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BGGCT-131: Physical Geography

BGGCT-131: Physical Geography

IGNOU Solved Assignment Solution for 2023

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Assignment Code: BGGCT-131/TMA/2023

Course Code: BGGCT-131

Assignment Name: Physical Geography

Year: 2023

Verification Status: Verified by Professor




All Questions are compulsory and carries 10 marks each


1) Explain in detail dualistic concept of origin of earth.

Ans) The dualistic concept of the origin of the Earth is a theory that postulates that the Earth was created through a process of dualism or dichotomy, where two opposing and complementary forces or entities acted to form the planet. The dualistic concept of the origin of the Earth is a theory that postulates that the Earth was created through the process of dualism or dichotomy. This idea can be traced back to a number of different ancient cosmologies, religious traditions, and philosophical schools of thought.


One of the earliest examples of a dualistic cosmology can be found in ancient Persian religion. This religion postulates the existence of two primal forces: Ahura Mazda, the good god of light, and Angra Mainyu, the evil god of darkness. These two deities are said to have coexisted since the beginning of time. The conflict between Ahura Mazda and Angra Mainyu is said to have resulted in the creation of the Earth and the rest of the material cosmos as a result of the subsequent chaos.


The yin-yang philosophy of ancient China is another well-known example of dualistic cosmology. This theory proposes that the cosmos is made up of two opposing yet complimentary energies, which are referred to as yin (which is connected with darkness, femininity, and passivity) and yang (associated with light, masculinity, and activity). According to this school of thought, the Earth came into being as a result of the interaction between yin and yang, which resulted in the formation of the four fundamental elements—earth, water, fire, and air—that later combined to form the physical world.


The work of the Greek philosopher Empedocles is most closely associated with the dualistic concept of the origin of the Earth in Western philosophy. Empedocles postulated the existence of four elements (earth, water, air, and fire) and two opposing forces (love and strife) that acted upon them. Love and strife were thought to be the driving forces behind the creation of the Earth. The ancient Greek philosopher Empedocles believed that the Earth was created when love brought together the four elements, while conflict drove them away.


In these current times, the dualistic view of the beginning of the Earth has largely been overtaken by scientific hypotheses such as the Big Bang and plate tectonics. Despite this, many aspects of dualism continue to remain dominant in popular culture and religion, in addition to philosophical discussions over the nature of reality and the link between the mind and the body.


2) Critically discuss the concept of Cycle of Erosion of Davis.

Ans) The American geographer William Morris Davis devised a conceptual model of the progression of landscapes known as the Cycle of Erosion in the latter half of the 19th century and the early part of the 20th century. The model makes an effort to describe how landscapes shift over the course of time in response to the effects of weathering and erosion. The Cycle of Erosion has been the subject of debate and improvement in geomorphology, despite the fact that it has played an important role in the development of the field.


The idea that landscapes move through a succession of stages, or cycles, as they are eroded by water, wind, and other forces is the foundation of the concept known as the Cycle of Erosion. The first phase of a landscape's development is referred to as its youth and is distinguished by the presence of steep slopes and narrow valleys. The next stage is the mature stage, which is characterised by the terrain becoming more rounded and flattened, with wider valleys and gentler slopes. This stage comes after the juvenile stage. The final stage of the landscape's development is called "old age," and it is characterised by a generally featureless plain that has become relatively flat as a result of erosion.


Many shortcomings of the model have been brought out by those who disagree with the Cycle of Erosion theory. The model, for one, makes the assumption that erosion is the only significant force acting on landscapes, although in reality, many other processes, such as tectonic uplift, volcanic activity, and changes in sea level can also have substantial impacts on landscapes. In addition to this, the model has a propensity to oversimplify the intricate relationships that exist between erosion, sedimentation, and the formation of landforms. For instance, the model does not take into consideration the function that lateral erosion plays, which can contribute to the formation of alluvial fans and deltas by widening valleys and making them deeper.


The Cycle of Erosion is still a useful tool for understanding how landscapes change over the course of time, despite the critiques that have been levelled against it. In addition to having an impact on disciplines like ecology and hydrology, the model is still utilised by a significant number of geomorphologists as a conceptual framework for the investigation of erosion and the formation of landforms. Nevertheless, it is essential to be aware of the constraints imposed by the model and to make use of it in conjunction with a variety of other strategies and data sources.


3) Explain in detail the factors governing insolation.

Ans) The amount of insolation reaching the earth's surface and its effectiveness depends on various factors. They are:


Angle of Incidence or Inclination of the Sun's Rays: The angle at which the sun's rays hit the Earth's surface is an important factor in determining the amount of insolation. The angle of incidence is determined by the latitude of the location and the time of day. The angle is highest at the equator, where the sun is directly overhead, and decreases towards the poles. When the angle of incidence is low, the sunlight is spread over a larger area, reducing the amount of insolation received by that area. The inclination of the sun's rays also affects the effectiveness of insolation. When the angle of incidence is perpendicular to the surface, the insolation is most effective and vice versa.


Duration of Sunshine: The length of time that a location is exposed to sunlight is another factor that contributes to the total quantity of insolation it receives. There is a correlation between latitude and the number of daylight hours. At the equator, the difference between the duration of the day and the night is rather constant throughout the year. On the other hand, the length of both the day and the night changes dramatically from one season to the next near the poles. The polar regions enjoy virtually unbroken daylight during the summer months, but during the winter months they are enveloped in almost unbroken darkness.


Distance between the Earth and Sun: Due to the elliptical path that the Earth takes around the Sun, the distance that separates the Earth and the Sun shifts throughout the course of a year. When the Earth is at its perihelion, which is the point in its orbit at which it is closest to the Sun, the quantity of insolation that the planet receives is somewhat greater than when it is at its aphelion (aphelion). However, the significance of this variance is not sufficient to bring about dramatic alterations in the climate of the earth.


Transparency of the Atmosphere: The amount of sunlight that makes it to the surface of the Earth is somewhat determined by the Earth's atmosphere. Incoming radiation is partially scattered and partially absorbed by the atmosphere, which results in a decrease in the amount of insolation that reaches the surface of the Earth. The density and make-up of the atmosphere both have an effect on the quantity of scattering and absorption that takes place. The amount of sunlight that is able to penetrate the atmosphere and reach the surface of the earth can also be influenced by atmospheric particles such as pollution and dust.


4) Describe the bottom reliefs of Atlantic Ocean.

Ans) The Atlantic Ocean is the second largest ocean in the world and takes up around 20 percent of the surface area of the earth. The bottom terrain of the Atlantic Ocean can be broken down into several distinct characteristics, the most prominent of which are the abyssal plain, the continental shelf, the continental slope, the continental rise, and the mid-ocean ridge.


Continental Shelf: The continental shelf is a platform that stretches from the shore all the way to the continental slope. It is quite shallow and has a gentle slope. There is a large amount of variation in the width of the continental shelf, which can range from only a few kilometres in width to several hundred kilometres in width. Although the depth of the continental shelf is normally between 100 and 200 metres, there are several places on the planet where it can be significantly deeper.

Continental Slope: The continental slope is a steep slope that runs from the continental shelf all the way down to the bottom of the deep ocean. Submarine canyons and channels cut into the continental slope, giving it a depth that ranges anywhere from 200 to 3,000 metres on average. The continental slope can be identified by these features.


Continental Rise: The continental rise is a region that has a mild slope that stretches all the way from the bottom of the continental slope all the way up to the abyssal plain. Sediment deposits that have been deposited from the continental shelf and slope by turbidity currents are often what distinguishes the continental rise from other features of the ocean floor.


Abyssal Plain: The abyssal plain is a vast, flat plain that covers most of the ocean floor. The abyssal plain has an average depth of around 4,000 meters and is covered by a layer of sediment that is several kilometres thick. The abyssal plain is relatively featureless, although it is punctuated by seamounts, guyots, and other volcanic features.


Mid-Ocean Ridge: The mid-ocean ridge is a massive underwater mountain range that runs through the center of the Atlantic Ocean. The mid-ocean ridge is the longest mountain range in the world and has an average height of around 2,500 meters. The mid-ocean ridge is the site of frequent volcanic activity and is characterized by hydrothermal vents, which support unique ecosystems of deep-sea creatures.




All Questions are compulsory and carries 10 marks each


5) Discuss in detail Mountain Building Theories of Kober, Holmes and Plate Tectonics.

Ans) Mountain building is a geological process that involves the uplift and folding of rock layers to create mountain ranges. There are several theories that explain the mechanism of mountain building, including the theories of Kober, Holmes, and Plate Tectonics.


Kober's Theory

Kober's theory, also known as the "crustal thickening" theory, explains mountain building as the result of horizontal compression and the thickening of the Earth's crust. According to this theory, the forces that cause crustal thickening are generated by the cooling and contraction of the Earth's interior. As the Earth's interior cools, the outer layers of the Earth contract, causing horizontal compression and the thickening of the crust. This thickening results in the uplift and folding of the Earth's crust, creating mountain ranges.


Holmes' Theory

Holmes' theory, also known as the "mantle convection" theory, explains mountain building as the result of the movement of the Earth's mantle. According to this theory, the mantle of the Earth is in constant motion, with warmer, less dense material rising and cooler, denser material sinking. This movement creates convection currents that cause the Earth's crust to move and deform. As the crust is subjected to these forces, it can uplift and fold, creating mountain ranges.


Plate Tectonics

Plate tectonics is a theory that explains mountain building as the result of the movement and interaction of the Earth's tectonic plates. According to this theory, the Earth's lithosphere is broken up into several large plates that are in constant motion. As these plates move, they interact with one another, resulting in a variety of geological features, including mountain ranges. There are three main types of plate boundaries: divergent boundaries, where plates move away from each other; convergent boundaries, where plates move towards each other; and transform boundaries, where plates slide past each other. Mountain building can occur at convergent boundaries, where one plate is forced under another in a process called subduction. This can result in the formation of volcanic arcs, fold mountains, and other mountainous features.


In summary, the theories of Kober, Holmes, and Plate Tectonics all provide different explanations for the mechanism of mountain building. Kober's theory explains mountain building as the result of crustal thickening, Holmes' theory explains it as the result of mantle convection, and Plate Tectonics explains it as the result of plate movement and interaction. While these theories differ in their specific details, they all emphasize the importance of geological forces and movements in shaping the Earth's surface.


6) Discuss Koppen’s climatic classification.

Ans) Koppen's climatic classification system, which is also known as the Koppen-Geiger climate classification, is a system that is frequently used for classifying the climates of the world based on temperature, precipitation, and patterns of vegetation. Koppen's climatic classification system also goes by the name the Koppen-Geiger climate classification. Koppen and Geiger were the ones that came up with this system. After its initial presentation in the year 1900 by the German botanist and climatologist Wladimir Koppen, it was later modified by Wladimir Koppen's student Rudolf Geiger in the decade of the 1950s.


The climates of the world are categorised by this method into the following five broad categories: tropical, dry, temperate, continental, and polar. After that, these groupings are further subdivided into categories based on the range of temperatures and amounts of precipitation that they experience.


The Five Main Groups

  1. Tropical Climates: These can be found in locations that are somewhat close to the equator and are distinguished by their high temperatures and abundant precipitation. The tropical rainforest, the tropical monsoon, and the tropical savanna are the three divisions that are further subdivided within them.

  2. Dry Climates: These are found in areas that receive a low amount of precipitation and are further subdivided into two categories: arid (also known as deserts), and semi-arid (steppe).

  3. Temperate Climates: These are found in regions with moderate temperatures and rainfall. They are further divided into four subcategories: Mediterranean, humid subtropical, marine west coast, and humid continental.

  4. Continental Climates: These climates are further subdivided into two types, subarctic climates and humid continental climates, as they are located in places that experience significant temperature swings between summer and winter.

  5. Polar Climates: These are found in regions close to the poles and are characterized by extremely cold temperatures and low precipitation. They are further divided into two subcategories: tundra and ice cap.


The climate categorization system that Koppen developed is one that is often used in fields such as geography, ecology, and climatology. Koppen's system can be found in all three of these fields. It provides a helpful method to understanding the vast array of climatic conditions that can be found all over the planet.


7) What are the main characteristics of Igneous rocks? Classify Igneous rocks on the basis of place of origin and chemical composition.

Ans) The cooling and subsequent solidification of molten magma or lava results in the formation of igneous rocks. In addition to sedimentary and metamorphic rocks, plutonic rocks are considered to be one of the three primary forms of rocks. Igneous rocks are characterised primarily by the following characteristics:

  1. There are two different types of igneous rocks: intrusive and extrusive. The formation of intrusive rocks occurs when magma cools and solidifies slowly underneath the surface of the Earth, whereas the formation of extrusive rocks occurs when lava cools and solidifies rapidly on the surface of the Earth.

  2. The rate at which the magma or lava cooled determines the grain size distribution of the igneous rocks that result, which can range from extremely fine to extremely coarse. Rocks with finer grains are produced by a rapid cooling process, whereas rocks with coarser grains are produced by a long cooling process.

  3. Igneous rocks can have a mineral composition that is vastly different from one another, depending on the chemical make-up of the magma or lava from which they were formed. Quartz, feldspar, mica, and pyroxene are all examples of minerals that are frequently found in igneous rocks.


Based on their place of origin and chemical composition, igneous rocks can be classified into several categories:

  1. Intrusive Igneous Rocks: These rocks are formed from magma that cools and solidifies slowly beneath the Earth's surface. Examples include granite, diorite, and gabbro.

  2. Extrusive Igneous Rocks: These rocks are formed from lava that cools and solidifies quickly on the Earth's surface. Examples include basalt, andesite, and rhyolite.

  3. Volcanic or Pyroclastic Igneous Rocks: These rocks are formed from fragments of volcanic material, such Plutonic or Hypabyssal Igneous Rocks: These rocks are formed from magma that cools and solidifies at a shallow depth below the Earth's surface. Examples include porphyry and pegmatite.

  4. Felsic Igneous Rocks: These rocks are rich in silica and aluminium and have a lower density. Examples include granite and rhyolite.

  5. Intermediate Igneous Rocks: These rocks have a moderate amount of silica and aluminium and have a density between felsic and mafic rocks. Examples include andesite and diorite.

  6. Mafic Igneous Rocks: These rocks are rich in iron and magnesium and have a higher density. Examples include basalt and gabbro.

  7. Ultramafic Igneous Rocks: These rocks have a very low silica content and are rich in iron and magnesium. Examples include peridotite and dunite.




8) Write Short notes on the following. All Questions are compulsory and carries 5 marks each.


a) Cryosphere.

Ans) The region of the Earth's system where water is found in its frozen state is referred to as the cryosphere. This include things like snow, ice caps, glaciers, ice sheets, sea ice, permafrost, as well as frozen lakes and rivers. The cryosphere is an essential part of the Earth's water cycle and plays a significant part in determining the climate on Earth as well as the level of the oceans throughout the world.


The ability of the cryosphere to reflect sunlight back into space is one of the most important aspects of this layer of the planet's atmosphere since it contributes to the maintenance of a consistent temperature on Earth. This reflecting surface is diminished as the cryosphere continues to melt as a result of climate change, which leads to more solar radiation being absorbed and an increase in global temperatures. The significance that the cryosphere plays in the global water cycle is another significant aspect of the icy realm. The thawing of permafrost can cause enormous amounts of carbon and methane to be released into the atmosphere, which can further exacerbate climate change. Sea level rise is a potential consequence of the melting of glaciers and ice sheets, which can also contribute to it.


The cryosphere is essential to human societies as it supplies a source of freshwater and maintains a large number of ecosystems, particularly in polar regions. However, as the cryosphere continues to change, it may have substantial effects on human society. These effects may include a rise in the frequency and severity of flooding and coastal erosion, as well as interruptions to the availability of water and food.

b) Monthly variation and yearly variation of tides.

Ans) The gravitational pull of both the Sun and the Moon causes a periodic rise and fall in the level of the sea, which is referred to as the tides. On a daily, weekly, monthly, and yearly basis, the height of the tides and the times at which they occur change. The monthly change of tides is primarily caused by the shifting position of the Moon in relation to the Earth that occurs as a result of the Moon's orbit around the Earth. When the gravitational forces of the Sun and Moon are aligned and reinforce each other, which occurs during the full Moon and the new moon phases, the tides are at their maximum levels. The tides that occur during spring are known as spring tides. Lower tidal ranges, known as neap tides, are caused when the gravitational forces of the Sun and Moon act against each other during the first and third quarter phases of the Moon. This results in the Moon going through its first and third quarter phases.


The changing positions of the Earth and Moon in relation to the Sun, the tilt of the Earth's axis, and the elliptical shape of the Moon's orbit around the Earth are all factors that contribute to the yearly variation in tides. Other factors include the tilt of the Earth's axis and the tilt of the Moon's orbit around the Earth. The relative positioning of these components can either result in a greater or a lesser range of tidal heights. For instance, the tidal range may be at its greatest during the winter solstice, when the Earth is at its greatest distance from the Sun and the Moon's orbit is at its greatest proximity to the Earth. The tidal range may be at its lowest around the summer solstice, which occurs when the Earth is at its greatest distance from the Sun and the Moon is at its greatest distance from the Earth in its orbit.


c) Types of precipitation.

Ans) The process by which water droplets from the atmosphere make their way down to the surface of the earth is referred to as precipitation. There are three primary categories of precipitation, each of which has its own set of conditions and a distinct set of characteristics.

  1. Orographic Precipitation: When wet air is pushed to rise over a mountain range or other high terrain, a phenomenon known as orographic precipitation can occur. The climb in altitude causes the air to lose heat and become more humid, conditions that are necessary for the development of clouds and the onset of precipitation. This kind of precipitation is typical in mountainous regions, such as the Pacific Northwest of the United States, where there are many tall mountains.

  2. Convective Precipitation: When the air close to the ground becomes heated, it causes the air to rise quickly and create clouds, which can then produce convective precipitation. The development of precipitation is caused by the air being cooler and more humid as it ascends higher into the atmosphere. This kind of precipitation is typical in places that have high temperatures and high levels of humidity, such as tropical climates.

  3. Cyclonic Precipitation: The formation of cyclonic precipitation happens when warm, moist air travels around a low-pressure system (such a hurricane or a cyclone), which causes the air to rise and cool down. The production of clouds and precipitation is directly related to the reduction in temperature and subsequent condensation of the air. This kind of precipitation is typical in regions that are subject to a high number of cyclones, such as the coastal regions of the United States.


d) Factors affecting salinity in the oceans.

Ans) The salinity of saltwater, which is the concentration of dissolved salts and minerals, is an essential component of the ocean's physical and chemical properties. Salinity can be measured in parts per million (ppm). The salinity of saltwater is influenced by a number of different things, including the following:

  1. Evaporation: The dissolved salts and minerals in saltwater are carried away by the water vapour during evaporation, which causes the water that is left behind to become more salty. This process occurs more frequently in areas that are warm and dry, and it is one of the factors that contributes to the high saline of tropical oceans like the Atlantic.

  2. Precipitation: The salinity of saltwater can be lowered when it is diluted by precipitation of any kind, including rain and snow. It is common practise to find lower levels of salinity in regions that see high quantities of precipitation, such as the Pacific Northwest of the United States.

  3. Influx of Freshwater from Rivers: The freshwater that is carried into the oceans by rivers has the potential to reduce the saltiness of the seawater. Estuaries, which are formed when rivers empty into the ocean, typically have lower salinity levels than the surrounding ocean.

  4. Atmospheric Pressure and Wind Direction: Changes in atmospheric pressure and wind direction can cause ocean currents to shift, leading to changes in salinity. For example, winds blowing from the poles towards the equator can cause warm, salty water to move away from the equator, leading to lower salinity levels in those regions.

  5. Oceanic Circulation or Movement of Ocean Water: The salinity of the water can also be affected by the patterns of circulation found in the ocean. For instance, the Gulf Stream transports water that is warm and salty from the equator all the way up to the North Atlantic. This is one of the factors that contributes to the high salinity levels in that region.


e) Airy’s theory on isostasy.

Ans) In the year 1855, the Astronomer Royal, George B. Airy, proposed that the mass surplus of the mountains was maintained by a mass deficit, similar to the way that an iceberg in the ocean is maintained by a mass shortage. It is the only thing that can be helpful in this situation. Additionally, that the depth of its projection downwards is of such a character that the enhanced force of flotation achieved is about similar to the weight above from the topography. The process by which the lighter crust of the earth is transformed into lava, which is more solid.


According to George Airy, the heavier material that rests on top of the mountains is counterbalanced by the lighter stuff that is underneath them. Sial's crust floats on Sima's denser substratum. The Himalayas are like a boat in that they float on denser magma, with the majority of their mass being submerged in it. This gives them the appearance of being a boat. If the crust and the substratum have average densities of 2.67 and 3.0, respectively, then there must be 9 parts of the crust contained within the substratum for there to be one part of the crust located above it. This is because the average density of the crust is lower than the average density of the substratum. The law of floatation states that "the ratio of free board to draught is 1:9."


Airy believed that the Himalayas were drawn to the region because the substratum included a long root of lighter material. This root was located in the lower layer of the rock. According to what he said, a greater percentage of the land column that is placed above the substratum will be drowned if the land column itself is larger, but a smaller amount of the land column would be submerged if the land column itself is smaller. It was his contention that topographic features such as mountains, plateaus, and plains all have the same density. a constant density throughout the entirety of the available thicknesses


f) Orogenic Movements.

Ans) Orogenic motions are the geological processes that cause the collision and convergence of tectonic plates, which ultimately results in the formation of mountain ranges. These movements can take place at convergent plate boundaries, which describe a situation in which two plates are moving toward each other, or at transform plate boundaries, which describe a situation in which two plates are sliding past each other.


At the boundary of two plates that are moving closer together, there is a possibility that one plate will be pushed under the other, creating a subduction zone. It is possible that the subducted plate will melt and generate magma as it descends deeper into the mantle. This will result in the construction of volcanoes and igneous rock formations at the surface. The uplift and folding of rocks can also be caused by the compression and deformation of the plates as they clash, which can lead to the creation of mountain ranges. This can happen when the plates collide. At the boundaries of transform plates, the motion of the plates can produce shearing and fracturing of the rock, which can then lead to the formation of faults and the elevation of the crust. This uplift has the potential to lead to the creation of mountains and other geological structures over long periods of time.


Orogenic motions have the potential to have enormous effects on the surface of the Earth as well as its climate. These effects can include the formation of new land masses, the modification of ocean currents, and the induction of global weather patterns. The uplift and erosion of rock can disclose mineral riches that are significant for human cultures. Mountain ranges can provide homes for a diverse diversity of plant and animal species. Mountain ranges can also have important geological and biological effects. For this reason, gaining an understanding of the processes that are responsible for orogenic motions is necessary in order to accurately predict and manage the effects that geological processes have on the natural world.

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