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Extreme
Environments
Hot
Deserts
Why are these
Deserts so Hot?
Reason 2 Angle of Suns rays
Parallel rays
of sunshine
Deserts are hot because of their proximity to the equator. The earth
is curved. This means that the energy from Ray B is spread/
dispersed over a
X
greater area – the
energy is less
intense. This is
shown by ‘X’ on the
picture.
Whereas the energy
Y
from Ray A is
concentrated on a
smaller area. This is
shown by ‘Y’ on the
Diagram.
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Extreme
Environments
Hot
Deserts
What are Hot
deserts like?
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
Hot
Deserts
Extreme
Environments
Hot
Deserts
Why are these
Deserts so Hot?
Reason 1 Distance of Travel
Features of hot deserts
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Why do deserts
receive very little
rainfall?
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
Deserts are hot because of their proximity to the equator. Ray B
has to travel further, through the atmosphere, dust & clouds,
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.
Parallel rays
of sunshine
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
Why do deserts
receive very little
rainfall?
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 side
Coastal 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
Hot
Deserts
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How does wind
affect how dry the
desert is?
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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Extreme
Environments
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Hot
Deserts
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Rain &
clouds
TRADE WINDS
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
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
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
Rain Shadow
The 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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Extreme
Environments
Hot
Desert
How have people
reacted to Hot Deserts
(media)
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
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Coastal Desert -Caused by cold Currents
Cold ocean currents affect the climate of the
coastal area. The colder sea cools down the land
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
Cold
the moisture from
Currents
the fog.
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Extreme
Environments
Hot
Desert
How have people
reacted to Hot Deserts
(media)
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.
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Extreme
Environments
Hot
Deserts
Where are hot deserts
found?
Hot deserts are found near to the tropic of Capricorn &
Cancer & Often between 150 - 300 N and South of the Equator
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Extreme
Environments
Hot
Deserts
Why are Deserts Cold
During the Night?
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Extreme
Environments
Hot
Deserts
What are hot deserts
like? Climate
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Extreme
Environments
Hot
Deserts
Why are Deserts Hot
During the Day?
There is a large Diurnal (daily) range in
temperatures in the desert.
Why are Deserts Hot
During the Day?
Why are Deserts Cold
at Night?
During the day, the
sun heats up the
ground. This is
because there are v.
few clouds to stop
the suns rays.
At night a lot of heat
escapes. This is
because there are v.
few clouds, which
means that the heat
can escape.
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Extreme
Environments
Hot
Deserts
What are hot deserts
like? Climate
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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Extreme
Environments
Hot
Deserts
What are Hot Deserts
like? Vegetation
For any vegetation to survive in a desert it must
adapt. The main challenge is the heat & lack of water
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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Extreme
Environments
Hot
Deserts
What are Hot Deserts
like? Vegetation
For any vegetation to survive in a desert it must
adapt. The main challenge is the heat & lack of water
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Extreme
Environments
Hot
Deserts
Xerophytes A sketch to
show key features of a cactus
2a) Ephemerals (plants)
What are Hot Deserts
like? Vegetation
Ephemerals Desert
after a ‘rain’ event
Hot
Deserts
What are hot deserts
like? Animals
How have camels adapted to life in deserts?
Thick fur & underwool –
warmth at night & insulation
against sun in day
Fat Stored in humps
- energy reserve
Concentrated urine
to retain as much
water as possible
Broad, flat leathery
pads on hooves to
spread out weight
on sand
Two rows of
eyelashes– protects
against sand & sun
Nostrils can be
closed to keep out
sand
Thick leathery
patches on knees to
protect when
resting on hot sand
Long, strong legs – carry
heavy loads & body
further away from sand
Hot
Deserts
What are hot deserts
like? Animals
Animals need to adapt in order to survive in desert
environments.
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.
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
Extreme
Environments
Extreme
Environments
They have to cope with extreme temperatures, lack
of food and lack of water.
These plants lie dormant for months, or even years in
the desert until it rains.
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Many desert animals do not have to drink at all –
they get all of their water from the moisture in food
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Extreme
Environments
Hot
Deserts
What are hot deserts
like? Weathering &
Erosion
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 refreezes) and exfoliation (sun heats layers of rock & they
break off like layers of an onion)
Freeze-Thaw
Weathering
Exfoliation /
onion skin
weathering
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Extreme
Environments
Hot
Deserts
What are hot deserts
like? Weathering &
Erosion
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.
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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Extreme
Environments
Hot
Deserts
What are hot deserts
like? Physical
features – Zeugen 1
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Extreme
Environments
Hot
Deserts
What are hot deserts
like? Physical
features – Zeugen 2
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Extreme
Environments
Hot
Deserts
Formation of Zeugen
Formation of Zeugen
Formation of Zeugen
Stage 1
Stage 2
Stage 3
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
Once the joints are
opened up, they are then
eroded away further by
the wind (abrasion).
The Zeugen can stand
between 3m – 36m high.
Extreme
Environments
Hot
Deserts
Now that abrasion starts
to erode the softer rock
(which is less resistant),
rock pedestals will often
form
This forms ridges and
hollows. At this stage
the erosion starts to
reach into the soft rock
What are hot deserts
like? Physical Features
Rock Pedestal
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
Example of a Rock Pedestal Classic mushroom resistant) rock
shape at he top
erodes more quickly
More resistant rock than harder (more
worn away slowly
resistant) rock and
because much of
Less resistant rock
worn away quickly
the erosion takes
Most erosion within place within the first
first metre of ground
metre of the ground
as wind lifts material
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Extreme
Environments
Hot
Deserts
What are hot deserts
like? Physical
features – Yardang
Yardang: Formation
Yardangs often form in alternate vertical bands
of hard and soft rocks. The weaker rocks are less
resistant and erode Stage 1 – flat surface
more quickly. The
harder rocks are
more resistant and Stage 2–Differential erosion due to abrasion
left as ridges.
Key
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Hard, Resistant Rock
What are hot deserts
like? Physical
features – Zeugen 3
Softer, less resistant rock
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Extreme
Environments
Hot
Deserts
What are hot deserts
like? Physical
features – Yardang
Yardang: Formation Stage 3 – Ridges become more pronounced
Yardangs are long and
thin in appearance. The
ridges become more
pronounced. Can be up
Cross section view
to 15m high
They also often occur
parallel to the prevailing
(most common) wind
direction, this is when
most erosion will occur.
Diagram is plan view
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Extreme
Environments
Hot
Deserts
What are hot deserts
like? Physical
features – Wadi
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.
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Extreme
Environments
Steep
Sides
Flat
bottom
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Extreme
Environments
Hot
Deserts
What are hot deserts
like? Physical features
Barchan Dunes
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.
Sand
deposited
Prevailing
Wind
Loose
Material
Hot
Deserts
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Some
plants
How do people use
hot deserts?
Oil and Gas
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.
Oilfield
drilling
rig
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.
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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Extreme
Environments
Cross
section
Hot
Deserts
How do people use
hot deserts?
Tourism
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Extreme
Environments
Hot
Deserts
What are hot deserts
like? Physical features
Barchan Dunes
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, therefore
they 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
Hot
Deserts
How do people use
hot deserts?
Agriculture
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.
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 underground aquifers (water holding rocks).
Positives People are able to find out about different cultures.
Some money from tourism will go to locals.
Positives – allows greater areas of desert
to be used. Creates employment.
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.
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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Extreme
Environments
Hot
Deserts
How do people use
Hot Deserts?
The Bedouin The Bedouin are pastoral (raise animals)
Lighting a
fire
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.
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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Extreme
Environments
Hot
Deserts
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Extreme
Environments
Hot
Deserts
Desertification
This 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
What Challenged do
hot deserts pose?
Desertification 1
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Extreme
Environments
Hot
Deserts
What Challenged do
hot deserts pose?
Desertification 2
Desertification - Physical Causes:
Less Rainfall – Overall, there has been a reduction in the
amount of rain for the Sahel over the last few years
Less Reliable Rainfall – Also, the rain is less reliable – it may
be many years before its rains properly in an area
Higher 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 recover
Over 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.
What Challenged do
hot deserts pose?
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.
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