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Geography P1 (Physical) > Hot deserts > Flashcards

Hot deserts Flashcards

1
Q

Desert energy inputs

A

-insolation
-wind
-precipitation

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2
Q

Where are deserts located?

A

30 degrees north and south of the equator

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3
Q

Arid desert

A

receives less than 250mm precipitation per year

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4
Q

Semi-arid desert

A

250-500mm precipitation per year

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5
Q

Aridity index

A

the ratio between precipitation (P) and potential evapotranspiration (PET)

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6
Q

Water balance

A

The relationship between the annual
precipitation received and the amount of water lost to
potential evapotranspiration

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7
Q

Hot deserts climate characteristics

A

-Wildly varying temperatures annually and diurnally (day and night)
-low humidity=low cloud cover=high insolation
-

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8
Q

Why is soil development so slow in hot deserts

A

-lack moisture
-extremely high temperatures and high rates of
evaporation
-sparse vegetation and limited organic material

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9
Q

How and where are mineral salts found in desert soils?

A

-basic mineral salts found at the surface of the soils due to capillary movement
-capillary movement is where any
moisture in the soil or subsoil moves upwards through
the tiny spaces between soil particles (capillaries)
-most effective when PET exceeds P

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10
Q

Main zonal soil type in hot deserts

A

Aridisols (alkaline pH and high salt conc.) - two main categories:
-sierozems (semi-arid areas)
-raw mineral (arid areas)

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11
Q

Soil profile of an aridisol

A

TOP- A horizon with prismatic structure, brown or grey
TOP MIDDLE- B horizon with clay accumulation
BOTTOM MIDDLE- Bk horizon thick calcium carbonate accumulation
BOTTOM- C horizon where salts are carried upwards in solution through capillary action

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12
Q

Raw mineral soil properties

A

-coarse texture and gravelly due to physical weathering
-chemical weathering occurs where there is water in subsoil (capillary action leads to accumulation of calcium carbonate and salt at the surface)
-limited variation between horizons due to little leaching
-infertile
-unproductive

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13
Q

Sierozems

A

-darker colour suggests some organic material
-develop ‘desert shrubs’
-soils used for cultivation
-if irrigated, calcium rich B horizons develop beneath a thin A horizon

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14
Q

What plants tend to be found in hot deserts?

A

xerophytes

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15
Q

What are plants adaptions in hot deserts?

A

-store moisture in stem and leaves (succlents)
-procure water with extensive root systems
-respond rapidly to sporadic rainfall (shallow roots to access the wet top layer of soil)
-drought tolerance
-salt tolerance
-protection from animals (spiny, bitter, toxic)

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16
Q

Causes of aridity in hot deserts

A

-atmospheric circulation
-continentality
-relief rainfall
-cold ocean currents
-winds

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17
Q

What is global atmospheric circulation

A

-High angle of incidence at equator causes air to heat and rise, which causes cloud formation and precipitation
-Rising air is replaced by air rushing from the north and south, creating a low pressure inter-tropical convergence zone (ITZC)
-Cooler air descends creating a high pressure environment

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18
Q

What is continentality

A

-has an impact on rainfall and temperature
-distance from the sea has far more extreme temps and drier climate due to less blocking of insolation from clouds

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19
Q

What is relief rainfall

A

-around mid latitudes, dry regions on the leeward sides of mountains (rainshadow effect)
-prevailing winds meets range of mountains and forced to rise which cools and condenses air forming clouds and relief rainfall
-Once over the summit air descends on leeward side and warms as it sinks increasing humidity

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20
Q

What are cold ocean currents

A

-wind cools over the ocean
-increases humidity as any water vapour that was in the air condenses
-fog and mist created offshore
-sun burns mist away
-cool air can’t hold much moisture as it’s too cool

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21
Q

Abrasion

A

Material carried by moving wind or water hits exposed rock surfaces, thus wearing it away (sandpaper)

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22
Q

Deflation

A

Wind removes dry, loose sand, silt and clay particles from the surface and transports them away

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23
Q

Deposition

A

Velocity of wind decreases until it can no longer transport the grains it was carrying

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24
Q

Endoreic streams

A

Rivers occupy drainage basins that are closed and don’t flow out to sea or other rivers

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25
Ephemeral streams
Streams that flow intermittently in hot deserts following heavy thunderstorms (extremely short lag times)
26
Exfoliation
Mechanical weathering that results in breaking, splitting and peeling off outer layers of rock from pressure changes in the rock as only the outer layers were exposed to the cycles of heating and cooling. Tends to be mixed with chemical
27
Exogenous streams
rivers that originate externally to the desert
28
Mass movement
Movement of material downhill under the influence of gravity, but may be assisted by rainfall
29
Saltation
Sand sized particles transported by bouncing and hopping along the surface
30
Sediment budget
Balance between inputs and outputs of sediment
31
Surface creep
Saltating particles return to the surface and hit larger particles that are too heavy to hop, and slowly creep along the surface
32
Suspension
transport by wind where the smallest particles are held in the air
33
Thermal fracture
Mechanical weathering of rock resulting from rapid and repeated heating and cooling. huge diurnal range gives rhythmic heating
34
Weathering
Breakdown and decay of rock at the Earths surface creating regolith that remains in situ until moved by erosional processes -mechancial,chemical,biological
35
Why is insolation an important energy input into deserts?
-High angle of incidence from the sun (12hours of daylight) -assists weathering processes
36
Why is wind an important energy input into deserts?
-agent of erosion and transport -winds blow to the edges to deserts
37
Why is runoff an important energy input into deserts?
-rare intense storms can be significant agent of erosion and transportation of sediment
38
Origins of desert sediment
-weathering of parent material -fluvial in origin -aeolian from beyond desert margins (deposited by wind as loess)
39
Areas dominated by erosion...
are a SOURCE of sediment -net sediment loss
40
Areas dominated by deposition...
-net sediment gain
41
What material does weathering produce
regolith
42
mass movement dominated by...
rock falls , where small blocks of rock become detached from an exposed cliff face and fall freely to the base of the cliff rock slides , where there is a failure throughout the rock as a whole and the material collapses en masse , rather than as individual blocks.
43
What can erosion cause
denudation (degradation of the Earths surface)
44
Traction
larger stones and boulders are rolled along the channel bed by the movement of water downstream. Traction occurs with higher levels of energy and discharge
45
Chemical weathering rates
is slow in hot deserts because they have little soil and moisture levels are low
46
Chemical weathering examples
-Crystal growth (water in pores etc. are evaporated and salts are deposited) -Hydration (absorb water available causing swelling, which can chemically change them to e.g. become weaker) -Hydrolysis (where mildly acidic water reacts or combines with minerals in the rock to create clays and dissolvable salts which degrades the rock) -Oxidation (the breakdown of rocks by oxygen and water, leading to reddish-brown rock)
47
Block disintergration
Repeated cycles of freezing and thawing or thermal expansion can lead to blocks of rock being dislodged
48
Granular disintergration
Where rocks have a more granular structure they can be broken down into separate grains both by freeze thaw or differential thermal expansion
49
Why are aeolian processes common
-cloudless skies and high angle of incidence so air at surface is heated and rises, so cooler air moves in to replace it. It is this movement of air that results in winds -relatively barren with few surface features to create friction to reduce wind speed, therefore, winds can blow unimpeded for considerable distances.
50
Deflation
wind removes dry, unconsolidated sand, silt and clay particles from the surface and transports it away. can create desert pavements
51
Deflation hollows
wind removing very significant amounts of material from the surface
52
Movement of particles through wind is dependent on...
-the wind strength and direction -the amount of turbulence -the duration of the wind the relief and surface features -the amount and nature of any vegetation
53
surface creep
saltating particles return to the surface and hit larger particles that are too heavy to hop, they slowly creep (slide or roll) along the surface from a combination of the push of the saltating grain and the movement of the wind.
54
What causes rainfall in hot deserts
Disruption of the high-pressure cells along the subtropical high pressure belt can also lead to troughs, or gaps , in the high pressure at the surface, allowing more moist air to move north and create low pressure areas and rainfall
55
What can cause rainfall in deserts LOCALLY
local water sources to provide moisture for the atmosphere, if conditions are favourable, the intense heating of the desert surface can lead to localised warming and rising of air and localised low pressure systems developing
56
Sheet flooding
the impermeability of some desert surfaces and the sheer speed and amount of rainfall can lead to sheet floods and can carry and deposit loose sediment
57
channel flash flooding
overland flow is funnelled into steep-sided narrow valleys and can move significant sediment and cause erosion
58
ventifact
aeolian -exposed rock abraded -smooth flattened sides +sharp edges -
59
desert pavements
aeolian landform
60
yardangs
aeolian landform -streamlined parallel ridge of rock -aligned in direction of prevailing winds
61
zeugen
aeolian landform -rock pillars, rock pedestals and rock mushrooms -less-resistant rock underlies a layer of more resistant geology at the surface
62
barchans
aeolian landform -crescent-shaped sand-dunes with a gently sloping convex windward side with two horns or wings extending laterally
63
What conditions are needed for sand dunes
-a ready supply of sand -prevailing winds strong enough to transport sediment, but not strong enough to remove more than is deposited -steady winds from one dominant direction -an obstacle to trap the sediment and encourage deposition to occur.
64
sief dunes
aeolian landform -knife-edged ridges of sand or longitudinal dunes form long parallel ridges of sand separated by wind-scoured depressions
65
wadis
water landform -steep-sided, wide-bottomed, gorge-like valleys -rarely filled with water -occasionally occupied by ephemeral streams (often braided due to deposited material)
66
bahadas
water landform -linear mountain range has several parallel wadis in close proximity, the alluvial fans may coalesce, covering the pediment
67
pediments
water landform -distinct break in gradient as highland regions meet a more gently sloping lowland area or depression -deposited load forms alluvial fans as distributaries run out from wadis onto the pediment (coarsest material left upstream, smallest material downstream)
68
playas
water landform -dry lake bed -consists of evaporites carried by water e.g. NaCl giving colour of a beach
69
inselburgs
water landform -are more rounded steep-sided hills that rise abruptly from a lowland plain - 1 theory: the surrounding slopes retreated in parallel as pediments encroached into the remaining highlands in a process called pediplanation - 2 theory: deep chemical weathering when the resistant rock was buried beneath surface - both suggest deserts used to be wetter environments
70
Badlands
water landform dry terrain where softer sedimentary rocks and clay-rich soils have been extensively eroded. They are characterized by steep slopes, minimal vegetation, lack of a substantial regolith, and high drainage density
71
Mojave desert USA landforms (case study)
-Cima dome desert pavement -Kelso dunes – star dunes, barchans -Lucy Gray Fan- alluvial fan -Lucy Gray mountain canyon- wadis -Soda dry lake (playa) -Badlands (Death valley)
72
Causes of aridity in the Mojave
-Atmospheric circulation=under falling limb of hadley cell -releif rainfall over the Sierra Nevada -Californian cold ocean current
73
Mojave climate
-Higher rainfall than other deserts -Peak temp 27 degrees in July
74
Mojave vegetation
-Succlents (cacti) -Limit water loss by conservation (Desert Holly) -Drought tolerance (Mojave Poppy) -Salt tolerance (Saltbush)
75
Mojave aridity index
-Arid - 5-20 (aridity index) - 25-200mm/yr
76
Mojave exogenous river
Colorado

Geography P1 (Physical) (5 decks)

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