Hot Desert Systems and Landscapes Flashcards
Desert
A place receiving less than 250 mm of rainfall per year
Different stages of Aridity
Arid- less than 250mm per year
Semi arid- 250-500mm per year
Hyper arid- very dry, not enough water to support life
What is an open system?
Matter and material is free to move out of the system into the surroundings
Dynamic equilibrium
When there is a balance between inputs an outputs so the stores stay the same
Positive feedback
When one element changes and the other stay the same and assistant a change of state
Negative feedback
When a system returns to what it used to be
Global distribution of deserts
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
Four characteristics that define deserts
Climate
Soils
Vegetation
Animals
Desert climate
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
Desert soil
Poor quality and lacks organic content
Thin- lacks ‘horizons’
Highlight saline
Majority is aridisol which has a high pH (7-8.5)
Types of vegetation and their adaptations
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
Four causes of aridity in deserts
Formation of subtropical high-pressure cells
Continentality affect
Rainshadow affect
Cold current affect
Subtropical high-pressure cells- Hadley cells
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
The continentality affect
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
The rainshadow affect
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
Cold current affect
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
Three sources of energy in the desert
Insolation
Winds
Run off
Sediment sources, cells and budgets
Inputs-
Rivers, wind, rain
Stores
Landforms, deposits
Outputs-
Erosion, transportation
Area dominated by erosion- net sediment loss
Area dominated by deposition- net sediment gain
Five geomorphological processes
Weathering mass movement erosion transportation deposition
What is weathering
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
Mechanical weathering
Rocks are physically broken down
Forms of mechanical weathering include exfoliation, differential expansion, shattering/thermal fracture
LEARN EACH PROCESS
Chemical weathering
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
Mass movement
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
What is a erosion?
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
What is transportation?
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
Deposition in deserts
Water and when deposit material when they experience reduction in capacity- causes a loss of energy
Role of wind in erosion in the desert
Causes abrasion and deflation
Role of the wind in transportation in the deserted
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
What is wind deposition?
Because when the velocity of the wind increases until it can no longer transport the grains is Currin
Four main sources of water in the desert
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)
Name all of the fluvial landforms in a desert
Wadi Alluvial fan Bajada Pediment Playas Mesa Buttes Inselbergs READ DESCRIPTION
Name all of the Aeolian landscapes in the desert
Venitfacts Yardangs Zuegen Deflation hollows Desert pavements
Name the two types of Sand dune
Sief dunes
Barchan dunes
Brachan dunes
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
Seif dunes
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
How are desert landscapes characterised
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
What is desertification?
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.
Causes of desertification
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
Reasons for why population growth cause desertification
Intensification of agriculture to feed large populations
Over-cultivation, overgrazing and deforestation- means vegetation cannot be established and causes of soil erosion
Areas at risk of desertification
1 billion people and 100 countries are at risk of desertification
12,000,000 ha of land been lost to the desertification
Impacts of desertification
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
Alternative futures the local populations
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
