write short note on transportational and depositional work of wind
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Answer:
Wind Transportation:
Material transported by wind consists of:
(a) Bed load
(b) Suspended load.
The bed load is transported by rolling, or by jumping or saltation (i.e. moving the material along the surface in a series of short jumps)
i. Rolling:
A wind moving in a straight direction rolls the sand grains along the surface. As the sand particles roll along ripple marks are generally produced. Some eddies in the wind and variations in the size of the particles moved cause the formation of alternating shallow depressions and low ridges. The ripple marks advance with the wind by the grains rolling up the gentle windward slopes of the small ridges and then rolling down the steeper leeward slopes into the depressions.
ii. Saltation:
Great quantities of desert sand are transported by a combination of impact and saltation (i.e. jumping). The process starts usually where the sand grains are being picked up by the wind as it moves across on an irregular land surface. As these grains are carried forward, they fall and with a combined downward and forward motion strike, other loose sand grains still on the ground.
The impact from the falling grains drives those still on the surface up into the air stream and they in turn are blown forward. Hence, each moving grain after advancing a few centimetres, starts another grain on its short jump.
The combination of countless individual hops over a surface gives rise to an apparently smooth advance of the sand. Vertical and cross currents of the wind produced by irregularities of the land and objects over it may increase or otherwise modify the saltation produced by a straight moving wind.
iii. Suspension:
Particles are carried in suspension whenever the velocity of the wind is sufficiently great. The greater part of the sand grains so carried are transported within a metre or two of the ground because the lower currents being relatively slow currents (due to the numerous obstructions they encounter on the surface) are unable to lift the greater part of the sand particles to the higher currents that might be able to transport them.
Dust that is carried upward into the faster-moving wind above may be transported for great distances. A strong wind blowing for 2 or 3 days in one direction may produce as a result of transported dust, haziness of the air and highly coloured sunsets and sunrises in windward regions.
The dust particles that fall in the polar regions and upon vessels in mid-oceans are transported in swift currents. The red rains (called blood rains) of Northern Italy furnish a very interesting example of long distance transportation.
Strong winds starting in the desert area of Northern Africa, where they pick up minute particles of hematite worn off of the sand grains of the desert, sweep across the Mediterranean and as they cross the Alps, their moisture is condensed to rain that carries the red particles down upon Northern Italy.
The finely a accumulated dust blown from Icelandic volcanoes in the coast of Norway in 1875, and subsequent to the eruption in 1883, the ship Beaconsfield of Philadelphia while at a distance of 1330 km from the source sailed for three days through clouds of dust which fell upon the decks at the rate of 25 mm per hour.
The day following the explosive eruption of St. Vincent in 1812 the Barbados Island, 128 km to the windward, was completely shrouded in darkness for many hours, the light of the sun being almost obscured by the cloud of dust which in the form of a slow silent rain fell over the whole island.
In general transportation of wind-blown dust is worldwide.
Wind Deposition:
Sediments carried by wind are deposited where the velocity of the wind current falls below the level required to hold the solid loads in suspension, or at places where precipitation washes the air and force the sediments to fall down to the surface.
The decrease in wind velocity may be brought about by obstacles on the surface such as fences, trees, houses etc. Dust carried by wind is universally distributed. Forested areas and grasslands receive much fine wind-blown material, which soon becomes mixed with the local soil and loses its identity.
Mountainous regions adjacent to deserts receive large quantities of dust, though most of it soon find its way into the streams unless the region is covered with forests.
Accumulations of wind-blown sediment are particularly conspicuous in the world’s dry lands and along sandy coasts. These wind deposits are of two distinctive types viz mounds and ridges of sand from the wind’s bed load called dunes and extensive blankets of silt called loess which was carried in suspension.
The manner the materials are carried by the wind depends on various factors like their size, shape and density. In general, dust particles are carried in suspension, sand grains are moved by traction which generally induces saltation, rolling or creep. (As an agent of transportation, wind is far less effective than water in moving large amount of sedimentary material)
Answer:
Transportation - Transport or transportation is the movement of humans, animals and goods from one location to another. Modes of transport include air, land (rail and road), water, cable, pipeline and space. ... Transport is important because it enables trade between people, which is essential for the development of civilizations
depositional - Depositional plains are mostly fertile areas which have been formed by the deposition of sediments carried by various agent of nature like wind running water etc. their types are: alluvial depositional plains which are fertule due to silt deposition by rivers. glacial deposition formed by glacial action.