ZIMSEC O Level Geography Notes:Characteristics and Location of Hot deser
NB:It is important to note that the Ordinary Level syllabus confines our study to hot deserts that are otherwise known as tropical deserts. Other deserts such as the cold deserts of Siberia are beyond the scope of the syllabus and thus we will limit our notes to hot deserts.
Characteristics of hot deserts
A desert is an area that receives little precipitation and is characterised by aridity or semi-aridity.
Most hot deserts rarely ever receive more than 250mm of rainfall per annum.
Such deserts are referred to as arid deserts for example some parts of the Sahara are referred to as being hyper-arid i.e. they receive less than 50 mm of rainfall per annum.
Some hot deserts are referred to as being semi-arid which means they receive at least 500 mm of rainfall per annum.
The Kalahari Desert is an example of a semi-arid hot desert.
However this rainfall may fall in one big storm followed by extended dry periods.
Deserts are mostly dry throughout the year except during freak storms that fall in some deserts e.g. the Namid Desert.
It is the shortage of moisture or the deficit in the water balance of desert areas that gives them most of their characteristics.
They have sandy soils.
They have experience heavy winds for example Harmattans and dust storms.
They have scant vegetation cover most of which is adaptive for example cacti (plural of cactus) or is confined to or near oases.
The shortage of wind means there is little cover to protect the soil from the effects of wind and thus wind erosion tends to be prevalent.
They have very large diurnal temperature ranges i.e. they are very hot during the day with some parts of the Sahara just approaching 50°C and very cold at night with temperatures often falling below freezing point.
Sometimes the temperature range is as high as 20°C or more.
Due to lack of shade and minimal cloud cover deserts have high evapotranspiration rates.
As has been already said above: precipitation in the form of rain is infrequent and unreliable in deserts.
These sporadic rains tend to come result in flash floods and can be associated with short periods of vegetative growth.
The flash floods may also create steep walled scarps and gulleys.
Landforms tend to have angular features because the lack of rain results in minimal chemical weathering.
The landscape of reg deserts consists of mostly pebbles, stones and gravel which cannot be blown away by the wind.
These landscapes are also known as desert pavements.
The surfaces of such desert landscapes are covered with closely packed, interlocking angular or rounded rock fragments of pebble and cobble size.
Some Western parts of the Sahara Desert have such landscapes.
The terms Reg (in the western Sahara), or Serir (in the eastern Sahara) or Gibber Plain (Australia), or Saï (Tarim Desert, central Asia), apply to a sandy plain or broad depression largely covered by lag gravels or angular boulders, from which the finer soil and sediment has been stripped by eolian ablation.
This is a type of desert landscape consisting of high, largely barren, hard, rocky plateaus, with very little sand because this has been removed by deflation.
The difference between Hamada and Reg is that Reg occurs as stony plains or depressions covered with gravels or boulders, rather than as highland plateaus( Hamada).
Hamada or hammada therefore is a desert high plain or plateau where deflation has removed the fine grained surface materials and left behind a surface of sand-scoured bedrock with or without a veneer of pebbles or boulders.
An erg is a broad, flat area of desert covered with wind-swept sand with little or no vegetative cover.
The word erg is Arabic for “dune fields” meaning a landscape covered by sand dunes.
They are a result of wind deposited sand piling up into sand dunes.
The landscape is hardly fixed nor is it stationary as the sand dunes and ridges are constantly moving as a result of wind action.
The Sahara Desert is the largest Erg desert in the world.
Erg deserts are sometimes known as Sand seas.
This owing to their undulating plains of sand the surface of which is blown into ripples and sand dunes.
N.B. As has already been said most deserts have all of the landscapes above within their boundaries. For example while the Sahara desert is for the most part an Erg desert some parts of it have both Hamada and Reg landscapes.