Hot Deserts (Physical) Flashcards
Where are hot deserts located?
Many of the earth’s hot deserts are found around the tropics of capricorn and cancer. Others can be found in continental interiors (e.g Africa or Australia) or adjacent to mountain ranges (e.g the Andes)
How much of the Earth’s land surface do hot deserts cover?
25-30%
What is the difference between a landform and a landscape?
am individual landform may extend for several hundred metres but a desert landscape can cover thousands of square kilometers - it comes down to a matter of scale. Desert landscapes result from complex interactions between geological structures and the processes of weathering, mass movement, wind and water. Land forms have developed over long periods of time, during which the landscape-forming processes have changed.
Name the three main types of desert landscape
Hamada - bare rocky surfaces such as plateaux
Reg- a stony desert where rock fragments are scattered over a large plain
Erg - predominantly sand (sometimes called a “sand sea”)
Give some examples of desert inputs
precipitation, solar radiation, descending air at the ITCZ
Give some examples of desert outputs
runoff, reradiation of long-wave radiation from the Earth’s surface into the atmosphere, evaporation
Give some examples of desert energy
latent heat associated with changes in the state of water, energy associated with flowing water and moving air
Give some examples of desert stores/components
playas, sand dunes, landforms, vegetation
Give some examples of desert flows/transfers
wind-blown sand, surface runoff, salinisation, sediment transfer
Give an example of a positive feedback loop within a desert system
the presence or absence of vegetation can affect the regional climate. If vegetation is removed(overgrazing or deforestation) this will reduce the moisture emitted into the atmosphere. Reduced humidity may lead to less rainfall, which then reduces the extent of vegetation further.
Give an example of a negative feedback loop within a desert system
Intense weathering of a slope leads to a build-up of an apron of scree against the mountainside. Without removal (erosion) this apron extends up the mountainside, protecting the lower slopes from weathering
Give an example of dynamic equilibrium within a desert system
Seasonal cycles of winds in some desert regions can lead to small-scale and short term adjustments in sand dune profiles, but from year to year their shape remains broadly the same.
Describe desert climates
- lack of rainfall and extremely high average temperatures in the summer
- high amount of direct sunlight due to absence of clouds (high pressure zone)
- large diurnal range due to little cloud cover
- strong winds and sandstorms
- thunderstorms can be triggered by intense converse activity
- some coastal areas (Atacama Desert) can have coastal fog
Describe desret soils
the climate is too dry to support extensive vegetation so soils tend to be poorly developed. When the scarce vegetation dies, the lack of water prevents it rotting to produce humus to enrich a developing soil.
Soils tend therefore to be very dry and sandy. However, the lack of rainfall means that leaching (removal of nutrients by water) will be minimal
Why can desert soils sometimes be referred to as “red desert soils”
The red colour, typical of many hot deserts is the result of the weathering process of oxidation, where oxygen reacts chemically with iron-rich rocks. They are highly porous and permeable with poor moisture retention.
Describe desert vegetation
Deserts are highly hostile environments for plants due to the low rainfall, high temperatures and hgih rates of evapotranspiration.
How can plants adapt to be better suited to desert environments
Drought avoidance - some plants avoid drought by only living for one season. They dry up and die during the drought but store moisture, oil, fat, sugar and protein in seeds. Other plants use a long taproot to seek secure water supplies deep underground
Drought resistance -to resist drought, some plants are able to adjust their metabolism, effectively becoming dormant. Others drop their leaves to conserve moisture
Water storage - succulent plants, such as cacti and agave, have shallow roots so that they can quickly absorb water during a storm. Water is then stored in fleshy leaves, stems and roots
What causes aridity and the formation of deserts
1-Atmospheric processes
2-continentality
3-relief rainfall/rain shadow effect
4-cold ocean currents
Explain how Atmospheric processes cause aridity
The main factor affecting the distribution of hot deserts is the global atmospheric circulation system.
Air dissing in the Intertropical Convergence Zone (ITCZ) diverges and spreads both north and south to two distinctive tropical circulation cells (the Hadley cells). The air moving poleward cools and converges with the equatorward limb of the Ferrel cells, causing it to sink towards the ground. As the air sinks, it warms and becomes drier, establishing a broad belt of high pressure. Sinking air associates with these anticyclones result in cloudless skies and the subsequent lack of rainfall associated with deserts.
The lack of cloud accounts for the high sunshine totals and the extremes of temperature. High rates of evapotranspiration are common under these conditions, which further increases the levels of aridity on the ground.
Explain how Continentality cause aridity
Continentality is the way that a large land mass affects weather and climate. Aridity tends to be higher in continental interiors, such as in Central Africa, Asia and Australia. This is because the influence of moist air streams from the ocean is reduced.
