IGNOU BGYCT 131 Solved Free Assignment 2023- Helpfirst

BGYCT-131

PHYSICAL AND STRUCTURAL GEOLOGY

BGYCT 131 Solved Free Assignment

Section A

Q 1.Write short notes on the following:

a) Applied and allied branches of geology

Ans. a) Applied and allied branches of geology:

Applied geology: the study of how geological knowledge can be used in practical applications such as mineral and resource exploration, environmental management, and engineering.

Petroleum geology: the study of the formation, occurrence, and exploration of oil and natural gas.

Economic geology: the study of the formation, occurrence, and extraction of mineral resources.

Engineering geology: the study of how geological factors affect the planning, construction, and maintenance of human-made structures.

Hydrogeology: the study of the movement, distribution, and quality of water in the subsurface. BGYCT 131 Solved Free Assignment

Environmental geology: the study of how geological factors affect the natural environment and how human activities impact the Earth’s surface and subsurface.

Geophysics: the use of physical methods, such as seismology and magnetometry, to study the Earth’s interior and its relationship to surface processes.

Oceanography: the study of the Earth’s oceans, including their physical and chemical properties, circulation, and marine life.

Planetary geology: the study of the geology of other planets and moons in the solar system.

Note: The above are examples of various branches of geology, but the field is vast and there can be many other branches as well, these are few of them.

BGYCT 131 Solved Free Assignment
BGYCT 131 Solved Free Assignment

b) Formation of the solar system

Ans. Formation of the Solar System:

The solar system is believed to have formed around 4.6 billion years ago from a cloud of gas and dust known as the solar nebula.

The nebula began to contract under its own gravity, forming a spinning disk with a dense central region, known as the protosun, at its center.

The protosun continued to contract and heat up, eventually igniting nuclear fusion and becoming the sun. BGYCT 131 Solved Free Assignment

The spinning disk of gas and dust surrounding the protosun began to clump together through collisions and gravity, forming small solid bodies known as planetesimals.

These planetesimals continued to collide and merge, forming larger and larger bodies, eventually forming the planets, moons, and other small bodies in the solar system.

The outer planets, Jupiter, Saturn, Uranus and Neptune, formed from the leftover gas and ice.

The inner planets, Mercury, Venus, Earth and Mars, formed from the leftover rock and metal.

The leftover dust and debris from the planetesimal collisions eventually formed the asteroid belt and Kuiper belt. BGYCT 131 Solved Free Assignment

Note: The above is the widely accepted theory of the solar system formation called “nebular hypothesis” and is based on scientific evidence and observations. There are other theories as well, but this one is the most widely accepted one.

Q 2. Give an account of the layering and composition of the Earth

Ans. The Earth can be divided into four main layers based on composition and mechanical properties: the crust, the mantle, the outer core, and the inner core.

The crust is the outermost layer of the Earth and is composed primarily of solid rock. It is the thinnest layer, typically around 30-40 kilometers thick under the continents and 5-10 kilometers thick under the oceans.

The crust is composed mainly of silicate minerals such as quartz and feldspar.

The mantle is the layer below the crust and is composed mainly of solid rock. It is the thickest layer, making up about 84% of the Earth’s volume.

The rock in the mantle is mainly composed of silicate minerals such as olivine and pyroxene. The upper part of the mantle is cooler and more solid, while the lower part is hotter and more fluid. BGYCT 131 Solved Free Assignment

The outer core is the layer below the mantle and is composed mainly of liquid metal, primarily iron and nickel.

It is about 2200 kilometers thick. The high temperatures and pressures in the outer core cause the metal to be in a liquid state.

The inner core is the innermost layer of the Earth and is composed mainly of solid metal, again primarily iron and nickel. It is about 1220 kilometers in radius.

The high pressure in the inner core causes the metal to be in a solid state despite the extremely high temperatures.

Overall, the Earth is composed mostly of rock, metal and other minerals. The Earth’s structure is constantly changing due to processes such as plate tectonics and volcanic activity. BGYCT 131 Solved Free Assignment

Q 3. Explain depositional landforms resulting from aeolian activities with the help of neat well labelled diagrams.

Ans. Aeolian activities refer to the processes involving wind, such as the erosion, transportation and deposition of sediments. There are several depositional landforms that result from aeolian activities, which include:

Dunes: Dunes are mounds or ridges of sand that are formed by the wind. They can be classified into different types based on their shape and direction of the wind.

The most common types of dunes are barchan, transverse, longitudinal, and star dunes.

Sand sheets and sand plains: A sand sheet is a flat area of sand that is covered by a thin layer of windblown sand. A sand plain is an area of sand that is covered by a thicker layer of windblown sand. BGYCT 131 Solved Free Assignment

These landforms are formed by the accumulation of sand in an area that is not affected by regular water erosion.

Loess: Loess is a type of fine-grained soil that is made up of windblown silt. It can form thick deposits in areas where the wind is strong enough to move silt-sized particles over long distances, such as on the Great Plains of North America.

Deflation basins: Deflation basins are shallow depressions that are formed by the erosion of soil and sediment caused by the wind.

They can be found in areas where the wind is strong enough to remove loose material, such as on desert surfaces.

Yardangs: Yardangs are long, narrow ridges of rock that are formed by the wind erosion of a softer rock. BGYCT 131 Solved Free Assignment

They are typically found in arid regions where the wind is strong enough to erode the rock, and are common in deserts like the Gobi desert in China.

It is worth to note that these landforms are formed over long time scales, and the specific landform depends on the nature of the sediment, wind strength, direction, and duration.

Q 4. What is weathering? Describe its types and he factors affecting weathering

Ans. Weathering is the process by which the physical and chemical properties of rocks and minerals are changed by exposure to the atmosphere and other natural agents such as water and organisms.

Weathering can occur at or near the Earth’s surface, and it is an important factor in the formation of soil, the erosion of landscapes, and the formation of landscapes.

There are two main types of weathering: mechanical and chemical weathering. BGYCT 131 Solved Free Assignment

Mechanical weathering: Also known as physical weathering, is the process by which rock is broken down into smaller pieces without changing its chemical composition.

This process includes processes such as frost wedging, freeze-thaw weathering, and abrasion.

Chemical weathering: Is the process by which rock is chemically altered, changing its composition and structure. This process includes processes such as dissolution, oxidation, hydrolysis, and acid rain weathering.

The factors affecting weathering include:

Climate: Temperature, rainfall, and other climatic factors can all affect weathering. For example, in cold climates, mechanical weathering is caused by the freezing and thawing of water in rock cracks, while in warm climates, chemical weathering dominates. BGYCT 131 Solved Free Assignment

Relief: The topography of an area can also affect weathering, with steeper slopes and cliffs eroding faster than gentle slopes.

Vegetation: Plant roots can also affect weathering by breaking up rocks and helping to hold soil in place.

Parent rock: The type of rock that makes up the area can also affect weathering. For example, some rocks such as granite are more resistant to weathering than others, such as limestone.

Time: Weathering is a slow process and can take place over thousands or millions of years.

Human activities: Human activities such as pollution, deforestation and urbanization can also greatly accelerate weathering processes.

Overall, weathering is an ongoing process that affects the Earth’s surface in various ways, and it is influenced by several factors such as climate, relief, vegetation, parent rock and time. BGYCT 131 Solved Free Assignment

Human activities play a big role in the acceleration of weathering processes.

BGYCT 131 Solved Free Assignment
BGYCT 131 Solved Free Assignment

Q 5 Describe various types and stages of rivers with the help of neat diagrams.

Ans. Rivers are natural channels that transport water and sediment from higher elevations to lower elevations. They are dynamic systems that change over time in response to changes in climate, tectonics, and human activities.

There are several types of rivers based on their characteristics and stages of development, which include:

Youthful rivers: Youthful rivers are characterized by a high slope, fast-moving water, and a narrow channel. They typically have a V-shaped cross section and are found in mountainous regions. BGYCT 131 Solved Free Assignment

They are actively eroding the channel and the valley sides, creating steep-sided valleys.

Mature rivers: Mature rivers are characterized by a lower slope, slower-moving water, and a wider channel. They typically have a U-shaped cross-section and are found in lowland regions.

They are depositing sediment in the channel, creating a wide, flat-bottomed valley.

Old age rivers: Old age rivers are characterized by a very low slope, slow-moving water, and a wide channel.

They typically have a flat-bottomed cross section and are found in coastal regions. They are depositing sediment in the channel, creating a delta.

Braided rivers: Braided rivers are characterized by a large number of channels that split and merge as the river flows. They are found in regions with high sediment loads and are typically found in mountainous regions.

Meandering rivers: Meandering rivers are characterized by large bends, or meanders, in the channel. They are typically found in regions with low gradient, low sediment loads, and a wide floodplain.

Anastomosing rivers: Anastomosing rivers have multiple channels that split and merge in a complex pattern. They are typically found in regions with a high sediment load and a wide floodplain. BGYCT 131 Solved Free Assignment

It’s worth noting that these stages of river development are not mutually exclusive, and a river may have characteristics of multiple stages simultaneously.

These are not fixed stages but rather a gradual transition from one stage to another.

Section B

Q 6 Describe elements of a fold. Also discuss classification of folds based on their special properties giving neat well labelled diagrams.

Ans A fold is a three-dimensional deformation of rock layers caused by compressive forces in the Earth’s crust. There are several elements of a fold that are important to understand: BGYCT 131 Solved Free Assignment

Axial plane: The axial plane is a flat surface that runs down the center of the fold, and it is parallel to the direction of compression.

Axial trace: The axial trace is a line that marks the intersection of the axial plane with the surface of the rock layers.

Limbs: The limbs are the two sides of the fold that slope away from the axial plane.

Crest: The crest is the highest point of the fold, located at the top of the limbs.

Trough: The trough is the lowest point of the fold, located at the bottom of the limbs. BGYCT 131 Solved Free Assignment

Folds can be classified based on their special properties, and the most common classifications include:

Anticline: An anticline is a fold in which the limbs dip away from the axial plane, with the oldest rocks on the bottom and the youngest rocks on top.

Syncline: A syncline is a fold in which the limbs dip towards the axial plane, with the youngest rocks on the bottom and the oldest rocks on top.

Monocline: A monocline is a fold that has a single steep limb and a gentle limb, with the oldest rocks on the bottom and the youngest rocks on top.

Recumbent fold: A recumbent fold is a fold that has been pushed past its breaking point, resulting in a near-horizontal axial plane.

Overturned fold: An overturned fold is a fold where the axial plane is tilted more than 90 degrees, resulting in the youngest rocks on the bottom and the oldest rocks on top. BGYCT 131 Solved Free Assignment

It is worth noting that these classifications are not mutually exclusive, and a fold may have characteristics of multiple classifications.

Q 7 Differentiate the following :

a) Contraction and expansion hypotheses of mountain building

Ans The contraction and expansion hypotheses of mountain building refer to two different explanations for the formation of mountains.

Contraction Hypothesis: The contraction hypothesis, also known as the “downdraw” or “collision” hypothesis, proposes that mountains are formed by the contraction of the Earth’s crust as a result of cooling and solidification of the interior.

This contraction causes the crust to crack and fold, resulting in the uplift of mountain ranges. This theory was first proposed by Eduard Suess in the late 19th century, and it was widely accepted for many years.

Expansion Hypothesis: The expansion hypothesis, also known as the “upwelling” or “divergence” hypothesis, proposes that mountains are formed by the expansion of the Earth’s crust as a result of heating and upwelling of material from the interior. BGYCT 131 Solved Free Assignment

This expansion causes the crust to crack and bulge, resulting in the uplift of mountain ranges.

This theory was first proposed by Tuzo Wilson in the 1960s, and it is considered an alternative to the contraction hypothesis.

It is worth noting that, today the most widely accepted explanation for mountain building is the Plate tectonics theory, which explains the mountain formation by the movement and collision of tectonic plates, rather than contraction or expansion of the Earth’s crust.

In plate tectonics, mountains can be formed by several processes, such as:

Convergent boundary: when two tectonic plates collide, one plate is pushed under the other, leading to the uplift of the upper plate and formation of mountains. BGYCT 131 Solved Free Assignment

Divergent boundary: When two tectonic plates move apart, new crust is formed and rising magma pushes the crust above the surface, leading to the formation of mountains.

Transform boundary: When two tectonic plates slide past each other, the movement can cause stress and deformation in the crust leading to the formation of mountains.

It is worth noting that, the contraction and expansion hypotheses are considered obsolete today, but it is important to know the history of the scientific understanding on the subject.

b) Measurement of strike and dip of an inclines bed

Ans The strike and dip of an inclined bed are important measurements in the field of geology and structural geology, as they provide information on the orientation and attitude of a rock formation or bed.

The strike is the compass direction of a line formed by the intersection of the bed and a horizontal plane. This is typically measured as a bearing, such as N40E, which indicates a strike direction of 40 degrees east of true north.

The strike measurement is taken in the horizontal plane and is typically measured using a compass. BGYCT 131 Solved Free Assignment

The dip is the angle of inclination of the bed from the horizontal plane. The dip angle is measured in degrees and can range from 0 to 90 degrees.

A bed with a dip angle of 0 degrees is considered horizontal, while a bed with a dip angle of 90 degrees is considered vertical.

The dip measurement is taken in the vertical plane and is typically measured using a clinometer or a geological hammer with a built-in inclinometer.

The combination of strike and dip measurements can be used to determine the attitude or orientation of the bed in three-dimensional space.

A dip direction can also be determined by taking the bearing at 90 degrees to the strike.

It is important to note that when measuring strike and dip, the measurements should be taken from a representative sample of the bed, and multiple measurements should be taken to ensure accuracy.

Also, when measuring strike and dip on an outcropping rock, the measurement should be taken on the most planar surface, which is typically the bedding plane or foliation plane. BGYCT 131 Solved Free Assignment

Q 8 What is a joint? Explain genetic classification of joints giving suitable diagrams.

Ans A joint is a planar or roughly planar fracture in a rock, through which no movement has occurred. It is a type of structural feature that forms as the rock cools and contracts, leading to the development of cracks.

Joints are typically perpendicular to the direction of the maximum compressive stress.

They can be straight or curved, and they can form a variety of patterns, such as parallel or intersecting sets. BGYCT 131 Solved Free Assignment

Joints can be classified based on their genetic origins, or the processes that formed them. Some common genetic classifications of joints include:

Thermal joints: These joints form as a result of cooling and contraction of a rock mass. They are typically found in igneous rocks and are parallel to the cooling surfaces.

Tectonic joints: These joints form as a result of tectonic stress and deformation of a rock mass. They can be caused by compression, extension, or shear stress and can be found in a variety of rock types.

Stress-relief joints: These joints form as a result of the release of stress in a rock mass. They can be caused by erosion, unloading, or changes in temperature or humidity.

Solution joints: These joints form as a result of the dissolution and removal of material from a rock mass. They are typically found in limestone and other soluble rocks. BGYCT 131 Solved Free Assignment

Joints related to mineral growth: These joints form as a result of the growth and expansion of minerals within a rock mass. They can be found in a variety of rock types.

It is important to note that joints can also be classified based on their shape, spacing, and orientation, and that some joints can have multiple genetic origins.

Q 9 Give an account of classification of mountains with the help of suitable diagrams.

Ans Mountains can be classified based on a variety of factors, including their origin, shape, and geologic structure. Some common classifications of mountains include:

Volcanic mountains: These mountains are formed by volcanic activity and are characterized by steep slopes and a central crater or caldera. Examples include Mount Fuji in Japan and Mount Vesuvius in Italy.

Fold mountains: These mountains are formed by the collision of tectonic plates and are characterized by long, parallel ridges and valleys. Examples include the Himalayas in Asia and the Rocky Mountains in North America.

Dome mountains: These mountains are formed by uplift and erosion of a dome-shaped feature, and are characterized by a rounded shape and a central peak.

Examples include the Black Hills in South Dakota and the Adirondack Mountains in New York. BGYCT 131 Solved Free Assignment

Block mountains: These mountains are formed by the uplift and erosion of a block of rock, and are characterized by a jagged or irregular shape.

Examples include the Teton Range in Wyoming and the Matterhorn in Switzerland.

Plateau mountains: These mountains are formed by the uplift and erosion of a plateau or high plain, and are characterized by a broad, flat top and steep sides. Examples include the Masai Mara in Kenya and the Tibetan Plateau.

Q 10 Write short notes on the following:

a) Criteria for recognition of faults in field

Ans a) Criteria for recognition of faults in field:

  • Faults are recognized in the field based on a combination of structural and stratigraphic observations.
  • Structural criteria include the presence of offset or displacement of bedding planes, fractures, or other rock features, as well as the presence of fault breccia or other deformation-related features such as crushed or sheared rock.
  • Stratigraphic criteria include the presence of a change in rock type or lithology across the fault, as well as the presence of angular or erosional unconformities or other stratigraphic markers that indicate movement along the fault.
  • Fault planes can also be recognized by their surface expression and geomorphology, such as linear valleys or ridge, escarpments, linear drainage pattern. BGYCT 131 Solved Free Assignment
  • Faults can also be recognized by geophysical techniques such as seismic surveys, gravity, and magnetic surveys.
  • Fault can also be recognized by their relationship with other structural features such as folds, joints, and dikes.

b) Principles of plate tectonics

Ans Principles of plate tectonics:

Plate tectonics is the scientific theory that explains the movement and behavior of the Earth’s lithosphere, which is divided into several large, rigid plates that move around on the softer, underlying asthenosphere.

The Earth’s lithosphere is composed of several large tectonic plates, including the North American Plate, South American Plate, African Plate, and Pacific Plate, among others.

These plates are constantly moving and interacting with each other at their boundaries, where three types of plate boundaries can be recognized: divergent, convergent, and transform.

At divergent plate boundaries, two plates move away from each other and new crust is created as magma rises to the surface and solidifies. This is the process that forms oceanic spreading centers, such as the Mid-Atlantic Ridge.

At convergent plate boundaries, two plates move toward each other and interact in one of three ways: oceanic crust is subducted beneath continental crust, oceanic crust is subducted beneath another oceanic crust, or continental crust is pushed up to form mountains. BGYCT 131 Solved Free Assignment

Transform plate boundaries are where two plates slide past each other horizontally and no new crust is created or destroyed. These boundaries often have frequent earthquakes and can form a transform fault.

The theory of plate tectonics also explains the movement of continents, the creation and destruction of oceanic crust, and the origin of earthquakes, volcanic activity, and mountain building.

The heat energy for plate tectonics comes from the Earth’s interior and it drives the movement of the plates. BGYCT 131 Solved Free Assignment

Plate tectonics is a unifying theory that helps to explain a wide range of geological phenomena and it has revolutionized the way scientists understand the Earth.

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