Natural Hazards & Disasters MCQs for UPSC Prelims

Correct answer: D - All four

Volcanic eruptions throw out solid pyroclastic debris and fine ash and dust, so items 1 and 2 qualify. Volcanic gases include sulphur compounds such as sulphur dioxide and also nitrogen and its compounds, so items 3 and 4 qualify too. All four are recognised products of volcanism, making option (d) correct. Any choice limiting the count to fewer than four understates the range of solid and gaseous volcanic emissions.

Correct answer: B - Inter-Tropical Convergence Zone seldom occurs

Tropical cyclogenesis needs the large-scale convergence and vorticity that the ITCZ supplies. Over the South Atlantic and the South-Eastern Pacific the ITCZ rarely shifts south of the equator, partly because the cold Benguela and Humboldt currents keep it pinned to the north, and vertical wind shear there is also strong, so cyclones almost never form. Low sea surface temperature is a contributing condition created by these cold currents, but the keyed primary reason is the near absence of the ITCZ. The Coriolis force at comparable tropical latitudes is no weaker than in cyclone-prone basins, and cyclones form over open ocean anyway, so the presence or absence of land is irrelevant.

Correct answer: A - 1 only

Barren Island in the Andaman Sea is India's only active volcano, so statement 1 is correct; however it lies near Port Blair (about 135 km north-east of it), not 140 km east of Great Nicobar, so statement 2 is wrong; and it has erupted several times after 1991 (including 1994-95 and the 2000s), so statement 3 claiming dormancy since 1991 is wrong. Hence only statement 1 is correct and the answer is (a). The location and eruption-history errors make the other statements false.

Correct answer: A - Both A and R are true, and R is the correct explanation of A

Both A and R are true and R correctly explains A. The Bay of Bengal records more frequent and intense tropical cyclones than the Arabian Sea. This is because the Bay generally has warmer sea surface temperatures, lower vertical wind shear, and a steady inflow of freshwater and warm moist air that maintains a warm, low-density surface layer favouring rapid cyclone intensification. The Arabian Sea historically had cooler waters and higher wind shear, suppressing cyclone formation. Hence R is the correct explanation of A.

Correct answer: A - Typhoon

Tropical cyclones in the western Pacific (e.g., near Japan, the Philippines and China) are called typhoons. Hurricanes are the same storms occurring over the Atlantic and the eastern Pacific. Willy-willies is a term used in Australia. A tornado is a small but violent funnel of rotating air over land, not a tropical cyclone. Hence typhoon is correct.

Correct answer: A - 1 and 2 only

Statements 1 and 2 are correct. Tsunamis are most often triggered by large submarine earthquakes at subduction zones that displace the sea floor (statement 1). In deep water they travel as long-wavelength, low-amplitude waves that ships barely notice (statement 2). Statement 3 is wrong: as a tsunami enters shallow coastal water it slows down and its energy is compressed, so its wave height increases dramatically (shoaling), not decreases. Hence only 1 and 2 are correct.

Correct answer: A - It has a very long wavelength and great speed in the open ocean but small height there, growing very tall only on approaching shallow coastal waters

A tsunami is typically generated by sudden displacement of the sea floor (earthquakes, submarine landslides or volcanic eruptions). In the deep open ocean it has very long wavelength, travels at high speed (hundreds of km/h) yet has only a small height, so ships may not notice it; as it enters shallow coastal water its speed decreases and energy compresses, causing the wave to pile up into a destructive high wall. It involves the whole water column (not just the surface) and is not wind-generated. Wave speed in shallow water decreases, not increases, contradicting the last option. Hence the first option is correct.

Correct answer: A - A large basin-shaped depression formed by the collapse of a volcano after a major eruption

A caldera is a large, roughly circular depression that forms when the summit of a volcano collapses into the emptied magma chamber following a major eruption; many are later filled by water to form crater lakes. The narrow vertical pipe is a volcanic vent or conduit, the wide spread of fluid basaltic lava is a lava flow or sheet, and the small ash-and-cinder cone is a cinder cone, none of which is a caldera.