Geomorphology: UPSC Previous Year Questions (Geography)

Explanation

Statement 1 is correct: Radiometric dating techniques have confirmed that the rock formations along the eastern coast of South America (Brazil) and the western coast of Africa are similar in age, type, and structure. This is one of the most compelling geological evidences supporting the theory of continental drift.

Statement 2 is correct: Ghana, located on the west coast of Africa, has rich gold deposits along its coast, yet there is no local source rock to account for this mineral wealth. The likely explanation is that these gold deposits originated from the Brazil Plateau which, before the continents drifted apart, lay adjacent to what is now Ghana. This is one of the pieces of evidence supporting the theory of continental drift.

Statement 3 is correct: The Gondwana system of sedimentary rocks, particularly tillite deposits (sediments formed from glacial activity), found in India, have strikingly similar counterparts in six different landmasses in Southern Hemisphere namely Africa, Antarctica, Australia, Madagascar, Falkland Islands, and South America. These similarities provide evidence that these landmasses were once part of a supercontinent called Gondwanaland.

Explanation

Statement II is correct: Chalk is porous, meaning it contains numerous small holes or voids that can absorb water. This porosity contributes to its high permeability, as the interconnected pores facilitate water movement through the rock. Hence, it explains Statement I.

Statement III is Incorrect: Clay is not completely non-porous. It possesses a high porosity due to its fine-grained structure; however, the pores are so small and poorly connected that they prevent significant water flow, resulting in low permeability. Hence, only one of the Statements II and III is correct and that explains Statement I.

Explanation

Statement I is correct: Rainfall plays a key role in weathering rocks through both physical and chemical processes. For instance rainfall water seeps into cracks, causing rocks to expand and contract. Over time, this weakens the rock structure. Similarly, In colder regions, rainwater freezes inside crevices and expands. This leads to cracks and eventually breaks the rock apart. Heavy rainfall also washes away loose particles, speeding up erosion. Chemically, rainwater reacts with minerals in the rock, causing slow decomposition and dissolution. Over time, these processes break down and lead to weathering of rocks.

Statement II is correct: Rainwater absorbs carbon dioxide (CO₂) from the atmosphere, forming a weak acid solution known as carbonic acid (H₂ CO₃). This acidic rainwater reacts with minerals in rocks, leading to chemical weathering, particularly in limestone and carbonate rocks, which dissolve in acidic conditions. This process is responsible for the formation of karst landscapes, caves, and sinkholes in limestone regions.

Statement III is correct: Rainwater absorbs oxygen (O₂) from the atmosphere, which plays a crucial role in oxidation reactions in rocks containing iron and other reactive minerals. Oxygen reacts with iron-rich minerals (e.g., magnetite, pyrite) in rocks to form iron oxides (rust), which weakens the rock structure. Both Statement-II (CO₂ in rainwater) and Statement-III (O₂ in rainwater) are correct. They both explain Statement-I, as they contribute to rock weathering through chemical processes like carbonation and oxidation.

Explanation

A volcano is an opening or rupture in the Earth’s crust through which molten rock (magma), gases, and ash escape from beneath the surface. When magma reaches the surface, it is called lava. Volcanic eruptions can shape mountains and islands, affecting both the environment and climate. Example:

Mount Etna(Italy), Kilauea (USA) The materials that reach the Earth’s surface in volcanoes include: lava flows pyroclastic debris volcanic bombs ash and dust gases such as nitrogen compounds sulphur compounds minor amounts of chlorine, hydrogen and argon etc.

Explanation

Statement 1 is correct: There are two types of body waves-P and S waves. The P-waves and S-waves are also known as primary waves and secondary waves, respectively. The P-waves move faster and are the first to arrive at the surface. Therefore, in a seismograph, P waves are recorded earlier than S waves. The S-waves arrive at the surface with some time lag.

Statement 2 is correct: In P-waves, the media particle vibrates parallel to the direction of the wave. Thus it causes the to-and-fro motion. Further, in the S-waves media particles vibrate perpendicular (up and down at right angles) to the direction of wave propagation i.e. in the right angle. P-waves S-waves Arrival Times Surface Waves Amplitude

Explanation

Black cotton soil, also known as regur soil, is highly valued in India because of its excellent moisture-retaining properties and suitability for cotton cultivation. Black cotton soil is primarily formed from the weathering of basaltic rocks, which are a type of fissure volcanic rock. These basaltic rocks were originally erupted during the Cretaceous period as part of the Deccan Traps in the northwest Deccan plateau. The weathering process of these volcanic rocks releases minerals that, combined with climatic factors, result in the formation of the distinctive black soil. The high clay content of black cotton soil enables it to retain moisture efficiently. Its properties make it particularly suitable for cotton cultivation, hence the alternative name "black cotton soil."

Explanation

Statement 1 is correct: Continental drift is the gradual movement of Earth’s continents due to tectonic plate activity. It causes geographical isolation, leading to divergent evolution and speciation. Species adapt to new environments, creating distinct biogeographical patterns like the unique primates in Australia and South America. This process has shaped evolutionary changes over time.

Statement 2 is correct: Periodic advances and retreats of ice sheets, impacting climate and sea levels. It creates environmental pressures, pushing species to adapt. Glacial cycles result in population bottlenecks, migration, or extinction and influences evolutionary paths. The Pleistocene glaciations played a crucial role in shaping the distribution and diversity of many species observed today

Explanation

Soil erosion is the process by which soil is displaced and transported from one location to another by natural forces such as wind or water. It is a natural process that occurs over time, but human activities such as deforestation, overgrazing, and construction can accelerate the process, leading to significant environmental damage.

Statement 1 is incorrect: Terrace cultivation is a *method to * prevent soil erosion, not a factor associated with it. Terraces are leveled platforms built into hillsides to slow down the flow of water and reduce soil loss. So, this option is incorrect.

Statement 2 is correct: Deforestation is one of the major reasons for soil erosion. It includes cutting and felling of trees, removal of forest litter. Browsing and trampling by livestock, forest fires, also leads to deforestation, etc. Vegetation plays a critical role in anchoring soil, reducing the impact of rainfall, and protecting against wind erosion. When forests are cleared, the soil becomes exposed and vulnerable to erosion.

Statement 3 is incorrect: While a tropical climate can contribute to soil erosion in some cases (heavy rainfall can increase water erosion) but it isn’t a direct cause in itself. Many tropical areas with dense vegetation have relatively low erosion rates. The lack of vegetation (often due to deforestation) in a tropical climate is the real problem.

Explanation

Statement 1 is correct: The distinctive red colour is one of the key characteristics of laterite soils. It appears red due to the high concentration of iron oxides. In tropical climates, heavy rainfall causes intense leaching, washing away silica and other bases while leaving behind iron and aluminum oxides, which give the soil its distinctive red color.

Statement 2 incorrect: Laterite soils are poor in nitrogen, phosphorus, and potash (potassium). The intense leaching caused by heavy rainfall in tropical regions washes away these soluble nutrients.

Statement 3 is incorrect: Laterite soils are primarily found in the humid tropical regions of India, such as the Western Ghats, parts of Eastern Ghats, and some northeastern states. Rajasthan and Uttar Pradesh (UP) have a drier climate which is not suitable for the formation of laterite soils.

Statement 4 is correct: The agro-climatic conditions of laterite soils support the cultivation of crops such as tapioca, cashew nuts, groundnut, coffee, and rubber. These crops are well-adapted to the moisture-retaining and nutrient-poor nature of laterite soils.

Explanation

Statement 1 is incorrect: The Gondwana beds are primarily famous for containing coal reserves, with nearly 98% of India’s coal reserves found in them. They are not significant for natural gas reserves. Natural gas in India is more commonly associated with other formations such as sedimentary basins such as the Cambay Basin or the Krishna-Godavari Basin.

Statement 2 is correct: Kodarma in Jharkhand is a well-known region for mica production, which has been an important mineral in India’s mineral resources. Mica is found abundantly here and Kodarma is often referred to as the "mica capital" of India.

Statement 3 is incorrect: The Dharwar system of rocks is not known for petroleum production. The Dharwar rocks are particularly valuable for metallic minerals like high-grade iron ore, manganese, and copper. Petroleum is not found in the Dharwar rock system but in other formations like the Cambay Basin or the Rajasthan Basin.