Test: Indian Deserts - UPSC MCQ

• This consists of stretches of bare rocks, swept clear of sand and dust by the wind.

• The exposed rocks are thoroughly smoothed and polished. The region is bare and sterile.

• The best known rocky deserts are those of the Sahara Desert, e.g. the Hamada el Homra, in Libya, which covers almost 20,000 square miles.

Erg or sandy desert:

• This is a sea of sand that typifies desert scenery's popular idea. Winds deposit vast stretches of undulating dunes in the heart of the deserts.

• The intricate patterns of ripples on the dune surfaces indicate the direction of the winds. The Calanscio Sand Sea in Libya is characteristic of a sandy desert. In Turkestan, sandy deserts are also known as koum.

• Badlands: The term 'badlands' was first given to an arid area in South Dakota, U.S.A., where occasional rain-storms badly eroded the hills into gullies and ravines.

• The extent of water action on hill slopes and rock surfaces was so great that the inhabitants abandoned the entire region. Deserts with similar features are now referred to as badlands, e.g. the Painted Desert of Arizona, which lies south-east of the Colorado River's Grand Canyon.

• Deflation: This involves the lifting and blowing away of loose materials from the ground. Such unconsolidated sands and pebbles may be carried in the air or rolled along the ground depending on the grain size.

• The finer dust and sands may be removed miles away from their place of origin, and be deposited even outside the desert margins. Deflation results in the lowering of the land surface to form large depressions called deflation hollows. The Qattara Depression of the Sahara Desert lies almost 450 feet below sea level.

• The sandblasting of rock surfaces by winds when they hurl sand particles against them is called abrasion.

• The impact of such blasting results in rock surfaces being scratched, polished and worn away. Abrasion is most effective at or near the base of rocks, where the amount of material the wind can carry is greatest.

• This explains why a covering of metal protects telegraph poles in the deserts for a foot or two above the ground. A great variety of desert features are produced by abrasion.

The correct answer is d) Neither of them.

Explanation:

• Statement 1 is correct: Grooves and hollows are indeed cut into rock surfaces by wind action, carving them into unique pillars, commonly called rock pedestals.

• Statement 2 is also correct: The process of undercutting, which happens when wind erodes the lower part of the rock more quickly than the upper part, can create mushroom-shaped rocks. These are often called mushroom rocks or gour and are found in desert regions like the Sahara.

Since both statements are correct, the answer is d) Neither of them.

Additional Information:

• Rock pedestals form when wind erosion cuts into rock surfaces, creating tall, thin structures with grooves and hollows.

• Mushroom rocks are shaped by wind erosion, where the lower part of the rock erodes faster than the upper part, giving it a mushroom-like appearance. These are common in deserts like the Sahara.

• Zeugen: These are tabular masses with a layer of soft rocks lying beneath a surface layer of more resistant rocks. The sculpting effects of wind abrasion wear them into a weird-looking 'ridge and furrow landscape.

• Mechanical weathering initiates their formation by opening up joints of the surface rocks. Wind abrasion further eats' into the under Irving softer layer so that deep furrows are developed.

• The hard rocks then stand above the furrows as ridges or Eugen and many even overhang. Such tabular blocks of zeugen may stand 10 to 100 feet above the sunken furrows. Continuous abrasion by wind gradually lowers the zeugen and widens the furrows.

Inselberg:

• This is a German word meaning 'island-mountain'.

• They have isolated residual hills rising abruptly from the level ground. They are characterised by their very steep slopes and rather rounded tops.

• They are often composed of granite or gneiss and are probably the relics of an original plateau which has been almost entirely eroded.

• Inselbergs are typical of many desert and semi-arid landscapes in old age, e.g. those of northern Nigeria, Western Australia and the Kalahari Desert.

• Dunes: Dunes are, in fact, hills of sand formed by the accumulation of sand and shaped by the movement of winds. They may be active or live dunes, constantly on the move, or inactive fixed dunes, rooted with vegetation.

• Dunes are most well represented in the erg desert where a sea of sand is continuously moved, reshaped and redeposited into various features.

• If you look at the world map carefully, you will find that there is a certain definite pattern to the location of the world's deserts. You will realise that almost all the deserts are confined within the 15 to 30° parallels of latitude north and south of the equator. 
• They lie in the trade wind belt on the western parts of the continents where Trade Winds are off-shore. They are bathed by cold currents which produce a 'desiccating effect.