates (Middle East), Indus (Pakistan)

62
Q

What are Endoreic Rivers?

A

Flow into deserts but terminate within them, usually in an inland lake or sea such as the River Jordan that drains into the Dead Sea

Many of them are incredibly saline because the heat causes the water to evaporate

63
Q

What are Ephemeral streams?

A

Flow intermittently after periods of rain and are very short-lived

64
Q

4 types of moving water bodies in deserts?

A

Exogenous rivers, Endoreic rivers, Ephemeral streams, Episodic flash floods

65
Q

What are Episodic flash floods?

A

Infrequent events unleash huge amounts of water in a short period of time.

Large rates of overland flow create sheet floods that spread over the surface, and channel floods if they are confined in river channels.

They can result in huge amounts of sediment being transported and deposited in large alluvial fans.

66
Q

5 types of fluvial erosion

A 
Splash erosion
Sheet erosion
Rill erosion
Gully erosion
Bank erosion
67
Q

What is splash erosion?

A

The force of falling rainwater displacing soil particles

68
Q

What is sheet erosion?

A

Water running as a sheet over impermeable surfaces or compacted soil washing away disturbed particles

69
Q

What is rill erosion?

A

Sheet wash wears down the soil to form a definite path to form rivulets in the soil, called rills

70
Q

What is gully erosion?

A

Over time, rills become wider and deeper to form gullies

71
Q

What is bank erosion?

A

Fast water flow wears away the streamsides, causing the banks to collapse and the channel to widen

72
Q

8 types of fluvial landforms

A 
Wadi
Alluvial fan
Bajada
Pediment
Playa
Inselberg
Mesa
Butte
73
Q

What is a wadi?

A

Features of erosion and deposition

Arabic word for a dried up river bed

Usually characterised by a steep sided ‘slot’ canyon with a flat bottom filled with sediment

Sizes can vary considerably from few m’s wide and deep to several km’s long

74
Q

What is an alluvial fan?

A

Deposition from wadis usually creates alluvial fans as sediment is washed out of the canyon and spreads out in a characteristic fan shape as large amounts of sediment can block channels resulting in a complex network of braiding

Alluvial fans show evidence of sorting and stratification: coarser sediment is concentrated closest to mountain and finer material is transported further away as it’s lighter

75
Q

What is a bajada?

A

Where several alluvial fans join up

76
Q

What is a pediment?

A

Gently sloping (1-7 degrees) aprons of bare rock at the foot of mountains – often partially or completely covered by sediment washed down by rivers

Relic fluvial feature, not continuously eroded

Periodic sheetwash removes material and leaves a smooth surface

Commonly a distinct change in slope between start of pediment and foot of mountain

Cliffs are weathered and eroded – steep scree slopes created

Further debris is brought later washed down as alluvial fans and further sheet floods

77
Q

What is a playa?

A

Lowest part of the pediment – essentially an ephemeral lake fed by endoreic rivers (e.g. Dead Sea)

Deposition of fine material creates flat landscape and then evaporation removes water and mineral salts are left behind

Water flows over pediments and surface deposits carrying fine material onto the desert floor.

Some water percolates to soil and be transferred underground to collect in hollows

Evaporation and lack of new water will eventually cause this collection of water to dry up.

Can create salt flats – evaporation leaves very flat saline surface

78
Q

What is an inselberg?

A

An isolated rounded hill

An inselberg is a smooth-sided version of a butte.

They are found in arid and semi-arid areas

They are formed from crystalline rocks such as granite and are believed to have been subject to extensive chemical weathering which is more common in humid areas.

They probably formed during wetter periods – pluvials – further evidence of climate change.

79
Q

What is a mesa?

A

Mesas are plateau like features that are flat on top with steep edges

The land has probably been uplifted and there has been extensive erosion. There will be scree slopes.

80
Q

What is a butte?

A

A butte is a version of a mesa which may be smaller (erosion) or separate. It is a bit like a sea stack.

81
Q

What is a plateau and how is it formed?

A

Plateau – an elevated area of relative smooth terrain, frequently separated from adjacent areas by steep slopes

Plateaus can be formed by a number of processes, including upwelling of volcanic magma, extrusion of lava, and erosion by water and glaciers.

Magma rises from the mantle, causing the ground to swell upward; in this way, large, flat areas of rock are uplifted and this uplifted rock forms a plateau

82
Q

What is King’s Arid Cycle of Erosion?

A

Youthful - Following tectonic uplift, processes of weathering, mass movement and erosion (primarily water) result in the parallel retreat of mountain fronts, leaving behind a gently angled rock slope - the pediment.

Mature - Over time, the uplifted landscape is gradually eroded away, leaving coalescing pediment surfaces and isolated remnants of the mountains - relic hills called inselbergs

Old Age - Eventually these isolated hills crumble, leaving behind a largely flat surface known as a pediplain. With further uplift, the whole process will start again.

83
Q

How has distribution of arid areas changed over 10,000 years?

A

Last glacial maximum:
• Widespread aridity
• Far north deserts were cold deserts
• Southern deserts in similar locations to today but more extensive

Early Holocene:
• Interglacial conditions – warmer and more humid
• Aridity fell dramatically – widespread forests
• Present day deserts were grassland

5000 years ago to present:
• Aridity returned especially to Africa and Asia
• 3000 years ago conditions similar to today
• Potential vegetation – not including cleared forest

84
Q

What is desertification?

A

The persistent degradation of dryland ecosystems by variations in climate and human activities.

It results in a reduction or loss of the biological or economic productivity of drylands.

85
Q

Desertification figures

A

It can take 500 years for 2.5cm of soil to form but not long to destroy it

1/3 of land is affected by desertification

Land covering 12,000 hectares (size of Bulgaria) is lost every year to degradation

86
Q

What is the process of desertification?

A
  1. Many people in LEDCs are poor so have large families, this results in rapid population growth.
  2. As the population grows, people plant more crops and so have to chop down more trees
  3. The population also needs more wood for building fires, building homes and fences, and fodder for animals
  4. The people move to another area of land and begin to clear some space for their homes and crops
  5. The crops and animals rapidly use all nutrients in the soil. The lack of tree roots weakens the structure of the soil.
  6. The land is not allowed to rest so loses its fertility and becomes exhausted
  7. The soil loses its structure and is easily eroded, blown away by the wind
  8. The soil becomes so infertile that crops will not grow and there is nothing for animals to eat
  9. Desertification happens when land (usually on the edge of deserts) becomes too infertile to support people
  10. The land becomes barren (infertile) and so the people have to move on to somewhere else
87
Q

Who is affected by desertification?

A

2.7 billion people. 90% of whom live in developing countries

88
Q

What are the 4 major human causes of desertification?

A

Deforestation - soil not covered, and nutrients lost due to a lack of vegetation

Overgrazing - constant removal of nutrients as livestock eat them

Over cultivation of crops - nutrients taken up by the crops so when they are farmed, there are none left in the soil

Inappropriate irrigation - fertilisers increase salt content and acidification

89
Q

What are the 2 major physical causes of desertification?

A

Climate change - the warming of ground = loss of water

Erosion from wind or water - can remove nutrients from the soil

90
Q

Why is it difficult to accurately measure and map rates of desertification?

A

It is very complex and there is a lot of missing/unreliable information.

There are also many different definitions

Land degradation can’t be globally mapped by a single indicator

91
Q

Environmental consequences of desertification

A

Loss of biodiversity

Deforestation - global warming

Growth in more invasive shrub species

92
Q

Social consequences of desertification

A

Food insecurity due to infertile land

Often need to skip meals

Dust storms are bad for health

People need to keep relocating

93
Q

2 Economic consequences of desertification

A

Loss of land means a significant loss in GDP

People lose money in farming

94
Q

How does future development affect desertification?

A

Population growth will increase food demand and drive expansion and intensification of cultivated lands

More globalisation could mean international laws might be passed in order to prevent it however the likelihood of these laws being passed is very slim

95
Q

What is the link between desertification, global climate change, and biodiversity loss

A

Desertification diminishes biodiversity which is needed for many services provided to humans by dryland ecosystems.

As the land gets drier, more vegetation is lost, and vegetation is key for social conservation and regulation of surface water and local climate.

Desertification also contributes to climate change as carbon stored in soils is released into the atmosphere.

Increased global climate change also increases desertification as it heats up the soil and causes water to evaporate.

Geography (8 decks)

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