Desert Flashcards
describe hot desert regions
- a large and dry region with little vegetation and high temp. Any desert has less than 250mm of precipitation a year.
describe the desert climate
- Many hours of sunshine due to absence of clouds
- located in sones of high atmospheric pressure
- lack of cloud cover causes large diurnal temperature variation, 30
- strong winds and sandstorms
- thunderstorms may be triggered by intense connective activity
describe desert soils
- soil is poorly developed due to lack of extensive vegetation
- dry and sandy/red desert soils
- lack of rainfall = lack of leaching, so with proper irrigation and soil management, plants can grow
describe desert plants adaptation
- drought avoidance:
> only live for a season, and store moisture/fat/sugar/proteins in seeds
> plants use a taproot to seek secure water supplies underground
describe atmospheric processes as a cause for deserts
- the global atmospheric circulation model (GACM) main factor distribution of deserts
- Air rising at the ITCZ forms two tropical cells called Hadley cells
- This air moves away from the equator and converges with a ferrel cell
- Air sinks towards ground
> As it towards the ground it warms
and becomes dryer
> And forms a high-pressure band
30 degrees north and south,
resulting in cloudless skys and
low precipitation
describe continentality as a cause for deserts
- Continentality is the way that a large land mass affects weather and climate
- Aridity gets higher in continental interiors as the moist airstreams from the ocean are reduced
describe relief as a cause for deserts
- moist air from the ocean moves towards a mountain
- mountain forces air to rise, causing it to cool and condense
> releasing rain - when air descends on leeward side it becomes warmer and drier
- Atacama desert in south america
- Andes mountain
describe cold ocean currents as a cause for desert
- cold ocean currents cool the surrounding air
> cold air is unable to pick up moisture
> little precipitation - the cold air remains low to the ocean and increases humidity
> may for fog and mist off shore - aridity is increased as rain formation is suppressed
- sun burns away mist and fog
- Atacama desert in South America
what are the three sources of energy in deserts
insolation, wind and water
what is insolation as an energy source
- Insolation is the amount of heat energy that reaches the earth’s surface.
- Insolation is high in desert regions due to the lack of cloud cover to absorb some of the suns heat energy.
- Insolation drives many weathering processes in desert regions
- Insolation leads to variable warming of the deserts surface which leads to wind, which can shape desert landforms
how is wind as an energy source
- Wind is driven by the atmospheric circulation system
- It’s an important secondary source of energy in hot deserts
- 20-50% of deserts surfaces are covered in sand which is transported and shaped by wind.
what is water as an energy source
- Little water in deserts
- But it’s important in developing landscapes.
- After infrequent heavy storms water will flow, increasing erosions rates in a short amount of time.
- A few rives flow in deserts as well and are an important source of energy, transporting sediment and creating landforms
weathering definition
- Weathering is the breakdown or disintegration of rocks in situ or close to the grounds surface
Mechanical weathering definition?
- The gradual disintegration of rocks without any chemical change.
what is thermal fracture?
- Rocks expand when heated and contract when cooled this is thermal fracture which causes them the rocks to breakdown
> Moisture in the rocks believed to
promote it, moister most likely
from dew
what are the 4 types of thermal fracture?
- Granular disintegration, granular rocks breakdown into sand, as different minerals in the rock heat up at diff rates
- Block separation, rock with defined joints breakdown at the joint into big blocks
- Shattering, rock without joints tent to shatter into sharp pieces
- Exfoliation, rocks are poor conductors of heat, so the surface of the rock which is heated and cooled repeatedly flake / peel off
what is salt crystallisation
- when it rains, the water dissolves salts in the soil.
- the rate of evaporation draws the water to the surface, and the sal crystals are deposited on the ground surface.
- over time the salt crystals grow and expand causing stress that breaks rocks.
what is frost shattering
- frost shattering happens when temperatures fluctuated below and above freeing from day to night
- freezing moisture in the cracks and pores of rocks which then expands and the contracts when it melts causing the rock to shatter
- its not common in hot desserts
what is chemical weathering
- rocks that change as a result of chemical action, usually in the presence of water