Hot Deserts

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Phreatophytic
Roots which extend far
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Halophytes
Tolerant to high salt levels
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Xerophytic
Fleshy to store water
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Ephemeral
Become dormant/ loose their leaves, often look dead
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What is the soil type in hot deserts?
Aridisols, which fall in two main categories, raw mineral and sierozems
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Colour of the soil?
Reddish yellow to grey brown
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Depth of soil
Usually less than 100 cm
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What are the four horizons?
A=Prism structure B=Clay accumulation Bk= Thick calcium carbonate C= Salts
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Temperature Range
30 degrees to 55 degrees
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What is the distribution of hot deserts?
They run parallel to the equator but not on it (North and south). Semi arid and arid cover 15%of the earth's surface and Hyper arid cover 4%
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What type of system are hot deserts?
Open
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Inputs of hot deserts?
Insolation, wind energy, water energy, weathering, climate change
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Outputs of hot deserts?
Landforms of erosion, landforms of deposition, water and sediment losses
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Processes in hot deserts?
Wind erosion, water erosion and mass movement
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Causes of aridity
Atmospheric circulation, relief, continentality, cold ocean currents
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Which deserts have changed the most over the last 10,000 year?
The Sahara as there was no change 8000 years ago then 5000 years ago it grew rapidly and same with the Arabian desert
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Which have changed the least over the last 10,000 years?
The Gobi desert as it was present 8000 years ago and has only grown a small amount and the northern and southern polar regions as they still have not had a hot desert
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How much land is degraded every year?
30%
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How much land is becoming decertified annually?
12 million ha
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How many countries are at risk of desertification?
110
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How have deserts changed over the last 10,000 years?
The area has more than doubled, they have covered a wider range of locations, 10,000 years ago there was a glacial period and the air was much cooler, the population has increased, now a hot desert on every continent apart from Antarctica
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Describe insolation as a source of energy
The sun is almost directly overhead 12 hours a day. The angle of incidence is also high so light is very concentrated
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Describe wind as a source of energy
With a mid latitude location along high pressure belts many large hot deserts are subject to localised winds. The winds blow towards the edge of the deserts e.g. Irifi in the western Sahara
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Describe rainfall as a source of energy
Rainfall in deserts if often described as 'spotty' as it is often localised and unpredictable. This causes rapid overland run off.
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What is weathering?
The breakdown and/ or decay of rock at or near the earth's surface creating regolith that remains in situ until it is removed by an erosional process
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What is thermal fracture?
(Mechanical) Air temperature is the day are around 40 and at night 0 degrees. Surface of rocks can reach 80 degrees causing the rocks to expand in the day and contract at night. Eventually the pressure causes them to crack
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What is crystal growth?
(Chemical) Water is present in pores and moves up via capillary action carrying salt. The water reaches the surface, evaporates but leaves the salt behind, over time crystals grow
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What is exfoliation/ "Onion skin weathering"?
(Mechanical) Breaking splitting and peeling of outer rock. Pressure changes in the rock from heating and cooling cause expansion and contraction
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What is oxidation?
(Chemical) Break down of rocks by oxygen as iron minerals oxidise
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What is hydration?
(Chemical) Some rocks can absorb water, the more water absorbed the more stress builds up meaning they are more vulnerable to other weathering
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What is hydrolysis?
(Chemical) Mildly acidic water reacts with the minerals on the rock to create clays which makes the rocks weaker
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What is block disintegration?
(Chemical) Rocks have large fractures meaning water can move into them. With constant heating and cooling and chemical weathering pieces dislodge
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What sort of desert is a Reg?
Reg is a large, flat area strewn with gravel and small stones.
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What sort of desert is an Erg?
The erg, or sandy desert, which is characterized by sand dunes, is the most commonly known desert landscape.
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What sort of desert is a Hamada?
Hamada contains desolate areas of bare rock.
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What sort of soil is raw mineral?
They have a coarse texture and are often rocky or gravelly due to physical weathering. They tend to be slightly alkaline. Chemical weathering occurs however with little moisture there is little downwards movement of minerals.
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What sort of soil is sierozem?
Their darker colour suggests the presence of some organic material
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Name some human causes of desertification?
Intensification of agriculture, deforestation, over-grazing, fossil fuels, farming practices, population pressure from urbanisation, diverting river flows, lack of environmental policies, population growth from natural increase
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Name some physical causes of desertification?
Reduction in water supplies as rivers dry up, less and more unpredictable rainfall, higher temperatures means less local water supplies, high pressure systems prevent warm wet air moving towards higher latitudes, natural disasters like drought
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What are the three sources of water?
Exogenous-comes from outside the desert and passes through the desert. Endoric- closed drainage basin, the river starts and ends within the desert. Ephemeral- periodic surface flow when heavy rainfall occurs.
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What are the two types of mass movement?
Rock falls- rapid free fall of rock from a steep cliff possibly by freeze-thaw loosening rock. Rock slides- rock sliding on a concave plane, heavy rain, when water saturates over lying rock making it heavy
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How does water transport sediment?
Traction, saltation, suspension and solution
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How does wind transport sediment?
Saltation, suspension, surface creep
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How does wind erode via deflation?
The wind removed by dry sand, silt and clay particles from the surface and transports it away. The wind only remove fine materials so coarse pebbles are left. This is how Reg deserts are created.
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How does wind erode via abrasion?
Materials carried by the wind hits exposed rocks and created erosional features. Velocity, direction, frequency of the wind and size of the particle carries effects abrasion.
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What is sheet flooding?
It is caused by the impermeability of the desert's surfaces, intense down pours and the speed of the rain. It dislodges and moves surface material and overland flow causing flooding
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What is channel flooding?
When overland flow is channeled into steep sided narrow valleys (wadis). It causes the movement of a significant load of sediment.
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What is the definition of desertification?
The persistent degradation of arid and semi arid land by human and climatic change (UNESCO)
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What impact does desertification have on ecosystems?
Tipping points and extinction risks, species pushed to high altitudes and latitudes, changing distribution of pathogens, food webs affected, animals and plant life cycles including mating and migration
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What impact does desertification have on landscapes?
Increased salinity of soils, increased numbers of sand storms, increased amounts of sand on sand dunes, soil erosion and loss of top soil, increased sedimentation
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What impact does desertification have on populations?
Reduced soil fertility reduces crop yield, dust storms and drought means increased eye diseases and famine, loss of land and culture, 'forced' migration, break down of society as young and active may leave
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Other cards in this set

Card 2

Front

Tolerant to high salt levels

Back

Halophytes

Card 3

Front

Fleshy to store water

Back

Preview of the back of card 3

Card 4

Front

Become dormant/ loose their leaves, often look dead

Back

Preview of the back of card 4

Card 5

Front

Aridisols, which fall in two main categories, raw mineral and sierozems

Back

Preview of the back of card 5
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