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IGNOU BGYET-147 Previous Year Solved Question Paper in Hindi

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Q1. Briefly answer any five questions from the following : (a) Define Geomorphology. (b) List the stages involved in geomorphic evolution of river basin. (c) What is denudation ? (d) What is ice cave ? (e) Define mid-oceanic ridge. (f) What is Pangea ? (g) Name any four major tectonic plates. (h) Define any two types of plate boundaries.

Ans. (a) Geomorphology is the scientific study of the origin and evolution of topographic and bathymetric features (landforms) created by physical, chemical, or biological processes operating at or near the Earth’s surface. It involves understanding the endogenetic (internal) and exogenetic (external) forces that shape the planet’s surface.

(b) The geomorphic evolution of a river basin is typically described by the three stages of the ‘Geomorphic Cycle’ or ‘Cycle of Erosion’:

• Youthful Stage: Characterised by rapid vertical erosion, steep gradients, V-shaped valleys, and the presence of waterfalls and rapids.
• Mature Stage: Lateral erosion becomes dominant, leading to wider valleys, development of meanders, a well-integrated drainage network, and a smoother, gentler gradient.
• Old Age Stage: The river has a very low gradient, broad floodplains, and features like oxbow lakes and natural levees. The landscape is reduced to a low-lying, almost flat plain called a peneplain .

(c)

Denudation

is the collective term for the processes that cause the wearing away of the Earth’s surface, leading to a reduction in elevation and relief of landforms. It encompasses three main processes:

weathering

(in-situ breakdown of rock),

erosion

(transportation of weathered material by agents like water, wind, and ice), and

mass wasting

(the movement of rock and soil downslope under the influence of gravity).

(d) An ice cave is any type of natural cave that contains significant amounts of perennial (year-round) ice. The term can refer to two distinct types: caves formed within a glacier (known as glacier caves) or rock caves that are cold enough for ice to form and persist throughout the year.

(e) A mid-oceanic ridge is a continuous underwater mountain range system formed by plate tectonics. It occurs at a divergent plate boundary where seafloor spreading takes place. As plates pull apart, magma from the mantle rises to create new oceanic crust. A characteristic feature is a rift valley, known as an axial rift , along its crest.

(f) Pangea was a supercontinent that existed during the late Paleozoic and early Mesozoic eras. Assembled from earlier continental units about 335 million years ago, it incorporated nearly all of Earth’s landmasses. It began to break apart about 175 million years ago, leading to the formation of the present-day continents. The concept was proposed by Alfred Wegener.

(g) Four major tectonic plates are:

• Pacific Plate
• North American Plate
• Eurasian Plate
• African Plate

(h) Two types of plate boundaries are:

• Divergent Boundary: A boundary where two tectonic plates move away from each other. Magma from the mantle wells up in the opening, creating new crust. These boundaries form mid-oceanic ridges in oceans and rift valleys on continents.
• Convergent Boundary: A boundary where two plates collide. This can result in subduction , where one plate sinks beneath the other, or continental collision. These boundaries are responsible for creating mountain ranges, volcanoes, and deep-sea trenches.

Q2. Write short notes on any four of the following : (a) Geomorphology of Indian peninsula (b) Landforms developed along divergent plated margin (c) Longitudinal profile of a river (d) Differences between continental and oceanic crust (e) Geomagnetic coordinates (f) Processes at transform fault plate boundaries

Ans. (a) Geomorphology of Indian Peninsula The Indian Peninsula is an ancient, stable landmass, representing a part of the former Gondwana supercontinent. Its geomorphology is dominated by extensive plateaus, such as the Deccan Plateau and the Malwa Plateau, which are composed of old crystalline rocks and ancient lava flows. Key geomorphic features include:

• The Western Ghats: A prominent mountain range running parallel to the west coast, which is essentially a fault scarp. It is higher and more continuous than its eastern counterpart.
• The Eastern Ghats: A series of discontinuous and highly eroded low hills.
• Rift Valleys: The Narmada and Tapti rivers flow westwards through prominent rift valleys, an exception to the general east-flowing drainage of the peninsula.
• Residual Mountains: The Aravalli Range is an example of a residual mountain system, representing the heavily eroded remnants of one of the world’s oldest fold mountains.
• Drainage: Most peninsular rivers are in their mature stage, characterized by broad, shallow valleys and dendritic or radial drainage patterns.

(b) Landforms developed along divergent plate margins

Divergent margins are where tectonic plates pull apart. The landforms created depend on whether this occurs in oceanic or continental lithosphere.

• Oceanic Divergent Margins: The primary feature is a mid-oceanic ridge , an extensive submarine mountain chain. At the crest of the ridge is an axial rift valley , where magma erupts to form new oceanic crust. Features like pillow lavas (formed by underwater eruption of basaltic lava) and hydrothermal vents (like ‘black smokers’) are common. The Mid-Atlantic Ridge is a classic example.
• Continental Divergent Margins: When a continent rifts, a rift valley is formed, which is a large elongated depression with steep walls. This process is associated with block mountains (horsts) and grabens, and significant volcanic activity. The East African Rift Valley is a modern example. With continued rifting, a linear sea may form, such as the Red Sea.

(d) Differences between continental and oceanic crust

Continental and oceanic crust are the two primary types of Earth’s crust, differing significantly in their properties:

• Composition: Continental crust is primarily granitic (felsic), rich in silica and aluminum (often called SIAL ). Oceanic crust is basaltic (mafic), rich in silica and magnesium (often called SIMA ).
• Density: Continental crust is less dense (average ~2.7 g/cm³), allowing it to “float” higher on the mantle. Oceanic crust is denser (average ~3.0 g/cm³), which is why it subducts beneath continental crust at convergent boundaries.
• Thickness: Continental crust is much thicker, ranging from 30 to 70 km. Oceanic crust is thin, typically only 5 to 10 km thick.
• Age: Continental crust can be extremely old (up to 4 billion years), as it is generally not destroyed. Oceanic crust is much younger (rarely older than 200 million years) because it is continuously created at mid-oceanic ridges and destroyed at subduction zones.

(f) Processes at transform fault plate boundaries

At transform fault boundaries, two tectonic plates slide horizontally past one another. At these boundaries, lithosphere is neither created nor destroyed. The primary processes are:

• Shear Stress Accumulation and Release: As the plates grind past each other, their rough edges lock, and immense shear stress builds up. When the stress exceeds the strength of the rocks, the fault ruptures, releasing the stored energy as an earthquake.
• Seismic Activity: Transform boundaries are characterized by frequent and powerful shallow-focus earthquakes. The San Andreas Fault in California is a famous example, marking the boundary between the Pacific Plate and the North American Plate.
• Topographic Features: The lateral movement along the fault can create distinct landforms, including offset streams (where a river’s course is displaced by the fault), linear valleys and troughs that mark the fault line, and small ridges.

Q3. Answer any one of the following: (a) Discuss in detail the destructional geomorphic processes. Or (b) What is continental drift ? Discuss in detail the mechanism of continental drift with the help of neat well-labelled diagrams.

Ans. (b) What is Continental Drift? Discuss in Detail the Mechanism of Continental Drift with the help of Neat Well-labelled Diagrams. Introduction: What is Continental Drift? Continental drift is the theory, first proposed in detail by the German meteorologist Alfred Wegener in 1912, that the Earth’s continents have moved over geologic time relative to each other, thus appearing to have “drifted” across the ocean bed. Wegener postulated that all continents were once joined together in a single supercontinent he named ‘Pangea’ (meaning ‘all lands’), surrounded by a single global ocean called ‘Panthalassa’ . According to his theory, Pangea began to break apart around 200 million years ago, and the continents slowly moved to their current positions.

Evidence for Continental Drift Wegener compiled a wide range of evidence to support his theory:

1. Jigsaw Fit of Continents: The coastlines of continents on opposite sides of the Atlantic Ocean, particularly South America and Africa, show a remarkable fit.
2. Fossil Evidence: Identical fossils of land-dwelling animals and plants, such as the reptile Mesosaurus and the fern Glossopteris , were found on widely separated continents like South America, Africa, India, and Australia. It was implausible for these organisms to have crossed vast oceans.
3. Rock and Structural Evidence: There are matching rock types and geological structures, such as mountain belts, on different continents. For example, the Appalachian Mountains in North America are geologically similar to the Caledonian Mountains in Scandinavia and the British Isles.
4. Paleoclimatic Evidence: Evidence of past climates did not match the continents’ current locations. Glacial deposits were found in present-day tropical regions (India, Africa), while coal deposits (formed in warm, swampy conditions) were found in Antarctica.

Mechanism of Continental Drift Despite the compelling evidence, Wegener’s theory was initially rejected by the scientific community primarily because he could not propose a plausible mechanism. The forces he suggested— ‘pole-fleeing force’ (Polflucht) from the Earth’s rotation and tidal forces —were proven to be far too weak to move continents.

The modern theory of Plate Tectonics provides the accepted mechanism for continental movement. Continents do not drift on their own; they are part of rigid lithospheric plates that move over the semi-molten layer below, the asthenosphere. The primary driving force for this movement is mantle convection .

• Mantle Convection: Heat from the Earth’s core creates huge convection cells within the mantle. Hot, less-dense material rises, pushes plates apart at mid-oceanic ridges (a process called ridge push ), and then cools and sinks.
• Slab Pull: At convergent boundaries, a denser oceanic plate subducts, or sinks, into the mantle under its own weight. This sinking slab pulls the rest of the plate along with it. Slab pull is now considered the most significant driving force of plate motion.

(A diagram should be drawn here showing the layers of the Earth – crust, mantle, core. It should illustrate a convection cell in the mantle, showing rising magma at a mid-oceanic ridge (divergent boundary) and the subduction of a plate at a trench (convergent boundary).)

Diagram of the Mechanism of Continental Drift (Plate Tectonics)

[The diagram should depict: 1. Convection cells in the mantle. 2. A mid-oceanic ridge where plates are diverging. 3. A subduction zone (trench) where one plate goes under another. 4. A lithospheric plate carrying a continent.]
Conclusion:

While Wegener’s proposed mechanism was incorrect, his revolutionary idea of continental drift laid the foundation for the theory of plate tectonics, which now explains most of Earth’s major geological phenomena, from earthquakes and volcanoes to the formation of mountain ranges.

Q4. Answer any one of the following: (a) Discuss the types of glaciers. Add a note on causes of glaciation. Or (b) Describe the tectonic features developed at the convergent plate boundaries.

Ans. (b) Describe the tectonic features developed at the convergent plate boundaries. Introduction: Convergent plate boundaries are locations where two or more lithospheric plates move toward each other and collide. These zones of intense geological activity are responsible for some of the most dramatic topographic features on Earth. The specific tectonic features that develop depend on the type of crust involved in the collision: oceanic-continental, oceanic-oceanic, or continental-continental.

1. Oceanic-Continental Convergence When a dense oceanic plate collides with a less dense continental plate, the oceanic plate is forced to sink, or subduct , beneath the continental plate. This process creates several distinct features:

• Deep-Sea Trench: A long, narrow, and very deep depression forms on the ocean floor, marking the line of subduction. The Peru-Chile Trench off the coast of South America is a prime example.
• Continental Volcanic Arc: As the subducting oceanic plate descends into the hot mantle, it melts. This magma, being less dense, rises to the surface and erupts, forming a chain of volcanoes on the continental plate. The Andes Mountains are a classic example of a continental volcanic arc.
• Fold-and-Thrust Mountain Range: The immense compressional forces of the collision buckle and uplift the crust of the continental plate, creating a mountain range.
• Earthquakes: This zone experiences frequent earthquakes at shallow, intermediate, and deep levels along the descending slab, a zone known as the Wadati-Benioff zone .

2. Oceanic-Oceanic Convergence When two oceanic plates collide, the older, colder, and denser plate will subduct beneath the younger, warmer plate. This convergence results in the following features:

• Deep-Sea Trench: A trench is formed, similar to an oceanic-continental boundary. The Mariana Trench , the deepest point on Earth, is formed by this process.
• Volcanic Island Arc: Magma generated from the melting subducting plate rises to the ocean floor. Over time, repeated eruptions build up a chain of volcanoes that emerge from the sea as islands. Japan , the Philippines , and the Aleutian Islands are all examples of volcanic island arcs.
• Back-arc Basin: Tensional forces may develop behind the island arc, leading to the formation of a basin.
• Earthquakes: A Wadati-Benioff zone with shallow to deep earthquakes is also present here.

3. Continental-Continental Convergence When two continental plates collide, neither can easily subduct due to their low density and high buoyancy. Instead, the crust is intensely compressed, folded, faulted, and uplifted.

• Major Non-Volcanic Mountain Ranges: The collision results in the formation of massive and complex mountain ranges. The most spectacular example is the Himalayan Mountain Range , formed by the collision of the Indian Plate with the Eurasian Plate.
• Plateau Formation: The crustal thickening can create vast, high-elevation plateaus behind the mountain range, such as the Tibetan Plateau north of the Himalayas.
• Widespread Seismic Activity: These zones are characterized by widespread shallow and intermediate-focus earthquakes over a broad area.
• Lack of Volcanism: Because there is little to no subduction, there is minimal magma generation, and therefore, these collision zones are typically not associated with volcanism.

Conclusion: Convergent plate boundaries are the most geologically dynamic zones on the planet, creating Earth’s highest mountains and deepest trenches. The features they produce are a direct result of the powerful forces unleashed when lithospheric plates collide.