SHIKHAR Mains 2023 Day 32, Model answer English

Updated : 20th Jul 2023

Q1. सुनामी की उत्पत्ति के कारणों की विवेचना कीजिए।

Discuss the reasons for the origin of Tsunami. (8 Marks)

Approach:

Define Tsunami in introduction.
Enlist the reasons for the origin of the Tsunami.

Answer:

The word “tsunami” comprises the Japanese words”tsu” (meaning harbour) and “nami” (meaning wave). A tsunami is a series of enormous waves created by an underwater disturbance usually associated with earthquakes occurring below or near the ocean.

Causes of tsunamis:

Earthquakes: It can be generated by movements along fault zones associated with plate boundaries. Most strong earthquakes occur in subduction zones where an oceanic plate slides under a continental plate or another younger ocean plate.
For example,

The Great 1960 Chilean tsunami was generated by a magnitude 9.5 earthquake that had a rupture zone of over 1,000 km.
The Indian Ocean Tsunami of 2004 was caused by an undersea earthquake with a magnitude of 9.1 which struck off the coast of the Indonesian island of Sumatra.

Landslides: A landslide that occurs along the coast can force large amounts of water into the sea, disturbing the water and generate a tsunami. Underwater landslides can also result in tsunamis when the material loosened by the landslide moves violently, pushing the water in front of it.
For example:

On July 10, 1958 Southeast Alaska - A magnitude 7.8 earthquake triggered a number of submarine landslides, rock falls, and ice falls that generated tsunamis.

Volcanic Eruption: Although relatively infrequent, violent volcanic eruptions also represent impulsive disturbances, which can displace a great volume of water and generate extremely destructive tsunami waves in the immediate source area.

On January 15, 2022, a mostly submerged volcanic cauldron in the South Pacific named Hunga Tonga-Hunga Ha‘apai caused a tsunami in the Kingdom of Tonga.
One of the largest and most destructive tsunamis ever recorded was generated on August 26, 1883 after the explosion and collapse of the volcano of Krakatoa (Krakatau), in Indonesia. This explosion generated waves that reached 135 feet, destroyed coastal towns and villages along the Sunda Strait in both the islands of Java and Sumatra, killing 36, 417 people.

Extraterrestrial Collision : Tsunamis caused by extraterrestrial collision (i.e. asteroids, meteors) are an extremely rare occurrence. Although no meteor/asteroid induced tsunami has been recorded in recent history, scientists realize that if these celestial bodies strike the ocean, a large volume of water would undoubtedly be displaced to cause a tsunami. Scientists have calculated that if a moderately large asteroid, 5-6 km in diameter, strike the middle of the large ocean basin such as the Atlantic Ocean, it would produce a tsunami that would travel all the way to the Appalachian Mountains in the upper two-thirds of the United States.

India has developed the Indian National Centre for Ocean Information System (INCOIS), for early detection of Tsunami and preparedness of impacts of Tsunami.

Q2: पवनों का वर्गीकरण प्रस्तुत कीजिये। इसके साथ ही ग्लोब पर स्थित वायुदाब पेटियों के मध्य पवन संचलन का सचित्र विश्लेषण कीजिये । (12 Marks)

Give the classification of winds. Along with this, make a pictorial analysis of the wind movement between the pressure belts located on the globe. (12 Marks)

Approach-

Define wind in introduction.
Present the classification of winds in the first part.
In the second part, conclude the answer by analyzing the movement of wind between the pressure belts located on the globe.

Answer -

When the movement of air is in horizontal direction then it is called wind. The air flowing in the vertical direction is called air current, it is of two types namely convective current and concave current. Winds are classified on the basis of speed and nature. The lowest speed wind is called Sameer while medium speed wind is called Pawan. High speed winds are called currents.

On the basis of form, wind is classified into 3 forms.

Primary wind is also called prevailing wind / permanent wind / planetary wind / eternal wind. It lasts throughout the year, it is the result of primary air pressure belts and their direction is constant, covering the entire globe. It includes trade winds, westerlies and polar east winds.
Apart from this, secondary winds are also called periodic winds. These change in direction with time, they are the result of secondary belts. Example: Monsoon winds.

Tertiary winds blow over a small area only during a particular period of the day or year. These winds blow due to the difference in temperature and air pressure at a particular place. These winds can be of different types according to the local characteristics, such as hot, cold, snowy, dusty. Loo is a hot and dry local wind over the northern plains of India. Other main local winds include Mistral, Fohen, Bora, etc.

Wind transmission over the globe

The region between the equatorial low pressure belt and the subtropical high pressure belt

The subtropical high pressure belt is an area of divergence, the winds blowing in it are called trade winds (tropical east).
In the Northern Hemisphere, their direction is from the north-east to the south-west towards the equatorial low pressure belt, while in the Southern Hemisphere the situation is opposite.
The deflection of the trade winds is the least among all the winds / prevailing winds as they are approaching the equator where the Coriolis force becomes minimum.
The winds coming from both the sides converge near the equator, hence this region is called the Intertropical Convergence Zone (ITCZ).
The equatorial low pressure belt is also called the calm zone because winds are absent in the central part of the convergence zone. Both the trade winds start rising from the outer edge of the convergence zone.
As a result, these trade winds are not able to reach the central part.
Being a windless region, it is called a doldrum or a calm area.
However, in the new discovery, information is found in some places about the equatorial westerly wind moving from west to east, which blows from the western edge of the ocean to the east.
If the continent on the west coast of the ocean is present in such a way that it creates a favourable position for the accumulation of air in the area of convergence, then in the calm region, a pressure gradient force is formed from west to east. From which the equatorial westerly wind originates. The equatorial westerly wind is more developed in the Atlantic Ocean. It operates in a relatively small area.

The region between the subtropical high pressure belt and the subpolar low pressure belt

The wind that blows in this region is called westerly wind.
The wind which blows from the subtropical high pressure area to the subpolar low pressure area is called westerly wind.
Being located in the middle latitudes, the rate of deflection in it is higher than the trade winds, so gradually it starts moving in the direction from west to east, but the direction from west to east is not attained.
The westerly winds of the Southern Hemisphere are stronger and deflected because the friction force due to moving over the ocean is less while the moisture content is high. The lower the friction force, the higher the speed, due to which the deflection is greater.
The presence of moisture/water vapour in the air makes it lighter, which increases its speed, that is, the winds of the Southern Hemisphere are much more powerful than the Northern Hemisphere. That is why it is called Roaring Forty, Violent fifty and Screaming Sixty.

The region between the polar high pressure belt and the subpolar low pressure belt

This is the region of the polar east wind.
It has maximum deflection because it originates from the region of maximum Coriolis force.
The subpolar low pressure belt is a special type of convergence zone where two air masses with different physical properties converge. As a result of this, these air masses do not mix easily and form a transition zone where energy is exchanged. This transition zone is called the front where the temperate cyclone is formed.