It is generally said that Himalaya is a very young mountain and therefore, it has not much prospect for mineral resources. But this perhaps needs some classification. When we think about metallic mineral resources such as gold, silver, copper, lead, zinc, iron etc. The non-metallic mineral resources are equally important and essential for the development of any country. There are also other categories of useful geological materials such as fuel, minerals, coal, petroleum and other natural gas, precious and semiprecious stones, construction materials and dimensions.
His studies have shown that the Terai region is considered important for the oil, natural gas and the ground water resources. The Siwalik zone is studied important for coal and the radioactive materials. The lesser Himalaya is considered important for the metallic minerals like copper, zinc, lead, gold etc. and non-metallic deposits like limestone, magnetite, prosperity, coal etc. The higher Himalaya have shown the prospects for the natural thing. The sites for petroleum and natural gases are considered for the southern part of the country mainly in the Terai and the Chure region. The gas and the oil seepages in Padukasthan, Sirsasthan etc. in Dailekh and the gas seeps in Muktinath in Mustang are the indicators of the existence of the oil and natural gas in Nepal.
The agents which create or destroy the surface structure of the earth is known as geological agents or geomorphological agents of change. The agents that are responsible for the change of the structure are:
(1)Wind (2) Water (3) Glacier
The strong action of the air is called the wind. The geological action of wind is particularly effective in those areas where the region lacks plants and grasses. The wind has the considerable diurnal and seasonal temperature gradient i.e. its effect is particularly effective in the deserts and the semi-deserts where there are dry climatic regions. The action of wind is governed by its velocity.
The geological action of the wind consists of the destruction of the primary rocks and transportation and the accumulation of the breakdown of the products. As the wind is the moving air the differential heating of the atmosphere by solar heat causes the wind to blow. The wind is an agent of the active erosion and the deposition in the desert and the semi-desert area and is capable of producing distinct landforms.
The geological action of the wind can be divided into three stages:
a. Erosion b. Transportation c. Deposition
a. Wind erosion
The wind erosion is accelerated by the following processes:
Deflation is the lifting and caring of the loose particles of clay and the silt size. The rate of the deflation depends on the force of the wind, the nature of the rocks and the degree of the weathering.
The loose particles that are blown away by the wind, abroad the surface of the rock state is called abrasion. The surface of the rock is polished and covered with the stations depending upon the hardness of the rock.
Attrition is the mutual collision of the particles blown by the wind, which brings about some degree of grinding of the particles. The attrition enhances the rounding of the particles which reduces to the smaller dimensions.
b. Wind transportation
The wind is an active reagent for transporting the fine particles. The process is maintained by:
The particles of the diameter less than 0.05 mm are transported in the form of the dust cloud and remain in the form of the dust, cloud and in the air for some time and settle very slow.
The medium sized particles having the diameter between 0.05mm to 2mm are transported, which causes the rolling of the particles and it bounces up into the air, travels some distances in the parabolic path and strikes in the ground with considerable force. This leads the particles to bounce again or makes the other particle bounce again.
iii. Surface creep
The particles larger than 2mm can’t be transported by salvation and are transported by rolling and creeping along the surface.
Features produced by Deflation
The hard rock left behind due to sweeping away of the loose particles is known as Hamada.
Sometimes the deflation leads to the formation of the depressions as the result of blowing away of the exposed layer composed of the loose sediments known as deflation hollows. Sometimes the deflation operates continuously up to the water table and the formation of the shallow pond called ‘Oasis’ in the desert.
The finer particles of the surface are removed and the layer of the pebbles and cobbles scatter upon the surface due to deflation. Those residual pebbles and boulders are deposits.
The grooved or the furrowed topographic form produced by the wind abrasion which is elongated in the direction of prevailing winds and usually strongly undercut is called Yardang. It is developed in the vertically exposed rocks with layers consisting alternation of the hard and the soft rocks.
Venticafts are the pebbles of the rocks or minerals which have developed some plane faces due to wind abrasion, when the sand has blown over pebbles for a long time and results from the smooth polished surface.
When the softer rocks are capped by harder rocks, the softer rocks becomes more worn producing a mushroom shaped formed with upper rock resting upon thin rocks column, such feature is known as the pedestal rock. This is due to the reason that abrasion is nearer to earth’s surface than in the higher region.
Ripples are formed at the right angles to the direction of the wind and are small asymmetrical ridges stretching parallel to one another.
Mounds of the sand with an irregular surface are the sand hills.
The mounds of the sand formed of the ridge with the crest are called sand dune. The areas with the strong wind which blow in the same direction develop dunes which are mostly asymmetrical in cross- section. The presence of any barrier to the direction of the wind causes the development of a zone of a wind shadow, within which the velocity of the wind is much reduced. The sand particles travelling along with the blowing of the wind gets the first change of the dropping down within any such wind shadow and as they accumulate the dune is gradually build up. Once formed a dune acts as a barrier itself with further deposition gradually grows in size.
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