التصنيفات
الصف الثاني عشر

تقرير Deserts of the world للصف الثاني عشر


Deserts of the world

The Desert Biome
Deserts are places on earth that are characterized by little vegetation and rain. They are made up of sand or rocks and gravel. Deserts cover about one-fifth of all the land in the world. Most deserts lie along the Tropic of Cancer and Tropic of Capricorn, imaginary lines that lie north and south of the equator.

Deserts
The Middle East and North Africa make up the driest region of the earth. Nearly two thirds of the region is desert. A desert is land that receives an average of less than ten inches of rain per year. The Sahara of northern Africa is the largest desert in the world.

World’s Largest Deserts

Factmonster: Principal Deserts of the World

North American Deserts
North American Deserts

Sonora Desert

Sonoran Desert
The Sonoran Desert of Southern Arizona and Northwestern Mexico is well known for its beauty and many spectacular and grand cacti. The abundant cacti and other succulents simply defy the harsh climate with exuberant biodiversity.

Southwest Deserts
A traveler crossing overland from Los Angeles to Big Bend National Park in West Texas encounters three of North America’s four great deserts, each ecologically distinct and strikingly beautiful.

Great Basin Desert
The Great Basin Desert, the largest U. S. desert, covers an arid expanse of about 190,000 square miles and is bordered by the Sierra Nevada Range on the west and the Rocky Mountains on the east, the Columbia Plateau to the north and the Mojave and Sonoran deserts to the south.

Mojave Desert
The transition from the hot Sonoran Desert to the cooler and higher Great Basin is called the Mojave Desert. This arid region of southeastern California and portions of Nevada, Arizona and Utah, occupies more than 25,000 square miles.

The Chihuahuan Desert
Most of the Chihuahuan Desert — the largest desert in North America covering more than 200,000 square miles — lies south of the international border. In the U.S. it extends into parts of New Mexico, Texas and sections of southeastern Arizona. Its minimum elevation is above 1,000 feet, but the vast majority of this desert lies at elevations between 3,500 and 5,000 feet.

The Chihuahuan Desert Region
A desert region can be defined many ways. To a physical scientist such as a meteorologist, a desert can be defined as an area receiving an average annual rainfall of 10" or less.

Welcome to the Chihuahuan Desert
The Chihuahuan Desert is the easternmost and southernmost of the four North American deserts: the Great Basin Desert, the Sonoran Desert, the Mojave Desert, and the Chihuahuan Desert.

The Chihuahuan Desert
The Chihuahuan Desert is the easternmost, southernmost, and largest North American desert. Most of it is located in the states of Chihuahua and Coahuila in Mexico, but fingers of the Chihuahuan reach up into eastern Arizona, southern New Mexico, and Texas, and down to the states of Zacatecas, and San Luis Potosi in Mexico. This desert is quite large – about 175,000 square miles – making it bigger than the entire state of California.

White Sands Desert of New mexico
At the northern end of the Chihuahuan Desert lies a mountain ringed valley called the Tularosa Basin. Rising from the heart of this basin is one of the world’s great natural wonders – the glistening white sands of New Mexico.

Deathe Valley
Although Death Valley is in California, it’s right on the California-Nevada border, closer to Las Vegas than to Los Angeles. Apart from the unexpected snowcapped mountains of winter, it’s a lonely and arid place pockmarked with suspicious looking mounds and crackling salt flats, crisscrossed by crevassed earth and powdered with relentless sand dunes.

Death Valley National Park
Many first time visitors to Death Valley are surprised it is not covered with an endless sea of sand. Less than one percent of the desert is covered with dunes, yet the shadowed ripples and stark, graceful curves define "desert" in our imaginations.

OneWorld Magazine: Deserts of Our World
OneWorld Magazine would like you to experience the diversity and cultural richness of the world’s deserts, if only virtually. Over the next 4 weeks we will bring you a selection of articles, paintings, sculptures, poems and photographs of men and women who have been challenged by the uniqueness of a desert, defeated by its dimensions, rewarded by its remoteness. Our delivery is by no means comprehensive — for every grain of sand there is a desert word, a desert painting, a desert thought.

Asian Deserts
Gobi Desert

Middle Eastern/African Deserts
The Sahara Desert

Sahara Desert
Sahara Desert, is a great desert area, lying in Northern Africa, and the western portion of the broad belt of arid land ,extends from the Atlantic Ocean eastward past the Red Sea to Iraq.

Sahara Desert
Here’s a fact to challenge popular imagination: more people drown in the Sahara than die from exposure or thirst. It may not rain often and it may not rain long but, in the capricious ways of this vast inland plain, when it does rain, it rains with devastating ferocity.

Wadi Rum: Jordan
Catch a camel into the Wadi Rum desert and you’ll find yourself in ‘Heroic and Biblical Adventure’ country. You’d be forgiven for thinking that, at any moment, you’ll stumble across a bearded and besandalled Charlton Heston looking square-jawed and self-righteous. It was, after all, in this neck of the woods that seas got parted and the tribes of Israel did some serious wandering.

South American Deserts
Atacama Desert
The Atacama desert in Chile is as parched as a parson’s Sunday sermon. In fact, it’s the driest desert in the world. There are parts of it where rain has never been recorded and the precious little precipitation (1cm/0.3in per year) that does fall comes from fog.

Cold Deserts
Ultima Thule, Greenland
There’s nothing in the law books that says a desert has to be hot, sandy and unpleasant; it’s equally legitimate for a desert to be cold, icy and unpleasant. As long as it’s uncultivated and uninhabitable it makes the grade, desertwise, and Ultima Thule is a shoo-in.

Siberia, Russia
Think Siberia and think cold. Think hoarfrosted faces, howling wolves, frozen mountains, salt mines, human chain gangs and exile. Maxim Gorky once called it a ‘land of chains and ice’ and, until recently, the description still held good. Tsars and Party apparatchiks might have had opposing political ideologies but they were of one mind when it came to Siberia.

يتبع…

Deserts of the world

Desert
****************
Area – sq miles

Africa

Sahara
Northern Africa
3,320,000

Libyan
Libya, Egypt, and Sudan (part of Sahara)

Kalahari
Southwestern Africa
360,000

Namib
Southwestern Africa
52,000

Asia

Arabia
Southwestern Asia
900,000

Rub’al Khali
southern Arabian Peninsula
250,000

Gobi
Mongolia and northeastern China
500,000

Kara-Kum
Turkmenistan
135,000

Kyzyl-Kum
Kazakhstan-Uzbekistan
115,000

Takla Makan
northern China
105,000

Kavir
central Iran
100,000

Syrian
Saudi Arabia, Jordan, Syria, and Iraq
100,000

Thar
India and Pakistan
77,000

Dasht-e-Lut
eastern Iran
20,000

Australia

Great Victoria
Western and South Australia
250,000

Great Sandy
northern Western Australia
150,000

Gibson
Western Australia

Simpson
Northern Territory
56,000

North America

Great Basin
southwestern United States
190,000

Chihuahuan
northern Mexico
175,000

Sonoran
southwestern U.S. and Baja California
120,000

Colorado
California and northern Mexico

Yuma
Arizona and Sonora, Mexico

Mojave
southwestern United States
25,000

South America

Patagonian
southern Argentina
260,000

Atacama
northern Chile
54,000

يتبع …

Deserts of the world

A desert is a landscape form or region that receives very little precipitation

Deserts are defined as areas that receive an average annual precipitation of less than 250
mm (10 in). In the Köppen climate classification system, deserts are classed as (BW).

مقدمه

Geography

A satellite image of the Sahara, the world’s largest hot desert and second largest desert after Antarctica.
Deserts take up one-third of the Earth’s land surface.[1] They usually have a large diurnal and seasonal temperature range, with high daytime temperatures (in summer up to 45 °C or 113 °F), and low night-time temperatures (in winter down to 0 °C; 32 °F) due to extremely low humidity. Water acts to trap infrared radiation from $$$$ the sun and the ground, and dry desert air is incapable of blocking sunlight during the day or trapping heat during the night. Thus during daylight most of the sun’s heat reaches the ground. As soon as the sun sets the desert cools quickly by radiating its heat into space. Urban areas in deserts lack large (more than 25 °F/14 °C) daily temperature ranges, partially due to the urban heat island effect.
Many deserts are formed by rain shadows, mountains blocking the path of precipitation to the desert. Deserts are often composed of sand and rocky surfaces. Sand dunes called ergs and stony surfaces called hamada surfaces compose a minority of desert surfaces. Exposures of rocky terrain are typical, and reflect minimal soil development and sparseness of vegetation.

The snow surface at Dome C Station in Antarctica is a representative of the majority of the continent’s surface.
Bottomlands may be salt-covered flats. Eolian processes are major factors in shaping desert landscapes. Cold deserts (also known as polar deserts) have similar features but the main form of precipitation is snow rather than rain. Antarctica is the world’s largest cold desert (composed of about 98 percent thick continental ice sheet and 2 percent barren rock). The largest hot desert is the Sahara.
Deserts sometimes contain valuable mineral deposits that were formed in the arid environment or that were exposed by erosion. Because deserts are so dry, they are ideal places for artifacts and fossils to be preserved.

+++++

عمل جميل
:
شكرا لج
:
تنبيه .. يمنع وضع رواابط ((انتبهي))

Thanx

بارك الله فيج

سبحــــــــــــــــــــان الله و بحمده

التصنيفات
الصف الثاني عشر

تقرير Deserts of the world


Deserts of the world

The Desert Biome
Deserts are places on earth that are characterized by little vegetation and rain. They are made up of sand or rocks and gravel. Deserts cover about one-fifth of all the land in the world. Most deserts lie along the Tropic of Cancer and Tropic of Capricorn, imaginary lines that lie north and south of the equator.

Deserts
The Middle East and North Africa make up the driest region of the earth. Nearly two thirds of the region is desert. A desert is land that receives an average of less than ten inches of rain per year. The Sahara of northern Africa is the largest desert in the world.

World’s Largest Deserts

Factmonster: Principal Deserts of the World

North American Deserts
North American Deserts

Sonora Desert

Sonoran Desert
The Sonoran Desert of Southern Arizona and Northwestern Mexico is well known for its beauty and many spectacular and grand cacti. The abundant cacti and other succulents simply defy the harsh climate with exuberant biodiversity.

Southwest Deserts
A traveler crossing overland from Los Angeles to Big Bend National Park in West Texas encounters three of North America’s four great deserts, each ecologically distinct and strikingly beautiful.

Great Basin Desert
The Great Basin Desert, the largest U. S. desert, covers an arid expanse of about 190,000 square miles and is bordered by the Sierra Nevada Range on the west and the Rocky Mountains on the east, the Columbia Plateau to the north and the Mojave and Sonoran deserts to the south.

Mojave Desert
The transition from the hot Sonoran Desert to the cooler and higher Great Basin is called the Mojave Desert. This arid region of southeastern California and portions of Nevada, Arizona and Utah, occupies more than 25,000 square miles.

The Chihuahuan Desert
Most of the Chihuahuan Desert — the largest desert in North America covering more than 200,000 square miles — lies south of the international border. In the U.S. it extends into parts of New Mexico, Texas and sections of southeastern Arizona. Its minimum elevation is above 1,000 feet, but the vast majority of this desert lies at elevations between 3,500 and 5,000 feet.

The Chihuahuan Desert Region
A desert region can be defined many ways. To a physical scientist such as a meteorologist, a desert can be defined as an area receiving an average annual rainfall of 10" or less.

Welcome to the Chihuahuan Desert
The Chihuahuan Desert is the easternmost and southernmost of the four North American deserts: the Great Basin Desert, the Sonoran Desert, the Mojave Desert, and the Chihuahuan Desert.

The Chihuahuan Desert
The Chihuahuan Desert is the easternmost, southernmost, and largest North American desert. Most of it is located in the states of Chihuahua and Coahuila in Mexico, but fingers of the Chihuahuan reach up into eastern Arizona, southern New Mexico, and Texas, and down to the states of Zacatecas, and San Luis Potosi in Mexico. This desert is quite large – about 175,000 square miles – making it bigger than the entire state of California.

White Sands Desert of New mexico
At the northern end of the Chihuahuan Desert lies a mountain ringed valley called the Tularosa Basin. Rising from the heart of this basin is one of the world’s great natural wonders – the glistening white sands of New Mexico.

Deathe Valley
Although Death Valley is in California, it’s right on the California-Nevada border, closer to Las Vegas than to Los Angeles. Apart from the unexpected snowcapped mountains of winter, it’s a lonely and arid place pockmarked with suspicious looking mounds and crackling salt flats, crisscrossed by crevassed earth and powdered with relentless sand dunes.

Death Valley National Park
Many first time visitors to Death Valley are surprised it is not covered with an endless sea of sand. Less than one percent of the desert is covered with dunes, yet the shadowed ripples and stark, graceful curves define "desert" in our imaginations.

OneWorld Magazine: Deserts of Our World
OneWorld Magazine would like you to experience the diversity and cultural richness of the world’s deserts, if only virtually. Over the next 4 weeks we will bring you a selection of articles, paintings, sculptures, poems and photographs of men and women who have been challenged by the uniqueness of a desert, defeated by its dimensions, rewarded by its remoteness. Our delivery is by no means comprehensive — for every grain of sand there is a desert word, a desert painting, a desert thought.

Asian Deserts
Gobi Desert

Middle Eastern/African Deserts
The Sahara Desert

Sahara Desert
Sahara Desert, is a great desert area, lying in Northern Africa, and the western portion of the broad belt of arid land ,extends from the Atlantic Ocean eastward past the Red Sea to Iraq.

Sahara Desert
Here’s a fact to challenge popular imagination: more people drown in the Sahara than die from exposure or thirst. It may not rain often and it may not rain long but, in the capricious ways of this vast inland plain, when it does rain, it rains with devastating ferocity.

Wadi Rum: Jordan
Catch a camel into the Wadi Rum desert and you’ll find yourself in ‘Heroic and Biblical Adventure’ country. You’d be forgiven for thinking that, at any moment, you’ll stumble across a bearded and besandalled Charlton Heston looking square-jawed and self-righteous. It was, after all, in this neck of the woods that seas got parted and the tribes of Israel did some serious wandering.

South American Deserts
Atacama Desert
The Atacama desert in Chile is as parched as a parson’s Sunday sermon. In fact, it’s the driest desert in the world. There are parts of it where rain has never been recorded and the precious little precipitation (1cm/0.3in per year) that does fall comes from fog.

Cold Deserts
Ultima Thule, Greenland
There’s nothing in the law books that says a desert has to be hot, sandy and unpleasant; it’s equally legitimate for a desert to be cold, icy and unpleasant. As long as it’s uncultivated and uninhabitable it makes the grade, desertwise, and Ultima Thule is a shoo-in.

Siberia, Russia
Think Siberia and think cold. Think hoarfrosted faces, howling wolves, frozen mountains, salt mines, human chain gangs and exile. Maxim Gorky once called it a ‘land of chains and ice’ and, until recently, the description still held good. Tsars and Party apparatchiks might have had opposing political ideologies but they were of one mind when it came to Siberia.

يتبع…

Deserts of the world

Desert
****************
Area – sq miles

Africa

Sahara
Northern Africa
3,320,000

Libyan
Libya, Egypt, and Sudan (part of Sahara)

Kalahari
Southwestern Africa
360,000

Namib
Southwestern Africa
52,000

Asia

Arabia
Southwestern Asia
900,000

Rub’al Khali
southern Arabian Peninsula
250,000

Gobi
Mongolia and northeastern China
500,000

Kara-Kum
Turkmenistan
135,000

Kyzyl-Kum
Kazakhstan-Uzbekistan
115,000

Takla Makan
northern China
105,000

Kavir
central Iran
100,000

Syrian
Saudi Arabia, Jordan, Syria, and Iraq
100,000

Thar
India and Pakistan
77,000

Dasht-e-Lut
eastern Iran
20,000

Australia

Great Victoria
Western and South Australia
250,000

Great Sandy
northern Western Australia
150,000

Gibson
Western Australia

Simpson
Northern Territory
56,000

North America

Great Basin
southwestern United States
190,000

Chihuahuan
northern Mexico
175,000

Sonoran
southwestern U.S. and Baja California
120,000

Colorado
California and northern Mexico

Yuma
Arizona and Sonora, Mexico

Mojave
southwestern United States
25,000

South America

Patagonian
southern Argentina
260,000

Atacama
northern Chile
54,000

يتبع …

Deserts of the world

A desert is a landscape form or region that receives very little precipitation

Deserts are defined as areas that receive an average annual precipitation of less than 250
mm (10 in). In the Köppen climate classification system, deserts are classed as (BW).

مقدمه

Geography

A satellite image of the Sahara, the world’s largest hot desert and second largest desert after Antarctica.
Deserts take up one-third of the Earth’s land surface.[1] They usually have a large diurnal and seasonal temperature range, with high daytime temperatures (in summer up to 45 °C or 113 °F), and low night-time temperatures (in winter down to 0 °C; 32 °F) due to extremely low humidity. Water acts to trap infrared radiation from $$$$ the sun and the ground, and dry desert air is incapable of blocking sunlight during the day or trapping heat during the night. Thus during daylight most of the sun’s heat reaches the ground. As soon as the sun sets the desert cools quickly by radiating its heat into space. Urban areas in deserts lack large (more than 25 °F/14 °C) daily temperature ranges, partially due to the urban heat island effect.
Many deserts are formed by rain shadows, mountains blocking the path of precipitation to the desert. Deserts are often composed of sand and rocky surfaces. Sand dunes called ergs and stony surfaces called hamada surfaces compose a minority of desert surfaces. Exposures of rocky terrain are typical, and reflect minimal soil development and sparseness of vegetation.

The snow surface at Dome C Station in Antarctica is a representative of the majority of the continent’s surface.
Bottomlands may be salt-covered flats. Eolian processes are major factors in shaping desert landscapes. Cold deserts (also known as polar deserts) have similar features but the main form of precipitation is snow rather than rain. Antarctica is the world’s largest cold desert (composed of about 98 percent thick continental ice sheet and 2 percent barren rock). The largest hot desert is the Sahara.
Deserts sometimes contain valuable mineral deposits that were formed in the arid environment or that were exposed by erosion. Because deserts are so dry, they are ideal places for artifacts and fossils to be preserved.

+++++

عمل جميل
:
شكرا لج
:
تنبيه .. يمنع وضع رواابط ((انتبهي))

Thanx

بارك الله فيج

لا الـــه الا الله

التصنيفات
الصف العاشر

بحث , تقرير إنجليزي جاهز / DESERTS للصف العاشر

بسم الله الرحمن الرحيم

هذا تقرير الأنجليزي
DESERTS


Deserts are mainly found around the tropic of Cancer and tropic of Capricorn in Northern and Southern Hemispheres respectively. The common definition of desert is a region that receives less than 25cm of rain a year on average.

When people think of deserts, the following image comes to their minds : hot and arid land, vast expanses of sand, soil of reddish brown color, a sky of brilliant blue, no or very few plants, cacti, spiny leaves and camel is the only animal that they can think of.

The truth is not like that. It is not very common to find sand in a desert, but small rocks, pebbles and loose gravel on the surface layer instead. Only 15% of the world’ s desert surface is pure sand. (Parts of the Sahara and Arabia desert)

Desert occupies about one fifth to one third of the earth’ s surface. The rainfall pattern is not a seasonal one. Instead, rain usually falls in the form of sudden, violent thunderstorms. There may be several storms in a year or none for several years. The " average rainfall each year" is not calculated based on one year’ s rainfall, but on the total rainfall in a long period of time.

" How about the polar regions with sheets of floating ice?" You may ask. Large amount of water is locked up in the icecap. The average rainfall in the cold deserts located in polar regions is within 25cm.

The rate of evaporation ( known as " Moisture Index" ) can be used to classify deserts as there are extremely high temperatures, low humidities and very little cloud cover.

How extreme are the temperatures ? The daytime air temperature can reach 58oC (136oF) in the Sahara. Soil temperature may reach 80oC (176oF). For half a year, the average temperature of the Mongolian desert is below the freezing point. In Antarctica, the winter mean temperature is -30oC (41oF).

First of all lets talk about the weather in deserts .We all know that rain rarely falls in desert and when it comes, it comes in the form of thunderstorm.

In sandy desert, the rain usually drains away promptly and only change the landscapecomparatively slightly. In contrast, the torrential downpour in rocky deserts drains into wadis (rocky watercourses that is dry except after heavy rain). This deepen the dry valleys. Heavy downpour can build up into flash flood, carrying sand, gravel and then large rocks and boulders. Thus, at the end of most wadis, there is an enormous bank of sand and stone( known as "alluvial fan" ). The surplus sediment from the flash flood forms muddy lakes of different size and duration
Between wadis, there are flat plateaux in different extent called mesas. The mesas are isolated by the continuously widened wadi. The isolated mesas then become flat-topped, step-sided island in the desert, know as a buttle.

These lakes are particular seen in Australian desert. They lasts long enough to breed creatures like shrimps, frogs and wildfowl. Some of the lakes formed have high salt ************************************************** *************, which is thought to be derived from salt in the atmosphere, brought from oceanic spray.

Shallow, low-bottom-gradient lakes can be moved by wind stress over many square kilometers. When they dry up, an area of clay, silt, or sand encrusted with salt is found, known as playa.

Action of wind
Wind dehydrates soils and living things. Sand and dust particles are moved by desert winds. Desert winds also remove organic debris that makes the soil fertile. Since plants are scarce in deserts, wind erosion occurs more easily. Take Prairie States of North America as an example, a productive area was reduced in the 1930s to desert by desert wind (devastating tornado winds from desert), over-cropping and over-cultivating. The fine dust can be carried to kilometers away and thousands of meters up. Large amount of the fine duct rest in more temperate or moister regions and from the basis of loess (a fertile soil).

Impact of changes in temperature
Heat and cold produces the least observable effect in sandy desert. In contrast, their impact is much greater in rocky deserts.

In cold desert, rainfall is frozen at night in winter. When water goes into the tiny cervices and expands, the rocks are forced to split up.

In hot deserts, the fragmenting force of temperature is slower. Rock surfaces reach 70oC or 80oC at midday and cool down to freezing point at midnight. Expansion under the sun and contraction at night weaken the surface layers and cause flaking.

Secondly , lets talk about the different inhabitats that live in such places and how they adapt themselves in order to survive in such harsh weathers .

Desert plants have developed various ways to get as much water as possible and to reduce water loss.

Some plants have long roots to get water deep in the soil, or branched roots to get water over a wide area. With thick waxy layer on the stems and leaves, water can be retained and the tissues are protected from strong sunshine. Some plants have pin-like leaves to reduce water loss. Barrel Cactus

Many desert plants are succulents and they store water in their swollen stems or leaves.

Some desert plants are the " drought evaders" . They exist as seeds before the rain comes, and grow when it rains. They flower quickly to produce seeds and then die. There are " drought resisters" — perennial plants that possess the abilities of storing water, locating underground water or minimizing the use of water by various measures.

Very often, when people think of mammals in desert, they usually think of camels only. In fact, almost all of the mammalian orders have their representatives in the deserts.

To avoid the heat, some small mammals live in shelters underground, where the temperature fluctuations are not as much as those on the surface. Most important of all, the maximum temperature in burrows is much lower than that on the surface. They usually come out at night to search for food and store the food in burrows.
The Kangaroo Rat

Large mammals, like gazelles, onyx, asses and camels, find their shelters in the shade of a rock or tree. As the excessive heat may kill them, some of them lose heat by evaporation, which can only increase the staying power by 2-3oC. Of course, water must be available for sweating. They get water from waterholes and by eating plants and preys. The Mountain Lion

The small mammals have greater surface area to weight ratio. They gain and lose heat quickly and thus face greater problems in maintaining an acceptable body temperature range. Any animal living in desert has to have a gut that is able to excrete almost dry faecal material and a kidney that draws minimum water from blood. There are "summer hibernates" that minimize their ****bolic rates in summer to avoid water lost through respiration.

Some mammals, like hares, have large ears densely populated with blood vessels to remove heat.
Desert Carnivores obtain water from their preys. The dog and cat families lack sweat glands. They remove heat by panting which in turn lose much water so they are found mostly at the desert margins near a permanent water source.

With feathers, birds can keep out of external cold, heat loss and as well as external heat gained, for feathers can trap a layer of insulating air. The feathers are under muscular control and can be held erect. When there is a breeze, the upright feathers direct the air movement down to cool the skin.

Birds cannot sweat. They pant or flutter to remove heat.

Some flesh-eating birds don’ t need to drink as they can get enough moisture from their preys. The seed-eating birds need to drink daily and thus they are restricted in a number of places
where they can nest. Roadrunner
Birds find shelters underground, in the shade of rocks or bushes. Flying at high attitudes enables them to avoid heat. Birds can tolerate 3oC body temperature rise above normal level. No birds can survive at above 45oC.
Reptiles possess scaly skin to conserve moisture. They can control their body temperature by gaining or losing heat from surroundings. By using external heat, they do not need as much energy as the birds and mammals. Hence they need less food and breathe at a lower rate, which help them to conserve moisture.

Black-collared Lizard
The skins of the amphibians are soft and moist. This property allows the skin to respire and absorb oxygen from air and water. It seems unlikely that they can be found in deserts. Though, some frogs and toads manage to survive in the arid area. They must complete their life cycles before the wetlands evaporate after the rain, for their eggs have to develop in lakes or pools.

Most of the small animals like insects and arachnids (eg. Spiders, scorpions) have waterproof cuticles or shell mainly composed of a substance called chitin, which is hard, strong and impervious to many gases and liquids. It prevents them from drying up by the heat. The different stages of the invertebrates have various ways to prevent drying up. The egg is surrounded by a tough shell that is impervious to drought. It can last for months or even years, waiting for the rain to come. The larval stage often develops underground to avoid the heat. In the pupal stage, the cocoon or chrysalis protect the moth. The adult invertebrates, as protected by the chitinous exoskeleton, may live a long and productive life. It may lead a short life in the extreme, depending on the fat stored in its body. The short life is long enough for it to mate and lay eggs.
Tarantulas

Have you ever thought of the problems that face people who live in deserts ??Well there are quite a few .

If on the morning of a hot summer day, a healthy adult is placed in the middle of a desert without water for an hour, he will lose 0.9l of water by perspiring and he will be very thirsty. At the mid afternoon, he will lose about 5 to 8 kg of his weight. At night, if the daytime temperature is higher than 48.9oC, he may be dead. 3.8l of water a day is still not enough to save a man’s life from the heat for a week.

Loss of salt and clothing are also major problems .Through continuous sweating and intake of fresh water, the salt concentration in the body falls and causes severe cramping of muscles and headaches. Thus not only water , a source of salt is also essential.To avoid the heat, people in deserts have to dress up carefully :The long, flowing robes shield the skin from the sun and allow air to reach the body. The clothes are loose-fitting to prevent immediate sweat evaporation so that the body does not dehydrate so quickly in the very dry air. Headgear shields the head from the sun. Veils protect the face and keep the sand out of the mouth. The clothes also keep the people warm at night and in winter.

As for the homes ,some people live in permanent homes such as the mud houses of some Native Americans. The nomads carry with them portable homes as they move their livestock from place to place. All desert homes need to be well insulated from extreme heat and cold. Tents made of densely woven goat’s hair or thick-walled homes are suitable. Since rain is torrential, they need to be water proof.

Peolpe living in the deserts are called nomads who can be classified into three main groups : hunter-gatherers, pastoralists and traders.

Hunter gatherers move as small, independent bands within the area in which they know where are the waterholes, important trees, patches of smaller food plants and potential food animals. They move daily, monthly or semi-annually.

Postoralists move from place to place depending on the needs of their domesticated stock like sheep, goats or camels. Their targets are places with prolonged and predictable grass supply. Some of them may also hunt while others may cultivate an area near where they settle and grow cereal crops. They may also trade when they get a chance.

Traders are mobile merchants with trains of pack animals like camels, asses, mules or yaks with them. They supply goods produced on one side of the desert to the town people.

To conclude , you can see that there are lots of information that most people don’t know about deserts . Most of us think there is only one type of deserts , hot deserts , and even a bigger number of people don’t know the variuos plants and animals that live in deserts and how they cope themselves to the weather conditions . This report is just a summary of the great wonders of deserts as there is lots more that scientists are trying to discover nowadays .

Resources:
Eyewitness Guides — Desert by Miranda Macquitty (A Dorling Kindersley Book)
Deserts, A Miracle of Life by Jim Flegg (Blandford Press)
Life Nature Library — The Desert (Time-Life Books Inc.)

مسروق خخ , أن شاء الله يعجبكم مشكورين على المرور مقدما

مشكووووور ع ـالموضووع

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هههههه أي سرقه ما عليك

شكرا لج

موفقين

شكرا شكرا شكرا شكرا……………………
|…………………………………شكرا

الحــــــــــــــــــــــمد لله

التصنيفات
الصف الثاني عشر

English report about deserts of the world للصف الثاني عشر

بليييييييييييييييييييز اي حـــــــــــــــــد مسوي تقرير انجليزي ينزله حقي بليييييييييييييييييييييييز
يوم الاحد اخر يوم ولازم اسلم التقرير

بليييييييييييييييييييييييييييييييييز

اختكم
عازفة الصمت

تسلمين يالغالية بس انشاء الله ما تكون وحده من بنات العطاء ماخذتنه وبعدين هذا التقرير مب طالبتنه المعلمة
هوو موجود داخل كتب ثاني عشر

اسمحيلي والله كان ودي اساعدج

بس ماعندي وانا للحينه ادور

اللعم اعز الاسلام و المسلمين

التصنيفات
الصف الثاني عشر

تقرير عن Deserts للصف الثاني عشر

أبي تقرير عن Deserts

me too

سبحــــــــــــــــــــان الله و بحمده

التصنيفات
الصف الثاني عشر

ابي تقرير عن … Deserts of the world … -تعليم اماراتي

السلام عليكم …
أخبـــاركم عساكم بخير …
فديتكم يالغاليين لا تردوني ..
يوم الخميس اخر يوم في تسليم التقرير ..
وبصرااحه تعبت وانا ادور ..
ف يااااليت لو تساعدوني …

ابي تقرير عن … Deserts of the world

يتظمن التقرير ..
مقدمه / Introduction
معنى الصحراء / Meaning of Desert
أنواع اصحـراء / Kinds of deserts
المواقع /
الطقس والمناخ / Weather & Climate
حيوانات / Animals
خــاتمه / Conclusion
مصادر ومراجع / source & References

وسلامتكم … بليز ساعدوني لو بكلمه

Deserts
In geography , a desert is a landscape form or region that receives very little precipitation Generally deserts are defined as areas that receive an average annual precipitation of less than 250 mm (10 inches). The terminology used to define deserts is complex. ‘True deserts’ where vegetation cover is exceedingly sparse, correspond to the ‘hyperarid regions of the earth, where rainfall is exceedingly rare and infrequent. Deserts are however part of a wider classification of regions that, on an average annual basis, have a moisture deficit (i.e. they can potentially lose more than is received). These areas are collectively called ‘drylands’ and extent over almost half of the earth’s land surface. Because desert is a vague term, the use of ‘dryland’, and its subdivisions of hyper arid, arid, semiarid and dry-subhumid, is to be preferred, and is approved by the United Nations.
Deserts cover at least one-fifth of the Earth’s land surface. Deserts are very arid (dry) and can have high temperatures in excess of 50°C. Even though the desert is very hot in the day, it is extremely cold at night. Deserts have quite rough terrain, many sand dunes and present an overwhelmingly hostile environment. Humans that travel unprepared into deserts have a slim chance of survival due to the relative dearth of water.
Etymology
The English, French (désert), Italian (deserto), all come from the Latin deserta. This name is derived from the old Egyptian language, from the word deshert, meaning the ‘red land’ that bordered the black land (kemet) in the nile valley from the east and the west.
Types of desert
Most classifications rely on some combination of the number of days of rainfall, the total amount of annual rainfall, temperature, humidity, or other factors. In 1953, Peveril Meigs divided desert regions on Earth into three categories according to the amount of precipitation they received. In this now widely accepted system, extremely arid lands have at least 12 consecutive months without rainfall, arid lands have less than 250 millimeters of annual rainfall, and semiarid lands have a mean annual precipitation of between 250 and 500 millimeters. Arid and extremely arid land are deserts, and semiarid grasslands generally are referred to as steppes.
However, lack of rainfall alone can’t provide an accurate description of what a desert is. For example, Phoenix, Arizona receives less than 250 millimeters (10 inches) of precipitation per year, and is immediately recognized as being located in a desert. The North Slope of Alaska’s Brooks Range also receives less than 250 millimeters of precipitation per year, but is not generally recognized as a desert region.
The difference lies in something termed "potential evapotranspiration." The water budget of an area can be calculated using the formula P-PE+/-S, wherein P is precipitation, PE is potential evapotranspiration rates and S is amount of surface storage of water. Evapotranspiration is the combination of water loss through atmospheric evaporation, coupled with the evaporative loss of water through the life processes of plants. Potential evapotranspiration, then, is the amount of water that could evaporate in any given region. Tucson, Arizona receives about 300 millimeters, (12 inches), of rain per year, however about 2500 millimeters, (100 inches), of water could evaporate over the course of a year. In other words, about 8 times more water could evaporate from the region than actually falls. Rates of evapotranspiration in other regions such as Alaska are much lower, so while these regions receive minimal precipitation, they should be designated as specifically different from the simple definition of a desert: a place where evaporation exceeds precipitation.
That said, there are different forms of deserts. Cold deserts can be covered in snow; such ********s don’t receive much precipitation, and what does fall remains frozen as snow pack; these are more commonly referred to as tundra if a short season of above-freezing temperatures is experienced, or as an ice cap if the temperature remains below freezing year-round, rendering the land almost completely lifeless.
Most non-polar deserts are hot because they have little water. Water tends to have a cooling, or at least a moderating, effect in environments where it is plentiful. In some parts of the world deserts are created by a rain shadow effect in which air masses lose much of their moisture as they move over a mountain range; other areas are arid by virtue of being very far from the nearest available sources of moisture (this is true in some middle-latitude landmass interior ********s, particularly in Asia).
Deserts are also classified by their geographical ******** and dominant weather pattern as trade wind, mid-latitude, rain shadow, coastal, monsoon, or polar deserts. Former desert areas presently in non-arid environments are paleodeserts.

Montane deserts
Montane deserts are arid places with a very high altitude; the most prominent example is found north of the Himalaya, in parts of the Kunlun Mountains and the Tibetan Plateau. Many ********s within this category have elevations exceeding 3,000 meters (9,843 feet) and the thermal regime can be hemiboreal. These places owe their profound aridity (the average annual precipitation is often less than 40mm) to being very far from the nearest available sources of moisture. Deserts are normally cold.
Rain Shadow Deserts
Rain shadow deserts form when tall mountain ranges block clouds from reaching areas in the direction the wind is going. As the air moves over the mountains, it cools and condenses, causing precipitation on the upwind side. Moisture almost never reaches the downwind side of the mountain, therefore causing a desert. When that air reaches the downwind side, the air is dry, because it has already lost all of its moisture. The air then warms and expands and blows across the desert. The warm air takes all the small amounts of moisture in the desert away.
Desert features
Sand covers only about 20 percent of Earth’s deserts. Most of the sand is in sand sheets and sand seas—vast regions of undulating dunes resembling ocean waves "frozen" in an instant of time. In general, there are 6 forms of deserts:
• Mountain and basin deserts;
• Hamada deserts, which comprise of plateaux landforms;
• Regs which consist of rock pavements;
• Ergs which are formed by sand seas;
• Intermontane Basins; and
• Badlands which are located at the margins of arid lands comprising of clay-rich soil.
Nearly all desert surfaces are plains where eolian deflation—removal of fine-grained material by the wind—has exposed loose gravels consisting predominantly of pebbles but with occasional cobbles.
The remaining surfaces of arid lands are composed of exposed bedrock outcrops, desert soils, and fluvial deposits including alluvial fans, playas, desert lakes, and oases. Bedrock outcrops commonly occur as small mountains surrounded by extensive erosional plains.
There are several different types of dunes. Barchan dunes are produced by strong winds blowing across a level surface and are crescent-shaped. Longitudinal or seif dunes are dunes that are parallel to a strong wind that blows in one general direction. Transverse dunes run at a right angle to the constant wind direction. Star dunes are star-shaped and have several ridges that spread out around a point.
Oases are vegetated areas moistened by springs, wells, or by irrigation. Many are artificial. Oases are often the only places in deserts that support crops and permanent habitation.

Vegetation
Most desert plants are drought- or salt-tolerant, such as xerophytes. Some store water in their leaves, roots, and stems. Other desert plants have long tap roots that penetrate to the water table if present. The stems and leaves of some plants lower the surface velocity of sand-carrying winds and protect the ground from erosion. Even small fungi and microscopic plant organisms found on the soil surface (so-called cryptobiotic soil) can be a vital link in preventing erosion and providing support for other living organisms.
Deserts typically have a plant cover that is sparse but enormously diverse. The Sonoran Desert of the American Southwest has the most complex desert vegetation on Earth. The giant saguaro cacti provide nests for desert birds and serve as "trees" of the desert. Saguaro grow slowly but may live 200 years. When 9 years old, they are about 15 centimeters high. After about 75 years, the cacti develop their first branches. When fully grown, saguaro are 15 meters tall and weigh as much as 10 tons. They dot the Sonoran and reinforce the general impression of deserts as cactus-rich land.
Although cacti are often thought of as characteristic desert plants, other types of plants have adapted well to the arid environment. They include the pea and sunflower families. Cold deserts have grasses and shrubs as dominant vegetation.
Water
Rain does fall occasionally in deserts, and desert storms are often violent. A record 44 millimeters of rain once fell within 3 hours in the Sahara. Large Saharan storms may deliver up to 1 millimeter per minute. Normally dry stream channels, called arroyos or wadis, can quickly fill after heavy rains, and flash floods make these channels dangerous.
Though little rain falls in deserts, deserts receive runoff from ephemeral, or short-lived, streams fed considerable quantities of sediment for a day or two. Although most deserts are in basins with closed, or interior drainage, a few deserts are crossed by ‘exotic’ rivers that derive their water from outside the desert. Such rivers infiltrate soils and evaporate large amounts of water on their journeys through the deserts, but their volumes are such that they maintain their continuity. The Nile River, the Colorado River, and the Yellow River are exotic rivers that flow through deserts to deliver their sediments to the sea. Deserts may also have underground springs, rivers, or reservoirs that lay close to the surface, or deep underground. Plants that have not completely adapted to sporadic rainfalls in a desert environment may tap into underground water sources that do not exceed the reach of their root systems.
Lakes form where rainfall or meltwater in interior drainage basins is sufficient. Desert lakes are generally shallow, temporary, and salty. Because these lakes are shallow and have a low bottom gradient, wind stress may cause the lake waters to move over many square kilometers. When small lakes dry up, they leave a salt crust or hardpan. The flat area of clay, silt, or sand encrusted with salt that forms is known as a playa. There are more than a hundred playas in North American deserts. Most are relics of large lakes that existed during the last ice age about 12,000 years ago. Lake Bonneville was a 52,000-square-kilometer lake almost 300 meters deep in Utah, Nevada, and Idaho during the Ice Age. Today the remnants of Lake Bonneville include Utah’s Great Salt Lake, Utah Lake, and Sevier Lake. Because playas are arid land forms from a wetter past, they contain useful clues to climatic change.
When the occasional precipitation does occur, it erodes the desert rocks quickly and powerfully. Winds are the other factor that erodes deserts – they are constant yet slow.
The flat terrains of hardpans and playas make them excellent race tracks and natural runways for airplanes and spacecraft. Ground-vehicle speed records are commonly established on Bonneville Speedway, a race track on the Great Salt Lake hardpan. Space shuttles land on Rogers Lake Playa at Edwards Air Force Base in California.
Mineral resources
Some mineral deposits are formed, improved, or preserved by geologic processes that occur in arid lands as a consequence of climate. Ground water leaches ore minerals and redeposits them in zones near the water table. This leaching process concentrates these minerals as ore that can be mined.
Evaporation in arid lands enriches mineral accumulation in their lakes. Playas may be sources of mineral deposits formed by evaporation. Water evaporating in closed basins precipitates minerals such as gypsum, salts (including sodium nitrate and sodium chloride), and borates. The minerals formed in these evaporite deposits depend on the composition and temperature of the saline waters at the time of deposition.
Significant evaporite resources occur in the Great Basin Desert of the United States, mineral deposits made forever famous by the "20-mule teams" that once hauled borax-laden wagons from Death Valley to the railroad. Boron, from borax and borate evaporites, is an essential ingredient in the manufacture of glass, enamel, agricultural chemicals, water softeners, and pharmaceuticals. Borates are mined from evaporite deposits at Searles Lake, California, and other desert ********s. The total value of chemicals that have been produced from Searles Lake substantially exceeds US$1 billion.
The Atacama Desert of South America is unique among the deserts of the world in its great abundance of saline minerals. Sodium nitrate has been mined for explosives and fertilizer in the Atacama since the middle of the 19th century. Nearly 3 million tonnes were mined during World War I.
Valuable minerals located in arid lands include copper in the United States, Chile, Peru, and Iran; iron and lead-zinc ore in Australia; chromite in Turkey; and gold, silver, and uranium deposits in Australia and the United States. Non****llic mineral resources and rocks such as beryllium, mica, lithium, clays, pumice, and scoria also occur in arid regions. Sodium carbonate, sulfate, borate, nitrate, lithium, bromine, iodine, calcium, and strontium compounds come from sediments and near-surface brines formed by evaporation of inland bodies of water, often during geologically recent times.
The Green River Formation of Colorado, Wyoming, and Utah contains alluvial fan deposits and playa evaporites created in a huge lake whose level fluctuated for millions of years. Economically significant deposits of trona, a major source of sodium compounds, and thick layers of oil shale were created in the arid environment.
Some of the more productive petroleum areas on Earth are found in arid and semiarid regions of Africa and the Mideast, although the oil fields were originally formed in shallow marine environments. Recent climate change has placed these reservoirs in an arid environment. It’s noteworthy that Ghawar, the world’s largest and most productive oilfield is mostly under the Empty Quarter and Al-Dahna deserts.Currently the verification of SALINITY is unavailable on this page.
Other oil reservoirs, however, are presumed to be eolian in origin and are presently found in humid environments. The Rotliegendes, a hydrocarbon reservoir in the North Sea, is associated with extensive evaporite deposits. Many of the major U.S. hydrocarbon resources may come from eolian sands. Ancient alluvial fan sequences may also be hydrocarbon reservoirs.

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