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A-Level AQA Geography > Hot Deserts: Deserts as natural systems & Systems and Processes > Flashcards

Hot Deserts: Deserts as natural systems & Systems and Processes Flashcards

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1
Q

What type of systems are hot deserts?

A

Open system (have inputs and outputs for energy and matter)

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2
Q

What are some inputs into hot deserts?

A
  • energy from the Sun
  • precipitation
  • wind
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3
Q

What are the flows in hot deserts?

A

erosion and weathering -> water and wind transportation -> water and wind deposition

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4
Q

What are the stores in hot deserts?

A
  • erosional landforms and landscapes (e.g. Wadis, ventifacts, yardangs)
  • Depositional landforms and landscapes (e.g. sand dunes)
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5
Q

What are the outputs of hot deserts?

A
  • sediment carried out by wind and water

- clear skies allow large amounts of energy to re-radiate back into space

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6
Q

When is a hot desert system in a state of equilibrium?

A

When the geomorphological processes continually shape the desert landforms

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7
Q

What is the difference between a landscape and a landform?

A

Landscape is a characteristic

Landform is an element

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8
Q

Q: Explain the role of positive feedback in the development of hot desert landscapes? [4 marks]

A
  • positive feedbacks occur when there is a change to the desert system that triggers further changes to the system
  • for example the formation of sand dunes (landform formation in a landscape) wind carrying sediment hits an obstacle -> deposition of material -> sand dune increases in size
  • positive feedback can change the system’s equilibrium to make a new dynamic equilibrium
  • eventually the sand dune will be so large that wind flow can no longer reach top and deposit sediment, dune stops growing and a new dynamic equilibrium has been reached
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9
Q

What is another example of a positive feedback loop?

A

Removal of vegetation from deforestation and overgrazing -> reduces moistures emitted into atmosphere -> reduced humidity -> reduces vegetation growth

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10
Q

Q: Explain the role of negative feedback in the development of hot desert landscapes? [4 marks]

A
  • Negative feedback loops restore the balance of the system when there is a change to it
  • this can help maintain the landscape in it existing form
  • for example the intense weathering of slopes -> build-up of an apron of scree -> this apron extend up the mountainside -> lower slopes are protected from weathering
  • keeping the elements of the system the same, less development
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11
Q

What is the distribution of hot deserts?

A
  • linear pattern of hot deserts across the Tropics of Cancer and Capricorn, 20º-30º North and South of the Equator
  • Majority of hot deserts found in the Northern Hemisphere
  • largest deserts are concentrated in the centre of deserts (e.g. Saharan Desert in Africa)
  • Anomalies of this pattern are the Atacama and Namib Deserts as they are in the Southern Hemisphere on the west coasts of large continents
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12
Q

What is an arid climate?

A

The climate of an area that receives less than 250mm of precipitation per year

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13
Q

What is a semi-arid climate?

A

The climate of an area that receives between 250-500mm of precipitation every year

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14
Q

What is the aridity index?

A
  • the ratio between mean annual precipitation (P) and mean annual evapotranspiration (PET)
  • simplified way of classifying how arid a place is
  • varies as ratios are different
    hyper arid is <0.03
    arid is 0.03-0.2
    semi-arid is 0.2-0.5
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15
Q

What are some common characteristics of hot deserts?

A
  • diurnal temperature range due to cloudless skies (highest ever temp recorded was 57.7ºC at Al Aziziyah in Libya in 1922)
  • Low humidity due to little precipitation
  • Cloudless skies due to little evaporation from little precipitation
  • Insolation levels are low due to no clouds
  • less than 250mm a year from lack of water
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16
Q

Why are there geographical variations in climate?

A

Geographical location of the desert

  • e.g. if the desert is closer to the coast there are less extremes of temperature (Atacama)
  • This can also affect precipitation levels, American deserts = 280mm and Atacama = 15mm
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17
Q

Q: Evaluate the causes of aridity in hot deserts [20 marks]

A
  • The most important cause is Global Atmospheric Circulation…
  • The least important cause is relief rainfall…
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18
Q

The most important cause of aridity in hot deserts is global atmospheric circulation…

A
  • process that works at a global scale (largest of all the causes of aridity)
  • as Hadley and Ferrel cells descending limbs meet with cool air, causing no cloud formation and this aridity (all the warm air has condensed and released ppt)
  • This is the main cause of aridity in Sahara, high pressure from falling limb of Hadley cell (10º-30ºN) is the main cause of aridity there
  • However this doesn’t cause hyper-arid deserts, Sahara has an aridity index of 0.18 making it an arid desert
  • global atmospheric circulation works with other causes to create aridity in deserts, as the Sahara is in the centre of a continent as is mostly arid due to continentality
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19
Q

What is continentality?

A
  • coastal areas receive higher amounts of precipitation as the moist air is dropped as precipitation
  • distance from the sea reduces cloud formation as air reaching the centre of continents has low moisture content
  • this can also create greater temperature extremes, no clouds to block insolation and land has a low specific heat capacity to keep warm at night
  • work at a large scale but don’t cause hyper-arid deserts
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20
Q

What are cold ocean currents?

A
  • causes hyper-arid deserts but works on a more local scale
  • wind is cooled as it travels above cold water
  • reduces ability to hold moisture, released as precipitation before reaching land
  • insolation burns off any fog as air drifts onland, leaving cool dry air
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21
Q

The least important cause for aridity in hot deserts is relief rainfall…

A
  • mostly work on local levels and is never the main cause of aridity in hot deserts
  • it amplifies some of the larger causes already present, like continentality or global atmospheric circulation
  • moist air rising over a mountain range cools and condenses, forming clouds and resulting in precipitation on the windward side of the mountain, therefore air on opposite side has no moisture and can’t form clouds
  • however the scale of this factor can vary depending on the size of the mountain range
  • and does contribute greatly to the hyper-arid Atacama Desert from the rain shadow on the Andes, however, cold currents are still a prevailing cause there
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22
Q

What is the typical soil profile of a an aridisol?

A

(top going down)
A horizon
B horizon
Bk horizon (thick zone of calcium carbonate accumulation)
C horizon (salts are carried up in the solution)

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23
Q

What are aridisols?

A

infertile, alkaline and saline soils of desert areas

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24
Q

What is capillary movement?

A

moisture in the soil moves upwards through tiny spaces between soil particles most effective when evaporation exceeds precipitation

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25
Q

What is leaching?

A

Downward movement of minerals due to movement soil moisture, when precipitation exceeds evaporation

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26
Q

What are the main 2 types of aridisols?

A
  1. Sierozem
  2. Raw Mineral Soils
    (variation due to aridity, precipitation, vegetation and evaporation)
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27
Q

Describe the sierozem soil profile

A
  • calcium rich B horizon can develop underneath thin A horizon
  • weathered and solid bedrock
  • infertile
  • alkaline pH
  • depth of less than 100cm
  • extremely slow rate of development
  • high salinity
  • greyish colour!
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28
Q

Describe the raw mineral soil profile

A
  • unproductive (not really infertile)
  • accumulation of Ca and Na salts near the surface, limited variation between horizons
  • slightly alkaline pH
  • depth of less than 100cm
  • extremely slow rate of development
  • high salinity as salt crusts form at surface
  • reddish yellow to grey-brown colour
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29
Q

What are the similarities between sierozems and raw mineral soils?

A
  • No O horizon (organic matter) -> lack of dead organic material or water hinders decomposition
  • coarse texture -> physical weathering
  • capillary action dominates
30
Q

What is an erg desert?

A

a sand sea

the name for desert areas without vegetation

31
Q

What is Net Primary Productivity?

A

The amount of carbon uptake after subtracting plant respiration from gross primary productivity

32
Q

What is Gross Primary Productivity?

A

The total rate at which ecosystems capture and store carbon as plant biomass for a given length of time

33
Q

What are xerophytes?

A
  • succulent plants
  • Plants with compounds or cells in fleshy leaves, stems or roots where they can store water
  • can survive in very dry habitats
34
Q

What are phreatophytes?

A

Plants with shallow and very extensive root systems to procure water from damp soils following brief rainstorms.

35
Q

What are ephemerals?

A

Plants that cope with drought by becoming dormant or losing leaves during extreme dry spells

36
Q

What are halophytes?

A

Plants that can tolerate high levels of salinity

37
Q

How are plants adapted to increase water storage?

A

xerophytes contain cells in fleshy leaves/stems/roots where they can store water

38
Q

How are plants adapted to limit water loss?

A
  • thick waxy cuticles
  • closed stomata during the day
  • leaves reduced to spikes or needles
39
Q

How are plants adapted to increase access to soil water?

A

Having very shallow but very wide root systems (phreatophytes)

40
Q

How are plants adapted to tolerate drought?

A

Ephemerals become dormant or lose leaves during dry spells, appearing dead

41
Q

How are plants adapted to tolerate high salinity?

A

Halophytes

42
Q

How are plants adapted to cope with sporadic rainfall?

A

Some ephemerals have extremely short life cycles, coming into bloom shortly after rainfall

43
Q

Q: Assess the impact of aridity and soil characteristics on plant adaptations in desert environments?

A

Arid climates in deserts lead to long period of little precipitation and therefore drought….
A characteristics of desert soils is the alkaline soils…

44
Q

Arid climates in deserts lead to long period of little precipitation and therefore drought….

A
  • only plants tolerant to drought or dry environments will grow
  • for example the Colorado desert has an aridity index of 0.09, making it an arid desert
  • the Saguaro cactus is a xerophyte with fleshy leaves and stems so it can store water in drought and it is a phreatophyte as it has a shallow root system to collect water after brief rainstorms
  • these adaptations due to the very arid climate allow the plant to collect and store water for long periods and survive
  • root system enables plant to absorb any soil moisture before evaporation and fleshy leaves can store water between these periods of rain
45
Q

A characteristics of desert soils is the alkaline soils…

A
  • aridisols only allow for plants with tolerance to high salinity to grow, raw mineral salts soils and sierozems both have high salinity, in particularseroizems insemi-arid regionshave a high concentration of calcium carbonate in the B horizon.
  • Saltbush, a halophyte has salt bladders on its leaves that remove excess salt.
  • This adaptation allows the saltbush to draw moisturefrom B horizon of seriozemsin semi-arid areas, despitethe concentration of calcium carbonate (live in high salinity soils)
  • HOWEVER the soil profile is greatly affected by climate and rainfall, as rocks and gravels have been physically weathered to create these soils and capillary action is a large process making large salt crusts in raw mineral soils
46
Q

What are the plant adaptations of the resurrection plant?

A

Ephemeral

  • dormant periods during periods of no rain, rehydrates during rainfall and grows
  • folds up tight into a ball in dormant periods creating small SA for water to evaporate
  • small roots so can move with wind in search of standing water
47
Q

How to plan an answer to “Assess the impact of aridity and soil characteristics on plant adaptations in desert environments?”

A

Characteristic
Example of this characteristic
A plant adaptation
How this helps the plant overcome the problem of this characteristic

48
Q

Q PLAN: analyse the adaptations of this desert plant in relation to the climate and soils of its environment.

A

ideas…
xerophyte -> fleshy stems -> store water during long periods of no rainfall
phreatophyte -> shallow but wide root system -> drains any soil moisture -> sierozem soils have a thin, hard baked top layer which encourage surface run-off after heavy desert rains
plant may have thick cuticles and waxy epidermis -> reducing transpiration during the day from the plant
one deep tap root -> access any available groundwater as moisture is quickly evaporated away, or drawn to the surface by capillary action

Must address relation to soil AND climate

49
Q

What are the adaptations of the saguaro cactus?

A

Xerophyte
- fleshy leaves, stem and roots -> stores water during long period between rain events
- large amount of parenchyma -> large amounts of water storage to prevent plant temperature rising to lethal levels
- spines -> prevents animals eating them
- thick epidermis waxy cuticle -> prevents water loss and reduces transpiration
one tap root and shallow root system -> collect both groundwater and water from infrequent rain

50
Q

What are the adaptations of the saltbush?

A

Halophyte

  • sharp spine leaves to drop them during drought
  • stem and leaves covered in small white scales helps conserve water
  • bloom in summer and spring which often coincides with seasonal rain
  • salt bladders on leaves removes and deposits excess salt
51
Q

Q: Outline the climate of hot desert systems (4 marks)

A
  • Climate of hot desert system are aris due to infrequent and little rain they receive
  • Less than 250mm every year and when it does rain it’s in very intense and short-lived storms
  • Hot desert systems also experience extreme temperatures in the diurnal range, from 0ºC at night to 50ºC during the day
  • Due to no clouds blocking insolation during the day and no clouds for insulation of heat at night
52
Q

Q: Evaluate the relative importance of different sources of energy in hot desert environments

A
  1. Insolation is the most important - largest source, gives characteristics of land but little impact on the land itself
  2. Wind - impacts the elements in the system and a large process
  3. Precipitation is the least important
53
Q

Why is insolation the most important energy source?

A
  • a constant input of energy (all year round)
  • effect of intensity is amplified by the high angle of incidence (as deserts are found in mid-low latitudes) and no clouds, creating it as a high energy contributor
  • causes the climate characteristic of a diurnal temp range as cloudless skies don’t block any insolation coming into the system
  • any water that does evaporate makes the ground dry and makes sediment more mobile
  • However, not directly responsible for change in the system other processes of wind and water are. Insolation gives a significant energy source for weathering (thermal fracturing) but drives work of wind and water
54
Q

Why is wind the second most important energy source?

A
  • constant process (all year-round) as wind moves from high pressure in centre of deserts to margins with low pressure
  • large impact on the land as erosion, deposition and transportation of sediment happen constantly (e.g. the formation of dunes)
  • influences elements in the system from these processes, contributing to creating an active landscape
  • However, rapid temperature changes caused by insolation can cause steep pressure gradients that drive strong winds
55
Q

Why is precipitation the least important energy source?

A
  • doesn’t contribution but energy as it is a small and rare process (couple of times a year), for example the Atacama desert receives only 15mm of precipitation yearly
  • However, when it occurs it is very intense and brings strong erosional processes that help shape the land
  • mostly from overland flow as the baked ground and lack of vegetation prevents infiltration
  • has disproportionate influence on elements in system through erosion and transportation
56
Q

What are the 3 sources of sediment in hot desert environments?

A
  1. weathering of underlying bedrock
  2. fluvial, brought into system by rivers
  3. aeolian, brought into system by the wind
57
Q

What is loess?

A

loose material deposited by the wind

58
Q

What is regolith?

A

loose material from weathering

59
Q

What are the 5 geomorphological processes in deserts?

A
  1. Weathering
  2. Mass Movement
  3. Erosion
  4. Transport
  5. Deposition
60
Q

What is weathering?

A
  • The breakdown or decaying of material in situ that produces regolith
  • occurs anywhere with the processes of weathering: mechanical, chemical and biological
61
Q

What is mass movement?

A
  • movement of material downhill under the influence of gravity
  • rocks can be weakened by weathering, vulnerable to mass movement
  • deserts have little moisture, vegetation and soil, dominance of rock falls and rock slides
62
Q

What is erosion?

A
  • the processes that wear away land surface by mechanical action
  • by processes of water and wind
63
Q

What is transport?

A
  • Processes that moves material from the site where erosion took place to the site of deposition
  • by wind and water
  • traction, saltation, suspension and solution
64
Q

What is deposition?

A
  • water and wind depositing load of material when they experience a reduction in the capacity it can carry
  • happens due to loss of energy or evaporation of water
65
Q

What are the ancient sources of sediment in hot deserts?

A
  • before the desert existed the areas had different climates, some even wet enough for rivers or lakes
  • sediment was transported in by waterways
  • deposited into lake beds, lakes dried up as sediment become available for building dunes etc
66
Q

What are the sources of sediment in hot deserts?

A
  • weathering of underlying parent material
  • rivers may bring sediment (fluvial)
  • left behind in dried up riverbeds (ephemeral)
  • winds (aeolian)
67
Q

Can deserts be a source of sediment themselves?

A

yes

e.g. when dust clouds form, strong winds blow fine sediment out of the desert for thousands of miles

68
Q

What is the sediment budget?

A

The difference between the amount of sediment being brought into an area and the amount leaving is the sediment budget

69
Q

What happens if sediment inputs are higher than outputs?

A

Sediment budget is positive, net sediment gain

- landscape is dominated by depositional landforms and depositional processes/transportational

70
Q

What happens if the sediment outputs are higher than the inputs?

A

Sediment budget is negative, net sediment loss

  • landscape is dominated by erosional landforms and erosional processes
  • becomes a source of sediment

A-Level AQA Geography (13 decks)

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