Test: Geomorphology - 2 - UPSC MCQ

Fold mountains are formed due to compressive action of forces in the Earth's crust. These are driven by magmatic convection.

• Formation of Fold Mountains: Rivers deposit huge quantities of sediments in depressions called geosynclines. Over millions of years, the sediments arc compressed into sedimentary rocks such as sandstone and limestone. The plates move together forcing the sedimentary rocks upwards into a series of folds by the movement of tectonic plates. This causes the thickness of the rocks in fold mountains.

• There are three types of mountains: Fold Mountains, Block Mountains and the Volcanic Mountains.

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  The Himalayan Mountains and the Alps are young fold mountains with rugged relief and high conical peaks.

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  The Aravalli range in India is one of the oldest fold mountain systems in the world. The range has considerably worn down due to the processes of erosion.

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  The Appalachians in North America and the Ural mountains in Russia have rounded features and low elevation. They are very old fold mountains

• The Himalayan Mountains and the Alps are young fold mountains with rugged relief and high conical peaks. The Appalachians in North America and the Ural mountains in Russia have rounded features and low elevation. They are very old fold mountains.

• Block Mountains are created when large areas are broken and displaced vertically. The uplifted blocks are termed as horsts and the lowered blocks are called graben. The Rhine valley and the Vosges mountain in Europe are examples of such mountain systems.

• The Aravalli range in India is one of the oldest fold mountain systems in the world yet not associated with volcanic activity.

All are due to tectonic reasons. Some plateaus like these are found between fold mountains such as the Bolivian plateau. These are distinct from the volcanic plateaus that are formed due to the flow and consolidation of lava.

• A dissected plateau is an area that has been severely eroded and divided into several smaller pieces.

• The natural agents, such as the Sun, the rain, the wind, the running water and the Glacier, wear away the soft rocks of the upland areas.

• The resistant rock masses are left there standing on the ground above the surroundings.

• The sometimes from the almost level surface, cut by rivers and streams. These upland areas together form a dissected plateau.

• As stated by Wegner, all the continents were once formed as a single continental mass, and this mass was surrounded by a mega ocean.

• He argued that Pangaea, the supercontinent, began to split around 200 million years ago.

• He also suggested that the pole-fleeing force and tidal force cause the movement that was responsible for the drifting of the continents. The pole-fleeing force is related to Earth’s rotation.

• As argued by Wegner, all the continents were once formed as a single continental mass (supercontinent, called PANGAEA [meaning all Earth]), and this mass was surrounded by a mega ocean, known as PANTHALASSA (meaning all water).

• He further argued that Pangaea, the supercontinent, began to split around 200 million years ago. Subsequently, their components broke up into various smaller continents that exist today.

• Plate tectonics is the modem version of continental drift, a theory first proposed by scientist Alfred Wegener in 1912. Wegener didn’t have an explanation for how continents could move around the planet, but researchers do now. Plate tectonics is thus said to be the unifying theory of geology.

• The driving force behind plate tectonics is convection in the mantle. Hot material near the Earth’s core rises, and colder mantle rock sinks.

• The plates act like a hard and rigid shell compared to Earth’s mantle. This strong outer layer is called the lithosphere.

• The peninsular plate is an integral part of the Indian plate.

• Plates are divided between major and minor plates based on their geographical coverage. The Indian plate is thus a major plate.

• The subduction zone along the Himalayas forms the northern plate boundary in the form of continent convergence.

• In the east, it extends through Rakim Yoma Mountains of Myanmar towards the island along the Java Trench. The Western margin follows Kirthar Mountain of Pakistan.

• The northward movement of the Indian plate is continuing and it has significant consequences on the physical environment of the Indian subcontinent.

• The Peninsula stands erect, with some exceptions on its western coast, which is under the sea and some other parts also changed because of tectonic activity. This does not affect the original basement.

• The Peninsula is a part of the Indo-Australian Plate, with various vertical movements and block faulting. Some examples are the rift valleys of the Narmada, the Tapi and the Mahanadi and the Satpura block mountains.

• The river valleys here are shallow with low gradients.

• Harry Hess (1961) proposed a hypothesis known as the ‘seafloor spreading’ based on a thorough analysis of the magnetic properties of the rocks that are present on either side of the mid-oceanic ridge.

• He argued that the rupture of the oceanic crust is due to the constant eruptions at the crest of oceanic ridges. Here, new lava wedges into the crust and pushes it on either side. Thus, the ocean floor spreads.

• Hess thinks about the consumption of the oceanic crust because of the following two factors: the younger age of the oceanic crust and the spreading of one ocean at the cost of the shrinking of the other. He further said that the ocean floor that is pushed because of volcanic eruptions at the crest is immersed at the oceanic trenches and gets consumed.

• Mapping of the ocean floor a paleomagnetic rock studies of ocean regions disclosed the below facts:

(i) Volcanic eruptions are common in the mid-oceanic ridges, and enormous amounts of lava were brought to the surface by these eruptions.

(ii) There are striking similarities formation, chemical composition and magnetic properties between the rocks that are present equidistant on either side of the crest of mid-oceanic ridges.

(iii) The continental rocks are older than the ocean crust rocks. The oceanic crust rocks’ age is not more than 200 million years and some continental rocks are older than 3,200 million years.

(iv)The deep trenches have deep-seated earthquake occurrences while in the mid-oceanic ridge areas, the quake foci have shallow depths. It means lava is in close vicinity.

• The energy emanating from within the Earth is the main force behind endogenic geomorphic processes.

• This energy mostly generated by radioactivity, rotational and tidal friction and primordial heat from the origin of the Earth.

• This energy due to geothermal gradients and heat flow from within induces diastrophism and volcanism in the lithosphere.

• Due to variations ii geothermal gradients and heat flow from within, crustal thickness and strength, the action of endogenic forces are not uniform and hence the tectonically controlled original crustal surface is uneven.

• Gravity causes movement of ocean current, induces landslides, influences river movements etc. causing dynamic change on the landscape of Earth.

• Tectonic forces can build mountains.

• Sun’s radiation, that is, light, is electromagnetic. All landforms and life on Earth ultimately come from the Sun.

• It causes plate movements (tectonics), results in volcanic eruptions and is, therefore, a significant factor in the evolution of landforms on Earth.

• If vegetation cover is high, it protects the surface from rain splash as root mass is sufficient to stabilise the materials on the slope. Even surface runoff becomes less effective in carving out landforms in areas where there is dense vegetation since there is little scope for soil erosion.

• When water freezes to ice, its volume increases. Under specific circumstances, this expansion can displace or fracture rocks where water exists in its pores. Repeated frost action thus weathers (breaks) the rocks.

• In some mountains, there are permanently frozen rivers of ice. They are called glaciers. Glaciers move at a very slow rate. When they do, they erode the soil beneath them.

• Also, the formation of glaciers and their retreat affects the soil profile of the region and thus the landforms.

1. Hydrostatic and pore pressure: These pressures can influence the behavior of rocks by affecting the physical conditions under which the rocks exist. While hydrostatic pressure is the pressure exerted by fluids at rest, pore pressure refers to the pressure of groundwater held within a rock or soil, in gaps between particles. These pressures can indeed contribute to the formation of geological folds as they can influence the stress regime within the crust and also affect the ductility of rocks. Higher pore pressures, for example, can reduce the effective stress borne by the rock framework, making it more susceptible to deformation.

2. Temperature gradient on the surface of the Earth: Temperature gradients can influence rock behavior, but temperature gradients at the surface of the Earth are less likely to be a direct cause of folding. Folds generally form due to tectonic forces at depth within the Earth, where rocks are subject to higher pressures and temperatures than at the surface. The surface temperature gradient might play a role in weathering processes but not typically in the formation of folds deep within the crust.

Therefore, while hydrostatic and pore pressures can be a factor in the formation of geological folds, the temperature gradient on the surface is not typically a direct cause of geological folds. The temperature gradient at depth, related to geothermal gradients, would be more relevant.

The correct statement is: 1 only

• This comes due to geomagnetism. Magnetic response of rocks is determined by amounts and susceptibilities of constituent minerals. Sedimentary rocks have very low susceptibility to the magnetic field of Earth. So, there is little alignment in their constituents in response to Earth’s magnetic field. For ultramafic rocks, it is the highest.

• Foliation refers to repetitive layering in metamorphic rocks. When the pressure is greater in one direction than in the others (directed pressure), it causes the minerals in the original rock to reorient themselves with the long and flat minerals aligning perpendicular to the greatest pressure direction. This reduces the overall pressure on the rock and gives it a striped look.

• A rock is an aggregate of one or more minerals but without definite composition of constituent minerals. Rocks from which minerals are mined are known as ores.

• Although more than 2,800 types of minerals have been identified, only about 100 are considered ore minerals. The Katanga, or Shaba, Plateau is a farming and ranching region in the Democratic Republic of the Congo.

• Located in the southeastern Katanga Province, it is 1220 m (4,000 ft) above sea level and is rich in copper and uranium deposits. It is the source of the Lufira River, which becomes the Lualaba River.

• Lake Tshangalele, an artificial lake created by a dam on the Lufira, is an important ecological site on the plateau.

• Felspar is more quickly weathered than the quartz. Hence Statement 2 is wrong.

• The key difference between intrusive and extrusive rocks is that the intrusive rocks are formed from magma whereas the extrusive rocks are formed from lava. Rest of the differences follow from the basic structure.

Intrusive rocks: With no air to cool the magma, these rocks are formed very slowly Composition of these rocks reflects the presence of large crystals. These crystals interlock to form the rock. These rocks take a very large amount of time to solidify and they remain buried deep inside the surface of the Earth being surrounded by country rocks that have been there already.

Extrusive rocks: Sometimes, molten rocks find a way to come out of the surface of the Earth through cracks and openings. This magma flows in the form of lava and cools down quickly as it comes into contact with air. Igneous rocks that are formed from the magma that pours out of the surface of the Earth arc called extrusive rocks. As these rocks cool down and solidify very quickly, they do not get sufficient time to form target crystals. Thus, they have small crystals and boast a fine texture.

1. Generally metallic minerals are found in igneous and metamorphic rock formations that form large plateaus.

   • This statement is correct. Metallic minerals such as gold, silver, copper, iron, and nickel are often found in igneous and metamorphic rocks, which are commonly associated with large plateau regions.

2. Sedimentary rock formations of plains and young fold mountains contain non-metallic minerals.

   • This statement is also correct. Non-metallic minerals such as limestone, gypsum, and coal are typically found in sedimentary rock formations. These formations are common in plains and young fold mountain regions.

3. Sedimentary rocks can be formed organically also.

   • This statement is correct as well. Sedimentary rocks can indeed form organically from the accumulation and lithification of biological materials, such as shells, plant material, and other organic debris. Examples include limestone from shells and coal from plant material.

Since all three statements are correct, the answer is: All of the above.

• Igneous rocks are formed by solidification of magma and crystals arc formed upon cooling.

• Sedimentary rocks contain fossils. Basaltic rocks which are also the type of igneous rocks are basic due to lower silica content. The development of radiometric dating techniques in the early 20th century allowed scientists to quantitatively measure the absolute ages of rocks and the fossils they host.

• Shale is metamorphosed into Schist. Whereas sandstone is metamorphosed into Quartzite

• Granite is metamorphosed into Gneiss

• Clay is metamorphosed into Slate