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BGGCT-131: Physical Geography

BGGCT-131: Physical Geography

IGNOU Solved Assignment Solution for 2021-22

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Assignment Code: BGGCT-131 / TMA / 2021 - 2022

Course Code: BGCT-131

Assignment Name: Physical Geography

Year: 2021 -2022

Verification Status: Verified by Professor




All Questions are compulsory and carries 10 marks each


Q1) Describe all the three layers of Earth's interior with the help of a figure.

Ans) The interior of the Earth is divided into three layers: crust, mantle, and core. In the simplest terms, it's similar to the process of peeling a boiled egg. The crust, middle layer, and inner layer all have hard and thin layers that resemble the crust, mantle, and core, respectively.


The Figure below shows the different layers of the Earth’s interior:


According to him, the Earth's crust is encased in a thin sheet of sedimentary rocks with an exceedingly thin thickness. It is composed up of crystalline rocks that include the mineral silicate. Mica and feldspar are two of the most important minerals. Its upper section is made up of light silicate matter, while its lower portion is made up of heavy silicate matter.



The dramatic increase in the intensity of earthquake waves characterises the mantle. The border between the lower crust and the upper region of the mantle is known as the ‘mesosphere.' At the base of the lower crust, seismic waves travel at a speed of 6.9 kilometres per second. Due to the discontinuity, it quickly jumps to 8.1 kilometres per second. It is located between the lower crust and upper mantle separation zones. The speed of earthquake waves slows down gradually towards the top zone of the upper mantle. The mantle is abundant in silicate minerals such as iron and magnesium.



The Earth's core is the deepest and most distant zone in its interior. It's also called a 'barysphere.' From the lower regions of the mantle to the Earth's centre at a depth of 6371 kilometres, the extent of the core is located at a depth of 2900 kilometres. The density of the core layer is nearly double that of the mantle. The outer and inner cores are the two sections of the core. The disappearance of secondary seismic waves in the outer core indicates that it is molten. The inner core's boundary runs from 5150 kilometres up to 6371 kilometres down to the Earth's centre.


Q2) List the characteristics of igneous rocks and classify them on the basis of place of origin and on the basis of chemical composition.

Ans) Igneous rocks are formed when heated magma cools during the early stages of earth formation. Igneous rocks make up approximately 80% of the earth's crust. Nearly 3.6 billion years ago, the earliest known igneous rocks were discovered. And, because the rock cycle is a continuous and recurring natural process, the creation of younger igneous rocks is currently ongoing as you read this lesson. Igneous rocks are frequently referred to as parent or primary rocks. Igneous rock is the source of all rock kinds, either directly or indirectly. Magma is a molten mixture of minerals and gases that is extremely hot. It frequently leaks to the earth's surface at weak areas or is trapped under the surface for a period of time. The classification of igneous rocks is based on a number of variables. These parameters include the hot magma's cooling position, mineral content, mineral size, and acidity, among others.


The major characteristics are as follows:

  1. the rock forming elements are very compact which increases its hardness;

  2. the igneous rocks are very hard and heavy and therefore resistant to erosion;

  3. water cannot percolate through the rocks as there is no porosity;

  4. there is no layer as it is seen in sedimentary rocks;

  5. Igneous rocks do not contain any fossil but contains crystals and may be visible to the bare eyes.


The igneous rocks are classified primarily based on two parameters origin and chemical composition.


Based on Place of Origin

Intrusive igneous rocks form deep within the earth's crust and are referred to as such. Intrusive rock, such as granite, is an example. Intrusive rocks have bigger mineral sizes and can be seen with the naked eye by a careful observer. Some igneous rocks form deep within the earth's crust and include even bigger materials. Plutonic igneous rock is the name given to this type of intrusive rock. It is classified as hypabyssal igneous rock because it forms just beneath the earth's surface and has smaller mineral sizes.


Based on Chemical Composition

Silica is a crucial igneous rock component that influences the pH or acidity of the rocks. Rocks can be divided into four groups based on how acidic the igneous rock is.

  1. Acidic Igneous rock: The content of silica is more than 65%. Granite is an acidic igneous rock.2)     Basic Igneous Rock: Basalt is an example where the content of silica lies between 45-60%. Iron content of this rock is very high.

  2. Intermediate Igneous Rock: The pH of the rock is neutral and silica content is such that neither the rock falls in acidic nor in basic category. Diorite is an example of this type of rock.

  3. Ultra-basic: Igneous rock is peridotite. In this rock silica content is less than 45%.


Q3) Discuss the factors affecting the horizontal distribution of temperature on earth.

Ans) The temperature varies from one part of the globe to the next. Because insolation is the primary source of energy for the atmosphere, its distribution determines the earth's temperature. Thus, latitude, height, distance from the sea, surface features, and the nature of the terrain are all essential elements that influence temperature dispersion.


The horizontal distribution of temperature is not uniform on the earth's surface because of the following factors:

  1. Latitude: Temperature drops from the equator to the poles in general. Because when we travel north or south of the equator, the sun's rays fall more obliquely. Oblique rays cover a greater area than perpendicular rays, and they also pass-through thicker layers of the atmosphere, where their heat is absorbed by water vapour, dust particles, and carbon dioxide.

  2. Land-water contrasts: It is another important factor affecting the horizontal distribution of temperature. The land gets heated and cooled down more rapidly than the seas. Thus, the contrasts between land-sea temperature affect the horizontal distribution of temperature and isotherms take sudden bends at lands water edges.

  3. Ocean currents: The ocean currents also have great influence on the horizontal distribution of temperature. The warm currents increase the temperature while cold currents reduce it in the coastal regions.

  4. Winds: Cold and warm winds also affect the horizontal distribution of temperature. Warm winds increase the temperature whereas the cold winds reduce it.


Because insolation is highest at the equator, temperature should be highest there and lowest near the poles, but this is not the case. A few degrees north of the equator is where the world's highest temperature is recorded. Altitude is the second most important factor in determining a location's temperature. The temperature is also affected by the albedo of the surface.


The distribution of land and oceans is a major element influencing the distribution of Earth's temperature. Because the Northern Hemisphere has more land and the Southern Hemisphere has more water, and there is a large differential in the specific heat of land and water, the continents lose more heat than the oceans. In comparison to the oceans, the continents heat up and cool down faster. This explains why ocean temperatures are mild while continent temps are severe. Maritime impact refers to the cooling effect on land temperatures caused by the proximity of the seas. Continental Influence is defined as an increase in the temperature of the land at the interior of the continents.


Q4) Define ocean currents and discuss the factors affecting ocean currents.

Ans) Ocean currents are continuous water movements in the ocean that follow predetermined courses, similar to rivers in the sea. Ocean currents are divided into two sorts based on their temperature: cold currents and warm currents. The circulation of sediment supply is also influenced by ocean currents. Ocean currents are defined as a mass movement of water in the open sea caused by wind.


Factors which impact the ocean current formations are:


  1. Planetary winds: Permanent winds that blow from one pressure belt to the next are known as planetary winds. The oceanic circulation pattern is similar to the atmospheric circulation pattern on Earth. For example, in the Indian Ocean, the direction of ocean currents changes in tandem with the direction of monsoon winds.

  2. Temperatures: The temperature of ocean water differs due to the Sun's differential heating at the equator and poles. Warm water from the equator goes slowly over the surface of the sea to the poles, whereas cold water from the poles moves slowly down the sea's bottom to the equator.

  3. SalinityLow-salinity waters have a lower density, allowing them to flow on top of high-salinity fluids, while high-salinity waters flow at the bottom.

  4. Earth's rotation: Coriolis forces deflect winds and freely moving objects to the right in the northern hemisphere and to the left in the southern hemisphere, according to Ferrel's law. As a result, ocean currents in the northern hemisphere move in a clockwise direction, while in the southern hemisphere they move in an anti-clockwise direction.

  5. Landmass: A land mass blocks the flow of the ocean current and separates it into two streams, each flowing in a different direction.


Not only are there a variety of elements that influence the creation of ocean currents, but the ocean currents themselves have a significant role in defining regional and worldwide climate.



All Questions are compulsory and carries 10 marks each


Q5) Define exogenetic processes. Discuss the processes and landforms formed due to the work of glaciers.

Ans) Weathering, mass movement, fluvial, aeolian, glacial, periglacial, and coastal processes are all exogenetic processes that occur on or near the Earth's surface. The word is usually used in contrast to endogenetic processes, which have their origins on Earth. Exogenetic processes originating in the Earth's atmosphere are engaged in denudation, which alters the Earth's relief features.


Glaciers are icebergs that move and can alter entire landscapes. They create valleys, sculpt mountains, and transport massive amounts of rock and silt. By eroding, transporting, and depositing rock materials, glaciers can transform the landscape. Glacial erosion occurs when ice moves over a rock surface and is aided by rock pieces embedded in the ice as a result of partial melting and refreezing. Abrasion is a type of erosion that occurs at the ice-rock contact and aids in the detachment of small pieces of solid bedrock without causing it to move. Abrasion at a constant rate result in glacial smoothing and polishing. Scouring is the name for this abrasive procedure. Various types of characteristics are created through scouring. Melt water penetrates the fractures and joints of the glacier's granite floor and freezes during the scouring process. When water freezes, it expands and exerts enormous pressure on the rock, causing it to loosen. Glacial striations are scratches and grooves in the bedrock caused by rock pieces embedded in the ice at the bottom of a glacier.


Glacier valleys and cirques are examples of significant glacial erosion. Glaciers carve a series of distinctive valleys with steep walls and flat bottoms. Glaciers can erode valleys in a variety of shapes and sizes, including U-shaped valleys, fjords, and hanging valleys. The erosion of the glacier's base, which has steep walls and flatter floors, creates a U-shaped glaciated valley. The construction of hanging valleys is caused by tiny rivers entering the main glacier valley. Hanging valleys are the remnants of tributary glaciers that are less successful in bedrock erosion than the main glacial valley, causing the tributary valley to be severed from the main valley's sheer wall.


Glacially carried rock and debris make up the lateral and medial moraines. They grow on the sides of glaciers (lateral moraines) or at the meeting of two tributary glaciers (confluence moraines) (medial moraines). They frequently mark the borders of an ice body in either case. The farthest reaches of a glacier—its terminus—at any given time are marked by terminal and recessional moraines. They're frequently made of boulders and debris that get transported to the glacier's toe and melt there. As a glacier retreats, debris is carried away and deposited in a flat area below, generating an outwash plain. These outwash plains and other places with glacial deposits are frequently pockmarked by depressions known as kettles.


Q6) Describe the bottom relief of Indian Ocean with the help of a suitable sketch.

Ans) In the south, near Antarctica, the water meets the Pacific and Atlantic oceans. The ocean's average depth is 4000 metres. The block mountains of Gondwanaland have compacted and solidified a large portion of the Indian Ocean's coastline regions. The Indian subcontinent splits the Indian Ocean into the Arabian Sea and the Bay of Bengal in the north.


Figure below shows the Bottom Relief of Indian Ocean.


Bottom Reliefs of the Indian Ocean

  1. The Indian Ocean is smaller than the Pacific and Atlantic Ocean in areal extent and is bounded by, on all of its sides, Asia in the north, Africa in the west, Asia in the east, Australia in the south-east and Antarctica in the south.

  2. The ocean has contact with the Pacific and the Atlantic oceans in the south near Antarctica.

  3. The aver­age depth of the ocean is 4000m.

  4. Major parts of the coastal lands of the Indian Ocean formed by the block mountains of Gondwanaland are compact and solid.

  5. The coasts of the East Indes are bordered by fold mountain chains.

  6. The marginal seas are less in number than the Pacific and the Atlantic oceans.

  7. Significant marginal seas are Mozambique Channel, Red Sea, Per­sian Gulf, Andman Sea, Arabian Sea, Bay of Bengal etc.

  8. Malgasy (Madagascar) and Sri Lanka are the big islands whereas Suqutra, Zanzibar, Comoro, Reunion, Secychelles, Prince Edwards, Crozet, Kerguelen, St. Paul, Rodriges, Maldive, Laccadive, Andman-Nicobar, Christmas etc. belong to the category of small and tiny islands.

  9. Indian subcontinent in the north divides the Indian Ocean into Arabian Sea and Bay of Bengal.

  10. The ocean widens in the south


Q7) Discuss Penck’s model of cycle of erosion with the help of a suitable sketch.

Ans) Because of its publishing in cryptic German language and incorrect interpretation of his ideas by English translators, the Penck model of landscape evolution could not be fully interpreted, as stated at the outset.


Penck's conceptions of parallel slope retreat and continuous crustal movements were the most vulnerable targets for American geologists. It should be noted that earlier English translations of Penck's work revealed that he believed in parallel slope retreat, but later English translations revealed that he believed in slope replacement, in which each upper slope unit of the hillslope and valley sides was considered to be replaced by a lower slope unit of a gentler slope.


It's possible that the majority of the objections of Penck's morphological approach sprang from erroneous readings of his ideas. Some American critics sank so low that they said, "His unusual beliefs owed to his incomplete recovery from a brain wound sustained during World War I." His ideas on long-term upliftment and tectonic speculations were dismissed, but his ideas about slope development and weathering processes are unquestionably important in geomorphology.


The erosion cycle is a concept that describes the link between stream erosion and landscape change. The primary idea behind Penck's concept is that the landform evolution of a particular region is influenced by the region's tectonic activity.





Q8) Write Short notes on the following. Each question carries 5 marks.


Q8. a) Big Bang hypothesis

Ans) In a nutshell, the Big Bang hypothesis argues that all of the Universe's present and past matter came into existence at the same time. All matter in the cosmos, according to this hypothesis, existed in the form of dense and massive primordial matter. In this primaeval stuff, a violent explosion occurred. As a result, the dust particles in this substance were dispersed throughout the Universe, resulting in the current Universe.


A model has been developed in the United States to generate the circumstances of the big bang theory. Berkeley University scientists studied microwave radiation with helium balloons and found evidence to support the big bang theory. More than 5000 scientists at the European Organization for Nuclear Research in Geneva are participating in the experiment. These experts are hard at work doing studies to create the conditions for a massive explosion.


Q8. b) Briefly explain Airy’s views on isostasy with the help of a figure.

Ans) Isostasy refers to the dynamic balance between the lithosphere and the asthenosphere. The Earth's gravity forces parts of the lithosphere to shift upward or downward depending on their densities, according to this definition. This simply means that wherever equilibrium exists on the Earth's surface, an equal mass below it in the same area will balance the mass above it.

According to George Airy, the lighter material below balances the mountains' additional weight. The crust, which is made up of lighter materials, is floating on top of a denser substratum, i.e., Sial is floating above Sima. In the same manner as a boat float in water with its maximum portion sunk in the water, the Himalayas float in the denser magma with their maximum portion sunk in the magma.


According to Airy, the Himalayas exert their true attraction power because the substratum contains a lengthy root of lighter material that balances the above. According to him, if the land column above the substratum is larger, a larger portion of it will be submerged in the substratum, whereas if it is smaller, only a tiny portion will be submerged. He claims that the density of distinct geographical columns (mountains, plateaus, and plains) remains constant. ‘Uniform density with varied thicknesses' is what this term refers to.


Q8. c) Explain Coriolis force with the help of a figure.

Ans) The Coriolis force is an inertial or fictitious force that acts on moving objects inside a frame of reference that rotates with regard to an inertial frame in physics. The force applies to the left of the object's motion in a reference frame with clockwise rotation. The force acts to the right in an anticlockwise or counter clockwise spin. The Coriolis effect is the deflection of an object caused by the Coriolis force as shown in the diagram below:

If the ordinary Newtonian laws of motion of bodies are to be used in a rotating frame of reference, Coriolis demonstrated that an inertial force must be included in the equations of motion, acting to the right of the direction of body motion for counter clockwise rotation of the reference frame or to the left for clockwise rotation. The Coriolis force causes an apparent deviation of an object's path when it moves within a rotating coordinate system. The item does not truly depart from its route, but the motion of the coordinate system causes it to appear to do so.

The motion of the item, the motion of the Earth, and the latitude are all related to the Coriolis deflection. As a result, the size of the effect is given by 2v sin, where is the object's velocity, is the Earth's angular velocity, and is the latitude.


Q8. d) Differentiate between seasonal winds and local winds.

Ans) Type of Wind – Seasonal Wind

Winds that shift direction as the seasons change. Seasonal Winds are the name given to certain types of winds. In low-latitude settings, a monsoon is a seasonal wind that changes direction between winter and summer. In India, monsoons are common.

Type of Wind – Local Wind

These only blow in a small area during a specific time of day or year. Consider the difference between a land and a sea breeze. The following are the several forms of local wind:


Land Breeze – It is a wind that flows from the land towards the sea. It flows often at night.

Sea Breeze – It is a wind that blows towards land from the direction of a large water body. Sea breeze develops due to differences in air pressure created by the differing heat capacities of water and dry land.

Anabatic Winds – These Winds are upslope winds driven by warmer surface temperatures on a mountain slope than the surrounding air column.

Katabatic Winds – Katabatic winds are downslope winds created when the mountain surface is colder than the surrounding air and creates a downslope wind.


Q8. e) Explain hydrological cycle with the help of a figure.

Ans) The natural water recycling system on Earth is known as the hydrological cycle, sometimes known as the "water cycle." Water evaporates from the sea, lakes, and other bodies of water due to sun radiation. The mechanism of transpiration allows water to evaporate from plant leaves as well. As the steam rises in the atmosphere, it cools, condenses, and falls as precipitation on the land and sea. Precipitation falls as surface water on the earth's surface, forming streams of water that eventually become lakes and rivers. Aquifers are formed when rainwater penetrates the ground and flows downward via the perforations. Finally, some surface and subsurface water flows into the sea. Water is changed into all three stages during this journey: gas, liquid, and solid.


Figure below shows the Hydrological Cycle:


The hydrological cycle is crucial to life on Earth, and it plays a key role in the cycling of solar energy, sediments, and chemical elements required for life. It appears that life is both a product of and a cause influencing changes in the hydrological cycle.


Q8. f) Differentiate between spring tides and neap tides.

Ans) The tidal range of a Spring Tide is more defined, whereas the tidal range of a Neap Tide is less defined. Although Spring Tides and Neap Tides are both forms of Tides and so share some characteristics, they are vastly different in many aspects.


The distinction between Springtide and Neap tide is that with a Spring tide, the difference between high tide and low tide is always bigger than usual. The difference between high and low tide during a Neap Tide, on the other hand, is often smaller than usual.

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