Rocks and Earth Sciences

51. Chemical weathering of rocks is much greater in a place with

Chemical weathering of rocks is much greater in a place with

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cold and dry climate
hot and humid climate
hot and dry climate
cold and humid climate
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UPSC NDA-1 – 2018
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The correct answer is (B) hot and humid climate. Chemical weathering involves chemical reactions like hydrolysis, oxidation, carbonation, etc., which break down rocks. These reactions are significantly accelerated by higher temperatures and the presence of water. A hot climate increases the rate of chemical reactions, and a humid climate provides the necessary moisture (water) for these reactions to occur.
Chemical weathering is most effective in environments with high temperatures and abundant moisture, as these conditions promote the chemical breakdown of minerals in rocks.
In cold climates, physical weathering (like freeze-thaw) is more dominant. In dry climates, both chemical and physical weathering rates are generally lower due to lack of water, although some forms of weathering like exfoliation (due to thermal expansion/contraction) can occur. Hot and dry climates might see relatively faster chemical weathering than cold climates if some moisture is available, but hot and *humid* is the most conducive environment for chemical weathering.

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52. Fold Mountains are formed in which type of tectonic settings ?

Fold Mountains are formed in which type of tectonic settings ?

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Divergent
Convergent
Transform
Rifting
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Fold Mountains are primarily formed at convergent tectonic plate boundaries. When two continental plates collide, neither subducts significantly; instead, the crust is compressed, folded, and uplifted to form large mountain ranges like the Himalayas, Alps, and Andes. Collision or subduction at convergent boundaries generates immense pressure that causes the rock layers to buckle and fold.
– Convergent boundaries involve plates moving towards each other.
– Compression forces at convergent boundaries lead to folding and faulting of crustal rocks.
– Divergent boundaries involve plates moving apart.
– Transform boundaries involve plates sliding past each other.
Other mountain types include block mountains (formed by faulting and uplift/subsidence of crustal blocks, often at divergent or transform boundaries), volcanic mountains (formed by accumulation of volcanic material, often at convergent or divergent boundaries), and erosional mountains (remnants of dissected plateaus).

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53. Which one of the following pairs of principal chemical constituents in

Which one of the following pairs of principal chemical constituents in water and their source is correct ?

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Ca : Amphiboles, Feldspars, Gypsum
NO₃ : Apatite, Fluorite, Mica
CO₃ : Feldspars, Clay minerals
F : Dolomite, Gypsum, Anhydrite
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UPSC Geoscientist – 2024
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This question requires matching common chemical constituents found dissolved in water with their primary source minerals. Water flowing over or through rocks and soil dissolves minerals, contributing to its chemical composition.
– **Calcium (Ca):** Calcium is a common cation in natural waters, often sourced from the dissolution of calcium-bearing minerals. Gypsum (CaSO₄·2H₂O) is a readily soluble mineral containing calcium. Plagioclase feldspars (e.g., anorthite, CaAl₂Si₂O₈) and some amphiboles are silicate minerals that also contain calcium and release it upon weathering. Option A correctly lists common sources of calcium in water.
– **Nitrate (NO₃⁻):** Nitrates are anions usually derived from the nitrogen cycle, including decomposition of organic matter, agricultural fertilizers, and sewage. While nitrogen is present in some minerals (e.g., saltpeter), the significant source of nitrates in water is typically biogeochemical processes and human activities, not the mineral types listed (Apatite – phosphate, Fluorite – fluoride, Mica – silicate). Option B is incorrect.
– **Carbonate (CO₃²⁻):** Carbonates are derived from the dissolution of carbonate rocks like limestone (primarily CaCO₃) and dolomite (CaMg(CO₃)₂). While weathering of silicate minerals like feldspars contributes to alkalinity and the formation of bicarbonate (HCO₃⁻) or carbonate, feldspars and clay minerals themselves are not primary sources of the carbonate ion in the same way carbonate rocks are. Option C is incorrect.
– **Fluoride (F⁻):** Fluoride in natural water often comes from the dissolution of fluoride-bearing minerals like Fluorite (CaF₂), cryolite (Na₃AlF₆), and some micas and apatites. Dolomite, Gypsum, and Anhydrite are calcium/magnesium carbonates or sulfates and are not primary sources of fluoride. Option D is incorrect.
The chemical composition of natural water is largely determined by the geology of the area it flows through and human activities. Understanding the weathering processes and mineral compositions helps identify the origins of dissolved substances. Option A provides the most accurate set of sources for Calcium among the choices.

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54. A ‘Spit’ can be defined as a:

A ‘Spit’ can be defined as a:

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beach of sand or shingle linked at one end to the land.
ridge that links the mainland to an island.
ridge formed by consolidated dunes on the beach.
shingle ridge formed along the beach above the high water mark.
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UPSC Geoscientist – 2021
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A spit is a coastal landform, specifically a strip of sand or shingle, which is connected to the mainland at one end and projects into the sea or a body of water.
Spits are formed by longshore drift and deposition of sediment along the coast.
Option B describes a tombolo, which connects an island to the mainland. Options C and D describe types of beach ridges or dunes, but not the characteristic shape and attachment of a spit.

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55. Roughly conical hills, composed of sorted glacio-fluvial deposits, are

Roughly conical hills, composed of sorted glacio-fluvial deposits, are called:

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Erratics
Drumlins
Kames
Eskers
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UPSC Geoscientist – 2021
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Kames are irregular, roughly conical hills composed of stratified sand and gravel deposited by meltwater streams at the edge or on the surface of a retreating glacier, or in contact with stagnant glacial ice.
The description “roughly conical hills, composed of sorted glacio-fluvial deposits” perfectly matches the characteristics of Kames.
Erratics are large boulders transported and deposited by ice. Drumlins are elongated, streamlined hills formed by glacial ice, composed of till (unsorted). Eskers are long, sinuous ridges formed by meltwater streams flowing within or beneath a glacier.

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56. Which one of the following is not an example of chemical weathering

Which one of the following is not an example of chemical weathering ?

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Acid action
Hydrolysis
Salt Crystal Growth
Oxidation
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UPSC CDS-2 – 2024
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Chemical weathering involves processes that change the chemical composition of rocks and minerals. Acid action (like carbonation, where carbonic acid dissolves minerals), Hydrolysis (reaction of water with minerals), and Oxidation (reaction with oxygen) are all examples of chemical weathering. Salt Crystal Growth (also known as salt weathering or haloclasty) is a process where salt crystals grow in pores and cracks within rocks, exerting pressure that forces the rock apart. This is a physical process that breaks down the rock without changing its chemical composition, making it an example of physical or mechanical weathering, not chemical weathering.
Weathering is the breakdown of rocks, soil, and minerals through contact with the Earth’s atmosphere, water, and biological organisms. It is broadly classified into physical (mechanical), chemical, and biological weathering.
Salt weathering is particularly effective in arid and coastal environments where evaporation leads to the crystallization of dissolved salts within the rock pores.

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57. Which kind of mass wasting processes are commonly associated with cree

Which kind of mass wasting processes are commonly associated with creep ?

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Fast speed with soil
Slow speed with rock
Slow speed with ice
Slow speed with soil
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UPSC CDS-2 – 2024
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Creep is a type of mass wasting characterized by the slow, gradual, and continuous movement of soil or regolith down a slope. It typically occurs over long periods and is often imperceptible except through observations of its effects, such as tilted poles, fences, or tree trunks. It is predominantly associated with the slow movement of unconsolidated material like soil.
Mass wasting processes are classified based on the type of material, speed, and nature of movement. Creep is the slowest form of mass wasting involving soil or regolith.
Other types of mass wasting include flows (like mudflows, debris flows – faster, involving water), slides (rockslides, landslides – movement along a plane), and falls (rockfalls – free-fall of material). Creep is influenced by factors like freeze-thaw cycles, wetting and drying of soil, and animal activity.

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58. Which one of the following landforms is/are formed by wind erosion ?

Which one of the following landforms is/are formed by wind erosion ?

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Cirque
Stack
Zeugen
Stack and Zeugen both
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UPSC CDS-2 – 2023
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Zeugen is a landform formed by wind erosion.
Wind erosion, also known as aeolian processes, can create distinctive landforms, particularly in arid and semi-arid regions.
A Cirque is a bowl-shaped depression carved by a glacier at the head of a valley. A Stack is a vertical column of rock on a coastline, formed by wave erosion wearing away surrounding rock. A Zeugen is a type of yardang, an elongated streamlined hill carved by wind erosion in arid regions, often resembling a mushroom shape where differential erosion occurs on layers of varying hardness. Therefore, only Zeugen among the given options is primarily a result of wind erosion.

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59. Which one of the following processes leads to expansion of certain min

Which one of the following processes leads to expansion of certain minerals as they take up water, causing additional stress in the rock ?

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Hydrolysis
Hydration
Oxidation
Carbonation
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UPSC CDS-2 – 2022
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The correct answer is B) Hydration.
Hydration is a form of chemical weathering where water molecules are added to the molecular structure of a mineral. Some minerals, like gypsum, anhydrite, and certain clay minerals, absorb water and expand in volume as they are hydrated. This increase in volume creates stress within the rock, which can lead to disintegration and breakdown.
Hydrolysis involves the reaction of water with minerals, specifically where water splits into H+ and OH- ions that react with the mineral’s components (e.g., feldspar weathering into clay). Oxidation is the reaction of minerals with oxygen, often leading to the formation of rust (iron oxides). Carbonation is the reaction of carbonic acid (H₂CO₃), formed by CO₂ dissolving in water, with minerals, particularly carbonates like calcite. While all are chemical weathering processes, Hydration is the specific process leading to the expansion of minerals upon taking up water.

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60. ‘Pingos’ are associated with which one of the following process?

‘Pingos’ are associated with which one of the following process?

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Glacial
Peri-glacial
Aeolian
Fluvial
This question was previously asked in
UPSC CDS-2 – 2022
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The correct answer is B) Peri-glacial.
Pingos are large, ice-cored hills or mounds found in periglacial environments. They are formed when water beneath a layer of permafrost is confined and subjected to freezing, causing the water to expand and push up the overlying sediment into a dome shape. Periglacial refers to conditions or processes occurring in areas adjacent to glacial ice sheets or in regions of permafrost, involving repeated freezing and thawing.
Glacial processes involve the action of glaciers and ice sheets. Aeolian processes relate to the action of wind. Fluvial processes relate to the action of rivers or streams. Pingos are distinct geomorphological features formed specifically by the unique interactions of water and ice in permanently frozen ground conditions, characteristic of periglacial landscapes.

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