موضوع انجليزي عن desert

موضوع انجليزي عن desert

برجراف عن استصلاح الصحراء بالانجليزي

paragraph about desert reclamation

تعبير عن رحلة الى البر بالانجليزي

تعبير عن رحلة الى الصحراء

برجراف عن تحويل الصحراء الى ارض خضراء

موضوع تعبير عن استصلاح الصحراء

جمل عن الصحراء

information about desert

Deserts

Dune fields, rocky plains, dry steppes: one-third of the world's land is dying of thirst. Infertile regions where the rain is scarce, where the fauna, the flora and the man deploy a thousand tricks to survive. Hang on to the caravan for a great crossing of the deserts.

Agglutinated in both tropics, they display as far as the eye can see their sand dunes, pebbles and slabs of mud. Long sheltered from curious explorers, they are now flattened on all maps of geography, the label "desert", they are now flattened on all maps of geography, the label "desert" across. They already monopolize a third of the land and, according to experts, nibble nearly 10,000 ha each day of the year ...

And if the tectonic plates continue on their current momentum, in a hundred million years, the globe will be transformed into a desert rock emerging in the middle of the puddle of the oceans ... But will we be here to see it, that's another question.

Any handful of earth in the sun can not be called a desert; geologists have long torn their hair to find a precise way of qualifying them: for a long time were recognized desert lands that received no more than 25 cm of water per year. In comparison, in Paris, it is the deluge; There is an average of 62.4 cm of water per year. But in some parts of the world, although it rains a little more than 25 cm a year, the heat is such that the water evaporates immediately. It is therefore necessary to take into account not only precipitation, but also evaporation. When the quantity of water fallen from the sky is less than that which goes into steam, the soil becomes arid, and the region becomes desert.

Arabian desert: the country of the thousand and one dunes

Between the Persian Gulf and the Indian Ocean, spread over 2,300,000 km² an infinity of dunes. Or the largest stretch of sand in the world: the Arabian desert. No mountain range on the horizon to hold the clouds, yet the drops desert the region. The boycott of the peninsula is the result of a complicated game of air movement: above the equator, where the sun beats hard, the air heats up easily. Hot air being lighter than cold air, the air mass above the equator rises. This column of warm, light air forms a low pressure zone at this location.

But during her ascent, she gradually loses her heat. While cooling, the water vapor that it contains is transformed into drops of water: it often rains near the equator. The cloud, thus rid of its water, continues to move away from the equator and descends a little further to a latitude of + 30 ° and -30 °, on both sides of the equator, above the tropics exactly. An area of ​​high pressure formed by dried air masses is formed at this location. This dense and dry cloud pumps all the water from the ground and causes a great evaporation of the surface water. This is why the majority of deserts are stuck in the tropics.

Under these dry skies, the Arabian desert looks like a field of croissants as far as the eye can see. Crest against slope, dune against dune, waves at the regular pace never repeat. Dunes dancing with the winds; Aridity and breath of air sculpt the landscape: in the absence of water, the rocks become friable and the wind manages to pick up particles of sand. More and more loaded in grains, the wind slows down and deposits first the big heavier grains and then the others. The whole forms a crescent that presents its back to the wind. Then gradually the grains that are at the back of the dune are transported to the ridge. From there they roll towards the base and fill the hollow of the crescent. Thus fades a dune to reform immediately a few meters further. The same pile of sand moves about ten meters a year.

Gobi desert: drought on a plateau

A few scattered tufts and a handful of pebbles lost in the sand, perched at 1000 m altitude, the Gobi desert is a collection of large natural bowls. Camped at the same latitude as Paris, it is simply too far from the sea to enjoy the arrival of moist air.

The story begins 100 million years ago. At the time, the Indian peninsula was stuck to ... Antarctica. Asia, surrounded by oceans, paddled quietly: the sea wind brought a good dose of moisture and fertilized the regions. About 95 million years ago, India comes off and sails at a rate of 30 cm per year through the ancestor of the Indian Ocean. A tectonic journey that ends 50 million years ago when the Indian plate hit Asia hard. This titanic shock that continues today gave rise to the Himalayan mountain range and, as a result, isolated the central regions of Asia. Far from the sea and a little protected by mountains that stop the masses of humid air, the heart of Asia has gradually dried up in Gobi desert. The arid zone has extended from Turkestan to Mongolia.

The king camel

The caravan, overwhelmed with heat, stopped for a moment at the top of a mound bristling with pebbles. Below, a palm grove spreads out under the eyes of camel drivers. Already, the dromedaries have felt the coolness of the water and hasten the pace. At the oasis, the animals are unloaded and taken to the watering place. Legs apart and heads bowed, the camels begin to drink. Ten minutes later, they get up, stomach swollen with 135 liters of water! They can again do without drinking for a fortnight without putting their lives in danger. In periods of abstinence, the dromedary rehydrates his body by "burning" the fats of his bump. One hundred grams of oxidized lipids give exactly 107 g of water. A camel with a huge bump of 40 kg carries therefore on its back a tank of more than 40 liters! Such a reserve does not prevent it from being cautious and economical. The dromedary sweats very little. It begins to lose water through the skin only when its internal temperature reaches 40 ° C.

In the desert, living beings sweat as little as possible and use various methods to cool off: the fennec, the fox hungry, the Cape hare or the sand cat have ears that are out of proportion to their heads. Irrigated by many small blood vessels, they act as heat exchangers between the body and the surrounding air: the warm blood of the animal is cooled in the ears. The animals thus decrease by a few degrees their internal temperature. In general, the fauna of the Sahara avoids cooking in full sun. During the day, the animals stay cool in their burrow. The fennec, for example, only comes out one hour before sunset to go hunting. This little fox hunts rodents and birds. The meat and blood of his prey is enough to bring him the amount of water he needs. The fennec, as also the Cape hare or the cat of the sands, almost never drinks!

Gangas are less fortunate: eating only hard, dry seeds, these birds have to periodically go to the oases to refuel. However, they have a big advantage: they fly! And so can fetch water where it is, sometimes several tens of kilometers. Nestlings, on the other hand, are stuck to the nest, and adult gangas use Canadair's technology to quench their children's thirst. When they drink, the parents immerse their chest sometimes for a quarter of an hour in the pool before returning to the fold. The feathers of the belly, of a very particular conformation, absorb the water like a sponge, and act as a reservoir. When the adults are back, it is enough for young people to rummage with the beak in their plumage to quench their thirst.