Y2) TERM 1- DESERTS Flashcards
(48 cards)
Describe typical hot desert characteristics
Typical hot desert characteristics would include dry (less than 250mm precipitation per yea), large diurnal temperature range, little biomass, and hot! (20-30oC)
How does atmospheric circulation cause aridity?
Atmospheric circulation causes aridity as high pressure (dry and cloudless) is created at the tropics due to the falling limb of the Hadley and Ferrel cells (driven by convection at the equator)
How does continentality cause aridity?
Continentality causes aridity since moisture becomes less available with distance from a large body of water – the further inland you go, the drier it gets
How does relief/ orography cause aridity?
Relief/ orography causes aridity by forcing warm and moist air to rise, cool and condense, which forms clouds (which rains!) – the leeward side therefore receives no rainfall, and is likely to be arid
How do cold ocean currents cause aridity?
Cold ocean currents cause aridity by limiting the amount of evaporation that can occur (as air is cooled, thus unable to contain much moisture) – air may be foggy, but not really “wet”!
What is the aridity index?
The Aridity index is a measure of dryness, as a ratio on precipitation vs potential evapotranspiration; the lower the value, the drier a place is.
What is the aridity index?
The Aridity index is a measure of dryness, as a ratio on precipitation vs potential evapotranspiration; the lower the value, the drier a place is.
Describe the “Soil Moisture Budget”
The “Soil Moisture Budget” shows how soil moisture varies throughout a year, depending on the relationship between precipitation (input) and evapotranspiration (output)
What is “positive feedback”? (Can you think of an example in a desert setting?)
“Positive feedback” is a self-perpetuating/ self-reinforcing cycle, that spiral further away from equilibrium. E.g., a lack of vegetation = reduced evapotranspiration = reduced rainfall = reduced vegetation = reduced evapotranspiration….
What is “negative feedback”? (Can you think of an example in a desert setting?)
“Negative feedback” is where a “check” occurs (an event that stops everything spiralling out of control/ further from equilibrium) Example: weathering = build up of sediment at slope bases (called “scree”) = protection of the slope = reduced weathering
describe desert soils
Desert soils – thin, infertile, alkaline (pH 8.5), often saline, minimal leaching, soil development is slow (hundreds of years), lack of vegetation (organic matter), capillary action occurs where evaporation exceeds precipitation, which draws salts upwards towards the surface from bedrock,. E.g. aridosols (which tend to be coarse in structure, free draining and, if hot enough a hard crust can form on the surface
Describe the soil moisture budget
The “Soil Moisture Budget” shows how soil moisture varies throughout a year, depending on the relationship between precipitation (input) and evapotranspiration (output)
Summerise typical desert soil characteristics
Desert soils – thin, infertile, alkaline (pH 8.5), often saline, minimal leaching, soil development is slow (hundreds of years), lack of vegetation (organic matter), capillary action occurs where evaporation exceeds precipitation, which draws salts upwards towards the surface from bedrock,. E.g. aridosols (which tend to be coarse in structure, free draining and, if hot enough a hard crust can form on the surface
Describe typical desert vegetation
Typical desert vegetation is small, occurs in patches, huddles together in each others shade, may have long/wide roots, will be succulent, corrugated, hydronasty
What are the inputs into a desert system?
Desert inputs include: water, heat and sediment
Summarise typical desert soil characteristics
Desert soils – thin, infertile, alkaline (pH 8.5), often saline, minimal leaching, soil development is slow (hundreds of years), lack of vegetation (organic matter), capillary action occurs where evaporation exceeds precipitation, which draws salts upwards towards the surface from bedrock,. E.g. aridosols (which tend to be coarse in structure, free draining and, if hot enough a hard crust can form on the surface
Describe typical desert vegetation
Typical desert vegetation is small, occurs in patches, huddles together in each other’s shade, may have long/ wide roots, be succulent, corrugated, hydronasty…
What is weathering?
Weathering is the process of breaking down a rock in situ (i.e. no movement); water and heat are very important (but deserts have very little water!)
List some examples of weathering…
Weathering types:
- Mechanical: Thermal fracture // Salt weathering // Frost shattering
- Chemical: Oxidation // Hydration // Carbonation
- Biological: Roots // Lichen
Abrasion…deflation… what’s the difference?
Abrasion is the “sand-blasting” effect of particles colliding with surfaces up to ~2m in height, gradually wearing it away; deflation is the ground surface gradually lowering as finer material is removed
Saltation…suspension…traction… what’s the difference?
Saltation is where small particles “bounce” along, suspension is where smaller particles are “carried” along, and traction/ surface creep is where the heaviest material is dragged/ rolled along
What are the 3 main types of river found in a desert?
The 3 main types of river found in a desert are exogenous, endoreic, ephemeral
What is episodic rainfall?
sodic rainfall = occasional/ sporadic rainfall
Water in the desert
Water in the desert – rare, but powerful
