deserts
TRANSCRIPT
Ideas How to use the revision cards:- Colour code the cards to show how confident you are with the topic- Ask someone at home to test you-Test yourself & highlight key words- Annotate (label) the cards- Re-write your own definitions- ‘Look, cover, check’- Draw a mind map to for some topics- Expand on key words- Read through cards- Cut out cards & stick around a room
Features of hot deserts
Hot Deserts have many different features:
- They are all dry and arid
-They may have a sandy, rocky or stony surface.
- They have very little rainfall
-They are often a lot hotter during the day, than at night
Extreme Environments
What are Hot deserts like?
Hot Deserts
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Reason 1 Distance of Travel Deserts are hot because of their proximity to the equator. Ray B has to travel further, through the atmosphere, dust & clouds,
Extreme Environments
Why are these Deserts so Hot?
Hot Deserts
Par
alle
l ray
s of
sun
shin
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therefore not as much heat reaches the poles. Whereas Ray A has a shorter distance to travel – meaning that it retains more of the heat from the sun.
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Reason 2 Angle of Suns rays Deserts are hot because of their proximity to the equator. The earth is curved. This means that the energy from Ray B is spread/
Extreme Environments
Why are these Deserts so Hot?
Hot Deserts
Par
alle
l ray
s of
sun
shin
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dispersed over a greater area – the energy is less intense. This is shown by ‘X’ on the picture. Whereas the energy from Ray A is concentrated on a smaller area. This is shown by ‘Y’ on the Diagram.
X
Y
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To understand why deserts receive little rain, we first need to know why rain occurs.Rain only forms when moist air rises, cools and condenses. Often this is by:Convection current – The sun heats the earth, which heats the air above it. The air becomes less dense, rises & then condenses. E.g. Tropical Rainforests at the equator
Frontal Rain – Two air masses meet. One is less dense than the other and is forced over the top of the other one. Meaning that it rises, cools and then condenses. E.g. UK
Relief Rain. An air mass is forced over an area of high land. The air rises, cools and condenses. E.g. in Hilly areas
Extreme Environments
Why do deserts receive very little rainfall?
Hot Deserts
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Extreme Environments
Why do deserts receive very little rainfall?
Hot Deserts
In deserts, the air does not contain much moisture & the air is usually falling meaning that it cannot condense to produce rain. Reasons why air falls:Trade Winds - Due to suns heat, air rises at the equator & falls near to the tropics (Cancer/Capricorn)
Rain Shadow - Air blows across a mountain. The air then loses all of its moisture on the other sideCoastal Deserts - If the ocean is particularly cold, then the air around the coast is cooled, meaning that it will not rise & condense
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Extreme Environments
How does wind affect how dry the desert is?
Hot Deserts
The prevailing (most common) wind direction also plays a very important role in desert climates. E.g. The Prevailing wind for the
Sahara desert in Africa is from the North East. This wind blows over land, so is quite ‘dry air’ as it does not pick up moisture from the sea. The same is true for other deserts.
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Rain ShadowThe rain gets forced up and over the (windward) side of the mountain. As the air rises, it cools and
condenses. The rain falls over the mountains. By the time the clouds reach the other (leeward) side there is no moisture left in the air
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Coastal Desert -Caused by cold Currents
Which means that the air is cool and not able to rise. Sea fog can form on the coast. Some plants have adapted so they are able to use the moisture from the fog.
Cold ocean currents affect the climate of the coastal area. The colder sea cools down the land
Cold Currents
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TRADE WINDS
forming cloud (B) and rain (C). This is why tropical Rainforests have so much rain. The air then moves away from the equator. Before it then falls. The air
Rain & clouds
The sun is most powerful at the equator. Here, the sun heats the earth (A) and the air Rises = low pressure system. As the air rises, it cools and condenses
then starts to fall at approx 300N (D) & 300S of the equator (E). As it falls, it warms up - the air can’t then produce rain = High Pressure system
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Hot deserts are depicted in a number of ways through different types of media. Accounts of historical expeditions The extremes of deserts may be stressed, & meeting different cultures. E.g. Across the empty quarter Thesiger
Through films Lawrence of Arabia & the English Patient.
Historical Newspaper articles “Across the sahara by caterpillar” The Observer Jan 14th 1923, by Major Gordon Home &The Murder of Major Gordon Laing Guardian August 2nd 1828
Extreme Environments
How have people reacted to Hot Deserts (media)
Hot Desert
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• http://www.youtube.com/watch?v=OxfZHP1HHHg
• http://www.youtube.com/watch?v=OlhLOWTnVoQ
• http://www.youtube.com/watch?v=lLaWj7d6PiE• http://www.youtube.com/watch?v=t65VrYZ2U9s
Through TV Bear Grylls, Travel Programmes, Michael Palin (Sahara and Pole to Pole)
Through Paintings ‘Pear Blossom Highway’ Hockney. ‘St John in the desert’ Veneziano
Each source of information will depict the desert in a different way. Sometime they will focus on the hardships of the desert and sometimes they will focus upon the difficulties. The desert may be portrayed much more positively - the mystical quality/romance of the desert may be highlighted.
Extreme Environments
How have people reacted to Hot Deserts (media)
Hot Desert
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Hot deserts are found near to the tropic of Capricorn & Cancer & Often between 150 - 300 N and South of the Equator
Extreme Environments
Where are hot deserts found?
Hot Deserts
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There is a large Diurnal (daily) range in temperatures in the desert.
Extreme Environments
What are hot deserts like? Climate
Hot Deserts
Why are Deserts Cold at Night?
At night a lot of heat escapes. This is because there are v. few clouds, which means that the heat can escape.
Why are Deserts Hot During the Day?
During the day, the sun heats up the ground. This is because there are v. few clouds to stop the suns rays.
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Extreme Environments
Why are Deserts Hot
During the Day? Hot
Deserts
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Extreme Environments
Why are Deserts Cold
During the Night? Hot
Deserts
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Extreme Environments
What are hot deserts like? Climate
Hot Deserts
You may be asked to describe what these graphs show. Refer to: Highest, Lowest, trends, anomalies. Include Data, months, increases/decreases seasons, links between Rain/Temp
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For any vegetation to survive in a desert it must adapt. The main challenge is the heat & lack of water
Extreme Environments
What are Hot Deserts like? Vegetation
Hot Deserts
1) Xerophytes These plants have made physical adaption's to survive the desert e.g. Cacti. Some of the features are:
- Spines – These deter predators and help to break up wind – reducing the amount of transpiration of water moisture
-Shallow roots – these quickly draw up any surface rainwater.
-Deep roots – Reach towards deep underground water stores.
-‘pleated’ body – The cactus can swell up to take in water
-Green body – body takes on role of photosynthesis.
-Small surface area – to reduce transpiration
-Thick waxy body – the make sure no water is lost
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For any vegetation to survive in a desert it must adapt. The main challenge is the heat & lack of water
Extreme Environments
What are Hot Deserts like? Vegetation
Hot Deserts
2a) Ephemerals (plants)
These plants lie dormant for months, or even years in the desert until it rains.
These plants grow & flower very quickly (within a few days) before the water gets evaporated or soaked away.2b) Ephemerals (seeds)In deserts there are many seeds waiting to be germinated. When the rains come they will quickly start to grow into plants, taking advantage of the conditions
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Extreme Environments
What are Hot Deserts like? Vegetation
Hot Deserts
Ephemerals Desert after a ‘rain’ event
Xerophytes A sketch to show key features of a cactus
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Animals need to adapt in order to survive in desert environments.
They have to cope with extreme temperatures, lack of food and lack of water.
To avoid daytime heat, many desert animals are Nocturnal; they burrow beneath the surface or hide in the shade during the day, emerging at night to eat.
Many desert animals do not have to drink at all – they get all of their water from the moisture in food
Extreme Environments
What are hot deserts like? Animals
Hot Deserts
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How have camels adapted to life in deserts?
Extreme Environments
What are hot deserts like? Animals
Hot Deserts
Two rows of eyelashes– protects against sand & sun
Nostrils can be closed to keep out sand
Thick fur & underwool – warmth at night & insulation against sun in day
Broad, flat leathery pads on hooves to spread out weight on sand
Thick leathery patches on knees to protect when resting on hot sand
Long, strong legs – carry heavy loads & body further away from sand
Fat Stored in humps - energy reserve
Concentrated urine to retain as much water as possible
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Weathering is the breaking up of rocks in the place that they are found. For Example:a) Physical Weathering. This includes Freeze-Thaw Weathering (ice expanding in a crack, thaws, then re-freezes) and exfoliation (sun heats layers of rock & they break off like layers of an onion)
Extreme Environments
What are hot deserts like? Weathering & Erosion
Hot Deserts
Freeze-Thaw Weathering
Exfoliation / onion skin weathering
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b) Chemical Weathering. This includes Salt Crystallisation (water evaporates & leaves behind salt, which expands) and Hydration (water reacts with chemical in the rock)
c) Biological Weathering. This is when plant roots grow into crack in the rock and force the cracks open.
Extreme Environments
What are hot deserts like? Weathering & Erosion
Hot Deserts
Erosion is the wearing away and removal of material. In deserts erosion is mainly caused by the wind. Although flash flooding can also happen & moves lose material. Both occur as there is little vegetation hold /bind sand.Deposition is the laying down of material that has already been eroded. Material from wind erosion often deposits is often laid down to form Dunes & flash floods carry material further down the valley & across flood plains
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Formation of Zeugen
Stage 1
When there are alternating layers of hard & soft rock there can sometimes be weaknesses in the joints. When the temperature changes and dew occurs at night, chemical weathering breaks up the rock and starts to open up the joints
Extreme Environments
What are hot deserts like? Physical features – Zeugen 1
Hot Deserts
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Formation of Zeugen
Stage 2
Once the joints are opened up, they are then eroded away further by the wind (abrasion).
This forms ridges and hollows. At this stage the erosion starts to reach into the soft rock
Extreme Environments
What are hot deserts like? Physical features – Zeugen 2
Hot Deserts
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Formation of Zeugen
Stage 3
The Zeugen can stand between 3m – 36m high.
Now that abrasion starts to erode the softer rock (which is less resistant), rock pedestals will often form
Extreme Environments
What are hot deserts like? Physical features – Zeugen 3
Hot Deserts
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Extreme Environments
What are hot deserts like? Physical Features Rock Pedestal
Hot Deserts
Rock Pedestal–These are sometimes called mushroom rocks as they are often ‘top heavy’. Over time, the wind (which carries particles of sand) wears away the rock. This type of erosion is called abrasion. A rock pedestal erodes more in places than others. This is because softer (less
resistant) rock erodes more quickly than harder (more resistant) rock and because much of the erosion takes place within the first metre of the ground
Example of a Rock Pedestal Classic mushroom shape at he top
More resistant rock worn away slowly
Less resistant rock worn away quickly
Most erosion within first metre of ground as wind lifts material
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Yardang: Formation
Yardangs often form in alternate vertical bands of hard and soft rocks. The weaker rocks are less resistant and erodemore quickly. The harder rocks are more resistant and left as ridges.
Extreme Environments
What are hot deserts like? Physical features – Yardang
Hot Deserts
Stage 1 – flat surface
Stage 2–Differential erosion due to abrasion
Hard, Resistant Rock Softer, less resistant rockKey
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Yardang: FormationYardangs are long and thin in appearance. The ridges become more pronounced. Can be up to 15m highThey also often occur parallel to the prevailing (most common) wind direction, this is when most erosion will occur.
Extreme Environments
What are hot deserts like? Physical features – Yardang
Hot Deserts
Stage 3 – Ridges become more pronounced
Diagram is plan view
Cross section view
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Extreme Environments
What are hot deserts like? Physical features – Wadi
Hot Deserts
A Wadi is a steep sided, deep, flat floored (dry) valley in a desert. Usually they do not have any water in them. There may be a few desert plants in the Wadi.
The material in the wadi is often loose. Therefore, when there is a flash flood, lots of material in the wadi is transported (moved) & then deposited (dropped) further down the valley.
Steep Sides
Flat bottom
Loose Material Some
plants
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Extreme Environments
What are hot deserts like? Physical features Barchan Dunes
Hot Deserts
Cross section
There are lots of different types of Sand Dune. They will differ according to the strength/direction of the wind, amount of vegetation, amount and type of sand. As the sand is loose, many types of sand dunes will migrate (move), due to the wind. Sand dunes mostly form when there is an obstacle – the sand builds around the obstacle – e.g. vegetation.
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Prevailing Wind
Sand deposited
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Extreme Environments
What are hot deserts like? Physical features Barchan Dunes
Hot Deserts
A Barchan Dune has a particular shape. It is a crescent shape with ‘horns’ pointing downwind. The upwind slope is approx 340 & the downwind slope is approx 150. Barchan dunes occur where there’s a limited supply of sand, thereforethey may by up to 100m apart. They form around an obstruction. The obstruction causes the wind to lose speed & then deposits, which causes a greater obstruction & more material is deposited. They will move over time
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Extreme Environments
How do people use hot deserts? Oil and Gas
Hot Deserts
General Beneath the Sahara are layers of sedimentary rock. Oil and gas is trapped beneath after is was formed from the remains of microscopic organisms millions of years ago.
Positives Exporting oil and gas can make a lot of money for countries.
Negatives The money isn’t distributed equally in the country & companies are often owned by overseas companies.
Oilfield drilling rig
It is very expensive to find oil and gas. Many of the larger, easy to find oil wells have now been used up. Transport oil and gas through pipelines is very expensive. Oil & gas are non-renewable resources – one day they’ll run out & burning these releases CO2.
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Tourism Many people find deserts to be fascinating and like the idea of visiting a desert. There are many tour companies that offer desert holidays, catering for different experiences – e.g. self drive, buggies, Bedouin tents/camel treks.
Extreme Environments
How do people use hot deserts?Tourism
Hot Deserts
Positives People are able to find out about different cultures. Some money from tourism will go to locals.
Negatives Some areas may have delicate environments which could be damaged by tourism. Some tours companies are foreign owned, meaning that not all money goes to the locals.
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Extreme Environments
How do people use hot deserts?Agriculture
Hot Deserts
In deserts, there is lots of flat, cheap land which makes it ideal for agriculture. Of course, water is needed for crops to grow. This can either come from irrigation channels which take water from rivers, or from well which takes water from under-ground aquifers (water holding rocks).
Positives – allows greater areas of desert to be used. Creates employment.
Negatives – River levels affects, aquifers will run out of water. Lots of chemicals are needed to feed the plants, as desert sand/soil has v few nutrients.
Desert
Agriculture
Irrigation channel
Water pumped up from aquifer
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The Bedouin The Bedouin are pastoral (raise animals) nomads (they move around from place to place. They overcome problems in the following ways:Water – They plan routes from water source to another. Also, use other indicators such as lines of plants and insects to find hidden underground water.Transport – Bedouins traditionally use camels as transport as they are able to carry large loads.
Extreme Environments
How do people use Hot Deserts?
Hot Deserts
Lighting a fire
Clothing - They traditionally wear woollen, loose fitting clothes, from their animals. These insulate against the heat of the day & provide warmth at night. Covering their bodies means that the amount of sweating is reduced, therefore reducing dehydration.Shelter–They need to be able to carry their shelter with them & pack up quickly. Their tents are made from Goat hair cloth as it is warm & waterproof. They are long/narrow allowing breeze to blow
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DesertificationThis is the process by which land turns into desert. After a ‘dry period’ land will often recover. Desertification is when the land is so damaged that it can’t recover.
The damage can be caused by physical (Natural) processes, or by Human (due to people) processes
One of the areas at risk of desertification is the Sahel, in Africa. It is on the southern edge of the Sahara. It is an area where some farming occurs & is mainly grassland
Extreme Environments
What Challenged do hot deserts pose? Desertification 1
Hot Deserts
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Desertification - Physical Causes:Less Rainfall – Overall, there has been a reduction in the amount of rain for the Sahel over the last few yearsLess Reliable Rainfall – Also, the rain is less reliable – it may be many years before its rains properly in an areaHigher Temps–This increases the amount of moisture/water lots through evaporation & transpiration (water from plants)Desertification - Human Causes:Irrigation–water for growing crops is quickly evaporated, salt in the water is left on the ground=unsuitable for future farming Over grazing – Herds of animals eat lots of vegetation. Too many animals means that the vegetation cannot recoverOver farming – Soil can’t recover from lots of farming. It loses it nutrients and loss of vegetation means that it blows away.More people - Many people in the Sahel use firewood. More people means too much may be collected-plants cannot recover.
Extreme Environments
What Challenged do hot deserts pose? Desertification 2
Hot Deserts
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Some of the other challenges that Hot Deserts Pose:
Drought – This is caused by lack of water of a long period of times causes drought - Crops may fail.
Famine – This is caused by drought. Large numbers of people are not able to access food/water.
Cultures – Over time, cultures change. The Bedouin for example, find it more and more difficult to maintain their traditional way of life. Many cultures have dies out. This is sometimes due to desertification, they are not enough resources to support the Bedouin.
Extreme Environments
What Challenged do hot deserts pose?
Hot Deserts
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