Geomorphology: UPSC Previous Year Questions (Geography)

Explanation

Option (a) is correct: Aristotle was the first to provide empirical evidence for the Earth’s spherical shape. In his work On the Heavens (De Caelo), he argued that the Earth must be a sphere based on observations such as:

The way ships disappear hull-first over the horizon. The circular shadow of the Earth on the Moon during a lunar eclipse. The changing position of stars when traveling north or south. These arguments strongly supported the idea that the Earth was not flat but spherical. Options (b), (c) and (d) are incorrect:

Nicolaus Copernicus is known for formulating the heliocentric model, which proposed that the Sun, not the Earth, was at the center of the universe. Claudius Ptolemy, an astronomer and geographer, expanded on the spherical Earth concept in his famous work Almagest. He developed the geocentric model (Earth-centered universe), which became dominant for over a thousand years. Strabo was a Greek geographer who described the Earth’s shape as a sphere in his work Geographica. But he relied on earlier works, especially those of Aristotle and Eratosthenes.

Explanation

Common types of Sedimentary rocks include sandstone, shale, limestone, and conglomerates. They often host resources like coal, petroleum, and natural gas.

Statement 1 is correct: Sedimentary rocks form through the accumulation and lithification of sediments. The hydrological system (water cycle) plays a crucial role in their formation, as water transports, deposits, and compacts sediments. Rivers, lakes, oceans, and glaciers contribute to sediment deposition.

Statement 2 is correct: Sedimentary rocks originate from weathered materials of pre-existing rocks (igneous, metamorphic, or other sedimentary rocks). Weathering processes (physical, chemical, and biological) break down rocks into smaller particles. These sediments are transported and deposited before undergoing compaction and cementation to form sedimentary rocks.

Statement 3 is correct: Fossils are primarily found in sedimentary rocks because these rocks form in low-temperature and low-pressure environments that preserve organic remains. Limestone, shale, and sandstone commonly contain fossils.

Statement 4 is correct: Sedimentary rocks typically occur in distinct horizontal layers or strata, reflecting different periods of deposition. This characteristic layering is a key identifier of sedimentary rocks.

Explanation

Volcanic eruptions are mostly associated with tectonic activity, particularly along plate boundaries along divergent boundaries (e.g., mid-ocean ridges), convergent boundaries (e.g., Pacific "Ring of Fire") and hotspots (e.g., Hawaii).

Option (a) is correct: The Baltic Sea is located in a tectonically stable region of Northern Europe, far from active plate boundaries. This stability means that volcanic activity is entirely absent in and around the Baltic Sea. Options (b), (c) and (d) are incorrect:

Caspian Sea: Although primarily tectonically stable, certain nearby areas (like the Caucasus Mountains) exhibit minor geological and volcanic activity. Black Sea: While not highly active, the Black Sea contains regions with dormant and extinct volcanic formations, indicating past geological and volcanic activity. Caribbean Sea: Located along an active tectonic boundary, where the Caribbean Plate interacts with the North American Plate. Known for volcanic islands like Montserrat, St. Lucia, and Martinique, it is a region of frequent volcanic eruptions.

Explanation

Option (c) is correct: Quartzite is a metamorphic rock that forms when quartz-rich sandstone undergoes metamorphism due to intense heat and pressure. The process causes the quartz grains in the sandstone to recrystallize, forming a hard, dense rock with interlocking quartz crystals.

Option (a), (b) and (d) are incorrect:

Limestone metamorphoses into marble due to recrystallization of calcite under high pressure and heat. Famous for its use in sculpture and architecture. Obsidian: Not a metamorphic rock but an igneous rock that forms from the rapid cooling of lava, creating volcanic glass. Shale metamorphoses into slate, which can further transform into phyllite, schist, or gneiss with increasing metamorphic grade.

Explanation

Soil erosion is a natural process involving the detachment, transportation, and deposition of soil particles, primarily due to water or wind. The stages of water-induced soil erosion occur in the following sequence: Splash Erosion Sheet Erosion Rill Erosion Gully Erosion Fig: Stages of Water Induced Soil Erosion 1. Splash Erosion: This is the initial stage of erosion where raindrops hit bare soil surfaces, dislodging soil particles. It creates a loose layer of soil vulnerable to further erosion by runoff. 2. Sheet Erosion: A thin, uniform layer of soil is removed over a large area by surface runoff. In this stage, a thin, uniform layer of soil is washed away over a large area by surface runoff, without noticeable channels. Often goes unnoticed but contributes significantly to soil loss. 3. Rill Erosion: When runoff becomes concentrated, it forms small channels or rills in the soil. Rills disrupt agricultural fields and increase erosion intensity.

4. Gully Erosion: As rills expand and deepen, they turn into gul-lies, creating large channels that severely degrade the land and make it unsuitable for cultivation. The most destructive stage, often requiring intensive reclamation efforts.