Daily Quiz #23 UPSC Prelims Marathon – September 27, 2019

Explanation: The mapping of the ocean floor and palaeomagnetic studies of rocks from oceanic regions revealed the following facts:
i.It was realised that all along the midoceanic ridges, volcanic eruptions are common and they bring huge amounts of lava to the surface in this area.
ii.The rocks equidistant on either sides of the crest of mid-oceanic ridges show remarkable similarities in terms of period of formation, chemical compositions and magnetic properties. Rocks closer to the mid-oceanic ridges have normal polarity and are the youngest. The age of the rocks increases as one move away from the crest.
iii.The ocean crust rocks are much younger than the continental rocks. The age of rocks in the oceanic crust is nowhere more than 200 million years old. Some of the continental rock formations are as old as 3,200 million years.
iv.The sediments on the ocean floor are unexpectedly very thin. Scientists were expecting, if the ocean floors were as old as the continent, to have a complete sequence of sediments for a period of much longer duration. However, nowhere was the sediment column found to be older than 200 million years.
v.The deep trenches have deep-seated earthquake occurrences while in the midoceanic ridge- area, the quake foci have shallow depths.
These facts and a detailed analysis of magnetic properties of the rocks on either sides of the mid-oceanic ridge led Hess (1961) to propose his hypothesis, known as the “sea floor spreading”. Hess argued that constant eruptions at the crest of oceanic ridges cause the rupture of the oceanic crust and the new lava wedges into it, pushing the oceanic crust on either side. The ocean floor thus spreads. The younger age of the oceanic crust as well as the fact that the spreading of one ocean does not ‘cause’ the shrinking of the other, made Hess think about the consumption of the oceanic crust. He further maintained that the ocean floor that gets pushed due to volcanic eruptions at the crest, sinks down at the oceanic trenches and gets consumed.

Explanation: In India, debris avalanches and landslides occur very frequently in the Himalayas. There are many reasons for this. One, the Himalaya is tectonically active. They are mostly made up of sedimentary rocks and unconsolidated and semi-consolidated deposits. The slopes are very steep. Compared to the Himalayas, the Nilgiris bordering Tamilnadu, Karnataka, Kerala and the Western Ghats along the west coast are relatively tectonically stable and are mostly made up of very hard rocks; but, still, debris avalanches and landslides occur though not as frequently as in the Himalayas, in these hills. The reason is that many slopes are steeper with almost vertical cliffs and escarpments in the Western Ghats and Nilgiris. Mechanical weathering due to temperature changes and ranges is pronounced. They receive heavy amounts of rainfall over short periods. So, there is almost direct rock fall quite frequently in these places along with landslides and debris avalanches.

Explanation: Erosion involves acquisition and transportation of rock debris. When massive rocks break into smaller fragments through weathering and any other process, erosional geomorphic agents like running water, groundwater, glaciers, wind and waves remove and transport it to other places depending upon the dynamics of each of these agents. Abrasion by rock debris carried by these geomorphic agents also aids greatly in erosion. By erosion, relief degrades, i.e., the landscape is worn down. That means, though weathering aids erosion it is not a pre-condition for erosion to take place. Weathering, mass-wasting and erosion are degradational processes. It is erosion that is largely responsible for continuous changes that the earth’s surface is undergoing.
Denudational processes like erosion and transportation are controlled by kinetic energy. The erosion and transportation of earth materials is brought about by wind, running water, glaciers, waves and ground water. Of these the first three agents are controlled by climatic conditions. They represent three states of matter —gaseous (wind), liquid (running water) and solid (glacier) respectively.
The work of the other two agents of erosion-waves and ground water is not controlled by climate. In case of waves it is the location along the interface of litho and hydro sphere — coastal region — that will determine the work of waves, whereas the work of ground water is determined more by the lithological character of the region. If the rocks are permeable and soluble and water is available only then karst topography develops.

Explanation: Characteristics of different types of soils:
•Alluvial soil:
Loamy
Coarse and dry in upper reaches of the river, gets finer and moist as the river flows down.
Rich in minerals especially potash and lime.
Poor in nitrogen and humus.
•Black soil:
Clayey
Black in colour
Rich in lime, magnesium
Poor in phosphorous, nitrogen and organic matter
Very fertile
•Red soil:
Loamy or sandy
Red in colour due to large amounts of iron oxide
Deep and fertile in lowlands; thin and poor in highlands
Poor in nitrogen, phosphorous, potassium and organic matter
•Laterite soil:
Coarse and porous
Red due to iron oxide
Poor in lime, nitrogen and magnesium
High acidity and low moisture retention

Explanation:
Coal is a readily combustible, black or brownish-black sedimentary rock, predominantly made of carbon. It is formed over millions of years through geological pressure applied on plant remains buried under the soil. The heat value of coal reserves in our country (measured in Gross Calorific Value (GCV)), is unfortunately lower than that of international coal reserves.
Types of coal found in India:
Anthracite: It is the highest grade of coal containing a high percentage of fixed carbon. It is hard, brittle, black and lustrous. It is found in smaller quantity in regions of Jammu and Kashmir only.
Bituminous: It is a medium grade of coal having high heating capacity. It is the most commonly used type of coal for electricity generation in India. Most of bituminous coal is found in Jharkhand, Odisha, West Bengal, Chhattisgarh, and Madhya Pradesh.
Lignite: It is the lowest grade coal with the least carbon content. It is found in the regions of Rajasthan, Tamil Nadu, and Jammu & Kashmir.
Peat: Contains less than 40 to 55 per cent carbon i.e more impurities. It contains sufficient volatile matter and lot of moisture [more smoke and more pollution]. When left to itself, it burns like wood, gives less heat, emits more smoke and leaves a lot of ash.