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Physical Geography > Hot Desert Systems and Landscapes > Flashcards

Hot Desert Systems and Landscapes Flashcards

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1
Q

Desert

A

A place receiving less than 250 mm of rainfall per year

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2
Q

Different stages of Aridity

A

Arid- less than 250mm per year
Semi arid- 250-500mm per year
Hyper arid- very dry, not enough water to support life

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3
Q

What is an open system?

A

Matter and material is free to move out of the system into the surroundings

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4
Q

Dynamic equilibrium

A

When there is a balance between inputs an outputs so the stores stay the same

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5
Q

Positive feedback

A

When one element changes and the other stay the same and assistant a change of state

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6
Q

Negative feedback

A

When a system returns to what it used to be

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7
Q

Global distribution of deserts

A

No deserts on the equator to air currents
Almost all deserts lie on the Tropic of Cancer and Capricorn
Cancer- Sahara desert, Syrian desert
Capricorn- Atacama desert, Namib desert

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8
Q

Four characteristics that define deserts

A

Climate
Soils
Vegetation
Animals

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9
Q

Desert climate

A

0-55 degrees
Day is hot- no cloud coverage, short wave radiation
Night is cold- no clouds to retain long wave radiation
Therefore deserts have a large diurnal radiation

Very little precipitation, rapid surface run-off and low infiltration
Negative water balance EVAPOTRANSPIRATION>PRECIPITATION

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10
Q

Desert soil

A

Poor quality and lacks organic content
Thin- lacks ‘horizons’
Highlight saline
Majority is aridisol which has a high pH (7-8.5)

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11
Q

Types of vegetation and their adaptations

A

Xerophytes- cactus-stores moistures in body
Phreatophytes- creosote bush- deep roots
Halophytes- salt bush- can tolerate high levels of saline soil
Ephemerals- Boerhavia- has a short life cycle

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12
Q

Four causes of aridity in deserts

A

Formation of subtropical high-pressure cells
Continentality affect
Rainshadow affect
Cold current affect

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13
Q

Subtropical high-pressure cells- Hadley cells

A

Net air at the equator heats up and rises- water vapour condenses and causes severe rainfall
Air moves poleward and begins to cool and fall
Sinking air causes high-pressure and therefore winds
This is where deserts form as the air quickly warms up and remains without water

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14
Q

The continentality affect

A

Maritime places have a high rainfall than those inland

Air moving over content masses lose water as they go inland- this is where most deserts lie

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15
Q

The rainshadow affect

A

Air from the sea contains moisture as it is forced inland it rises over areas of high topography
It loses all its water through precipitations and sinks down the leeward much more dry

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16
Q

Cold current affect

A

Called current move towards the equator from the poles and a soon as it comes in contact with heartland it condenses and falls as precipitation

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17
Q

Three sources of energy in the desert

A

Insolation
Winds
Run off

18
Q

Sediment sources, cells and budgets

A

Inputs-
Rivers, wind, rain

Stores
Landforms, deposits

Outputs-
Erosion, transportation

Area dominated by erosion- net sediment loss
Area dominated by deposition- net sediment gain

19
Q

Five geomorphological processes

A 
Weathering 
mass movement 
erosion 
transportation 
deposition
20
Q

What is weathering

A

The breaking down of rocks, soils and minerals as well as artificial materials to contact with the earths atmosphere biota and water. Weathering occurs in situ so it’s not the same as erosion

21
Q

Mechanical weathering

A

Rocks are physically broken down
Forms of mechanical weathering include exfoliation, differential expansion, shattering/thermal fracture
LEARN EACH PROCESS

22
Q

Chemical weathering

A

Amico process is reacting with minerals in the rocks causing them to break up
Forms of chemical weathering include crystal growth, oxidation, hydration and hydrolysis
LEARN PROCESSES

23
Q

Mass movement

A

Mass movement is the movement of material downhill under the influence of gravity but may also be assisted by rainfall
Due to minimal rainfall and vegetation mass movement in deserts is dominated by rockfalls and rockslides

24
Q

What is a erosion?

A

The process that wear away the land surface through mechanical action, erosion is a different form of weathering as it removes material by processes of wind and water

25
Q

What is transportation?

A

The process that moves materials from the site where erosion took place to the site of deposition
This is done through traction, saltation, suspension and solution

26
Q

Deposition in deserts

A

Water and when deposit material when they experience reduction in capacity- causes a loss of energy

27
Q

Role of wind in erosion in the desert

A

Causes abrasion and deflation

28
Q

Role of the wind in transportation in the deserted

A

Suspension- when particles very fine and easily picked up by the wind
Saltation- wind speeds exceed the threshold velocity and lifted vertically before falling back down, creating a bouncing motion
Surface creep

29
Q

What is wind deposition?

A

Because when the velocity of the wind increases until it can no longer transport the grains is Currin

30
Q

Four main sources of water in the desert

A

Exogenous rivers - permant rivers flowing through deserts e.g. The Nile
Endogenous rivers- water bodies with the source within the desert, have a severed flow to the ocean
Ephemeral streams- flow intermittently or seasonally after rainfall, generate high levels of discharge and surface run off
Episodic flash floods- three types (sheet flood, overland flow and channel flash flooding)

31
Q

Name all of the fluvial landforms in a desert

A 
Wadi
Alluvial fan 
Bajada 
Pediment 
Playas
Mesa
Buttes
Inselbergs  
READ DESCRIPTION
32
Q

Name all of the Aeolian landscapes in the desert

A 
Venitfacts
Yardangs 
Zuegen
Deflation hollows 
Desert pavements
33
Q

Name the two types of Sand dune

A

Sief dunes

Barchan dunes

34
Q

Brachan dunes

A

Crescent shaped mounds
backs face 90 degrees to the wind
Up to 30m tall and hundreds of meters long
Two faces
Gentle back slope and steep slip face
Forms when a prevailing wind in a constant direction blows with a limited sand supply
It moves when sand is added to the crest and the leeward face collapses and therefore causes a forward movement
E.g brachan dunes in southern Peru

35
Q

Seif dunes

A

Sinuous longitudinal dunes
200m tall
Form in areas of bi- directional wind regimes and limited sand supply
Stretch hundreds of meters
Has two faces
Form parallel to the wind direction , Wind approaches the dune obliquely and flows parallel through the troughs moving the sand down and in the elongating the Dune
Minimal movement, well-established and stable
E.g. Seif dunes in Morocco

36
Q

How are desert landscapes characterised

A

The lack of vegetation causing exposure and making geomorphical features clearly visible
Speed and nature of weathering dependent on diurnal temperature changes and rapid heating and cooling
The presence of moisture

37
Q

What is desertification?

A

The persistent degradation of dryland ecosystems by variation in climate and human activities. It results in a reduction or loss of the biological or economic production of drylands. It is a a process by which fertile land is becoming infertile.

38
Q

Causes of desertification

A

Climate change- loss in rainfall and higher temps

Desert population growth due to natural increase and migration as populations flee environmental/human problems in neighbouring areas

Change in farming

39
Q

Reasons for why population growth cause desertification

A

Intensification of agriculture to feed large populations

Over-cultivation, overgrazing and deforestation- means vegetation cannot be established and causes of soil erosion

40
Q

Areas at risk of desertification

A

1 billion people and 100 countries are at risk of desertification
12,000,000 ha of land been lost to the desertification

41
Q

Impacts of desertification

A

Species lost
Reduction habitats
Increased competition between species
Extinction risks

Drought and famine
Forced migration
Loss of land
Loss of culture

Increase salinity of soils
Increased numbers of sandstorms
Vegetation and damaged by sandblasting from desert winds

42
Q

Alternative futures the local populations

A

Global Orchestration- increase in globalised world but ecosystem management is reactive to current issues and development initiatives are top down

TechnoGarden- Technology is shared to allow populations affected by future desertification to be proactive in prevention by using green technologies

Order from strength- Community is on power to react to environmental problems as the development focus is more bottom up to concentrate on security and economic growth

Adapting Mosaic- bottom up proactive scenario where the emphasis is on empowering the development of local adaptations and learning

Physical Geography (2 decks)

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