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BGYCT-131: Physical and Structural Geology

BGYCT-131: Physical and Structural Geology

IGNOU Solved Assignment Solution for 2021-22

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

Course Code: BGCYT-131

Assignment Name: Physical And Structural Geology

Year: 2021- 2022

Verification Status: Verified by Professor


Note: Attempt all questions. The marks for each question are indicated against it. Write all answers in your own words; do not copy from the course material.


Part A


Q1. Write short notes on the following:

Q1. a) Causes and effects of tsunami (5)

Ans) Tides cause waves to form on the ocean's surface, which rise and fall. However, due to certain circumstances, ‘wave trains' (i.e., numerous waves) are formed, with the initial waves being larger than typical and being followed by several much larger waves. These waves move at high speeds across the vast ocean before crashing into big waves in the shallow water of a beach. These massive waves are known as tsunamis, harbour waves, or seismic sea-waves, and they are extremely tall and powerful.



A tsunami is caused when the ocean floor moves suddenly, forcing the water column to flow rapidly. Undersea earthquakes, landslides, massive volcanic eruptions, or even a meteorite strike in the ocean water could all be factors in the formation of a tsunami. These events cause a significant volume of water to be displaced, generating a disturbance that becomes a wave. This wave has the ability to travel 800 kilometres per hour across the ocean. The majority of tsunamis are triggered by huge earthquakes on the sea floor, which result in the abrupt shift of the overlying water column as rock pieces collide.



Possible effects of a tsunami may be the following:

  1. massive loss of life, plants and natural resources

  2. damage to property, sewer drainage and water supply system, etc.

  3. change in soil salinity affecting crop-yield,

  4. change in landscape such as erosion of islands,

  5. severe flooding,

  6. disease caused by stagnant and contaminated water, solid waste, debris and contamination of soil and water by hazardous materials and toxic substances, etc., and

  7. environmental effects.


Q1. b) Criteria for recognition of folds(5)

Ans) Folds in the field can be identified using a variety of criteria.


The following criteria may be used to recognise or detect folds in the field:

  1. Direct observation: Folds may be recognised by direct observations on the outcrops exposed along the valley walls, stream, road or railway cuttings, quarries or tunnels.

  2. By measuring the attitudes of beds: If the folds are larger than outcrops, they are recognised by measurements of dip and strike data of bedding planes.

  3. By repetition patterns of beds: A symmetric repetition of beds helps in recognising the fold in the field. For example, on a linear path if the repetition occurs in the pattern DCBCD, this would mean that the fold axis is located in bed B which divides the rock sequence into 2 halves which are mirror image to each other (Fig. 10.24).

  4. By variation in thickness: If the thickness of the bed is gradually increasing or decreasing, there might be fold.

  5. By cleavage- bedding relationship: The cleavage bedding relation criteria can be used to find the fold. The top bottom of bed can also be used to identify the folds.


Q2. Discuss plate tectonics explanations of earthquakes, volcanoes, continental drift and sea floor spreading. (10)

Ans) The lithosphere is divided into a number of plates, each of which moves horizontally in the pattern of torsionally rigid solids meeting at their boundaries, creating seismic and tectonic activity.



The plates are constantly moving, yet we can't see them since they move too slowly to be observed in a human's lifetime. The movement is on the order of your nail growth rate; say 2.5 cm per year to 15 cm per year. Existing stable rocks on the planet naturally oppose this movement, causing stresses to build up in the rocks. These accumulating stresses eventually exceed the strength of the rocks, causing them to burst. As a result, the stored strain energy is abruptly released, resulting in earthquake vibrations. Because the two plates are moving in opposite directions, earthquakes are common along convergent plate borders.



Plate tectonics is a set of concepts and principles that describes two types of plate borders where volcanic activity can occur. The divergent plate boundary and the convergent plate boundary are the two types of plate boundaries. The Mid-Oceanic Ridges are located near the divergent plate boundary, where two plates move away from each other. Underwater, volcanic activity is always calm and there are no large explosions. This is because the magma finds a simple path between two opposing moving plates, and the overlying crust provides no major barrier. Only a short distance from the deep oceanic trenches or the convergent plate boundary do these volcanoes appear on the overriding plates.


Continental Drift and Sea Floor Spreading

Plate tectonic theory states that continents drift away from divergent plate borders, which are typically seen at Mid Oceanic Ridges, where two convection current cycles rise higher and diverge as they reach the asthenosphere. As a result, the lithospheric plates that float above these currents diverge, causing the lithospheric plate's continental part to drift away. As a result, new lava accumulates on the ocean floor, forming new crust on both divergent plates. One of the essential assumptions of plate tectonic theory is that new lava does not exist as a separate entity after it solidifies, but rather becomes a component of one of the two plates over which it solidifies. The newly produced oceanic crust is causing the entire plate, including the continental portion of the plate, to move symmetrically away from the spreading centre, the Mid-Oceanic Ridge. As a result, continents wander away from MOR, which is known as continental drift.


Q3. Explain erosional landforms resulting from fluvial activities with the help of neat well labelled diagrams. (10)

Ans) The following are examples of erosional features and landforms caused by river activity:


1.  River Valleys

Significant erosional landforms are the valleys cut out by rivers. With the progression of the stages of the fluvial cycle of erosion, the shape and dimensions of fluvially formed valleys alter. Rivers erode valley beds and banks as they make their way to a lake or the sea. As seen in figure, the cross-sectional profiles of the valley created in the early and youthful stages of the fluvial cycle are notably ‘V' shaped. The valley is small and deep. V-shaped valleys of this sort are the result of a faster pace of downcutting (vertical erosion and valley deepening).


2. Waterfalls

Waterfalls are created by a quick descent or abrupt interruption in the longitudinal course of rivers as a result of a variety of reasons, including variations in the relative resistance of rocks, topographic relief, sea level drops, and Earth motions. When rivers run into tougher rock, waterfalls are frequently generated. Waterfalls are created by a quick descent or abrupt interruption in the longitudinal course of rivers as a result of a variety of reasons, including variations in the relative resistance of rocks, topographic relief, sea level drops, and Earth motions. When rivers run into tougher rock, waterfalls are frequently generated.


3. Potholes and Plunge Pools

Potholes are smooth, rounded, bowl or cylindrical shaped depressions produced on the riverbed of river valleys in the shape of a kettle. Mechanical abrasion and downcutting by rock pieces trapped in swirling currents are the causes. Plunge Pools form on the riverbed primarily as a result of hydraulic activity, in which water falls from a great height, causing bedrock erosion.


4. River Terraces

River terraces are the narrow flat surfaces on either side of the valley floor that represent the level of former valley floors and relics of older flood plains. River terraces are formed by the subdivision of flood plain fluvial deposits deposited along a valley floor.


Q4. Define mass wasting. Explain its types, factors responsible and causes. (10)

Ans) Mass wasting is a group of processes that use gravity to transfer weathered rock, silt, and soil down a slope. The flow of rock and soil down a slope under the effect of gravity is known as mass wasting. It refers to all of the processes that cause weathered and un-weathered Earth materials to slide downslope under gravity's impact.


Types of Mass Wasting

Types of mass wasting are  described below:

1. Rockfall and debris fall

When a concentration of cemented rock fragments is released and falls vertically under the influence of gravity, fast from a cliff or by leaps down a slope, rockfall occurs. Debris falls are similar to rockfall, except they include dirt, regolith, vegetation, and rocks. Landslides are the most frequent name for them.

2. Rockslide and debris slide

When a slope fails along the plane of weakness, it causes a rockslide. Unconsolidated rock, debris, and regolith characterise a debris slide. While a rock fall normally lacks conventional detritus, it usually consists of a chaotic mass of rock blocks. At the base of a mountain or hill, the rapid sliding descent of a rock mass down a slope frequently generates heaps and is confused irregular mounds of rubble.

3. Slump

The abrupt downward slippage of a rock block or regolith along a curved surface of rupture is referred to as slump. A scarp faces downslope as a result of the movement. Slump is particularly common in regions where slopes are steep and cliff, such as along stream banks and coastal cliffs, due to erosion at their bases.

4. Debris flow

The rapid downslope movement of clasts ranging in size from clay particles to boulders, as well as a significant volume of woody debris. It occurs when water collects quickly in the ground as a result of heavy rain or snow melt. It usually takes the shape of an apron or tongue, with an irregular surface.

5. Mudflow

Mudflow is a type of debris flow that is mostly made up of mud and is saturated with water.


Factors Responsible for Mass Wasting

The following elements determine the likelihood of mass wasting and the safety and stability of hill slopes, cuts, and highways:

Nature of rocks occurring along the slope or cutting walls: In comparison to large hard and compact rocks, hill slopes with loose unconsolidated material are unstable (like granite, gabbro, sandstone, marble, gneiss, quartzite). In both scenarios, the slope stability varies.


Geological structure of the country rocks: It is common knowledge that the existence of faults, shear zones, and other weak zones reduces the strength of any rock.


Prevailing ground water conditions along the slope or cutting wall: The presence of water increases landslides, compromising slope stability. As a result, the area's ground water conditions and water table should be continuously monitored to ensure slope and highway stability.


Causes of Mass Wasting

Earthquakes, blasting for quarrying or building, and other factors contribute to mass wasting. additional splits and fissures in the rocks due to lack of surface drainage, increased water percolation, and eventual sliding Slope steepening for various applications Because of quarrying, mining, and other activities, the slope became saturated with water due to poor drainage.


Q5. Discuss the significance of geology in our daily lives. (10)

Ans) Geology knowledge is required, if not required, for comprehending the natural environment and planning for a more pleasant human living. Only by understanding geology can we recognise the fact that the Earth can provide humans with resources and energy (both fossil and nuclear). Let's look at three options:

1. Natural Resources

For the exploration and exploitation of such resources, systematic geological studies are critical:

Metals: Metals like iron, aluminium, manganese, copper, lead, zinc, chromium, silver, gold, tin are important and have always been indispensable for our civilisation.

Minerals: Minerals like clays are used in cosmetic and ceramic industry. Mica is used as an insulator, sulphur bearing minerals are used in paint and pigment industry, diamond in abrasive industry.

Fertilizers: Rocks on weathering provide elements like phosphorus, potassium, nitrogen, and sulphur to the soil used as plant nutrients.

Gemstones: We get precious and semiprecious stones like diamond, emerald, ruby, and moonstone, amethyst which are used by human beings for ornamental and decorative purposes.

Medicinal: Various metallic ores are utilised for preparing bhasmas used in ayurvedic medicine.


2. Water Resources

Water scarcity is a major issue in the world right now. Water is an essential necessity for all living organisms. It is the most basic need for human life, encompassing personal needs, agriculture, and other activities. Rivers and glacier melts, as well as rains, underground water, and mineral springs, provide us with water. For effective water planning, exploration, conservation, and utilisation, geological investigations are essential.


3. Power Resources

  1. Power generation is a critical part of overall development in daily living. The Earth provides mankind with power and energy in the form of biological, thermal, and nuclear sources. Power and energy are provided by the natural resources listed below. Geologists are in charge of exploring and exploiting them.

  2. Coal is used in both home and industrial applications. It's also utilised to generate electricity in thermal power plants. Coal is used to generate electricity at several power plants across the country.

  3. Petroleum encompasses a wide range of products, including oil and natural gas.

  4. Atomic minerals containing uranium and thorium are vital for the country's nuclear power generation and development.

  5. Volcanoes, fumaroles, geysers, steaming fields, and hot springs are surface manifestations of geothermal energy, which is a massive store of heat energy in the Earth's interior. Geothermal energy is currently being commercially used for electricity generation.



Part B


Q6. Differentiate between planner and linear structures giving neat well labelled diagrams. (10)

Ans) Planar Structures

Planar structures are those found in the rocks as a plane or a surface, and they go hand in hand with linear structures.


The following types of planar structures:

1. Bedding plane: Two beds are separated by a bedding plane in a sedimentary rock. Bedding planes are also considered as a primary foliation because these planar features are formed at the time of formation of rocks.

2. Joints: Joints are the regular or irregular planar fracture that separates two adjacent blocks by a gap.

3. Fault plane: Fault planes are fractures along which the co-existing rock blocks have been displaced. Fault is a fracture along which measurable displacement has taken place between two blocks.

4. Metamorphic foliation: Metamorphic foliations are those planar structures which are formed after the formation of rock during its subsequent deformation and metamorphism. Hence, they are the secondary foliations, as already discussed earlier in this unit. Metamorphic foliations or simply ‘foliation’ is characteristically found in the metamorphic rocks.

Linear Structures

As the name implies, linear structures are structures that are continuous and occur in a line. They are mesoscopic (medium-sized) structures that point in a specific direction and can include the following:

1. Mineral lineation: Mineral lineation occurs when the longer dimension of minerals is aligned in a particular direction, or when a deformed group of minerals is oriented in such a way that their longer dimension is aligned in a certain direction parallel to each other.

2. Crenulation lineation: If a planar surface, such as foliation, is impacted by minute or microscopic folding, the hinge lines of these folds align in a specific direction, resulting in crenulations lineation.

3. Slickensides: Frictional lines emerge on the fault plane as a result of movement between two faulted blocks, and they are frequently polished.

4. Boudinage, pinch-and-swell, mullions and roddings: They are linear formations that arise as competent or stronger layers lie between incompetent layers deform. Boudinage is a construction made up of layers that have been stretched and segmented. Individual boudins are frequently substantially longer in one dimension than the other two, forming a lineation. The layer shows pinching and swelling but no segmentation in the pinch and swell structure. Linear corrugations in the rocks are described by Mullions and Rodding. The structure is called mullion if the corrugations are generated by the rock itself and rodding if they are formed by a specific mineral, usually quartz.


Q7. Differentiate the following :

Q7. a) Fold and erosion mountains (5)

Ans) Fold Mountains:

The impacts of folding on strata within the top part of the Earth's crust create fold mountains. Uplifted folded sedimentary rocks make up the majority of the Fold Mountains. Folding of rocks is caused by horizontal compressional pressures acting on a massive pile of deposited sedimentary rocks in the oceanic basin during millions of years. As time passes, Earth motions cause the rocks to be uplifted to a significant height, resulting in the formation of Fold Mountains.

They're found in a straight line with fairly parallel ridges. They are folded structurally and are composed of thick sedimentary successions deposited primarily in shallow marine environments.

Fold mountains show tectonic activity such as faulting, thrusting, and igneous activity associated with metamorphism.


Erosion Mountains

They are thought to represent the last relics of the final phase of mountain development. These mountains are generated when old mountains formed by magmatic intrusions are eroded to their current altitudes by external pressures and isostatic readjustment. Because of the upwarping of the exposed surface, they are also known as Dome Mountains. Because intruded magma produces upwarping and eventually exposes itself as the overlaying material is eroded, Dome Mountains are compared to blisters on the Earth's surface. Erosional Mountains is another name for them.


Q7. b) Disconformity and angular unconformity (5)

Ans) Disconformity: An unconformity in which the beds above and below the surface are parallel is referred to as disconformity. Most disconformities have erosional relief, solution features, weathering profiles, or other physical evidence of a sedimentary record break. The unconformity may not be visible in the field without such evidence, and its presence must be established on fossil evidence of a significant time gap.


Angular Unconformity: The folding of an old sedimentary sequence, the smoothing of the tilted strata by erosion, and the deposition of a modern sedimentary sequence on the old, truncated strata are all represented by angular unconformity. The older and younger sequences over the unconformity surface have an angular relationship in an angular unconformity. This occurs as a result of the deposition of younger rock sediments on older rock formations that had already tilted prior to the commencement of younger sequence deposition.


Q8. Explain the layering and composition of the Earth giving suitable diagrams. (10)

Ans) The Composition and Structure of Earth

Compositional divisions include core, mantle, and crust. The crust, which is made up primarily of oceanic crust and continental crust, accounts for less than 1% of the Earth's total mass. The mantle is extremely heated and accounts for roughly 68 percent of the Earth's mass. Finally, the core is primarily composed of iron metal. About 31% of the Earth's mass is made up of the core. Mechanical qualities separate the lithosphere and asthenosphere. The crust and a section of the upper mantle that acts like a brittle, inflexible solid make up the lithosphere. The asthenosphere is molten upper mantle material that may flow and behaves plastically.


The three major layers of the Earth are crust, mantle and core.


The outermost solid layer of the Earth's surface is called crust. It is made out of fragile rock that easily breaks. Depending on whether it is oceanic or continental, it has different thickness and chemical makeup. They are generated by geological processes that are quite different. The Earth's crust is made up of a relatively thin layer of hardened heterogeneous materials.


Between the crust and the core is the mantle. Its upper surface lies 5 to 10 kilometres beneath the marine crust and 20 to 80 kilometres beneath the continental crust. The ‘Moho' or Mohorovicic discontinuity is an imaginary line that separates the lithosphere from the mantle.


The Earth's core, located beneath the mantle, is the deepest portion of the planet. The core has been separated into outer and inner cores based on the research of earthquake waves. Gutenberg discontinuity separates the core from the mantle. The core stretches from 2890 kilometres to 6371 kilometres. Gutenberg discontinuity marks its top boundary.

Figure showing the Cross section of Earth showing the crust, mantle and core with major boundaries. Depths are in km from surface; temperature in degrees K; figures on left are mass density in 103 kg/m3.


Q9. Discuss the erosional and depositional landforms developed by geological actions of underground water with the help of suitable diagrams. (10)

Ans) The following are examples of erosional landforms caused by subsurface water:

Landslides: Underground water seeps into fissures and crevices in the rocks, acting as a lubricant and aiding movement. Under the effect of gravity, the massive unstable rock pile may fall downward, triggering landslides.

  1. Caves: They are formed as a result of solution activity in the soluble rocks like limestone.

  2. Underground channels: These are groundwater-flowing underground tunnels generated by the dissolving of rocks, primarily carbonates like limestones. These passageways could link the caves together. Carbon dioxide is dissolved in shallow groundwater, forming a mild acid.

  3. Caverns: These are interconnected underground cavities in limestone that are generated by ground water's solution action. Streams occasionally run through these subsurface caverns and canals. The horizontal gallery and vertical linking route the shaft can connect the caverns.

  4. Sinks, sinkholes, dolines, uvala and swallow hole: These are hollows in the shape of a basin or a funnel that form in limestone regions as a result of underground solution. When this water percolates downhill through limestone rock, it dissolves a significant percentage of the rock. As a result of the construction of a basin and the subsequent collapse of the roof into it, these sinks take on the shape of funnels. Such a concentrated solution can result in the formation of roughly circular surface depressions known as sinkholes or dolines, which are common in karst settings. Swallow holes are another name for dolines.

  5. Solutional valley: A solutional valley is formed when many solutional structures are absorbed together in a valley in the limestone region.


Depositional Landforms

Some of the depositional landforms resulting due to activity of groundwater.

  1. Geyserite: There is a lot of stuff dissolved in the hot water in a geyser. When it reaches the surface, it cools, and the material is deposited as geyserites or sinter deposits around the mouths of springs.

  2. Replacement: Percolating water dissolves some substances and deposits an equal volume of the material carried in solution by the water. This type of substitution is usually done molecule by molecule to preserve the original structure of dissolved compounds.

  3. Petrification: The cellulose is replaced by silica in this process. The woody structure is kept precisely because the substitution is done volume for volume.

  4. Geode: Cavities in basic volcanic rocks are usually filled with silica, calcite, zeolites, and other mineral solutions brought in solution by subsurface water.

  5. Concretions: As a result of percolating underground water, concretions of irregular shape and size are formed. These are nodular shaped and often occur in sedimentary beds or upon the surface. They are harder than surrounding rock and so stand out prominently e.g., Kankar. They are formed by deposition of calcium carbonate.

  6. Stalactites and stalagmites: In limestone caves, these are depositional features. They are made up of calcium carbonate (CaCO3). Stalactites are masses that dangle from the cave's roof. Stalagmites, on the other hand, are deposits that occur at the cave's base. Tuffa calcareous: CaCO3 is accumulated in layers on the cave floor.


Q10. Write short notes on the following:


Q10. a) Importance of geological fieldwork (5)

Ans) Geologists try to decipher what has been "written on rocks" in order to learn more about the Earth's lengthy past. Geologists use the Earth as a natural laboratory; therefore, fieldwork is an important element of their job. They can see the Earth's characteristics and functioning surface activities up close. The fieldwork begins with the gathering of samples and information on the rocks and geological structures, followed by laboratory analysis of the field data. Geologists use an integrated approach to understand the Earth's geological history, including its origin, evolution, composition, structure, palaeogeography, paleoclimate, and past life. The term palaeogeography relates to the distribution of land and water in the past. A paleoclimate is the climate that existed at a specific point in time in the geological past.


Exploring and utilising mineral resources, subterranean water, building materials, coal and petroleum resources, and locating ideal sites for engineering projects such as dams, bridges, highways, and railway lines, among other things, requires fieldwork. Geologists are now playing an increasingly essential role in the management and utilisation of natural resources, as well as the zonation and mitigation of natural disasters, which allows them to evaluate and appraise various environmental issues and the impact of Earth processes on life systems.


Q10. b) Mountain building periods. (5)

Ans) At various times on Earth, the process of mountain formation has been seen. Mountain formation occurs in what are known as orogenic periods. There are various orogenic phases in an orogenic epoch. The Orogenic Belt is made up of one or more mountain ranges that have been distorted during an orogenic epoch.


The geological processes that underpin the formation of mountains are referred to as mountain formation. Large-scale motions of the Earth's crust are linked to these processes (tectonic plates). Folding, faulting, volcanic activity, igneous intrusion, and metamorphism are all examples of orogenic mountain formation. The geological structures observed on mountains are not always related to their development.

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