Desert is an amazing landform of the earth.
An arid region with low rainfall with very sparse or no vegetation is called DESERT. The desert receives rainfall
less than 10 inches per year. Approximately about one-third portion of the earth's land surface is dessert.....Amazing...ya?
In general, it is considered that desert means sand desert but a desert may also be a vast arid region of rocks, pebbles and gravels with few plant.
In fact only 20% of the earth's deserts are sand desert while 50% of desert surfaces are covered by pebbles. The remaining 30%
of desert surfaces are covered by exposed bedrocks, fluvial deposits, desert soils etc.
Desert may contain valuable mineral deposits that were formed in the arid environment or may be exposed by the agents of erosion mainly
wind. Several gold deposits are known in sand deserts.
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Rocky and pebbly desert
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Wadi
Although it is not very common to see rainwater runoff in a desert, but some times rain may cause disastrous flow in a desert. Poor vegetation and absence of enough water causes the upper layer of the earth surface to become very loose. The picture to the right shows wadi created by the strong and sudden flow of rainwater from mountainous region. This picture is from Oman-U.A.E. border area. Here high mountain ranges are standing next to gravel plains and boulder flats. When it rains heavily in the mountainous region, rainwater with a great force runs along the mountain valleys and gushes in to the flat regions. The flow is so strong that it cuts the ground and carries away the soil material. This results in creation of wide channels called wadis. When energy of flow drops, big angular boulders and pebbles are deposited along the channel bed. Such sudden and strong flows into the wadis are called flash floods and they are so strong that the energy of such flow is enough to even drag away a heavy truck that might be passing. Since the rainwater comes from the mountain area while it may not be raining in the flat areas with wadis, it gives a very little time for some one passing through the wadi. Such flash floods are so sudden and dangerous that hardly anyone can escape from it.
Amazing power of nature...isn't it?
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Sand Desert and Sand Dunes.....
Sand desert itself is an another wonder of the world. Conditions are very severe in the desert; temperature in the summer goes well above 50°C in the noontime. Sand becomes hot and very loose which makes travelling a difficult task and can not be made unless fully equipped. Picture to the left shows sand dunes with ripple marks.
For adventure lovers sand dune are very attractive
and challenging. You may also have admired its beauty by looking at the beautiful images.....but ever thought how these sand dunes are formed?
Because of lack of water and vegetation, the surface sand is very loose. There is no enough water or plant roots to hold the sand down, which makes sand to move quickly from one place to other.
When wind, carrying sand come across an obstacle (such as rock, bush, plant etc.), speed of the wind is reduced. Slow wind can not carry sand any more thus deposits the sand along the obstacle and forms a core. Once a core is formed, it prevents further movement of the sand and slowly such sand deposition results in a big pile of sand called Sand Dune.
An interesting fact is that most of the sand dunes move from one place to another. Strong wind can blow sand from dunes and make it move in the wind ward direction. If the wind direction changes that may also cause the dune to move in another direction.
Sand dunes are found in different shape and sizes.
The most common type is crescent shaped dunes called Barchans. They are small in size with limited amount of sand supply. In such type of dunes the limbs are pointed in the windward direction. The dune moves progressively in down wind direction. Transverse type of dunes are formed when large amount of sand is available. Sand dunes are formed in lines that are perpendicular to the wind direction. Longitudinal dunes are formed parallel to the wind direction. Such types of dunes are created when a very small amount of sand is available and the wind is very strong.
Coastal dunes have large supply of sand from the beach part. They result from strong and continuos winds from the sea.
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Moving Dunes !!!!!!
Image to the right gives a clear picture of dune movement. Wind works as a strong agent of transport in the desert. Here sand blowing from the crest of the dune can be seen clearly in the picture. This way a dune moves forward and may travel across a desert......... AMAZING !!!!!!!!! |
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Desert Panaroma .........
Deserts have always been an amazing dream lands for photographers. Its undulating dunes, its contoured shadows of ripple marks, clean surroundings and adventurous valleys are admired by several artists of different interests. |
Working in Desert ........
However........driving into the loose sand of desert requires specific desert driving skills with special desert vehicles. Sometimes driving skills and good cars may be defeated by the very loose sand of the desert. This makes life tough for the people working in the desert. |
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Ground Water in Desert..........
It is a difficult and expensive affair to find groundwater in the desert. To locate
groundwater several geophysical methods are used which is further supported
by studying the regional geological setting of the area. After locating water
another difficult task is to drill in the desert. Movement of heavy drilling rig and
transportation of associated material to the drill site needs construction of temporary roads.
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Pumping fresh water from a well in a desert tells a story of big efforts
The image to the right show ground water pumped out in a desert in eastern part of Abu Dhabi Emirate in an area called Khusub. Presence of ground water in such harsh conditions is also a wonder of the nature. Finding ground water in such climatic conditions is a challenge for Geologists. |
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Green Desert !!!!!!!!!!
Image to the left is from northeastern part of Abu Dhabi emirate. Originally this was an open desert that was leveled and irrigated to make a vegetable farmland. This amazing green desert extends over a vast land of 40 X 5 kms. This is irrigated by almost fresh or slightly brackish groundwater.
Another interesting fact is that this water is pumped from far distant water well field, located in eastern part of Abu Dhabi Emirate. Pipe line that extends over more than sixty kilometers brings this water to the farm land area.
Creating such a big green patch in mid of the desert needs a big infra structure and big investment with lot of efforts. The main credit goes to the PRESIDENT of UNITED ARAB EMIRATES - HIS HIGHNESS SHEIKH ZAYED BIN SULTAN AL NAHYAN.
Pumping ground water from Khusub Well field in the eastern part of the Abu Dhabi Emirate fulfills major requirement of the water. Finding ground water in a desert itself is a difficult job and this becomes further difficult due to harsh working conditions. Getting fresh water in the desert is an another big challenge for the geologists. The Khusub well field is a big field with more than 450 ground water wells. Most of the wells here are fresh water wells with some having slightly brackish water. This was a big achievement gained by the GEOLOGICAL SURVEY SECTION of Private Dept. for H.H. Sheikh Zayed.
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Sand Consolidation.......
Picture to the right shows consolidation of sand in desert. This mainly occurs in interdunal depression where draining rainwater accumulates and is evaporated quickly due to desert climatic conditions. This results in deposition of fine sand, silt and clay, which acts as cementing material. Thus results in quickly cemented sandstones. Such rocks are fragile in nature, as compaction is very poor. |
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Mushroom Rocks........
Mushroom rocks are the characteristic rocks of desert with a narrow base and broad top, giving mushroom like structure.
They are formed due to differential wind erosion. When a rock comprised of alternate layers
of hard and soft beds, under goes wind erosion, the softer layer tends to get eroded faster than the harder layer, resulting in such mushroom shaped rocks. |
Sabkha......
Sabkhas are saline flat landforms. They are mainly found in arid climates. Such Sabkhas characteristically lie just above the water table. Here crust rich in gypsum and halite veins normally underlie thin layer of sand and silt. |
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Shallow Ground Water in Desert .......
It is very common to see shallow water zones in desert, especially in sabkhas.
Such shallow water is normally highly saline in nature and can not be even used for irrigation of salinity resistant plants. |
Effect of wind erosion in desert
Scroll to the right to see an amazing picture of sandstone arc formed due to differential erosion in a desert area by the action of wind. |
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