Model Answers- Answer Writing Practice- Day 1

Day 1: Model Answers for Mains Questions on 17th June

1. Discuss the global distribution of volcanoes along with the reasons for the same. 

Approach:

1. Explain briefly about volcanism phenomenon briefly
2. Give an account of global distribution of volcanoes
3. Mention the reasons for such a distribution.

Answer:

The natural geological phenomenon of volcanism is an extremely powerful process of melting, differentiation and segregation in the interior hotlayers of the planet Earth since the initial stages of its evolution over 4 billion years ago. Water vapor, carbon dioxide, and other volatiles that originated from volcanic emanations over the centuries are distributed across the Earth’s hydrosphere and atmosphere. 

Areas of volcanic eruption are home to millions of people around the world like cities such as Naples in Italy, Kagoshima in Japan, Hilo in Hawaii, agricultural districts in Indonesia, the Philippines, Japan, Mexico, and other countries.

 Global distribution of volcanoes:

With regard to the major distribution region of the world, about 62% of all active volcanoes in the world are located around the margins of the Pacific Ocean, although their distribution along this rim is irregular.  For instance, the East Pacific Island Arc includes 45% of the world’s active volcanoes, but the Central and South America segments contain only 17%. 

About 14% of the volcanoes are located in the Indonesian Islands arc while, of the remaining 24%, 3% are located in the mid-Pacific Ocean, 1% in mid-Indian Ocean islands, 13% on mid-Atlantic Ocean islands, and the last 7% are situated in the Mediterranean Sea and Central Asia and the inner part of continents, for example, the African Rift.

 Figure: Distribution of volcanoes across the world

                        Source: Researchgate.com

Broadly the global distribution of volcanoes can be divided into the following seven regions:

1. Volcanoes of the Pacific Ocean island arcs and Alaska continental rim
2. Volcanoes of the East Pacific continental rim
3. Volcanoes of alpine-Indonesian mountain belt
4. Volcanoes of East African–Arabian belt
5. Volcanoes of the rifts and mountains of Eurasia
6. Volcanoes of the West Indies island arc and 
7. Volcanoes of the ocean floor

Reasons for the distribution of volcanoes:

• The reason behind the large amounts of volcanoes and volcanic activity in the area of Pacific Ring of Fire is the movement of tectonic plates in the areas called subduction zones where many plates collide and overlap at convergent boundaries. In these areas of subduction, a plate that lies beneath another is pushed down and subducted by one resting on top thus resulting into the melting of the subducted rock which turns it into magma.
• In the North American and Eurasian tectonic plates belt, the plates move apart and the hot magma rises to the surface. As time passes, the combination of the upward movement and cooling of the magma constructs tall ridges on the ocean floor and forms the Earth’s longest uninterrupted volcanic mountain range almost 60,000 kilometres long. 
• Coming to the mid-ocean ridges, molten rock and gases will be released into the ocean by the vents and fissures thus the majority of submarine volcanoes are located in these ridges.  
• In the mantle, a volcanic "hotspot" is an area from which heat rises as a thermal plume from deep in the Earth. Because of the high heat and lower pressure at the base of the lithosphere, melting of the rock takes place and forms magma that rises through cracks and erupts to form volcanoes.

Thus, Globally volcanoes are found along the active plate margin and in hotspot regions. With a good network of seismic sensors, thermal sensors and satellite images, we can refine the maps of the Global distribution of volcanoes mainly the submarine volcanoes and dormant volcanoes, as Dormant volcanoes can become active volcanoes based on the plate tectonic movement and convection cells. 

2. What is frontogenesis? Describe the formation of different fronts along with the climatic conditions observed around these fronts. 

Approach:

1. Define the term frontogenesis clearly.
2. Discuss about warm front and associated climatic conditions
3. Discuss about cold front and associated climatic conditions
4. Discuss about occluded front and associated climatic conditions
5. Discuss about stationary front and associated climatic conditions

Answer:

Literally the word “front” means the forward margin of something and implies a sort of boundary between two air bodies of quite different nature. The word “genesis” means beginning or method of formation or evolution of something.

In short, the word frontogenesis implies the generation of a front. The fronts on the planet earth have significance because of their modification of the weather of the area under their influence very significantly. Opposite to frontogenesis, there is a term called “frontolysis” meaning the decaying of fronts.

In general, fronts are formed in the temperate areas because of favorable conditions of their formation i.e. occurrence of the contrasting air bodies.

Formation of various fronts:

1. Warm front: It is the gentle sloping frontal belt along which the warm air moves over the area which has been occupied by the cold air and the cold wedge present in the frontal zone retreats. These fronts generally move slowly and are considered to be less violent compared to a cold front. Most of the time they are associated with moderate rainfall but sometimes may result in thunderstorms. Weather signals for their arrival in a region are the arrival of cirrus clouds, altostratus cloud, altocumulus cloud and finally the stratus cloud and the fogs.
2. Cold front: When the cold air mass in the frontal zone moves under the warm air mass, a cold front is formed. The cold air being the dense air settles downs and forces the warm air to uplift. Associated weather conditions include bad weather that brings with it thick clouds, heavy precipitations, thunderstorms, and lightning. In comparison to the warm front, the slope of a cold front is much steeper. These are the fastest moving front and it is associated with the most violent kind of weather conditions.
3. Stationary front: When two air masses converge in a manner that they are parallel to each other, a new form of front named stationary front is formed. As a result of this parallel placement, no vertical movement of the air takes place in the stationary front and it remains stationary in its position. They mostly occur over an ocean sea area.
4. Occluded front: Occluded fronts are created when while traveling the cold front overtakes the warm fronts and the warm air is totally displaced from the ground surface. Occluded fronts are again of two kinds namely Cold Occlusion and Warm Occlusion.
   1. Cold Occlusion front occurs when the cool air that is present behind the cold front is colder than the advancing cold air which is present ahead of the warm front.
   2. Warm occlusion occurs when the air which is present behind the cold front is warmer than the advancing air which is present ahead of the warm front.

Conclusion: 

Thus fronts ( From frontogenesis to frontolysis ) are an important atmospheric phenomenon in the temperate latitude which has varied climatic conditions at different points in time, based on the air mass movement.