Test: Geomorphology - 3

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Texturally mature sediment is usually well rounded and well-sorted due to:

1. Rounding of sediment increases with transport distance and time.

2. Sorting gets better as larger chunks arc left behind and smaller chunks arc carried away.

Which of the above statements is/are correct?

  • Sediment maturity refers to the length of time that the sediment has become in the sedimentary cycle.

  • Texturally mature sediment is sediment that is well rounded (as rounding increases with transport distance and time) and well sorted (as sorting gets better as larger clasts are left behind and smaller clasts arc carried away).

  • If the fragments arc angular, it indicates that they have not been transported very far and the sediment is poorly sorted.


Geologists study sedimentary rocks because

1. They provide a record of Earth’s history.

2. They may contain important mineral resources.

3. They may contain fossils, providing a history of life including human evolution.

Select the correct answer using the code below:

Solution: Sedimentary rocks make up about three-quarters of the rocks at the Earth’s surface.
  • Sedimentary rocks preserve a record of the environments that existed when they formed. By looking at sedimentary rocks of different ages, scientists can figure out how climate and environments have changed through Earth’s history. Fossils of ancient living things are preserved in sedimentary rocks too.

  • Quartz, K-feldspar and muscovite are some of the important minerals found there.


Sedimentary rocks can be directly formed from which of the following?

1. Magma

2. Igneous rocks

3. Mclamomhic rocks

Choose the correct answer using the codes below:

Solution: Sedimentary rocks are formed when sediments (broken from a rock) are deposited and consolidated under pressure or temperature or in other ways. Only igneous rocks can be directly formed from magma, not sedimentary rocks.


Consider the following:

1. Metamorphism

2. Convergent plate boundaries

3. Volcanic activity

Which of the following rocks is often associated with the above?

Solution: Gneiss usually forms by regional metamorphism at convergent plate boundaries. It is a high-grade metamorphic rock in which mineral grains recrystallised under intense heat and pressure associated with mountain building and volcanic activity.


Metamorphic rocks are formed due to

1. Cementation of sedimentary rocks

2. Proximity of sedimentary rocks with molten magma

3. Cooling and solidification of lava

Select the correct answer using the codes below:

  • Metamorphic rocks are made by either heating up or squashing the Earth’s crust. They are often found in mountainous regions. One example is slate. Slate was originally a black mud laid down on the bottom of the sea or lake.

  • Sometimes, metamorphic rocks are formed when rocks are close to some molten magma, and so get heated up. When metamorphic rock is formed under pressure, its crystals become arranged in layers. Slate, which is formed from shale, is like this. Slate is useful for making roof tiles because its layers can be split into separate flat sheets.


Which of the following are not sedimentary rocks?

1. Sandstone

2. Limestone

3. Marble

4. Slate

Choose the correct answer using the code below

Solution: Marble and slate are metamorphic rocks.


All rocks whether igneous or sedimentary can become metamorphic rocks under great temperature and pressure. In this regard, which of the conversions to metamorphic rocks below is correct?

1. Clay to slate

2. Coal to graphite

3. Sandstone to quartzite

4. Shale to schist

Which of the above statements is/are correct?


The basic source of all minerals on Earth is

Solution: Magma cools slowly as it rises towards Earth’s surface. It can take thousands to millions of years to become solid when it is trapped inside Earth. As the magma cools, solid rocks form (igneous). These rocks arc mixtures of minerals. Granite is a common rock that forms when magma cools.


The major characteristics of the Archaean rock system is that

  • The Azoic Age was used to describe the age of rocks formed before the appearance of life in the geologic sequence. Also known as Pre-Cambrian rocks, these are the oldest rocks of the Earth’s crust.

  • The Archaean period covers over 85 % of the total geological history time of Earth and therefore is very significant. This period marks the development of the first photosynthesis, the life support atmosphere.

  • The Archaean or Purana rock system in India is found in Aravallis mountains, two- thirds of the Deccan peninsula and some parts of the North-east.


Consider the following about the rock systems of India:

1. The Archaean rocks are found in the Deccan Peninsula and parts of the North-east.

2. The Dharwar rocks are rich in iron ore.

Which of the above statements is/are correct?


The Archean or Purana rock system in India is found in Aravallis mountains, 2/3rd of the Deccan peninsula and some parts of north east. These rocks have abundant metallic and non-metallic minerals such as iron, copper, manganese, bauxite, lead, zinc, gold, silver, tin, tungsten, mica, asbestos, graphite, etc.

 The iron-ore reserves of India are associated with the Dharwar rock systems. The Dharwar rocks are rich in iron ore, manganese, gold, zinc, lead, silver, etc. They are named after the Dharwar region of Karnataka.



Despite such a large geographical spread, why is the Himalayan region poor in mineral resources?

  • In the Himalayas, geological processes have led to the major displacement of rock strata. This has disturbed the arrangement of rocks and made it complex, making the Himalayas poor in mineral resources.

  • The rugged terrain and adverse climatic conditions make exploration of minerals difficult and costly, but it can’t be a reason for lack of mineral resources.

  • Our rich mineralised zone is largely confined to the old, crystalline rock structures of plateaus and low hills of peninsular India.


The Siwalik series of rocks in India

1. Contain fine brown clays.

2. Belong to the Cenozoic era and thus considered to be bereft of fossil remains.

Which of the above statements is/are correct?

  • The Siwalik series comprehends the two zones of strata forming the outermost ranges of the Sub- Himalayas.

  • Petrologically, this group consists either of coarse conglomerates or fine, brown clays, the latter being indistinguishable, in hand specimens, from the modern alluvium of Punjab. The conglomerates occur mainly on the lines of the large rivers, being replaced in the intervals by the clays.

  • A Siwalik system of rockfalls under Cenozoic Era and belongs to the Middle-Miocene, Pliocene and Lowe Pleistocene period or Epoch. This system of rocks is considered to be one of the largest storehouses of mammalian remains and other vertebral fossils.


In India, rocks of which of the following regions was formed the earliest?

  • Khasi hills, one of the youngest, belong to the Tertiary period (to which a large area in North-east also belongs). Shivalik are part of Himalayas, so given the reasoning below.

  • The alluvium which is found in the Indo- Gangetic plain belongs to the Quaternary period. It was eroded from the Himalayas by the rivers and the monsoons since the Himalayas were formed after Deccan traps, and are very young.

  • The Deccan Plateau in India is one of the oldest plateaus in India made mainly from igneous rocks.


Which of the following factors aid the weathering of rocks?

1. Intense heating during the day and rapid cooling at night

2. Pore pressure of water seeping into rocks

3. Thawing of rocks

Which of the following is/are correct?

  • Some applied forces determine the physical or mechanical weathering processes. Following are the few applied forces:

(i) Gravitational forces like overburden pressure, load and shearing stress;

(ii) Expansion forces due to changes in temperature, crystal growth or animal activity;

(iii) Water pressures controlled by wetting and drying cycles.

Many of these forces act both at the surface and within different Earth materials, causing fracture of the rocks. Thermal expansion and pressure release are responsible for most of the physical weathering processes. Though these processes are slow and small, rocks suffer continued fatigue due to repeated contractions and expansions that greatly damage the rocks.


Which of the following processes contributes to the enrichment of minerals in rocks?

  • Enrichment of many low-grade ores occurs when the metal-bearing solutions of these valuable metals drain downwards along the vein or other deposits and then are re-precipitated into concentrated, bonanza- grade deposits at shallow depths.

  • Some of these enriched deposits are quite large, being the product of long, continued forces of weathering with the descending mineral salts acting to concentrate the metal values from a great thickness of vein matter and rocks that were once located above the current outcrop, but now have been removed by erosion.

  • This process of natural concentration is how the action of weathering can produce such amazingly rich ore bodies.


How is the phenomenon of weathering important for us?

1. It aids in the formation of soil by eroding rocks and hard surfaces.

2. It helps in the enrichment of valuable minerals on Earth for their commercial extraction to be made possible.

3. It is responsible for shaping and denuding large landforms on Earth.

Select the correct answer using the codes below:

  • Weathering processes are responsible for breaking down the rocks into smaller fragments and preparing the way for the formation of not only regolith and soils but also erosion and mass movements. Biomes and biodiversity is basically a result of forests (vegetation) and forests depend upon the depth of weathering mantles.

  • Without weathering taking place, the concentration of the same valuable material may not be sufficient and economically viable to exploit, process and refine since they would be scattered across a large area.

  • Weathering aids mass wasting, erosion and reduction of relief and changes in landforms are a consequence of erosion.


Regarding mass movements of soil, consider the following statements:

1. Soil creep is a fast, continuous movement of soil down hillslopes

2. Soil flow or solifluction is a slow, gradual movement of soil down hillslopes

3. In soil creep, soil acts as liquid and hence it creeps fast

Which of the above is/are incorrect?

Solution: Soil creep indicates slow movement while solifluction is fast movement.


Exfoliation refers to

Solution: Exfoliation is the separation of successive thin shells, or spalls, from massive rock such as granite or basalt; it is common in regions that have moderate rainfall. The thickness of an individual sheet or plate may be from a few millimetres to a few metres.


Consider the following statements regarding rivers:

1. A river drains the water collected from a specific area, which is called its 'catchment area’.

2. An area drained by a river and its tributaries is called a drainage basin.

3. The boundary line separating one drainage basin from the other is known as the watershed.

4. Watersheds are small in area while the basins cover larger areas.

Which of the statement(s) given above is/are incorrect?

Solution: All are correct.
  • The catchments of large rivers are called river basins while those of small rivulets and rills are often referred to as watersheds.

  • There is, however, a slight difference between a river basin and a watershed. Watersheds are small in area while the basins cover larger areas.

  • River basins and watersheds are marked by unity. What happens in one part of the basin or watershed directly affects the other parts and the unit as a whole.

  • That is why they are accepted as the most appropriate micro-, meso- or macro-planning regions. Every tributary too has a watershed. Sum of watersheds gives rise to river basin.


Regarding river rejuvenation, consider the following statements:

1. A fall in sea level rejuvenates a river.

2. If there is submergence of land, it will also rejuvenate a river.

Which of the above is/are correct?

Solution: Uplift of land and fall in sea level rejuvenates a river as it has to cut deeper to reach a new base level. On the other hand, submergence of land drowns the valleys and coasts slowing the flow of the river.
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