Deserts

http://au.youtube.com/watch?v=rA89xxCzrm8 Intro vid to music Intro Flash vid to Jack Johnson music http://blip.tv/scripts/flash/blipplayer.swf?autoStart=false&file=http://blip.tv/file/get/Adtastic2001-Deserts994.flv?source=3

• Deserts occur where evaporation is greater than precipitation or where precipitation is less than 250 millimetres a year

• These areas cover about 30% of the earth’s surface.• Some of the worlds deserts are hot and others are cold• All, however are dry.

HOTCOLD

Types of Desert• The world’s deserts are often classified according to the

amount of precipitation they receive.

ClassificationClassification Amount of PrecipitationAmount of Precipitation

Extremely Arid

No Precipitation for 12 consecutive months

AridLess than 250 millimetres of

precipitation per year

Semi Arid Between 250 millimetres and 500 millimetres of precipitation per

year

HotHot Deserts Deserts• Hot deserts generally lie around the

tropic of cancer or the tropic of Capricorn.

• They have very hot summers and warm winters.

• Temperature extremes are common, as cloud cover is rare and humidity is very low.

• This means there is nothing to block the heat of the sun during the day or prevent its loss at night.

• Temperatures can range between around 45° and -15 ° Celcius in a 24 hour period.

ColdCold Deserts Deserts•Cold Deserts lie on high ground generally north of the Tropic of Cancer and south of the tropic of Capricorn.

•They include the polar deserts

•Any precipitation falls as snow

•Winters are very cold and often windy; summers are dry and mild to warm.

24 Deserts Game http://www.purposegames.com/game/111

Where are deserts located?

• Cold ocean currents exist off the Western sides of continents. Winds blowing over these currents lose their moisture over the sea and are dry by the time they get to land.

• In the interior of continents • Winds blowing over continents are dry by

the time they get to the interior of continents.

Location of Deserts

• Depressions/basins in the interior of continents

• The surrounding highlands around depressions/basins cause a rainshadow effect leaving the depression dry.

Location of Deserts

• The leeward side of tall mountains

• Moisture carrying winds are blocked by the side (windward side) of tall mountains. The other side (leeward side) is consequently dry, and deserts may be formed there.

Account for the location of deserts?

1. Cold ocean currents off the west coast of continents

2. Dominance of high pressure systems

3. Lack of relief rainfall

Cold ocean currentsCold ocean currents

There are cold ocean currents off the west coast of most continental landmasses. Evaporation rates from cold water are low. This limits the amount of moisture in the air and the amount of precipitation.

Dominance of high Dominance of high pressure systemspressure systems

Deserts & windsDeserts & winds

Deserts: where & whyDeserts: where & whyDeserts & windsDeserts & winds

Deserts: where & whyDeserts: where & whyDeserts & windsDeserts & winds

Australia

• Apart from Antarctica, Australia is the driest continent in the world. About 35% of the continent receives so little rain, it is effectively desert. In total, 70% of the mainland receives less than 500mm of rain annually, which classes it as arid, or semi-arid.

Flash of atmospheric circ http://www.school-portal.co.uk/GroupDownloadFile.asp?GroupId=12426&ResourceID=40425

Australia's deserts, listed below, are distributed throughout the western plateau and interior lowlands. The total desert

area equates to 18% of the total mainland area of Australia.

Lack of relief rainfallLack of relief rainfallDeserts & windsDeserts & winds

Middle-latitude desertsMiddle-latitude deserts

exist in rain shadows.

Orographic RainfallOrographic Rainfall

The dry air mass becomes warmer, with little chance of rain. Deserts are often found on the leeward side of large mountain ranges

Warm moist air approaches a mountain barrier

The air mass is forced to rise as it hits the mountain and condenses into clouds

Orographic rainfall occurs on the windward side of the mountains

The air mass, now drier, flows down the leeward side of the mountains

Orographic RainfallOrographic Rainfall

The dry air mass becomes warmer, with little chance of rain. Deserts are often found on the leeward side of large mountain ranges

Warm moist air approaches a mountain barrier

The air mass is forced to rise as it hits the mountain and condenses into clouds

Orographic rainfall occurs on the windward side of the mountains

The air mass, now drier, flows down the leeward side of the mountains

Climate (Atmosphere and Hydrosphere)

• The desert temperature is not always hot. During the night, desert temperatures are quite cold, even below freezing point. The daytime temperatures are hot because there is very little cloud cover. This means that maximum radiation from the sun reaches the surface of the earth. In summer the temperature can reach as high as 40°C, while in winter, the temperature can reach 24°C.

Large diurnal range

• At night time, the lack of cloud cover allows the heat of the day to escape quickly, resulting in cold, even freezing, temperatures. The difference between the daily minimum and maximum temperatures is known as the diurnal range.

Extremely hot days and very cold nights:

• Cloudless skies allow the sun to heat the atmosphere very quickly to very high temperatures. At night this same lack of cloud cover means that there is no insulation to hold the heat in and it escapes very quickly to the clear night sky.

• So night temperatures are very cold and can even drop below freezing.

• Deserts have a very high DIURNAL (daily) range of temperatures, usually more than 20C.

• The annual temperature ranges are also (difference between summer and winter) are also relatively high in deserts.

Task: Construct a climate graph for Wadi Halfa

Desert Landforms

• A plateau is a broad, level, elevated region commonly bounded partly by cliffs.

• A mesa is smaller, flat-topped hill bounded by cliffs. They are usually wider than they are high.

• A butte is a narrow hill of resistant rock bounded by cliffs. Buttes are usually higher than they are wide.

• A wadi is steep sided, flat floored desert watercourse (river or creek) which is usually dry.

• Alluvial Fans are fan-shaped deposits of material in zone of deposition. They form where water flowing down wadis meets the desert and dumps its sediment.

• Playa Lakes are ephemeral (temporary) lakes where water flows into a desert depression. Eventually the water evaporates and salt pans or clay pans are formed.

• Inselberg is an isolated hill of harder rock.

• A Bolson is the flat desert basin.

A sandy desert or an erg surface

A stony desert or an reg surface (known as a gibber plain in Australia)

A rocky desert or hamada surface

Using pg 255 of the text draw and Annotate and label

All 4 sand dunes in figure 12.2eUse the heading Sand Dunes.

Then read p254 and describe the 4 types of dunes

Transverse dunes

Reg or stony desert

Erg or sandy desert

Inselbergs

Barchan dune

Star dunes

Alluvial fan

Arch Animation http://www.classzone.com/books/earth_science/terc/content/visualizations/es1601/es1601page01.cfm?chapter_no=visualization

Butte

Badlands

Desert Landforms

• Examine the following 5 photographs

• What have these pictures got in common?

• Divide them into two types of landscape.

• Which is the odd one out?

Photo 1 – Monumental hills

Photo 2 The

mountains above a stream

Photo 3 – sand and sky

Photo 4 – “Badlands landscape”

Photo 5 The archway

The photos and the questions

• Monumental hills

• The mountains above a stream

• Sand and sky

• “Badlands” landscape

• The archway

• 1 What have they all got in common?

• 2 Which is the odd one out? [and why]

• 3 If you had to put them into 2 groups – which ones would you put together ? Explain.

Here is what one pupil thought!

They all look rather mountainous with exposed rock and very steep slopes.I put these three together – I think!

These photos seemed to form another group

They both have flat areas which are kind of bumpy – but not seriously mountainous like the others?

This was the odd one out!This was the odd one out!

• This was the odd one out because it had water in running and that would have eroded the landscape in a different way to all the others!

• Do you agree Do you agree with the pupil’s with the pupil’s opinions?opinions?

Processes affecting landform shapes:

• Erosion:

• Erosion is the picking up and removal of material. Erosion occurs as a result of the action of wind, water, ice, waves and gravity.

Weathering:

• Weathering is the breaking down of materials (rock and soil) into smaller materials through the action of weather such as temperature changes, rainfall and wind.

Deposition:

• Deposition is the accumulation of sediment by the action of agents such as water and wind. Water can deposit sediment to build landforms such as alluvial fans: wind can deposit sediment, such as sand, to build sand dunes.

Interactive game 2 players

• http://www.games4geog.com/cg/desertintro.swf

Desert Keyword Quiz

10 Questions

Name the landform11

What type of desert is Mr Anderson in?

22

Name the landform33

Name the landform44

Name the landform55

Name the landform66

Name the landform77

What type of desert is this?88

Name the landform99

Name the landform1010

Desert Keyword Quiz

10 ANSWERS

Name the landform11

wadi

What type of desert is Mr Anderson in?

22 erg

Name the landform33

alluvial fan

Name the landform44

mesa

Name the landform55

sand dune

Name the landform66

butte

Name the landform77

escarpment

What type of desert is this?88

reg

Name the landform99

oasis

Name the landform1010

playa

DESERT DESERT ANIMALSANIMALS

Animal Facts- Animal SurvivorsAnimal Facts- Animal Survivors

• Because of the lack of vegetation, there are very few food chains in deserts.

• Most desert animals are small, which keeps heat gain and loss to a minimum. They are also mostly nocturnal.

• Most avoid the heat by hiding in burrows or under rocks by day and being active during the night or early morning.

• Some desert animals also have adaptations for conserving water.

• Insects and reptiles have thick outer coverings so that they lose little water as possible through evaporation.

Fat reserves stored for when food is scarce

Nostrils that can be closed during sand storms

Able to carry large amounts of water (equal to about 25% of its body weight in its stomachCAMEL

KANGAROO RAT

Collects dry seed, which it stuffs into its cheeks. It empties the seeds into its burrow, where they soak up water vapour exhaled in the rats breath. When it eats the seed it get its water back.

No sweat glands, so they don’t lose water through perspiration.

Small to keep heat gain and loss at a minimum

Camels

• The camel originally came from Asia where it was domesticated and then introduced into Africa. It has been used there by nomadic tribes such as the Tuareg in their camel caravans, carrying goods such as dates, salt and millet. Camels have a large number of adaptations allowing them to survive in the desert. Many of these adaptations can be seen in these photographs.

Camel Adaptations

• Wide spreading feet to prevent the camel from sinking into the sand

• Tough patches of skin on their knees for kneeling

• Thick fur to insulate them from the sun

• The hump, used for storing fatty tissue (not water), to provide energy

Adaptations

• Tough lips for eating hard, thorny plants • Long eyelashes, hairy ears and nostrils that

close to keep sand and dust out • Camels can also go for days without drinking

water. • They can smell water, which can be quite a

number of kilometres away • They can drink salty water • They can drink up to 100 litres (or 1⁄3 of their

body weight) in 10 minutes and then travel for 100 kilometres on this supply.

• Desert plants are called xerophytes. They have adapted to the harsh climatic conditions of low and irregular rainfall, extreme temperatures and high evaporation by being able to store water or reduce moisture loss through transpiration so that they can survive.

• http://www.purposegames.com/game/1669/info Desert Animals Game

DESERT DESERT PLANTSPLANTS

Plant survivors• Drought resistant plants are known as xerophytesxerophytes• Many of these plants are known as succulents,

which means they are able to store water in their tissues.

• Most desert plants have small leaves that are spiky or wax coated. This reduces transpiration and deters animals.

• Some send their roots deep into the ground to tap into the ground water table.

• They spread their shallow roots to increase their personal catchment area for when it rains, and are widely spread to avoid competition for water.

• Many plants are ephemeralsephemerals, which means they can complete their full life cycle in just 2 – 3 weeks taking advantage of any rain that falls.

Photosynthesis takes place in the green stem (the cactus has no leaves)

Thick cell walls that do not break when they dry out

A thick, waxy coating keeps the water inside the cactus from evaporating.

Instead of leaves, most cacti have spines or scales (which are modified leaves). These spines and scales do not lose water through evaporation (unlike regular leaves, which lose a lot of water). The spines protect the cactus from predators (animals that would like to eat the cactus to obtain food and/or water)

Deserts Multiple Choice Quiz

• file:///G:/28%20April%202008%20Thumbstick/8%20Geography/12.Deserts/SOSE%20Alive%20Geography%201.mht Now in keep but not use file in Intro file

Going To Extremes: Hot

• http://news.nationalgeographic.com/news/2004/02/0227_040227_TVhot.html Dallol, in northern Ethiopia's Danakil Depression.

• http://www.smh.com.au/news/world/a-walk-through-the-desert-in-the-shoes-of-the-people/2008/05/02/1209235156062.html?page=fullpage#contentSwap2 2008 SMH article on Afar