Systems and processess

Question 1

Sources of energy in hot desert environments

Answer 1

• Runoff
• Insolation
• Wind

Question 2

Sources of energy in hot desert environments : Runoff

Answer 2

• Rainfall is localised and unpredictable in terms of time and space
• Ground conditions of baked earth act like concrete and there is limited vegetation
• all increase overland flow (runoff) which becomes an agent of erosion and transportation

Question 3

Sources of energy in hot desert environments : Insolation

Answer 3

• Changes in temperature drive processes
• 12 hours of sunshine a day
• Sun is high, giving a high angle of incidence, so raditation is concentrated on a small surface
• moisture enables latent heat to escape as water evaporates
• As there is little moisture, there is no cooling effect of the escape of latent heat

Question 4

Sources of energy in hot desert environments : wind

Answer 4

• Localised winds e.g harmattan of the Sahara
• Winds blow outwards towards the edge of the desert
• Winds act as an agent of erosion and transporaition

Question 5

Sediment sources

Answer 5

• Weathering of parent material
• Fluvial sources - River : -if they are ephemeral (they dry up) the sediment is left behind on dry river beds
• Aeolian - wind blow deposits

Question 6

Sediment cells and budgets

Answer 6

• Areas dominated by erosion are a source of sediment for other areas and their system has a net sediment loss
• Areas dominated by deposition receive sediment and their system has a net sediment gain

Question 7

Geomorphological processes

Answer 7

• Deposition
• Erosion
• Mass movement
• Weathering
• Transportation

Question 8

Geomorphological processes :Transportation

Answer 8

• Traction = large stones and boulders rolled along
• Saltation = bouncing actions of smaller stones and pebbles
• Suspension = silt and clay carried in wind and water
• Solution = dissolved minerals within water

Question 9

Geomorphological processes : Mass movement

Answer 9

• Rock falls = free-falling small blocks of detached rock, main form of mass movement due to lack of moisture
• Rock slides = material collapse of a rock face

Question 10

Geomorphological processes : Weathering

Answer 10

Main processes forming desert landscapes due to :

• Regular heating and cooling of surfaces
• Presence of even small amounts of moisture
• Presence of living organisms
• Types = Chemical = crystal growth, hydration, Mechanical = thermal fracture, exfoliation, Weathering = biological

Question 11

Distinctively arid geomorphological processes : Thermal fracture (Mecanical)

Answer 11

• Thermal fracture = High diurnal temperatures ranges cause expansion and contraction in rock, leading to disintegration over a long period of time

Question 12

Distinctively arid geomorphological processes : Exfoliation (Mecanical)

Answer 12

• Exfoliation =

‘onion skin weathering’

• During daytime, the rocks are exposed to the sun which causes the rocks to expand. However during the night, the rock contracts because of the cooler temperature. 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.

Question 13

Distinctively arid geomorphological processes : Chemical (Crystal growth, Hydration, Oxidation and Hydrolosis)

Answer 13

Crystal growth = Water present in joints and bedding evaporates, leaving salts behind. Crystals grow over time, exerting pressure. Heating and cooling lead to expansion and contraction, which assist in the physical breakdown of rock

• Hydration = absorption of even the smallest amount of moisture (such as dew) causes rock to swell, making rock vulnerable to further mechanical breakdown

Oxidation = 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)

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

Question 14

Distinctively arid geomorphological processes Block and granular disintegration

Answer 14

Block disintegration = is when the rocks split along joints forming large rectangular shaped blocks. .

Granular disintegration = is when grains of a rock become loosened and fall out, to leave a pitted, uneven surface because of changing temperature

Question 15

Role of wind

Answer 15

• As deserts are so dry and vegetation cover so limited, there is little to protect the desert surface against the action of the wind.

Question 16

Role of wind : Deflation

Answer 16

• main erosional effect, removal of fine particles such as sand, silt and clay particles. Can result in duet storms.

Main methods of transportation are :

• Creep = sand grains slide and role across the surface (>0.25mm diameter)
• Saltation = skipping motion of sand grains as they are lifted and fall again (0.15-025mm)
• Suspension = very small dust particles can be carried in the air (<0.15mm)

Question 17

Role of wind : Abrasion

Answer 17

• a sand blasting effect, where fine material carried in the wind as blocks. Forms rock Pedestals, Ventifacts, Yardangs and Zeugens

- dependent on Velocity of wind
Frequency of wind
Wind direction
Rock lithology
Size of loose particles on the desert floor

Question 18

Water in deserts :

Answer 18

• River actions are also important in the moulding of desert landscapes.
• Although rainfall quantities are low overall, substantial amounts of rainfall may occur from time to time.

Question 19

Water sources :

Answer 19

• Exogenous = perennial rivers which flow in hot desert environments but gain their water in humid areas
• Endoreic = perennial and flow into an inland drainage basin in the desert, terminate inland. Often seasonal
• Ephemeral = short lived and flow only after heavy rain. as rain can’t infiltrate into the baked desert surface and flows over land. When they dry up they are known as wadis

Question 20

Characteristics that enable them to generate considerable runoff from quite low rainfall intensities :

Answer 20

• Limited vegetation cover provides little organic matter on the surface to absorb water
• The sparseness of the vegetation means that humus levels in the soil are low, and combined with minimal disturbance by plant roots, this makes the soil dense and compact
• As there is virtually no plant cover to intercept rainfall, rain is able to beat down on the soil surface with maximum force
• Fine particles, unbound by vegetation, are redistributed by splash to lodge in pore spaces and create a surface of much reduced permeability.

Question 21

Flooding in deserts

Answer 21

• Sheet floods result when there is an intense downpour that quickly runs off hard-baked surfaces which are imperable. Slow moving, even flow
• Overland flow intensifies
• This movement of water can become an effective erosional force
• channel flash flooding occurs, very strong, sudden and rapid. Have lots of energy causing traction and erosion